The 1991 Gulf War Oil Spill

The 1991 Gulf War Oil Spill 

Its ecological effects and recovery rates of 

intertidal ecosystems at the Saudi Arabian Gulf 

coast - results of a 10-year monitoring period 

Wissenschaftliche Arbeit 

Im Rahmen des Habilitationsverfahrens im Fach Geographie 

an der Philosophischen Fakultät III der Universität Regensburg 

(gemäß § 5 der Habilitationsordnung) 

vorgelegt von 

Dr. Hans-Jörg Barth 

Regensburg, den 02.07.2002

Foreword 

In early 1991, when in the course of the Gulf War Iraq released about one million tonnes of 

crude oil into the Arabian-Persian Gulf, the largest oil spill in human history hit the Saudi 

Arabian coastal ecosystems. About 770 km of coastline from southern Kuwait until Abu Ali 

Island were smothered with tar and oil. The Project “Establishment of a Marine Habitat and 

Wildlife Sanctuary for the Gulf Region” funded by the European Union and the National 

Commission for Wildlife Conservation and Development (NCWCD), started in October 1991. 

Its first phase ended in April 1992, and the second phase, which started immediately 

thereafter, was concluded in January 1994. It was then when I had the possibility to join the 

project as a graduate student, due to the encouragement of Dr. Friedhelm Krupp. Although my 

objectives were the ecological mapping of the inland area rather than wading through the 

intertidal habitats, I joined the intertidal crew as often as possible in order to learn from the 

interdisciplinary team. My duty in the third phase of the EU-NCWCD project, which lasted 

until July 1995, was again focused on the inland area. I studied the grazing capacity of the 

region in order to develop a grazing management plan for sustainable use of the region’s 

resources. But it was time enough for occasional trips to the intertidal monitoring sites, this 

time mainly with two biologists, Jaime Plaza and Alistair Jolliffe, and the chemist Dr. Geoff 

Smith. During this time I decided to come back in order to study the soil component of the 

intertidal zones, which in my opinion was neglected during the interdisciplinary EU-NCWCD 

project. The first opportunity came in spring 1996 and the second in spring 1999. At that time 

I had sufficient material for applying for a research grant. A very successful meeting with 

H.E. Prof. Dr. Abdulaziz H. Abuzinada in Riyadh and the support of the German Research 

Foundation led to the establishment of the project “The coastal ecosystems 10 years after the 

Gulf War oil spill”. Field trips in autumn 2000, spring 2001, and 2002 as well as the hard 

work of eight graduate students who have been staying 7 months in Jubail altogether, 

provided the material necessary to accomplish this work. With the results of this study I hope 

to present new insights into the processes of natural recovery and also into the processes 

preventing recovery at certain locations. This work is not only aiming at the scientist but also 

at environmental managers who, with their decisions, help to protect and conserve the natural 

resources of the Arabian Gulf. 

Kempten, June 2002 

I

Acknowledgements 

This work could not have been done without the continuous support of H.E. Prof. Dr. 

Abdulaziz H. Abuzinada, Secretary General of the National Commission for Wildlife 

Conservation and Development (NCWCD) in Riyadh, Kingdom of Saudi Arabia. Due to his 

encouragement, I managed to bring eight graduate students to the Jubail Marine Wildlife 

Sanctuary Centre for seven months of field work between October 2000 and April 2001. I 

also wish to express my sincere thanks to Prof. Dr. Abuzinada for providing the necessary 

visa and travel permits for each trip to the Kingdom of Saudi Arabia. 

I am very grateful to Prof. Dr. Klaus Heine (Head of Department of Physical Geography, 

Institute for Geography, University of Regensburg) for his valuable advice and 

encouragement. He supported this project from the very beginning. Particularly during the last 

year, he released me from several duties and thus making this research possible. 

Furthermore, I have to thank the German Research Foundation (DFG) for financially 

supporting the Project (Project No. BA 1917-3-1). On behalf of the Saudi Arabian Project 

partner, NCWCD provided all necessary research facilities in the Jubai Marine Wildlife 

Sanctuary Centre, an offroad vehicle for the time we spent in Jubail and accommodation for 

myself and the eight graduate students. The DAAD provided the travel expenses for some of 

the students involved. 

Many special thanks are due to the staff at the Jubail Marine Wildlife Sanctuary Centre, 

particularly Mr. Khalid Al-Sheik and Mr. Ahmad Salah, to Dr. Hossam Jabbad (Head of the 

Laboratory of the Royal Commission Industrial College), who analysed the samples for trace 

metals; Prof. Dr. König and Dr. Vasold (Dept. of Organic Chemistry, University of 

Regensburg) for their patience and help in gas chromatography, and Tanja Heindl and 

Michael Sigl for the hydrocarbon extractions in our laboratory in Regensburg. 

I wish to express my gratitude to the following persons for their interest, encouragement, and 

support: Mrs. Marion Würth, Prof. Dr. Thomas Höpner (Dept. for Marine Biology, University 

of Oldenburg, Germany) Dr. Friedhelm Krupp (Senckenberg Institute, Frankfurt, Germany) 

Prof. Dr. Jörg Völkel (Dept. of Soil Science, Institute for Geography, University of 

Regensburg, Germany), Dr. Lucien Hoffmann (Université de Liège, Belgium), Jaime Plaza 

(University of Bangor, UK), Dr. Uwe Zajonz (Senckenberg Institute, Frankfurt), Dr. Benno 

II

Böer (UNESCO, Doha, Qatar), Mr. Ernst Ardelean (Cartography, Institute for Geography, 

University of Regensburg, Germany), Mr. Wolfgang Reimer, Mrs. Karin Zenisek, Mr. Frank 

Steinkohl, Mr. Anton Obermüller, Mr. Christian Siebert, Mr. Andreas Zellhuber, and Mr. 

Christian Pikalek. 

III

Contents 

Foreword I 

Acknowledgements II 

Contents IV 

List of figures VII 

List of tables X 

List of photos XII 

Abbreviations XIII 

Summary XIV 

1 Introduction 

1.1 Terminology 2 

1.1.1 Ecosystem type 2 

1.1.2 Long term 3 

1.1.3 Recovery 4 

1.2 Objectives 5 

2 Methods 

2.1 Measurement of climatic parameters 6 

2.2 Vegetation and fauna 7 

2.3 Mapping of the coastal ecosystem types 7 

2.4 Selection of the study sites 7 

2.5 Soil samples: collection and preparation 8 

2.6 Petroleum hydrocarbon analysis 9 

2.7 Trace metal analysis 10 

2.8 Radiocarbon analysis 11 

2.9 Water analysis 11 

3 Physical setting of the study area 

3.1 Geology 12 

3.1.1 The Arabian Shield 13 

3.1.2 The Arabian Shelf 13 

3.1.3 The Arabian Gulf coastal region 14 

3.1.4 The study area 15 

3.2 Climate 18 

3.2.1 General pattern of the Gulf region 18 

3.2.2 Climate in the study area 20 

3.3 Hydrology 27 

3.4 Vegetation 28 

3.5 The Arabian Gulf 31 

1 

6 

12 

IV

3.5.1 Sea level changes 32 

3.5.2 Hydrographical influences 34 

3.6 Ecosystem types 40 

3.6.1 Salt marshes 41 

3.6.2 Mangroves 43 

3.6.3 Sabkha shores 44 

3.6.4 Sandy shores 44 

3.6.5 Rocky shores 45 

4 Previous work 

5 The Gulf War 1991 and the oil spill 

5.1 The fate of the oil after the release 52 

5.1.1 Crude oil 52 

5.1.2 Natural weathering processes after the oil spill 54 

6 Ecosystem types and their response to oil impact 

6.1 Salt marshes 59 

6.1.1 Halocnemum transect 62 

6.1.1.1 Soil properties 63 

6.1.1.2 Groundwater characteristics 76 

6.1.1.3 Microclimate 80 

6.1.1.4 Vegetation 88 

6.1.1.5 Fauna 90 

6.1.1.6 Cyanobacteria 92 

6.1.2 Arthrocnemum transect 102 

6.1.2.1 Soil properties 103 




6.1.2.5 Fauna 117 


6.1.3 Sabkha – salt marsh transect 121 

6.1.4 Bomb Crater Bay – transect 1 125 

6.1.5 Bomb Crater Bay – transect 2 130 

6.1.6 Intertidal transect 133 

6.1.7 Coast Guard transect 141 

6.1.8 Natural cyanobacteria mudflat 147 

6.1.9 Salt marsh ecosystems - Discussion 151 

6.1.9.1 Hydrocarbons 151 

6.1.9.2 Trace metals 160 


6.1.9.4 Groundwater 166 



47 

50 

57 

V

6.1.9.7 Fauna 170 

6.2 Mangrove 173 

6.2.1 Mainland transect 173 

6.2.1.1 Soil characteristics and oil contamination assessment 175 




6.2.1.5 Fauna 183 

6.2.2 Qurmah Island transect 186 


6.2.2.2 Groundwater chemistry 188 


6.2.2.4 Fauna 190 

6.2.3 Mangrove sites - Discussion 191 

6.3 Sabkha shores 195 

6.4 Sandy shores 199 

6.4.1 High energy shores 199 

6.4.1.1 Abu Ali - sandy beach 200 

6.4.1.2 Abu Ali - sandy/rocky beach 202 

6.4.2 Low energy sandy shore 203 


6.4.2.2 Fauna 208 

6.4.3 Sandy shores - Discussion 209 

6.5 Rocky shores 211 

6.5.1 Rocky shore south of Jabal an-Nuquriyah 212 

6.5.2 Ras al Bukhara 214 

6.5.3 Rocky shores - Discussion 216 

7 General discussion and conclusion 

8 Recommendations 

9 Further research 

References 228 

Appendix 237 

218 

225 

227 

VI

List of figures 

Fig. 3.1 Geology of the Arabian Peninsula and tectonic movements. 14 

Fig. 3.2 Location of the study area and the meteorological stations. 15 

Fig. 3.3 Geology of the study area. 16 

Fig. 3.4 Pressure zones influencing the Arabian Peninsula in July and January. 19 

Fig. 3.5 Climatological diagram of the intertidal station Mardumah Bay. 20 

Fig. 3.6 Mean temperatures at meteorological stations within the study area. 21 

Fig. 3.7 Temperatures of a day in summer and winter. 21 

Fig. 3.8 Relative humidity at three station in August 1994. 22 

Fig. 3.9 Relative humidity at Abu Ali and Abu Kharuf in January. 22 

Fig. 3.10 Precipitation on the 11 th of December 1994 at the three stations. 24 

Fig. 3.11 Wind diagram for June 1995 (Abu Kharuf station). 25 

Fig. 3.12 Wind rose for the Abu Kharuf station. 26 

Fig. 3.13 Groundwater aquifers of the Arabian Peninsula. 28 

Fig. 3.14 Conventional floristic regions of the Arabian Peninsula. 30 

Fig. 3.15 Carbonate content of surface sediments in the Gulf. 32 

Fig. 3.16 Palaeogeographic map showing the Arabian Gulf during the 

post-glacial transgression. 33 

Fig. 3.17 Sea level changes of the Arabian Gulf during the last 8000 years. 34 

Fig. 3.17 Tides in the Arabian Gulf. 36 

Fig. 3.18 Average height of high tides within the study area. 37 

Fig. 3.19 Sea surface temperatures of the Arabian-Persian Gulf. 38 

Fig. 3.20 A: Concentrations of anorganic phosphate in µg/l. 

B: Concentrations of silicate in µg/l. 39 

Fig. 3.21 A: Concentrations of petroleum hydrocarbons (ppb) in the Gulf water. 

B: Concentration of petroleum hydrocarbons in sediments (ppm). 40 

Fig. 3.22 Schematic profile of a salt marsh at the Gulf coast. 42 

Fig. 3.23 Schematic profile of a mangrove habitat at the Gulf coast. 43 

Fig. 5.1 Oil slicks (red colour) as seen from the Landsat Thematic Mapper satellite. 50 

Fig. 5.2 Extend of oiled coastline along the western Gulf shore. 51 

Fig. 5.3 The structure of some hydrocarbons. 53 

Fig. 5.4 Evaporation rates of different oil types. 54 

Fig. 5.5 Main weathering processes acting on crude oil after an oil spill. 56 

Fig. 5.6 Percentage of weathering processes on Kuwait medium crude oil. 56 

Fig. 6.1 Different tidal zones. 57 

Fig. 6.2 Location of different coastal ecosystem types in the study area. 58 

Fig. 6.3 Schematic profile of a salt marsh ecosystem. 61 

Fig. 6.4 Location of salt marsh ecosystems in the study area. 61 

Fig. 6.5 Location of the Halocnemum transect. 62 

Fig.6.6 Soil sections of the Halocnemum transect – lower part. 64 

Fig. 6.7 Soil sections of the Halocnemum transect – upper part. 68 

Fig. 6.8 Rapid assessment oil prints. 71 

Fig. 6.9 Mean values of the oil load at different sites along the Halocnemum transect. 72 

Fig. 6.10 Oil load along the transect and trace metal concentrations. 73 

Fig. 6.11 Penetration resistance of the substrate on mounds and the flat areas 

in between. 74 

Fig. 6.12 Vane shear force of the substrate on mounds and the flat areas in between. 75 

Fig. 6.13 Soil water content between the 15 and 150 m mark. 76 

Fig. 6.14 Electrical conductivity in October 2000 and January 2001. 77 

Fig. 6.15 Electrical conductivity and chloride concentration in winter 2000/2001. 78 

VII

Fig. 6.16 Magnesium and calcium concentration at the 150 m mark. 78 

Fig. 6.17 Magnesium concentration in March and April 2001 along the transect. 79 

Fig. 6.18 Sulphate concentration along the transect during the winter period. 80 

Fig. 6.19 Groundwater temperatures along the transect between November and April. 81 

Fig. 6.20 Temperature profile between -40 and 100 cm height above soil surface 82 

Fig. 6.21 Temperature profile between -40 and 100 cm height above soil surface 83 

Fig. 6.22 Temperature 10 cm below surface and 2 m above. 85 

Fig. 6.23 Soil temperatures in July. 86 

Fig. 6.24 Soil temperature along the Halocnemum salt marsh transect at 12:00. 87 

Fig. 6.25 Potential evaporation along the profile in February, March and April. 87 

Fig. 6.26 Average counts of crab burrows > 0.5 cm along the transect. 91 

Fig. 6.27 Average counts of crab burrows < 2 mm along the transect. 92 

Fig. 6.28 Different morphology types of cyanobacteria communities in the 

study area. 93 

Fig. 6.29 Chemical soil properties and microbial zones in the upper soil layer. 95 

Fig. 6.30 Development of cyanobacteria along the transect. 97 

Fig. 6.31 Location of the Arthrocnemum transect. 102 

Fig. 6.32 Soil sections showing the oil residues within the sediments. 103 

Fig. 6.33 Soil sections showing the oil residues within the sediments - upper part. 106 

Fig. 6.34 Erosion of tar crust between October 2000 and April 2001. 107 

Fig. 6.35 Soil water content. 109 

Fig. 6.36 Profiles of electrical conductivity in October 2000 and January 2001. 110 

Fig. 6.37 Development of chloride concentration and electrical conductivity 

in winter. 110 

Fig. 6.38 Magnesium concentration in October 2000, January 2001 and April 2001. 112 

Fig. 6.39 Profiles of sulphate concentration in October 2000, January 2001 and 

April 2001. 113 

Fig. 6.40 Temperature profiles of intertidal location and dry sandy location. 114 

Fig. 6.41 Temperature profiles of intertidal location on a clear and a cloudy day. 115 

Fig. 6.42 Temperature differences between -5 and -10 cm. 115 

Fig. 6.43 Changes of cyanobacteria morphology along the transect during winter 117 

Fig. 6.44 Location of the salt marsh-sabkha transect. 121 

Fig. 6.45 Bomb Crater Bay – transect 1. Birdseye view. Summary of situation 

in 2001. 125 

Fig. 6.46 Bomb Crater Bay – transect 2. Situation in 2001. 130 

Fig. 6.47 Rapid assessment oil prints. 133 

Fig. 6.48 Intertidal transect. Birdseye view. Summary of situation in 2001. 134 

Fig. 6.49 Rapid assessment oil prints of samples along the intertidal transect. 140 

Fig. 6.50 Coast Guard transect. Birdseye view. Summary of situation in 2001. 141 

Fig. 6.51 Sections in the Coast Guard transect in 2001. 142 

Fig. 6.52 Smoothing process of Cleistostoma-salt marsh relief 144 

Fig. 6.53 Rapid assessments prints of the samples described above. 145 

Fig. 6.54 Location of the natural cyanobacteria mudflat. 147 

Fig. 6.55 Pattern of tidal pools. 150 

Fig. 6.56 A: Development of hydrocarbon concentration between 1993 and 2001. 

B: Oil distribution within the sediment of the Halocnemum salt marsh 

in 2001. 152 

Fig. 6.57 Profile of oil concentration at different soil depths in 2001 153 

Fig. 6.58 Oil distribution within the sediment of the undisturbed transect 

in 1992 and 2001. 153 

Fig. 6.59 Oil load at the ploughed and non-ploughed site – mean values. 155 

VIII

Fig. 6.60 Portions of the total resolved aliphatics at the ploughed and 

non-ploughed site. 156 

Fig. 6.61 Gas chromatographic spectra of the 1-5 cm depth horizon at the ploughed 

and non ploughed site 157 

Fig. 6.62 Gas chromatographic spectra of the 1-5 cm depth horizon at the ploughed 

and non ploughed site 158 

Fig. 6.63 Gas chromatographic spectra of oil below a cyanobacteria mat in 1994 

and 2002. 159 

Fig. 6.64 Trace metal concentrations in 1994 and 2002. 160 

Fig. 6.65 Simplified successions at oiled Cleistostoma-salt marshes. 162 

Fig. 6.66 Annual layers of flat cyanobacteria. 165 

Fig. 6.67 Distribution of mangrove habitats within the study area. 173 

Fig. 6.68 Mangrove transect on the western shores of Dawhat ad-Dafi. 174 

Fig. 6.69 Rapid assessment oil prints of mangrove samples. 178 

Fig. 6.70 Distribution of oil residues within the mangrove soils in 1992 and 2001. 178 

Fig. 6.71 Electric conductivity of selected stations between December and April. 179 

Fig. 6.72 Sulphate concentration of selected stations between December and April. 180 

Fig. 6.73 Groundwater temperature of selected stations between December and April. 180 

Fig. 6.74 Temperature profiles of the coastal and mangrove island location. 181 

Fig. 6.75 Species diversity and abundance between 1991 and 1995. 183 

Fig. 6.76 Species distribution and abundance in 1993. 184 

Fig. 6.77 Transect on Qurmah Island. 186 


Fig. 6.79 Chemical properties in a muddy soil. 194 

Fig. 6.80 Distribution of sabkha shores within the study area. 195 

Fig. 6.81 Location of the sabkha shore transect. 196 

Fig. 6.82 Distribution of sand beaches within the study area. 199 

Fig. 6.83 Location of the two sand beaches. 200 

Fig. 6.84 Oil distribution at the Abu Ali transect in 1994. 201 

Fig. 6.85 Location of the low energy sandy shore transect. 204 

Fig. 6.86 Rapid assessment oil prints of samples along the transect. 207 

Fig. 6.87 Oil distribution within the sediment in 1992 and 2001. 208 


Fig. 6.89 Distribution of rocky shores within the study area. 212 

Fig. 6.90 location of the rock transect. 212 

Fig. 6.91 Petrography of the cliff at Ras al-Bukhara and the intertidal flat at its 

bottom. 214 

Fig. 6.92 Species diversity and abundance for Ras al-Bukhara. 217 

Fig. 7.1 Oil conservation and degradation processes at the Gulf shores. 220 

IX

List of tables 

Tab. 3.1 Types and number of major precipitation events. 19 

Tab. 3.2 Dew in the winter months between 2000 and 2001. 23 

Tab. 3.3 Precipitation events per rain season at the three stations. 

24 

Tab. 6.1 linear extent of coastal ecosystem types. 

58 

Tab. 6.2 Section 1 at the 370 m mark of the Halocnemum transect. 65 













Tab. 6.15 Section 17 at the 30m mark of the Halocnemum transect. 70 

Tab. 6.16 Oil load at heavily oiled sites, medium oiled sites and non oiled sites. 72 

Tab. 6.17 Vegetation profile of the Halocnemum transect. 89 

Tab. 6.18 Section 1 at the 285 m mark of the Arthrocnemum transect. 104 














Tab. 6.32 Grain size distribution of collected sediments. 110 

Tab. 6.33 Section 1 at the 50 m mark of the sabkha-saltmarsh transect. 122 



X



Tab. 6.38 Section 1 at the 10 m mark of the Bomb-Crater Bay-1 transect. 126 










Tab. 6.48 Section 1 at the 0 m mark of the intertidal transect. 134 













Tab. 6.61 Salinity gradient and fish populations in tidal pools. 146 

Tab. 6.62 Section 1 at the 5 m mark of the cyanobacteria transect. 148 



Tab. 6.65 n-C18/phytane indices for the ploughed and non-ploughed site. 156 

Tab. 6.66 n-C17/pristane indices for the ploughed and non-ploughed site. 157 

Tab. 6.67 Calculation of extent of oil induced cyanobacteria areas. 163 

Tab. 6.68 Phosphate concentration in soil pore water. 166 

Tab. 6.69 Groundwater oxygen and resulting plant condition. 167 

Tab. 6.70 Section 1 at the 0 m mark of the mangrove mainland transect. 175 






Tab. 6.76 Oxygen saturation in Avicennia/Arthrocnemum site in 2002. 181 

Tab. 6.77 Section 1 at the 0 m mark of the Qurma transect. 187 





Tab. 6.82 Section 1 at the 0 m mark of the sabkha transect. 196 





XI



Tab. 6.89 Section 1 at the 0 m mark of the low energy sandy shore transect. 205 




Tab. 6.93 Section 5 at the 20 m mark of the low energy sandy shore transect 206 



Tab. 6.96 Section 8 at the 35 m mark of the low energy sandy shore transect 207 

Tab. 7.1 Recovery status of the different coastal ecosystem types in 2001. 219 

Tab. 7.2 Cleanup techniques and their results. 223 

List of photos 

Photo 3.1 A: conical tower of the crab Ocypode rodundata. 

B: feeding trench and piles of sand pellets of the crab 

Scopimera crabicauda 45 

Photo 6.1 Soil sections showing the oil residues within the crab burrows 10 years 

after the Gulf war oil spill. 68 

Photo 6.2 Halocnemum s. salt marsh test area (seaward view). 88 

Photo 6.3 Status of salt marsh plants at different locations along the transect in 2001. 90 

Photo 6.4 A: Cyanobacterium Lyngbya aestuarii. 

B: Bundles of trichomes of Microcoleus chthonoplastes. 95 

Photo 6.5 Flat laminated cyanobacteria mat. 96 

Photo 6.6 Different pinnacle cyanobacteria mat morphologies. 96 

Photo 6.7 Little elevated areas around former salt marsh plants. 98 

Photo 6.8 Fragments of polygons are peeling off removing tar. 98 

Photo 6.9 Black pinnacle mats on elevated patches. 99 

Photo 6.10 Contraction of cyanobacteria mats caused by desiccation. 100 

Photo 6.11 Black pinnacle mats. 100 

Photo 6.12 Remains of a former continuous cyanobacteria mat between 

crab burrows. 123 

Photo 6.13 Large amount of crab burrows at the edge of the channel. 124 

Photo 6.14 Well decomposed oil residues within sandy sediment at the 260 m mark. 124 

Photo 6.15 Arthrocnemum macrostachyum growing in isolated patches of 

eroded tar crust. 127 

Photo 6.16 A: “tar mesas” at the HWN and B: section within such a tar mesa. 129 

Photo 6.17 A: countless active burrows of resettled crab population. 

B: Macrophthalmus depressus. 133 

Photo 6.18 Gastropod/cyanobacteria pinnacles. 135 

Photo 6.19 dead Arthrocnemum zone with characteristic tidal channels and 

dry pools. 136 

Photo 6.20 Tidal channels and –pools. 137 

Photo 6.21 Upper part of the core at the 475 m mark. 139 

Photo 6.22 Tidal channel flowing into the sea (upper right end). 142 

Photo 6.23 Leathery cyanobacteria breaks away on top of little mounds. 143 

XII

Photo 6.24 Extensive growth of blistered cyanobacteria. 144 

Photo 6.25 Life in saline tidal pools. 146 

Photo 6.26 Oxidation around a new crab burrow 176 

Photo 6.27 Linear (A) and polygonal (B) structures within the Cleistostoma 

burrow relief. 185 

Photo 6.28 remains of dead Avicennia on severely affected areas on Qurmah Island. 

190 

Photo 6.29 Calcified oiled sediments which form a micro cliff at the island shore (A). 

Close up of a calcified crab burrow (B). 193 

Photo 6.30 Oiled burrows of polychaetes and crabs in the mid eulittoral. 198 

Photo 6.31 A: Scattered oil pebbles are the only residues of the 1991 oil spill. 

B: The ghost crab Ocypode rotundata searching the trashline for food. 202 

Photo 6.32 A: Recent tar layer between the HWN and HWS. 

B: The rocky outcrops below the HWS. 203 

Photo 6.33 Oil residues at selected sites along the transect (see text for explanation). 206 

Photo 6.34 Narrow tar band along a sandy beach on Jinnah Island. 210 

Photo 6.36 Cliff of Ras al-Bukhara at high tide. 215 

Photo 6.37 Polygonal pattern of cracks in the tar cover. 215 

Photo 6.38 Narrow band of beachrock at an exposed shore. 216 

Abbreviations 

API American Petroleum Institute 

EU European Union 

GC Gas chromatography 

HPLC High performance liquid chromatography 

HWN High water neap 

HWS High water spring 

ICBM Institut für Chemie und Biologie des Meeres 

IMO International Maritime Organisation 

ITOPF International Tanker Owners Pollution Federation 

IUCN World Conservation Union 

KFUPM/RI King Fahd University of Petroleum and Minerals / Research Institute 

MEPA Marine and Environmental Protection Agency 

MHWM Mean high water mark 

NCWCD National Commission for Wildlife Conservation and Development 

NOAA U.S. National Oceanic and Atmospheric Administration 

RCJY Royal Commission for Jubail and Yanbu 

ROPME Regional Organisation for the Protection of the Marine Environment 

UCM Unresolved complex matrix 

XIII

Summary 

In 1991, the Gulf War led to the largest oil spill in human history. 770 km of coastline from 

southern Kuwait to Abu Ali island were smothered with oil and tar, erasing most of the local 

plant and animal communities. From 1991 until 1995, a joint project funded by the European 

Union and the National Commission for Wildlife Conservation and Development, Riyadh, has 

been carried out in order to assess the ecological damage and the regeneration processes. The 

EU/NCWCD reports, publications in international journals, and conference proceedings as 

well as press releases, presented a picture which was often very optimistic regarding the 

overall situation at the shores of the Arabian Gulf. Repeated field trips after 1995 showed that 

most salt marshes, which cover almost 50% of the coast line, are severely affected by the oil 

and that recovery was by far not complete. These findings and the fact that literature about the 

long term effects of oil spills is scarce, were the motivation for this study. It summarizes the 

results of the first four years after the oil spill and closes the gap between 1995 and 2001. 

Additionally, different ecological parameters (hydrology, groundwater chemistry, micro 

climate, and variation in abundances of certain organisms such as cyanobacteria) have been 

monitored continuously (every 2 weeks) through the whole winter period from October 2000 

until May 2001. As a result, the regeneration processes of different ecosystem types can be 

demonstrated for a 10-year monitoring period. Such a compilation of scientific information 

has not been attempted before for an oil spill in a subtropical environment. The main 

objectives are: mapping of the coastal ecosystem types; evaluation of the present situation 10 

years after the oil spill - including the weathering status of the oil residues within the intertidal 

soils; documentation of regeneration within the different coastal ecosystem types, based on 

the previous work carried out during the EU/NCWCD project until 1995; determination of the 

major processes that lead to recovery; determination of the major processes that prevent 

recovery; estimate the future development; provide recommendations for environmental 

managers how to improve the way we respond to oil spills. 

The methods used, cover soil analysis (including ICP/AES for trace metals), groundwater 

analysis, hydrocarbon analysis (weathering status, extraction and gas chromatography), 

measurements of standard climate parameters (including 1 year of subsurface temperature 

measurement in intertidal soils), and the assessments of vegetation and fauna. 

In contrast to previously published reports the results show that, a great number of coastal 

areas in 2001 still show significant oil impact and in some places no recovery at all. The salt 

marshes show the heaviest impact compared to the other ecosystem types after 10 years. 

XIV

Within the salt marsh transect, the upper intertidal zones, particularly the littoral fringe and 

the upper eulittoral, are most affected by the oil residues. Completely recovered are the rocky 

shores, high energy sand beaches, and most mangroves. Low energy sand beaches are on the 

best way to complete recovery. The main reason for the delayed recovery of the salt marshes 

is the absence of physical energy (wave action) and the mostly anaerobic milieu within the 

oiled soils. The latter is caused by tar crusts or cyanobacteria which forms mats impermeable 

for nutrients and oxygen, thus preserving the oil in its original state. The availability of 

oxygen is the most important criteria for oil degradation. The only organisms which are able 

to break the surface tar or cyanobacteria layers - if soft enough - are crabs. They usually come 

from the lower intertidal or tidal channels. Resettlement by crabs is limited by the hardness of 

the surface substrate apart from oiled soils. Surface sediments displaying penetration 

resistances above 2.7 kg/cm² are not likely to be settled by crabs. Generally, burrowing fauna 

colonises destroyed habitats a few years before the salt marsh halophytes. Under certain 

environmental conditions cyanobacteria are able to stop the succession after the oil impact 

creating a new ecosystem that preserves the oil below the organo-sedimentary surface layers. 

The micro climate of some locations is still affected by the oil residuals in a way (increase of 

temperature extremes) that might still affect the germination success of salt marsh Chenopods. 

The petroleum hydrocarbon distribution in the soils generally display a decrease in the upper 

soil layers and an increase in the layers below suggesting a slow downward migration. This 

migration was even more pronounced for most oil associated trace metals. The overall results 

show that several processes leading to recovery are taking place. However, the time which is 

necessary to finally reach normal conditions is much longer than 10 years for the low energy 

coastal flats. Because of the slow regeneration and the fact that cleanup operations were not 

successful, the future research has to focus on oil spill prevention technologies in order to 

protect the valuable coastal ecosystems of the Arabian Gulf shores. A few examples aiming at 

environmental managers are given in the recommendations. 

XV

1 Introduction 

The Arabian Gulf, a shallow northern extension of the Indian Ocean, has been exposed to oil 

since the 1950s, when oil production commenced in the Eastern Province of Saudi Arabia. 

Transportation by large tankers as well as offshore production essentially involves a certain 

amount of pollution. The first major accident in the Arabian Gulf area, which is listed in the 

Oil Spill Intelligence Report occurred in 1972 when the Sea Star lost 115,000 t of crude oil. 

Although the marine ecosystems suffered also in the following years, scientific interest was 

never aroused until in 1991 the Gulf War lead to the largest oil spill in human history. Over 

770 km of coastline from southern Kuwait to Abu Ali Island were smothered with oil and tar, 

erasing most of the local plant and animal communities. Research institutes and 

environmental protection agencies in the region initiated extensive research programmes 

supported by international scientists. Repairing the ecological damage posed a formidable 

challenge. Beside several attempts to repair the ecological damage, the monitoring of different 

coastal ecosystems continued until 1994 and in some cases until 1995. During this time a lot 

of scientific material has been collected and it has been published more than in the entire 

period before the Gulf War. After 1995 it became silent along the Saudi Arabian shores and 

no more interdisciplinary research was carried out, although the oil impact was still obvious. 

The EU/NCWCD reports, some publications in international journals, and conference 

proceedings as well as press releases presented a picture which was often too optimistic 

regarding the overall situation at the shores of the Arabian Gulf. The reasons are manifold. In 

most cases the focus was on ecosystem types which indeed recovered nicely, in example 

rocky shores or mangroves. Some ecosystems such as the coral reefs were not affected at all. 

Other studies (e.g. Jones et al. 1995) describe salt marsh sites which were to a large degree 

recovered, but are not representative for this ecosystem type within the study area. Taking all 

this into account, the status of salt marsh areas which cover almost 50% of the coastline is in 

fact not known to the scientific community as well as to the public. These salt marshes are the 

main focus of the present study. 

This work summarizes the studies of the first four years after the oil spill and closes the gap 

between 1995 and 2001. As a result, the regeneration processes of different ecosystem types 

can be demonstrated for a 10-year monitoring period. Such a compilation of scientific 

information has not been attempted before for an oil spill in a subtropical environment. In 

order to understand the processes which lead to natural regeneration, long term monitoring 

information is essential. The main objective therefore was: a continuous monitoring of several

Introduction 

ecological parameters, the evaluation of the ecosystems regarding their status of regeneration, 

and the processes which lead to their improvement. As a conclusion, there are several 

recommendations which aim at decision makers in the field of marine and nature 

conservation, environmental management, and urban development. 

This work could not have been done without the generous support of the National 

Commission for Wildlife Conservation and Development (NCWCD) in Saudi Arabia and the 

German Research Foundation (DFG) in Germany. 

I hope that this book presents the reader a comprehensive study regarding the natural 

regeneration potential and processes of coastal ecosystems at the shores of the Arabian Gulf. 

1.1 Terminology 

1.1.1 Ecosystem type 

The term ecology is discussed since its first introduction by the biologist E. Haeckel in 1866. 

He defined it as the science of “the relations of organisms to their environment” (cited in 

Finke 1994). The history of definitions is reviewed by Finke (1994). The term ecosystem was 

introduced in 1939 by the British Forest ecologist Tansley as the complex interrelationships 

between the biota of a certain community and the abiotic environmental factors. Interpreting 

the environment (the complex interrelationships between the biota and the abiotic 

environmental factors) as open systems, which show a certain capacity of self regulation, is a 

common approach in modern ecology since the 1970s (Ellenberg 1972). The ecosystem 

represents the combined use by plants and animals of the resources provided, in one place at a 

time by the surroundings. Abiotic factors, such as air, water, nutrients, heat, and light are 

variously utilized, transformed, stored and returned to the nonliving state (Strahler & Strahler 

1999). In physical geography the question is: “Where is the boundary between one and the 

other ecosystem?” Environmental geo-ecosystems (focusing on the physical aspect rather than 

the biological one) are orderly established configurations of matter in which energetic inputs 

are causing processes and changes. Thereafter, geo-ecologically defined spatial units are 

characterized by a dynamic functional system, in which structural relationships of the 

elements (such as climate, geology, relief, soil, water, vegetation) are integrated in threedimensional 

space. Thus, in order to define geo-ecological units, a complex analysis has to be 

carried out by the specification of the elements, relationships, states, and processes of a 

17

Introduction 

certain area. Because such a complex analysis is extremely difficult, abstraction and 

simplification is required. This abstraction is achieved through the construction of models. 

Commonly used models in physical geography are topographic and thematic maps. The 

present research work is based on modelling in the sense of a mapping process with the 

following parameters as substantial elements: Relief, geological structures, soils, hydrology, 

and vegetation. So far the geo-ecological units map is static, representing the structure of the 

environmental system rather than processes going on within it and its environment. 

Functional processes can only be understood by the development of dynamic models. This is 

particularly important if the model is to be used to predict the behaviour of the system. Such 

dynamic elements are the processes of matter and energy transfer within the system itself and 

also between adjacent systems. The scope of this work is to define spatial units, not only 

representing the abiotic components but also the biota. Usually the biota of a certain area is 

the integral part of all physical parameters, which means that gradients in certain dominant 

species usually parallel physical gradients and thus mark a boundary. The most obvious 

determining parameter in the coastal area is the inundation by sea water, which results in 

different intertidal zones - each displaying its characteristic life forms. Because the definition 

of all major biotic and abiotic boundaries would have lead to hundreds of units, these were 

classified according to the relief, the dominant substrate, and the dominant vegetation. 

Because there are different intertidal zones in each of these classes, as well as differences 

regarding other parameters, the units were called ecosystem type. The ecosystem type 

represents a variety of similar habitats, which may differ in detail but are all represented by 

certain key species and the same relief and substrate. 

1.1.2 Long term 

The definition of long term varies with each author. Some long term studies comprise the 

period of shortly more than one year (Hoff et al. 1993), others cover the period of four years 

(Mendelssohn et al. 1993), and very few consider the time frame of 10 years or more (Baker 

et al. 1993). Because ecosystems are complex systems its parameters usually show 

fluctuations (Gleick 1987). These fluctuations may have a periodicity of one year or several 

years. Southward & Southward (1978) report that there were massive predatory-prey 

imbalances with marked oscillations in species population dynamics after the Torrey Canyon 

oil spill. These oscillations took 12 years before settling back to normal population balances. 

18

Introduction 

Therefore, if we are interested in changes within the ecosystem after a certain impact, we have 

to cover a time frame large enough to include the natural fluctuation patterns. The longer the 

monitoring period is, the better is the probability to cover the natural fluctuations as well as 

the fluctuations caused by the impact. Up to now there exist only few studies with monitoring 

periods longer than 5 years. Because most ecosystems in extreme environments do not 

completely recover within this time frame, it is important to continue the ecological 

monitoring until the development is complete and the ecosystems in fact reached their former 

condition. In this case, the processes leading to regeneration can be effectively documented 

and analysed. To present the ecological development of the study area for 10 years is a 

decision which is not based on certain achieved steps in recovery, but rather on the 10 th 

anniversary of the catastrophic oil spill. This study reveals for each different ecosystem type 

how many years the optimal time frame has to be, in order to cover the whole recovery 

process. 

1.1.3 Recovery 

An important question is the concept of ecological recovery. How should it be defined and 

how can it be measured? The most commonly used definition of recovery is “return to the 

conditions as they were before the impact”. This relatively simple concept is difficult to apply 

because there is virtually no information about “the way things were” before the 1991 Gulf 

War oil spill. An other problem is the fact that most coastal ecosystems are subject to change. 

These are dynamic systems where physical and biological conditions are likely to shift over 

time. The only possible method is to compare animal and plant diversity and abundance with 

unoiled sites, displaying a similar environment (control sites). Since most of the coastline 

north of Jubail was oiled the control sites were all located south of Jubail. Parallelism is 

considered to be one important measure of recovery. If there is parallelism in population 

patterns, diversity and abundance, then the ecosystem should be considered as recovered. In 

some cases the biota showed parallelism although the soil texture and hydrocarbon values 

were by far not as they were before. At such sites it is essential to distinguish the biotic and 

abiotic parameters. When the biota shows parallelism, it is usually only a matter of some more 

years until the abiotic parameters change to normal. In the following work a coastal 

ecosystem was considered to be recovered when biota (reduced to key species) showed 

19

Introduction 

parallelism in all intertidal levels and when the soil substrate was free of oil induced 

alterations. 

But still there remains the question whether recovery is at all possible for all ecosystems. In 

most cases recovery is the process of a secondary succession (Wallace 1992). The 

environment which was the original habitat of the community is still the same (at least after 

the oil has been degraded). Thus, gradually the same species will recolonise the habitat again, 

finally reaching a climax or at least the previous condition as before the oil spill. But if the 

process is a primary succession, then certain pioneer species will colonise the habitat which 

has been changed due to the oil impact, and prepare the environment (change physical and 

chemical parameters) for succeeding species. The result may be the same (climax) condition 

as before or a different one. In the latter case a recovery would be impossible. The most 

prominent example is the change of a Cleistostoma-salt marsh community which turned into a 

stable cyanobacteria habitat. The curiosity of this case is, that the pioneer species community 

also seems to be the climax community under the present environmental conditions (see 

chapter 6.1.7. and 6.1.9). 

1.2 Objectives 

The study was initiated in order to assess the conditions of the different coastal ecosystem 

types 10 years after the Gulf War oil spill. It was also designed to find out the major processes 

that lead to recovery - or prevent recovery of certain ecosystem types. These objectives 

include: 

Mapping of the coastal ecosystem types 

Evaluation of the present situation 10 years after the oil spill, including the weathering 

status of the oil residues within the intertidal soils 

Documentation of regeneration within the different coastal ecosystem types based on 

the previous work carried out during the EU/NCWCD Project until 1995 

Determination of the major processes that lead to recovery 

Determination of the major processes that prevent recovery 

Estimate the future development 

Provide recommendations for environmental managers how to improve the way we 

respond to oil spills 

20

2 Methods 

2.1 Measurement of climatic parameters 

The three automatic weather stations (Adolf Thies GmbH & Co KG, Göttingen, Germany) are 

distributed in a way that the terrestrial climate of the coastal lowlands (Abu Kharuf station) as 

well as the maritime Gulf climate (eastern tip of Abu Ali island) is recorded (fig. 3.1, chapter 

3). The third station represents the climate of the intertidal areas within the shallow 

embayment of the dissected coast line at Mardumah Bay. The weather stations are 

permanently recording air temperature, humidity, air pressure (all in a height of two meters 

above the surface), wind direction, wind speed (in a height of 10 meters), and precipitation 

(in a height of 1 meter). The data logger (Thies, DL 15) collects ten-minute mean values based 

on readings in 10 second intervals. The data was transferred to a personal computer via 

memory card (256k). Data processing was carried out with a personal computer and Unisoft 

(Thies) as well as MS Excel software. The data analyzed was collected during the years 1993- 

1996 and in winter 2000/2001. 

Temperature profiles were measured by a set of thermometers fixed at different heights. The 

surface and soil temperatures were determined using digital thermometers. For permanent 

temperature recordings in the intertidal soils Stow Away TidbiT Temperature loggers with 

optic communication (Onset computer corporation, USA) were used. Data processing was 

carried out on the Onset BoxCar 3.6 Starter Kit for Windows. 

Dew measurements were carried out by a dew balance (Lambrecht, Germany) which was 

installed in a distance of 200 m from the tidal fringe an a low energy sand beach close to the 

project center. The dew was weighed and automatically recorded. 

Evaporation was measured by the use of Piche evaporimeters that were fixed in various 

heights above the soil surface. Evaporation directly at the soil surface was determined by 

buried plastic vials which were filled by a defined volume of water. After 24 hours the water 

loss was measured. This method does not provide any absolute values, but the relative values 

allow the comparison of different sites and locations, which was the main goal of the study.

2.2 Vegetation and fauna 

Methods 

Ecological data on the plants have been collected during repeated visits to the study area in 

1994, 1995, 1996, 1999, 2000, 2001 and 2002. Additional data was available for the period 

between 1991 and 1994 in the reports and interim reports (unpublished) by Böer (1992, 

1994a). Vegetation monitoring was carried out along permanent transects and additional 

transects representative for each of the different ecosystem types. Three test squares (100 m²) 

were established at each of the permanent transects. During the mapping and assessment at 

other sites, vegetation was counted and ground cover estimated within test squares between 

25 and 100 m² size. Ground cover was estimated using a 1 m² frame with 0.01 m² mesh, 

measuring the ground cover to the left and right of a 10 m straight line. 

Epifauna was measured with the method described by Jones et al. (1994) by taking five 

random replicates of a 1 m² square, recording the organisms as percentage cover or counting 

them individually. Crab populations were counted by the amount of crab burrows per m² as 

described by Apel (1994). Infauna was measured after Jones et al. (1994), using a core which 

was sieved through a 1 mm mesh in order to collect the macrofauna. For identification 

assistance was provided by Jaime Plaza (University of Bangor, UK), Lucien Hoffmann 

(Université de Liège, Belgium) Alistair Jolliffe (University of Warwick, UK) and Uwe Zajonz 

(Senckenberg Research Institute, Germany). The diversity and abundance values were 

compared with unoiled control sites in order to estimate the status regarding recovery. 

2.3 Mapping of the coastal ecosystem types 

The different coastal ecosystem types were identified by mapping the relief, the dominant 

substrate, and the dominant vegetation. This was carried out during several field studies 

between 1994 and 2001, when almost every stretch of the coast line was visited. Additional 

data was provided by two helicopter flights along the coastline in 1993 and 1995. 

2.4 Selection of the study sites 

The permanent study sites were established where Böer (1992, 1994) and some other 

scientists collected data before. This was essential in order to compare the development of the 

22

Methods 

ecosystem for the complete time from 1992 until 2001. The permanent test sites comprise one 

intertidal transect dominated by Halocnemum strobilaceum, one dominated by Arthrocnemum 

macrostachyum, one of a mixed mangrove and salt marsh community, one of a mangrove 

community, one at a low energy sandy shore, one at a high energy sandy shore, and one at a 

rocky shore. Several other transects were established and revisited occasionally in order to 

check whether the permanent transect lines show a different development. The permanent 

transects are concentrated within the southern part of the study area for practical reasons. It 

was essential that the transects are easily accessible within a 1 hour drive. Otherwise the 

intensive monitoring program during the winter period of 2000/2001 would not have been 

possible. 

2.5 Soil samples: collection and preparation 

Soil samples were collected at each visited transect in various depths according to changes in 

colour or substrate. Each sample incorporated three individual subsamples from the same 

location. Soil texture was analysed using a standard sieve set. Electric conductivity was 

measured with an LF 92 (WTW, Germany), pH was measured with a pH 91 set (WTW). Soil 

water content was determined by weighing before and after drying at 80°C for 8 hours. Fine 

sediment analysis of the fraction below 0.063 and 0.02 mm was difficult because of the high 

calcium carbonate content of the samples. Therefore in the fraction finer than 0.063 it was not 

differentiated between silt and clay. The calcium carbonate content was analysed by means of 

the Scheibler apparatus. The soil colour was determined with the standard soil colour charts 

by Oyama & Takehara (1970). 

Soil hardness (penetration resistance) was determined by an Eijkelkamp penetrometer and the 

vane shear force by the Eijkelkamp vane shear force meter. 

Sedimentation on cyanobacteria flats 

For measuring the amount of material deposited on top of the cyanobacteria in the upper 

intertidal, near section 9 (165 m mark) and 10 (150 m mark) of the Arthrocnemum transect, 

the material on top of the leatherlike mat was collected from 100 cm², dried and weighed. To 

determine the amount of material transported by the tidal waters, a circular sedimentation 

measurement device with 15 cm diameter was buried between the cyanobacteria to form a 

level surface. It worked in a way that substrate transported by the water would be collected in 

the container. The device consists of a container (20 cm deep) and a lid with 4 metal bars, 

23

Methods 

leading tidal waters and suspended substrate into the container. This container was emptied 

every two weeks. Three of these devices were installed. 

2.6 Petroleum hydrocarbon analysis 

Solvent extraction 

The dried homogenized soil samples were packed into glass Soxhlet extraction thimbles. The 

extraction was carried out with a Soxtherm S 306A extraction device (Gerhardt, Germany). 

The samples were Soxhlet extracted using dichloromethane for 12 hours. Extracts were rotary 

evaporated down to a minimal volume for gas chromatography. The total weight of organic 

material extracted from the sediment was determined using an aliquot of the sample. After 

rotary evaporation the extract was weighed. The amount of hydrocarbon is expressed as gram 

per kilogram dry soil. 

Gas chromatography 

For the analysis in 2001 and 2002 the same method that was applied by Smith (1995) was 

used in order to be able to compare the results. The extracted organics were transferred to a 

chromatography column containing 5% water deactivated silicia and alumina in pentane, 

which was prepared by the method of Law et al. (1988). The aliphatic hydrocarbons were 

initially eluted from the column using 40 ml n-pentane; the polyaromatic hydrocarbons were 

eluted secondly using 20 ml 10% dichloromethane in n-pentane followed by 20 ml 20% 

dichloromethane in n-pentane. Each fraction was evaporated down to a minimal volume and 

transferred to a pre-weighed vial for subsequent GC, HPLC and gravimetric determinations. 

Analysis by Smith (1995) was carried out on a Varian Star 3400 gas chromatograph in the 

Jubail research centre. A carrier gas of helium and a nitrogen make-up gas were used with a 

flame ionisation detector. A 30mSE54 capillary column (Alltech, UK) was used along with a 

temperature program of 50 to 300°C at 10°C/min. For calibaration n-tridecane was used as a 

standard. The high performance liquid chromatography (HPLC) was performed on a Varian 

9010 quaternary pump with a Varian 9070 programmable, pulsed Xenon fluorescence 

detector. A 15 cm Sperisorb S5 PAH column was used with a reverse phase 1 cm guard 

column. A solvent system of HPLC grade water and acetonitril was used at a flow rate of 1.5 

ml/min with a solvent gradient of 43% to 100% acetonitril in 40 min. Each poly-aromatic 

24

Methods 

hydrocarbon was individually optimised to specific excitation and emission wavelengths for 

enhanced sensitivity. 

Later analysis (after 1994) was carried out by the Jubail laboratory of the Royal Commission 

for Jubail and Yanbu (RCJY) Industrial College by Mr. Hossam Al Jabbad. The samples 

collected in spring 2002 were analysed in the Department for Organic Chemistry at the 

University of Regensburg, Germany, by Dr. Varsold with the friendly support of Prof. Dr. 

König. 

Rapid assessment oil prints 

The oil print rapid assessment was developed in Jubail. This method is based on the fact that 

oil is floating on water. Multiple rinsing of a 10 g sample with a defined volume of water (5 x 

20 ml water) and collection of the extract (in a vessel with a capacity of exactly 100 ml so, 

that after filling, the water-oil surface is level with the vessel fringe), leads to a sufficient 

amount of oil floating on the water surface, which can be printed on a stable absorbent paper. 

The oil is absorbed by the paper as soon as it contacts the water-oil surface. In most cases the 

oil is absorbed completely by one paper print. More degraded oil constituents develop a 

strong hydrophobia. It can therefore not be separated from the sediment and will not show on 

the paper print, thus indicating the high weathering status. This is an important advantage to 

the quantitative hydrocarbon extraction with solutes, where well degraded oil residues are also 

extracted and might indicate a high degree of oil in the sediment, no matter how the 

degradation status is. 

2.7 Trace metal analysis 

Prior to analysis, the samples were freed of soluble salts with deionised water and dried at 

40°C. The total trace elements abundances were analysed after complete sediment digestion 

with nitric acid and hydrofluoric acid (HNO5/HF). Partial extraction with 0.53 N HCl was not 

performed, because in the 1994 sampling period only complete sediment digests were 

analysed. Analysis of total digests and partial extracts for Cr, Ni, V, Cu, Pb, Cd, As and Zn 

were accomplished by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP/AES) 

at the laboratory of the Royal Commission for Jubail and Yanbu Industrial College in Jubail, 

by Dr. Hossam Jabbad. Calibration curves were constructed on standard solutions and blanks 

25

Methods 

in the matrix matching the analyte solution. Two replicates of each sample were run. If 

deviation was more than 10% a third replicate was analysed and the mean value calculated. 

2.8 Radiocarbon analysis 

Some air dry samples of laminated cyanobacteria mats were radiocarbon dated in order to 

determine the fraction of fossil carbon (originating from the oil). The analysis was carried out 

at the laboratory of the Niedersächsisches Landesamt für Bodenforschung, Hannover, 

Germany, by Prof. Dr. M. Geyh. 

2.9 Water analysis 

Groundwater samples were collected from plastic tubes at the same locations where soil 

samples were collected from (only at the permanent transects). The tubes were dug into the 

soil to a depth of 70 cm (unless beachrock prevented it) in a manner that groundwater but not 

seawater could enter. The tubes were perforated at the lower part, which was buried in the 

soil, and the bottom of the tubes was closed by a fine aluminium mesh to separate the water 

from the substrate. Above the surface the tubes were closed by a plastic lid to prevent rain 

water from entering. Groundwater samples were analysed by a Merck photo spectrometer SQ 

118 in Jubail. Calcium and Magnesium concentrations were determined by the use of a Hach 

digital titrator, model 16900-01. Oxygen content was measured with a WTW Oxi 92 set. 

Temperature and salinity were measured with the WTW LF 92 set. 

26

3 Physical setting of the study area 

3.1 Geology 

The geologic situation of the Gulf region is basically the result of continuous sediment 

accumulation since Paleozoic times. The present structure was established during major 

tectonic processes in the Tertiary period. The Arabian Peninsula originally was attached to 

the African (Nubian) Shield. At the beginning of the Cambrian to the north and the east of the 

Arabian Peninsula a great sedimentary basin (Tethys) had developed. Throughout the 

Paleozoic, Mesozoic, and early Cenozoic times sediments, accumulated in this slowly 

sinking trough. In the wide epicontinental seas between the Tethys and the Arabian 

Peninsula, a relatively thin succession of almost flat lying Paleozoic, Mesozoic, and early 

Cenozoic strata was deposited (Chapman 1978). These strata spread widely over the 

eastern Arabian Peninsula. In the late Cretaceous, orogenic movements constituted the first 

stage of the Alpine orogeny. The second stage began in the late Tertiary, when the deformed 

rocks of the geosyncline started to rise leading to the formation of the Taurus, the Zagros 

mountains, and the Oman mountains. The Arabian Peninsula itself was little affected by this 

uplift except for being tilted towards the eastern Arabian Gulf region. There subsidence 

continued. In the middle Tertiary (25 Ma ago), when these events were at progress, the 

Arabian plate started to split away from the African Shield along the large rift system which 

extends from the Gulf of Aqaba and the Dead sea rift in the north to the Afar triangle in 

Ethiopia. There it diverges through the Gulf of Aden into the Arabian Sea and down the 

African mainland as the large African Rift Valley System in the south. The separated Arabian 

plate started moving northeastward with a slight counter-clockwise turn, sliding beneath the 

great Asian plate in Iran. The tensional forces along the rift lead to the formation of a graben 

structure (Red Sea depression) with a pronounced relief between the plateau and the floor of 

the rift. Magma rising up the faults covered large parts of the eastern Arabian Shield. This 

development continues until the present. The current Red Sea rift is estimated to be between 

2 and 3 cm each year (Stanley 1994). 

The Arabian Peninsula can be divided into two structural provinces. The Arabian Shield in 

the west is part of the Precambrian crustal plate, generally exposed except the parts which 

are covered by tertiary volcanic rock. The second structural province is the Arabian Shelf in 

the east which consists of the sedimentary sequences covering the plate.

3.1.1 The Arabian Shield 

Physical setting of the study area 

The Arabian Shield is an ancient land mass in the western part of the Arabian Peninsula, 

covering approximately one third of the Arabian Peninsula (fig. 3.1). It is a peneplain now 

sloping gently towards the north, northeast, and east and vanishes under a thin sedimentary 

cover in eastern Arabia. The Precambrian basement consists of the basement gneiss (mainly 

amphibolite facies), metamorphosed terrestrial sediments, and volcanic rocks of the 

greenschist facies and countless granitoid plutonic bodies. Long term terrestrial conditions 

eroded the Precambrian orogenes, forming a peneplain which was partly covered by extensive 

lava masses in the Tertiary period. Today about 15% of the shield are covered by volcanic 

rock (Child & Grainger 1990). 

3.1.2 The Arabian Shelf 

The Arabian Shelf lies to the east of the shield where it forms two thirds of the peninsula. Its 

foundation consists of the same Precambrian plate that makes up the shield. On top of this 

basement a series of continental and shallow water marine sediments accumulated, ranging 

from Cambrian to Pliocene age. These layers dip gently away from the shield into a number 

of deep basins (Chapman 1978). Thus the thickness of the sediment strata increases gradually 

from the west to the east where in the coastal lowlands 11,000 m are reached (Alsharhan & 

Nairn 1997). Beside the main Zagros Reverse Fault even 18,000 m of sediment has 

accumulated (Edgell 1996). Erosion exposed most of the sediments, forming a series of 

parallel strike escarpments facing westward, each capped with resistant limestone. These 

cuestas are exposed in a great curved belt along the eastern margin of the shield, reflecting the 

gently arched surface of the buried basement. Large parts of the basins in the southeast 

(Rub’al Khali), east (Gulf), and northeast (Nefud) are covered by quaternary sandy sediments. 

The Persian Gulf Basin is the largest basin with active salt tectonism in the world. The more 

than 900 km long Arabian/Persian Gulf is the present-day geosynclinal expression of the 2600 

km long Persian Gulf Basin. The Persian Gulf Basin consists of a number of NW-SE 

trending, geotectonic units such as the Arabian Plattform and the zone of marginal troughs, 

including the Zagros Fold Belt, limited on the northeast by the Main Zagros Reverse Fault 

(Edgell 1996). The Basin is crossed by several N-S structures, expressed by the major Qatar- 

Kazerun lineament (Qatar Arch). These rejuvenated uplifts have existed for 650 Ma. The 

Halokinesis in the Arabian/Persian Gulf originates where major intersecting basement faults 

(e.g. the Qatar-Kazerun lineament) cut the buoyant salt beds of the different formations 

28


(Edgell 1996). Diapiric oil fields as a result of salt tectonism account for 60% of the 

recoverable oil reserves of the Persian Gulf Basin (Edgell 1996). 

2 cm/year 

RED 

SEA 

Quarternaryl 

Tertiary volcanic rocks 

Miocene and Pliocene 

Oligocene 

Palaeocene / Eocene 

Cretaceous 

Jurassic 

Triassic 

Palaeozoic 

Precambrian 

Fig. 3.1 Geology of the Arabian Peninsula and tectonic movements (after Chapman 1978 and 

Johnson 1998). 

3.1.3 The Arabian Gulf coastal region 

ARABIAN 

GULF 

Rub’ al Khali 

3.2 cm/year 

2 cm/year 

The southern part of the Mesopotamian depression includes the Arabian Gulf and a narrow 

coastal strip of the Arabian Peninsula. This coastal strip is the Arabian Gulf coastal region. 

The elevation of the coastal region rises gradually inland at a rate of about one metre per 

kilometre. The coastline is irregular, low, and sandy and the water has many shoals, so that 

tidal changes cause the waterfront to shift back and forth up to several kilometres. Sabkhat 

(salt flats) are common all along the coast from Kuwait to the southern end of the Arabian 

Gulf (Barth 2002). Along the northwestern shores north of Jubail, low rolling plains, covered 

with a thin mantle of sand, are characteristic. These sand sheets are mostly covered by a 

29


semi desert vegetation. Further to the north the “Northern Plains” southwest of Kuwait is 

characterised by a wide gravel plain. This triangular plain has its apex near Al Qaysumah 

and spreads towards the northeast almost to the Tigris and Euphrates valleys. It is a large 

alluvial fan of the Wadi Ar Rimah – Wadi Al Batin drainage system, which brought rock debris 

from the eastern crystalline uplands during one of the pluvials in the Pleistocene period. 

Reconstruction of the former river system which is partly covered by sand was recently 

possible by means of radar satellite analysis (Dabbagh et al. 1998). Most of Kuwait’s surface 

consist of the Pleistocene alluvial sediments of the great “Arabian River” (El Baz & Al Sarawi 

1996). South of Jubail is a wide belt of drifting sand that widens southward and merges with 

the sands of the Al Jafurah desert. Areas that are not covered by sand or sabkhat consist of 

Tertiary limestones. The relief is generally weak. The coastal lowlands are bordered by the 

As Summan Plateau in the west. The eastern edge of the late Tertiary As Summan plateau is 

a prominent escarpment indented by ancient stream valleys. In front of the escarpment, 

several buttes and mesas project prominently into the coastal lowlands. Near the northern 

limits of the Rub’ al Khali, this escarpment fades out leaving a less distinct boundary. 

3.1.4 The study area 

Abu Kharuf 

meteorological station 

Mardumah Bay 

Abu Ali 

Fig. 3.2 Location of the study area and the meteorological stations discussed in chapter 3.2.2. 

The study area is located at the Arabian Gulf coast, north of Jubail Industrial City and covers 

about 400 km of coast line (fig. 3.2). It belongs to central coastal lowlands of the Eastern 

30


Province of Saudi Arabia. The relief between Ras az-Zawr in the north of Musallamiyah Bay 

and Jubail in the south is weak, although some rocky exposures in the form of minor 

escarpments (5-20 m high) and small domes are quite common. These belong to the Miocene 

and Pliocene Hadrukh- and Dam formations and consist of sandy limestone, marl, gypsum, 

and beachrock formations (fig. 3.3). 

height above sea level 

Dam formation 

Hadrukh 

formation 

sabkha 

Fig. 3.3 Geology of the study area. 

Dawhat al Musallamiyah 

0 5 km 

Khursaniya 

Dawhat ad-Dafi 

The outcrops of the Hadrukh formation occur in the western part of the study area. In the 

limestone of the Hadrukh formations chert and gypsum layers are prominent. The rocky 

outcrops in the northern part of the area under consideration belong to the Dam formation 

consisting of hard limey sandstone, marl, soft sandstone and beachrock with the typical fossils 

that are widespread in the region (Cerithium, Hexaplex, Vermetus). Occasionally remnants of 

Jinnah 

Sabkha 

Murayr 

31


former coastlines in the form of fossil cliffs and marine abrasion terraces can be found. 

Although the knowledge about the Pleistocene sea level fluctuations in the Arabian Gulf is 

modest, they were mentioned by a number of authors. Felber et al. (1978) found a series of 9 

terrace levels reaching from the early Pleistocene to the Neolithic pluvial in the middle 

Holocene. 

The largest part of the study area is covered by sand sheets and dunes. The sand sheets are 

flat sandy plains, mostly covered by scattered perennial grasses and herbs (vegetation cover 

ranges from 1 to 10%). The sands range from coarse to medium. In areas which have been 

positively identified as sand source areas by the existence of exposed root systems (Barth 

1999, 2001b), the top layer (0.5-1 cm) consists of unimodal coarse sand (median: 1.5 mm), 

which are sometimes arranged in giant ripples. The clay and silt fraction is missing, owing to 

aeolian activity. The dunes, which are prominent in the northern part of the study area 

around Dawhat al-Musallamiyah, document a more arid period in the Holocene and 

Pleistocene when aeolian activity had a much higher morphological impact on the formation 

of the topography. Dominant are degenerated longitudinal dunes with their axis in NNW-SSE 

direction, thus forming a sequence of sand walls with undulated ridges, sometimes several 

hundred metres long. The depressions in between are often characterized by deflational 

processes. Most of the dunes are stabilized by a diffuse pattern of perennial grasses and 

herbs. Where vegetation cover is less than 2% (due to overgrazing), the dunes are 

reactivated. In the south as well as in the west of the study area, active sand dynamic is 

reflected in transverse barchanoid dunes without any vegetation cover and movement up to 

3 m/yr (Siebert 2002). 

A particular feature, typical for the western and southern Gulf coast, is the flat and wide 

spreading coastal sabkha. Penetrating up to 10 km inland they cover areas of more than 100 

km². Sabkha is the Arabic term for flat salt-crusted desert. The local terminology of the Gulf 

region describes the extensive, barren, salt encrusted, and periodically flooded coastal flats as 

well as inland salt flats (Barth & Böer 2002). They consist basically of sand or finer 

unconsolidated substrate. Their surface is an equilibrium of deflation and aeolian 

sedimentation, controlled by the local shallow ground water level which is the lower limit of 

deflation. 

32

3.2 Climate 

3.2.1 General pattern of the Gulf region 


The climate of the Gulf region is a typical desert and semi-desert climate, characterized by 

high summer temperatures and aridity throughout the year, due to its geographical situation 

within the subtropical high pressure belt. Descending air is adiabatically warmed as it looses 

altitude and consequently dried. This leads to an almost complete dispersal of cloud and an 

absence of rain, except when this pattern is disturbed by incursions from outside. These 

occur in the winter months between October and April. Thus, in the coastal lowlands of the 

Eastern Province of Saudi Arabia, rain is confined to this period. The Trade Winds, which are 

generally north-easterlies, become north to northwest winds as a result of locally dominant 

pressure patterns over the Gulf and the Asian land mass to the east. The surface circulation 

in the summer months is influenced by two pressure zones. First, the eastern north African 

high pressure centre, which – because of its clockwise turn – leads to northern currents over 

the Arabian Peninsula. Second, the thermal continental low pressure cell over the Asian land 

mass that reaches from the Indian subcontinent into the Arabian Gulf. It provides – because 

of its anti-clockwise turn – a northerly current on its western flank (fig. 3.4 A). Due to the 

southward shift of the global pressure belts in the winter months, atlantic cyclones breaking 

free from the sub-polar low pressure belt move eastward across the Mediterranean Sea and 

pass across the northern part of the Arabian Peninsula. These depressions are gradually 

dissipated as they move east or southeast across Arabia, and the probability of rain thus 

decreases to the southeast. South-eastern winds are the result of currents on the southwestern 

flank of the continental Asian high pressure cell (fig. 3.4 B). 

Precipitation in the Gulf region in not exclusively due to the influence of Mediterranean 

depressions. Recent studies by Steinkohl (2002) demonstrate that the formation of new low 

pressure centres in Iraq, west to the Zagros mountains is equally important. Thermal 

convection, as well as the influence of currents from Sudan and Ethiopia, are other 

precipitation sources (tab.3.1). 

33

A 

B 

Africa 

Africa 

Europe 

Europe 


Arabia 

Africa India 

Arabia 

Arabia 

Indian Ocean 

Indian Ocean India 

Fig. 3.4 Pressure zones influencing the Arabian Peninsula in July (A) and January (B) after Breed et 

al (1979). The low pressure trough above the Arabian Gulf in summer leads to strong northern and 

northwestern currents of the Shamal. 

Tab. 3.1 Types and number of major precipitation events in the Eastern Province (Steinkohl 2002). 

Precipitation type 1993/1994 1994/1995 2000/2001 Total 

Mediterranean depressions 4 3 3 10 

Formation of new low pressure 

cells 

3 5 2 10 

Convection 2 3 4 9 

Currents from Sudan/Ethiopia 1 6 1 8 

others 0 0 2 2 

India 

34

3.2.2 Climate in the study area 


The climate in the study area is documented by the recordings of 3 meteorological stations 

distributed in a way that the terrestrial climate of the coastal lowlands (Abu Kharuf station), 

as well as the maritime Gulf climate (eastern Tipp of Abu Ali island), is recorded (fig. 3.2). 

The third station represents the climate of the intertidal areas within the shallow embayments 

of the dissected coast line at Mardumah Bay. 

Temperature 

Maximum and minimum temperatures of the coastal lowlands vary from more than 50°C in 

summer to 3°C in winter. In some inland areas even temperatures below 0°C were observed 

(Child & Grainger 1990). For the coastal region in the study area, the influence of the Arabian 

Gulf is reflected in less extreme values. Because of the shallowness of the Gulf (27.2% of the 

Gulf are less than 10 m deep (MEPA 1987)), and the restricted water exchange (see chapter 

3.5) the amplitude of the water temperature (18-33°C) is higher than in other oceans. 

Therefore, the reduction of the air temperature amplitude in the coastal region is less 

compared with other maritime locations of similar latitudes. The mean annual temperatures of 

the three stations vary between 25.2°C at the inland station (Abu Kharuf) and 26.5°C at the 

maritime station (Abu Ali). Extreme values were 49.2°C and 4.1°C at Abu Kharuf and 44.3°C 

and 12.1°C at Abu Ali station. The amplitude (45.1°C) at Abu Kharuf is 12.9°C higher. This 

and the lower annual temperature, demonstrates the increasing continental character in only 5 

km distance to the sea. The intertidal station at Mardumah Bay displays intermediate values 

(fig. 3.5 and 3.6). 

Fig. 3.5 Climatological diagram of the intertidal station Mardumah Bay (data of 4 years). 

35

temperature in °C 

36,0 

34,0 

32,0 

30,0 

28,0 

26,0 

24,0 

22,0 

20,0 

18,0 

16,0 

14,0 

12,0 

Jan 

Feb 

Mar 

Apr 


May 

Jun 

Jul 

Aug 

Sep 

Oct 

Nov 

Dez 

Abu Ali 

Abu Kharuf 

Mardumah Bay 

Fig. 3.6 Mean temperatures at the different meteorological stations within the study area. Gulf water 

temperatures after Hastenrath & Lamb (1979). 

The smoothing effect even of the shallow Gulf waters are of major ecological importance to 

the intertidal fauna and flora. Both live close to the limits regarding the temperatures and 

salinities. Therefore, absolute summer temperatures more than 5°C lower and winter 

temperatures more than 6°C higher than in adjacent inland areas are much in the favor of 

both, plants and animals (fig. 3.7). 

Temperature [°C] 

46 

44 

42 

40 

38 

36 

34 

32 

30 

28 

26 

1 3 5 7 9 11 13 

Time 

15 17 19 21 23 

Abu Ali Abu Kharuf 

Fig. 3.7 Temperatures of a day in summer (25. August, 1994) and winter (18. January, 2001) at the 

maritime and coastal station. Note the difference in the amplitude between the coastal and inland 

station. 

Relative humidity 

The monthly mean values of the relative humidity vary between 56 and 78% on Abu Ali 

island and 31.1 and 72.1 at Abu Kharuf. Mardumah Bay again displays intermediate values 

Temperature [°C] 

26 

24 

22 

20 

18 

16 

14 

12 

10 

Gulf 

8 

1 3 5 7 9 11 13 

Time 

15 17 19 21 23 

Abu Ali Abu Kharuf 

36


between 47.5 and 75.6%. The higher values are reached during the winter period. Absolute 

values range between 13 and 100%. At the intertidal station Mardumah Bay, the relative 

humidity never drops below 20%. Figure 3.8 demonstrates the intermediate values of the 

intertidal station compared to Abu Ali and Abu Kharuf. The daily pattern is closely related to 

the temperature curve. Increasing temperatures decrease the relative humidity (fig. 3.9). 

During night time the relative humidity often reaches more than 90%, which leads to 

significant dew precipitation in the coastal region. 

rel. humidity [%] 

90 

80 

70 

60 

50 

40 

30 

20 

10 

Mard.B. Abu Ali A.Kharuf 

0 

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 

days 

Fig. 3.8 Relative humidity at three stations in August 1994. 

rel. humidity [%] 

100 

80 

60 

40 

20 

0 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 

Fig. 3.9 Relative humidity at Abu Ali and Abu Kharuf in January (18.01.2001). 

time 

Abu Kharuf rel. humidity Abu Ali rel. humidity Abu Kharuf temperature Abu Ali temperature 

30 

25 

20 

15 

10 

5 

temperature [°C] 

37


Dew precipitation 

Dew is a frequent phenomenon at the coastal areas where it occurs at night with relatively 

higher values in winter than in summer. Dew measurements during the winter period 

2000/2001 close to the intertidal, provided the highest values in January with 0.04 mm per 

night. November values are 0.021 mm in average. The significant loss of data is due to 

strong winds and rain events, both of which prevent dew precipitation. The measured total 

was between 0.27 and 1.1 mm each month (tab. 3.2). This may not seem significant, 

regarding the total amount of water provided by dew (probably not more than 7-8 mm/year), 

but the fact that this water is deposited almost every night on top of the plant leaves make it 

a very important factor in water supply, especially because the high variability of the rain 

events. 

Tab. 3.2 Dew in the winter months between 2000 and 2001 (Jubail, 200m distance to the littoral 

fringe). The data loss is due to high winds or rain events, when dewfall would be minimal. 

Precipitation 

month total loss of data mean amount of dew/night 

[mm] days [mm] 

Nov 0,272 17 0,021 

Dez 1,058 4 0,039 

Jan 1,107 4 0,041 

Feb 0,665 7 0,032 

Mar 0,490 12 0,026 

Apr 0,629 11 0,033 

Precipitation in the Gulf region is confined to the winter months from October to early May. 

The annual rainfall at Dhahran over 39 years has ranged between extremes of 5 mm and 

277 mm (Mandaville 1990). This extreme variability of rain is a typical phenomenon in desert 

regions. An other characteristic for desert rains is the intensity. Most of the total annual 

precipitation is delivered in a few torrential rainfalls. This is well documented by the example 

in figure 3.10. An the 12 th of December, more than 50 mm fell at Mardumah Bay station, 

which is more than 60% of the long term total annual precipitation. Because such intensive 

rainfall is the result of convective thunderstorms, the rain distribution is very different locally. 

This is also well demonstrated by the December event on 1994 (fig. 3.10). In addition to the 

variability of the amount, there is also a strong local variability. Such events were also 

recorded in 1993 and in 2000 (Steinkohl 2002). 

38

mm 30 

25 

20 

15 

10 

5 


0 

1 3 

time 

5 7 9 11 13 15 17 19 

Abu Kharuf Abu Ali Mard. Bay 

21 

23 

Mard. Bay 

Abu Ali 

Abu Kharuf 

Fig. 3.10 Precipitation on the 11 th of December 1994 at the three stations. Note the high local 

variability. 

An other aspect which is very important for plant ecology is the number of precipitation 

events in a rain season and the timing of these rainfalls. For example at Abu Kharuf, 19 rain 

events were recorded in the 1993/94 rain season (tab. 3.3). In the following year, there were 

44 rain events which allowed a much better development of annual and perennial plants. 

Success of germination after rain events depends not only on the amount of rain, but rather 

on the weather in the following days. Hot sunny days increase evaporation and desiccate the 

upper soil layer, thus, preventing many desert annuals from germination. Cloudy days and 

one or two other rain events in the following week on the other hand will lead to a flush of 

germinating annuals within a few weeks. 

Tab. 3.3 Precipitation events per rain season at the three stations. 

Abu Kharuf Abu Ali Mardumah Bay 

1993/1994 19 14 13 

1994/1995 44 30 33 

2000/2001 25 no data 30 

Wind 

The mean wind velocities measured in the study area between 3.5 and 6.9 m/sec are typical 

for the Eastern Province and even low compared to world standards. There is mostly a 

diurnal pattern with calm winds at night and maximum values during midday or early 

afternoon (fig. 3.11). At night, cooling creates a stable surface layer. The temperature 

inversion prevents vertical air exchange. As the sun rises, convection disturbs the inversion, 

39


probably supported by gravity waves at the surface of the inversion (Warren & Knott 1983). 

The unstable atmosphere promotes turbulent vertical air exchange, bringing high velocity 

upper winds down to the surface often causing gusts. Wind speeds usually continue to 

increase until the afternoon, driven largely by convection. 

m/sec 

days (June) 

Fig. 3.11 Wind diagram for June 1995 (Abu Kharuf station) (Barth 2001b). 

Although the monthly mean values between 3.5 and 5.1 m/sec at Mardumah Bay station 

(complete data in appendix 1, tab. 4) are low, the wind speeds at midday are frequently 

above 6 m/sec, which is enough to move sand at sparsely vegetated areas. Gusts reach 

much higher values often exceeding 12 m/sec. These winds significantly increase the 

desiccating power of the already dry and hot atmosphere, they have a powerful effect in 

modelling topography, particularly in dune sands, and directly affect the root stability of 

individual plants. In the course of one year 6 different wind regimes occur (Barth 2001b). This 

is: (1) a high energy Mediterranean north-west regime from November to February; (2) a 

bimodal cyclonic end-phase in March; (3) a moderate eastern spring phase in April; (4) a 

complex transition phase in May; (5) a high energy summer Shamal regime from June to 

August; (6) a low energy autumn phase in September and October. It is characteristic for the 

Eastern Province that all the high energy winds (winds above 6 m/sec and thus 

morphologically relevant - phase 1 and 5) come from north to northwesterly directions 

creating a wide unimodal wind regime with intermediate energy in the sense of Fryberger & 

Dean’s (1979) wind classification (fig. 3.12). 

40


Abu Kharuf, 10 m.a.s.l. 

106 days with daily mean above 6 m/sec (=100%) 

56 days 6-8 m/sec 

40 days 8-10 m/sec 

10 days > 10 m/sec 

Abu Kharuf, 10 m.a.s.l. 

Fig. 3.12 Wind rose for the Abu Kharuf station (after Barth 2000). 

Evaporation 

High temperatures - especially in summer - , low relative humidity, and permanent wind 

(during daytime) result in extreme evapotranspiration rates. There is no reliable data 

available regarding the evapotranspiration in the Gulf region. Mean annual values of class-A 

pan measurements in Hofuf (50 km inland) are 2660 mm (Saudi Arabian Ministry of 

Agriculture and Water Resources 1980) which is about 42 times the annual precipitation. 

Towards the south and further inland evaporation increases. Mean values of class-A pan 

measurements in As Sulayyil at the western edge of the Rub’al Khali desert are 5250 mm 

(Mandaville 1990). But these values are certainly higher than the potential 

evapotranspiration, mostly due to the isolation effect of the water filled pan. Most 

measurement devices do not reflect the real evaporation values. By means of formulas and 

correction factors, the potential evapotranspiration can be estimated – but only for the 

climatic conditions that they were designed for. The problems of evaporation and 

evapotranspiration measurements is treated by several authors (e.g. Haude 1954, Besler 

1972, Rosenberg et al. 1973, Henning & Henning 1984, Weischet 1995, DVWK 1996, Barth 

1998, Obermüller 2002) and will not be discussed here. Regarding different calculation after 

Penman, Thornthwaite, Haude and Besler the potential evaporation in the Jubail coastal area 

is estimated to be between 2200 (Barth 1998) and 3500 mm (Obermüller 2002) per year. 

Regarding the intertidal area which is regularly inundated the actual evaporation is near the 

potential evaporation. The upper intertidal, which is only periodically flooded shows only 

41


slightly less evaporation because of the permanent wet soil surface due to capillary force. 

Obermüller (2002) measured the actual evaporation in coastal sabkhat close to the intertidal 

north of Jubail. These data indicate an annual evaporation of 3500 mm. Therefore we can 

assume the same values for the intertidal during the times when the surface is not covered 

by sea water. 

3.3 Hydrology 

Low annual precipitation rates, high variability in quantity and locality, and high evaporation 

throughout the year result in a permanent water deficiency. The obvious result is the 

absence of perennial streams within the Arabian Peninsula. Even the Wadis in the western 

mountains display only periodical flows. The main water divide of the Arabian Peninsula runs 

along the highest ridges of the western mountains in north-south direction. The impermeable 

basement rocks (except some basalt flows) prevent infiltration and any substantial 

groundwater recharge. The overland flow, especially after torrential rains, is therefore high 

and has a powerful effect in modelling topography, particularly at the western side of the 

mountains with frequent knife edge ridges and deep canyons. In contrast to the western 

impermeable surface there are permeable sediment sequences with the enormous 

underground aquifers in the cuesta landscape of the Arabian shelf (fig. 3.13). Limestone 

sequences and some sandstones show excellent transmissibility and water bearing 

properties. The aquifers are sometimes divided by impermeable silt, clay or marl layers. The 

most important freshwater aquifer is the Paleocene Umm Er Radhuma formation, basically 

consisting of pure limestone. The outcropping curve is 50-100 km wide and extends from the 

Iraqi border to the Rub’al Khali. Because large parts of the outcropping Umm Er Radhuma 

formation are covered by dunes of the Ad Dhana desert, there is even some water 

replenishment in this formation. Studies by Dincer (1973) showed a replenishment of 2 mm 

per year, which would add approximately 30 million cubic metres of water each year only in 

the area that is covered by the Ad Dhana. The groundwater resources of the Arabian 

Peninsula can be divided in the underground aquifers (which are by far most important), the 

reservoirs within the gravels and unconsolidated substrates of the north-eastern part of the 

Peninsula, the groundwater within the wadi sediments (although their capacity varies with 

precipitation and size of the catchment area), and the groundwaters below the Tertiary basalt 

flows (also depending on precipitation). The groundwater of the eastern and central Rub’ al 

Khali is a brine that follows a slight gradient towards the Arabian Gulf in unconfined aquifers 

close to the surface. Sabkha groundwater exists close to the surface in the coastal lowlands. 

It is a highly mineralised brine due to excessive evaporation. At the sabkha edges, usually 

42


some fresh or brackish water (seeping out of the dunes and sand sheets) occurs on top of 

the dense sabkha brine. The natural artesian wells in the largest oasis Al Hasa emerges from 

the Paleocene Umm Er Radhuma formation and the overlying Mio- and Pliocene layers. In 

the oasis Al Qatif south of Jubail, the groundwater emerges from the Hofuf, Dam and 

Hadrukh formations. There also seem to be connections between these and the lower 

Eocene Dammam formation and the Umm Er Radhuma formation. The groundwater of 

Bahrain, as well as countless submarine wells along the Gulf coast, belong to system of 

aquifers of Al Hasa and Al Qatif. 

basement 

impermeable layer 

groundwater current 

saltwater 

fault 

infiltration 

reversing flow 

Fig. 3.13 Groundwater aquifers of the Arabian Peninsula. 

Al Hasa oasis 

discharging flow 

Arabian Gulf 

modified after Hötzl & Zötl (1984) and Barth (1998) 

Pliocene 

Miocene 

Eocene 

Paleocene 

Cretaceous 

43

3.4 Vegetation 


The vegetation in desert and semi desert environments is basically determined by the 

availability of water. Where there is no additional surface or underground water input, the 

ground cover of the vegetation is directly proportional to the amount of precipitation (Klink & 

Mayer 1983). Therefore the semi desert coastal plains of the Gulf region are characterized 

rather by large patches of bare sand or rock between the plant individuals than by a dense 

vegetation cover. The harsh environmental factors - in the coastal and intertidal areas as well 

as at sabkha edges, salinity provides additional stress – are not only responsible for low 

ground cover rates but also for a low diversity of plant life. 

The flora of the Gulf region mainly comprises thorny shrubs, therophytes, xerophytes, 

phraetophytes, halophytes, and some hydrophytes in the inundated intertidal ecosystems. 

Throughout eastern Arabia, summer is the unfavorable season for plant growth, leading to 

dormancy or the evasion of drought by the production of seeds. Therefore, the growth cycle 

for most plants begins in the autumn or winter period. Some perennial plants show a 

resumption of active growth as early as September, well before the arrival of the first rains 

(Mandaville 1990). This may be associated with the increase in atmospheric humidity which 

occurs at this season in the coastal areas. The arrival of the first winter rains often leads to a 

flush of germinating annuals within a few weeks. Along with the germination of annuals 

comes a resumption of new shoot and leave production by the perennials, many of which 

died back completely during the summer drought. Geographic areas of growth and 

reproduction of both annuals and perennials may be extremely patchy when rains come from 

small local storms (Mandaville 1990). A contrasting pattern is found in the saltbushes of the 

family Chenopodiaceae. These are in active vegetative growth during the summer period and 

most of them flower and fruit in October and November. Mandaville (1990) assumes in their 

pronounced winter die-back an ancestral adaptation to harsh winter conditions in an Irano- 

Turanian homeland to the north. 

The floristic classification of the Middle East is strongly influenced by the work of Alexander 

Eig and Michael Zohary. They divide the Arabian Peninsula into the Sudanean region and 

the Saharo-Arabian region (Zohary 1973). Far to the north in Iraq and in the Iranian Zagros 

mountains there is the border of the Irano-Turanian region (fig 3.14). Due to the collection of 

new floristic data, Mandaville (1984) realigned the border between the Sahar-Arabian and 

Sudanian region basically on a consideration of the Acacia-dominated plant associations of 

central Arabia. 

44


Saharo-Arabian 

Zohary (1973) 

Mandaville (1984) 

Sudanian 

Irano-Turanian 

Fig. 3.14 Conventional floristic regions of the Arabian Peninsula and adjacent regions and the new 

defined boundary by Mandaville (1984). (Satellite image Orb View-2, 3-2-2000 VE Record ID:3240). 

The border is additionally marked by the significant decrease of abundance and diversity of 

annuals - which is typical for the Saharo-Arabian deserts – towards the Rub’al Khali in the 

south. The diversity of desert annuals decreases from about 110 in the central coastal 

lowlands to less than 20 in the northern Rub’ al Khali (Mandaville 1990). 

In the study area, a systematic classification of the communities in the sense of Braun- 

Blanquet (1964) is only of limited use, because the most important desert plant communities 

(covering thousands of square kilometres of Eastern Arabia) are characterized by woody 

dominants of a single species. According to the dominant and co-dominant species in the 

study area, the following vegetation types are classified by Barth (1998): 

1. Calligonum-type 

2. Panicum-type 

3. Zygophyllum-type 

4. Haloxylon/Calligonum-type 

5. Rhanterium-type 

6. Leptadenia-type 

7. Lycium-type 

8. Phoenix-type 

For the littoral fringe and lower supratidal, several species are important which may all be 

dominant in one or the other place. But still, most areas are dominated by one or two species 

45


comparable to the sandy habitats. There are the following important types of coastal 

vegetation: 

1. Halopeplis/Zygophyllum-type (near sabkha edges) 

2. Seidlitzia-type (especially on the offshore islands) 

3. Suaeda-type (on coastal sands) 

4. Limoneum-type (on silty coastal sands) 

5. Salsola-type 

6. Sporobulus-type 

Within the intertidal four vegetation types occur: 

1. Halocnemum-type 

2. Arthrocnemum-type 

3. Avicennia-type 

4. Salicornia-type 

Besides the availability of water and soil- and groundwater-salinity, the soil type (grain size 

distribution, mineral contents such as gypsum, calcium carbonate, quartz, and feldspar) 

determines the presence of certain vegetation types. Böer (1996) published results regarding 

the interdependences between plant communities and soil characteristics at the Saudi 

Arabian coast. Additional data was also provided by Barth (1998) for the area north of Jubail. 

3.5 The Arabian Gulf 

The Gulf is a sedimentary basin, about 1000 km long and between 200 and 300 km wide. The 

average depth is presently 35 m. The sea floor is dipping towards the east. The deepest areas 

are in front of the Iranian coast, reaching from 60 m to about 100 m at the entrance to the 

Strait of Hormuz. Thus, the whole Gulf lies within the photic zone. The shoreline at the 

Arabian side displays a gradual slope with a wide intertidal zone, compared to the steep and 

narrow shoreline at the Iranian side where the Zagros mountains rise more than 1000 m. As a 

consequence of the gradual topography and of the favourable environment to carbonate 

producing biota, the Gulf is a strongly sedimentary province with a dominating soft substrate 

benthos. Sediments of biogenic carbonates - mostly foraminifera - exist over much of the Gulf 

floor (Sheppard et al. 1992). Highest carbonate concentrations are to be found in the shallow 

waters of the western and southern Gulf (fig. 3.15). Within a depositional setting along the 

southern Gulf coast the offshore bank is progressively extending (Kendall et al. 2002). 

46


Terrestrial sediments are limited to the northwest where the waterway of the Shatt al Arab 

discharges into the Gulf, and the eastern Iranian shoreline where terrestrial fluvial sediments 

from the Zagros mountains occasionally are accumulated in the nearshore region. Offshore, 

underlying salt domes have forced upwards numerous islands and banks of hard substrate 

which are now colonized by corals. 

Fig. 3.15 Carbonate content of surface sediments in the Gulf (modified after Sheppard et al. 1992). 

3.5.1 Sea level changes 

> 40% CaCO3 

30-40 % 

20-30% 

Considerably lower sea levels and even complete evaporation of the Gulf occurred in the 

Pleistocene. The period between 110 ka BP and 30 ka BP was characterised by considerable 

sea level fluctuations within the range of 30 and 60 m below present lea level (Sheppard et al. 

1992). These sea levels correspond to the depths of major wadis, especially at the Read Sea 

coast. After 30 ka BP the sea level fell rapidly to a minimum at about 17 ka BP. The values 

provided by various authors range between 120 and 150 m below present sea level. This 

implies that the Arabian Gulf was completely dry during that period. At about 15 ka BP 

global surface temperatures increased, which lead to the Holocene transgression. The rise in 

sea level commenced about 14 ka BP and proceeded rapidly to near present levels at about 6 

ka BP. This transgression was especially pronounced during periods at 12 ka, 11 ka, 9.5 ka, 

8.5 ka, and 7 ka BP (Teller et al. 2000, Glennie 1998) (fig. 3.16). The average horizontal 

47


transgression between 13 ka and 6 ka must have been 140 m/year, but during periods of 

intense sea level rise this distance increased to more than 1000 m (Teller et al. 2000). The 

transgression reached its maximum at about 6 ka BP. At that time the sea level was between 

2.5 (Felber et al. 1978) and 3.5 m (Lambeck 1996) above the actual level. 

15,000 BP (Felber et 

al. 1978) 

12,000 BP (Glennie 1998) 

11,000 BP (Glennie 1998) 

9,500 BP (Uchupie et al. 1999) 

Strait of Hormuz 

Gulf of 

Oman 

Fig. 3.16 Palaeogeographic map showing the Arabian Gulf during the post-glacial transgression 

(source: Barth 2001, Uchupi et al. 1999, Glennie 1998, Felber et al. 1978). 

About the succeeding development there are different opinions. Felber et al. (1978) and Evans 

et al. (1969) state that the maximum sea level situation persisted for about 2000 years before 

regression started gradually. Kassler (1973) and Al-Asfour (1978) assert a considerable 

regression to 2 meters below the present sea level at 5000 BP and a following transgression 

back to the 6000 BP-level at 4000 BP. The later development was characterised by alternation 

of trans- and regression (fig. 2). Evans et al. (1969), Felber (1978), and Hötzl et al. (1984) as 

well as more recent studies (Alsharhan et al. 1995) promote the idea of a more gradual 

regression starting at 4000 BP and reaching today’s level at about 1000 BP (fig. 3.17). 

48

sea level in m 

5 

0 

-5 

-10 

-15 

-20 

-25 

-30 


8 6 4 2 0 

Kassler, 1973 

Al-Asfour, 1978 

Felber et al., 1978 

years B.P. 

in 1000 

present 

sea level 

Fig. 3.17 Sea level changes of the Arabian Gulf during the last 8000 years (based on 14 C-dates of 

calcareous shells)(Barth 2001a). 

But even later than 1000 BP the coastal geography at the western and southern Gulf coast 

experienced significant changes. Seaward progradation of carbonate intertidal flats in the 

UAE amounts up to 7 km during the last 4000 years (Kinsman 1964). Coastal marine 

sediments, found in a distance of more than 2 km from the present intertidal zone north of 

Jubail, provided 14 C dates (of cyanobacteria) of 700 BP. This implies an average progradation 

of more than 3 m/year (Barth 2001a). 14 C dates of cyanobacteria by Evans et al. (1969) in the 

Abu Dhabi sabkha indicate an average progradation rate of 1 m/year for the last 1000 years. 

Evans (2002) points out that the recent cyanobacterial mats lie slightly higher than the 

remains of older mats further inland. This may be due to local tectonics or some change in 

coastal morphology and the rate of supply of sediment, but there is also the possibility that it 

reflects a slight sea level rise (Evans 2002). Studies carried out by Al-Mansi (1992) may 

indicate a minimal rise of sea level in the Arabian Gulf of 2 to 3.8 cm between Ras Tanura 

and Saffaniya in the time period from 1980 to 1991. 

3.5.2 Hydrographical influences 

The marine environment of the Arabian Gulf along the Saudi Arabian shores is a unique 

ecosystem among the world’s oceans. Primary determining factors are its restricted water 

exchange with the Arabian Sea, its high evaporation and low fresh water input, and its 

isolation (Hunter 1983). 

49

Salinity and circulation 


Fresh water enters the Arabian Gulf through the Strait of Hormuz at 36.5-37 ppt and 

circulates in a general counter-clockwise direction with northward currents along the Iranian 

shores and southward currents along the Saudi Arabian shores. With increasing distance from 

the Strait of Hormuz there is a general decrease in nutrients and increase in salinity because of 

excess of evaporation over fresh water input. The diluting influence of the Shatt al Arab at the 

northwest corner of the Gulf is evident throughout the year, but especially in winter when 

flow is greater (Sheppard et al. 1992). The dense saline water of the western Gulf (now 40 

ppt) sinks towards the trough along the Iranian coast and is returned southward in greater 

depths. It exits the Arabian Gulf via the Strait of Hormuz as a deep water current, providing 

the driving force for the renewal of the Gulf water. In winter, temperature gradients increase 

the density flow, since water retained in the south cools more than the inflowing water. The 

total exchange rate of the Gulf water is estimated from 3-5 years (Sheppard et al. 1992). 

Going southward along the coast of Saudi Arabia, the salinity increases dramatically south 

from Al-Khobar where restricted water exchange in the Gulf of Salwah, due to the Peninsula 

of Qatar, promotes highly saline conditions. Salinities range between 38-42 ppt in the region 

north of Al-Khobar and 52-59 ppt in the open waters of the Gulf of Salwah (KFUPM/RI 

1988). In the embayment system of the study area the sea water salinity in open waters range 

between 40 and 51 ppt and in coastal flats between 56 and 74 ppt. Tidal channels show 

salinities up to 78 ppt. Because salinity is a controlling factor for occurrence and abundance 

of organisms, the waters south of Al-Khobar display a less diverse plant and animal life 

(Coles & McCain 1989). Studies carried out by the KFUPM/RI (1988) showed, that salinity is 

the physical variable most highly correlated with changes in plankton abundance. Reef corals 

and many other major taxonomic groups are not found south of Tarut Bay, and the number of 

species and individuals of benthic infaunal organisms and zooplankton decrease significantly 

with increasing salinity (Cole & McCain 1989). 

Tidal pattern 

In the Arabian Gulf, the tidal pattern is complex and does not correlate with the tides of the 

Indian Ocean, although they are driven to some extent by the tidal forces propagating through 

the Strait of Hormuz. In the Gulf there are two amphidromic points where tidal range is zero 

(and around which tidal waves rotate). One is off the northern Saudi Arabian coast and the 

second off the UAE coast. The tidal regime in the central part is complex and basically semi 

diurnal (tidal cycle over 12 hours so that, on successive days, high and low tides occur 

50


approximately 1 hour later). However, in some areas of the Gulf there is only one daily, or 

diurnal, tide (fig. 3.17). Over most of the Gulf away from shore, tidal range is


high and low water peaks towards the neap tide period. To some degree the diurnal pattern 

ameliorates the harsh environmental conditions for shallow and intertidal biota. In summer, 

high tides cover large parts of the intertidal zone during daytime when temperatures are 

extreme (above 45°C). In winter, when temperatures drop below 6°C, the high tide occurs at 

night (Jones et al. 1994). These conditions differ largely from the coast of central Saudi 

Arabia, Bahrain and Qatar where low tides commonly expose the gradually sloping intertidal 

region during daytime in summer. This results in significant differences regarding species 

diversity and abundance of intertidal biota. 

Generally, the high tides in the study area are significantly higher in summer than in winter 

(fig. 3.18) (RCJY 1992). Additional changes in tidal levels are caused by the influence of 

wind. Strong onshore winds in shallow nearshore areas may push tidal waters up to 50 cm 

higher than normal. That is what happened several times in spring 1991 when exceptional 

high tides pushed the oil slick far into the upper intertidal zone until it reached the littoral 

fringe. 

height above chart datum 

2,4 

2,2 

2 

1,8 

1,6 

1,4 

1,2 

1 

Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez 

Fig. 3.18 Average height of high tides within the study area (data: RCJY 1992). 

mean H.T. 

min H.T. 

max H.T. 

Temperature 

The high temperature amplitudes are another controlling factor regarding the distribution of 

fauna and flora in the Arabian Gulf. Particularly at nearshore areas, where annual fluctuations 

of temperature exceed 20°C (16-36°C; compared to 17-34°C in open Gulf waters) 

(KFUPM/RI 1988), marine communities must withstand environmental conditions typical for 

tropical as well as for temperate regions. Thus, the species diversity is low. However, in 

shallow inshore areas with restricted circulation like Dawhat ad-Dafi, summer water 

temperatures can exceed 36°C and winter values may fall below 15°C (Jones et al. 1994). 

52


There is a general gradient from the northern towards the southern Gulf (fig. 3.19). The 

gradient is highest in winter when the difference between the open Gulf waters of Kuwait and 

the UAE is 8°C (fig. 3.19, January situation). Towards summer this gradient decreases to less 

than 2°C. In October, when the lower temperatures in the north are reflected in the sea surface 

temperature, the gradient increases again. 

Fig. 3.19 Sea surface temperatures of the Arabian-Persian Gulf (source: FNMOC OTIS 

http://152.80.49.210/PUBLIC/). 

Chemistry 

30.1.02 12.3.02 7.5.02 

23.8.01 20.11.01 21.12.01 

FNMOC OTIS 4.0: 

SST Analysis 

Optimum Thermal 

Interpolation System 

The chemical environment in the Arabian Gulf is characterized by relatively low 

concentrations of nutrients (compared to other oceans), utilized in primary production by 

marine algae and higher plants. Because there is evidence of nutrient limitation, the true 

pelagic productivity in the Gulf is reduced. Thus, the Gulf can be considered to be one of the 

most productive bodies of water in the world regarding benthic production (Sheppard et al. 

1992). In general, the concentrations of nutrients correlate negatively with the salinity. 

Phosphate, one of the most important nutrients, decreases rapidly south of Al-Khobar and 

with proximity to the shoreline (Cole & McCain 1989, fig. 3.20). This suggests rapid 

utilisation of phosphate and that it may be limiting to primary production. Silicate though - 

important as a structural component of phytoplanctonic diatoms and silicio-flagellatesgenerally 

shows high concentrations in the Gulf and significantly increasing values at the 

southern Saudi Arabian shores (fig. 3.21). According to Cole & McCain (1989), ammonia, 

turbidity, and suspended solids follow a similar pattern like silicate with values increasing 

with proximity to the shoreline and into the Gulf of Salwah. Nitrate and nitrite concentrations 

show no clear spatial distribution. 

53


A B 

Fig. 3.20 A: Concentrations of anorganic phosphate in µg/l (source: KFUPM/RI 1988). B: 

Concentrations of silicate in µg/l (source: KFUPM/RI 1988). 

Petroleum hydrocarbon pollution of the Arabian Gulf 

The Arabian Gulf is the most affected sea in the world regarding hydrocarbon pollution (Cole 

& McCain 1989). The total annual oil spillage was estimated to range between 100,000 and 

150,000 tonnes under normal circumstances prior to the first Gulf War (Golum & Brus 1980). 

The amount of spilled oil was certainly higher during hostile activities in the war. The largest 

war related event was the Nowruz oil spill in 1983. The estimated average post war oil 

pollution is between 150,000 tonnes (Krupp et al. 1996) and 160,000 tonnes per year (Höpner 

1991). 

The general pattern and level of petroleum hydrocarbon contamination in the Gulf water and 

sediments were subject of continuing investigations of the KFUPM-Research Institute for 

more than 10 years. The results are summarized in fig. 3.21. The highest hydrocarbon 

concentration in the seawater as well as in the sediments are concentrated around Ras Tanura 

and Ras Tanajib between Safaniya an Manifa (KFUPM/RI 1988). These are the major oil 

54


loading terminals and the principal producing oil field. Because of the high biodegradation 

potential (see chapter 5.1.2) of the Arabian Gulf, these values are not critical. Compared to 

other oil contaminated areas elsewhere in the world, where sediment concentrations have been 

reported as high as 6000 (Cole & McCain 1989), the Saudi Arabian values are low. 

A B 

Fig. 3.21 A: Concentrations of petroleum hydrocarbons (ppb) in the Gulf water. B: Concentration of 

petroleum hydrocarbons in sediments (ppm) (source: KFUPM/RI 1988). 

Due to the environmental factors in the Arabian Gulf (high evaporation and temperatures), 

volatile compounds in spilled oil are rapidly volatilised (see chapter 5.1.2). The residues are 

often tar balls drifting in the water or sinking to the bottom. Drifting tar is finally settled at the 

shoreline. Such beach tar accumulations reached up to 28.8 kg/m of beach front along the 

Saudi Arabian coast (KFUPM/RI 1988, Price 1987). Within the study area the highest 

concentrations are to be found on Abu Ali Island, where tar ball accumulation reach up to 8 

kg/m and at sites where areas are covered by a closed tar layer (see chapter 6.4.1.2) more than 

40 kg/m. 

55

3.6 Ecosystem types 


The main coastal ecosystem types are differentiated on the dominant substrate and 

vegetation type (see chapter 1.1.1). The coastal wetlands include salt marshes, mangroves, 

sabkha, sandy, and rocky beaches. Generally the muddy shores at the Saudi Arabian Gulf 

coast have a highly abundant intertidal community. Abundances of organisms larger than 0.2 

mm in size reach up to 600,000 individuals per square metre, substantially greater than 

values previously reported for various areas elsewhere in the world (Cole & McCain 1989). 

Species diversity though are within the average of the range of world values. Abundance and 

diversity are controlled by the tidal level, salinity, and petroleum hydrocarbon concentration 

of the sediment substratum as well as the sediment characteristics. Generally, the greatest 

diversity and abundance occurs in the lower eulittoral of muddy shores (Jones et al. 1994). 

Elevated salinity favours the increase in a restricted number of salt tolerant species, resulting 

in a significantly lower species diversity with still high abundances (Cole & McCain 1989). 

The diversity of fauna generally decreases with the depth (Basson et al. 1981). This reflects 

a shortage of oxygen in the sediment, which is also displayed in a greyish or black colour of 

the substrate due to free sulphides. It results from the action of bacteria on organic matter in 

the absence of oxygen and indicates the presence of excess organic matter in the sediment 

as well as anaerobic conditions (Basson et al. 1981). This grey layer may occur between 1 

cm (e.g. in tidal channels or pools) and 30 cm (e.g. within sandy substrate) below the 

sediment surface. The tidal flats which can be muddy, sandy, rocky, or mixed forms are the 

dominant intertidal environment along the Saudi Arabian Gulf coast. In terms of area Basson 

et al. (1981) estimate the extent of the Saudi Arabian tidal flats between 500 and 1000 km². 

In contrast the narrow strip of intertidal along the exposed sand and rock beaches is minimal. 

3.6.1 Salt marshes 

The salt marshes and adjacent muddy tidal flats are the most important type of intertidal 

environment along the Saudi Arabian Gulf coast. Salt marshes occur in bays and other 

sheltered locations where wave energy is low. Thus, the substrate mostly consists of mud or 

very fine sand. Due to the high productivity of the mudflats, excess organic matter is 

accumulated and trapped in the sediment. Degradation by bacteria provides an energy source 

for burrowing animals, especially meiofauna. Due to the slow oxygen flow into the interstitial 

spaces of the fine grained substrate, the organic matter can only partly be oxidized. This leads 

to a mostly anaerobic environment only a few centimetres below the surface, which is 

56


characterized by free sulphides – obvious because of the rotten egg smell of hydrogen 

sulphide. 

Tidal mudflats are mostly characterized by a series of well defined zones, each occupied by a 

different community of organisms. Typical for salt marshes is the presence of halophytic 

plants in the upper eulittoral zone and additionally some flowering herbs and grasses, fringing 

the coast above the littoral fringe. Such salt marsh halophytes are prevalent along the Gulf 

coast and often forms the only coastal vegetation. Members of the Zygophyllaceae and 

Chenopodiaceae are the dominant salt marsh families. The typical vegetation zones (fig. 3.22) 

- controlled by tidal inundation, soil and groundwater salinity - are the cyanobacteria zone, the 

Salicornia zone, Arthrocnemum zone, Halocnemum zone, and landward of the littoral fringe 

follows the Limonium – Suaeda – Seidlitzia – Halopeplis zone. 

Fig. 3.22 Schematic profile of a salt marsh at the Gulf coast. 

The most common invertebrates along the Saudi Arabian salt marshes include the crab 

Cleistostoma dotilliforme dominant in the upper eulittoral. This crab excavates burrows in the 

mud (up to 50 cm deep), and piles up the excavated material around the entrance, thus 

forming a distinctive mound or turret. These burrows occur at high densities of up to 40/m². 

An other crab that occurs virtually in all intertidal zones, Metopograbsus messor, is less 

abundant, does not build burrows, but seeks shelter in open burrows of other crabs. 

Cyanobacteria is distributed almost everywhere below the high water spring line, where 

bioturbation by crabs is limited. In tidal pools the oxygen concentration was significantly 

increased, due to the photosynthesis in the cyanobacterial mat (Basson et al. 1981). A 

variety of microscopic animals inhabit the cyanobacterial mats including gastropods, 

ostracods, nematodes, flatworms, copepods, and oligochaete worms. Larger animal life is 

usually absent where cyanobacterial mats are well established. Normal populations of the 

crab Macrophthalmus depressus and gastropods such as Cerithium scabridum and Pirinella 

conica 

57


keep the substrate constantly bioturbated and the mud surface churned up, preventing the 

cyanobacteria from forming a mat. Where a mat is established, crabs may have difficulties in 

tunnelling there and fail to become established. In the lower mid eulittoral and lower eulittoral 

zone, usually a zone of wet liquid mud is prominent. The upper portion of this region is 

occupied by a community dominated by several species of burrowing deposit feeding crabs. 

The most abundant of these is Macrophthalmus depressus. Densities may exceed 50 

adults/m² (Basson et al. 1981). The lower eulittoral is dominated by the gastropod Cerithidea 

cingulata which may reach abundances of more than 2000/m². Salt marshes can be found 

almost continuously along the Saudi Arabian coast (MEPA 1992). During the MEPA survey 

(1992) salt marshes were recorded at 72% of the shores. However, the MEPA data is not 

sufficient to determine the precise linear extent along the Saudi Arabian coast, but certainly it 

is the most prominent ecosystem type at the western Gulf shores. 

3.6.2 Mangroves 

Mangroves, which are represented by a single species, Avicennia marina, are salt tolerant 

trees found from the mean high tide level down to the mid eulittoral. Often they occur in 

association with salt marsh halophytes, mainly Arthrocnemum macrostachyum and Salicornia 

europaea. The mangroves in the Gulf are poorly developed compared to their counterpart at 

the Red Sea because of the cold winter temperatures. They provide food and shelter to many 

small invertebrates, including commercially important shrimp and act as a nursery for many 

species of young fish. The mangrove stands occur only patchy at sheltered sites on 

waterlogged, soft anaerobic mud. The mangrove roots are only able to survive by means of 

pneumatophores which project above the ground and conduct oxygen to the buried portions of 

the root system. The species assemblages supported by mangroves are not very different from 

those of intertidal mudflats in salt marsh ecosystems (fig. 3.23). Nevertheless, they are treated 

as a separate ecosystem type, since the mangrove trees form a biotope that is very distinctive 

with special local cultural and ecological value. 

58


Fig. 3.23 Schematic profile of a mangrove habitat at the Gulf coast. 

The most conspicuous invertebrates are again crabs whose burrows form a characteristic 

feature around mangroves and intertidal flats. Other common invertebrates associated with 

mangroves include barnacles (e.g. Balanus and Euraphia) on pneumatophores, various 

gastropods (Cerithidae cingulata and Pirinella conica), hermit crabs, and bivalves. 

Mangroves are of limited occurrence and can be only found on restricted small stands. The 

most northerly occurrence is within the study area north of Jubail. These stands belong to the 

most northern mangrove occurrences in the world. There is only one site at the Egypt Red Sea 

coast which is still further to the north. The southerly limit at the Saudi Arabian coast is just 

to the west of Dammam port (MEPA 1992). But there are also extensive mangroves stands in 

the UAE (e.g. Abu Dhabi Emirate). According to MEPA (1992), the linear extent of the 

mangroves is 12 km of the Saudi Arabian Gulf coastline, but this possibly is underestimated, 

because in the Dawhat ad-Dafi area there are already 6 km of coastline with mangrove stands. 

3.6.3 Sabkha shores 

Sabkha shores occur adjacent to sabkhat (low, evaporitic supratidal flats) without higher 

vegetation. High salt concentrations render the habitat unsuitable for growth of halophyte 

plants. Since coastal sabkhat are a common geomorphological feature along the Saudi 

Arabian Gulf coast, there are frequently intertidal areas which turn into sabkha on their 

landward side. Such intertidal areas are composed either of sandy or muddy substrate. They 

are not significantly different compared to the intertidal zone at sandy shores or salt marshes. 

The MEPA study (1992) found sabkha shores at 19% of the sites investigated. 

59

3.6.4 Sandy shores 


Sand beaches begin in the supratidal zone which is composed of beach dunes mostly 

vegetated by Halophytes such as Suaeda maritima or Seidlitzia rosmarinus and the 

beachgrass Halophyrum mucronatum. At higher energy sand shores, the ocypodid ghost crab, 

Ocypode rodundata, occurs frequently near the littoral fringe. It is especially conspicuous 

because of the large (up to 30 cm high) conical towers built by male crabs in the breeding 

season (mainly in spring) (photo 3.1A). Lower down the beach in the eulittoral, there are few 

signs of visible life. But beneath the sand, over 200 species of macroscopic animals have been 

recorded. On mixed sand-rock or sand-mudflats this number was even higher. Marine snails 

are the dominant group with 48 recorded species (Basson et al. 1981). Secondary with more 

than 20 species there are pelecypods (clams and cockles), polychaete worms, peracaridans 

(isopods and amphipods such as sandhoppers), and decapod Crustacea. Sand flats are 

prevalent in areas where wave or tidal energies are higher than those associated with mudflats. 

Outcrops of rock -mainly beachrock- may sometimes be found in the vicinity of sand flats. 

The small deposit-feeding crab, Scopimera crabicauda, particularly its burrows (often greater 

than 100/m² with typical feeding trench and piles of sand pellets – photo 3.1.B), is a 

conspicuous feature on the sand flats (MEPA 1992). Gastropods commonly found on sand 

flats include: Cerithium scabridum, Cerithidea cingulata, Mitrella blanda, and Nassarius 

plicatus. Other important invertebrates are polychaetae that occur beneath the intertidal sand. 

The lower tidal level is characterised by polychaetes and shells. Encrusting mats by 

cyanobacteria and diatoms are generally not well developed on sand flats. Sandy shores are 

very common along the Saudi Arabian Gulf coast. The linear extend is not known because it 

is hard to distinguish sand-mud and sand-rock flats without close inspection. 

Photo 3.1 A: conical tower of the crab Ocypode rodundata. B: feeding trench and piles of sand pellets 

of the crab Scopimera crabicauda. 

60

3.6.5 Rocky shores 


This shore type consists principally of flat beachrock in sheets, often with a thin veneer (1-10 

cm) of sand or sandy mud. On the landward side there may be a narrow sand beach or rock 

platforms building small cliffs between a few centimetres until nearly 20 m. The rocky shores 

in Saudi Arabia are not as productive as the other ecosystem types. The main reason is the 

heat and desiccation during low tide in summer which limits the growth of algae. Therefore 

the fauna is limited to animals which inhabit crevices, rock pools, holes, and the underside of 

boulders, or else are mobile forms capable of retreating to suitable shelter when tide is low 

(Basson et al. 1981). Permanently attached, sessile animals such as the barnacles (e.g. 

Euraphia sp., Balanus amphitrite), tube dwelling serpulid polychaetes (e.g. Pomatoleios 

kraussii) and bivalves (e.g. Isogomon legumen, Brachidontes sp.) mostly are plankton feeders 

and occur along the Saudi Arabian rocky shores, usually in crevices and on the underside of 

pieces of rock. They are either cemented to the rock, attached by a bundle of threads, or they 

live wedged into crevices in the rock. Some mussels even bore into the rock (e.g. 

Lithophaga). Tube worms and barnacles are usually found in dense clusters covering large 

parts of the rock where conditions are favourable. In contrast to the sessile forms are vagile 

animals, able to move about freely on the rock surface. The most important group in this 

category are the gastropods or snails (Basson et al. 1981). A majority of them are herbivorous 

and graze on algae and cyanobacteria. The dark or black colour, typical for intertidal rocks 

along the Gulf coast, is mostly due to the presence of cyanobacteria. Important grazing 

gastropods are Nodolittorina subnodosa, Planaxis sulcatus, Cerithium scabridum, Mitrella 

blanda, and the top shell Trochus erythraeus. A few common snails are carnivorous like 

Thais sp., feeding on sessile animals. Crabs are also an important group at rocky shores. The 

ubiquitous Metopograpsus messor is mostly herbivorous. Others such as Thalamita admente 

are predatory. Because rock beaches are highly stressed environments the structure and 

behaviour of their inhabitants are merked by traits enabling them to avoid or withstand the 

adverse conditions. Compared to other coastal biotopes, the exposed beaches are poor in both 

quantity and diversity of life (Basson et al. 1981). The linear extend of rock flats along the 

Saudi Arabian shores is about 240 km (MEPA 1992). 

61

4 Previous work 

The impact of oil spills on coastal ecosystems and their ability to exhibit long term recovery 

has received increased attention in recent years. This is well documented on the increasing 

interest in the International Oil Spill conferences (IMO) which are conducted every two years 

(1999 Seattle, 2001 Florida) and other congresses and workshops on petroleum contamination 

(such as the int. Congress on petroleum contaminated soils, sediments, and water, London 

2001). Oil spills can have significant short term impacts on coastal marshes and a substantial 

literature exists on those. The long term effects and eventual recovery though, are not well 

documented in the current literature. Gundlach & Hayes (1981) assess the impact of oil on 

temperate coastal ecosystems at the North Sea in a time frame of two years. Mendelssohn et 

al. (1993) assess the recovery of a brackish marsh in Lousiana within four years. Hoff et al. 

(1993) present results on salt marsh recovery after 16 months at the northern Puget Sound, 

Washington. In this case, all salt marsh plants were growing again by the second growing 

season after the spill. Only on heavily oiled patches recovery could not be observed. Baker et 

al. (1993) are one of the few who in fact presented long term results of oiled salt marshes. 

Their study sites were in Wales and Chile. According to their investigations, complete 

recovery was reached in Wales after 15 years whereas at the site in Chile badly affected areas 

showed no vegetation recovery after 17 years. Southward & Southward (1978) report about 

massive predatory-prey imbalances, with marked oscillations in species population dynamics 

after the Torrey Canyon oil spill. These oscillations took 12 years before settling back to 

normal. Probably the best long term monitoring results are provided by the Hazardous 

Materials Response Division (HAZMAT) of the National Oceanic and Atmospheric 

Administration (NOAA). HAZMAT has been conducting a monitoring study since 1990, one 

year after the Exxon Valdez oil spill in Prince William Sound. This study will continue until 

2005. Annual monitoring of 20 study sites tracks changes in the biological community over 

time (NOAA 2000, internet 2). The definition of “long term” is very variable in literature and 

generally used when the monitoring exceeds the period of one year. Only very few authors 

published results of monitoring periods longer than 10 years. The obvious lack of research 

was the reason for the establishment of the EU/NCWCD project “Marine Habitat and Wildlife 

Sanctuary for the Gulf Region” after the 1991 Gulf War oil spill. But again, after 4 years, 

when the project was officially closed down, research stopped and no more studies were 

carried out, although the ecosystems were far from being recovered. The importance of

Previous work 

extending the research period to even more than 10 years is essential, because most low 

energy shore ecosystems did not completely recover within this time frame. 

4.1 Research in the study area 

Regarding the Gulf region, there is almost a complete lack of literature dealing with oil impact 

on coastal ecosystems until 1991. The 1983 Nowruz spill in the Arabian Gulf was not further 

investigated due to the continuing Iran-Iraq war. The studies carried out during the 

EU/NCWCD project after 1991 are the first long term interdisciplinary research on this 

subject in the Gulf region. The current work presents the most important results compiled 

during the EU/NCWCD project until 1995 and extends the research to 2001. Thus, it is the 

most comprehensive documentation of the environmental changes after a severe oil impact 

for the Gulf region, as well as for the rest of the subtropical regions in the world. 

Many different studies have been carried out in the area of consideration before (MEPA 1991) 

and during the EU/NCWCD projects from 1991-1995. All results of these studies are 

collected in the three final reports (1992, 1994, and 1995) which were submitted to the EU 

and NCWCD. Some of this work and results of the Mt. Mitchel cruise have also been 

published in scientific magazines and conference proceedings (e.g. Böer 1996, Hayes et al. 

1993, 1995, Jones et al. 1993, the proceedings of the “International Conference on the long- 

term environmental effects of the Gulf War” in Kuwait 1996). A compilation was published 

by Krupp et al. in 1996. 

Höpner et al. (1992) documented the hydrocarbon contamination of the intertidal sediments. 

Kinzelbach et al. (1992) assessed the fauna of the littoral fringe, Jones & Richmond (1992) 

and Jones et al. (1994) did the same for the microfauna of the intertidal zone. Fiege (1992) 

dealt with the Polychaetae and Apel & Türkay (1992) and Apel (1994) described the 

Crustaceae of the intertidal. Warnken, J. (1994) and Böer (1994a) studied the vegetation, De 

Clerck & Coppejans (1994) the marine algae, Hoffmann (1994) the cyanobacteria, Basson & 

Round (1994) the intertidal diatom populations. The subtidal was monitored by Richmond 

(1994) and Vogt (1994). The results of theses reports demonstrate that most of the fauna and 

flora between the high water neap and high water spring was destroyed. The physical and 

morphological differences of the coastal ecosystems (covering a wide variety of habitats such 

as the more than 500 m wide muddy intertidal and salt marsh areas, mangroves, sandy 

intertidal, narrow sand beaches and rocky shores) promised a very differentiated development 

63

Previous work 

in the future. In the following years until 1995, additional studies were carried out at different 

time intervals in order to monitor the regeneration of the coastal ecosystems (Smith 1996a, 

1996b, Höpner et al. 1996, Watt 1996, Jones et al. 1996; all in Krupp et al. 1996). Part of the 

results were presented at the 1995 International Oil Spill Conference in Long Beach, 

California (Hayes et al. 1995). The different ecosystems displayed a heterogeneous 

development. The extremes cover all states from oil soaked salt marshes until completely 

recovered areas (Höpner et al. 1993, Abuzinada & Krupp 1994, Hayes et al. 1995, Krupp et 

al. 1996). Mostly the low energy shores showed the least recovery after 4 years of monitoring. 

A report published in 1993 by UNEP states that the marine ecosystems recovered within one 

year after the oil spill. This report ignored the situation at the Saudi Arabian coast, but it was 

responsible for the dismissal of the ecological Gulf War disaster from the interest of the 

media. Soon the public interest also ceased to exist. After the closure of the EU/NCWCD 

project in 1995, no further research at the Saudi coast was conducted except regular visits 

by Prof. Dr. Thomas Höpner (ICBM Oldenburg, Germany) (who visited 24 locations since 

1992 on a regular base) and the author of this work. This means that most studies mentioned 

above report about the development of the first two years until 1993. Only a few incorporate 

results that are from 1994 and there is virtually no data presented more recent than 1995. 

64

5 The Gulf War 1991 and the oil spill 

On January 16 th the Gulf war broke out when the allied air force struck a first blow on Iraqi 

positions. Allied ground forces entered the war on February 25 th . Between the 20 th of January 

and May 1991 oil was released from Mina Al-Ahmadi Island, Mina Saud and Mina Al-Bakr 

as well as from the bombing of oil tankers (Alam 1996). 

The intention for the oil release was a strategic one and not, as the media pointed out, an 

environmental terror. The oil was released into the Bay of Kuwait in order to prevent a 

landing operation by the allied army. Most engines of the landing vessels have a cooling 

system based on seawater. Should oil enter the cooling system of the diesel engine it would 

overheat within a short time. Thus the released oil would effectively have prevented a landing 

operation in the Bay of Kuwait if General Schwarzkopf had decided to attack from the sea. 

Altogether, about one million tonnes of crude oil were released into the Arabian Gulf (UNEP 

1991). The prevailing northern winds as well as the prominent Gulf currents moved the oil 

slick in southern direction along the Saudi Arabian coast. After a change in wind direction the 

oil was washed ashore. The islands Batina and Abu Ali prevented the oil from drifting further 

south (fig. 5.1). Altogether about 770 km of coastline from southern Kuwait until Abu Ali 

island was affected by a continuous band of oil. The combination of onshore winds and 

extremely high tides (considering the time of the year) carried the oil far inland. 

0 5 km 

Fig. 5.1 Oil slicks (red colour) as seen from the Landsat Thematic Mapper satellite in spring 1991 

drifting into the Dawhat ad-Dafi and Dawhat al Musallamiyah embayment system.

The Gulf War 1991 and the oil spill 

A comparison to such oil spills as Exxon Valdez which lost 33,000 t and oiled more than 1700 

km of shoreline (Owens & Teal 1990, Gundlach et al. 1993) indicates that the extent of oiled 

shoreline from the Gulf war (fig. 5.2) could have been far greater, considering the large 

amount of oil released into the Gulf waters. The comparably minor extent is due to the 

uniform circulation pattern of the Arabian-Persian Gulf (see chapter 3.5) and the geography of 

the coastline north of Jubail with the exposed location of Abu Ali island. This island funnelled 

the oil into the bays and prevented it from drifting further south where, apart from valuable 

ecosystems, industrial plants as well as the worlds larges desalination plant would have been 

severely affected. 

Jubail 

Industrial City 

desalination plant 

0 100 km 

oiled coastline 

Fig. 5.2 Extend of oiled coastline along the western Gulf shore. Terra Satellite Image, MODIS sensor, 

provided by NASA (http://visibleearth.nasa.gov/). 

The following organisations participated in the oil recovery and wildlife rescue operations 

since May 1991: The Meteorological and Environmental Protection Administration (MEPA), 

The Royal Commission for Jubail and Yanbu (RCJY), the National Commission for Wildlife 

Conservation and Development (NCWCD), Saudi ARAMCO, the International Maritime 

Organisation (IMO) and several private contractors. NCWCD and the RCJY set up the 

Wildlife Rescue Centre in Jubail Industrial City. 

NCWCD in conjunction with MEPA and the King Fahd University of Petroleum and 

Minerals (KFUPM) drafted an environmental response plan. On the basis of this plan the 

66


establishment of a “Marine Habitat and Wildlife Sanctuary for the Gulf Region” was 

suggested. This project was then launched and executed jointly by NCWCD and the European 

Union (EU). 

In early 1992 the Regional Organisation for the Protection of the Marine Environment 

(ROPME), in conjunction with the U.S. National Oceanic and Atmospheric Administration 

(NOAA), conducted a 100 day cruise with the RV “Mt. Mitchell” to study the marine ecology 

after the Gulf war. 

In late 1992 the Tokyo University of Fisheries in cooperation with ROPME visited the area 

for two weeks with the RV “Umitaka Maru”. This was repeated in the two following years. In 

1995 the last project on the Gulf war impact carried out by the European Union and NCWCD 

was closed down. 

5.1 The fate of the oil after the release 

As mentioned above, the oil spill was not a single event but a continuous release of crude oil 

from different sources into the Arabian Gulf environment, between the end of January and 

May 1991. Kuwait crude is classified as a group 3 oil (National Research Council 1985) 

which means that the specific gravity is between 0.85 – 0.95 and the viscosity between 

Arabian medium and Arabian heavy. It is therefore a relatively light crude oil, rich in volatile 

components, more fluid and less persistent. In the next paragraphs the constituencies of crude 

oil will shortly be described as well as the successive weathering processes after its exposure 

to the marine environment. 

5.1.1 Crude oil 

Crude oil is a complex mixture of hydrocarbons with 4 to 26 or more carbon atoms in the 

molecule (Clark 1992). According to the arrangement of these carbon atoms, straight chains, 

branched chains, and cyclic chains including aromatic compounds are distinguished (fig. 5.3). 

Some polycyclic aromatic hydrocarbons are known to be toxic to the environment. But most 

of these toxic compounds are also the most volatile fractions of the oil and evaporate in less 

than a few days. Besides pure hydrocarbons (which contribute 80-83% to the crude oil) other 

substances such as hydrogen (11-15%), sulphur (up to 6%), oxygen (up to 5%), nitrogen (up 

67


to 0.5%), vanadium, and other trace metals are constituents of the crude oil (van Buuren 

1984). The exact composition of the oil is highly variable according to the characteristics of 

each oil field. Therefore also the physical and chemical properties of crude oil have a wide 

range. Figure 5.3 shows different types of hydrocarbon molecules. 

H 

H 

C H 

H 

Methane (CH4), the 

simplest hydrocarbon 

H 

H 

C 

C 

H 

C 

C 

H 

C 

C 

Benzene (C6H6), the 

simplest aromatic 

hydrocarbon 

H 

H 

H 

H H H H H H H 

C C C C C C C H 

H H H H H H H 

a straight-chain alkane 

(paraffin): heptane (C7H16) 

H 

H 

H H 

Fig. 5.3 The structure of some hydrocarbons. 

C 

C 

H 

H 

C 

C 

H 

H 

C 

C 

H 

H 

H 

H 

H 

H 

H 

C 

C 

H 

H 

H C H 

H H H H H 

C C C C C C H 

H H H H H H 

a branched chain-alkane 

H 

C 

C 

H 

C 

C 

H 

H 

C 

C 

C 

C 

C 

C 

C 

H 

C 

C 

C 

C 

C C 

C H 

H H H 

a cyclo-alkane (naphthene) Benzopyrene, a polycyclic 

aromatic hydrocarbon (PAH) 

The persistency of the crude oil grows with a larger molecular weight of the oil constituents. 

Low molecular parafines and naphthenes or mono- and dicyclic aromatics are faster 

eliminated than long chain hydrocarbons, polycyclic aromatic hydrocarbons, and asphaltenes 

(van Buuren 1984). Asphaltenes are hardly degradable and remain as long term residues. The 

toxicity of the oil is positively correlated to the percentage of aromatic hydrocarbons. 

68


5.1.2 Natural weathering processes after the oil spill 

After entering the marine environment, oil spreads out on the water surface forming a thin 

film – an oil slick. The composition of the oil changes with the time it is spilled (fig. 5.5). 

Wave action will break up the oil slick and the most volatile (low molecular weight – 

fractions) components evaporate. This is the single most important weathering process in the 

first 48 hours after the spill. The relatively high water temperatures and intense solar 

radiation, especially towards the end of the Gulf War, accelerated the evaporation process of 

the volatile components. A calm sea and relatively low wind velocities hampered evaporation. 

Therefore evaporation within the first 48 hours might have been neither especially high nor 

below average. Evaporation experiments carried out by Floodgate (1994) showed that within 

the first 24 hours 25% of the medium and light oil is lost to the atmosphere (fig. 5.4). The 

losses decreased significantly in the next 24 hours. The following evaporation was lower than 

the values presented in the literature. This is due to the different environment. Oil spilled in 

the sea is exposed to water currents and wave action which mix it and enlarge the surface, 

thus increasing evaporation. 

evaporation in % 

35 

30 

25 

20 

15 

10 

5 

0 

0 24 48 

hours 

72 90 

Fig. 5.4 Evaporation rates of different oil types (data: Floodgate 1994). 

extra light 

light 

medium 

heavy 

Water soluble components dissolve in the water column. Only a few components in the oil 

are soluble in water at all (Moeinzadeh 1984), which makes dissolution not an effective 

degradation process and involves only a small fraction of the oil (API 1999 – internet 1). 

Wave action and turbulence breaks part of the oil slick into droplets of oil with a range of 

sizes, that create an oil-in-water emulsion. Some droplets remain in suspension while the 

larger ones rise back to the surface, eventually forming a thin film or coalesce with other 

droplets to reform a slick (ITOPF 1986). The increased surface area of dispersed droplets in 

69


suspension promote other processes, such as biodegradation and sedimentation. But the low 

wave action in the Arabian Gulf may have reduced the process of dispersion. 

The rate of emulsification has also been low because of the low wave energy. Waves washing 

over fresh oil first disperse tiny droplets and when the oil viscosity increased over time, tiny 

droplets of water become suspended in the oil. Such water-in-oil emulsions may contain 70- 

80% of water (Clark 1992). But in the case of the Gulf War oil spill the emulsion certainly 

contained a significantly lower amount of water. The persistence of water-in-oil emulsions is 

dependent on the concentrations of asphaltenes. Oils with asphaltene contents greater than 

0.5% tend to form stable emulsions, often referred to as “chocolate mousse” (ITOPF 1986). 

Emulsions may separate out again if heated by sunlight, or stranded at shorelines both of 

which was the case at the Saudi Arabian Gulf coast. 

The heavy residues of the crude oil form tar balls from less than 1 mm up to 20 cm size which 

are either washed ashore or accumulate at the ocean floor. Sedimentation at the ocean floor 

usually occurs because of the association with inorganic or organic matter suspended in water 

(Moeinzadeh 1984). Shallow waters and especially the Saudi Gulf coast are laden with 

suspended solids, providing favourable conditions for sedimentation. Oxidation of floating 

water-in-oil emulsions might also be responsible for parts of the oil to sink. Many of these 

reactions are promoted by sunlight. If exposed to intense sunlight, water-in-oil emulsions 

form higher molecular weight compounds which increases the density of the petroleum to the 

point where it can sink. Many stranded tar balls along the sand beaches (see Chapter 6.4.1.1) 

consist of a solid outer crust combined with sediment particles surrounding a softer, less 

weathered interior. 

A wide range of micro-organisms utilise oil as a source of carbon and energy, a process which 

is called biodegradation. Biodegradation is the dominant long term weathering action on an 

oil spill. All hydrocarbons are naturally occurring materials and represent a energy source for 

over 90 species of naturally occurring bacteria (API 1999). Such organisms are ubiquitous in 

all oceans but they are more abundant in chronically polluted waters like the Arabian Gulf 

(see chapter 3.5). The main factors that affect the rate of biodegradation are the concentration 

of the oil, abundance and species of micro organisms, temperature, the availability of oxygen, 

and nutrients (especially compounds of nitrogen and phosphorous) (Linden 1984). Generally, 

the flora of micro organisms in shallow polluted areas is better adapted to degrade petroleum 

components than populations in off-shore and unpolluted areas (Linden 1984). Therefore, the 

conditions in the Arabian Gulf are most favourable for biodegradation. In temperate waters 

daily rates of oil removal, due to biodegradation, range between 0.001 and 0.03 grams per 

70


tonne of sea water. In chronically oil polluted areas such as the Gulf 60 grams per tonne of sea 

water may be reached (Clark 1992). According to Höpner (1984) the nitrogen demand (60 

kg/t of oil) during a major oil spill is much larger than the capacity of the Arabian Gulf. 

Therefore, the biodegradation in the Arabian Gulf is basically limited by the nitrogen supply. 

Because most biodegrading organisms live in sea water, the process can only effectively take 

place at the oil-water interface. Stranded oil above the high water mark, such as the 

continuous oil band along the Saudi Arabian coast north of Jubail, will therefore persist much 

longer. The fate of the stranded oil and the processes leading to its breakdown are the central 

part of this study and will be discussed in the following chapters (6.1-6.8). 

Fig. 5.5 Main weathering processes acting on crude oil after an oil spill (data: API 1999, ITOPF 1986, 

Moeinzadeh 1984, Van Buuren 1984). 

50 

45 

40 

35 

30 

% 25 

20 

15 

10 

5 

0 

45 

evaporation 

solution 

5 5 

Fig. 5.6 Percentage of weathering processes on Kuwait medium crude oil (data: MEPA 1991, Morris 

1976). 

photochemical 

oxidation 

30 

microbial 

degradation 

15 

sedimentation 

71

6 Ecosystem types and their response to oil impact 

The Saudi Arabian shoreline of the Arabian Gulf consists of several different coastal types according 

to their physical characteristics. Due to the slightly dipping bedrocks of the Arabian shelf, far-reaching 

inlets, forward leaping peninsulas, sand banks, extensive sand, and mudflats are the dominant features. 

The prominent flatness of many coastal areas lead to pronounced horizontal zones within the intertidal 

area due to different inundation frequency by seawater. The total shift in the waterfront may be more 

than 2 kilometres in extreme cases. The different intertidal zones -originally determined by 

characteristic life forms on rocky shores by Stephenson (Hawkins & Jones 1994), than modified and 

adapted to all shore types in current literature- are displayed in figure 6.1. 

supralittoral upper eulittoral 

2 

1 

0 

littoral fringe 

mid eulittoral 

HWS HWN LWS 

lower eulittoral 

sublittoral fringe 

Fig. 6.1 Different tidal zones (HWS = high water spring, HWN = high water neap, LWS = low water 

spring, LWN = low water neap). 

The dynamics of tidal fluctuations were responsible for transport and accumulation of the oil 

during the Gulf War in 1991. All shores within the area of consideration were affected by the 

petroleum hydrocarbons. The oil came ashore during high tides and was deposited between 

the levels of high water springs (HWS) and high water neaps (HWN) on all coasts. 

sublittoral 

As emphasised by Basson et al. (1977) and Jones (1986) the Gulf shores are in some cases 

mixed and thus it is possible to obtain a range of intertidal habitats on the same shore. 

Therefore the coastal types discussed in this work are to be regarded solely as the most typical 

of each category within the study area. The following coastal ecosystem types were 

distinguished: salt marshes (comprising mud- and sand-mud shores), sabkha (sabkha-mudflat 

without higher vegetation), sand beaches (high- and low energy sandy shores, sand flat), 

rocky shores (cliff, rock boulder and rock flat) and mangrove. 

The total coastline of the sanctuary covers 401 km (Barth et al. 1994). The basis for 

evaluation were helicopter flights in 1993/1994 and ground truth cartography in the filed from 

LWN 

Arabian Gulf

Ecosystem types and their response to oil impact 

1994-2001. The location of the different ecosystem types is presented in figure 6.2. Their 

linear extent is given in table 6.1. 

Tab. 6.1 Linear extent of coastal ecosystem types. 

linear extent Remark 

salt marsh 190 km 145 km wide salt marsh (vegetated zone wider than 15 m) and 45 km 

narrow salt marsh (vegetated zon narrower than 15 m) 

sand beach 146 km 90 km low energy shore (minimal wave action) and 56 km high energy 

shore (wave action) 

sabkha 45 km no vegetation 

rocky shore 14 km rocky shore, occasionally cliffs 

mangrove 6 km 

Fig. 6.2 Location of different coastal ecosystem types in the study area. 

Oil and its effects on biota 

Very limited data exist on the effect of oil on tropical ecosystems such as mangroves, coral 

reefs and their associated biota (Watt 1994). Fish eggs and larvae are usually found in the 

surface water or in shallow coastal environments where they are most likely to encounter oil 

slicks. Their sensitivity to toxins is great and intensive contact to hydrocarbons causes 

73


immediate casualties (National Research Council 1985). Adult and juvenile mobile fish avoid 

oil slicks and are therefore relatively unaffected. There is little evidence of increased 

accumulation of oil and its by-products in the higher predatory members of the food web 

(Watt 1994). Population changes due to oil spills are hard to understand because of the limited 

understanding of natural population fluctuations. Little is known about the metabolic 

derivatives of oil hydrocarbons formed in the tissues of marine organisms. Anecdotal data of 

changes or cessation of feeding have been recorded as an early indication of oil toxicity, while 

individual hydrocarbons such as naphthalene are known to affect respiration, photosynthesis, 

ATP production, carbon assimilation, lipid formation and related processes (National 

Research Council 1985). In the intertidal zones smothering is the widespread effect caused by 

oil often resulting in complete eradication of the ecosystem. 

The following chapters discuss the oil impact and the observed regeneration of each ecosystem type 

separately. In chapter 7 a general discussion of the regeneration processes within the study area is 

presented. 

74

6.1 Salt marshes 


Salt marshes are the most abundant coastal ecosystem type along the Saudi Arabian Gulf 

coast. About 47% (190 km) of the total coastline within the study area is covered by salt 

marshes. Due to the low lying coast the intertidal zone is very extensive and can reach more 

than 2 kilometre in width (Krupp & Khushaim 1996). The average is estimated to be around 

200 to 300 metres (see fig. 6.3). Salt marshes grow on mudflats which form in areas where 

wave and current energies are low. Fine particles are therefore the main sediment fraction that 

settles in such an environment, which is often cut by meandering tidal channels through 

which the ebb tide drains. The salt marshes are composed of halophytic plants, which are 

capable of withstanding inundation by seawater. Halocnemum strobilaceum, one of the major 

phanerogams of these ecosystems, is the most salt-tolerant plant in the salt marsh community 

and therefore covers the most landward, slightly elevated areas with the highest salinites. 

Adjacent to the landward side follow sabkhat or sandsheets. In some cases transition zones to 

adjacent sabkhat are colonised by the highly succulent dwarf shrub Halopeplis perfoliata, 

which prefers coarse sandy sediments and tolerates salinity to the same extend as 

Halocnemum. The intermediate zone between littoral fringe and eulittoral is dominated by 

Arthrocnemum macrostachyum. In some cases the grey mangrove Avicennia marina occur 

adjacent to or associated with Arthrocnemum macrostachyum (the mangrove ecosystems will 

be discussed separately in chapter 6.2). 

According to the tidal movements of the sea water the number of inundations of the most 

seaward edges of each vegetation type varies. Avicennia is frequently inundated more than 48 

times each month throughout the year. Salicornia is also frequently inundated with more than 

31 times each month but according to the little higher location not as much as Avicennia. 

Within the range of the Arthrocnemum zone there is already a pronounced difference in the 

course of the year with more than 16 inundations during the winter months and around 50 

during the summer months (there is a pronounced annual variation of tidal height between 

winter and summer which is explained in 3.5). The Halocnemum zone is only occasionally 

flooded in winter (around 5 times each month) and periodically in summer (around 30 times 

each month). The habitats of Halopeplis are inundated only episodically and exclusively 

during the summer months (between 1 and 20 times each month). Detailed information on 

monthly inundation is given in Böer (1994). 

The mudflats between the lower lying halophytes are often covered by extensive cyanobacteria mats, 

which show a variety of surface morphologies (see 6.1.1.5). Although these communities of bacteria 

75


are very abundant within this sort of ecosystem and therefore wide spread along the whole Gulf coast, 

literature dealing with their ecology is rare. Therefore it is not known exactly which environmental 

conditions lead to their expansion and what function they have in the ecosystem. Their role in 

bioremediation of hydrocarbons has so far not been studied. The work about cyanobacteria, which was 

carried out during the EU/NCWCD project, basically keeps to a description of their morphology. 

Macroalgae is very rare within the intertidal zone of salt marshes (Coppejans 1992). The most 

important benthic intertidal animals in the salt marsh ecosystem are crabs, e.g. Cleistostoma 

dotilliforme, gastropods, e.g. Pirinella conica, molluscs and polychaetes, e.g. Perinereis 

vancaurica (see 6.1.1.4). But to the observer, apart from vegetation, only the colonies of crabs 

with millions of individuals are most obvious at first sight. 

metres 0 100 

200 300 

silt/clay sand 

h ll fragments S licornia 

silt/clay and sand coarse sand beach rock 

H l /Arthrocnemum 

Fig. 6.3 Schematic profile of a salt marsh ecosystem. 

The salt marshes are common in the whole study area except the northern shores of Abu Ali island. 

The highest concentration of these ecosystems lies in the embayment system of Dwhat ad-Dafi where 

numerous islands provide excellent conditions for the flourishing of salt marshes (fig. 6.4). 

76


Musallamiyah 

salt marshes 

49°20’ 49°30’ 

ARABIAN GULF 

Dawhat 

Ad-Dafi 

Fig. 6.4 Location of salt marsh ecosystems in the study area. 

Abu Ali 

Due to the extensive intertidal zone and the unusual high tides in March 1991, the oil moved 

up from the mid and lower shore to become permanently settled on the upper shore. 

Consequently salt marshes as the most prominent upper shore biota were most severely 

affected by the oil resulting from the Gulf war. The zone between the spring high water mark 

and the neap high water mark were covered by a continuous band of oil and tar with 

devastating effects to the fauna and flora of the ecosystems. 

For permanent ecological monitoring, two test sites were chosen where Böer 1993 and 1994 

already collected material. They represent an Arthrocnemum and a Halocnemum salt marsh, 

which are the most widely distributed types in both oiled and non-oiled areas. Besides, several 

additional transects were studied along the coast within the Dwhat ad-Dafi embayment. 

5 km 

N 

27°20’ 

27°10’ 

77

6.1.1 Halocnemum transect 

m above 

chart datum 

2 

1 

0 

W 


0 5 10 km 

metres 0 15 30 45 60 75 90 120 150 180 210 240 260 290 310 340 370 

silt/clay sand shell fragments 

d d H l d A throcnemum 

silt/clay / sand coarse sand beach rock 

living H l 

Fig. 6.5 Location of the Halocnemum transect. 

49°20’ 49°30’ 

ARABIAN GULF 

The Halocnemum transect is called after the dominant plant species Halocnemum 

strobilaceum (Pall.) M. B. It is located at 27°09’34” N / 49°24’06” E and faces the Arabian 

Gulf in the east (fig. 6.5). To the west it is bordered by a 15-25 m wide sand sheet. Adjacent 

there is a zone of Halocnemum nabkhat (local expression: ghuspan) on sabkha surface. About 

100 m further the nabkhat decrease in size and then disappear completely. Bare sabkha is then 

dominant for some kilometres. 

This salt marsh was severely affected by the oil in 1991. All life was extinguished seaward 

from the 120 m mark until the lower intertidal zone. A 250-300 m wide dead zone was 

smothered along this shore. Until 2001 some improvement is obvious, especially within the 

lower and middle intertidal zone. The upper middle and the upper intertidal still remain in a 

N 

27°20’ 

27°10’ 

E 

78


very bad condition. This site was chosen for detailed ecological analysis because it represents 

a typical salt marsh community along with the Arthrocnemum community which also became 

a test site of intensive studies (see 6.1.2). In addition to this, it already was a test site from 

1992-1994 were Böer (1994) conducted some ecological studies, which provide additional 

data for this work. 

6.1.1.1 Soil properties 

The soils of salt marshes are basically semisubhydric soils. They are characterised by a frequent 

inundation of tidal water. In such areas sections do rarely show clear soil horizons. Towards the littoral 

fringe, where vegetation is abundant, the upper centimetres tend to be rather brownish than grey due to 

organic components. Beachrock layers are a typical phenomenon, which was observed frequently 

within the sediments of the intertidal zone. The dominant soil fractions are either silt and clay or - if 

dominated by sand - the soil contains a considerable portion of the fine substrates. These fine 

sediments are transported by the tidal waters. In suspension especially clay minerals form aggregates 

which will be deposited when weight increases (Irion 1998). The formation of these aggregates is 

mainly caused by the salt concentration of the sea water, which increases towards the intertidal flats 

within the dissected embayment systems. Calcium carbonate concentrations of the substrate are very 

high throughout the profile and show maximum values of 80% and only few below 60%. The 

following sections will be discussed with emphasis on the status of oil contamination 10 years after the 

oil spill. 

Oil contamination assessment in 2001 

The oil contamination is illustrated by soil sections along the transect in the figures 6.6 and 

6.7. The following description begins at the seaward end of the transect. It is presented as a 

table for each section with additional information given in separate remarks. 

79

1 


10 cm 

50 cm 

9 8 7 

5 4 3 2 

m 150 180 210 240 260 

290 310 340 370 

heavily oiled (upper part) 

silt / clay coarse sand tar 

less oiled (lower part) 

layer 

silt with sand shell fragments oiled patches 

animal burrows 

Fig. 6.6 Soil sections of the Halocnemum transect – lower part. 

The first tidal channel in the intertidal zone towards the sea is located at the 375 metre mark 

within unconsolidated soft sediments. 

80


Tab. 6.2 Section 1 at the 370 m mark of the Halocnemum transect. 

Section 1 


Section 2 340 m 

0-15 cm: mud (for detailed grain size data see appendix 1, tab.1) 

15-35 cm: sand fraction increases to about 60% fine and middle sand 

35 cm: hard beach rock layer 

Remarks: 

Hundreds of grazing gastropods and empty shells at the surface. Some of them are oiled. No trace of 

oil in sediments. 



0-0.5 cm: beige coloured fine silt 

0.5-4 cm: grey silt 

4-5 cm : 

hydrocarbons) 

dark grey oiled silt (weak odour of petroleum 

5-13 cm: silty sand well weathered oil residues 

13-30 cm: grey silt, oil residues well weathered and restricted to crab 

burrows 

Remarks: 

Shell and gastropod fragments within the first 20 cm of the section. 


Section 4 

370 m 

Landward side of the channel. Shows no horizons. The sediments are dominated by 

fine sands and silt. The sand fraction is increasing slightly beneath 15 cm depth. 

Shells are abundant within the sediment. At the surface living gastropods (cerithids) 

are prominent as well as some inhabited crab burrows. 

calcium carbonate concentration at: -10 cm: 68.1% 


290 m 

0-0.5 cm: beige coloured fine silt 

0.5-30 cm: grey silt, well degraded oil residues in relic crab burrows 

30-55 cm : grey sand, no oil 

55-60 cm: coarse grey sand with plenty of shell fragments 

81


Remarks: 

The surface is partly covered by a thin tar layer enclosing dead cerithide shells (gastropods). At some 

places the tar is covered by some new sediment which itself is colonised by cyanobacteria at the 

surface. Crab burrows shelter old oil which is partly oxidised and degraded to a more advanced 

degree. There are almost no shell fragments anymore within the sediment of the first 40 cm. 


Section 5 

260 m 

0-5 cm: dark brown silt, oiled, sticky with strong petroleum hydrocarbon 

5-12 cm: 

odour. Total hydrocarbon concentration averages 24.6 g/kg. Oil not 

well degraded, dark brown rapid assessment oil print (see fig. 6.8). 

lighter brown silt; oiled; sticky with strong hydrocarbon odour 

12-18 cm : light grey silt; lightly oiled; relic crab burrows contain oil of low 

degradation status, strong hydrocarbon odour 

18-40 cm: grey sandy silt; average oil concentration in 20 cm depth 4.9g/kg; crab 

burrows contain liquid oil (photo 6.1) 

40- 50 cm: grey sand; few crab burrows filled with oil; shell fragments 

Remarks: 

Although the fine sediment prevented the oil from penetrating deeper, the large amount of 

crab burrows acted as oil tubes leading the oil in regions as deep as 50 cm. In some of these 

burrows anaerobic conditions preserved the oil as a liquid fluid not to be distinguished from 

new crude oil. The water which below the ground water level seeps out of the substrate 

displays typical interference colours caused by oil constituents. Where crab burrows were cut 

liquid oil is floating in dark brown patches on the water surface (photo 6.1). 

The soil surface displays a distinct relief with elevated patches around former Arthrocnemum 

plants. The roots must have accumulated sediment as well as the oil when it drifted towards 

the shore. These elevated areas are covered by a hard tar crust (see for further description 

“sediment compaction by oil residues” on page 74). Burrows of the crab Cleistostoma 

dottiliforme which were abundant around the plants are mostly fossilised. The area between 

the plants is covered by cyanobacteria, the elevation itself only partly show cyanobacteria. It 

is important to note that the material of the little elevations is significantly harder than the 

surrounding substrate. 

Section 6 same as section 7 

82



Section 7 

Remarks: 

The material of the elevations is still much harder than the spaces in between which is 

displayed by the figures 6.11 and 6.12. But now even the elevations are covered by 

cyanobacteria. 


Section 8 


Section 9 

210 m 

0-0.5 cm: Cyanobacteria (polygonal) 

0.5-7 cm: dark brown silt; heavily oiled; sticky, strong odour 

7-15 cm: lighter brown silt; oiled; sticky with strong odour 

15-20 cm : grey silt; lightly oiled; relic crab burrows contain oil of low 


20-25 cm: dark grey-black reduction patches of intensive H2S odour; total 

hydrocarbon concentration of this layer 3.7 g/kg 

25-40 cm: grey silt; crab burrows contain liquid oil 

40-50 cm: grey sand; no oil; 

180 m 

0-0.5 cm: Cyanobacteria (polygonal) 

0.5-6 cm: dark brown silt; heavily oiled; sticky, strong odour 

6-12 cm: lighter brown silt; oiled; sticky with strong odour 

12-25 cm : grey silt; lightly oiled; relic crab burrows contain oil of low 


25-30 cm: dark grey-black reduction patches of intensive H2S odour 

30-45 cm: grey sandy silt; crab burrows contain liquid oil; plenty of shell 

fragments 

150 m 

0-1 cm: Cyanobacteria (polygonal) 

1-2 cm: tar layer 

2-7 cm: dark brown silt; heavily oiled; sticky, strong odour; total petroleum 

7-14 cm: 

hydrocarbon content is 34 g/kg of low degraded oil (dark brown 

colour of rapid assessment print – fig 6.8) 

lighter brown silt; oiled; sticky with strong odour; transition to less 

oiled grey silt below from 10-14 cm 

14-25 cm : grey silt; lightly oiled; relic crab burrows contain liquid oil of low 


25-55 cm: grey sand; crab burrows until 40 cm depth; they contain liquid oil 

83


Photo 6.1 Soil sections showing the oil residues within the crab burrows 10 years after the Gulf war 

oil spill. A: liquid oil seeping out of crab burrows and floating on top of the ground water surface. B: 

crab burrows in the upper soil section. The dark colour displays the oil residues which are degraded 

where oxygen was available (mostly in the upper parts of the burrows). 

10 cm 

50 cm 

18 17 15 

13 12 11 10 

m 

105 120 135 150 

0 15 30 45 60 75 90 

heavily oiled (upper part) 

silt / clay coarse sand tar 

less oiled (lower part) 

layer 

silt with sand shell fragments oiled patches 

animal burrows 

84


Fig. 6.7 Soil sections of the Halocnemum transect – upper part. 


Section 10 

135 m 

0-0.5 cm: cyanobacteria (polygonal) 

0.5-3 cm: tar layer 

3-13 cm: dark brown silt; heavily oiled; sticky, strong odour; total petroleum 

13-20 cm: 

hydrocarbon content is 28.5 g/kg of low degraded oil (brown colour of 

rapid assessment print – fig 6.8) 

lighter brown silt; oiled; sticky with strong odour 

20-24 cm : transition to less oiled grey silt below 

24-35 cm: grey sandy silt; not oiled; relic crab burrows contain liquid oil of low 


35 58 c d b b h ll fragments in lower 10 cm 



0-0.5 cm: cyanobacteria (crinkled, brainlike) 

0.5-1.5 cm: tar layer 

1.5-7 cm: dark brown silt; heavily oiled; sticky, strong odour; 

7-20 cm: light brown/grey silt; lightly oiled; sticky with medium petroleum 

hydrocarbon odour 

20-30 cm : grey silt; no oil; relic crab burrows contain liquid oil of low 

degradation status 

30-50 cm: grey sandy silt; not oiled; no crab burrows; shell fragments in lowest 5 

cm 

50 55 cm: d d t h ll fragments 



0-0.1 cm: cyanobacteria (flat, pimple like surface, could also be due to 

evaporates that crystallized at the surface) 

0.1-2 cm: deep brown oiled silt, well degraded oil residues (no colour in the 

rapid assessment oil print although the oil concentration is relatively 

high); 17.8 g/kg hydrocarbons 

2-7 cm: light brown silt; well degraded oil residues; odour of garden soil 

7-30 cm: grey silt 

30-62 cm : grey sand; scattered shell fragments 

85




0-0.1 cm: cyanobacteria (flat, pimple like surface, could also be due to 

evaporates that crystallized at the surface) 

0.1-5 cm: brown lightly oiled sandy silt, well degraded oil residues 

5-40 cm: homogeneous sandy silt; light beige 

40-60 cm: light grey sand with scattered shell fragments 

60 cm: beachrock 

l i b t t tion at 10 cm: 62.1% 



Section 15 


Tab. 6.15 Section 17 at the 30m mark of the Halocnemum transect. 

Section 17 

60 m 

0-0.1 cm: no cyanobacteria, only some evaporates that crystallized 

at the flat surface) 

0.1-5 cm: yellow beige sandy silt 

5- 30 cm: light grey sandy silt 

30-45 cm: light grey silt 

45-58 cm: grey sand with some shell fragments 


30 m 

0-5 cm: conspicuous brown very fine silt layer, obviously due to organic 

components derived from the dense salt marsh vegetation 

5-20 cm: yellow beige silt 

20-45 cm: light grey sand 



calcium carbonate concentration at -5 cm: 10.2% 


86


Sec.12 –5 cm Sec.10 –10cm Sec.9 –5cm Sec.7 –25cm Sec.5 –10cm Sec.5 –20cm 

17.8 g/kg 28.5 g/kg 34 g/kg 3.7g/kg 24.6 g/kg 4.9 g/kg 

Fig. 6.7 Rapid assessment oil prints. Sec.= section. 

2001 Oil load compared to 1993/94 

It is hard to compare the oil load because the oil deposition was not homogenous within the 

sediment. Variations are therefore high. But by homogenizing samples large enough and 

calculating mean values, trends were clearly obvious. In 1993 samples were collected by 

Smith (1994) at the 60 m, 260 m, and 360 m marks along the transect. In 2001 at the same 

location samples were collected and their total concentration of hydrocarbons was 

determined. For all sediments the concentration of extracted hydrocarbons decreased with 

increasing sediment depth. In 1993 the oil generally is more degraded in the top soil 0-10 cm 

than below where 1993 the n-aliphatic alkanes above the unresolved complex matrix (UCM) 

are much more pronounced. The overall concentration of hydrocarbons though is much higher 

between 0-10 cm depth. The increase of the n-C17/pristan and n-C18/phytane degradation 

indices with increasing depth at the 360 m mark and the lower intertidal (0.28/0.22 at -5 cm 

and 0.8/1.9 at -15 cm depth), may not indicate a higher degradation status near the surface as 

stated by Smith 1994. They are probably higher because of the presence of biogenic lipid 

material which increases the concentration of especially n-C17. In 2001 the non-oiled zone 

shows no hydrocarbons. At the 260 m mark the concentrations are about 25% of the 1993 

concentrations in the top soil sediments. But between 10 and 20 cm soil depth the petroleum 

hydrocarbon concentration increased from 1.4 to 4.9 g/kg which indicates that in this zone 

some of the oil from the top soil moved into deeper layers (fig. 6.9). At the 360 m mark in 

2001 there are almost no hydrocarbons in the sediments. The low concentrations could well 

be attributed to the presence of lipids. 

87

g/kg 

40 

35 

30 

25 

20 

15 

10 

5 

0 


1993 / 0-10cm 

1993 / 10-20cm 

2001 / 0-10cm 

2001 / 10-20cm 

75 60 m 

260 m 360 m 

Fig. 6.9 Mean values of the oil load at different sites along the Halocnemum transect. The 1993 value 

of the top soil was 101 which could not fully be displayed in this graph. The high variation is indicated 

by the standard deviation of 53.8. 

In 1994 the samples were collected from three zones according to the condition of the plants (Böer 

1994 and Smith 1994): 

1. Non oiled areas – healthy plants 

2. medium oiled areas – partial mortality 

3. heavily oiled areas – total mortality 

In 2001 these zones were sampled again to check whether the oil load of the sediments decreased 

during the last 7 years or not (tab. 6.16 and fig. 6.10). 

Tab. 6.16 Oil load at heavily oiled sites, medium oiled sites and non oiled sites. 

kg/m² kg/m² g/kg 

heavy oil impact 1994* 2001 2001 

Site 1 7,21 5,7 28,5 

Site 2 7,87 6,8 34 

Site 3 6,36 4,8 24 

medium oil impact 

Site 1 3,66 3,1 15,5 

Site 2 2,99 1,94 9,7 

Site 3 2,47 2,38 11,9 

no oil impact 

Site 1 0,02 0,02 0,1 

Site 2 0,05 0,03 0,15 

Site 3 0,32 0,01 0,05 

*data: Smith 1994 

101/sd 53.8 

88


Although it is difficult to compare the results it is obvious that in 2001 there is still a significant 

amount of oil in the soil substrate. The overall concentrations seem to be slightly lower than in 1994. 

The hydrocarbons from the non-oiled sites are probably due to lipids which have nothing to do with 

the oil spill. 

Trace metal concentrations 

The concentration of nine trace metals was analysed from samples collected at the same site 

like the samples for hydrocarbon analysis (complete data in appendix ). It is surprising that 

the overall concentrations are lower at the 135 m mark with higher hydrocarbon 

concentrations. The lower values at the 350 m site are expected due to the lower hydrocarbon 

concentrations. Compared to 1994, the nickel and vanadium values decreased in the upper soil 

layer and increased in the lower soil layers, indicating a percolation of the trace metals (see 

also chapter 6.1.9). 

depth in cm 

mg/kg 

0 

-10 

-20 

-30 

-40 

-50 

35 

30 

25 

20 

15 

10 

5 

0 

15 

135 m - 

5 

30 

45 

135 m - 

10 

60 

75 

135 m - 

20 

90 

105 

Nickel Vanadium Zinc Chromium 

120 

135 

250 m - 

5 

150 

165 

250 m - 

10 

180 

195 

250 m - 

20 

350 m - 

5 

350 m - 

10 

oil in burrows medium oiled heavily oiled degraded oil 

210 

225 

240 

255 

270 

285 

300 

315 

350 m - 

20 

Fig. 6.10 Oil load along the transect and trace metal concentrations at three locations in 5, 10 and 20 

cm depth. 

330 

345 

360 

m 

89

Sediment compaction by oil residues 


Generally the sediment mixed with oil that was exposed to the atmosphere (especially the 

sun) hardened, forming a tar crust. Most of the substrate containing degraded oil residues is 

harder than unpolluted sediment near the surface. Although there is not much of a tar crust left 

in 2001, there are large areas with a more compact surface than the underlying sediment. One 

special phenomenon are the little mounds which formerly accumulated around Halocnemum 

and Arthrocnemum plants. On top and around these little mounds more oil was deposited than 

in the interstitial spaces. Therefore the tar crust on most of these mounds in 2001 is still 

present. Cyanobacteria is abundant in the flat spaces between the mounds and occasionally 

also on top of the mounds. In such cases the tar crust is located immediately below the 

bacterial mat. 

Measurements of penetration resistance and vane shear force of the sediment, as well as the crust, 

indicate that the surface material on top and directly around the mounds is much harder than at the 

spaces in between (figs. 6.11 and 6.12). Near the 300 m mark the largest mounds occur which results 

in the hardest substrate even below the cyanobacterial mats (fig. 6.11). Figure 6.12 shows the highest 

values at the surface (tar crust) and a decrease with depth. At -6 cm the typical values between 1.3 and 

1.7 kg/cm² as for undisturbed sediments of this type (comparable to unpolluted sites) can be found, 

except near the 300 m mark where the mounds display the most compact substrate. 1.5 kg/cm² within 

this zone is reached in an average depth of 10 cm. In this “hard crust” zone the surface measurement 

was impossible because the material would break away above 7-9 kg/cm². Because of this reason no 

value is presented in figure 6.12. 

kg/cm² 

0,5 

0,45 

0,4 

0,35 

0,3 

0,25 

0,2 

0,15 

0,1 

0,05 

0 

0.06 0.49 0.57 0.18 0 0 standard deviations 

0.82 0.43 0.51 0.47 0 0.27 

180 270 300 

cy. mound 

below cy. mound 

cy. flat 

below cy. flat 

Fig. 6.11 Penetration resistance of the substrate on mounds and the flat areas in between. 

Characteristic sites between the 180 and 300 m mark are displayed. Were standard deviation is 0 all 

values were 4.5 or higher (which was out of range with the measurement device used). 

90

kg/cm² 

5 

4,5 

4 

3,5 

3 

2,5 

2 

1,5 

1 

0,5 

0 


180 270 300 

mound surface 

mound -3 cm 

mound -6 cm 

interstitial space 

interstitial s. -3 cm 

interstitial s. -6 cm 

Fig. 6.12 Vane shear force of the substrate on mounds and the flat areas in between. Characteristic 

sites between the 180 and 300 m mark are displayed. *** values out of range but higher than 7. 

Standard deviations was in all cases less than 0.9. 

Sediments which are hardened by tar present a physical barrier for crabs. According to 

measurements around burrows of pioneer crabs, the animals are not able to dig into substrate 

with higher vane shear than 2.5 kg/cm². Penetration resistance within sediments inhabited by 

Cleistostoma dotilliforme (the dominant crab species within this intertidal zone) usually were 

below 0.2 kg/cm². During longer periods without inundation by seawater the surface substrate 

may desiccate and harden to a certain degree at the surface. This desiccation effect is 

generally restricted to the uppermost 0.5-1 cm The maximum observed increase in penetration 

resistance due to desiccation was 0.9 kg/cm². 

Soil water content 

The soil water content in the study area generally is higher closer to the sea. But still there are 

significant differences which are not due to the inundation time and frequency but to the sediment 

type. The substrate is dominated by fine sediments which results in a high capability to retain 

moisture. This and the availability of water by high tides and rains during the winter season lead to 

relatively high values of around 30% (by weight). Figure 6.13 displays a moisture profile during one 

month in spring 2001. 

* 

* 

* 

91

water content in weight % 

45 

40 

35 

30 

25 

20 

15 

10 

5 


0 

0 15 30 45 60 75 90 105 120 135 150 m 

10/3/-10cm 

23/3/-10cm 

6/4/-10cm 

10/3/-20cm 

23/3/-20cm 

6/4/-20cm 

Fig. 6.13 Soil water content in the upper part of the transect between the 15 and 150 m mark. 

It can be clearly seen that the coarse sandy sediments at the 0 m mark contain much less water than the 

fine substrate in seaward direction. In addition there is a sharp decline in 10 cm depth between March 

and April which is due to the increasing air temperatures. From 15 to 135 m there is not much change 

which reflects the uniformity of the sediment. At the 150 m mark increasing soil water content is 

caused by tidal waters. Here the substrate in 20 cm depth contains around 40% water which is 

considered as saturated. The groundwater rarely drops below this depth. 

6.1.1.2 Groundwater characteristics 

Electrical conductivity 

The total ionisation of the groundwater is expressed in the electrical conductivity. The most important 

constituents are chloride and sodium and therefore responsible for most of the electrical conductivity. 

There is a general trend from sea water concentrations at the lower intertidal to increasing values 

towards the littoral fringe and adjacent supratidal areas. In the scope of this study it was important to 

find out about the development of the groundwater constituents during the winter season with lower 

temperatures and the influence of rain. 

92

conductivity mS/cm 

160 

150 

140 

130 

120 

110 

100 

90 

80 

70 

60 


Oct Jan 

m 

15 30 45 60 75 90 105 120 135 150 

Fig. 6.14 Electrical conductivity in October 2000 and January 2001 between the 15 and 150 m marks 

of the profile. 

Figure 6.14 shows the gradual increase of the values with the distance from the sea in October 

as well as in January. The January values follow the same trend but they are between 20 and 

40 mS/cm lower than the October values. This is most probably due to the influence of 

rainwater combined with lateral groundwater flow (further explanations in the following 

paragraph). 

Figure 6.15 displays the changes of groundwater ionisation as well as the concentration of 

chloride. The correlation is obvious although there are some minor discrepancies. The lowest 

values in both electrical conductivity and chloride were measured in January, except at the 15 

m mark where the minimum was already in November. This can be explained by the location 

close to the sand sheet and an intensive rainfall event from November 9 th which provided 30 

mm of rain (precipitation data in appendix 1). High infiltration in the sand sheet lead to a 

groundwater flow in seaward direction which could be noticed at the adjacent station. The 

increase in December is interesting because 5 days before the measurements there was again a 

heavy rain event which brought 30 mm of rainfall. What makes the difference compared to 

the November situation? The only possible explanation could be the increased lateral 

groundwater flow from the adjacent sabkha. Rain water causes solution of salts in the upper 

sabkha soil. The enriched rainwater penetrates the substrate until it reaches the groundwater 

much higher mineralised than before. This mineralised rainwater mixes with the sabkha 

groundwater and moves seawards. On its path it increased the December values at the stations 

above the high water mark. Direct infiltration is not likely because of the fine sediments in the 

top soil layer. 

93

1.5 

1 

0.5 

200 

150 

100 

50 

0 

15 m 

mS/cm Cl- 


120 

100 

80 

60 

40 

20 

0 

mS/cm 

140 

120 

100 

80 

60 

40 

20 

0 

Oct 

Dec 

75 m 

Feb 

Apr 

mS/cm Cl- 

100 

80 

60 

40 

20 

0 

g/l 

mS/cm 

140 

120 

100 

80 

60 

40 

20 

0 

Oct 

150 m 

Dec 

Feb 

Apr 

100 

80 

60 

40 

20 

0 

mS/cm Cl- 

m 

120 135 150 

0 15 30 45 60 75 90 105 

Fig. 6.15 Electrical conductivity and chloride concentration in winter 2000/2001. 

Magnesium 

infiltration 

The magnesium concentrations within this transect show a distinct pattern according to the time of the 

year. High values in summer (up to 4500 mg/l) and a significant decrease in winter when 

concentrations almost reach the sea water concentration which is between 1700 and 2000 mg/l in the 

area of consideration. 

mg/l 

groundwater flow 

5000 

4000 

3000 

2000 

1000 

0 

Oct Jan Feb Mar Apr 

30 

25 

20 

15 

10 

5 

0 


Ca++ 

Mg++ 

°C 

g/l 

94


Fig. 6.16 Magnesium and calcium concentration at the 150 m mark. 

Fig 6.16 illustrates the gradual decrease of the magnesium concentration until February and 

the following increase which is almost symmetrical. The calcium values range around 2000 

mg/l in winter time. Since data of the summer period is missing, the October value of 1000 

mg/l indicates a decrease sometime during the summer period. It seems not likely that the 

magnesium decrease in winter is caused by consumption due to higher calcium values in the 

winter period, because the strong magnesium increase in spring could not be explained then, 

since the calcium values remain constant. Probably the higher magnesium concentrations are 

due to the general increase in ionisation caused by higher evaporation as well as solution 

processes as a result of higher groundwater temperatures (fig. 6.16). 

The magnesium values along the transect follow a clear trend in the winter period with 

increasing concentrations towards the landward side of the transect (fig. 6.17). The overall 

variation though is in the range of 500 mg/l. With increasing temperatures in spring this trend 

is broken. Figure 6.17 displays a general increase of the concentration at all stations. The 

maximum increase is at the seaward side of the transect where the concentration almost 

doubled (compared to January values). This observation (the extreme increase near the sea) is 

supported by other data from coastal sabkhat in 1996 (Barth 1998). Areas more inland show 

only minor increase of magnesium concentrations. 

mg/l 

5000 

4500 

4000 

3500 

3000 

2500 

2000 

1500 

15 30 45 60 75 90 105 120 135 150 m 

Fig. 6.17 Magnesium concentration in March and April 2001 along the transect. 

Sulphate 

The sulphate concentrations generally show a higher variability than total mineralisation and chloride. 

But still there are visible trends (fig. 6.18). 

Mar 

Apr 

95

mg/l SO4 

13.000 

12.000 

11.000 

10.000 

9.000 

8.000 

7.000 

6.000 

5.000 

4.000 


15/10 

04/11 

16/11 

29/11 

14/12 

31/12 

14/01 

29/01 

10/02 

10/03 

06/04 

150 m 

120 m 

Fig. 6.18 Sulphate concentration at different locations along the transect during the winter period. 

At all stations along the transect there is a general decrease until early spring followed by an intense 

increase in the following month. The most seaward station (150 m mark) displays the lowest 

concentrations throughout the whole winter period. Further inland there is a gradual increase of 

sulphate concentrations. The maximum values were measured at the most landward station. 

Explanations might be similar to the ones discussed for magnesium. Gypsum crystallisation and 

solution seems one possible control for the variations. The constant calcium concentrations do not 

exclude this process because the abundance of carbonaceous sediments provide the necessary calcium 

source. 

Calcium 

As already mentioned before the calcium concentration remains constant through most of the 

winter period at around 2000 mg/l. There is no difference between the upper and the lower 

intertidal. The lowest concentrations were observed in October when the values were between 

1000 and 1500 mg/l. This decrease can be attributed to higher water temperatures in summer 

(see next paragraph), which reduce the solubility of calcium carbonates. PH varies between 

7.2 and 7.6 during the year which excludes pH variations as a controlling factor for calcium 

concentrations. 

Groundwater temperature 

The groundwater temperature in the salt marsh ecosystem are strongly related to the sea water 

temperature. The closer to the sea the lower are the recorded temperatures (fig. 6.19). The 

temperatures vary with a maximum of 5°C within the profile. High gradients like this occur 

75 m 

30 m 

15 m 

96


only in the winter months when the sea water cools down to less than 15°C. With increasing 

sea water temperatures the gradients become less than 2°C. Higher heat absorption further 

inland warms the groundwater. The maximum temperature range in the course of one year is 

23° (13-36°C). 

29 

27 

25 

23 

°C 

21 

19 

17 

15 

15 30 45 60 75 90 105 120 135 150 

Fig. 6.19 Groundwater temperatures along the transect between November and April. 

6.1.1.3 Microclimate 

Temperature 

Temperature measurements were taken every hour 50 m seaward of the mean high water 

mark (MHWM). This location is considered to be representative of the salt marsh ecosystem 

periodically inundated by seawater with a cyanobacteria cover on top of the soil surface and 

some Arthrocnemum macrostachyum which in this case were dead due to the oil spill in 1991. 

Measurements were carried out in October, December and February. The data collected in 

February displays the absorption and emission characteristics of this ecosystem type best (fig. 

6.20). With the first sunlight after sunrise at 7:00 the air temperature rises to 14°C at 8:00. 

Absorption heats the surface which leads to 4°C higher temperature there. The same heat 

gradient exists between the surface and the soil in 5 cm depth. From there on there is a 

positive heat gradient towards deeper layers. The temperature reaches the constant value of 

19°C (which resembles the daily average air temperature for this time of the year) at a depth 

of 40 cm shortly above the beach rock layer. During the next hours increased absorption heats 

the surface to 27.5°C at 10:00 which is already 8° above the air temperature in 1 m height. At 

this time the maximum gradient of 12° between the surface and 5 cm soil depth is reached. 

Below 5 cm the heat gradient is again positive. 

29/11 

14/12 

31/12 

14/01 

29/01 

10/02 

10/03 

06/04 

97


5 10 15 20 25 30 


100 50 20 10 5 0 -5 -10 -20 -30 -40 

height / depth in cm 

Fig. 6.20 Temperature profile between -40 and 100 cm height above soil surface at an upper intertidal 

site. 

The maximum surface temperature of 29°C is reached at 12:00 equal to maximum insolation. 

Now the heat flux towards deeper soil layers becomes obvious within the first 10 cm below 

the surface. In the early afternoon the surface still shows a high temperature of 28°C. 

Continuous heat emission warms the air layers close to the surface which then transport the 

heat to higher air layers by the means of turbulent air flow. This is demonstrated by the 

increase of air temperature to 23°C in 100 cm height. At 16:00 the heat flow reverses and the 

maximum temperature is now 5 cm below the soil surface. Reduced insolation leads to 

emission (irradiation) and a heat loss of the top soil layer towards the surface as well as 

towards deeper soil layers. The minimum soil temperature is now 18.5°C at 20 cm depth. The 

air temperature in 100 cm height did not significantly change during the last two hours. 

Sunset at 17:30 leads to a sharp drop of the air temperature to 16°C at 18:00 (a cloudless sky 

minimises re-emission). Continuous heat flow towards the surface, as well as towards deeper 

soil sections, reduces the soil temperature in 5 cm soil depth from 23.5 to 22°C. In the 

following hours the process of irradiation becomes very clear directly at the soil surface. The 

temperature of the surface is - due to the intensive heat loss - up to 1.5°C lower than the air 

temperature above. At midnight the heat loss of the soil surface cools the air layers above 

which means that the difference between the air temperature in 100 cm and the surface near 

16:00 

18:00 

20:00 

22:00 

00:00 

02:00 

04:00 

06:00 

08:00 

10:00 

12:00 

14:00 

98


air layers is not as significant as it was two hours before. The gradual heat loss of the surface 

near soil advanced so far that now there is only one positive gradient towards deeper layers. 

There is a uniform heat flow from 19°C in 40cm soil depth towards the surface. This heat 

flow intensifies in the early morning hours until the surface cools down to 7.5°C at 6:00. 

Immediately after the sunrise the same cycle starts again. 

If this temperature profile is compared to the temperature profile of a dry sandy surface more 

inland (fig. 6.21), the typical characteristics of the salt marsh climate become clear. 


0 5 10 15 20 25 30 

100 50 20 10 5 0 -5 -10 -20 -30 -40 

height/depth in cm 

Fig. 6.21 Temperature profile between -40 and 100 cm height above soil surface at a supratidal 

sandy surface. 

The much higher absorption of salt marsh surfaces at low angle insolation is most obvious. At 

8:00 the sandy surface is only 2°C warmer than the air temperature, whereas the difference is 

already 4° in the salt marsh. Another important difference is the slower heat flow in the salt 

marsh soil due to the high water content. The amplitude in the sand is still 3°C at a depth of 

30 cm, whereas there is almost no amplitude at all in the salt marsh soil. As a result, the heat 

emission at the surface is much higher immediately after sunset (4°C compared to less than 

1°C temperature difference between air temperature and surface temperature in salt marshes). 

This generally leads to a significant milder climate near the soil surface apart from the marine 

16:00 

18:00 

20:00 

22:00 

00:00 

02:00 

04:00 

06:00 

08:00 

10:00 

12:00 

14:00 

99


influence. Minimum temperatures as well as maximum values during the summer months are 

less extreme. 

This pattern changes with the influence of a tar crust covering the surface. The sealing of the 

surface by a tar cover has two consequences. First, the surface is much less permeable which 

means that the influence of moisture present in the soil below is reduced to a minimum. 

Cooling by evaporation is minimised. Second, the dark tar crust increases the absorption 

which leads to generally higher temperatures near the surface. The general temperature 

increase above tar crusts within salt marshes is between 2°C and 5°C during sunny days in 

April 2001 (air temperature: 35°C). Also the soil substrate 2 cm below the surface is between 

3 and 6°C warmer than the unoiled counterpart. Measurements in 1994 (at 36°C air 

temperature) revealed up to 8°C increased surface temperatures and 11°C increased 

subsurface temperatures (in 2 cm depth). Watt 1994 reports temperature differences of as 

much as 15°C in 1992. The ecological impact of this temperature increase will be discussed in 

chapter 6.1.9. At night, the temperatures were generally 1-2°C lower above tar crusts (in April 

2002, 19°C air temperature). In many cases the present tar crusts have the same influence like 

dry cyanobacteria mats. They also prevent moisture exchange between the top soil and the 

surface and the absorption of low angle insolation is about the same. But compared to the tar 

crusts which are permanent (at least for some more years) the dry cyanobacteria mats are only 

present between January and April. This means that particularly the temperature increase in 

the hot summer months above tar crusts is an unnatural impact to the microclimate of the salt 

marsh ecosystems. 

Temperature measurements in the upper salt marsh soil layers were compared with the air 

temperatures in 2 m height (Marduma Bay intertidal station). The temperature data loggers were 

installed 5 and 10 cm below the surface near the 150 m mark which is located shortly above the mean 

high water line (which means that the station is inundated only periodically). The surface is covered 

by the typical cyanobacteria mat. For sediment characteristics see 6.1.1.1. 

100

30 

25 

20 

15 

10 

5 

21 

18 

19 

16 

14 

17 

12 

15 

10 

13 

8 

11 

16 

3 

14 


1 

12 

23 

10 

21 

8 

19 

6 

17 

4 

15 

2 

13 

0 

11 

22 

9 

20 

7 

18 

5 

16 

3 

14 

1 

12 

23 

10 

21 

Fig. 6.22 Temperature 10 cm below surface (lower part, blue) and 2 m above (upper part, red). Note 

the delay of minimum and maximum values of 4 hours in average. Values from 19.2.2001 until 

7.3.2001. 

A rapid increase of the values after sun rise (during sunny days, blue shade in fig. 6.22) and 

a much slower decrease during afternoon and night (green shade in fig. 6.22) is 

characteristic for the air temperature curve. The amplitude is between 6° and 16°, which is 

usual for this time of the year. 10 cm below the surface the amplitude is only between 2° and 

4° and the duration of temperature increase is between 1 and 5 hours longer (blue shaded 

bar). It is also obvious that there are no pronounced peaks (maximum as well as minimum). 

There is rather a plateau with little change for some hours in most cases. The minimum 

values during night show the same characteristic although the time of low temperatures 

above the surface is much longer (dark green bar in fig. 6.22). Generally, the reversal at the 

temperature maximum follows about 5 hours later whereas the reversal of the minimum is 

only 3 hours behind. This fact may be attributed to the longer low temperature period (with 

gradually slightly decreasing values until sunrise) above the surface and intensive heating of 

the surface due to absorption after sunrise. The slight temperature decrease in the early 

morning hours can not be recognised 10 cm below the surface because of the low gradient 

and therefore slow heat flow. A much higher gradient (reversed) after sunrise is more 

effective and reverses the trend below the surface. Therefore the reversal point is much 

closer to the surface reversal than after the maximum values in the afternoon. 

The temperature reversal in 10 cm depth is around 2 hours delayed compared to 5 cm depth. 

Remarkable is the fact that there is no clear difference between minimum and maximum 

temperature reversal. It must also be noted that the soil temperatures in 5 cm soil depth 

8 

19 

6 

101


frequently reach values higher than 40°C during the summer months. In May 2001 it 

happened two times, in June 9, in July 11 and in August 9 times. The absolute maximum 

(47.7°C) was reached in July (fig. 6.23). Such values might have some effects on the salt 

marsh vegetation and will be discussed in chapter 6.1.9. The daily amplitudes in 10 cm soil 

depth range between 5°C in winter and 10°C in summer (in average). The soil layer at 5 cm 

depth experiences daily temperature variations up to 20°C. The annual temperature 

amplitude in 10 cm depth is 36 °C (5-41°C) and in 5 cm depth 44°C (4-48°C). Additional data 

for other months is given in the appendix no. 6. 

Temperature in °C 

50 

45 

40 

35 

30 

25 

20 

15 

10 

1 

July 2001 

-5 cm -10 cm 

Fig. 6.23 Soil temperatures in July in the upper eulittoral below a flat polygonally cracked 

cyanobacteria layer. 

The temperature transect (fig. 6.24) displays a clear trend from the lowest temperatures at 

the high water line with the strongest influence of the low sea water temperatures. This is 

obvious in the April profile where the sea water reached the 150 m mark during the last tide 

before the measurement. The inundation caused a temperature drop of 5° within the upper 

soil (fig. 6.24). Towards the landward end of the salt marsh (supralittoral) the temperatures 

increase gradually. Darker soil and a high soil moisture content absorb the heat. Only within 

the sand sheet (0 metre mark) the temperature decreases, which is clearly due to the lack of 

moisture within the sandy substrate. The higher the temperatures, the higher is also the 

temperature difference between higher and lower soil layers. The layers near the surface 

become warmer due to intensive absorption. The soil moisture causes a higher heat capacity 

which results in a lower heat flow towards deeper soil layers. This is already obvious in April, 

i.e. at the 45 m mark where the temperature difference between -5 and -10 cm is 7°C. 

102



40 

35 

30 

25 


10.3.01 

20 

0 15 30 45 60 75 90 105 120 135 150 

40 

35 

30 

25 

6.4.01 

20 

0 15 30 45 60 75 90 105 120 135 150 m 

Fig. 6.24 Soil temperature along the Halocnemum salt marsh transect at 12:00. 

-5 cm 

-10 cm 

-5 cm 

-10 cm 

Evaporation 

The measured potential evaporation along the transect shows a clear trend towards higher 

evaporation at the high water line (fig. 6.25). 

mm/day 

4500 

12 

4000 

3500 

9 

3000 

2500 

6 

2000 

1500 

1000 3 

500 

0 

0 30 60 90 120 

metres 

Fig. 6.25 Potential evaporation along the profile in February, March and April. 

This makes sense regarding the vegetation, the cover of which increases towards the 

supralittoral. At the 120 m mark there are only dead Arthrocnemum and Halocnemum plants 

with virtually no cover at all. The flat surface minimises friction which results in the highest 

wind speeds at the surface where evaporation was measured. The winds speed is the most 

important variable regarding the potential evaporation in a desert ecosystem. At the 15 m 

mark the Arthrocnemum plants have a cover of 50-70% and an average height of 30 cm. 

This reduces the wind speed at the surface almost to zero which results in much lower 

m 

Mrz 

Apr 

Feb 

103


potential evaporation values. The difference between the 120 and 0 m marks is smaller, the 

larger the open water surface of the measurement device is. 

The increase of the potential evaporation with the higher temperatures in spring is obvious. 

The mean temperature increases from 16,6°C in February to 20,8°C in March and 26,5°C in 

April. When temperature is the critical variable alone (near the 0 m mark in the profile) the 

increase in evaporation is higher compared to the 120 m mark in the profile, where wind 

speed also controlled potential evaporation. There are significant differences within a salt 

marsh regarding the potential evaporation which will certainly also be true for the evapotranspiration. 

There is a gradient between the densely vegetated supralittoral and upper 

eulittoral to the mean high water line where maximum potential evaporation occurred. 

6.1.1.4 Vegetation 

The transect starts adjacent to a sand sheet which is situated about 30-50 cm higher than the 

seaward lying salt marsh. The vegetation cover there is between 7-15%. The halophytes 

Zygophyllum qatarense and Halocnemum strobilaceum, sporadically Halopeplis perfoliata 

and Limonium axillare are tyypical. Seaward of the sand sheet there is a dense salt marsh 

vegetation which decreases towards the Gulf in cover and size. Photo 6.2 displays the view 

towards the Gulf from the 30 m mark. The transition between the living and dead area is 

clearly visible. 

Photo 6.2 Halocnemum s. salt marsh test area (seaward view). 

transition between living 

and dead zone. 

From the 5-10 m mark within the highly saline and damp salt marsh soil, Halocnemum 

strobilaceum is the only plant species covering about 60% of the soil. The individuals grow 

up to 40 cm high and cover 1 m² in average. Most of the shrubs are growing on little mounds 

of 10-15 cm height compared to the interstitial spaces that are not vegetated. In seaward 

104


direction the size of the individual plants and the ground cover decreases gradually (see tab. 

6.3). At the 75 m mark, the Halocnemum plants are all living but their appearance is not as 

healthy as of the others more landward. Between the 75 and 90 m mark the mortality 

increases significantly to average 3.5 per m² (sd 2.1) dead individuals at the 90 m mark. It is 

here where the first Arthrocnemum macrostachyum is associated with Halocnemum. Up to 

now no new plant individuals germinated. Regeneration is restricted to the recovery of some 

damaged individuals (photo 6.3B and 6.3C). At the 105 m mark all plants within 300 m² are 

dead except one individual. The mounds around the plants were almost not perceptible at this 

location. The vegetation cover was measured around the remaining wooden parts of the 

plants. In 1992 several test squares (1 m²) were established around damaged but still living 

plants around this location of the transect. In 1996 all of them died (photo 6.3D) . Most 

Arthrocnemum plants that were damaged by the oil produced flowers and seeds in 1992. After 

seed production those plants started to die (Böer 1994a). The slow die-off continued until 

1995. Around the 135 m mark the remains of the former Arthrocnemum individuals are much 

larger than before. The plants must have been between 0.1 and 0.16 m² in size. The little 

mounds are also present again. About 100 m further towards the sea the mounds increase in 

size up to 10 cm height. They are preserved by the tar cover (resulting from oil which 

accumulated around the mounds). Most of the crab burrows around the mounds are also 

preserved by the tar crust. No recovery or any living plants were visible seawards of the 105 

m mark which means that a zone of more than 200 m of salt marsh vegetation is still dead 10 

years after the oil spill. 

Tab. 6.17 Vegetation profile of the Halocnemum transect. 

15 m 30 m 45 m 60 m 75 m 90 m 105 m 120m 135 m 150 m 

cover / 60% 45% 42% 32% 17,5% 7,5% 8,5% 4,7% 5,7% 3,7% 

sd 5,2 8,9 14,7 15,3 5,1 4,6 7,4 4,5 6,6 3,6 

seize m² 0.7 0.25 0.25 0.17 0.09 0.04 0.01 0.003 0.002 0.002 

condition healthy healthy healthy healthy living living / 

dead 

dead dead dead 

remains 

dead 

some 

regenera 

tion 

are 

larger 

height of 

mounds 

5-8 cm 5-8 cm 5 cm 1-5 cm 1-3 cm 1 cm 0 0 2 cm 1-3 cm 

105


A: Halocnemum s. near the 30 m mark. B: Living and dead plants at the 90 m mark 

C: Recovery of Arthrocnemum m. (90 m) D: Dead plants in test square (105 m mark). 

Photo 6.3 Status of salt marsh plants at different locations along the transect in 2001. 

6.1.1.5 Fauna 

The most typical and also most affected part of the fauna in the Halocnemum salt marsh 

were the brachyuran Crustacea. The oil impact killed almost all animal living in the upper 

intertidal soil from the 90 m mark until the lower mid eulittoral. Through crab burrows the oil 

could penetrate even fine sediments to a depth of more than 50 cm. All crab burrows within 

the oiled zone became oil traps. 

In 2001 counts of crab burrows reveal useful information about the state of recolonisation by 

crabs. Within the non oiled upper part of the transect in 2001, in average 9 inhabited 

Cleistostoma dotilliforme burrows are found near the 15 m mark. This number decreases in 

seaward direction to 3.8 burrows in average at the 45 m mark and 0.8 burrows at the 75 m 

mark. The standard deviation (related to the average value) indicates the higher variability of 

burrows seaward of the 60 m mark (fig. 6.26). 

106

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 


15 30 45 60 75 90 

number 

Fig. 6.26 Average counts of crab burrows > 0.5 cm along the transect (sd. = standard deviation). 

Further seaward no inhabited Cleistostoma burrows are found anymore until the 350 m mark 

(it is not clear whether these burrows were inhabited by Cleistostoma or an other species). 

According to comparable unpolluted sites, populations of 15-20 burrows would be normal 

within the Arthrocnemum/Halocnemum salt marsh (Apel 1994). The unpolluted part of the 

Halocnemum salt marsh is situated higher above chart datum which results in naturally lower 

crab populations. Therefore it can be concluded, that the upper part of this transect is in a 

quite normal condition. The crabs seem not to be affected by the adjacent oiled zone in 

seaward direction in 2001. The decrease towards the polluted zone is the result of changed 

environmental conditions. Even in the upper part were the oil residues are well degraded no 

crabs were observed. Some very small (0.5-2 mm) burrows (up to 10/m²) are the only sign of 

life (fig. 6.27). Samples occasionally reveal some polychaetes that inhabit those burrows, but 

other small crabs could also be possible inhabitants. 

Polychaetes are also observed seaward of the 210 m mark of the transect. The first living 

cerithides in 2001 occur at the 300 m mark where they are grazing on clean sediment. 

Further seaward there are no differences to unaffected shores. 

m 

sd 

107

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 


15 30 45 60 75 90 105 120 135 150 

number 

Fig. 6.27 Average counts of crab burrows < 2 mm along the transect (sd. = standard deviation). 

6.1.1.6 Cyanobacteria 

Morphology types 

Cyanobacteria are aquatic and photosynthetic bacteria which are often visible in nature 

without the aid of a microscope. Although they are prokaryotes, belonging to the kingdom of 

eubacteria (Woese 1987), they are often called „blue-green algae“ due to their algal-like 

appearance. But this does not reflect any relationship between cyanobacteria and other 

organisms called algae. Their capability of fixing nitrogen makes the designation algae even 

less appropriate, as it could erroneously be implied that eukaryotes are capable of nitrogen 

fixation. Cyanobacteria are unique organisms in the sense that they can perform both nitrogen 

fixation and oxygenic photosynthesis. Cyanobacteria, which form leatherlike mats of different 

morphology (fig. 6.28) are a common feature of the intertidal zone along the whole Gulf 

coast. They are widely distributed in the intertidal zone (from upper to lower intertidal) but 

never occur higher than the supratidal zone. The morphology of cyanobacterial mats depends 

on species composition and environmental factors like time of inundation. From the lower 

intertidal zone to the lower supratidal zone pinnacle mats (fig. 6.28a), polygonal or flat 

laminated mats (fig. 6.28b), folded or blister mat (fig. 6.28c), and finally a thin flat mat (fig. 

6.28d) can be differentiated. 

m 

sd 

108

HWN 

regularly flooded 


periodically flooded 

occasionally flooded 

HWS 

supratidal 

pinnacle mat polygonal mat brain like mat flat mat salt crust 

(laminated) 

Fig. 6.28 Different morphology types of cyanobacteria communities in the study area. 

Most abundant are the laminated mats dominated by the oscillatoriacean cyanobacterium 

Lyngbya aestuarii and the filamentous cyanobacteria Microcoleus chthonoplastes (photo 6.4) 

and Schizothrix spp. (Hoffmann 1994). According to Hoffmann (1994) Phormidium and the 

heterocystous genus Scytonema are also of importance in some salt marshes within the study 

area. 

Folded or brainlike mats are an important part of the upper intertidal zone in the Halocnemum 

and Arthrocnemum salt marsh between 1.6 and 1.9 m above chart datum and therefore 

inundated only occasionally. The leathery skin of the convoluted crinkled mat is between 1 

and 2 mm thick. The mat is only loosely attached to the sediment below and the lobes of the 

mat are hollow. This structure is probably due to extensive horizontal surface expansion. The 

dominant species in this community are of the genus Schizothrix, Microcoleus chthonoplastes 

and Lyngbya aestuarii (photo 6.4a). Sulphur bacteria and Beggiatoa are absent. 

The flat mats occur in a wide range of intertidal habitats. It is found below the halophyte zone, 

in channels, depressions between crab turrets as well as in the lower intertidal. Below the flat 

leathery surface there is usually 0.5-1 mm of filamentous cyanobacteria dominated by 

Microcoleus chthonoplastes which traps and stabilises sand grains. This species is 

characterised by bundles of trichomes within a copious mucilaginous sheath (photo 6.4b). 

109


According to Hoffmann (1994), this polysaccaride sheath may help the organism to resist 

prolonged periods of desiccation. Secondary cyanobacterial constituents of the community are 

Oscillatoria Iloydiana, Chroococcus marinus, Spirulina subsalsa, Spirulina labyrinthiformis, 

Johannesbabtista pellucida, Aphanothece cf. halophytica and pennate diatoms (species 

identification: Dr. L. Hoffmann, pers. comm.). The reddish layer often observed in pools is 

generally dominated by purple cells of the genus Chromatium containing numerous elemental 

sulphur granules. Other sulphur bacteria resemble the genus Thiocystis. A black surface is 

often caused by a thin layer of Lyngbya aestuarii which is composed of short disc like cells 

surrounded by a brownish sheath (photo 6.4a). Between the cyanobacteria and the sulphur 

bacteria there is occasionally also Beggiatoa present. 

The bacterial community in cyanobacteria mats consists of well defined zones according to 

the physic-chemical vertical gradients within the mat. These are gradients of light, oxygen, 

redox potential and concentrations of dissolved minerals such as sulphid, nitrogen compounds 

and phosphate (fig. 6.29) (Hoffmann 1996). These chemoclines are established by the 

metabolic activities of the different constituent micro-organisms. Below the uppermost 

surface sediment layer (0.1-1 mm) cyanobacterial communities and eukaryotic algae, 

particularly diatoms, are distributed within the sediment forming the cyanobacteria mat. 

Within this zone carbon dioxide is consumed and oxygen increased due to photosynthesis by 

the use of chlorophyll a as the main light harvesting pigment and water as the source of 

electrons. Beneath this layer intensive decomposition of organic matter utilize the oxygen 

forming an anaerobic milieu. This anoxic layer is the zone of the white sulphur bacteria 

Beggiatoa and the purple sulphur bacteria (e.g. Chromatium and Thiobacillus species). These 

photosynthetic prokaryotes have bacteriochlorophyll as light harvesting pigments and they 

depend on sulphide as electron donor (Boaden & Seed 1985). They require oxygen to oxidize 

sulphur, sulphide and thiosulphate to sulphate. This generates energy which is used in the 

synthesis of organic compounds from carbon dioxide. The necessary low-oxidation-state 

sulphur compounds are produced by bacterial protein decomposition and by sulphate 

reduction through the activity of anaerobe respires. The layers beneath the photosynthetic 

prokaryotes are in complete darkness. They are the habitat of anaerobe bacteria such as 

Desulphovibrio and different heterotrophic and chemolithotrophic processes (Jorgensen et al. 

1992). Various iron-sulphur compounds are formed in anaerobic conditions and there is a 

shift from trivalent to bivalent iron. Their formation is accompanied by the reduction of ferric 

phosphate, thus solubilizing the phosphate. Because sulphide is a strong complexing ligand 

110


(and most of the metal-sulphides are insoluble) metallic ions tend to be accumulated in 

anaerobe sediments. 

RPD 

Eh pH O2 

-200 0 +200 mV 

l i g h t, w a t e r, a i r, CO2, N2 

mg/l 5 10 

H2S 

100 200 mg/i 

Fe 2+ 

Fe 3+ 

Fig. 6.29 Chemical soil properties and microbial zones in the upper soil layer, determined by different 

environmental conditions (modified after Boaden & Seed 1985, Stal et al. 1985, and Hoffmann 1996). 

5 µm 

2 4% 

CO2 

CH4 

A 

Photo 6.4 A: Cyanobacterium Lyngbya aestuarii. The brown sheath surrounding the disc like cells 

can be seen clearly. B: Bundles of trichomes of Microcoleus chthonoplastes. The sheath is not visible 

at this picture. 

The flat mat may crack into polygons due to desiccation. Contraction of fine grained sediment 

overlying coarser material causes saucerlike polygons the edges of which may curl up and finally 

break loose. Flat laminated mats (photo 6.5) often occur in the middle intertidal habitats and in water 

logged depressions within the halophyte zone (upper intertidal). They may also break into polygons. 

NO3 - 

NO2 - 

NH3 

beige 

grey 

black 

B 

10 µm 

mud 

cyanobacteria 

Beggiatoa 

purple sulphur bacteria 

sulphate reducing bacteria 

111


The surface layer is dominated by the oscillatorean cyanobacterium Lyngbya aestuarii. Other 

constituents are Microcoleus chthonoplastes, Schizothrix sp. and pennate diatoms. Organosedimentary 

layers underlie the living mat. 

1 cm 

1 cm 

Photo 6.5 Flat laminated cyanobacteria mat – cross section. Note the annual layers. 

The lamination depends on sedimentation and growth rate of the filamentous cyanobacteria. During 

periods of slow growth or high sedimentation (mostly the cold winter period), the cyanobacteria mat is 

covered by a sediment layer which will produce a pale layer in the deposit. On top of the sediment 

new mats resettle during favourable conditions (summer period). In some places the annual cycle of 

growth and sedimentation can be recognised for the last 3 decades where the layers reach a thickness 

of around 10 cm. This phenomenon will be discussed in detail in chapter 6.1.7. Pinnacle mats show a 

variety of morphologies (photo 6.6) which range from pyramidal to cauliflower. It is built by 

filamentous bacteria dominated by Lyngbya, Microcoleus and Schizothrix. Associated were also 

Phormidium spp., Spirulina subsalsa, Spirulina labyrinthiformis, Johannesbabtista pellucida, 

Gomphosphaeria salina, Beggiatoa spp. and pennate diatoms. 

Photo 6.6 Different pinnacle cyanobacteria mat morphologies. 

The cyanobacteria at the Halocnemum transect during winter 2000 / 2001 

112

m 

2 

1 

0 

W 

340 370 m 

flat mat 

polygonal flat mat 

pinnalce mat 


06.04.2001 

23.03.2001 

20.02.2001 

14.01.2001 

15.10.2000 

0 15 30 45 60 75 90 120 150 180 210 240 260 290 310 

large crinkled mat 

peeling mat 

small crinkled mat 

crinkled mat / flat mat 

patches of pinnacle mat 

open spaces between mat 

Fig. 6.30 Development of cyanobacteria along the transect between October 2000 and April 2001. 

In October 2000, starting at the lower supratidal, no cyanobacteria was recorded. At the 15 m mark 

very thin traces of cyanobacteria were found. But the 1 mm thin crust at the soil surface is more due to 

evaporites which stain the surface at some places white. Near the 45 m mark the flat surface turns into 

a very thin micro folded mat with 2-5 mm relief. Still salt crystallisation is visible. This micro folded 

mat continues until the 90 m mark. There it turns into a flat mat (0.5-1 mm thick) with a micro 

pimpled surface (1-2 mm relief). Near the 120 m mark the flat mat becomes more visible with 2 mm 

thickness and grey colour. From 125 m on it shows a folded morphology which turns into a brain like 

mat at 145 m with about 0.5 - 1 cm thickness. At 165 m it is more folded with the folds forming 

polygonal patterns. At the 180 m mark the mat is 1-2 cm thick and laminated in the centre of the 

polygons. The size of the polygons averages around 30 cm in diameter. Now there is a pronounced 

relief because of sediment accumulations around former salt marsh plants which are now covered by a 

hard tar crust. These higher areas of 5-10 cm relief are not colonised by cyanobacteria and appear in 

white (photo 6.7). 

E 

113


Photo 6.7 Little elevated areas around former salt marsh plants remain dry and therefore appear in 

light colour (30-40 cm in diameter). These dry patches are not colonized by cyanobacteria. 

From 200 m on fragments of the polygons are peeling off which are then removed by tides and wind 

(photo 6.8). At this location there is a tar layer directly beneath the cyanobacteria layer. By removing 

of the cyanobacteria, little parts of the tar material are sticking to the bacteria. In this way the peeling 

process physically removes part of the oil residues. This process has been described by Höpner 1996 

and will be discussed in chapter 6.1.9. 

Photo 6.8 Fragments of polygons are peeling off removing small amounts of the underlying tar layer. 

The spaces between the polygons decrease and from 235 m on they are almost closed. At the 250 m 

mark small pinnacles grow on the folds which form the polygons. The higher areas (sediment 

accumulations around former salt marsh plants) appear in light colour and are now covered by flat 

mats (compared to the situation at the 180 m mark). At 290 m the pinnacles occur more often but still 

isolated. The cyanobacteria mats are here only 2-4 mm thick and many dead cerithides are enclosed by 

the bacteria. At the 310 m mark the pinnacle structures are only found on top of the scattered higher 

areas (former salt marsh plants or crab burrows) which appear in black (photo 6.9). 

114


Photo 6.9 Black pinnacle mats on elevated patches which are remains of former salt marsh plants or 

crab burrows. 

Erosion seems to be the dominant process here because many dead cerithides are exposed out 

of tar encrusted material. At 340 m cyanobacteria is very thin and only rarely found 

(exclusively on elevated areas). 

In January the cyanobacteria mat is hard to see in the first 90 m and very thin. From 100 m on 

the mat is around 2 mm thick but still flat. At the 120 m mark the mats grow thicker and show 

folds which are about 1 cm in height. Some of the triple points of the folds are broken. At 150 

m these folded mats are laminated below and up to 1 cm thick. At the 170 m mark the folds 

increase to a relief of 3 cm. Some of the folds are broken and form polygonal structures. 

During the next 40 m these polygons break along the folds. But the mat is only rarely peeling 

off. At the 210 m mark pieces with a diameter of 10-15 cm are now peeling off. The 

following 50 metres display polygons averaging around 50 cm in diameter with laminated 

mats of 3 cm thickness in their centre. Where water remains in the centre of deeper polygons 

the bacteria displays a red colour. From 270 m to 290 m the mat is not polygonal anymore but 

flat with initial linear cracks of 5-15 cm length. From 290 m on there was no change. From 

330 m until 350 m new pinnacles of 1 cm height formed along scattered folds or on higher 

areas. 

In February the only change within the first 90 m was the formation of little brain like mats 

below Halocnemum plants. From 90 m until 120 m there are little folds of 2-3 mm height 

indicating the typical pattern of folded mats. The surface though still does not look like 

cyanobacteria mat but more like salt encrusted sand. At 120 m the folded mat starts with little 

change. At the 160 m mark the first folds are now breaking and little pieces are removed. 

From the 170 m mark on the spaces between the polygons increase and more parts are being 

115


removed (photo 6.10). In a circle of about 1 m radius around former plants the mats are not as 

dissected as in the areas in between. From 200 until 250 m the polygon centres are not flat 

anymore but show also folded structures. Sometimes a few pinnacles could be observed on 

top of the folds. The spaces between the broken folds are about 5 cm in width (photo 6.10). 

From 270 m to 290 m the linear cracks turned into triple junctions and grew in length to 10-20 

cm. Photo 6.11 shows the pinnacle mats on top of little elevations near the 310 m mark. 

Around the elevations some fine carbonate sediment was deposited which is now dry and 

displays a nice contrast to the black pinnacle mats. 

Photo 6.10 Contraction of 

cyanobacteria mats caused by 

desiccation leads to polygonal 

open spaces of around 5 cm width 

between the cyanobacteria 

patches. 

Photo 6.11 Black pinnacle mats display a nice contrast 

to the bright fine carbonate sediments around. 

In March there is no change in the first 135 m except that the folds grew to about 2-4 mm height from 

120 m on. At the 140 m mark new mat is growing, but there are many little pieces of dry folded mat 

lying around. This tendency can be observed now along the whole transect until the 290 m mark. In 

the spaces where cyanobacteria was removed, new bacteria was observed. 

In April some of the cracks were already closed and most of the broken dry material lying around in 

March has been removed. 

116


Summary of the major changes in cyanobacteria morphologies and distribution 

Cyanobacteria are abundant throughout the whole salt marsh ecosystem. In the course of the 

significantly changing climatic conditions during the winter time it seems that the bacteria 

adapt to this cycle. After the hot summer in the most landward and therefore saline part of the 

salt marsh, a micro folded structure developed. This seems to consist of cyanobacteria as well 

as salt and is thin and fragile (the comparison of salt crust morphologies with cyanobacteria 

mat morphologies shows many similar aspects). This is not surprising, because the cause of 

folds in both cases is surface expansion. Crystallisation of sodium and potassium salts can 

lead to a 30% increase in volume. The growth of the filamentous bacteria can increase the 

surface more than 100% (the observed maximum in a dense brain like structure was even 

200%). Rain events in winter seem to destroy this crust due to solution of the salt 

components. With the increase in temperature in spring first little blisters and then the 

microfolds develop again. It is interesting that around the Halocnemum shrubs little brain like 

cyanobacteria mats were present throughout the whole observation period. Their morphology 

was up to 5 mm and the mat about 1 mm thick. It was restricted to the slightly elevated parts 

around the plants. Lower salinity in these parts may be responsible. 

At the mean high water level the mat was folded or brine like. In early spring parts of it 

cracked into pieces and at some patches parts were peeling off. In April already new bacteria 

established at the places were it was removed before. This tendency could be observed until 

the lower end of the middle intertidal zone. The pinnacle morphology was present at the lower 

end of the middle intertidal. It basically grew at elevated places such as existing folds or 

around mounds of former plants. Some pinnacles established in and between the polygons of 

the middle intertidal between January and February. There they remained until April but were 

not present in October the year before. It remains open whether they disappeared in the 

summer period or not. Fluctuations of pinnacle mats were also observed by Watt (pers. 

comm.) between 1992 and 1993 in the lower intertidal zone. 

It is interesting that the brainlike crinkled mat which dominated the upper intertidal before the oil spill 

(between the 130 and 180 m mark) did not reappear in the first 3 years after the oil spill. After the 

peeling of the oiled bacteria in 1995 the first new crinkled mats were observed. It must also be noted 

that Hoffmann (1994) did not observe any pinnacle mats at this study site until 1994. 

117

6.1.2 Arthrocnemum transect 

The Arthrocnemum transect is called after the dominant plant species Arthrocnemum 

macrostachyum (Moric.) Moris et Delponte. It is located at 27°09’34”N / 49°24’06”E and 

faces the Arabian Gulf in the East (fig. 6.31). To the West it is bordered by a flat sand sheet 

some hundred metres wide. Adjacent to it is a large coastal sabkha. 

m above 

chart datum 

2 

1 

0 

W 

0 5 10 km 

metres 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 

silt/clay sand shell fragments dead Arthrocnemum 

silt/clay / sand coarse sand beach rock living Arthrocnemum 

Fig. 6.31 Location of the Arthrocnemum transect. 

49°20’ 49°30’ 

ARABIAN GULF 

At the 120 m mark there is a small sandy beach ridge, which effectively prevented the 

entrance of the oil into the remaining salt marsh. In seaward direction though, not a single 

plant survived the oil spill. Therefore, this test site displays affected as well as unaffected 

parts. 

6.1.2.1 Soil properties 

N 

27°20’ 

27°10’ 

E


The soils that occur at this transect are similar the soils of the Halocnemum transect. Again 

beach rock layers are a typical phenomenon which was observed frequently within the 

sediments of the intertidal zone. The dominant soil fractions are either silt and clay, or if 

dominated by sand, the soil contains a considerable portion of the fine substrates. 

Carbonate concentrations of the substrate are high and show the maximum values of 65% 

near the littoral fringe were the accumulation of Cerithides and shell fragments are 

responsible. But also in the fine sediments adjacent to the beach ridge concentrations of 50% 

were observed regularly. The following sections (fig. 6.32) will be discussed especially 

regarding the status of oil contamination 10 years after the oil spill. Each section will be 

presented as a table and additional information is given in separate remarks. 

Oil contamination assessment in 2001 

9 8 7 6 5 4 3 2 1 

m 165 180 195 210 225 240 255 270 285 300 315 

silt/clay sand tar layer 

silt/clay / sand shell fragments oil patches crab burrows 

sand beach rock degraded oil black layer (H2Spatches 

reduction horizon) 

Fig. 6.32 Soil sections showing the oil residues within the sediments 10 years after the Gulf war oil 

spill - lower part. 

At the 300 and 315 metre mark there is a 10 to 20 m wide beach rock layer consisting of 

shell fragments, carbonates, calcified burrows, bivalves, barnacles, and some cerithides. 

10cm 

50cm 

oiled sediment (upper part) 

light oiled sediment (lower p.) 

119


Around the 290 to 300 m mark the beach rock layer is fairly thin and can be broken by hand. 

It is covered by one or two centimetres of sandy sediments on top of which a 0.1 – 0.2 mm 

layer of cyanobacteria is established. Gastropods are grazing on the thin cyanobacteria 

layer. 

Tab. 6.18 Section 1 at the 285 m mark of the Arthrocnemum transect. 

Section 1 

Remarks : 

The water which seeps out of the substrate displays typical interference colours caused by oil 

constituents. 


Section 2 

Remarks: 

The water which seeps out of the substrate displays brown patches of liquid oil. 


Section 3 

285 m 

0-1 cm: beige sand (0.2 mm cyanobacteria) 

1-10 cm: grey sand (detailed grain size data in appendix 2, tab.2); at 5 cm 

a 1-2 cm thick band of oiled material emits a strong odour 

similar to raw oil 

10-15 cm: grey coarse sand with shell fragments 

15 cm: beachrock layer 

calcium carbonate: -13 cm: 70.5% 

270 m 

0-1 cm: beige sand (0.2 mm cyanobacteria) 

1-16 cm: grey sand (detailed grain size data in appendix 2, tab.2); at 7 cm 

a 2-3 cm thick band of oiled material emits a strong odour 

similar to raw oil 



calcium carbonate: - 5 cm: 62% 

255 m 

0-0.2 cm: flat cyanobacteria layer 

0.2-2 cm: dark grey-black anaerobic horizon which emits a strong 

hydrogen sulphide odour. 

2-16 cm: grey sand; between 7 and 10 cm there is a continuous dark 

brown-black oil band (not patchy anymore). 



calcium carbonate: -5 cm: 46% 


Section 4 

240 m 




2-16 cm: grey fine sand; between 7 and 10 cm dark brown-black oil 

120

Remarks: 


The amount of oil within the water seeping out of the substrate increased significantly. 


Section 5 

Remarks: 

The crab burrows seem to result from the time before 1991 because they were filled with oil 

which is now degrading. Around the burrows the oiled sediment displays an orange colour 

typical for oxidation processes. 


Section 6 

225 m 




1-9 cm: beige fine sand; burrows of polychaetes and small crabs 

9-13 cm: oiled sand 

13-25 cm: grey sand 

25-60 cm: coarse grey sand with shell fragments 


210 m 




1-9 cm: beige fine sand; burrows of polychaetes and small crabs 

9-13 cm: degraded oil patches in fine sand 

13-25 cm: grey fine sand 

25-60 cm: coarse grey sand with shell fragments 


Remarks : 

The water seeping out of the sediment shows no more oil floating on its surface and almost no 

interference colours. 

121



Section 7 


Section 8 


Section 9 

195 m 


0.3-10 cm: medium sand; burrows of polychaetes and small crabs, oiled but 

well weathered 




180 m 


0.3-10 cm: medium sand; burrows of polychaetes and small crabs, oiled but 

well weathered 





165 m 

0-0.3 cm: pinnacle cyanobacteria up to 1 cm high 

0.3-1 cm: tar layer 

1-15 cm: dark brown oiled sediment; emits strong petroleum hydrocarbon 

odour; sticky 

15-25 cm: grey silt, crab burrows filled with liquid oil 

25-40 cm: grey sand, with plenty of shell fragments 



Remarks: 

Liquid oil is seeping out of the substrate between 15 and 25 cm depth. 

122


17 16 15 14 13 12 11 10 

m 0 15 30 45 60 75 90 105 120 135 150 

silt/clay sand tar layer 

silt/clay / sand shell fragments oil patches crab burrows 

oiled sediment (upper part) 

light oiled sediment (lower p.) 

sand beach rock degraded oil black layer (H2S- 

patches reduction horizon 

Fig. 6.33 Soil sections showing the oil residues within the sediments 10 years after the Gulf war oil 

spill - upper part. Behind the beach ridge no oil was deposited. 


Section 10 150 m cyanobacteria on top of the tar layer is not continuous, some 

parts peeled off 

0-1.5 cm: tar layer, intensive petroleum hydrocarbon odour 

1.5-12 cm: dark brown oiled sediment; emits strong petroleum 

hydrocarbon odour; sticky; more oiled between 1.5 and 5 cm 

and between 8-12 cm. 

12-30 cm: grey silt, crab burrows filled with liquid oil until 25 cm 

30-58 cm: grey sand, with plenty of shell fragments 


calcium carbonate: -10 cm: 52,7% 

Remark: 

Liquid oil is seeping out of the substrate between 15 and 25 cm 

10cm 

50cm 

123


The tar crust is being removed gradually during high tides and spring tides. The rate of 

erosion was monitored at two test sites. Because the material of the tar crust shows more 

resistance towards erosion than the underlying and surrounding sand, a micro cliff of 1-2 cm 

developed. During high tides this micro cliff is being attacked by sea water. Soft sediments 

below the tar crust are carried away and eventually a part of the crust breaks away. 

However, the rate of erosion is slow. Figure 6.34 displays the situation in October 2000 and 

April 2001. The dark area resembles the eroded part of the tar crust. The edge of the tar 

layer remained constant or shifted back between 1 and 13 cm. 

Fig. 6.34 Erosion of tar crust between October 2000 and April 2001. 


Section 11 

Remarks: 

At some places the tar layer is covered by some centimetres of cerithide rich sands. 


Section 12 

10 cm 

10 cm 

135 m cyanobacteria is peeling off 

0-1 cm: tar layer, degraded granular structure 

1-11 cm: brown oiled sediment; emits petroleum hydrocarbon 

odour; medium degraded 

11-30 cm: grey sand (only 11% silt and clay) 

30-50 cm: silty sand 

50-60 cm: sandy with plenty of shells fractions 


120 m located on the seaward side of the beach ridge 

0-4 cm: light brownish colour caused by degraded oil residues 

4-25 cm: sand dominated by middle sand (60%), only 2% silt and 

clay, no oil 


50-60 cm: sand with plenty of shell fragments 



124

Section 13 


Remarks: 

No oil has reached this area. The section is located within a patchy vegetated area 


Section 14 

Section 15 to 17 are quite similar to section 14 and show a typical soil for salt marshes at the 

upper littoral fringe, which in this case was not affected by the oil. The first 5-7 cm display 

brown carbonate rich fine sediments, characterised by 40-50% silt and clay, and around 50% 

carbonate. The substrate underneath is generally coarser but still the silt and clay fraction 

makes up for 25-35%. Finer layers may be interspersed e.g. section 16 at the 60 m mark 

between 25 and 30 cm depth. Deeper than 60 cm, coarser sand fractions dominate. They 

usually show slightly higher carbonate concentrations than the upper layers, which is due to 

a higher content of shell and cerithide fragments. 

Soil water content 

105 m 

0-5 cm: light brownish silt 



55-65 cm: at 55 cm depth there is a clear transition to a bright 

yellow coarse sand which is dominated by 83% of middle 

sand 

calcium carbonate: -10 cm: 59,5 

90 m located within a patchy vegetated area 

0-7 cm: light brownish silt 


25-35 cm: silt 


60-70: cm: yellow coarse sand which is dominated by 83% of middle 

sand 


The soil water content is generally higher in the study area the closer to the sea. But still 

there are significant differences which are not due to the inundation time and frequency but 

to the sediment type. The substrate is dominated by fine sediments which results in a high 

capability to retain moisture. This, and the availability of water by high tides and rains during 

the winter season lead to relatively high values of around 30% (by weight). Figure 6.35 

displays a moisture profile during one month in spring 2001. It can be clearly seen that the 

coarser sediments at section 12 near the beach ridge have a significantly lower water 

content in 10 cm depth, than the rest. At 20 cm it is not that obvious because of the 

groundwater influence. The lower values at sections 10 and 11 can also be explained by a 

more sandy sediment. The variability throughout the year is high. October values between 

125


5.4% at section 12 (-10 cm) and 9.6% at section 14 (-10 cm) demonstrate the situation after 

the pronounced summer drought. 

soil water content in % 

40 

35 

30 

25 

20 

15 

10 

5 

0 

10.Mar -10cm 23.Mar -10cm 10.Apr -10cm 

10.Mar -20cm 23.Mar -20cm 10.Apr -20cm 

17 16 15 14 

sections 

13 12 11 10 

Fig. 6.35 Soil water content. The profile demonstrates the differences in grain size distribution. Note 

the differences between 10 and 20 cm depth due to the drying of the upper sandy sediments at station 

12. 

Sedimentation measurements 

Sedimentation rates were measured in a circular sediment collector buried in the salt marsh 

(see chapter 2.5). During a two month period in spring 2001 at section 9 (165 m mark) every 

two weeks in average 23.5g (sd. 8,2) of sediment was deposited. The second station at 

section 10 (150 m mark) collected 30.1g (sd. 14,1). The average grain size distribution is 

displayed in table 6.4. 

Tab. 6.32 Grain size distribution of collected sediments. 

station >2 mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm 

1 section 9 0.4 17.2 37 7.7 37.9 

2 section 10 19.3 36.5 24.6 7.3 14.6 

Near the beach ridge which at that place is the mean high water mark (MHWM), more coarse 

material accumulated which was transported by the tides. This is especially obvious because 

the 19.3% material coarser than 2 mm is totally made up of cerithide shells, which are very 

abundant around the beach ridge, and some dried sea grasses. At section 9 fine, carbonate 

rich sediments are the dominant fraction. This resembles what can be found between 

cyanobacteria in laminated mats which occur a little further towards the sea (see 6.1.2.5). 

126




The total ionisation of the groundwater is expressed in the electrical conductivity. The most 

important constituents are chloride and sodium and therefore responsible for most of the 

electrical conductivity. There is a general trend from sea water concentrations at the lower 

intertidal to increasing values towards the littoral fringe and adjacent supratidal areas. In the 

scope of this study it was important to find out about the development of the groundwater 

constituents during the winter season with lower temperatures and the influence of rain. 

Figure 6.36 shows the gradual increase of the values with the distance from the sea in 

October. This is due to high evaporation in the hot summer months. In winter no gradient can 

be observed. Rain water and flooding are responsible for the dilution in the upper intertidal 

zone. 

conductivity mS/cm 

130 

120 

110 

100 

90 

80 

70 

60 

October January 

17 16 15 14 13 12 11 10 

Fig. 6.36 Profiles of electrical conductivity in October 2000 and January 2001. 

The following figure 6.37 displays the changes of ground water ionisation as well as the 

concentrations of chloride. The perfect correlation is obvious. 

Chloride 

16 14 12 10 

127

80000 

60000 

40000 

20000 

0 

Oct Nov Dec Jan Feb Mar 

Conductivity 

120 

100 

80 

60 



80000 

60000 

40000 

20000 

110 

100 

90 

80 

70 

60 

0 



section no. 

70000 

60000 

50000 

40000 

30000 

20000 

10000 

0 

110 

100 

90 

80 

70 

60 



80000 

60000 

40000 

20000 

16 14 12 10 

0 

110 

100 

90 

80 

70 

60 



Fig. 6.37 Development of chloride concentration and electrical conductivity between October 2000 

and March 2001. 

The lowest values in both electrical conductivity and chloride concentration were measured in 

January. The general trend of decrease until January and the following increase is also 

obvious. More interesting is the increase of chloride concentrations in December which could 

be observed at all eight stations. The values of electrical conductivity increase only in two 

cases and in two other cases they remain constant (for data see appendix 2, Tab.4). Böer 

(1992, unpublished report) mentions a significant drop in groundwater salinity after heavy 

rain events. But this is only partly the reason, for there was a thunderstorm with around 30 

mm rainfall in December 9 th , only 5 days before the measurements. Vertical infiltration is not 

probable because of the fine sediments. Therefore the same processes of horizontal 

groundwater fluxes as explained in 6.1.1.2. are supposed to be dominant. 

128

Magnesium 

mg/l 


4000 

3500 

3000 

2500 

2000 

1500 

1000 

500 

October January April 

0 

section no. 

17 16 15 14 13 12 11 10 

Fig. 6.38 Profiles of magnesium concentration in October 2000, January 2001 and April 2001. 

The magnesium concentrations also follow the trends that were shown by the electric 

conductivity. There is a gradual increase in the warmer and dry months from the lower 

intertidal zone towards the inland. Concentration vary then from 2500 mg/l to 3600 mg/l. In 

winter this trend is not present or extremely weak with values between 1900 mg/l and 2000 

mg/l. Explanations for the concentration decrease in winter are given in chapter 6.1.1.2. 

Sulphate 

The sulphate concentrations display a more variable development compared to other 

components like magnesium and chloride. Only in October a general increase of sulphate 

concentrations towards the inland could be observed. It is supposed that this is also true for 

the dry summer months. The values range between 6000 mg/l at station 10 and almost 9000 

mg/l at station 17. During the winter months the concentrations are generally lower than in 

October. Between January and April there was not much change in the upper intertidal zone 

which is flooded only occasionally. In the middle intertidal zone all concentrations increase 

between January and April. This increase is more pronounced the closer to the sea. It should 

be noted that the April values in the middle intertidal zone are similar or even higher than the 

concentrations measured in October. 

129

mg/l 

10000 

9000 

8000 

7000 

6000 

5000 

4000 

3000 

2000 

1000 


October January April 

0 

section no. 

17 16 15 14 13 12 11 10 

Fig. 6.39 Profiles of sulphate concentration in October 2000, January 2001 and April 2001. 

Calcium 

The profiles of calcium concentration do not vary significantly. The values from the lower 

intertidal towards the upper intertidal zone are quite similar. In the course of the year the 

lowest concentrations were observed in October displaying concentration of around 1000 

mg/l. They increase to about 2000 mg/l in December. In the following months until April 

there is not much change. The decrease during the summer months could be due to the 

crystallisation of calcium carbonates because of the high water temperatures. As the pH 

values vary between 7.2 and 7.6 with no clear pattern during the course of the year, the high 

temperature differences might be the main factor controlling calcium carbonate crystallisation 

and –solution. With the decline in ground water temperature solution processes could lead to 

the increase of calcium ions. 

Ground water temperature 

The ground water temperatures in the intertidal zones are strongly related to the seawater 

temperatures. The recorded temperatures vary with a maximum of 2°C within the profile. The 

temperature range is quite similar to the observations made at the Halocnemum transect 

(chapter 6.1.1.2). 


130


The intertidal climate is characterized by the climatic observations at Mardumah Bay station, 

which measures the coastal climate within the large embayment systems. But there are a lot 

of differences and modifications regarding the micro climate near the soil surface to a 

maximum height of 50 cm. Here the influences of vegetation, soil surface, soil water content, 

and surface crusts are important. 

Temperature 

Vertical temperature profiles were measured above different soil surfaces and under different 

weather conditions. Direct solar radiation (insolation) leads to absorption in the upper soil 

surface and emission of infrared radiation (heat). Therefore the soil surface shows the 

highest temperatures. The temperature decrease of the air layers above depends on the 

wind velocity and turbulences. 

Sunny days in winter time with temperatures of about 20°C and low winds display 

temperature profiles like the following examples. 

50 

20 

10 

5 

0 

-5 

-10 

10 12 14 16 18 20 22 24 

Temperature °C 

height 

above/ 

below 

surface 

in cm 

Fig. 6.40 Temperature profiles of intertidal location and dry sandy location. 

50 

20 

10 

5 

0 

-5 

-10 

10 12 14 16 18 20 22 24 26 28 


Station 11 cyanobacteria 29.01.2001 12:00 Station 18 sand 29.01.2001 12:00 

It was generally observed that the cyanobacteria layers (dry) are between 3°C and 5°C 

warmer than the air temperature (2m). In contrast dry sandy surfaces are 6°C - 10°C warmer 

than the air temperature. The low temperatures below the soil surface in the intertidal (station 

11) are due to the high water content of the sediment. 

131

50 

20 

10 

5 

0 

-5 

-10 


10 12 14 16 18 20 22 24 26 28 30 32 


Station 10 cyanobacteria 10.03.2001 12:00 

height 

above/ 

below 

surface 

in cm 

50 

20 

10 

5 

0 

-5 

-10 

10 12 14 16 18 20 22 24 26 28 30 32 


Fig. 6.41 Temperature profiles of intertidal location on a clear and a cloudy day. 

Figure 6.41 shows the influence of clouds. Without direct sunlight the temperature of the soil 

surface is only a little higher than the air temperature. 

The temperature differences between 5 cm and 10 cm depth (between 12:00 and 13:00) are 

displayed in figure 6.42. It is obvious that the gradient varies even at the same location, 

although the time of measurement was almost the same. At location 12 and 17 the gradients 

are higher than at the other stations. At station 12 the low water content due to the coarse 

sediment is responsible for the fast warming of the surface near layer (-5 cm). At station 17 

the only explanation is the dark brown colour of the surface because the sediment type and 

the water content are not much different from stations 16-14. For station 10 and 11 no 

influence of the degraded oil residues could be observed. 

difference 

in °C 

6 

4 

2 

0 

Dec Jan Feb Mar 

station 

17 16 15 14 13 12 11 10 

Fig. 6.42 Temperature differences between -5 and -10 cm. 

Station 10 cyanobacteria 06.04.2001 16:00 

cloudy 

132



The vegetation at the Arthrocnemum transect is dominated by Arthrocnemum macrostachyum 

which is the only species except some Salicornia and Suaeda maritima plants. The 

Arthrocnemum community along the upper part of the transect (until station 13) was not 

affected by the oil spill. Here the vegetation cover which is almost exclusively due to the 

presence of Arthrocnemum (the other species can be neglected because of their small size) is 

around 40% at site 17, between 20 and 30% at site 14 and around 10-20% at site 13. 

At section 12 Arthrocnemum which survived the oil spill are regenerated. Here the vegetation 

cover is around 5%. Near station 10 there are a few isolated individuals of Arthrocnemum 

which survived the 1991 oil spill. New plants first occurred in 1996 and are still rare in 2001. 

Beyond station 10 in 2001 still no colonisation of salt marsh plants could be observed. The 

original salt marsh before 1991 went until station 9. Böer reported 1993, that after the impact 

surviving Arthrocnemum plants developed flowers and seeds in October 1992. After the seed 

production period most of the plants started to die. 

6.1.2.5 Fauna 

At this transect no detailed studies on fauna were carried out. There will be only a brief 

description of observations starting at the lower intertidal. Several pools are scattered in the 

beach rock area. They are inhabited by hundreds of gastropods such as Pirinella conica 

grazing on the accumulated sediments as well as crabs, bivalves and some fish. Species 

composition as well as abundance shows no differences when compared to non oiled control 

sites (see chapter 6.1.9). From the 270 m until the 165 m mark no crabs and no new crab 

burrows are observed. The only present life form are polychaetes although their numbers with 

3-10/m² were low. This can be explained by the dominance of fine sediments. Polychaetes 

usually occur in more sandy environments. At the 150 and 135 m mark no living organism is 

found in the soil sediments. Starting at the 105 m mark, active crab burrows are present 

around the Arthrocnemum plants. The upper part of the transect never displayes more crab 

burrows than 1-5/m². The maximum concentration is located between the 105 and 90 m mark. 

This is less than one would expect at a natural undisturbed site but still not unusual. Therefore 

it is not obvious if the oil impact is responsible for the low numbers or not. 

133



Cyanobacteria is present almost everywhere along the transect. At the lower intertidal zone 

very thin layers colonize the sediment surface. These layers grow in thickness from 0.1 to 2 

mm until station 7 at the 195 m mark. The transect from the 180 m to the 0 m mark was 

subject to detailed studies regarding the cyanobacteria morphology and distribution during 

the winter period. 

metre 

above 

chart 

datum 

flat mat brainlike mat brainlike and flat 

cracked mat peeling mat pinnacle mat 

pinnacle/flat micro brainlike cracked brainlike mat 

06.04.2001 

11.03.2001 

15.02.2001 

11.01.2001 

13.10.2000 

2 

metres 0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 

Fig. 6.43 Changes of cyanobacteria morphology along the transect between October and April. 

In October the flat, 3 mm thick mat shows little pinnacles starting at the 165 m mark. Here, it 

grows directly on the oiled material. These little pinnacles are sitting widely spaced on top of 

the flat mat. They grow in this habit until the 135 m mark. For the next 10 metres they turn 

into a flat folded mat which disappears on the beach ridge. After the beach ridge at 110 m the 

brain like folded mat occurs again for 15 metres. Now there are some first cracks between the 

mat indicating drying and breaking of the mat in the future. From about 100 metres pinnacles 

of 1-2.5 cm height are the dominating morphology. From the 80 m mark on the pinnacles turn 

into a brain like structure with 1 cm height. The thickness of the mat is 3-4 mm. Towards the 

supratidal the brain like structure becomes more flat and the thickness decreases to 1-2 mm. 

134


Around the Arthrocnemum plants the mats are higher and the brain structure is more clear 

than in the surrounding areas. 

Until January in the upper intertidal there is not much change. The brain like mats between 

100 and 110 m are cracking into polygons and squares of 5-10 cm diameter. Seaward of the 

beach ridge the mats start cracking and peeling off. Most of the pinnacles between 140 and 

170 m already broke away. Between the remaining pinnacles the mat became brain like. 

From 150 – 170 m the mat is now broken into polygons and starts drying. 

Until February all pinnacles disappeared seaward of the beach ridge. From the 180 m mark 

the flat mat breaks into polygonal pieces of 5-20 cm size (diameter). It is now partly dry and 

some of the dry pieces are being removed by wind and tide. At 150 m the flat mat turns into 

folded mat. The spaces where the cyanobacteria mat has been removed grow wider (up to 

50 cm at the 140 m mark). From 110 m to 100 m the brainlike mats become also dry and the 

cracks between the polygons are now 1-3 cm in width. The size of the polygons mostly is 

about 5-10 cm in diameter. Some of the polygons start breaking away. Around plants the 

mats are not dissected. Also the following pinnacle zone breaks into square sized polygons 

of 5-10 cm size. The brainlike mat still starts at the 80 m mark. But they are also broken into 

polygons. The size of the polygons varies between 10 and 30 cm. Some dry pieces now 

break away. Between 40 and 65 m, the upper side of the brain structure breaks where it 

became dry and the resulting small pieces of 0.5-1 cm size look like little Dachziegel. At the 

30 m mark the olive green and grey colour changes into a brownish colour. It starts breaking 

in the whole area. In morphology there are no changes. 

In March, the mats between 130 and 180 m are dry and peeling off, except in little 

depressions where there is more moisture. Landward of the beach ridge, a 5-10 m wide zone 

is covered by small brain like cyanobacteria about 1-2 mm in thickness, which is not dry and 

dissected. Then the brainlike mat is broken into polygons like in February until the 95 m 

mark. The mat is now broken into pieces of around 5 cm diameter. The cracks between these 

pieces are now 2-4 cm wide. Starting at the 80 m mark the pure pinnacle mat turns into a 

brain like structure as before. But there are scattered pinnacles growing in between now until 

70 m. The mat is not dissected and it shows no polygons anymore. It looks as if the pinnacles 

as well as new folded mat grew in the spaces between the polygonal pieces. From 60-50 m on, 

the small brain structures are still breaking at the upper more exposed parts which leads to the 

small Dachziegel pieces lying around. 

135


In April, the area from 180 to 140 m is covered by a very flat 1 mm thin new cyanobacterial 

mat. 5 – 10 metres before the beach ridge there are patches with little brain structures growing 

on. The area between the beach ridge and the 100 m mark shows little brain like mats without 

polygons. The open spaces where old cyanobacteria broke away are now almost closed by 

new bacteria. From 100 to 90 m it looks as if new pinnacles were growing also closing the 

spaces between former polygonal pieces. Between the 90 and 80 m mark the mat is still 

dissected like in the last month. Starting with the 65 m mark, new bacteria are growing 

between the brain like patches which are still peeling off. When removed, the free space is 

immediately colonized by the new bacteria which form thin flat mats. 

Very obvious is the drying and peeling of the cyanobacteria mats between the 10 and 105 m 

marks and the eventual growth of new bacteria with the beginning of April. The cracking and 

peeling of these mats occurred also seaward of the beach ridge until the 165 m mark. The 

pinnacle mats showed significant changes during the period of investigation. Basically the 

observations made at this transect were more or less similar to the Halocnemum transect ( 

chapter 6.1.1.6). 

136

6.1.3 Sabkha – salt marsh transect 

This transect is located 1 km south west of the main land mangrove site (see 6.2.1) and about 

3 km southwest of the Arthrocnemum transect (6.1.2). It is the continuation of the muddy 

mangrove flats further to the north, dissected by several tidal channels. In landward direction 

the salt marsh turns into a coastal sabkha bare of any vegetation. 

NE 

brainlike 

flat 

cyanobacteria / 

salt crust 

0 5 10 km 

salt marsh 

area 

49°20’ 49°30’ 

ARABIAN GULF 

HWS 

Fig. 6.44 Location of the salt marsh-sabkha transect. 

Soil characteristics and oil contamination assessment in 2001 

SW 

locations 

described in text 

The following sections of the transect are presented in tables. Additional information is given 

in separate remarks. 

HWN 

240 m 

260 m 

0 m 

140 m 

50 m 

90 m 

N 

27°20’ 

27°10’ 

N


Tab. 6.33 Section 1 at the 50 m mark of the sabkha-saltmarsh transect. 

50 m 

Remarks: 

From the beginning of the profile at the HWN, the salt marsh vegetation (Halocnemum, 

Arthrocnemum and Salicornia) is dead within a 50 wide zone. More inland there are some 

scattered living plants. Below the HWN, there are scattered individuals of 4-5 years old 

Avicennia marina and rarely some young Arthrocnemum macrostachyum (about 2-3 years 

old). The typical Cleistostoma-salt marsh relief is still preserved. Cyanobacteria covered most 

of the area after the oil spill. In 2001 it is still present but patchily distributed and mostly 

restricted to the more elevated parts. On top of the mounds the bacterial mats are dry, 

dissected, and at many places peeling off. In contrast to the so far described salt marshes the 

crabs, mainly Cleistostoma dottiliforme recolonize the complete belt of dead salt marsh 

plants. The numbers with 35 burrows/m² at the 50 m mark indicate a normal (pre oil spill) 

abundance, although most of them are still located in the depressions and not within the 

mounds. The mud on top of the mounds is dry and hardened by well weathered hydrocarbons. 

Total hydrocarbon content is 16.5 g/kg. These hardened sediments are preventing the crabs 

from building burrows within the substrate of the mounds. The penetration force is 3.6 kg/cm² 

(in average, sd. 0.51), and the shear force resistance is in average 5.4 kg/cm² (sd. 1.03). The 

highest penetration force value beside a crab burrow is 3.1 kg/cm². The average values are 

much lower (1.4 kg/cm², sd. 0.43). This high value is an exception and could be due to drying 

and hardening of the muddy substrate by the sun. This would indicate that the burrow was 

dug when the sediment was softer. 


90 m 

0-6 cm: dry mud, oiled but oil residues well weathered; material 

hardened; total hydrocarbon concentration: 16.5 g/kg 

6-13 cm: soft grey mud, no oil residues 



0-0.3 cm: cyanobacteria, patchy 

0.3-12 cm: light brown, dry, sandy silt; granular structure; oil well weathered 

12-19 cm: colour transition from light brown to light grey 


Remarks: 

At the 90 m mark, it is very obvious how the bioturbation of the crabs reduces the 

cyanobacteria. The cyanobacteria is not able to persist where the sediment is moved and 

turned over. In the photograph (6.12) it only remains in the depression where there are no crab 

burrows yet. Continuous activity by crabs will eventually remove all cyanobacteria mats. 

At the same location, the mounds around dead salt marsh plants are only rarely covered by a 

oiled hardened crust, and the material is much softer than at the 50 m mark (penetration force: 

2.56 kg/cm², sd. 1.06; vane shear force: 4.1 kg/cm², sd. 1.0). Between 20 and 40% of the area 

is covered by living Arthrocnemum and Halocnemum. Even young plants are scattered in 

between the older individuals that survived the oil spill. 

138


Photo 6.12 Remains of a former continuous cyanobacteria mat between crab burrows. 


140 m 

Remarks: 

At the 140 m mark, the abundance of crabs burrows decrease significantly to 6.7/m² (sd. 1.2). 

In contrast, cyanobacteria is more present. The cover of living vegetation decreases to 10%. 

Near this location it is interesting to note that the crabs obviously started recolonisation of the 

area from the tidal channels. The density of burrows has its maximum at the channel edge 

(photo 6.13). Crabs can enter the soft sediment at the edge of the channel, even if a hard tar 

crust covers the surface of the adjacent areas. Then the crabs try to come to the surface one or 

two metres within this area. This is mostly prevented by the hard tar cover. But at some places 

the break through will succeed. Then oxygen can enter the oiled sediment below the tar, and 

the oil degradation will be accelerated. Following this pattern, the crabs will successively 

penetrate the sediments to both sides of the channel. How fast this “subsurface-breakingthrough” 

technique succeeds depends on the hardness of the surface material or cyanobacteria 

mat, as well as on the amount of badly weathered oil within the substrate. 


240 m 

0-0.5 cm: cyanobacteria 

0.5-6 cm: light brown, dry, sandy silt; granular structure; oil well weathered; 

hardened 

6-14 cm: oiled beige sandy silt; oil residues concentrated in crab burrows; 

total hydrocarbon concentration: 24.5 g/kg; not well degraded – 

dark brown rapid assessment print (see appendix 5) 

14-22 cm: colour transition to grey, the sediment becomes finer 


0-2.5 cm: laminated cyanobacteria 

2.5-4 cm: black silt; strong H2S odour, crab burrows filled with liquid oil 

4-7 cm: oiled grey silty sand; oil concentrated in crab burrows; total 

hydrocarbon concentration: 19.3 g/kg; not degraded – dark brown 

rapid assessment print (see appendix 5) 

7-15 cm: grey sandy silt, oil in crab burrows 

15-40 cm: grey silt, no visible oil, but still 7.8 g/kg hydrocarbons in 20 cm 

depth. 

139


Remarks: 

There are no more living plants. Extensive blistered cyanobacteria mats cover the surface 

completely. The mounds of former Arthrocnemum plants are covered by a hard tar cover 

(>4.5 kg/cm²). No other life besides the cyanobacteria is present, except gastropods and some 

crabs at the channel edge (2-4 burrows /m²). 

Photo 6.13 Large amount of crab burrows at the edge of the channel where the sediment is soft. 


260 m 

0-0.5 cm: cyanobacteria and thin salt crust 

0.5-4 cm: light brown fine sand 

4-10 cm: brown oiled sand, oil residues are well weathered 

10-15 cm: beige sand, no oil 

15-40 cm: light beige silt 

Remarks: 

Near the 260 m mark, the sediment of the upper 10 cm below the now thin cyanobacteria 

turns into sandy substrate with typical sabkha characteristics such as sodium chloride and 

gypsum horizons near the surface and sand layers of different grain size. For about 20 more 

metres the upper 5-10 cm are brown due to oil, which is at that location well decomposed 

(photo 6.14). 

Photo 6.14 Well decomposed oil residues within sandy sediment at the 260 m mark. 

140


6.1.4 Bomb Crater Bay – transect 1 

The Bomb Crater Bay was named after the craters at the northern shore which were the result 

of shooting practice during the Gulf War in 1991. The site is located at 27°20’58”N / 

49°16’00”E and is perpendicular to the shoreline which results in a SSE NNW direction (fig. 

6.45). To the south it is bordered by a flat 100 m wide sand sheet which then turns into dunes. 

It is a wide intertidal area which in 2001 shows different cyanobacteria morphologies, a 

variety of oil loads, and generally a poor development of any live. Interesting and different 

from other salt marsh sites is the approximately 100 m wide sandy zone seaward of the 

cyanobacteria mats which shows distinct tar mesas at the HWN zone. Figure 6.45 summarizes 

the situation along the transect. 

NN SSE 

metres 370 340 300 260 220 180 150 130 100 30 0 

living crabs 

tar messas 

0 5 10 km 

exposed tar layer 

49°20’ 49°30’ 

ARABIAN GULF 

eroded tar layer 

mounds around 

dead Arthrocnemum 

plants 

sections 


oiled zone 

3 living Arthrocnemum individuals 

one 

brainlike 

cyanobacteria 

zone of dead Arthrocnemum plants 

Fig. 6.45 Bomb Crater Bay – transect 1. Birdseye view. Summary of situation in 2001. 

N 

27°20’ 

27°10’ 

storm berm 

tar layer 

weathered to a 

high degree 

141




in separate remarks. The soils are semisubhydric and characterised by frequent to periodic 

inundation of tidal water. The soils are usually fine grained but more sandy than the sites 

described so far. 

Tab. 6.38 Section 1 at the 10 m mark of the Bomb-Crater Bay-1 transect. 

10 m 

Remarks: 

The sediments are still affected by the oil to a major degree. The storm berm is to a large 

degree composed of shell fragments and sand. Directly adjacent to the storm berm, remains of 

the former Arthrocnemum salt marsh are still visible. All plants are dead and there is no sign 

of any recovery. The former plant individuals are highlighted by dry seagrasses which 

accumulated around the old stems. The soil surface is dark brown and hardened by 3 cm of 

oiled material (dominated by fine sand). The oil residues are weathered to a high degree with 

a granular structure. Below the brown layer there is a beige fine sandy substrate of the same 

composition as the surface material. 

After 30 m, a micro brainlike cyanobacteria mat covers the sediment. The cyanobacteria 

layer as well as the brainlike structure increases in size towards the sea, beginning at the 

100 m mark. At this location still all plants are dead without any sigh of recovery. Old burrows 

of polychaetes are brown due to the oil or oxidized to an orange colour and weathered to a 

high degree. New burrows are missing. Towards the 130 m mark the brown oiled layer 

becomes 10 cm thick with no change in weathering status of the oil or grain size 

composition. 


130 m 

0-3 cm: oiled fine sand; dark brown; highly weathered, but still hard 

3-30 cm: beige fine sand 

30-35cm: coarse sand with many shell fragments 

0-0.5 cm: cyanobacteria layer 

0.5-10 cm: oiled fine sand; dark brown; highly weathered, but still hard in the 

upper 3 cm 

10-30 cm: beige fine sand 

Remarks: 

Between 130 m and 150 m, the cyanobacteria changes into a flat mat and around the former 

plants, little mounds are still obvious. In contrast to the other sites, the material of the 

mounds is less compact than the surface of the interstitial spaces. 

142



150 m 


0.5-3 cm: oiled, compact brown silt 

3-15 cm: light grey-brown oiled fine sand, countless relic polychaete 

burrows, total hydrocarbon content is: 29.3 g/kg (in 10 cm depth); 

oil residues well weathered 

15-30 cm: light grey sand; no more oil present 

Remarks: 

At the 150 m mark, the oil residues are slightly less weathered which results in a light oily 

odour that is emitted by the sediment of the upper 15 cm. The amount of hydrocarbons 

present in 10 cm depth is 29.3 g/kg, which is surprisingly high. The rapid assessment print 

displays only some oil patches which indicates that most of the oil is weathered to a high 

degree (see appendix 7). 

Near the 190 m mark, the mounds disappear and the surface is dominated by flat 

cyanobacteria mats. At 220 m, at some locations the hardened surface material is eroded. 

Within two of these isolated patches new germinated Arthrocnemum macrostachyum was 

observed. The plants are not older than 4 years and around 30 cm in size (photo 6.15). 

Photo 6.15 Arthrocnemum macrostachyum growing in isolated patches of eroded tar crust. 

143



220 m 

Remarks: 

The sediment around the plants and below the tar layer is soft silt with a high fine sand and 

gastropod shell fraction. The oil content below the tar layer (-5 cm) is relatively low (14.5 

g/kg), and the rapid assessment print shows no colour at all, which indicates the advanced 

weathering of the remaining hydrocarbons. Sieving of the sediment shows some living 

cerithides and bivalves and one polychaete worm, but mainly only empty shells. 

Further to the sea at the 250 m mark, the tar layer is again covered by cyanobacteria mats 

which are polygonally cracked and some pinnacles. No sign of life except the bacteria and 

some lonely gastropods are present within this zone. 


300 m 

Remarks: 

From the 260 m mark on, the surface (tar layer) is covered by a fine sandy substrate. Near 

the 300 m mark there are again patches were the tar layer is exposed. Adjacent to the 

patches of exposed tar, the oiled layer is covered by new deposited sand. The profile below 

is similar to the one described for the exposed patches. Except some polychaetes (only 

rarely found) no other burrowing animals are to be found. 


340 m 

0-5 cm: tar layer 

5-10 cm: oiled sand, well weathered; total hydrocarbon content: 14.5 g/kg 

10-30 cm: grey sand; no more oil present 


0.3-2 cm: brown compact oiled fine sand, highly degenerated oil residues 

2-8 cm: beige brown lightly oiled sand, some oiled crab burrows; residues are 

also well weathered 

8-18 cm: beige sand with some shell fragments, no oil 


0-3 cm: hard tar layer, moist and sticky; total hydrocarbon content: 64.5 g/kg 

3-10 cm: softer dark brown oiled sand, highly degenerated oil residues 

10-25 cm: beige brown sand, not oiled 


144


Remarks: 

At the 340 m mark, there is a dissected micro cliff formed by the tar like compacted sand. 

The dark brown, almost black oiled tar like surface crust is 1-2 cm thick and more resistant to 

erosion than the still heavily oiled sand below, which eventually leads to the micro cliff and 

the “tar mesas” (photo 6.16 A). The section of such a “tar mesa” (340 m) (photo 6.16 B) 

displays the hardened surface crust (2-4 cm) and the softer dark brown oiled sand. The 

surface crust displays penetration resistance values between 2.7 and >4.5 kg/cm² (compared 

to 0.5 kg/cm² of the material between the tar mesas). The oiled material of the top 5 cm is 

surprisingly moist, and the oil residues are sticky and of some hydrocarbon odour. In this 

material, the highest total hydrocarbon concentration during the 2001 sampling period is 

measured with an average of 64.5 g/kg, whereas the rapid assessment print shows no colour 

at all, which indicates the high degree of degradation (appendix 7). Seaward of the tar mesas 

and also in some occasions in between, the first active crab burrows (1-2/m²) are observed. 

Oil is visibly present within the sediment until the 390 m mark. 

A B 

Photo 6.16 A: “tar mesas” at the HWN and B: section within such a tar mesa. 

145


6.1.5 Bomb Crater Bay – transect 2 

The Bomb Crater Bay transect 2 is located in N-S direction at the southern shore of the bay 

almost at its western end. 

S storm berm 

N 

m 0 10 20 50 70 100 150 180 200 250 260 

sections 


0 5 10 km 

zone of dead Arthrocnemum plants 

49°20’ 49°30’ 

ARABIAN GULF 

Fig. 6.46 Bomb Crater Bay – transect 2. Situation in 2001. 



in separate remarks. The storm berm is - as before - made up of shell fragments and some 

coarse sand. The fine grained material of the first 20 metres is oiled to a depth of 2-4 cm. It 

5 cm 

10 cm 

20 cm 

mud shell fragments oil 

N 

27°20’ 

27°10’ 

living crabs 

upper part heavily oiled 

lower part medium oiled 

sand silt / clay horizon of intensive reduction 

146


shows a brown-grey colour and the oil seems to be well degraded. All plants are dead and 

there is no sign of life anywhere within this zone. The surface material is compacted by the 

oil, which becomes obvious when the penetration force and shear vane force are considered. 

The average penetration force is 2.2 (sd 0.68) and the shear vane force is 3.6 (sd 0.72). 

Comparable sediments (moist) at non oiled locations show values of 1.4 and 2.5 

respectively. 

At about 40 metres a new sand layer has been accumulated on top of the oiled material. 


50 m 

Remarks: 

70 metres from the storm berm, the relic crab burrows become more frequent and the oil 

within the sediment is more degraded due to the higher oxygen availability. But neither any 

living plants nor any burrowing animals are present. 


100 m 

0-2 cm: new beige fine sand 

2-6 cm: black, organic rich silt layer; reduction processes obvious; H2S odour; 

heavily oiled; total hydrocarbon content in –5 cm depth: 46 g/kg; rapid 

assessment print very dark - indicating a low weathering status 

(fig.6.47) 

5-16 cm: dark brown medium oiled silty sand; strong petroleum hydrocarbon 

odour; sticky; in –10 cm depth: 22.3 g/kg; rapid assessment print dark - 

indicating a low weathering status (fig. 6.47); 

16-30 cm: grey fine sand, virtually no oil in the sediment (0.5 g/kg); abundant 

shell and gastropod fragments 

0-1 cm: laminated flat cyanobacteria 

1-4 cm: dark brown heavily oiled silty sand; strong petroleum hydrocarbon 

odour; sticky; 

4-8 cm: beige brown minor oiled silty sand; petroleum hydrocarbon odour; until 

the depth of 8 cm black patches (reduction) of a size between one and 

two cm are present. 

8-18 cm: beige sandy silt, no oil 

18-25 cm: beige sand 

25-30 cm: grey coarse sand with plenty of shell fragments 

At the 140 m mark the laminated cyanobacteria mats are peeling off. Their structure is 

polygonal with some pinnacles interspersed. The sediment characteristics are unchanged 

since the 100 m mark. At the 150 m mark the dark oiled upper layer is now around 7 cm 

thick. The total hydrocarbon load of the material in 10 cm depth is 23.5 g/kg and the dark 

rapid assessment print demonstrates the weak degeneration of the oil (fig. 6.47). 

147



180 m 

Remark: 

At the 180 m mark the first recent crab holes could be observed. They are situated where the 

cyanobacteria mat has been removed, either by erosion or probably by the crabs themselves. 


250 m 

0-0.5 cm: flat cyanobacteria 

0.5-3 cm: dark brown heavily oiled silt; strong petroleum hydrocarbon odour; 

sticky; 

3-8 cm: beige brown minor oiled silty sand; petroleum hydrocarbon odour; 

8-10 cm: light beige silt; 10.3 g/kg of hydrocarbons at 10 cm depth, medium 

weathered (fig. 6.47) 

10-15 cm: beige silty sand 


0-3 cm: beige silt 

3-6 cm: dark brown oiled silt; strong petroleum hydrocarbon odour; 

hydrocarbon concentration: 29 g/kg; low weathering status, intensive 

brown colour of rapid assessment oil print (fig. 4.47) 

6-8 cm: some oil patches within the silt; 

8-15 cm: light beige silt; 2.2 g/kg hydrocarbon concentration 


Remarks: 

250 m seaward of the storm berm, the populations of crabs seem to be normal again (30-45 

burrows/m², photo 6.17). This must have changed during the last 2 years. In 1999 only a few 

individual crab holes (

A B 


Photo 6.17 A: countless active burrows of resettled crab population. B: Macrophthalmus depressus. 

50 m –5 cm 50 m –10cm 150 m –10cm 180 m –10cm 250 m –5cm 250 m –10cm 260 m –5 cm 

46.0 g/kg 22.3 g/kg 23.5 g/kg 10.3 g/kg 29 g/kg 2.2 g/kg 15.9 g/kg 

Fig. 6.47 Rapid assessment oil prints. 

6.1.6 Intertidal transect 

The transect is located between 27°10’54’’N 49°19’57’’E and 27°10’42’’N 49°19’04’’E and is 

therefore oriented from east to west. The linear distance of the intertidal area covered by this 

transect is 1100 m and belongs therefore to the more extensive intertidal sites. To the west it 

is bordered by a carbonaceous sand sheet which, after 100 m turns into a 2 km wide 

supratidal sabkha. 

149


metres 0 200 320 500 700 970 1100 

one 

Fig. 6.48 Intertidal transect. Birdseye view. Summary of situation in 2001. 




Tab. 6.48 Section 1 at the 0 m mark of the intertidal transect. 

0 m 

W 

living crabs 

zone of surviving 

Arthrocnemum 

0 5 10 km 

oiled zone oiled 

living 

zone 

49°20’ 49°30’ 

ARABIAN GULF 

of dead Arthrocnemum plants 

Arthrocnemum individuals 

sand spit 

N 

27°20’ 

27°10’ 

0-1.5 cm: laminated cyanobacteria , some pinnacles 

1.5-4 cm: black reduced silt and clay emitting a strong H2S odour 



20-30 cm: grey sand containing a large number of shell fragments 

E 

HWS sand sheet 

Sections 


150


Remarks: 

The transect begins around 30 m seaward of the HWN mark. Laminated polygonally cracked 

and up to 5 cm thick, cyanobacteria is the dominant feature. There is a distinct relief of higher 

areas and patchy distributed flat tidal pools. Within the pools there are hundreds of grazing 

gastropods. On the higher areas, there are scattered cyanobacteria pinnacles up to 2 cm high 

and surprisingly hard. A closer view reveals tar encrusted gastropod shells on top of these 

pinnacles. Within the surrounding sediments there is no trace of the 1991 oil spill. A inversion 

of relief could have been happened. Erosion must then have been the dominant process. The 

tar encrusted shells resisted erosion, so that only the surrounding material was washed away. 

Cyanobacteria then grew beneath and around the elevated shells. 

Photo 6.18 Gastropod/cyanobacteria pinnacles. 

Near the HMN mark (30 m) the continuous flat cyanobacteria mats are replaced by the typical 

Cleistostoma dotilliforme colony relief which obviously was present before the oil spill. 

Cyanobacteria covered the relief of the colony completely in the years after the oil spill. In 

1999 the first active crab burrows were observed at this site. The number of crab burrows 

increased to 8/m² (sd 1,58) and their distribution is relatively homogeneous. Only in the 

mounds no crab burrows are observed, instead the cyanobacteria is still present on top of 

these mounds. But it is obvious that the mats are eroding and that they won’t persist much 

longer. 


85 m 


1-4 cm: brown silt with degraded oil residues; hardened; granular structure 

4-8 cm: beige silt; old burrows of polychaetes are visible due to degraded 

oil residues (light brown to orange streaks) 

8-15 cm: black silt due to reduction; strong H2S odour; displays a significant 

amount of lightly weathered oil (dark rapid assessment print, fig. 

6.49); total hydrocarbon concentration: 34.4 g/kg 

15-17 cm: beige sandy silt 


151


Remarks: 

Between 60 and 90 metres, the number of active crab burrows decreases towards zero. The 

mounds in this area are extremely hard (>4.5 kg/cm² penetration force) due to tar residues 

below the dry cyanobacteria. Between 80 and 230, metres the burrows are restricted to the 

edges of tidal channels. 


115 m 


2-4 cm: brown silt with degraded oil residues; hardened; granular structure 

4-10 cm: beige silt; rich in old burrows of polychaetes are visible due to 

degraded oil residues (light brown to orange streaks); some isolated 

black spots between 8 and 10 cm (0.5-2 cm in size) 

10-12 cm: black silt due to reduction; strong H2S odour; displays a significant 

amount of liquid oil; total hydrocarbon concentration: 22.7 g/kg 

12-20 cm: dark grey silt; medium oiled; total hydrocarbon concentration: 10.0 

g/kg (at –20 cm); no colour on rapid assessment print (fig. 6.49) 


Remarks: 

Remains of dead Arthrocnemum individuals are preserved on top of little mounds. It is a 100- 

120 m wide dead zone, which extends parallel to the sea as far as the eye can sea. Photo 6.19 

shows the relief of flat tidal channels, dry pools, and mounds within the dead Arthrocnemum 

zone. At the edges of some tidal channels, scattered active crab burrows are encountered. The 

area beside the channels is completely dead. Not even polychaetes are observed. The section 

is located on top of a little mound (with some Arthrocnemum remains). 

Photo 6.19 dead Arthrocnemum zone with characteristic tidal channels and dry pools. The surface is 

covered by a tar like crust and cyanobacteria. 

Near the 180 m mark, the first living Arthrocnemum macrostachyum and some Halocnemum 

strobilaceum can be observed. These living plants are present within a 100-130 m wide zone. 

152


The maximum ratio of living and dead plants is around 1. In average one third of the plants 

are living. It is interesting that only very few new plant managed to germinate in this 

environment. Most living plants are survivors of the oil spill (photo 6.20). 

Photo 6.20 Tidal channels and –pools. About 50% of the Arthrocnemum and Halocnemum plants 

survived the oil spill. Younger plants are totally absent in this area. The area between the plants is 

covered by a thick blistered cyanobacteria mat. 


205 m 

0-2 cm: dark brown oiled and compacted silt; oil residues are well weathered; 

granular structure 

2-15 cm: beige silt; rich in old burrows of polychaetes and crabs; hydrocarbon 

concentration in 5 cm depth: 23.8 g/kg10-12 cm: black silt due to 

reduction; strong H2S odour; displays a significant amount of liquid 

oil; total hydrocarbon concentration: 22.7 g/kg; no colour in rapid 

assessment print indicates advanced weathering status (fig. 6.49) 

15-18 cm: a black H2S emitting oily layer; the hydrocarbon content of this layer 

is 25.6 g/kg; the brown rapid assessment print indicates that in this 

depth the oil degradation is not as advanced as in the top soil (fig. 

6.49) 

18-25 cm: grey silt; total hydrocarbon concentration: 11.6 g/kg medium 

weathered (fig. 6.49) 


Remarks: 

The section is located in the vicinity of two living and one dead Halocnemum individual. The 

cyanobacteria has already been peeled off. 

153


In the following 100 m, the cyanobacteria turns into a blistered mat. From 230 m on, the 

polygonaly cracked mats are restricted to the higher parts of the mounds. The tidal pools 

show no life, except very low numbers of gastropods. 


320 m 

Remarks: 

At 320 m, the last living Arthrocnemum is observed, which is followed by a 10 m wide belt of 

dead Arthrocnemum. Adjacent to this belt thick cyanobacteria mats dominate. They are 

laminated and 3-5 cm thick. Large blisters (up to 4 cm high) and large brainlike structures are 

characteristic for this zone. The flat areas between the blisters, as well as flat dry pools, are 

covered by a thin white salt crust. The cyanobacteria at the bottom of the flat tidal pools often 

displays a red colour (purple sulphur bacteria). 

The next 100 m, nothing in the morphology of the cyanobacteria changes. In the sediment 

below, the oil content increased significantly, though. 


420 m 

0-3 cm: flat laminated cyanobacteria layer 

3-3.5 cm: black reduced and H2S emitting horizon composed of very fine 

sediments 

3.5-10 cm: grey sandy silt with; no visible oil content; hydrocarbon content of 

5.2 g/kg 

10-30 cm: light grey silt; no oil present 

0-2 cm: flat laminated cyanobacteria layer 

2-8 cm: oily, dark brown layer of gypsum rich sand; oil of liquid consistency; 

total hydrocarbon content is 35.9 g/kg; strong odour and only lightly 

weathered (intensive brown rapid assessment print, fig. 6.49) 

8-20 cm: grey sandy silt with; oil restricted to crab and polychaete burrows; 

total hydrocarbon concentration in 10 cm depth is 6.2 g/kg 




42-60 cm: almost white silt 

154


Near the 520 m mark, no more oil is present in the gypsum sand. The cyanobacteria now 

has a fine brain like morphology. At 630 m, the cyanobacteria turns into a flat mat which 

disappeared towards the 700 m mark. At the 700 m mark, there is a 70 m wide beach ridge, 

mainly composed of shell fragments. 


780 m 

From 450 m on, the surface becomes more and more 

instable and the brain like structure of the cyanobacteria 

decreases in size. 


475 m 

0-1 cm: flat cyanobacteria 

1-13 cm: gypsum sand, soaked with liquid 

oil; hydrocarbon content: 42.4 

g/kg; dark rapid assessment print 

(fig. 4.49) 

13-23 cm: grey silty sand, black isolated spots 

due to reduction processes, as well 

as oil in crab and polychaete 

burrows; hydrocarbon 

concentration in sediment: 4.4 g/kg 

23-31 cm grey silt 

31-50 cm grey sand 

780 m 

0-30 cm: different layers of more or less fine gypsum- and quartz sand, beige 

30-43 cm: several 0.5-2 cm thick carbonaceous marine silt layers are 

interspersed 

43-45 cm: old laminated cyanobacteria 

45-53 cm: different sand layers (beige) 

53-63 cm: different layers of laminated cyanobacteria 




155


Remarks: 

The section displays different layers of gypsum, sand, and several cyanobacteria layers below 

the depth of 50 cm. This section is very similar to other sections further inland which revealed 

cyanobacteria below 70 cm of sediments that were described, dated, and published prior to 

this study (Barth 2001 and chapter 6.1.9.2). 

From 800 until 880 m the surface sediment is oiled again. 


840 m 

0-5 cm: dry brown oiled quartz sand; granular structure; the oil residues are well 

degraded although the total hydrocarbon content is still 44.4 g/kg; no 

colour in rapid assessment oil print 

5-45 cm: beige medium grained sand 

45-55 cm: old laminated cyanobacteria 


The area landward of the 880 m mark is not oiled. At 900 m there is the HMS and the sand 

sheet begins near the 1100 m mark. Some debris in front of the sand sheet indicates the 

extent of extreme flood events. 

85 m –10cm 150 m –10cm 150 m –20cm 205 m –5cm 205 m –10cm 205 m –25cm 

34.4 g/kg 22.7 g/kg 10.0 g/kg 23.8 g/kg 25.6 g/kg 11.6 g/kg 

320 m –10 cm 420 m –5cm 420 m –10cm 475 m –10cm 475 m –20cm 840 m –3cm 


Fig. 6.49 Rapid assessment oil prints of samples along the intertidal transect. 

156

6.1.7 Coast Guard – transect 


This transect is located 1 km north of the Dauhat ad Dafi coast guard station, which provided 

the name. It is a flat Arthrocnemum salt marsh with a dense network of tidal channels towards 

the sea. 

SE NW 

locations 


tar layer 

0 5 10 km 

brainlike 

cyanobacteria 

D 

49°20’ 49°30’ 

ARABIAN GULF 

metres 200 180 150 100 70 50 10 3 0 

Fig. 6.50 Coast Guard transect. Birdseye view. Summary of the situation in 2001. 

C 

oiled zone 

one 

mound and 

pool area 

zone of dead Arthrocnemum 

some living Arthrocnemum individuals 

channel 

living crabs 

zone of recolonisation 

by crabs 

lower intertidal 

The transect begins directly at a large tidal channel. The sediments within the channel are oil 

free, extremely fine grained (83% silt and clay), and the biota seems to be normal. Directly 

next to the tidal channel, the sediment is well turbated and the density of Cleistostoma 

dotilliforme burrows is in average 10/m² (sd. 2.1). With increasing distance to the channel the 

B 

N 

A 

27°20’ 

27°10’ 

157


density of crab burrows decreases significantly. In a distance of 10 m, the average value is 

only 2 (sd. 1.58). In a distance greater than 15 m, no active burrow is observed. Towards the 

sea this belt of Cleistostoma crabs widens gradually. The vegetation is still in a bad shape 

(photo 6.22). Between the remains of formerly large Arthrocnemum strobilaceum plants, only 

scattered living individuals can be observed. It is interesting that all green plants are 

individuals that survived the oil spill in 1991. Younger plants are not present in 2001. 

Photo 6.22 Tidal channel flowing into the sea (upper left end). The devastating condition of the biota 

is obvious. Only isolated Arthrocnemum individuals survived in the still hostile environment. The 

remains of dead plants dominate this area (foreground). 


The following sections (fig. 6.51) of the transect are presented in tables. Additional 

information is given in separate remarks. 

A B C D 


Fig. 6.51 Sections in the Coast Guard transect in 2001. 

5 cm 

10 cm 

25 cm 

sand silt / clay horizon of intensive reduction 

burrows oiled crab burrows 

upper part heavily oiled 

lower part medium oiled 

158


3 m beside the tidal channel is section A (fig. 6.51A). 


A: 3 m 


B: 50 m 

0-1 cm: blistered cyanobacteria mat 

1-6 cm: oiled silt; hardened; granular structure; oil residues weathered to a 

high degree (colourless rapid assessment print, fig. 6.53); total 

hydrocarbon concentration: 41.7 g/kg 

6-8 cm: black anaerobe silt (emits a strong H2S odour) 

8-19 cm: dark grey silt with a dense network of relic burrows, filled with 

liquid oil of low degradation status; hydrocarbon concentration: 

53.4 g/kg; weathered to a medium degree 

19-30 cm: grey sandy silt free of oil 

0-1 cm: cyanobacteria mat, partly peeling off 

1-10 cm: oiled silt; hardened; oil residues weathered to a high degree; 

granular structure; plenty of relic burrows 

10-15 cm: oiled silt; liquid oil; strong odour; sticky; low weathering status 

15-18 cm: black anaerobe silt (emits a strong H2S odour) 

18-25 cm: grey silt, free of oil 

Remarks: 

50 m further towards the beach, no living biota is observed. The soil is covered by leathery 

cyanobacteria mats. At slightly elevated places, such as mounds around former salt marsh 

plants the cyanobacteria mat occasionally brake away and reveal a hard brown tar encrusted 

material (photo 6.23) which is well degraded until a depth of 7-10 cm. The penetration force 

of this layer could not be measured since it was higher than 4.5 kg/cm². 

159


Photo 6.23 Leathery cyanobacteria breaks away on top of little mounds, revealing the hardened oiled 

substrate. 

20 m further, the surface becomes more wet and instable. No more remains of old salt marsh 

plants are visible. Finds of relic wood, covered by cyanobacteria in spring 2002, prove that 

the salt marsh extended at least to a distance of 90 m from the channel. The extensive 

cyanobacteria mats show a blistered morphology and they are between 2-4 cm thick (photo 

6.24). The characteristic relief of Cleistostoma-Arthrocmenum-salt marsh, which was present 

before 1991, is levelled by the excessive growth of the cyanobacteria mats. The mats create 

small depressions in which tidal water collects. Most of these depressions are located along 

former little channels. The former relief can be reconstructed by measuring the thickness of 

the cyanobacteria mats and the interspersed carbonate sediments inside the depressions and 

around their edges (fig. 6.52). 

5 cm 

15 cm 

laminated cyanobacteria 

Fig 6.52 The former relief of Cleistostoma-Arthrocnemum-salt marsh is levelled by cyanobacteria. For 

legend see fig. 6.51. 

Below the bacteria mats, the sediment is soaked by oil and water until 10-20 cm depth. Most 

of the oil is concentrated in the abundant relic crab burrows. The intensive stench and the 

consistency of the oil indicate a low weathering status. 

160


Photo 6.24 Extensive growth of blistered cyanobacteria mats cover the former salt marsh 

environment, levelling the morphology that was present before the oil spill. 

Near the 90 m mark, the cyanobacteria changes into a smaller brain like morphology. The 

surface is very wet and instable now. The following section at the 100 m mark is displayed in 

figure 6.51 C. 


C: 100 m 


D: 150 m 

0-2 cm: cyanobacteria mat 

2-10 cm: dark brown oiled mud which becomes lighter in colour due to less 

oil content until 10 cm 

10-15 cm: heavily oiled silt; liquid oil; strong odour; sticky; low weathering 

status; hydrocarbon content: 28.1 g/kg 

15-18 cm: black anaerobe silt (emits a strong H2S odour); oiled 

18-30 cm: grey silt, hydrocarbon content in 25 cm depth: 3.4 g/kg; free of oil 

below 30 cm depth 

0-3 cm: laminated cyanobacteria mat 

3-5 cm: dark brown oiled silt 

5-8 cm: sandy silt 


18-25 cm: old cyanobacteria layers intercalated between the silt. At 22 cm 

depth a 3-7 cm thick laminated cyanobacteria mat is preserved 

At the 180 m mark the small brainlike cyanobacteria disappears and a 10-15 m wide band of 

hard dry tar crust (2-4 cm thick and very well weathered – no trace of oil on rapid 

assessment print at the 190 m mark, although 31.4 g/kg hydrocarbon content) covers the 

beige silt sediments below. The storm berm marks the high water line near the 200 m mark. 

161




Fig. 6.53 Rapid assessments prints of the samples described above. 

Life in tidal pools 

Further towards the sea, the pools occur directly beside the channel. Here, the salinity of the 

water inside the pools increases with the distance from the channel because inundation 

frequency decreases (table 6.61). Remarkably, most of the pools were populated by up to 3 

different fish species. These are Cyprinodontidae (Lebias cf. dispar dispar Rüpell 1829) and 

Mugilidae – 2 species, probably Liza and Valamugil). Were electric conductivity (salinity) is 

higher than 190 mS/cm, generally most of the fish aree dead. The highest electric conductivity 

with 2 living fish was 199 mS/cm. The Mugilidae apparently are more susceptible to salinity. 

At conductivities of about 165 mS/cm most of them are dead, whereas Lebias seems healthy 

(photo 6.25 A). Below 155 mS/cm all fish are alive. At conductivities higher than 200 mS/cm 

only cyanobacteria thrives in this hostile environment. This is also the threshold where a thin 

salt cover appears on the water surface. It is also obvious that the larger fish died before the 

smaller ones. According to Zajonz et al. (2002), Lebias is the only fish species able to 

withstand the extreme salinities (above 160 mS/cm). The pools near the channel with 

conductivities below 140 mS/cm shows apart from the described fish, abundant life within the 

sediments. The bottom sediments of most of these pools are densely populated by gastropods 

and shrimps (1-1.5 cm length) (photo 6.25 B). These organisms compete with the 

cyanobacteria and they are successful. The grazing of the gastropods, as well as the turbation 

of the sediment, limits cyanobacteria growth. This is the first time that, apart from crabs and 

polychaetes, other higher organisms are observed to successfully compete with the 

cyanobacteria in the oiled environment. Any recovery of the old salt marsh ecosystem could 

only be triggered by erosion of cyanobacteria and subsequent increase of the pool sizes. 

Because the physical energy of the tidal water is extremely low, it is a very slow process. 

Whether salt marsh plants would return remains open, because the ecosystem including the 

physical parameters such as temperature, salinity, and sediment changed completely. 

162


Tab. 6.61 Salinity gradient and fish populations in tidal pools with increasing distance from the tidal 

channel. 

channel pool pool pool pool pool pool 

distance (m) 0 3-7 10-15 20-25 30-35 40-45 50 

mS/cm 94.7 130-138 150-160 160-170 180 190 >200 

Mugilidae ++ + ++ + # -- # -- # -- -- 

Lebias sp. ++ + ++ ++ + # -- + # -- -- 

shrimp ++ ++ -- -- -- -- -- 

gastropodes ++ ++ -- -- -- -- -- 

cyanobacteria -- -- ++ ++ ++ ++ ++ 

++ abundant, + present, # dead, -- absent, # -- dead or absent, + # -- present and/or dead or absent 

A B 

Photo 6.25 Life in saline tidal pools. A: Dead Mugilidae (silver) and living Lebias sp. B: Pool grazed 

by gastropodes. The shrimps are inside their burrows below the sediment surface. 

6.1.8 Natural cyanobacteria mudflat 

This mudflat is one of the few areas, where extensive growth of cyanobacteria and a 

distinguished zonation of different cyanobacteria morphologies occurred before the oil spill in 

1991. Salt marsh vegetation occurred only on the leeward side of a narrow sand bar adjacent 

to the littoral fringe. It is located at 27°08’05”N and 49°23’45”E. 

163


Fig. 6.54 Location of the natural cyanobacteria mudflat. 

The profile is a linear transect perpendicular to the coast line. It begins at the HWS an 

continues towards the LWN. At the HWS in 2001, there is still a 3-8 m wide tar cover on top 

of the coarse sandy sediment which consists almost exclusively of gastropods and shell 

fragments. Adjacent to the continuous band of tar there is a belt of little “tar mesas”, a zone 

where erosion processes slowly remove the tar crust. Measurements at different locations of 

the tar crust reveal an erosion rate between 5-65 cm from March 1999 until April 2002 (see 

also chapter 6.1.2). 



Tab. 6.62 Section 1 at the 5 m mark of the cyanobacteria transect. 

5 m 

0 5 10 km 

49°20’ 49°30’ 

ARABIAN GULF 

SW NE 

0 m 30 60 90 120 150 

N 

27°20’ 

27°10’ 

0-2 cm: well degraded tar layer 

2-5 cm: gastropod sand (95% coarse sand fraction) 

5-13 cm: beige sandy silt 

13-30 cm: light beige silt 

folded cyanobakteria 

pinnacle cyanobacteria 

tar layer 

164



30 m 0-0.5 cm: brainlike cyanobacteria mat 

0.5-6 cm: well degraded oil residues within gastropod sand; some 

Remarks: 

polychaetes present 

In 1999 there were 6-15 still cm: some light brown beige oil sandy droplets silt floating on the groundwater surface, whereas 

in 2002 the hydrocarbon 15-30 cm: degradation light beige reached silt a state where this was never observed. 


60 m 0-0.5 cm: brainlike cyanobacteria mat 

0.5-1.5 cm: slightly hardened oil/tar layer 

1.5-5 cm: grey oiled silt 

5-10 cm: older cyanobacteria layers 


15 m seaward, there 27-57 are cm: no more grey silty cyanobacteria sand below the 0.1-0.3 mm tar layer visible. The 

sediment is slightly 57 cm: oiled until beachrock a depth of 10 cm. Within this horizon there are plenty of crab 

burrows and a diffuse pattern of orange oxidation (mainly around the burrows) and dark grey 

reduction patches (mainly in between the burrows). Beach rock occurs in a depth of 50 cm. 


90 m 

0-3 cm: flat cyanobacteria mat 

3-3.3 cm: hardened oil/tar layer 

3.3-7 cm: fine sand; slightly oiled 


Remarks: 

At the 90 m mark, the brainlike cyanobacteria structure changes into a flat, sometimes 

polygonal pattern. There is also the beginning of a slight relief of depressions and adjacent 

higher elevated areas. But the total relief is not more than 2-4 cm. 

The laminated pattern which displays the annual growth of cyanobacteria in summer (the 

main growth season of cyanobacteria at the Gulf coast, especially Microcoleus sp. and Lyngba 

sp., is during the summer months) and the following sedimentation of fine carbonate mud in 

winter is extremely well documented at this site. High sedimentation rates (1-3 mm), as well 

as intensive cyanobacteria growth, result in layers perfectly visible to the human eye (fig. 6.66 

in chapter 6.1.9). 

At 120 m, the flat polygonal mats show scattered pinnacles between 1-2 cm size. The relief 

of depressions (pools) and elevated areas becomes more distinct (fig. 6.55). The 

depressions are filled with tidal waters, their bottom covered by black polygonal 

cyanobacteria (2-4 cm polygons). The elevated areas are about 10-15 cm higher than the 

pools (measured from the bottom surface) and covered by flat laminated cyanobacteria as 

described before. 

165


At 150 m, the pinnacles become more dense and show a wide variety of morphologies from 

plain pyramidal to cauliflower with several transitional states. Such a variety of pinnacles so 

far has never been observed within the study area. It is also not known to the author from 

any other site. The tidal pool relief is very distinct. The pools are between 2 and 4 m² and the 

elevated areas slightly larger. The bottom sediment of the pools consists of a sandy mud rich 

in gastropod and shell fragments. The substrate is dark grey or black, due to an anoxic 

environment, except 2 mm at the surface. The dark colour indicates that a large amount of 

organic material is being decomposed. As a result, oxygen is depleted faster than it can be 

supplied by diffusion. Anoxic conditions reduce sulphur and produce H2S. Below 10-20 cm of 

this type of substrate, there is a hard beach rock basis. Within the sediment, there is a high 

abundance of living gastropods, shrimp, and polychaetes. The edges of the elevations are 

populated by crabs. There is a plain regularity in the distribution of the elevations which is 

determined by the tidal currents, especially the ebb tide (fig. 6.55). Erosion processes at the 

edge of the elevations decrease their size, and sedimentation at the landward centre of the 

tidal pool and subsequent cyanobacteria growth lead to the formation of new elevations. This 

seems to be a dynamic cycle which repeats itself. Considering the erosion rates and the 

consistency of the laminated flat cyanobacteria mats on top of the elevated areas, the cycle 

might well take a couple of decades. 

10 cm 

erosion during 

ebb tide 

flow direction 

during ebb tide 

area of 

sedimentation 

beach rock fine carbonate mud 

cyanobacteria 

sand with shells 

laminated cyanobacteria 

Fig. 6.55 Pattern of tidal pools and elevated areas overgrown by flat laminated cyanobacteria. During 

the tides erosion and sedimentation processes occur. 

166


The next 50 m do not show much change regarding the pool morphology as well as the 

sediments. At the 280 m mark, the substrate of the elevated areas becomes soft and the 

cyanobacteria mat very thin. The beach rock now is only a few centimetres below the sandy 

mud. It is only 1-2 cm thick and can easily be broken. Towards the lower intertidal, there is no 

continuous beach rock layer any more. It is not known whether the beach rock formation is 

presently taking place or if it is being eroded away. 

It is not clear why there is no salt marsh vegetation and why the crabs do not colonize the 

elevated areas in the mid eulittoral zone. The sediments as well as the other environmental 

parameters, are suitable for mangroves and for other salt marsh plants. 

167

6.1.9 Salt marsh ecosystems - Discussion 

6.1.9.1 Hydrocarbons 

The main processes of hydrocarbon degradation occurs through oxidative abiotic chemical 

reactions and enzyme controlled reactions by a variety of organisms (Atlas 1981). When 

oxygen concentrations are low, biodegradation is therefore reduced (Baker et al. 1993). 

Besides oxygen, nutrients such as nitrogen and phosphorous, belong to the essential 

conditions of hydrocarbon biodegradation (Höpner et al. 1989, Harder et al. 1991). Nitrogen 

is important for cellular amino acid and protein production and phosphorous is needed for the 

synthesis of all membrane lipids. Low concentrations of such nutrients limit the growth of 

biodegrading micro organisms and therefore the oil degradation. 

In the gas chromatographic spectrum the unresolved complex matrix (UCM) indicates the 

presence of crude oil components. The degradation rate of its components can be slow (Baker 

et al. 1993). Larger pentacyclic aliphatics, as well as branched hydrocarbons such as pristane 

and phytane, resist oxidation to a greater extent than the n-aliphatic hydrocarbons. They are 

often visible above the UCM curve in the gas chromatogram. 

Ratios of n-heptadecane/pristane and n-octadecane/phytane have frequently been used to 

estimate the degree of microbial degradation (Atlas 1981). This is possible because n-alkanes 

are metabolised faster than the branched species of comparable retention (Atlas 1981). 

Therefore, low ratios indicate the presence of degraded oil, and higher ones reflect less 

degraded oil residues (Fusey & Oudat 1984). Due to the increased presence of biogenic lipid 

material within degraded oil residues, these indices could not be applied after 1993. Instead, 

they rather seem to be an indicator for active biogenic degradation of the oil residues within 

the sediments. Analysis of aerated sediments soaked with oil residues, carried out at the Jubail 

Industrial College in 2002, revealed values of 1.34 (sd. 0.54). Sealed oil residues in an 

anaerobic environment, such as the zone below cyanobacterial mats, generally displayed 

lower values of 0.26 (sd. 0.15). 

According to Smith (1995), the maximum lipid fraction that occurred in the sediments was 

0.13 g/kg. Analysis of low degraded samples collected in 2002 below a dense cyanobacterial 

mat consisted of a lipid fraction of 0.15 g/kg. 

The general trend of the greatest oiling towards the littoral fringe and the upper eulittoral 

remained constant through the 10 years of observation period. In 2001, the oiled substrate was 

restricted to the zone between the HWS and HWN with maximum oiling in between these two 

marks (fig. 6.56 B and transects 6.1.2 – 6.1.5 in appendix 3).

B 

depth in cm 

A 

0 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

-40 

-45 

-50 

W 

15 

g/kg 

30 

40 

35 

30 

25 

20 

15 

10 

5 

0 

45 


60 

1993 / 0-10cm 

1993 / 10-20cm 

2001 / 0-10cm 

2001 / 10-20cm 

HWS 

75 

75 60 mm 260 m 360 m 

90 

105 

120 

135 

101 

SD=53,8 

MHW 

(mean highwater) 

150 

165 

180 

195 

oil in burrows 3-10g/kg medium oiled 10-25g/kg 

heavily oiled >25g/kg well degraded oil residues 

Fig. 6.56 A: Development of hydrocarbon concentration between 1993 and 2001 at the 60, 260 and 

360 m mark of the Halocnemum salt marsh transect discussed in 6.1.1. (mean values out of 3 

samples). B: Oil distribution within the sediment of the Halocnemum salt marsh in 2001. 

This is probably the most pronounced change compared to the trend in 1994 where maximum 

oiling occurred directly at the HWS. This development is due to the more effective 

preservation in the zone of maximum cyanobacterial growth. Temporarily desiccation, due to 

less inundations near the HWS, break the bacterial mats and allow for a better oxygen supply 

of the surface near substrate. Thus oil degradation is more advanced there. Maximum total 

hydrocarbon concentrations occurred near the surface from 0-10 cm, decreasing in 

concentration with increasing sediment depth in 1994, as well as in the following years until 

210 

225 

240 

255 

270 

285 

300 

HWN 

315 

330 

345 

360 

E 

m 

169


2001. Between 1993 and 2001 the hydrocarbon concentrations increased in the soil layers 

between 10 and 20 cm depth. The top soil layers on the other hand had significant losses (fig. 

6.56 A). This indicates a slow movement of oil residues into deeper soil layers. Comparison 

of the situation in 1992 of the undisturbed sediments at the Bomb Crater Bay ploughing test 

site (which is discussed in detail below) with the situation in 2001 clearly shows the 

movement of oil residues into deeper soil layers (fig. 6.58). In 2001, tar and oiled sediment 

could not clearly be distinguished the way Höpner et al. (1992) did in 1992. The process of 

hydrocarbon percolation does not change the total hydrocarbon distribution which still 

displays much higher values in the top soil (0-10cm) than in the lower soil (fig 6.57, 6.58 and 

fig. 6.56 A). 

-5 4 

-10 3 

-25 2 

-30 

1 

0 5 10 15 20 25 30 

g/kg 

Fig. 6.57 Profile of oil concentration at different soil depths in 2001 (location described in 6.1.6, 205 m 

mark). 

depth in cm 

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 

6 

4 

2 

0 

-2 

-4 

-6 

-8 

-10 

-12 

muddy sand in 2001 oiled sediment in 2001 oiled sediment in 1992 tar in 1992 

Fig. 6.58 Oil distribution within the sediment of the undisturbed transect in 1992 and 2001. The 1992 

data was collected by Höpner et al. (1992). 

Usually, below 30 cm soil depth the substrate is free of oil, except in areas where crab 

burrows allowed a deeper penetration of the oil. The highest oil concentrations that were 

found between the HWS and HWN in 2001 were 64.5g of hydrocarbons per kg soil. More 

often concentrations between 40 and 45 g/kg occurred which are still only slightly lower than 

some of the highest results reported by Greenpeace (1992). 

170


Interesting is, that the oil, which penetrated the sediment through crab burrows until depths of 

50 cm, did in most cases not persist until 2001. Hayes et al. (1993) suggest that slow erosion 

rates and the large volumes of subsurface oil would contaminate the site (near the site 

described in 6.1.3) for decades. The reason for the hydrocarbon degradation below 30 cm soil 

depth is the location below the groundwater level. The groundwater, which is strongly 

influenced by seawater, carries nutrients and a certain amount of oxygen. The sediments 

below 30 cm often consist of coarser grain size fractions, due to shell fragments which allow a 

sufficient groundwater exchange and therefore nutrient supply. 

An other impact caused by the oil, is the formation of tar crusts and ‘hardcrusts’. Most of the 

sediments between the HWN and HWS that were soaked by oil and later exposed to sunlight 

changed the structure during the following years. The upper 3-6 cm became more compact, 

much harder, and display today a large granular structure. The consequences for 

microclimate, fauna, and vegetation are discussed separately. 

Ploughing experiment 1992-1994 

Because oxygen supply turned out to be the crucial factor controlling the biodegradation of 

the oil residues in 1993 a ploughing experiment was carried out already. The ploughing site is 

situated in a former salt marsh area on the southern shore of Bomb Crater Bay (27°19’57”N 

49°16’00”E). The sediments are predominantly fine grained muds as described in 6.1.1.1. The 

strips are 10 m wide and about 100 m long (perpendicular to the shoreline between spring and 

neap high water marks - more detailed information in Smith1994). 

In 1993, 16 months after the ploughing the following results were observed (data: Smith 

1994): Generally, the highest concentrations are to be found in the upper sediment layers 

between 1-5 cm depth. Along the transect, maximum values occur near the spring high water 

mark (compared to neap high water mark). At the spring high water mark the hydrocarbon 

concentrations in the upper sediment (1-5 cm depth) is 34.13 and 35.4 g/kg at the treated site 

and 91.54 and 45.81 g/kg at the non-ploughed site, which is almost 3 times as much. Between 

10 and 15 cm depth, the differences are not as significant. 10.29 and 16.53 g/kg are the 

concentrations at the treated site and 25.64 and 13.45 g/kg at the non-treated site. 

Near the neap high water mark the concentrations of the treated and untreated sites are almost 

similar with 57.78 / 31.71 g/kg at the treated site and 31.87 / 39.07 g/kg at the non-treated 

site. Between 10-15 cm depth 4.01 / 5.74 g/kg at the ploughed area and 1.86 / 7.48 g/kg at the 

non-ploughed site also show not much difference. 

171


In 1994 (33 months after the ploughing experiment), the situation changed regarding the 

overall concentrations of hydrocarbons. The HWS of the treated site did not much change 

with 40.9 / 30 g/kg and 18.4 / 15.4 g/kg, respectively for the 10-15 cm horizon (see fig. 6.59). 

Some values even increased which is probably due to the inhomogeneous pore structure and 

therefore variable oil load of the substrate. At the non-ploughed site though, a significant 

decrease of concentrations (53.6 / 19.8 g/kg in 1-5 cm samples and 11.7 / 15.4 g/kg in 10-15 

cm depth) is obvious. Regarding the overall hydrocarbon concentrations, treated and nontreated 

sites can not be distinguished anymore. 

g/kg 

80 

70 

60 

50 

40 

30 

20 

10 

0 

HWS -5 HWS -15 HWS -5 HWS -15 HWN -5 HWN -15 HWN -5 HWN -15 

treated non-treated treated non-treated 

Fig. 6.59 Oil load at the ploughed and non-ploughed site – mean values (data: Smith 1995). 

1993 

1994 

Due to the mentioned spatial variability of the oil load within the sediments, the portions of 

the total resolved aliphatics to the total weight of the oil extracted are more informative. The 

observations regarding the oil load are supported, although the differences between treated 

and untreated site are not as great (fig. 6.60). Proportions between 0.8 and 1.8% (compared to 

1.8-2.6% in 1993) in the ploughed surface sediments of the HWS are much lower than at the 

non-ploughed site with 2.3 - 2.6% (compared to 3.0-3.7% in 1993)(fig. 6.60). In the -15 cm 

layer these proportions are 1.7-1.9% for the treated site (compared to 2.0-2.1% in 1993) and 

2.8-2.9% for the untreated site (compared to 2.4-3.3% in 1993). For the HWN proportions are 

similar for ploughed and non-ploughed site but generally much higher. 

172

% 

7 

6 

5 

4 

3 

2 

1 

0 


HWS -5 HWS -15 HWS -5 HWS -15 HWN -5 HWN -15 HWN -5 HWN -15 

treated non-treated treated non-treated 

1993 

1994 

Fig. 6.60 Portions of the total resolved aliphatics at the ploughed and non-ploughed site – mean 

values (data: Smith 1995). 

The degradation indices n-C17/pristane and n-C18/phytane are often used to indicate the 

state of degradation (Atlas 1981). Large concentrations of n-C17 are characteristic of 

biological material (lipids) from an increased microbial activity, which can be attributed to the 

degradation of the oil residues within the sediments (see tab. 6.7). N-C18/phytane indices 

appear less prone to the effects of biological lipids but there still seems to be some, as the 

values of the ploughed and non ploughed sites (tab. 6.65) suggest. 

Tab. 6.65 n-C18/phytane indices for the ploughed and non-ploughed site. 

ploughed site n-C18/phytane indices non-ploughed site n-C18/phytane 

indices 

MHWS 1993 MHWS 1994 MHWS 1993 MHWS 1994 

0.09 0.11 0.20 0.04 

0.03 0.02 0.37 0.02 

0.03 0.10 0.12 0.02 

0.05 

Data: Smith 1994 

0.10 0.11 0.04 

Tab. 6.66 n-C17/pristane indices for the ploughed and non-ploughed site. 

ploughed site n-C17/pristane indices non-ploughed site n-C17/pristane indices 

MHWS 1993 MHWS 1994 MHWS 1993 MHWS 1994 

173

Data: Smith 1994 


0.16 1.92 0.52 0.29 

0.16 0.28 1.02 0.18 

0.06 0.70 0.17 0.34 

0.04 0.76 0.14 0.26 

These indices made sense in 1993, when the values of the obviously more degraded 

sediments at the ploughed site were much lower than the samples from the untreated. But in 

1994, especially the n-C17/pristane indices increased significantly and the n-C18/phytane 

indices were unchanged or slightly increased at the ploughed site. The significant increase in 

n-C17/pristane indices do not indicate less degradation due to the above mentioned 

presence of biogenic lipid material. Instead, they seem to be an indicator for active biogenic 

degradation of the oil residues within the sediments. As a result of these observations, which 

were similar at various other sites, the n-C17/pristane and n-C18/phytane indices were not 

used as indicators of oil degradation in the period after 1993. 

The typical gas chromatographic spectra of the 1-5 cm depth horizon clearly show that the 

upper intertidal ploughed site was more degraded 16 months after the experiment than the 

non-ploughed site. 

Fig. 6.61 Gas chromatographic spectra of the 1-5 cm depth horizon at the ploughed and non 

ploughed site (data: Smith 1995). 

Most straight-chain aliphatic hydrocarbons of the ploughed site have been sufficiently 

degraded in a way, that their peaks are barely resolvable from the unresolved complex 

matrix (UCM). The rate of degradation of the UCM is much lower than that of n-aliphatics. 

174


Therefore, it remains longer in the sediments. Branched hydrocarbons (such as pristane and 

phytane) and pentacyclic aliphatics are more resistant to microbial degradation and therefore 

still prominent in the ploughed site which can be seen in figure 6.61. At the non-treated site, 

most of the straight-chain aliphatics are prominent without signs of degradation. The spectra 

of the lower sites (HWN) are quite similar regarding the microbial degradation of the 

hydrocarbons. Just the UCM at the treated site is not as pronounced as at the non-treated 

site (fig. 6.62). 

Fig. 6.62 Gas chromatographic spectra of the 1-5 cm depth horizon at the ploughed and non 

ploughed site – lower part (data: Smith 1995). 

Ploughing experiment at a cyanobacteria habitat in 2001 

In March 2001, a ploughing experiment was carried out at the coast guard site (see chapter 

6.1.7). The 5 m wide stripe is 50 m long and perpendicular to a tidal channel, the edges of 

which is populated by crabs. The 1-3 cm thick laminated partly crinkled cyanobacteria mat 

was removed by dry tilling without penetrating the sediment deeper than 5 cm in order to 

avoid a secondary oiling. In April 2002, the plough marks were hardly visible, because the 

sediment again was completely covered by a 1 mm thick cyanobacteria layer. The 

surprisingly fast resettlement of cyanobacteria demonstrates the dominance of these 

organisms in the changed environment since the oil spill in 1991, due to the absence of 

grazing gastropods and burrowing animals. Crabs did not enter the ploughed site, most 

probably because the oil is still present in the substrate below. The degradation of the 

hydrocarbons is not significantly accelerated, because the exposure to oxygen was only for a 

short period of not more than a few months. Although there is still some diffusion of oxygen 

175


through the first layer of cyanobacteria, it will decrease towards zero after the settlement of 

the second layer in the summer period of 2002. Total hydrocarbon concentrations of the 

sediments in 2002 still range between 30 and 40 g/kg. 

In April 2002, at the same site oil samples from below the cyanobacteria layers were collected 

and prepared for GC analysis in order to compare the data with the spectra from 1994. The 

result is illustrated in fig. 6.63. The spectra are almost identical. Branched hydrocarbons such 

as pristane and phytane (which are more resistant towards microbial degradation) are still 

prominent above the UCM. The 2002 sample seems even less degraded than the 1994 sample, 

because the larger peaks of pentacyclic aliphatics are also pronounced above the UCM. The 

conclusion is, that oil which is trapped below laminated cyanobacteria mats, is not subjected 

to microbial degradation and therefore preserved for a long time. 

2002 

pentacyclic aliphatics 

Fig. 6.63 Gas chromatographic spectra of oil below a cyanobacteria mat in 1994 and 2002. 

Estimates of the oil load, still present in the severely damaged salt marshes, are based on the 

extent of cyanobacteria layers that prevent hydrocarbon biodegradation. The 1.55 km² (see 

chapter 6.1.9.2) of new stable cyanobacteria ecosystems carry about 7 kg hydrocarbons per 

m², which is almost 11.000 tonnes in total. Additionally, there are 12.3 km² of cyanobacteria 

1994 

176


zones with a long term potential of recovery, that carry in average 3 kg hydrocarbons per m². 

Therefore in 2001, the amount of hydrocarbons present below cyanobacteria mats is about 

50.000 tonnes in the Dawhat al Musallamiya and Dawhat ad Dafi embayment system. 

6.1.9.2 Trace metals 

Comparison of the trace metal values from 1994 and 2002 reveals a general decrease in the 

uppermost soil layer (0-5 cm). The concentrations at the lower intertidal site are also generally 

lower than at the mid intertidal site (fig.6.64). But there is an increase in nickel, vanadium, 

and copper in the lower soil layer (-20 cm) at the mid intertidal site. This indicates a 

percolation of the oil associated trace metals in deeper soil layers with time. The extreme 

value in copper at the lower site and zinc at the mid intertidal site (see data in appendix 5) can 

not be explained. They might be due to the weathering of trash in the intertidal zone. 

mg/kg 

60 

50 

40 

30 

20 

10 

0 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

250 m - 

5 

250 m - 

5 

250 m - 

10 

250 m - 

10 

Ni 1994 Ni 2002 

250 m - 

20 

350 m - 

5 

Cr 1994 Cr 2002 

250 m - 

20 

350 m - 

5 

350 m - 

10 

350 m - 

10 

350 m - 

20 

350 m - 

20 

mg/kg 

30 

25 

20 

15 

10 

5 

0 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 

250 m 

-5 

250 m - 

5 

250 m 

-10 

250 m - 

10 

V 1994 V 2002 

250 m 

-20 

250 m - 

20 

350 m 

-5 

Cu 1994 Cu 2002 

Fig. 6.64 Trace metal concentrations in 1994 and 2002 in the mid eulittoral and lower eulittoral of the 

Halocnemum transect. 

If the absolute values are compared with other results from the Gulf region, i.e. the non 

polluted Dawhat al Abu Ali (Basaham & Al-Lihaibi 1993), the lower intertidal values are 

only slightly increased (Ni 20%, V 10%, Cu 0%,) or lower (Cr 50%, Zn 30%), and the upper 

intertidal values are significantly increased (Cu 100%, Ni 200%, V 100%) or lower in the case 

350 m - 

5 

350 m 

-10 

350 m - 

10 

350 m 

-20 

350 m - 

20 

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of chrome. It must be noted that the overall concentrations are low compared to 

concentrations measured in intertidal sediments along the Kuwait coast where the 

concentrations of basically all trace metals are 5 to 10 times higher (Basaham & Al-Lihaibi 

1993). 


The initial extensive growth of cyanobacteria, especially on sites where they did not occur 

before the oil spill (e.g. Cleistostoma colonies), suggests that the growth of these mats is 

favoured by the absence of bioturbation of the sediment. Cyanobacteria do usually not occur 

where bioturbation caused by crabs and polychaetes is a dominant process. The bioturbation 

activities destabilise the sediment surface, and - together with grazing pressure by benthic 

animals - prevent the establishment of the cyanobacteria. After the oil polluted the shores and 

destroyed most of the crab colonies in the mudflats, the bioturbation process as well as 

grazing by gastropods stopped instantly. After the deposition of a thin layer of fresh sediment, 

the extensive growth of cyanobacteria started. The sedimentation of a certain amount of fine 

substrate seems to be a perquisite for cyanobacteria settlement. Observations in spring 2002 

showed that not the high temperatures on top of the tar layer prevent the growth of 

cyanobacteria (NCWCD/CEC 1992) but more likely the absence of fine grained substrate. 

The bacteria grow successfully in 60°C hot hyper-saline tidal pools. The filamentous bacteria 

with their polysaccharide sheaths bind sand grains and thus help to stabilize the sediment. In 

only a short time of 2 years large areas were covered by cyanobacteria. From this stage on, 

three scenarios were observed. The first possibility is the desiccation, cracking, and peeling of 

the cyanobacteria mats (see 6.1.1.6). The second is the resettlement of burrowing macrofauna, 

i.e. the crab Cleistostoma dotilliforme, and, or benthic animals, such as gastropods like 

Pirinella conica or Cerithium sp., which outcompete the cyanobacteria again (see 6.1.3). The 

third possibility is further extensive growth of cyanobacteria building thick laminated mats, 

sealing the oiled sediments and thus preventing any oil degradation as well as any 

resettlement by macrofauna (see 6.1.7). At such locations, in contrary to initial speculations 

(CEC/NCWCD 1992), the ecosystem changed completely. A new balance was established 

with optimum cyanobacteria growth based on light, sedimentation, inundation, nutrients, and 

the absence of competing macrofauna. The primary succession obviously came to an end after 

the settlement of the first pioneers (fig. 6.65). The crabs (Brachyura) are hindered by the oil 

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below the mats and the gastropods by the high salinity in most tidal pools and the dryness of 

the surrounding mats. Therefore regeneration is not possible under the current environmental 

conditions. This process was observed at several of the described sites (6.1.3, 6.1.6, 6.1.7), at 

the northern and western shores of Dawhat ad Dafi peninsula, the shore of Khursaniya 

sabkha, a stretch of southern shore at Bomb crater Bay, and at Musallamiya Bay Höpner’s site 

16 (Höpner, unpublished report 2001). 

oil 

impact 

cyanobacteria 

cyanobacteria 

desiccation, 

cracking, 

peeling 

grazing 

gastropods 

excessive 

growth 

oil conservation 

Fig. 6.65 Simplified successions at oiled Cleistostoma-salt marshes. 

The total known area of these new cyanobacteria habitats is about 1.55 km². There might be 

additional sites which were missed during the surveys. And there are much larger areas that 

are dominated by laminated cyanobacteria mats, but which still have some regeneration 

potential though it might need several decades for them to recover. Along 150 km of the 

coast line within the sanctuary, these areas are preset, although sometimes they cover only 

a narrow zone between 10 and 50 m. At 90 km of the coastline this zone is in average 80 m 

wide. In total, the area of oil induced cyanobacteria covers about 12.3 km² excluding the 

permanent cyanobacteria ecosystems (tab. 6.7). Considering this development, it can be 

stated that the oil spill did not damage the cyanobacteria sites (Al-Thukair & Al Hinai 1993), 

but promoted their extensive development to a high degree with a possibility of survival in the 

long term. 

Tab. 6.67 Calculation of extent of oil induced cyanobacteria areas. 

Stable cyanobacteria ecosystems: 

Site area in km² 

6.1.3 0.05 

oil degradation 

crabs halophytes 

no further 

development 

stable 

cyanobacteria 

community 

Cleistostoma 

-salt marsh 

community 

179


6.1.6 0.3 

6.1.7 0.4 

Dauhat ad’ Dafi Peninsula West 0.08 

Dauhat ad’ Dafi Peninsula North 0.345 

Khursaniya sabkha 0.23 

Bomb crater Bay 0.025 

Musallamiya Bay 0.12 

total: 1.55 

areas with long term regeneration potential: area in km² 

60 km coast with average 40 m wide cyanobacteria zone 2.4 

90 km coast with average 110 m wide cyanobacteria zone 9.9 

total: 12.3 

Erosion of cyanobacteria 

During longer periods without inundation, the leather like cyanobacteria mats desiccate. This 

desiccation causes the mat to shrink, crack into polygonal pieces, and eventually peel off, 

removing part of the underlying oiled sediment. Repetition of this process may lead to a 

substantial physical erosion of tar layers or oiled sediment directly beneath the cyanobacteria. 

This process was observed by Hoffmann 1994 and Höpner et al. 1996. Our own studies reveal 

that this process still takes place 10 years after the oil spill. At oil polluted salt marshes where 

this is the only action of bioremediation, the erosion of tar is a very slow process, which may 

take an other one or two decades to remove the oiled material. More important seems the aid 

of macrofauna that resettles the areas under consideration, aerating the sediment and thus 

contributing to an effective oil degradation. 

Resettlement of cyanobacterial flats 

After the oil degradation reached an advanced level and the cyanobacteria mats did not 

completely seal the soil surface, burrowing organisms like polychaetes (Perinereis 

vancaurica), or crabs such as Cleistostoma dotilliforme and Metopograpsus messor may 

resettle the sediments. Bioturbation by these organisms breaks the cyanobacterial mats and 

prevents their renewed establishment as the process continues (i.e. 6.1.3). At countless sites, 

adult Cleistostoma dotilliforme started to recolonize the upper eulittoral areas around tidal 

channels in 2001. Often, the original densities are not reached by far, and cyanobacteria mats 

are still present. But it is clear that the Cleistostoma population will further improve, and the 

cyanobacteria on the other hand will retreat and eventually disappear. At other locations, such 

as Höpner’s station 6 at 27°17’40”N 49°22’25”E (Höpner 2001, unpublished report) the 

recolonization process by Cleistostoma populations was much faster, starting in 1995 and 

reaching original densities in 1998. 

180


The role of grazing gastropods in reducing cyanobacteria depends on the environmental 

conditions, such as salinity, inundation, and probably species composition of cyanobacteria. 

The cyanobacteria mats in the lower eulittoral were the first to be colonised by Pirinella 

conica. Since this species, like most other grazing gastropods, is an ‘R’-strategist (produce 

large numbers of juveniles) its abundance increased at one test site from 61/m² in December 

1991 to 1884/m² in April 1993 (Jones et al. 1994). This was possible because of the absence 

of predators and the availability of food. In the following years, the extensive cyanobacteria 

mats in the lower eulittoral environment almost disappeared again. In most of the upper 

eulittoral areas, the extensive cyanobacteria mats are only periodically inundated by sea water 

which results in a partial dry surface, that can not be grazed by gastropods. Therefore, the 

mats can persist as long as the other environmental conditions are favourable. In the scattered 

tidal pools, gastropods are prominent as long as the salinity is not higher than 140 mS/cm. 

Lower salinity pools are grazed and do not show cyanobacteria mats covering the bottom 

sediments which are usually populated by several other benthic organisms. The gut content of 

Pirinella conica shows a high proportion of cyanobacteria, particularly Gomphosphaeria sp. 

and Phormidium sp. (CEC/NCWCD 1992). It remains open why the most abundant 

cyanobacterium Microcoleus chtonoplastes has not been found. But this could also be due to 

taxonomic errors, because of many similarities between Microcoleus sp. and Phormidium sp. 

Oil conservation by cyanobacteria 

Excessive cyanobacteria growth after the smothering of all intertidal biota by the oil builds 

thick laminated mats (by now up to 8 cm thick). Each year, new cyanobacteria is growing on 

top of the freshly settled carbonate sediment, forming clear annual cyanobacteria layers. 

These cyanobacteria layers, interspersed with fine carbonate sediments, completely seal the 

surface and hence produce an anaerobic milieu which inhibits oil degradation. As long as the 

cyanobacteria mat exists in this form, the oil will be preserved and regeneration is impossible. 

Cyanobacteria and their role of hydrocarbon transport 

The main growth season of laminated cyanobacteria (especially Microcoleus sp. and Lyngba 

sp.) is during the summer months. In the winter period, tides provide sediments which settle 

on top of the cyanobacteria (about 1-3 mm). In spring, the filamentous bacteria grows and 

covers the new sediments. This repeated process leads to one layer of sediment and 

cyanobacteria respectively every year. The older bacteria dies and remains in an anaerobic 

milieu. That is the reason why 700 years old cyanobacteria was found even 70 cm below 

181


sediments (Barth 2001). At one site (see chapter 6.1.8) different cyanobacteria layers growing 

on top of the 1991 oil residues were dated by the radiocarbon method (fig. 6.66). The first 

sample shows an age of 8800 years BP. The age of the following layers decreases 

significantly from 1070 BP (year 3) to 800 BP (year 6) and to 630 BP (year 9). This means 

that in the first layer of bacteria (after the oil spill) about 75% of fossil organic carbon was 

incorporated. The fraction of fossil carbon decreases gradually to 10% in the 9 th layer above 

the oil (9 years after the oil spill). 

1999 

1998 

1997 

1996 

1995 

1994 

1993 

1991 Gulf war oil 

635+/-135 Hv23243 

805+/-150 Hv23242 

1070+/-75 Hv23241 

annual cyanobacteria layers 

8830+/-230 Hv23240 

Fig. 6.66 Annual layers of flat cyanobacteria on top of the 1991 oil spill residues and radiocarbon 

dates. 

Because of the gradual decrease, the single impact from 1991 seems to be responsible for the 

fossil carbon. This implies that small amounts of the hydrocarbon carbon, deposited in the 

1991 oil layer, are able to rise to the surface. Most probably, because each new layer of 

cyanobacteria incorporates some of the carbon provided by the layer immediately below. 

Although some of the carbon out of the oil spill is used by the cyanobacteria, it seems clear 

that the cyanobacteria itself does not significantly degrade the oil. It may create growth 

conditions for heterotrophic bacteria, shelter, moisture, and nitrogen compounds (by N2fixation) 

which might be important for other organisms able to degrade the oil. But this could 

only be effective in an aerobe environment, which is in most cases not present below 

cyanobacterial mats. Therefore, such oil degrading communities could not be observed in the 

study area. The assumption by Coppejans (1992) that the cyanophyta might contribute to a 

high degree in the biodegradation of the oil can not be proved. It is also questionable, whether 

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their presence on a long term basis accumulates phosphate which may be provided by the 

decomposition processes in the trash line. The author finds no signs that the cyanobacterial 

mats lead to a type of raw soil which is needed by cormophyte pioneers of a salt marsh 

vegetation, as stated by Kinzelbach et al. (1992). 

6.1.9.3 Groundwater 

Water is the agent that carries the nutrients necessary for the metabolism of microorganisms 

as well as for plants. High salinities of the water on the other hand inhibit the growth of plants 

and may even be the limiting factor for their occurrence. Concentrations of the most 

important nutrients regarding oil biodegradation are phosphate and nitrogen, as well as 

oxygen. The phosphate concentrations of the coastal seawater remained constant between 

1992 and 1999 (tab. 6.8) 

Tab. 6.68 Phosphate concentration in soil pore water. 

Location Concentration µg P/l in 1992 Concentration µg P/l in 1999 

Seawater center 16.4 µg P/l ± 4.6 16.8 µg P/l ± 5.2 

Sand pores, center 25 µg P/l ± 4.0 23.6 µg P/l ± 5 

Seawater, oiled Abu Ali N-coast 19.25 µg P/l ± 6 11.51 µg P/l ± 3.5 

Sand pores, same location 141.0 µg P/l ± 60 31.4 µg P/ l± 8.6 

Sand pores Abu Ali NE end 46.54 µg P/l ± 9.4 26.2 µg P/l ± 6 

The concentrations of phosphate in sea water 1992 were not significantly different for 

affected and unaffected sites (CEC/NCWCD 1992). Eight years later, the concentrations 

were in the same range. The concentrations of phosphate in pore water of sandy sediments 

decreased significantly in the years after the oil spill, as it is shown tab. 6.8. The higher 

values in 1992 could not be explained. Anoxic conditions often lead to limited nutrient 

concentrations in pore water of oiled sediments. That is why rather lower concentrations 

were expected. The pore water values of clean sediments might be above the sea water 

concentration because of dissolution of phosphate from shell debris, which is abundant in 

most of the coastal sediments. 

Nitrate concentrations are generally below detection limit which is no surprise regarding the 

mostly anoxic conditions in oiled substrate. 

The oxygen content of the groundwater in most salt marshes and low energy shores is 

dependent on whether the soil surface is sealed or not. Measurements taken in 2000 and 2002 

183


demonstrated that below tar crusts, and especially below extensive laminated cyanobacteria 

mats, the groundwater is poor in oxygen. Between 1992 and 1993, measurements carried out 

by Böer (1994) demonstrate a correlation between plant condition and oxygen concentration 

in the groundwater. At Avicennia, Arthrocnemum and Halocnemum sites the condition of the 

plants was better, the higher the oxygen concentration of the groundwater was (Böer 1994). 

Tab. 6.69 Groundwater oxygen and resulting plant condition. 

O2 saturation in % plant condition 

34 all living 

5 some living 

51 all living 

4 all dead 

1 all dead 

2 all dead 

2 no plants 

2 no plants 

1 no plants 

100 open water 

Data: Böer 1994 

Measurements in the Avicennia site (which is considered to be completely recovered) in 2002 

reveal groundwater saturation values for muddy soils between Avicennia marina stands and 

Arthrocnemum stands of 11-45%. The mean value for all 15 measurements is 27.8% (sd. 9.7). 

The main oxygen source for the groundwater in salt marshes is the sea water covering the soil 

surface and more effectively (due to the fine grained sediments) the countless burrows of 

crabs, polychaetes, and other benthic life forms. 

The total ionisation of the ground water, expressed by its electric conductivity, shows a 

general trend at all measured salt marsh sites from seawater concentrations (60-70 mS/cm) in 

the lower intertidal to increasing values towards the littoral fringe. During the winter period, 

the salinity gradient is comparable to the summer situation, but the values are between 10 and 

30% lower, reaching their minimum in January. The decrease in ion concentration is mainly 

caused by a lateral groundwater flow from adjacent sand sheets towards the sea. In the winter 

period, precipitation infiltrates in the sand sheet areas and provides a certain amount of fresh 

water to the saline groundwater which flows in seaward direction. Additionally, rainwater 

penetrates the fine grained salt marsh sediments through the network of crab burrows. In 

184


summer, high evaporation concentrates the groundwater eventually increasing its salinity. 

Fluctuations of the individual constituencies depend on evaporation, temperature changes 

(annual amplitude of 23°C), and the resulting solution- and crystallisation processes (i.e. 

NaCl, KCl, CaSO4, CaCO3). PH level is only of minor importance because it remains constant 

most of the time (7.2-7.8). These variations of ground water salinities affect the salt marsh 

plants and are responsible, together with inundation characteristics, for the zonation of the 

different vegetation types in the upper intertidal and the lower supratidal. 

Hydrocarbon analysis by the means of GC spectra of groundwater along the salt marsh test 

sites (Halocnemum and Arthrocnemum) and along the Avicennia test site (chapter 6.2.1) were 

carried out by Smith 1994. They showed that there is no movement of contaminated 

groundwater from the oiled areas towards non-oiled sites at fine grained low energy salt 

marsh sites. This is no surprise, because the groundwater flow is towards the sea. In the 

intertidal, especially in the lower part, the ground water is being mixed with seawater, which 

means that hydrocarbon concentrations would be reduced. Regarding the processes of oil 

degradation, no direct influence of the ground water chemistry could be observed. Although, 

there may be effects on oil degrading microorganisms which are present in these semi sub- 

hydric salt marsh soils. 


The high water content of the salt marsh soils meliorate the daily amplitude of temperature. 

During night heat is emitted by the wet soils. Ecologically more important though, is the 

reduction of the surface temperature during day time by evaporation. Tar crusts, as well as 

cyanobacteria mats, affect the micro climate of salt marshes in a negative way. The 

permeability of the soil surface is reduced to almost zero. Therefore, the above mentioned 

influence of moisture retained in the top soil is minimised. Additionally, the heat absorption is 

increased by the hydrocarbon material itself and the dark colour of the oiled surface 

substrate. Even in 2001, the temperatures above tar crusts (by now of a light grey colour) 

were generally 2-5°C higher than above the non oiled sediments (values refer to 35°C air 

temperature, low wind and clear sky). In 1994, the difference under the same climatic 

conditions was 4-8° (darker grey and hydrocarbons not as dry as 2001). Watt (1994) reports 

temperatures above tar layers as much as 10-15°C higher than those found on the adjacent 

clean sediment. Mahmoud et al. (1983) and McMillan (1971) show that high temperatures 

significantly affect the germination success of salt marsh plants. As temperatures in summer 

are already extreme (up to 55°C surface temperature and 48°C in 5 cm soil depth), and the 

185


salt marsh vegetation is surviving close to its maximum temperature range, these elevated 

temperatures are critical to both, the surviving plants and the germination of young 

individuals. For plants adapted to extremely hot environments, the maximum temperature for 

photosynthesis is about 50°C (Adams 1990). At 65°C plasma will be irreversibly destroyed 

(Adams 1990). This means that the increased temperatures, especially during the first two 

years after the oil spill, most probably contributed to the loss of surviving individuals of 

Halocnemum strobilaceum and Arthrocnemum macrostachyum until 1994. The continuous 

investigations on the growth of cyanobacteria mats demonstrates that they are not at all 

susceptible to temperatures above 60°C, which was assumed by Watt (1994). 

The high environmental variability in the upper intertidal zone is reflected in pronounced 

changes of biota abundance as well as breeding behaviour and recruitment. For example 

juvenile Cleistostoma dotilliforme crab shows a significantly higher abundance in the upper 

eulittoral in the winter months (Apel 1994), when conditions are more favourable. 


According to Gale (1975), the combination of high salinity with high temperatures is the most 

important stress factor for the vegetation in the salt marsh areas. The vegetation shows a 

pattern which strongly correlates with the soil humidity, as well as with the salinity of the 

ground water and/or the soils. Thus, both are limiting ecoparameters although they are related 

to each other. The threshold salinities that plants like Halocnemum strobilaceum, Halopeplis 

perfoliata, and Limonium axillare are able to tolerate are slightly below the 10% given by 

Denffer (1983) for seacoast plants and vegetation of salt pans (Böer 1994). Additionally the 

large diurnal temperature differences (20°C), as well as annual differences in temperatures 

(min. 3°C, max. 51°C ), pose another environmental stress factor. The oil impact, apart from 

posing an additional stress factor (toxic substances) had two more negative effects. First, it 

reduced the oxygen availability in the salt marsh soils, and second, it increased the soil 

surface temperatures, thus changing the micro climate to the disadvantage of the investigated 

vegetation types. 

Most of the oiled areas show some patches where some salt marsh plants survived. Besides 

possible toxic effects of the oil, the sealed surface (tar and cyanobacteria) prevented the 

penetration of oxygen and therefore reduced the redox-potential of the water saturated soils. 

The amount of dissolved oxygen which is necessary for the root tips to survive has not yet 

been clearly defined (Böer & Warnken 1992). But it is assumed, that the gradual die-off of 

surviving Arthrocnemum and some Halocnemum until 1994 (after increased seed production) 

186


is caused by oxygen depletion in the soil (possibly in combination with raised temperatures at 

the sediment surface, see microclimate). Resettlement by these Chenopods only occurs 

where the oiled substrate is softened due to bioturbation by crabs. 

6.1.9.6 Fauna 

In the two years after the oil spill, almost all macrobiota was absent in the upper intertidal 

between the HWS and HWN. Especially striking was the complete extinction of the large 

Cleistostoma colonies which consisted of millions of individuals. In summer 1991, 

sporadically frequented Cleistostoma burrows have been found in oiled areas (Höpner, pers. 

comm.) Further observation showed their disappearance in the following months. Thererfore 

the few animals must have been survivors instead of pioneers. Some of the old Cleistostoma 

burrows (30-40 /m²) are now (1993-2000) inhabited by Metopograpsus messor as shelter (a 

crab which does not burrow and seems ubiquitous in all habitat types). Occasionally, 

Metopograpsus messor and Macrophthalmus depressus were observed in the eulittoral zone 

(Apel & Türkay 1992). Scopimera crabricauda was missing on all polluted beaches (typical 

for sheltered sandy beaches) whereas it was extremely abundant on unpolluted control sites. 

A complete species list compiled by Apel & Türkay (1992) one year after the oil spill is 

provided in the appendix. Cyanophyta were the only biota rapidly colonizing the oiled areas 

in 1992. 

According to Jones et al. (1994) and Apel (1994), the important key species of the littoral 

fringe and the upper eulittoral (the most affected areas) are: (Crustacea) Cleistostoma 

dottiliforme Metopograpsus messor and Scopimera crabricauda, (gastropodes) Pirinella 

conica and Mitrella blanda, (barnacles) Euraphia sp. 

In the mid eulittoral the key species are: (Crustacea) Macrophthalmus depressus and 

Ilyoplax frater; (gastropods) Pirinella conica, Mitrella blanda and Cerithium cingulata; 

(bivalve) Dosinia hepatica. 

Important key species of the lower littoral are: (Crustacea) Metaplax indiaca, 

Macrophthalmus depressus and Ilyoplax frater; (gastropods) Pirinella conica, Cerithium 

cingulata, Mitrella blanda; (bivalve) Dosinia hepatica, Solen vagina, Macrocallista 

umbonella. 

The first settlement of burrowing animals was observed in 1992 (Jones et al.). The polychaete 

Perinereis vancaurica, as well as Nereis sp. and some newly settled juvenile crabs of 

Cleistostoma dotilliforme. But these were observed at a salt marsh near the mangrove site 

187


(6.2.1), which was by far not as heavily oiled as most of the other salt marshes. The numbers 

of polychaetes in the salt marsh environment remained low even until 2001. These numbers 

and the low species diversity of Polychaeta in salt marshes is due to the high density of the 

substrate due to the low grain size, which inhibits penetration and building of burrows 

naturally. Higher numbers occur in sand mud or sand habitats, but in any case population 

densities do not reach the numbers of comparable habitats in temperate seas (North Sea) 

(Fiege 1992). 

The recruitment into the soft sediment shores of the salt marshes is documented by Jones et 

al. (1994). These observations indicate significant recovery processes for most test sites until 

1994, although population patterns do not show clear trends. This might be attributed to 

predator-prey imbalances, with marked oscillations in species population dynamics after the 

oil impact. Such was reported by Southward & Southward (1978) after the Torrey Canyon oil 

spill. But comparison with the described test sites (6.1.1.-6.1.8) demonstrate that, regarding 

the macrofauna, large zones in 2002 are by far not recovered. The abundance of key species 

that were observed by Jones et al. (1994) are much higher compared to counts in 2001 and 

2002. 

Counts of crab burrows reveal useful information about the state of recolonisation by crabs. 

The total number of individuals per m² is probably higher, since juveniles are often found 

associated with adult burrows (Apel 1994). Within most salt marshes there are more or less 

wide zones (40-300 m) devote of any macrofauna. Active crab burrows were generally 

observed near and seaward of the HWN, landward of the HWS, and along tidal channels. 

Where there are crab burrows in the area between the HWN and HWS, the regeneration 

actively takes place. The typical numbers of crab burrows of 20/m² in such an environment 

(Apel 1994) are rarely found between the high water levels. 

It was generally observed that bioturbating organisms, especially crabs, colonize oil affected 

zones some years before macrophytes. This is the result of the establishment of cyanobacterial 

mats and, or the presence of hard surface crusts which prevent the germination of 

Arthrocnemum or Halocnemum. The only organism effectively able to remove the crusts as 

well as the cyanobacteria are crabs, mainly Cleistostoma dotilliforme. Colonisation by crabs is 

hindered by a heavy oil load (low degree of degeneration) within the top soil sediments and 

by a substrate too hard for burrowing activities. The results collected at a variety of different 

salt marshes (i.e. Bombcrater Bay transect no. 2, chapter 6.1.5) indicate that Ilyoplax frater 

and Macrophthalmus depressus do not mind a certain amount of oil, as long as it is not 

188


distributed within the whole soil column. Cleistostoma dotilliforme was only once found in 

between oiled sediments (north of the site described in 6.1.3). 

An important factor is the hardness of the surface substrates. Penetration resistance and 

vane shear force of sediments was never before used in determining limiting factors for crab 

burrowing activities. Most of the sediments between the HWN and HWS that were soaked by 

oil and later exposed to sunlight changed the structure during the following years. The upper 

3-6 cm became more compact, much harder and display today a large granular structure. 

Measurements of penetration resistance mostly displayed values between 2 and 4 kg/cm² 

and shear vane force values between 3 and 6 kg/cm². Undisturbed muddy soils in contrast 

are characterised by 0.1-0.5 kg/cm² and 1-2 kg/cm², respectively. The measurements 

obtained during the salt marsh surveys indicate a maximum penetration resistance of 1.4 

kg/cm² and a maximum vane shear force of 2.7 kg/cm² in populated substrates. Values in 

densely populated colonies are much lower. Therefore, it must be concluded that the 

penetration ability of the sediment is a major factor controlling recolonisation by crabs. 

Tidal channels are the initial paths of recolonisation by crabs. Because of clean sediments 

within the channel, these are well populated. Soft sediments at the edge of the channels can be 

entered by crabs, which try to break through the hardened surface substrate at different places. 

At some places the break through might succeed. Then oxygen can penetrate the oiled 

sediment below the tar, and the oil degradation is accelerated. Following this pattern the crabs 

will successively penetrate the sediments to both sides of the channel. How fast this 

“subsurface-breaking-through” technique succeeds depends on the hardness of the surface 

material or cyanobacteria mat, as well as on the amount of badly weathered oil within the 

substrate. Areas with a dense network of channels are generally in an advanced state of 

regeneration compared to salt marshes with less or without tidal channels. The latter are the 

slowest to become resettled by crabs. 

189

6.2 Mangroves 

Mangroves are - like the salt marshes - an essential part of the characteristic habitats found 

along the shores of the Saudi Arabian Gulf, although they occur only sporadically at sheltered 

soft bottom sites. Compared to 190 km of the coastline in the study area, which is dominated 

by salt marshes, only 6 km is covered by mangroves (fig. 6.67). These habitats are composed 

of only one mangrove tree, Avicennia marina (Forssk.) Vierh. They generally occur in 

association with salt marshes. Tidal channels are widely distributed among the mangrove 

trees. Most mangroves located along those tidal channels were affected by the oil spill. Trees 

in greater distance to channels were only rarely reached by the oil. In total, about 50% of the 

trees were oiled and around 30% died off immediately or during the following years. 

Fig. 6.67 Distribution of mangrove habitats within the study area. 

6.2.1 Mainland transect 

mangrove 

areas 

0 5 10 km 

49°20’ 49°30’ 

ARABIAN GULF 

This location (27°08’47” 49°23’18E”) is a group of little islets, which are separated from each 

other and from the beach by tidal channels. The sheltered islets are dissected by tidal creeks 

and countless pools. This environment is habitat of mangroves (Avicennia marina), 

Arthrocnemum salt marsh and associated fauna. Tidal inundations of the most seaward edges 

of Avicennia stands vary between 40 and 55 each month. In the more central parts of the islets 

this number is reduced to about 30 inundations. The larger tidal channels are between 20 and 

30 m wide and in maximum between 50 and 200 cm deep, according to the tides. Due to the 

sheltered location, this habitat was only moderately impacted by the oil spill. 

N 

27°20’ 

27°10’


0 5 10 km 

49°20’ 49°30’ 

ARABIAN GULF 

N S 

channel 

Fig. 6.68 Mangrove transect on the western shores of Dawhat ad-Dafi. 

locations 


m 0 45 80 86 88 100 

The situation in 1992 

In 1992, life was extinct along the banks of the tidal channels and creeks. Roots of Avicennia 

marina growing in the creeks were oiled and rotted (Höpner 1992). The mud around the roots 

had an oil burden of 0.11 kg/m² (Höpner 1992). At the upper eulittoral, the hydrocarbon 

contamination was more intense. The oil crust on top of the sediment broke physically at the 

bank of the larger tidal channels. 

10 cm 

20 cm 

30 cm 

sand silt / clay oil reduction calcified crab 

burrows 

mud tar crust burrows shell fragments 

N 

27°20’ 

27°10’ 

191


On the highest stations (supralittoral) of this mangrove transect, the populations of 

Cleistostoma dotilliforme (measured by counts of fresh and oiled burrows) were reduced by 

50% (Jones & Richmond 1992). Arthrocnemum was also badly damaged. Wherever 

Avicennia marina and Arthrocnemum macrostachyum were located next to each other while 

receiving the same amount of oil, A. marina was less affected and in a better shape (Böer & 

Warnken 1992). If not completely dead, Arthrocnemum developed new green sprouts with an 

intact, fresh bark extending down to the root system (Böer & Warnken 1992). The same 

observation seemed true for Halocnemum strobilaceum. Although many trunks of Avicennia 

were oiled to a height of 50 cm, many plants looked healthy with signs of germinating 

seedlings. Some of the plants died in the following years and successful establishment of new 

seedlings was observed from 1994 on. 

In the upper eulittoral the shores were heavily contaminated and Cleistostoma populations 

extinct. The mid eulittoral revealed the presence of macrobiota consistent with the habitat 

type but often sparse in numbers of individuals and species diversity. Towards the lower 

eulittoral, the diversity and numbers increased in all cases. At the sublittoral fringe the biota 

appeared healthy and uncontaminated (Jones & Richmond 1992). 

6.2.1.1 Soil characteristics and oil contamination assessment in 2001 

The following sections will be presented as tables and additional information is given in 

separate remarks. The first section is located at the channel edge 30 cm below the HWS. 

Tab. 6.70 Section 1 at the 0 m mark of the mangrove mainland transect. 

0 m 


0.3-3 cm: beige fine sand poor in CaCO3 (2.1%) 

3-11 cm: beige silty sand; visibly oiled; total hydrocarbon concentration: 13.4 

g/kg; well weathered oil residues; no colour in rapid assessment 

print; relic crab burrows 

11-18 cm: grey silty sand 

18-30 cm: grey sand; relic crab burrows containing sticky oil residues; at 20 cm 

depth the hydrocarbon concentration within an oiled crab burrow is 

15.7 g/kg; oil residues sticky and only slightly weathered as 

displayed by the dark brown of the oil print (fig. 6.69); 4 cm beside, 

within apparently clean mud the hydrocarbon concentration is 6g/kg 

30-50 cm: dark grey sand; crab burrows containing some oil until 45 cm 

calcium carbonate concentration: at –20 cm: 13.1% 

192


Remarks: 

Remarkable burrowing activity by polychaetes is obvious. Crab burrows are present, but not 

in the usual numbers. They occur in larger numbers on the higher shore (10 cm below the 

HWS) 2 m further inland. A new crab burrow dug into the same sediment can be seen in 

photo 6.26. The pale colour directly beside the new burrow is visible. There, oxygen allowed 

oxidation processes, removing the darker grey shade. This indicates the importance of 

bioturbation in the anoxic environment to allow microbial activity and hence degradation of 

the oil. Further to the east there are some channels, the shores of which show comparable 

soils. 


45 m 

light beige colour due to oxidation 

oiled crab burrow 

dark shade due to anaerobic milieu 

Photo 6.26 Oxidation around a new crab burrow changes the 

grey colour of the sediment into a beige. 


0.3-3 cm: beige silt; CaCO3 (21%) 

3-40 cm: light grey silt; containing some shells and shell fragments below 20 

cm depth; no oil visible; total hydrocarbon content in 10 cm depth: 

0.9 g/kg 


-20 cm: 31.6% 

Remarks: 

The section is located at the southern side of the first island between two large channels at 

the 45 m mark. It is again 30 cm below the HWS, comparable to the first section. The 

material there is more wet and therefore instable. 

193



80 m 

Remarks: 

This section is located at the southern side of the second island. It is also 30 cm below the 

HWS. A large amount of crabs colonise this area as well as gastropods and some 

polychaetes. 

Between section 3 and 4 the HWS is clearly visible due to a little cliff. This 10-15 cm high cliff 

is cut into compacted and partly calcified mud, which was originally soaked by oil. The oil is 

still visible as a hard, thin grey surface crust, which is periodically covered by cyanobacteria. 

In front of the cliff, calcified crab burrows that were exposed by erosion of the surrounding 

sediments indicate the former extent of the hard substrate layer (photo 6.27). From the edge 

of the cliff the hard crust covers a one to three metre wide band of hardened sediment. 


86 m 

Remarks: 

In most cases the surface crust is still too hard for crabs to penetrate. Therefore, new crab 

burrows are rare. But immediately next to the surface crust, the substrate is softer and densely 

populated by crabs. Between the dry, dead Arthrocnemum macrostachyum new individuals 

germinated. 


88 m 


0.3-15 cm: light grey silty sand; no oil; dark patches due to reduction processes 

between 3 and 10 cm depth 

15-40 cm: light grey silt; containing shells and shell fragments below 20 cm 

depth; no oil visible; 


-20 cm: 40.6% 

0-0.3 cm: cyanobacteria, dry and partly peeling off 

0.3-1 cm: grey hardened tar crust 

1-4 cm: compact, hard silt, displaying a light brown colour due to well 

degenerated oil; the hydrocarbon concentration is 16.3 g/kg 

4-10 cm: calcified crab burrows within the sandy silt 

10-30 cm: grey sandy silt 


-20 cm: 52% 

0-2 cm: dry, light brown silty sand due to well degraded oil residues 

2-16 cm: light grey silty sand; containing shells and shell fragments below 20 

cm depth; 



-20 cm: 35.6% 

194


Remarks: 

The zone of oiled and hardened sediment turns into an extremely well bioturbated 

Cleistostoma colony. The remains of some dead Arthrocnemum plants are the only signs of 

the former destruction. 


100 m 

Remarks: 

The section is located between Avicennia marina trees and some Arthrocnemum individuals. 



Fig. 6.69 Rapid assessment oil prints of mangrove samples. 

The following figure summarizes the distribution of oil residues within the mangrove soil 

between 1992 and 2001. 

depth in cm 

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 

0 

-2 

-4 

-6 

-8 

-10 

-12 

no data for 1992 

0-4 cm: light grey silt with plenty of organics (leaf residues) 

4-40 cm: light grey silt; dense network of crab burrows and mangrove roots 


oil distribution in 2001 oil distribution in 1992 

Fig. 6.70 Distribution of oil residues within the mangrove soils in 1992 and 2001. 

The soil water content of the sediment in the mangroves is relatively homogeneous and varies 

between 27 and 35% with the higher values below 10 cm soil depth. 

195




The electric conductivity is given for the coastal station (0 m mark) and the central mangrove 

station (100 m mark). Additionally seawater values in the tidal channel (separating the 

mangrove island from the coastal station) are displayed. There is a slight general trend 

towards higher values during the warmer months. The seawater shows the lowest variation 

and varies between 80 and 88 mS/cm. Except in December, the mangrove groundwater is 

clearly more mineralised than the seawater. Between January and March, the mangrove 

groundwater shows higher values than the coastal station. The reason for the development 

of the electrical conductivity at the coastal station is not clear, but it is assumed that it is 

influenced by the rainwater which is able to percolate in the more sandy substrate there. The 

significant increase in April is due to the increased evaporation adjacent to the coastal 

sabkha. 

mS/cm 

120 

100 

80 

60 

40 

20 

0 

Dec Jan Feb Mar Apr 

coast 

island 

channel 

Fig. 6.71 Electric conductivity of selected stations between December 2000 and April 2001. 

Regarding sulphate, the trend towards higher ion concentrations during the warmer months 

of the year becomes more obvious (fig. 6.72). The island concentrations are between 10 and 

20% higher than the seawater concentrations in the channel, but they correlate precisely with 

the fluctuation of the seawater. The concentrations at the coastal station seem to be less 

related to the seawater. The winter values are much higher displaying a decrease until 

March, when they drop below the seawater concentration. This phenomenon was also 

observed at coastal sabkhat described by Barth (1998). Gypsum crystallisation or solution as 

a controlling factor like in sabkhat was never observed in intertidal environments, but it can 

not be ruled out. 

196

SO4-- / mg/l 

14000 

12000 

10000 

8000 

6000 

4000 

2000 

0 



coast 

island 

Fig. 6.72 Sulphate concentration of selected stations between December 2000 and April 2001. 

Calcium concentrations remain almost constant for all locations between 1000 and 2000 

mg/l, and Magnesium shows an increase of about 1000 mg/l (data in appendix 2) in April. 

Ammonium, nitrate, and nitrite were minimal or below detection limit. Groundwater 

temperature is closely related to the seawater temperature in the channel. The only 

exception is the strong increase of the seawater temperature in April, due to solar radiation 

and high air temperatures. The groundwater needs more time for the warming, due to slow 

water exchange. 


35 

30 

25 

20 

15 

10 

5 

0 


see 

coast 

island 

Fig. 6.73 Groundwater temperature of selected stations between December 2000 and April 2001. 

Generally, there is not much difference in groundwater composition and the annual variation 

compared to the salt marsh ecosystems below the mean high water mark. 

Measurements of the groundwater oxygen content in 2002 revealed groundwater saturation 

values for muddy soils between Avicennia marina stands and Arthrocnemum stands of 11 – 

45%. The mean value for all 15 measurements was 27.8% (sd.= 9.7) (tab.6.76). These values 

are close to normal and significantly higher than what was measured by Böer (1994) in 1993 

where groundwater saturations of 1 and 2% occurred below tar surface crusts. The main 

see 

197


oxygen source for the groundwater in mangroves is the sea water covering the soil surface and 

more effectively (due to the fine grained sediments) the countless burrows of crabs, 

polychaetes and other benthic life forms. 

Tab.6.76 Oxygen saturation in Avicennia/Arthrocnemum site in 2002. 

Measurement 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

O2 saturation 11 27 18 45 24 38 34 18 40 25 26 33 15 29 34 

in % 

6.2.1.3 Micro climate 

Temperature 

The temperature profiles measured in the mangrove area demonstrate that, compared to the 

terrestrial coastline, the climate on the mangrove islands is milder during warm periods 

although the interstitial spaces between the individual trees are wide. Measurements in the 

mangroves were taken at open spaces between the trees. The temperature differences, 

especially in the top soil, become more pronounced the higher the air temperature is (fig. 

6.74). Due to the wet surface soil, the surface temperature does not reach the high values of 

dry salt marsh soils. The difference between air temperature and soil surface temperature is 

usually below 5°C. 


15 20 25 30 35 40 45 

50 

20 

10 

5 

0 

-5 

-10 

coast Feb 

island Feb 

coast Apr 

island Apr 

Fig. 6.74 Temperature profiles of the coastal and mangrove island location in February and April 

2001. 

198



The coastal fringe in front of the first channel is dominated by a Halocnemum strobilaceum 

saltmarsh in association with Halopeplis perfoliata. The plants cover about 30% and are 

medium in size. Halopeplis is between 10 and 30cm in diameter and Halocnemum between 

30 and 60 cm. Most plants accumulate fine sand and form little nabkhat. The area in between 

is covered by a salt crust which turns into a brain like crinkled cyanobacteria crust 15 m 

before the channel is reached. Occasionally 3-5 years old (50 cm high), Avicennia individuals 

are distributed along the edge of the channel. 

On the island there are also some young mangrove trees (3-5 years old) distributed along the 

channel edge. It is interesting to note, that before the oil spill there were no mangrove trees so 

close to the main channel. The first trees occurred 10 m further inland. But already in 1992, 

Avicennia seeds and seedlings were observed along the branching secondary and tertiary 

channels (Kinzelbach et al. 1992). Only a few of them succeeded to establish themselves in 

1992. They were more successful after 1994. The maximum observed height of Avicennia 

trees is 2.2 m, but the median height is about 1.3 m. Along the channel edges, dense stands of 

Salicornia europaea cover the muddy sediments. The first new establishment of Salicornia 

was observed in 1993 (Böer 1994). But it took until 1996, until densities of more than 100 

plants per m² were reached at these sites, comparable to non oiled sites at Batina Island and 

Tarut Bay, south of Jubail. 

Arthrocnemum macrostachyum was in poor condition in 1992, and the living plants declined 

35%. However, by June 1993, more than 90% of the plants in the impacted areas were dead 

(Jones et al. 1994). In 2001, the surviving Arthrocnemum can easily be recognized because of 

the large parts of dry dead plant material. 

In 2001, the mangroves cover between 2 and 10% of the area, except in clusters of non oiled 

mangroves, where a plant cover of up to 60% is reached. The lower cover is mainly due to the 

size of juvenile plants in the area of regeneration. Arthrocnemum, in contrast to Salicornia, 

has not yet reached its normal cover which is between 5 and 30%. But at most locations, 

young and new germinated individuals are present. 

199

6.2.1.5 Fauna 


In contrast to other tropical areas, the Bostrychietum, an epiphytic algal association typical on 

pneumatopores and tree trunks, was not present in 1992. This did not change until 2001. In 

1992, the pneumatopores were mostly covered by cyanobacteria (Coppejans 1992). This was 

only occasionally observed in 2001. 

The important key species of the mangrove habitats, Cleistostoma dotilliforme, Euraphia sp., 

and Macrophthalmus depressus all represent numbers that indicate a complete recovery of the 

habitat in 2001. The work of Jones et al. (1995) already showed that this site was recovered in 

1994 regarding species diversity and abundance. Species diversity of the mid and lower 

eulittoral reached normal values (mean values of control site over 4 years) in 1993 and at the 

littoral fringe in 1994 (fig. 6.75). Only the upper eulittoral displayed still slightly lower 

diversity than the control but with gradually increasing values. Abundances apart from the 

littoral fringe all reached or exceeded the control mangrove levels. The higher abundances in 

1994-1995 are due to the settlement of the tubiculous polychaete Owenia sp. 

Abundance (no./m²) 

1200 

1000 

800 

600 

400 

200 

0 

2018 

1991 1992 1993 1994 1995 

1200 

1000 

800 

lo. 600 eulit. 

u. eulit. 

400 

lit. fr. 

m.eulit. 

200 

littoral fringe upper eulittoral 

mid eulittoral low er eulittoral 

0 

control site (mean over 4 years) 

species diversity 

16 

14 

12 

10 

8 

6 

4 

2 

0 

1991 1992 1993 1994 1995 

16 

u. eulit. 

14 

lo. eulit. 

12 

m.eulit. 

10 

lit. fr. 

8 


mid eulittoral lower eulittoral 

Fig. 6.75 Species diversity and abundance between 1991 and 1995 (data: Jones et al. 1995). 

Apel (1994) studied the crustacea within this habitat between 1992 and 1994. According to 

Apel (1994) the species diversity in 1993 was slightly reduced compared to non-oiled control 

sites (7 species compared to 8). But the species distribution shows marked differences. There 

were no living animals at the littoral fringe. Whereas in the upper eulittoral large numbers of 

juvenile C. dotilliforme were found underneath the polygonal cyanobacteria mats there. 

Similar densities were never observed at any of the control sites. The reason for this unusual 

6 

4 

2 

0 


200


accumulation might be the unfavourable conditions at the higher shores and probably a lack 

of competition by other species like P. arabicum (Apel 1994). Other species, except Ilyoplax 

frater, were only rarely observed. Figure 6.76 displays the distribution of the intertidal 

ocypodid fauna between an unoiled control and this transect in May 1993. 

Abundance 

500 

450 

400 

350 

300 

250 

200 

150 

100 

50 

0 

lit.fringe 1 2 lower 3 4eulittoral 5 lit.fringe 1 2 3lower 4eulittoral 5 

Illyoplax stevensi 

Metopograpsus 

messor 

Ilyoplax frater 

Paracleistostoma 

arabicum 

Cleistostoma 

dotilliforme 

Fig. 6.76 Species distribution and abundance in 1993 at a control site and the mangrove transect 

(data: Apel 1994). 

The condition of the macrofauna at this transect seems normal in 2001, except at two narrow 

belts of hardened surface substrate where species abundances are still reduced. Two metres 

above the 0 m mark of the transect, the surface sediment is clean until 4 cm depth where 

there is still an oiled horizon. These sediments were only scarcely populated in 1996. Three 

years later, a high number of polychaetes (mostly P. vancaurica) were present in the oiled 

substrate, as well as in the clean sediment above. In 2001, the same location showed plenty of 

crab burrows (Cleistostoma dotilliforme, 8-15 burrows/m²), whereas in 1999 they were rarely 

found. The number of polychaetes decreased, compared to 1999. 

At the 80 m mark, the population of crabs (Ilyoplax frater) seems normal with 20 burrows/m². 

Seaward there are smaller burrows (>0.5 cm). The amount is 25 burrows/m² in average. In the 

vicinity of the first pneumatopores (78 m mark) there are 27 burrows/m² (sd.= 4.2) in average. 

The density of pneumatopores lies between 10 and 46/m² (mean=30.4, sd.= 14). In the 

hardened and calcified band of sediment, new crab burrows are rare. Adjacent to the hard 

surface crust, Cleistostoma dotilliforme burrows reach a density of 29.4 (sd.= 10.3) 

burrows/m², although the sediment still contains some oil residues. 

201


At the 100 m mark, there is a pronounced relief of channels and mounds that can be attributed 

to the activities of the Cleistostoma dotilliforme. The burrows are restricted to the elevated 

areas. The burrow density is now in average 39.4 (sd.= 9). Between 98 and 120 m the relief 

displays a clear linear structure (photo 6.27 A). This linear structure changes then into a 

polygonal structure (photo 6.27 B). So far there is no explanation for this phenomenon. The 

density of Cleistostoma burrows in the polygonal structured area decreases slightly to 26.2 

(sd.= 5.3). Penetration resistance and vane shear force of the muddy sediments between the 

mangroves show normal values of 0.61 (sd.= 0.33) and 0.22 (sd.= 0.07) respectively 

(comparable to values from unpolluted control sites). 

A 

B 

Photo. 6.27 Linear (A) and polygonal (B) structures within the Cleistostoma burrow relief. 

202

6.2.2 Qurmah Island transect 

This location is the most heavily impacted mangrove shore within the study area. It is located 

on the south western side of Qurmah Island in Dawhat ad-Dafi at 27°07’59”N 49°29’14”E. 

Most of the western shores of the island are colonised by Avicennia marina. The study site is 

a dense mangrove stand, dissected by a dense channel network and protected towards the 

north by a 50 m long sand spit. 

SW 

0 5 10 km 

Fig. 6.77 Transect on Qurmah Island. 

HWS 

49°20’ 49°30’ 

ARABIAN GULF 

m 0 5 8 11 21 31 

N 

27°20’ 

27°10’ 

sand silt / clay oil oiled crab burrows 

mud burrows shell fragments organic components 

NE 

5 cm 

10 cm 

20 cm



The following sections will be presented as tables and additional information is given in 

separate remarks (soil texture data in appendix 8). The first soil section is located in the 

upper eulittoral. 

Tab. 6.77 Section 1 at the 0 m mark of the Qurma transect. 

0 m 


5 m 


8 m 


0.2-4 cm: light beige sandy silt; no trace of oil 

4-6 cm: dark grey patches in the sediment due to reduction processes; in 

polychaete burrows there are well degraded oil residues. 

6-8 cm: dark grey silt (reduction processes); emits a light hydrogen 

sulphide odour 

8-16 cm: light grey silt; scattered black patches; oil residues present 

(concentrated in polychaete burrows), below 10 cm depth not well 

degraded; emit a strong hydrocarbon odour and are still partly 

liquid 

16-20 cm: grey sandy silt; oil present 

20-22 cm : grey silt; oil free 

22-40 cm: grey sand; plenty of shell fragments and gastropods 

0-0.2 cm: cyanobacteria; some pinnacles 

0.2-2 cm: light beige sandy silt; hardened due to well weathered oil residues 

2-12 cm: light grey silt; oil residues present (concentrated in polychaete 

burrows); oxidation processes stained the sediment adjacent to the 

burrows brown and orange. 

12-25 cm: light grey silt; slightly oiled until 16 cm 

25-40 cm : grey sand; plenty of shell fragments and gastropods 

0-0.2 cm: flat cyanobacteria; shows little polygonal cracks 

0.2-5 cm: light brown sandy silt; hardened due to well weathered oil residues; 

some orange oxidised patches 

5-25 cm: silt; dark grey colour until the depth of 19 cm due to oil residues 

which are medium degraded and concentrated in burrows 

25-40 cm: grey sand; plenty of shell fragments and gastropods 

204


Remarks: 

The third section is located near the HWS. New crab burrows are rare. The penetration 

resistance of the surface material varies between 1.2 and 3.75 kg/cm² (mean: 2.4 kg/cm², 

sd=1.04). Vane shear force varies between 1.8 and 2.7 kg/cm² (mean: 2.3 kg/cm², sd=0.4). 


11 m 

Remarks: 

The surface substrate is soft with penetration resistance values between 0.1 and 1.0 kg/cm² 

(mean: 0.25 kg/cm², sd=0.16) and vane shear force between 0.2 and 0.6 kg/cm² (mean: 0.42 

kg/cm², sd=0.15). The soil is densely populated by crabs and well bioturbated. 


21 m 

0-0.3 cm: flat cyanobacteria; shows little polygonal cracks 

0.3-5 cm: light brown silt; well bioturbated by crabs; no oil visible; plenty of 

organic material such as fermented leafs 

5-40 cm: light grey silt; well bioturbated; no oil present 

0-10 cm: light brown silt; contains a large amount of organic material (4.5% 

of the soil sample weight, the material consisting of the remains of 

roots, leafs and bark). 

10-40 cm: light grey silt, dense network of burrows 

Remarks: 

There is a pronounced relief typical for Cleistostoma dotilliforme colonies. Mineralisation in 

oxygen poor soils is slow even with the aid of intensive bioturbation by crabs. But the light 

brown colour of the upper soil indicates that some mineralisation is taking place. 

6.2.2.2 Groundwater chemistry 

Because this transect was, due to logistic problems, not a permanent study site, no analysis 

was carried out regarding the groundwater chemistry. In April, the electrical conductivity of 

the seawater was 75mS/cm. The groundwater mineralisation along the transect was slightly 

higher, between 83 and 87 mS/cm. The surface water remaining in the tidal pools displayed 

an electric conductivity of 84 mS/cm. 

205



The development of new green leaves was recorded from damaged Avicennia marina trees in 

January1993 (Böer 1994a). Mangroves that survived the oiling developed branched aerial 

roots from the oiled pneumatophores and positively geotropic adventitious roots from the 

stems up to 50 cm above the soil surface (Böer 1994a). The number of branched aerial roots 

correlated with the intensity of the oiling. Oil which covered the pneumatophores often 

entered the tissue through the lenticels and accumulated within the epidermis. In cases where 

the oil penetrated into the endodermis, the section of the pneumatophore above died. The 

section below sometimes survived when it managed to develop new, branched 

pneumatophores. Total cover with bitumen meant the total destruction of the pneumatopore. 

During the first 3 years after the oil spill, also anomalous leaf development was recorded on 

oiled mangroves. New leafs grew directly in the area of the main stem below the normal 

position of the leaf canopy (Böer 1994a). Most plants that displayed the anomalous leaf 

development finally died. 

Examinations carried out by Böer (1994a) showed that the oldest trees on Qurmah Island are 

about 60 years old. Individuals of Arthrocnemum macrostachyum at the same location were 

even up to 95 years old. The mangroves on Qurmah Island are more dense and sometimes 

larger than the mangrove at the transect described in 6.2.1. The largest trees here reach 

heights of 2.5 to 3 metres. 

The mangrove area along the transect showed a variety of conditions during the last ten years. 

Most plants at the seaward fringe of the community died due to the oil load. Only scattered 

Avicennia plants survived with a high number of anomalous branched pneumatophores and 

adventitious roots. Towards the inland, the condition of the mangroves improved 

significantly. The die-off of the damaged mangroves was a slow process that took 2-3 years. 

In winter 1991/1992, only 10% of the trees on Qurmah Island were dead, whereas in May 

1993 the amount of dead trees increased to 25% (Böer 1994). The seaward 20 m fringe of 

mangroves were mostly dead. In 1994 the situation started to change. Aerial photographs 

taken in 1995 during a helicopter flight showed only 20% of dead trees. But this might be due 

to the fact that the dead trees were only hardly visible, regarding the increased vegetation 

cover close to the surface, where Salicornia, Arthrocnemum and new mangrove trees 

established themselves. In 2002, at section 3 new Arthrocnemum macrostachyum occurred, 

not older than one year. They germinated between the dense pattern of mangrove 

pneumatophores. Some of the young Arthrocnemum were seen at the height of section 2, 10 

206


m to the north. Only three metres further inland the dense belt of Avicennia and larger 

Arthrocnemum plants started. The plant cover in healthy stands reaches values of 80%. In the 

outer, oil affected parts the cover lies between 10 and 50%. In 2001, there were only few 

remains of dead plants from the 1991 disaster. 15-30 m further inland there were patches 

between 50 and 100 m² area which have originally been covered by mangroves. Most of them 

died until 1994. There the remains are still visible (photo 6.28). It is interesting that the 

renewed settlement of Avicennia here started only 3 or 4 years ago between 1998 and 1999. In 

2001 the soils were free of oil and densely populated by crabs. Further inland there is no more 

sign of the oil spill, except some scattered remains of dead mangrove trees along some of the 

tidal channels. 

Photo. 6.28 remains of dead Avicennia on severely affected areas on Qurmah Island. Note the 4-6 

years old plants in the foreground. 

6.2.2.4 Fauna 

The Fauna along the transect seems normal without any lasting effects by the oil. The only 

exception is the outer belt of hardened surface substrate between section 2 and 3. This belt is 

between 3 and 5 metres wide, where there is still almost no burrowing activity by crabs 

because of the hard sediment. The density of crab burrows is between 0 and 2 per m². At 

section 4, the population of Cleistostoma dotilliforme (which is the dominating species) is 

higher than what was considered to be normal by Apel in 1994. The density of burrows per m² 

varies between 21 and 45 (mean: 33.3, sd.= 10). There is not much change further inland. 

Species diversity and abundance studies carried out by Jones et al. (1995) indicate a 

regeneration after 1993. Species diversities have returned to normal values until 1995 except 

at the upper eulittoral, which still displayed oiled sediments in 2002. Abundances in 1995 

207


remain lower than normal only at the littoral fringe, where the crab populations were at their 

beginning. This has changed during the following 3 years. Species abundances increased 

rapidly on the lower and mid shore during 1994 due to the settlement by Owenia sp. and 

Dosinia hepatica (Jones et al. 1995). In the upper eulittoral the polychaete Perinereis 

vancaurica and the gastropod Pirinella conica increased in abundance, leading to the high 

values of 1995 (fig. 6.78). It must be noted, that this was an initial recovery pattern not yet 

representing the normal species abundance. Pioneer species, usually r-strategists produce 

large numbers of individuals (as seen in 1995), which decrease in number as other species 

occur and compete for resources. 


1600 

1400 

1200 

1000 

800 

600 

400 

200 

0 

1991 1992 1993 1994 1995 

1600 

1400 

1200 

1000 

u. eulit. 800 

lo. eulit. 600 

lit. fr. 400 

m.eulit. 200 



0 



16 

14 

12 

10 

8 

6 

4 

2 

0 

1991 1992 1993 1994 1995 

m.eulit. 16 

lo. eulit. 

14 

u. eulit. 

12 

lit. 10 fr. 

8 

6 

4 

2 

0 





6.2.3 Mangrove sites - Discussion 

The mangrove habitats within the study area are restricted to a few sheltered locations along 

the shores of Dawhat ad-Dafi and a larger site on Qurmah Island. They belong, together with 

some salt marsh areas, to the most productive ecosystems in the Gulf. Most mangrove sites 

were not as badly hit by the oil as the more exposed salt marshes. But still, on Qurmah Island 

all states of destruction could be seen in 1992 and 1993. Where larger amounts of oil was 

washed ashore, usually a 10 to 20 m wide belt of Avicennia plants died. Groundwater oxygen 

content was significantly reduced due to the sealing of the soil surface. Especially the 

condition of the salt marsh plants was closely related to the oxygen supply. Mangroves, due to 

the presence of pneumatophores, can tolerate at least some level of oxygen depletion in the 

soils (Tomlinson 1986). The mangroves that died all showed pneumatophores that were 

covered by several layers of oil. Böer (1994a) reports that Avicennia marina is able to develop 

208


branched pneumatophores and adventitious roots after the oiling. These enlarge the aerial root 

surface of the plant and thus the number of lenticels for gas exchange. Branching 

pneumatophores and adventitious roots also occur in non oiled habitats but in lower numbers 

(Colennette 1985). Their occurrence clearly correlates with the intensity of the oiling (Böer 

1994a). 

The tar band at the medium impacted site (6.2.1) decreased from 20 m in 1991 to 10 m in 

1992 and 5 m in 1993. In 2002, it is still 2-3 m wide and partly calcified. The cyanobacterial 

mats that established themselves on top of the tar layer decreased from a 20 wide band in 

1992 to 10 m in 1993. In 2002, they cover the remaining tar band. Renewed bioturbation 

began in 1992 and increased in 1993 which means that this site recovered significantly from 

1993 on. Except some narrow belts near the HWS and the mentioned calcified tar band, the 

site can be considered as completely recovered since 1999. This includes normal diversity and 

abundance of fauna as well as the establishment of Arthrocnemum, Salicornia, and Avicennia 

in former densities. At Qurmah Island (6.2.2), this process was slower at several sites due to 

more intense oiling. Descriptions by Jones et al. (1995), as well as studies along more 

impacted sediments between 1999 and 2002, indicate a clear pattern of recolonisation by 

benthic fauna. After low abundances in the initial phase, they explode due to intensive 

settlement of polychaetes. In the following years other burrowing macrofauna, especially 

crabs, follow. The presence of other species lead to competition which reduces the high 

abundance of polychaetes. Then a normal distribution will de established. 

The cliff and the calcified crab burrows at the mainland transect present a unique 

phenomenon which was never again found in the study area (photo 6.29). For some reason the 

material at the oil-sediment interface calcified during the three or four years after the oil spill. 

It is obvious that processes that lead to the formation of calcium carbonate around the crab 

burrows and the sediment surface are related to chemical or biochemical reactions of oil 

biodegradation. CO2 partial pressure variation, pH increase, and carbonate production are 

most likely to trigger calcification. The calcium source can be the seawater as mentioned by 

Höpner (2001, unpublished report) or the calcium carbonate rich sediment. The source of 

carbonate might be the conversion of the hydrocarbon-carbon to carbonate by biodegradation 

processes (mineralisation). Carbon 14 analysis carried out by Höpner (pers. comm., and 2001 

unpublished report) should indicate the amount of fossil carbon incorporated into the calcified 

209


material. But the results are negative, which means that there is no fossil carbon at all in the 

calcified crab burrows. Certainly, the rapid carbon exchange with sea water could be 

responsible for the missing fossil carbon. Despite the fact that a reasonable explanation for the 

calcification processes is still missing it is even more intriguing, why this calcium carbonate 

formation did not happen at other locations as well. 

calcified crab 

burrows 

A 

Photo. 6.29 The calcified oiled sediments which form a micro cliff at the island shore (A). Close up of 

a calcified crab burrow which has been exposed due to the erosion of the fine material (B). 

One possibility could be the combination of sediment characteristics (the presence of fine 

and very fine sand as well as a large amount of silt) of the upper soil layer, the hydrodynamic 

regime (characterized by the large channel – channels of this size occur only at this location), 

and the number of bacteria present in the sediment - usually mud displays bacterial weights 

of 57g/m² compared to fine sand with 5.5g/m² taking the top 5 cm of the sediment (Boaden & 

Seed 1985). 

Bacterial respiration requires an oxidative source. In the sediment this can be dissolved 

oxygen. Once this is utilized, any other organic matter can only be decomposed using other 

oxygen sources such as nitrate, sulphate, and carbon dioxide. These are reduced progressively 

to ammonia, hydrogen sulphide, and methane (fig. 6.79). Once the surface and the crab 

burrows were filled with oil, microbial degradation started in an anaerobe environment 

depending on other oxygen sources. One could have been carbon dioxide dissolved in the 

interstitial pore water. Rapid CO2 consumption by oil degrading bacteria would have changed 

B 

210


the calcium carbonate/carbon acid equilibrium, resulting in calcium carbonate deposition at 

the sediment oil interface. 

Eh pH O2 

-200 0 +200 mV 

6 8 

mg/l 5 10 

H2S 

100 200 mg/i 

Fig. 6.79 Chemical properties in a muddy soil. The redox potential indicates the oxygenation state. 

The zone where, by microbial oil degradation, oxygen could be derived from carbon dioxide is 

highlighted. Carbon dioxide consumption would change the calcium carbonate - carbon acid 

equilibrium, resulting in calcium carbonate deposition at the sediment oil interface. 

Fe 3+ 

2 4% 

Fe 2+ 

CO2 

CH4 

- 

NO3 

- 

NO2 

NH3 

beige 

grey 

211

6.3 Sabkhat shores 

Sabkhat is the Arabic term for salt-encrusted desert. The local terminology of the Arabian 

Gulf region describes the extensive, barren, salt encrusted, and periodically flooded coastal 

flats as well as inland flats (Barth & Böer 2002). Sabkhat are a widespread geomorphologic 

feature in the coastal lowlands of Saudi Arabia. Sabkhat which are bordered by tidal flats 

usually display several sabkhat types according to the frequency of inundation by seawater. 

According to the sabkha classification by Barth & Böer (2002), the typical succession is 

inland sabkha – supralittoral sabkha – coastal sabkha. The coastal sabkha finally turns into a 

tidal flat. High salinity prevents vegetation from growing in the supralittoral zone, as well as 

along the littoral fringe. Sabkha shores are bare of any vegetation. In some cases salt marshes 

can be found adjacent to coastal sabkhat. The environmental conditions, apart from the 

absence of vegetation, are quite similar to the salt marshes if fine sediments are dominant or 

to low energy sandy shores if sand is the dominant substrate type. According to the sediment 

type, the oil distribution as well as the benthic fauna is comparable to either salt marshes or 

low energy sandy shores. Therefore, the sabkha shores are not treated in detail. One example 

which is typical for this coastal type is presented here. 

0 5 10 km 

49°20’ 49°30’ 

ARABIAN GULF 

Fig. 6.80 Distribution of sabkha shores within the study area. 

The site is located at 27°17’15”N / 49°18’52”E, south of Dawhat al Musalamiya and the 

Nuquriya Peninsula. The coastal sabkha is about 2 km wide with sand sheets adjacent to the 

north as well as to the south. The Arabian Gulf is situated to the east (fig. 6.81). 

N 

sabkha shores 

27°20’ 

27°10’

5 

W 

cm 

10 

15 

20 

25 


Fig. 6.81 Location of the sabkha shore transect. 

The sections will be presented as tables. Additional information is given in separate remarks. 

Tab. 6.82 Section 1 at the 0 m mark of the sabkha transect. 

0 m 

Remarks: 

There is no driftwood or thrashline indicating the littoral fringe. The only sign is the brown 

coloured sand, due to the well weathered oil residues at the surface. From 10 metres on, 

new clean sediment covers the oiled substrate. On top of the clean sediment cyanobacteria 

is present. 


15 m 

HWS 

. . . . . . 

. . . . . . 

. . . . . . 

. . . . . . 

. . . . . . 

. . . . . . 

. . . . . . 

. -.-.-.-.- . . . . . 

. 

-.-.-.-.- 

. . . . . 

. .-.-.-.- 

.-.-.-.- . . . . . 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

. - - - - 

. . . . . 

. . . . . 

0 5 10 km 

--.-.-.-.- --------- -------- -- 

-.-.-.-.- 

-.-.-.-.- 

.--.-.-.- 

.--.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

-.-.-.-.- 

-.-.-.-.- 

.--.-.-.- 

.--.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

. . . . . 

. . . . . . 

. . . . . . . . 

. . . . . . . . . 

. . . . . . 

49°20’ 49°30’ 

ARABIAN GULF 

Nuquriya 

-.-.-.-.- 

-.-.-.-.- 

.--.-.-.- 

.--.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

.-.-.-.- 

. 

. . 

. . . 

. . . 

. . . 

. . 

. . 

. . . . . 

. . . . . 

. . 

. . 

. . 

. 

0-2 cm: tar crust; oil residues are well weathered 

2-12 cm : beige sand; no oil 

12-25 cm: sandy silt 


0.5-6 cm: clean silty sand 

6-8 cm : dark brown oiled layer 

8-22 cm: brown oiled sand 


N 

27°20’ 

27°10’ 

HWN 

E 

. . . . . . 

. . . . . . 

. . . . . . 

. . 

. . . 

. . . 

. . . 

. . . 

. . 

213



30 m 


45 m 

Section 5 at the 60 m mark is similar to section 4. 


75 m 

Section 7 at the 90 m mark shows no difference to section 6, except orange patches around 

active crab burrows due to oxidation processes. 


105 m 


0.5-6 cm: clean silty sand; substrate is now more stratified with silt layers 

intercalated at 1 3 and 4 cm depth 

6-8.5 cm : dark brown oiled layer; strong petroleum hydrocarbon odour, sticky 

8.5-16 cm : sandy silt; heavily oiled; low degradation status 

16-24 cm: sandy silt; medium oiled 

24-40 cm: grey sandy silt; no oil 


0.3-2 cm: dark brown oiled layer; strong petroleum hydrocarbon odour, sticky 

2-16 cm : oiled sand; emits a strong hydrocarbon odour; low degradation 

status of oil residues; oil concentrated in crab burrows 

16-40 cm: grey sandy silt; the transition between the brown oiled material and 

the grey sand below is not clear but rather patchy; liquid oil is 

oozing out of crab burrows 


0.4-7 cm: clean grey sand; populated by some small crabs and several 

polychaetes 

7-12 cm : oiled sand; the oil residues are more degraded than at the sections 

before; oiled layer is between 2 and 6 cm thick 



0.1-7 cm: clean grey sand; populated by some small crabs and several 

polychaetes 

7-10 cm : oiled sand; oil residues are well degraded; plenty of active burrows 

10-30 cm: grey fine silty sand; some oiled patches until 20 cm depth, mostly 

around former crab burrows that were filled by the oil (photo 6.30). 

214


Photo 6.30 Oiled burrows of polychaetes and crabs in the mid eulittoral of the sabkha transect. 


120 m 

0-15 cm: fine grey sand; populated by some small crabs and several 

polychaetes 

15-30 cm : light grey silt; crab burrows until 30 cm depth 

The sections of this transect resemble the characteristics of a typical salt marsh. Because 

other sabkha shores with a broad transition into the soft bottom tidal flats also display a 

comparable environment, except the total absence of any vegetation, this ecosystem type 

was not further investigated. 

215

6.4 Sand beaches 

Sand beaches are generally found at locations of higher physical wave energy (fig. 6.4.1). 

Along the coastline within the study area, there are 146 km of sandy shores. Most of them 

are located on the northern side of Abu Ali Island where high wave energy, due to the 

exposed location and dominating northern winds, allow only relatively narrow beaches. 

Others are located at the more exposed sites in the embayment system of Dawhat ad-Dafi 

and Dawhat al-Musalamiyah. 56 km of coastline are classified as high energy shores 

(horizontal tidal range less than 15 m) and 90 km as low energy shores. 

Fig. 6.82 Distribution of sand beaches within the study area. 

6.4.1 High energy shore 

0 5 10 km 

49°20’ 49°30’ 

ARABIAN GULF 

The northern shore of Abu Ali Island is a high energy shore from the eastern tip of the island 

until the most western extension. The littoral fringe is, except a few locations where rocks are 

dominant, composed of a fine to medium sand which is covered by seagrasses and trash at 

the different high water lines. Landward of the storm berm, there is a zone of vegetated little 

dunes with a more or less wide transition to flat sand sheets. Because of the similar 

environmental conditions, the north exposed beaches on Abu Ali Island resemble each other. 

In the mid and lower eulittoral zone, at most locations the surface is a mixed rocky and sandy 

zone. It is then mainly beachrock where the sand was eroded by wave action. But 

occasionally, some outcrops occur also in the upper eulittoral. In the sublittoral, close to the 

lower eulittoral, occasionally fringing coral reefs run parallel to the coastline. The first of the 

two described beaches is a sandy beach at the eastern tip of Abu Ali, the second is located 

at the northernmost shoreline, which is partly rocky in the mid and lower eulittoral zone. 

N 

sandy shores 

27°20’ 

27°10’


6.4.1.1 

Fig. 6.83 Location of the two sand beaches. 

6.4.1.1 Abu Ali - sandy beach 

N 

30 25 20 15 10 5 0 m 

trashline 

6.4.1.2 N S 

35 30 25 20 15 10 5 0 m 

beachrock 

0 5 10 km 

49°20’ 49°30’ 

HWN 

ARABIAN GULF 

The eastern tip of Abu Ali Island consists of little sand dunes which accumulated on a beach 

rock basis. There is no information available about the time of the beach rock formation. The 

sand dunes are between 50 and 150 cm high and partly covered by vegetation (vegetation 

cover is between 5 and 15%). The most prominent plants are Seidlitzia rosmarinus (shrubs up 

to 60 cm high), Suaeda maritima, Bienertia cycoptera, and the perennial grasses Sporobulus 

iocladus and Cyperus conglomeratus, and the parasitic Cynomorium coccineum and Cistance 

tupulosa. The sand consists mainly of quartz grains with some shell fragments that are 

responsible for 5-7% calcium carbonate content. Driftwood, pieces of coral, and plastic trash 

HWN 

tar layer 

HWS 

N 

HWS 

27°20’ 

27°10’ 

S 

217


can be found between the dunes in up to 50 m distance to the shore, telling of extreme storm 

events. 

The upper trashline mainly consists of the seagrass Halodule uninervis, cuttlebones of Sepia 

pharaonis, shells and snails, tar pebbles, driftwood and a lot of plastic garbage, fishing nets, 

etc. The sand below is medium grained sand (71% of the sample belong to this fraction) that 

shows no horizons. The HWS is located 5 metres towards the sea and marked by an other 

trashline. In 1994, there was a 2-3 cm thick tar cover and some tar free patches which showed 

the active erosion process. The sand below was oiled until 10 cm (fig. 6.84). In 1999, there 

was neither tar nor oiled sediment present anymore. The area was instead populated by the 

crab Ocypode rotundata, a species which is common on sandy beaches throughout the study 

area. The only remains of the former oil spill were some tar pebbles (which could not be 

attributed to the 1991 oil spill for certain – they could easily be more recent). 

depth in cm 

20 

15 

10 

5 

0 

-5 

-10 

-15 

-20 

-25 

-30 

30 25 20 15 10 5 0 

HWN 

oiled sediment tar cover new sand 

Fig. 6.84 Oil distribution at the Abu Ali transect in 1994. 

Between the HWS and HWN (10 m mark) in 1994 the beach seemed clean, due to clean 

sand which was accumulated on top of the oiled substrate. 15 cm below the surface, several 

more or less oiled sand layers were present until 40 cm depth. In 1999, non of these layers 

were found anymore. 5 m seaward at the HWN, there were 6 cm of new clean sand on top of 

11 cm of dark grey oiled sand, emitting a strong hydrocarbon smell in 1994. 5 m below the 

HWN the sediment was oiled below 3 cm of grey clean sand in 1994. The oiled stratum was 

between 4-6 cm thick. Beneath, 3 cm of coarse sand and shell fragments were situated 

above a hard beach rock layer. Again in 1999, there was no sign of any oiling in the past. At 

the 25 m mark the surface changed from sand to rock. Some of the beach rocks were 

covered by a thin tar crust which was peeling off at several places in 1994. In 1999, there 

were still tar layers present in this zone. But their consistency proved the younger age. They 

must have come from one of the plenty minor oil emissions which are side effect of the 

HWS 

218


intensive oil production within this area. In 2001, there were some tar patches distributed in 

this zone. Animal live seemed normal, as far as the rapid assessment showed. 

A B 

Photo 6.31 Scattered oil pebbles are the only residues of the 1991 oil spill. B: The ghost crab 

Ocypode rotundata searching the trashline for food. 

6.4.1.2 Abu Ali – sandy/rocky beach 

The second transect line is located at the northernmost shoreline, which is partly rocky in the 

mid and lower eulittoral zone. Additionally, there are some rocky outcrops near the littoral 

fringe. The sand dunes are between 50 and 200 cm high and covered by a diffuse distributed 

vegetation pattern (vegetation cover is between 10 and 25%). The vegetation is similar to the 

first site. The sand consists mainly of quartz grains with some shell fragments that are 

responsible for 5-8% calcium carbonate content. Driftwood, pieces of coral, and plastic trash 

can be found between the dunes in up to 30 m distance to the shore. The upper trashline 

consists mainly of the seagrass Halodule uninervis, cuttlebones of Sepia pharaonis, shells and 

snails, tar pebbles, driftwood, and a lot of plastic garbage, fishing nets etc. The sand between 

the rocky outcrops is medium grained sand (69%). The rocks consist of sand and shells which 

are calcified. The HWS again is located 5 metres towards the sea and marked by an other 

trashline. According to Höpner (1992), in 1992 the beach bore an asphalt cover from the 

HWS to the HWN. On beach rocks with an initially thin tar cover small tar free patches up to 

50 cm were the first sign of self remediation in 1992 (Höpner, 1992). The rocks at the HWS 

in 2001 (10 m mark) displayed a tar cover which during the last years gradually increased in 

thicknes (Höpner, 2001 unpublished report). This also must be attributed to more recent oil 

spills. The sand is clean and shows no horizons. The colour turns from a light beige to light 

grey in 40 cm depth. The scattered rocky outcrops 5 m below the HWS are all covered by a 

recent tar layer in 2001 (photo 6.32). At some patches, little pieces of tar have already been 

219


removed by wave action. The sand in between these rocks is clean. Some centimetres below 

the clean sand a 3-4 cm thick tar layer covers 5 cm of oiled sand. Deeper sand layers seem 

free of oil. Photo 6.32 shows the exposed tar layer between the HWN and the 10 m mark. At 

some places, this tar layer is up to 10 cm thick. Occasionally, the surface is soft. It seems not 

likely that any of this recent looking tar belongs to the 1991 oil spill. The zone lower than the 

HWN is completely free of oil, except some oiled rocks which might come from the upper 

shore. 

A 

Photo 6.32 A: Recent tar layer between the HWN and HWS. B: The rocky outcrops below the HWS 

are also covered by recent tar which is already peeling off again. 

6.4.2 Low energy sandy shore 

This location, which is located on the mainland northwest of Qurmah Island at 27°07’30”N 

49°27’48”E, was a permanent transect line during the EU/NCWCD Project (PTL 1). It is a 

shallow intertidal flat with intermittent narrow tidal channels and shallow tidal pools which 

remain during low tide. This beach was one of the most heavily impacted sandy shores. 

B 

49°20’ 49°30’ 

N 

220

S 

10 cm 

20 cm 

50 cm 


HWS 

0 5 10 km 

ARABIAN GULF 

0 m 5 10 15 20 25 30 35 

Fig. 6.85 Location of the low energy sandy shore transect. 


The transect starts at the upper trashline above the HWS. The following sections are presented 

in tables. Additional information is given as remarks where necessary. 

HWN 


27°20’ 

27°10’ 

sand silt / clay oiled crab burrows 

burrows 

N 

221


Tab. 6.89 Section 1 at the 0 m mark of the low energy sandy shore transect. 

0 m 

Remark: 

The trashline consists mainly of dry seagrass Halodule sp., driftwood, and a lot of plastic 

material. 


5 m 


10 m 

0-15 cm: homogeneous sand 

15-27 cm: dark brown oiled sand; oil residues weathered to a high degree; 

hydrocarbon content is 26.5 g/kg; rapid assessment print 

displays no colour (fig. 6.86) 

27-30 cm: black band of hardened oiled sand containing 35.1 g/kg 

hydrocarbons; no colour on oil print 

30-40 cm: coarse grey sand 

0-3 cm: sand 

3-20 cm: dark brown due to oil residues; crab burrows are visible and 

filled with a black tar of hard consistency (photo 6.33 A) 

20-30 cm: less oiled layers of sand and intercalated dark brown oiled layers 

- this distribution is likely to be the result of variation in the 

groundwater level 


calcium carbonate at -20 cm: 6.1% 

-30 cm: 5.2% 

0-6 cm: clean sand 

6-8 cm: there is a hard tar layer (photo 6.33 B). 

8-16 cm: dark brown sand; oil residues well weathered; rapid assessment 

print shows no colour; hydrocarbon concentration: 21.7 g/kg 

16-33 cm: dark brown oiled sand; oil is sticky; strong petroleum 

hydrocarbon odour; hydrocarbon content: 27.9 g/kg 

33-45 cm: oiled sand, liquid oil; strong hydrocarbon odour; hydrocarbon 

concentration: 46.7 g/kg; dark brown rapid assessment print 

indicates low weathering status (fig. 6.86) 

45-50 cm: dark grey sand; oil seeping out of the pores 

50-55 cm: coarse grey sand with plenty of shell debris 


-55 cm: 59,3% 

222



15 m 

Photo 6.33 Oil residues at selected sites along the transect (see text for explanation). 


20 m 


25 m 

0-6 cm: clean grey sand 

6-9 cm: oiled sticky layer; strong hydrocarbon odour (photo 6.33 C) 

9-28 cm: grey medium oiled fine sand; strong hydrocarbon odour 

28-40 cm: light grey carbonate rich silt 


-40 cm: 64% 

crab burrows filled with tar 

tar layer below new 

clean sand (aerobe) 

oiled sand below 

new clean 

A B C 


6-21 cm: oiled fine sand; strong hydrocarbon odour; hydrocarbon 

concentration is 15 g/kg; brown rapid assessment print (fig. 

6.86) indicates low weathering status; water which is oozing out 

of the sediment carries liquid oil 

21- 24 cm: shell debris and coarse sand 

24-40 cm: light grey carbonate rich silt 


-30 cm: 52.4% 


5-15 cm: oiled fine sand; hydrocarbon odour 

15- 25 cm: light grey carbonate mud 


-20 cm: 45.5% 

Remark: 

This is the first section where burrowing activity is observed. Several polychaetes are found 

as well as some active crab burrows. 

223



30 m 

Remark: 

At the surface, there are several tidal pools that remain during the ebb tide. 


35 m 

0-6 cm: clean grey sand; populated by several polychaetes and some 

crabs 

6-7 cm: oiled fine sand; slight hydrocarbon odour 

7-11 cm: several layers of coarse sand enriched with shell debris (mainly 

cerithides) and plain grey sand 



0-5 cm: clean grey sand; populated by several polychaetes and some 

crabs; no oil visible; hydrocarbon concentration: 4 g/kg; 

interference patterns on groundwater surface which indicate the 

presence of hydrocarbons 



Seaward, the sandy intertidal flat covers about 80 m. The sand layer on top of the beach rock 

decreases in thickness and at several locations within the lower intertidal beach rock material 

is scattered at the surface. No oil pollution is visible in this area. 

0 m –20cm 0 m –28cm 10 m –10cm 10 m –20cm 10 m –40cm 20 m –10cm 35 m –5cm 

26.5 g/kg 35.1 g/kg 21.7 g/kg 28.9 g/kg 46.7 g/kg 15 g/kg 4 g/kg 

Fig 6.86 Rapid assessment oil prints of samples along the transect. 

Oil penetration depths, measured by Höpner et al. (1992) in 1992 at the beach of this 

transect, showed maximum penetration at the HWS and a gradual decrease in seaward 

direction. Seaward of the 30 m mark no oil was in the sediment at that time. Ten years later, 

the general trend is that the oil percolated further down into deeper layers with the result that 

the total thickness of oiled sediment increased. On top of the oiled sediment new sand was 

224


deposited in different amounts (fig. 6.87). This new sand was the basis for recolonisation by 

macrofauna. 

depth in cm 

20 

10 

0 

-10 

-20 

-30 

-40 

-50 

0 m 

5 10 15 20 25 30 35 40 

new sand in 2001 oiled sediment in 2001 oiled sediment in 1992 

Fig 6.87 Oil distribution within the sediment in 1992 and 2001. 

6.4.2.2 Fauna 

HWS HWN 

In 1992, the fauna in the lower eulittoral seemed not very much affected by the oil 

Potamoleios kraussii was present on beach rock fragments, and gastropods (Cerithium sp.) 

were feeding on diatoms (Kinzelbach et al. 1992). From the upper mid eulittoral, the sand was 

considerably oiled (Höpner et al. 1992). The upper eulittoral was covered by a closed solid 

asphalt like layer. The sediment at the littoral fringe was soaked with oil until 30 cm depth 

(see previous paragraph). No living fauna was present in 1992. An attempt to remove the tar 

cover in 1992-1993 resulted in a further oil release which is reflected by the species diversity 

and abundance in 1993. New sand deposited on the upper eulittoral and littoral fringe 

provided the conditions for recolonisation (Jones et al 1995). The high abundances in 1995 

are comparable to the mangrove sites, due to the population explosion of certain species 

which are r-strategists. In this case, it was due to the polychaete Owenia sp. and the bivalve 

Dosinia hepatica and T. arsionensis (fig. 6.88) (Jones et al. 1995). The sediment 

characteristics at this beach do not resemble the conditions at the control site well. Jones et al. 

(1995) assume that the finer sediment at this location results in a higher productivity than the 

control. 

225


1200 

1000 

800 

600 

400 

200 

0 


1991 1992 1993 1994 1995 

6025 

1200 

4470 

4022 

m.eulit. 1000 

800 

600 

lo. eulit. 

400 

u. eulit. 

200 

lit. fr. 



0 



30 

25 

20 

15 

10 

5 

u. eulit. 

0 

1991 1992 1993 1994 1995 

30 

25 

20 

lo. eulit. 

15 

m.eulit. 

10 

lit. fr. 

5 




In 2001, these high abundances were not encountered in the mid and especially upper 

intertidal. In the upper intertidal all live was restricted to the clean new sediments above the 

oil layer. Within the oiled sediment no macrofauna was present in 2001. Beyond section 5 

on, polychaetes were present in the oiled substrate, but only at section 6 their number 

increased significantly to more than 100/m². At this section, also the first crab burrows by 

Scopimera crabicauda were found. Towards the lower shore, the biota increased in numbers 

and diversity. 

6.4.3 Sandy shores - Discussion 

Sand beaches are generally found at locations of higher physical wave energy. Waves drive 

oxygen into the sediment. In most cases just the physical energy of the waves was enough to 

rework the tar crusts, break and erode them within the first 2 - 4 years after the oil spill. Today 

the only remains of the oil spill are scattered oil pebbles or tar balls at the beaches. Often the 

oiled sediment was covered by a layer of clean sand. Where the oiled sediment was sealed by 

a tar crust (like the upper eulittoral zone of the described low energy site), the oil degradation 

was hampered, due to an oxygen deficit beneath the impermeable tar crust. At such locations, 

the oil was still present within the sediments in 2001. But regarding the typical sand beaches 

in the study area, hydrocarbon concentrations of more than 20 g/kg are exceptional. Higher 

oxygen concentrations in most sandy sediments lead to a significant degradation of the oil in a 

manner that it does not prevent colonisation by animal life for more than 5 years. Beaches like 

the described Abu Ali sand beach, where several oil layers were present in 1994, showed no 

0 


226


oil at all in 1999. Most oil and tar covers along the northern shores of Abu Ali are more recent 

than 1991. They are the result of the intensive oil production and transport in the marine 

environment of the Eastern Province of Saudi Arabia, and mainly of a minor extent. 

According to Jones et al. (1996), the species diversity in sandy shores already reached normal 

levels between 1993 and 1994. In this study, the northern Abu Ali shores were unfortunately 

not monitored – but because the monitored sites were lower energy sand beaches, the 

recolonisation should have been even faster at Abu Ali shores. At both shore types, recovery 

of diversity was most rapid in the mid and lower eulittoral. The good recovery result in the 

upper eulittoral of the low energy site was surprising, because the amount of oil in the 

sediment did not decline (here species diversity and abundance reached normal values already 

in 1992). It was only possible because of the accumulation of clean sand above the oiled 

layer, where life found natural conditions. Even in 2001, the oiled layers beneath the clean 

sediment were lifeless. Also the recovery of species diversity and abundance in the littoral 

fringe completely depends on the accumulation of clean sand. Where this happened – like the 

described low energy location – the values turned to normal in 1994. At places where the tar 

cover remained at the surface, no development of life was measurable until 2001. But such tar 

layers (photo 6.34), which could often be found at the littoral fringe in 1994, were rare on 

sand beaches in 2001. Thus, most sandy shores were already fully recovered five years after 

the 1991 Gulf War oil spill. 

Photo 6.34 Narrow tar band along a sandy beach on Jinnah Island. This band is being eroded by the 

physical energy of wave action during high tides (photo: 1994). 

227

6.5 Rocky shores 

The rocky shores are developed on beach rock, often leading to the formation of beach rock 

cliffs and terraces. Beach rock consists of consolidated marine beach sediments which is 

cemented by a calcium carbonate. It is also often occurring below the soft sediments in the 

salt marshes and sandy shores. Some of the layers are hard and thick, others only 2-3 cm thick 

and breakable. It is assumed that these layers of beach rock are contemporaneous and that 

they are still forming from the unconsolidated sediments (Whittle 1998). Höpner (2001 

unpublished report and pers. comm.) reports, that there is some beach rock formation in the 

tidal flats south of Abu Ali island. 

Most of the supratidal rocks are marine beach rock formations. All along the recent Gulf coast 

there are remnants of former coast lines in the form of fossil cliffs and marine abrasion 

terraces. These are caused by fluctuation of sea level during the Pleistocene and Holocene 

resulting in shifts of the shoreline along the Arabian Gulf (Felber et al. 1978). According to 

investigations published by Al-Sayari & Zötl (1978), for areas in the Eastern Province, there 

is a series of terrace levels, reaching from the earliest Pleistocene to the “Neolithic Pluvial” in 

middle Holocene times. The most impressive escarpments in the area are the cliffs of Jabal al- 

Bukhara at the southern edge of Mussalamiyah Bay and on Jinna island. The northerly 

exposed escarpment of Jabal Al-Bukhara is cut into the members of the Dam and Lower 

Hadrukh formations, which occur in scattered patches along the coast line (Barth & Niestle 

1992). Besides these prominent cliffs, some lower steps and terraces of beach rock were 

identified along the coast. A typical example is the twofold step of Jabal an-Nuquriyah at the 

coast line on the eastern flank of a northward projecting peninsula south of Jinna island. The 

lower step is built up by a marked cliff in limy beach rock mounting on a narrow terrace in 

2m height above high tide level. The second step is formed by a sandy slope reaching a wide 

terrace level at 7 m above the high tide line further inland. But although these remains of 

former beach rocks are conspicuous in the otherwise flat coastal environment, they are rare. 

More often, smaller cliffs of 20-80 cm height are to be found in the study area. The intertidal 

in front of these cliffs is rocky with crevices and rockpools, partly filled with tidal water. At 

some locations a thin sand layer has accumulated on top of the rock platform. From the total 

of 401 km of coastline in the study area, only 14 km area are pure rocky shores (fig. 6.89). 

Rocky platforms in the lower eulittoral are wider distributed and occur mostly along sandy 

shores. But since the severe oil pollution happened above the mid eulittoral, these shores were 

classified as sandy shores.


0 5 10 km 

Fig. 6.89 Distribution of rocky shores within the study area. 

6.5.1 Rocky shore south of Jabal an-Nuquriyah 

2m 

1 

0 

0 5 10 km 

Fig. 6.90 location of the rock transect. 

49°20’ 49°30’ 

Ras al Bukhara 

Nuquriya 

HWS HWN 

49°20’ 49°30’ 

ARABIAN GULF 

ARABIAN GULF 

N 

rocky shores 

N 

27°20’ 

27°10’ 

27°20’ 

27°10’ 

W E 

0m 10 20 50 

229


This shore consists of a 1.5 – 2 m high cliff at the HWS that consists of beachrock sediments. 

In front of the cliff there are some isolated, more resistant remains of beachrock up to 70 cm 

high. In sheltered sites and crevices in between the rocks, sand accumulated. The rock flat in 

the mid eulittoral consists of abundant rock fragments, outcrops of the continuous beachrock 

layer, and some sand. 

The 0 m mark at the bottom of the cliff is about 10 cm above the littoral fringe. There are sand 

accumulations and rock debris from the higher parts of the cliff. This zone is characterized by 

some Suaeda sp., Seidlitzia rosmarinus, Bienertia cycloptera, and the parasitic Cistance 

tubulosa. The trash line 2 m further consist of sea grasses Halodule and Halophila sp., wood, 

some trash, and turtle bones. For the next 20 m, there is a diverse morphology with isolated 

higher rocks (preserved due to more resistance towards erosion than the surrounding 

material), crevices, and sandy patches. The sand is clean and contained no trace of oil in 1999 

and 2001. In 1994, most of this are was still covered by tar and life was very restricted. On the 

surface of the sandy patches, there is a flat cyanobacteria mat of about 2 mm thickness. 

Gastropods (Pirinella conica, Cerithium scabridum) are grazing on the bacteria there. 

Occasionally burrows (1-7) of the crab Scopimera crabicauda can be found on the sand 

patches. The crab Metopograpsus messor is present below the rocks. Nodolittorina subnodosa 

populate most of the rock surfaces and pools. Densities vary between 10 and 600/m². On the 

rock surfaces there are scattered tar patches of different age and weathering status (photo 6.35 

A). But they are all more recent than the 1991 oil spill. The only possible remains of the 1991 

Gulf War oil spill still present in this zone, are the lower layers of up to 6 cm thick tar 

accumulations in sheltered depressions between the rocks in the upper part of the upper 

eulittoral. 

In the mid eulittoral 20-40 m, there are flat beachrock outcrops, some rock pools and many 

small rock boulders (5-10 cm). The rocks show a black colour due to some lichens and 

cyanobacteria on the rock surface. Some patches are covered by a thin sand layer. There is 

some oil below small rocks which seems like a recent deposition. The deposition is only in 

the upper 2-5 mm of the sand below the rocks, where it is obviously more protected than on 

the sandy surface without rock cover (photo 6.35 B). No oil residues are to be found there. 

The beach rock boulders show a dense settlement of the serpulid worm Potamoleios kraussii 

(on the interior surfaces and bottom sides) and numerous burrows leading to the upper side, 

barnacles such as Balanus amphitrite and gastropods such as Cerithium scabridum (photo 

230


6.35 C). The lower eulittoral 40-50m is also mostly rocky and populated by molluscs, 

decapod crustacea, and polychaetes. 

A B 

Photo 6.35 A: tar on rock surface. Note the different age of the upper and the lower patch. B: oil 

residues beneath small rocks where they are protected from erosion. C: rock surface covered by 

barnacles and gastropods. 

6.5.2 Ras al-Bukhara 

The transect at Ras al-Bukhara runs in south-north direction beginning at the foot of the cliff. 

The cliff itself belongs to members of the Miocene and Pliocene Hadrukh and Dam 

formations. A very resistant coarse grained limey sandstone as top layer is acting as a 

protective cover of the plateau surface. Beneath this vertical edge (Dam formation), a 

succession of different layers of sandy marl and clay are interspersed by more resistant 

sandstone and limestones, forming several steps in the steep part of the slope (fig. 6.91). 

N 

Hadrukh 

formation 

Dam 

f 

resistant sandstone 

coarse grained 

sandy limestone 



sandy marl, beachrock 

mud 

beachrock 

fine sandy marl 

HWN 

siltstone 

Fig. 6.91 Petrography of the cliff at Ras al-Bukhara and the intertidal flat at its bottom. 

sand 

tube of Cerithium s. 

Potamoleios k. 

C 

HWS 

Balanus a. Nodolittorina s. 

Trochus sp. 

S 

231


The lower part of the cliff cuts into sandy marl, clay marl, chert layers, and sandstone, 

belonging to the upper Hadrukh formation. This downward flattening footslope is covered by 

weathered materials and by rock debris from the upper front of the escarpment. 

At the east exposed side of the cliff a wide intertidal rock–sand flat lies adjacent to the littoral 

fringe, whereas at the more north exposed side a narrow rocky platform dips into the flat 

waters of the Gulf. The littoral fringe below the cliff of Ras al-Bukarah consists of rock debris 

from the upper part of the cliff. The upper eulittoral is formed by a rock platform with 

crevices and rock pools. The mid eulittoral zone shows a sand cover at protected sites. 

Towards the lower eulittoral, the surface material is mostly muddy with some sand and 

scattered rocks. 

In 1991, the whole mid and upper eulittoral as well as the rocks at the littoral fringe were 

covered by a tar layer. The oil burden in sandy parts of the upper eulittoral (east of this 

transect) was up to 20.6 kg/m² (Höpner 1992). The oil penetrated the sand between 10 and 25 

cm. In 1992, the flats below the cliff were covered by tar balls. In 1994, the remaining oil 

residues were covered by new sand. The upper eulittoral and littoral fringe obviously 

recovered fast. The tar cover was already peeling off in 1993, and large parts of the rocks 

were virtually oil free in 1994. Physical forces like wave action, wind and sun act on the tar 

crust. This results in a polygonal pattern of small cracks that widen and eventually enable the 

tidal water to remove little pieces during high tides (photo 6.37). In this manner most of the 

oil was removed during the first 3 years after the oil spill. The typical fauna returned 

surprisingly slow, although there was no more oil impact since 1994. This was due to the 

different reproduction patterns of the key species in the littoral fringe area (see discussion, 

next paragraph). 

Photo 6.36 Cliff of Ras al-Buhkara at high 

tide. 

Photo 6.37 Polygonal pattern of cracks in the 

tar cover. 

232

6.5.3 Rocky shores - Discussion 


Most rocky shores are characterized by moderate to high wave energy. At such locations 

most of the tar cover from the 1991 oil spill has already been removed in 1993. Physical 

forces like wave action, wind and sun act on the tar crust and contribute to the weathering 

and erosion process. Only in sheltered locations near the littoral fringe, tar from the 1991 oil 

spill is still present among several more recent layers resulting from other pollutions. In the 

upper eulitttoral, the oil resists erosion longest at places where it is covered by little boulders. 

But even there the persistence is not very high. 

Narrow rocky shores at exposed sites, that were subjected to the oil in 1991, often 

accumulated large quantities of oil in the upper eulittoral zone. Because the oil could not 

penetrate into the rocks (like in the soft sediments) it accumulated at the surface and thus 

was subjected to the sun and air and increased evaporation. The remains turned into a 

highly viscous tar within a few days. At such locations the tar was still present in 1993 (photo 

6.38). In 1999, even the most severe oiled rocks were free of tar. This demonstrates the 

effectiveness of wave action in erosion of hydrocarbon residues. 

Photo 6.38 Narrow band of beachrock at an exposed shore. The physical erosion of the beachrock 

can clearly be seen at the seaward edge. A black band in the upper eulittoral indicates the presence of 

tar (photo taken in 1993). 

The recruitment into the rocky shore areas shows different patterns than the other shore types. 

At some locations life was completely destroyed, and at others like Ras al-Bukarah small 

resident populations of Nodolittorina and Planaxis remained alive (Jones & Richmond 1992). 

Despite population fluctuations, the species diversity and abundance increased in the 

following years until 1995 when normal values -except in the littoral fringe zone- were 

reached (fig. 6.92). Much slower was the recruitment at sites were the fauna of the upper 

233


intertidal was completely destroyed such as the PTL 4 monitored by Jones et al. (1995) or the 

Nuquria site. Such heavily oiled sites showed no recovery until 1993 and 1994, respectively. 

Then species diversity and abundance increased but did not reach the values of non-oiled 

control sites (fig. 6.92). The retarded development of the littoral fringe is caused by the 

dominance of Nodolittorina subnodosa populations at the rocky shores of the Arabian Gulf. 

This species is viviparous (“brood protecting”), which means that the resettlement strategy is 

restricted to direct recruitment from small, patchy surviving adult populations. Thus the 

expansion is slow and vulnerable to environmental change, especially when compared to rstrategist 

planctonic species. Original numbers of more than 1000/m² for Nodolittorina s. and 

about 300/m² for Planaxis sulcatus, which has followed a similar trend (also viviparous), have 

almost been reached in 1999 at the Nuquria site. The large natural fluctuations of species 

abundance make counts difficult to compare. Ras al-Bukhara was not monitored anymore due 

to military activities in this area. In contrast, the settlement of species with planctonic larval 

stages (such as barnacles or the crab Scopimera crabicauda) was almost complete in 1995 

(Jones et al. 1995). Occasional high abundances of sedentary animals such as Balanus 

amphitrite, Pomatoleios kraussi, and Euraphia sp. in the mid eulittoral and the following 

decline between 1992 and 1995 is due to the presence of predatory gastropods (Thais sp. and 

Cronia margariticola). Whenever the barnacles declined, the number of predatory gastropods 

was relatively high (Jones et al. 1995). 


1400 

1200 

1000 

800 

600 

400 

200 

0 

u. eulit. 

1991 1992 1993 1994 1995 

lit. fr. 1400 

1200 

1000 

800 

600 

m.eulit. 

400 

lo. eulit. 

200 



0 



40 

35 

30 

25 

20 

15 

10 

5 

0 

u. eulit. 

m.eulit. 

1991 1992 1993 1994 1995 

40 

35 

lo. eulit. 

30 

25 

20 

15 

10 

lit. fr. 

5 

0 




Fig. 6.92 Species diversity and abundance for Ras al-Bukhara (data: Jones et al. 1995). 

234

7 General discussion and conclusion 

In 1991, the release of estimated one million tons of crude oil was the world’s largest oil spill 

to date. It exceeded the Ixtoc spill 1979 in the Gulf of Mexico which was 500,000 tons, and 

the Nowruz spill 1983 during the Iran-Iraq war which was around 250,000 tons. Along the 

Saudi Arabian shoreline north of Jubail, most intertidal habitats were affected by the oil. First 

impressions after helicopter flights in 1991 were that the entire intertidal zone was polluted. 

This had to be revised in 1992. It was then obvious that only the upper intertidal between the 

HWS and the HWN was heavily oiled. The lower areas only locally showed significant oiling. 

Frequent visits between 1993 and 2002 showed a very complex picture regarding the recovery 

of the different ecosystems. In chapter 6 the regeneration status and recovery processes are 

discussed in detail for each ecosystem type separately. The most important aspects are 

summarized below. 

The salt marshes, which are the most abundant ecosystem type along the shores within the 

study area, were most severely hit by the oil slicks and most biota was extinct in the upper 

intertidal zone in 1992 (see chapter 6.1). These are also the areas, where in 2001 the impact 

is still clearly visible and where recovery is far from being complete. The predictions for the 

future development varied from 5 years (McGlade & Price 1993), a number which, for most 

habitats, was confirmed by Jones et al. (1996) to a probable contamination for decades 

(Hayes et al. 1993). 

The continuous assessments in the years after 1995 revealed that the study areas covering 

the salt marsh ecosystems during the EU/NCWCD project are not representative for most of 

the salt marshes. In addition, only one out of 10 permanent transect lines (PTL 8) covered a 

real salt marsh ecosystem. Considering the fact that almost 50% of the total coastline is 

occupied by salt marshes, this is not representative. Until 2001 25% out of the damaged salt 

marsh area show no recovery at all (see tab. 7.1) and only 20% are fully recovered (which 

means that parallelism occurs in both species diversity and abundance as well as the 

complete degradation of oil residues). The remaining 55% still show significant amounts of oil 

residues and usually lower abundances than control sites. But these sites are along the road 

to recovery which may be complete in 5 or 10 more years. 

These results are in contrast to the UNEP (1993) report, as well as to most press releases 

and the EU/NCWCD reports, which present a very optimistic view regarding the recovery 

rates of the Saudi Arabian coast. This is due to the fact that in most cases the focus is on 

ecosystem types which indeed recovered nicely, in example rocky shores or mangroves. 

Some ecosystems such as the coral reefs were not affected at all. For the upper intertidal

Discussion and conclusion 

zone of salt marshes, species diversities are published by Jones et al. (1996), which are from 

0 to 50% below the diversities found on control sites. These values were - even in 2001 - not 

found at several different salt marsh sites. 

Tab. 7.1 Recovery status of the different coastal ecosystem types in 2001. 

ecosystem type damaged area in out of the damaged area out of the damaged area no 

% 1991 completely recovered in regeneration at all in 2001 

2001 (in %) 

(in %) 

salt marsh 90 20 25 

sand beach 80 80 0 

sabkha 90 0 25 

rocky shore 100 100 0 

mangrove 50 80 0 

Generally, the presence of oxygen along with nutrients belong to the essential conditions of 

hydrocarbon biodegradation. This is known from literature (Höpner et al. 1989, Harder et al. 

1991) and it is also one of the most obvious results obtained during the field work. In soil 

substrates which are well aerated (e.g. sand at high energy shores, see chapter 6.4.1), 

petroleum hydrocarbon degradation proceeds fast and biota returns quickly. Where oxygen is 

cut off because of tar layers or cyanobacteria mats, the oil is conserved and not biodegraded at 

all, thus no biota is able to return. The role of cyanobacteria in oil biodegradation is diverse. 

On the one hand it colonises the oiled substrate rapidly, contributing to its removal through 

the processes of desiccation, contraction, cracking, and finally peeling off, removing a thin 

layer of tar or oiled substrate (fig. 7.1). On the other hand it covers large areas, sealing the 

surface, thus preventing oxygen and nutrients from penetrating the oiled substrate. At several 

sites the vitality of these cyanobacterial mats seems strong enough to prevent a return to the 

original salt marsh-Cleistostoma community. Generally, it was observed that bioturbating 

organisms, especially crabs, colonize oil affected zones some years before macrophytes. This 

is the result of the establishment of cyanobacterial mats, and/or the presence of hard surface 

crusts which prevent the germination of Arthrocnemum or Halocnemum. The only organisms 

effectively able to remove the crusts as well as the cyanobacteria are crabs, mainly 

Cleistostoma dotilliforme. The burrowing activity of crabs breaks the surface crust or the 

cyanobacterial layer, allowing oxygen to penetrate the sediment and thus, accelerating the 

biodegradation of the oil residues (fig. 7.1). 

236

tar crust 

extensive growth 

sealing of 

surface 

hardening of soil 

surface / 

desiccation 

(upper eulittoral 

and higher zones) 

erosion of tar 

crust 

sea / 

wave action / 

tidal 

channels 

cyanobacteria 

main parameters determining 

environmental conditions 


sun 

oxygen and 

nutrients 

kinetic energy 

sediment erosion 

and deposition 

desiccation / 

cracking 

and peeling 

bioturbation 

biochemical 

aerobe 

degradation of oil 

stable condition process 

mechanical erosion 

recolonisation 

by crabs and 

crucial chain of processes 

for regeneration 

recolonisation 

by plants 

Fig. 7.1 Oil conservation and degradation processes at the Gulf shores determined by the three main 

controlling parameters: sun, cyanobacteria, and physical erosion by water. 

It turned out, that the tidal channels are the initial paths of recolonisation by crabs, because 

in the channels the sediment is clean and soft. The expansion at both sides of the channels 

is basically limited by the hardness of the surface sediment. It could be proved that the 

burrowing activity of most crabs is restricted to sediments softer than the oil soaked 

hardened surface layers. Therefore, it must be concluded that the penetration ability of the 

sediment is a major factor, controlling recolonisation by crabs. 

Sabkha shores (see chapter 6.3) in most cases show the same developments as most salt 

marshes in the mid and lower eulittoral. The upper eulittoral is dominated by cyanobacteria 

instead of salt marsh vegetation due to higher salt concentration of the soils. 

The Mangroves (see chapter 6.2) occur at very sheltered soft bottom sites, often in association 

with salt marshes. After the oil spill, around 50% of the trees were affected by the oil and 

around 30% died off. The survival rate of mangroves is higher compared to salt marsh plants, 

237


because the presence of pneumatophores enables the trees to tolerate at least some level of 

oxygen depletion in the soils. Natural regeneration started 2 years after the impact. Using the 

widely distributed tidal channels, burrowing organisms colonised the sediments adjacent to 

the channels and broke the surface tar crusts and allowed oxygen to penetrate into the 

sediments. Due to stronger water currents, a higher rate of inundation by sea water and a 

narrow network of tidal channels the process was much faster in this ecosystem type than at 

the salt marsh sites. The first mangrove seedlings germinated in the loosened substrate after 

two years. 10 years after the oil spill most sites are well bioturbated. Benthic organisms 

reached their original abundance and species diversity. The oil is well degraded or not 

detectable. Even at severely damaged sites 3-5 years after the impact new Avicennia seedlings 

re-colonised the area. Today the only signs of the impact are some remains of dead plants and 

very few tar residues. In these ecosystems the regeneration was even faster than previously 

estimated (Böer 1994a). Only 80% of the mangrove areas are classified as completely 

recovered. This is due to the fact that at several sites where mangroves germinated the trees 

are still very small. This means that abundance levels are much higher than normal and thus, 

parallelism is not yet established. But certainly these sites will be recovered within a few 

years from now. 

Sand beaches (see chapter 6.4) are generally found at locations of higher physical wave 

energy. Waves drive oxygen and nutrients into the sediment. In most cases just the physical 

energy of the waves was enough to rework the tar crusts, break and erode them within the first 

2 - 4 years after the oil spill. Today the only remains of the oil spill are scattered oil pebbles at 

the beaches. At some low energy sandy sites where a tar cover sealed the sand beneath, 

oxygen shortage prevented oil degradation. These are the locations where parallelism does not 

occur in the upper eulittoral even in 2001. Higher oxygen concentrations in most of the other 

sandy sediments lead to a significant degradation of the oil in a manner that it did not prevent 

colonisation by animal life since 1994. Therefore, today 80% of the sandy beaches can be 

considered as fully recovered. 

Wave action at most rocky shores removed the oil cover after only 2 years. In 1993 all key 

species were present again. Recovery of abundance was observed continually until 1995. 

Only at the littoral fringe abundances remained lower. These low densities were attributable 

to the slow population expansion of viviparous littorinids (gastropods). At most sites original 

densities were observed in 1999 which means that parallelism did finally occur. In 2001, 

100% of the rocky shores are recovered. Occasional oil or tar patches found today are related 

to the chronic oil pollution in the Arabian Gulf. 

238


The subtidal biotopes such as seagrass beds, corral reef biotops and silt sea beds showed no 

evidence to suggest that these were adversely affected by the 1991 oil spill (Richmond 1996). 

The offshore corral reefs were also not affected by the Gulf War oil spill (Vogt 1996). 

Findings of Roberts (1993) and Cava & Earle (1993) show that no damage to corals was 

observed in Saudi Arabian reefs. Occasional bleeching of Acopora specimens are believed to 

be caused by natural disturbances (Vogt 1996). The fish populations in the nearshore and 

offshore areas were affected by the oil spill. This is reflected by lower abundances of many 

species in 1992 and 1993. According to information provided by local fishermen in spring 

2002, the nearshore catches were reduced by about 50% in the 1992. While juvenile and adult 

fish escaped direct oil contamination, the reduced counts after the crisis were attributed to a 

reduction of planktonic eggs and larvae within the oil affected areas (Krupp & Almarri 1996). 

But already in 1994 the fish populations had recovered from the oil spill (Krupp & Almarri 

1996). 

Cleanup operations 

When in 1967 the supertanker Torrey Canyon grounded in the English channel around 

150,000 tons of Kuwait crude oil were released into the North Sea and onto the coastal 

ecosystems. In this case, most damage was caused by the subsequent clean-up activities. 

The detergent-based dispersants were more toxic than the oil itself. Since then a great deal 

of research has been conducted on major oil spills and the modern day dispersants are no 

longer toxic. Anyway, it was proved that in many cases i.e. Amoco Cadiz or Exxon Valdez, 

the clean-up activities are more destructive than the oil and therefore increase the damage 

done to the ecosystems in the long term (Watt 1994, Driskell et al. 1993). In the study area 

several different clean up techniques were tested. These tests were executed through the 

International Maritime Organisation’s (IMO) Persion Gulf Oil Pollution Fund between 1991 

and May 1992 (IMO 1993). The various cleanup techniques are discussed in detail by Watt 

(1994, 1996). The trials conducted in the area were evaluated and compared to adjacent uncleaned 

sites. The tested systems included: 

a sprinkler-flusher for the mangroves on Qurma island, 

a dry tiller at a mudflat in Dawhat al Musallamiyah 

a tiller-flusher at a sand and mud site in Dawhat ad-Dafi 

a autoflusher at a sand and mud flat in Dawhat ad-Dafi 

a autoflusher at the same sand and mud flat in Dawhat ad-Dafi in 1993 

a high pressure sea water jet at a rocky shore in Dawhat al Musallamiyah 

239


mechanical removal of oiled sand on Karan island 

dry tilling on cyanobacterial flat in spring 2001 

The results of each technique are briefly summarised in tab. 7.2. The over all results indicate 

that in most cases clean up operations result in marginal ecological improvement over time, if 

at all (Plaza & Al-Sanei 1995). The trial in 1993 lead to a secondary oiling of the upper shore 

with subsequent destruction of the newly established biota. The tilling experiment carried out 

in spring 2001 showed no improvement of the situation, because the cyanobacteria reconquered 

the surface substrate within only one year (see chapter 6.1.8). Deep tilling would 

release the still liquid oil and cause a secondary oiling. It remains open whether repeated dry 

tilling would finally remove the cyanobacteria, but in any case the substrate would be heavily 

disturbed without any chance for the sediment to settle back to a normal profile. Thus all 

results, except the removal of oiled sand from the beaches of Karan, agree with Sell et al. 

(1995) who have reviewed several case histories of previous oil spills over the last three 

decades, and concluded that there was little justification for cleanup operations on a purely 

ecological basis. 

Tab. 7.2 Cleanup techniques and their results. 

technique result 

sprinkler-flusher for the mangroves on Qurma prevents oil from adhering to the pneumato- 

island 

phores; plants seemed healthier where this 

system was applied 

dry tiller at a mudflat in Dawhat al Musallamiyah produces a marginal higher diversity after 3 years, 

although the sediment is still heavily disturbed. 

tiller-flusher at a sand and mud site in Dawhat ad- No enhanced recovery obvious 

Dafi 

autoflusher at a sand and mud flat in Dawhat ad- 

Dafi 

autoflusher at the same sand and mud flat in 

Dawhat ad-Dafi in 1993 

high pressure sea water jet at a rocky shore in 

Dawhat al Musallamiyah 

flushing causes oil to penetrate deeper into the 

sandy sediment; operation has not enhanced 

recovery at this site 

flushing released liquid oil which reduced faunal 

diversity 50% and abundance by 90% in the upper 

eulittoral and 40% in the mid eulittoral (Jones et 

al. 1995). Overall negative effect. 

destroys pockets of surviving fauna; no enhanced 

recovery even when applied in stripes 

perpendicular to the shore; recovery only 

dependant on proximity to sources of repopulation 

mechanical removal of oiled sand on Karan island successful; turtles returned for breeding 

dry tilling on cyanobacterial flat in spring 2001 not successful; cyanobacteria covers the whole 

240


area after one year 

Regarding the fact that more than 50% of the Saudi Arabian Gulf shores are low energy 

shores which need significantly more time for recovery than 10 years, and the low efficiency 

of cleanup operations, the consequence is, that oil must be prevented from drifting ashore. 

Therefore, the future research effort must focus on the problem, how to prevent oil from 

settling within the upper intertidal zone. 

241

8 Recommendations 

Due to the number of oil installations, the petrochemical industry, and associated shipping, 

there is a reasonable probability of future oil accidents and oil spills along the Saudi Arabian 

coast. Most of these oil spills will be minor ones and therefore affect only short stretches of 

coastline, but they may still destroy a valuable habitat without counter action. Therefore it is 

essential not only to develop a contingency plan (as done by Watt 1994b), but also to develop 

new methods in dealing with spilled oil in the shallow waters of the Gulf and to implement a 

working and efficient information network. Based on this study, several recommendations are 

given how to deal with future oil spills threatening the Gulf shores. 

In case of an oil spill at low energy shores, clean up activities should be concentrated 

on the mangrove ecosystems using sprinkler techniques to clean the pneumatopores of 

the Avicennia trees. 

Additionally beaches on the offshore islands need cleaning, in order to provide clean 

sand as a breeding area for endangered species such as the green turtle. 

For the rest of the area no cleanup operations are recommended. 

What can be bone in order to prevent oiling of the shallow shores? 

All coastal ecosystems along the shores of the Arabian/Persian Gulf should be 

assessed in order to define environmentally sensitive areas which have to be treated as 

priority areas in case of an oil spill. 

The collected information should be stored in a geographical information system 

(GIS). This information is to be combined with the coastal topography (an other GIS 

layer) in order to find out suitable locations for the establishment of booms and 

skimmers, in order to divert oil away and thus protect suitable locations (e.g. Qurmah 

island as suggested by Plaza et al. 1995) 

More important still, is to push research dealing with modern oil spill response 

technologies. For the Gulf Region a new adsorber based technology developed by the

University of Rostock, Germany, and the University of Szczecin, Poland, would be 

extremely efficient. The system is based on specially foamed small plastic elements 

(adsorbers) which have hydrophobic and oleophilic characteristics (EKU Development 

2002). These adsorbers are distributed by plane, helicopter or ships. The pore size of 

the adsorbers is adjusted to different viscosities of the oil. They are released from 

special containers under water to rise to the surface according to buoyancy. Oil within 

the water column will already be bound by the adsorbers on their way to the surface. 

The collection of the oil-soaked adsorbers is carried out by a conventional modified 

fishing technology which is carried by two ships. The adsobers could also be collected 

from the beaches, where hardly any oil remains polluting the beaches. The adsorbers 

can be cleaned for future use or disposed. The main advantage of this technology is 

the possibility to act in extremely shallow water, during high wind speeds and rough 

water as well as high currents. This highly effective system, which has been tested in 

temperate waters has still to be tested in the Arabian Gulf. Such tests should urgently 

be supported by decision makers and officials in the Gulf countries. By the means of 

such new technologies, combined with an effective information system, future oil 

spills might be under control before reaching the shores with their devastating effects 

to the biological communities. 

An other important field of research is the computing of efficient hydrodynamic 

models which are able to simulate the movement of oil slicks under different weather 

conditions. These models must also be developed for the coastal embayment systems 

(see next paragraph). 

243

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252

Appendix 1 

Chapter 3: climate 

Tab. 1 Total precipitation of three rain seasons. 

Abu Kharuf Abu Ali Mardumah Bay 

[mm] [mm] [mm] 

winter 1993/94 38,2 46,8 35,4 

winter 1994/95 86,3 69,1 135,5 

winter 2000/01 

* = no data 

77,6 * 132,5 

Tab. 2 Dew precipitation from November 2000 until April 2001 (Jubail center station). 

month total no data mean dew prec./night 

[mm] Tage [mm] 

Nov 0,272 17 0,021 

Dec 1,058 4 0,039 

Jan 1,107 4 0,041 

Feb 0,665 7 0,032 

Mar 0,490 12 0,026 

Apr 0,629 11 0,033 

Tab. 3 Relative humidity at three stations (1993-1995,2000,2001). 

month Abu Ali Abu Kharuf Mardumah Bay 

Jan 77,6 70,9 73,7 

Feb 75,6 66,9 69,5 

Mar 75,9 62,0 65,3 

Apr 74,5 58,8 56,1 

May 59,0 39,9 50,2 

Jun 56,0 38,6 49,4 

Jul 63,5 31,1 47,5 

Aug 66,3 37,5 56,3 

Sep 66,6 55,5 57,4 

Oct 68,1 64,4 64,9 

Nov 69,6 63,2 71,2 

Dec 78,0 72,1 75,6 

mean 69,2 55,1 61,4 

Tab. 4 Relative humidity at three stations (1993-1995,2000,2001). 

month Abu Ali Abu Kharuf Mardumah Bay 

[m/s] [m/s] [m/s] 

Jan 6,3 4,7 4,8 

Feb 6,4 4,9 5,0 

Mar 5,0 4,7 4,0 

Apr 4,8 4,9 4,3 

May 5,0 4,9 4,7 

Jun 5,4 5,4 5,0 

Jul 5,4 6,4 5,1 

Aug 4,6 4,9 4,4 

Sep 4,0 3,9 3,6 

Oct 4,0 3,8 3,5 

Nov 6,3 5,2 4,3 

Dec 6,9 4,7 4,9 

mean: 5,3 4,9 4,5 

253

Tab. 5 Rain events in the 2000/2001 rain season. 

date Abu Mardumah date Abu Mardumah 

Kharuf Bay Kharuf Bay 

[mm] [mm] [mm] [mm] 

01.11.2000 * 0,1 13.01.2001 0,2 0,2 

06.11.2000 * 5,8 14.01.2001 0,1 0,0 

08.11.2000 * 6,0 15.01.2001 0,1 0,0 

09.11.2000 * 9,3 16.01.2001 0,1 0,0 

17.11.2000 * 0,7 17.01.2001 0,1 0,2 

18.11.2000 * 10,4 22.01.2001 0,1 0,0 

19.11.2000 * 24,2 23.01.2001 0,1 0,1 

25.11.2000 * 3,2 02.02.2001 0,2 0,1 

26.11.2000 0,0 0,1 10.02.2001 1,9 0,1 

28.11.2000 3,6 0,4 02.03.2001 0,1 0,2 

09.12.2000 49,3 31,1 03.03.2001 0,2 0,1 

10.12.2000 3,2 1,1 14.03.2001 1,3 2,1 

13.12.2000 0,1 0,0 15.03.2001 0,0 0,1 

14.12.2000 1,2 0,2 22.03.2001 0,0 0,1 

19.12.2000 0,1 0,0 23.03.2001 0,0 0,3 

25.12.2000 0,5 0,1 24.03.2001 0,1 0,0 

31.12.2000 0,0 0,2 25.03.2001 0,0 0,3 

01.01.2001 0,1 0,0 

03.01.2001 0,2 0,2 total 77,6 132,5 

07.01.2001 0,0 1,4 

08.01.2001 14,5 34,1 number of days 

10.01.2001 0,1 0,0 with rain 25 30 

12.01.2001 0,1 0,0 

* = no data 

Appendix 2 

Chapter 6: 

Tab. 1 Soil texture Halocnemum transect (chapter 6.1.1.) 

sample > 2mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm CaCO3 colour 

15 m -2 0,8 9,2 14,8 8,4 66,8 10,2 10YR5/4 

15 m -20 13,7 23,7 29 19,6 14 75,4 10YR8/2 

15 m -45 13,3 11 28,7 28,7 18,3 61,7 2,5Y8/2 

45 m -2 0,3 11 12,3 44,3 32 27,4 10YR6/4 

60 m -20 5,7 16,7 24 29,1 24,5 

60 m -30 12,9 10,5 21 26,3 29,3 71,3 10YR8/2 

60 m -45 11,9 14,2 25,3 29,6 19 

90 m -5 5,2 11,7 22,3 23 37,8 63,8 10YR8/1 

90 m -25 9 9,7 26,7 12 42,7 66,7 5Y8/2 

254

90 m -50 13,8 15,3 19,3 20,3 31,3 70,1 2,5Y8/2 

120 m -15 8 11,7 32,7 33,7 14 55,6 5Y8/3 

120 m -20 2,2 9,8 13 27,2 47,8 58 

120 m -35 8 14,3 28,9 27,4 21,4 10Y8/1 

135 m -2 10Y6/1 

135 m -20 2,5Y4/2 

135 m -30 7,5YR8/1 

150 m -10 7,5YR8/1 

150 m -20 2,5Y8/1 

150 m -30 2 7,5YR5/8 

180 m -55 7 12,7 29,7 26,6 24 63,7 7,5YR8/1 

180 m -30 2,1 25,8 26,3 21,6 24,2 72,1 2,5Y7/2 

210 m -10 3,7 12 21,7 24 38,6 71,9 2,5Y8/1 

210 m -35 0,6 7,7 15,7 19,3 56,7 60,8 7,5Y8/1 

210 m -55 7,1 22,6 25,2 29,2 15,9 2,5Y8/2 

240 m -30 4,3 13 26,7 21,7 34,3 71,6 7,5Y8/1 

260 m -5 4,1 15,4 20,5 11,3 48,7 7,5Y7/2 

260 m -15 7 15,5 22,6 27,8 27 77,7 7,5Y8/1 

260 m -25 3,3 20,7 23,6 15,4 37 73,4 5Y8/3 

260 m -40 5,8 19,4 28,3 22,1 24,4 75 7,5Y8/1 

290 m -25 3,3 20,7 23,7 15,3 37 73,4 2,5Y8/1 

290 m -40 9,8 16,4 14,8 32,3 18,7 72,1 7,5Y8/1 

290 m -58 14,2 16,1 19,6 24,5 25,6 7,5Y6/1 

310 m -10 7,7 16 38,3 22 16 72,4 5Y8/2 

310 m -25 12,3 14 11,7 19,7 42,3 63,6 5Y8/1 

310 m -40 11,6 19,3 28,9 21,2 19 7,5Y8/2 

340 m -10 5,6 5 33,1 24,7 31,6 69,7 5Y8(2 

340 m -25 6,7 13,2 20,8 33,9 25,4 74,1 2,5Y8/1 

370 m -10 8 8,2 30 25,7 28,1 68,1 7,5Y8/1 

370 m -30 6,8 11,5 37,8 19,6 24,3 80,3 2,5Y8/3 

Tab. 2 Soil texture Arthrocnemum transect (chapter 6.1.2) 

Sample > 2mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm CaCO3 Colour 

0 m -5 0,3 5,7 21,7 23,7 48,6 25,3 10YR6/4 

0 m -40 12,7 9,3 41,7 23 13,3 43,2 10YR7/2 

45 m -5 3,5 12,5 19 27 38 49,1 2,5Y7/4 

45 m -40 7,3 11 40,3 25,4 16 53,7 2,5Y8/3 

90 m -5 0,8 8 32,8 33,2 25,2 53,8 2,5Y6/3 

90 m -40 5,6 6 29,2 29,6 29,6 56,3 2,5Y8/2 

105 m -10 0,8 4 30,4 28,4 36,4 59,5 2,5Y7/3 

105 m -40 4 8 32 23,7 32,3 54,5 2,5Y8/2 

105 m -65 0 1,5 83 12,5 3 2,5Y7/6 

120 m -20 4 15,7 59,3 18,7 2,3 59,7 2,5Y8/3 

120 m -40 6,7 13,7 37,3 18,3 24 64,3 2,5Y8/2 

135 m -20 10,7 23,7 41 13,3 11,3 65,9 2,5Y7/3 

135 m -40 6,3 8 36,7 21,3 27,7 54,3 2,5Y8/2 

150 m -10 8,7 16 46 17,3 12 52,7 10YR7/2 

150 m -25 6,3 10,3 37,3 20,3 25,7 53,9 2,5Y8/1 

165 m -20 4,9 7,6 12,4 30 45,1 53 7,5Y6/1 

165 m -30 7,7 7,1 42,4 29,3 13,5 55,5 7,5Y6/1 

180 m -15 6 8,1 35 22,1 28,8 56 2,5Y8/2 

255

180 m -23 3,9 6 15,2 28,9 46 51 2,5Y8/2 

195 m -20 5,7 8,3 12,3 29,7 44 49,3 2,5Y8/1 

210 m -20 4,3 6,3 50 30 9,4 45,5 2,5Y8/1 

225 m -10 2,3 7,3 53 28 9,4 38,2 5Y7/1 

225 m -30 12,8 19 30,6 22,7 14,9 60 2,5Y8/1 

240 m -10 6,8 9,3 38,5 29,6 15,8 28,1 5Y7/1 

240 m -30 6,6 10,5 46,9 18,4 17,6 56,5 5Y7/1 

255 m -5 4,9 13 35 23 24,1 46 2,5Y8/1 

255 m -15 9,6 9 41,8 19,6 20 59,7 5Y7/2 

270 m -5 6,4 8,8 37,4 22,1 25 62,9 5Y7/2 

270 m -15 12 11,8 30,8 24,1 21,3 72 2,5Y7/1 

285 m -5 7,1 9,9 39 21 23,3 57,9 5Y7/2 

285 m -13 10,6 14 28,2 22,7 24,5 70,5 2,5Y7/3 

Tab. 3 Groundwater chemistry of Halocnemum transect (chapter 6.1.1) 

Temperature Sulphate 

°C 29/11 14/12 31/12 14/01 29/01 10/02 10/03 06/04 

15 24 22,5 22,8 20,3 19,8 20 23 26,3 

30 22,9 21,5 21,4 19,3 18,2 20,1 23,2 26,7 

45 23 21,5 21,2 18,8 18,4 19,2 23 26,3 

60 22 21 21,4 19 18,2 18,8 22,3 26,1 

75 22,5 20,5 23 18,6 17,9 19,2 22,3 25,8 

90 22,5 20,5 22,3 19,2 18,3 18,7 22,5 26,6 

105 22 20,5 20,1 18,4 17,5 18,6 21,7 25,5 

120 22,2 20,5 20,4 19,1 17,6 18,7 21,8 25,7 

135 21,9 19,5 18,7 18,7 17 17,8 21,1 25,7 

150 21,5 19,5 17,8 18,1 15,5 17,6 21,2 25,1 

Chemistry for different locations during the winter months 

starting with the 150 m mark 

SO4- mg/l 150 m 120 m 75 m 30 m 15 m 

15/10 9.000 8.700 8.400 11.500 11.500 

04/11 8400 7200 8000 10100 10900 

16/11 6600 6700 7700 8800 9400 

29/11 7000 7500 9500 11500 10700 

14/12 5900 6300 8000 9400 10700 

31/12 6200 8000 7100 7500 9500 

14/01 5100 4800 5900 8600 9300 

29/01 5900 6100 6500 7900 9600 

10/02 6000 5000 6900 7900 8700 

10/03 7600 7000 5400 6100 5300 

06/04 8500 8000 11900 12000 11400 

Sample mS/cm °C Cl- SO4- Ca++ Mg++ NO2- NH4+ O2 Sample mS/cm °C Cl- SO4- Ca++ Mg++ NO2- NH4+ O2 

150 15.10 102/143 76.400 9.000 1.036 3.834 0,08 1 135 15.10 102,2 82.000 8.700 1.140 4.158 0,09 1 

150 4.11 117,5 71.000 8400 0,07 1 135 04.11 121 83000 9600 0,09 1 

150 16.11 76 46.000 6600 0,05 2 135 16.11 94 47000 7200 0,12 1 

150 29.11 86 21,5 46.000 7000 0,02 135 29.11 89 22 48000 7700 0,02 

150 14.12 85 19,5 41.000 5900 0,11 7135 14.12 85 20 40000 6700 0,06 7,9 

150 31.12 100 17,8 36.000 6200 0,05 7,9135 31.12 104 19 34000 6700 9,3 

150 14.01 80 18,1 24.000 5100 7,1135 14.01 86 19 30000 5700 9,3 

150 29.01 102 15,5 39.000 5900 2200 2340 0,09 9,8135 29.01 102/112 17 37000 7800 0,09 12 

150 10.02 93,4 17,6 33.000 6000 2000 1830 135 10.02 97 18 32000 5700 

150 10.03 110 21,2 57.000 7600 2200 2710 0,19 1 135 10.03 99 21 52000 5700 2360 2320 

150 06.04 133 25,1 75.000 8500 2240 3980 0,25 0,2 135 06.04 121 26 71000 9900 2480 4273 


120 15.10 105/117 71.600 8.700 1.084 3.653 0,04 1 105 15.10 103/119 78.400 8.400 1.186 3.658 0,16 1 

120 04.11 112 62000 7200 0,05 1 105 04.11 113 64000 7000 0,07 0 

120 16.11 77 43000 6700 0,04 1 105 16.11 95 40000 6100 0,05 2 

120 29.11 94 22,2 46000 7500 0,03 105 29.11 104 22 50000 8100 0,06 

120 14.12 83 20,5 41000 6300 0,08 6,3105 14.12 89 21 35000 6800 0,05 6,3 

120 31.12 96 20,4 30000 8000H2S 4,9105 31.12 108 20 34000 6000H2S 6,3 

256

120 14.01 82 19,1 31000 4800 9,1105 14.01 85 18 29000 5200H2S 9 

120 29.01 89 17,6 29000 6100 0,09 11105 29.01 89/96 18 28000 6900 2120 2120 1,06 11 

120 10.02 91 18,7 29000 5000 105 10.02 96 19 30000 4900 2040 2080 

120 10.03 92 21,8 47000 7000 2240 2200 0,07 1 105 10.03 93 22 50000 6100 2200 2344 

120 06.04 98,5 25,7 68000 8000 2400 3492 0,71 0,5 105 06.04 100 26 58000 6300 2480 3589 


90 15.10 104/125 66.800 9.400 1.216 3.687 0,16 1 75 15.10 100/124 78.000 8.400 1.112 3.707 0,25 2 

90 04.11 122 76000 9600 0,06 1 75 04.11 121 68000 8000 0,04 1 

90 16.11 102 41000 8000 0,01 2 75 16.11 95 43000 7700 0,02 2 

90 29.11 120 22,5 65000 9800 0,03 75 29.11 123 23 70000 9500 0,03 

90 14.12 107 20,5 53000 7300 0,04 675 14.12 110 21 78000 8000 0,07 6,8 

90 31.12 124 22,3 41000 5800H2S 675 31.12 122 23 40000 7100H2S 0,02 4,7 

90 14.01 96 19,2 33000 5400H2S 8,375 14.01 103 19 32000 5900H2S 8,5 

90 29.01 99 18,3 34000 6400H2S 0,09 1275 29.01 91/123 18 43000 6500H2S 0,15 9,4 

90 10.02 93 18,7 31000 5000 75 10.02 122 19 34000 6900 

90 10.03 93 22,5 49000 5600 2200 2100 0,07 1 75 10.03 105 22 58000 5400 2080 2662 

90 06.04 101 26,6 53000 7100 2360 3150 0,08 1 75 06.04 114 26 60000 11900 3280 3077 


60 15.10 96/137 75.600 9.700 1.192 4.258 0,48 1 45 15.10 80/153 80.400 10.500 1.072 4.234 0,38 0 

60 04.11 127 79000 12300 0,11 1 45 04.11 140 87000 11800 0,06 1 

60 16.11 88 41000 10600 0,02 2 45 16.11 106 50000 8900 0,01 1 

60 29.11 130 22 63000 9400 0,05 45 29.11 135 23 78000 11300 0,04 

60 14.12 121 21 85000 9000 0,05 5,9 45 14.12 128 22 67000 9600 0,08 6,3 

60 31.12 131 21,4 44000 9600 7,4 45 31.12 134 21 46000 8300 9,9 

60 14.01 94 19 34000 5900 9,6 45 14.01 113 19 35000 8200 7,1 

60 29.01 103 18,2 34000 6100 2320 2300 0,05 13 45 29.01 115 18 45000 6800 0,09 13 

60 10.02 94 18,8 30000 6100 45 10.02 104 19 32000 5800 

60 10.03 93 22,3 54000 7600 2080 2417 0,07 0 45 10.03 112 23 68000 5700 2360 2808 

60 06.04 112 26,1 62000 8400 2320 3760 0,03 2,4 45 06.04 129 26 76000 10000 2600 4224 


no no 

no no no 

30 15.10 93/143 87.600 11.500value 

value 0,24 15 15.10 no value 102.400 11.500value 

value value no value 

30 04.11 141 88000 10100 0,23 1 15 04.11 134 85000 10900 0,26 1 

30 16.11 106 54000 8800 0,02 1 15 16.11 116 51000 9400 0,02 1 

30 29.11 138 22,9 82000 11500 0,11 15 29.11 127 24 75000 10700 0,07 

30 14.12 130 21,5 69000 9400 0,05 6,4 15 14.12 129 23 81000 10700 0,07 7 

30 31.12 137 21,4 54000 7500 8,9 15 31.12 132 23 45000 9500 0,04 12 

30 14.01 129 19,3 64000 8600 9,2 15 14.01 129 20 56000 9300 9,2 

30 29.01 120 18,2 50000 7900 0,06 13 15 29.01 133 20 62000 9600 0,06 13 

30 10.02 137 20,1 54000 7900 15 10.02 135 20 55000 8700 2320 3660 

30 10.03 126 23,2 71000 6100 2320 3614 0,04 1 15 10.03 132 23 83000 5300 2520 3565 

30 06.04 127,3 26,7 71000 12000 2760 3931 1,1 2,2 15 06.04 131 26 75000 11400 2680 4371 

Tab. 4 Groundwater chemistry of Arthrocnemum transect (chapter 6.1.2) 

150 m markmS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 135 m markmS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 

13. Oct 99 6100 1000 2500 0,1 1 13. Oct 101 52000 6300 888 2657 0,1 3 3 

30. Oct 93 63000 7000 0 0 30. Oct 100 64000 7200 0,1 1 

16. Nov 83 39000 5000 0,1 2 16. Nov 83 35000 5800 0 

14. Dec 76 43000 5600 0 20,5 14. Dec 78 59000 5500 0 21 

31. Dec 79 29000 4900 0 18,6 31. Dec 82 32000 5000 20 

257

11. Jan 72 18000 16,7 11. Jan 63 18000 17 

29. Jan 82,6 22000 6800 2160 1710 17,8 29. Jan 81 20000 5200 0,1 18 

10. Feb 85 28000 5700 1880 2050 0,1 18 10. Feb 84 28000 6200 2000 2198 17 

10. Mar 92 46000 5900 2120 2198 0,1 0 21,1 10. Mar 86 40000 5000 2160 2539 21 

06. Apr 89 43000 7200 2040 2662 0,1 0,1 06. Apr 87 

120 m markmS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 105 m markmS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 

13. Oct 104 52000 5100 1020 3025 0,1 2 13. Oct 107 55000 7900 984 2984 0,4 3 

30. Oct 108 60000 8500 0,1 1 30. Oct 104 63000 7700 0 3 

16. Nov 80 34000 5800 0 1 16. Nov 77,5 35000 6100 0 2 

14. Dec 85 50000 8100 0 20,5 14. Dec 76,5 46000 5500 9,1 20 

31. Dec 87 44000 6200 20,8 31. Dec 78,5 31000 4900 20 

11. Jan 62 19000 3700 18,4 11. Jan 72,5 4100 20 

29. Jan 85 24000 6400 18,3 29. Jan 82 24000 5100 2080 1760 18 

10. Feb 83 25000 4600 0,1 18,6 10. Feb 80 26000 4900 1880 1900 0 18 

10. Mar 83 41000 6500 2040 2050 0,2 20,8 10. Mar 94 46000 6400 2200 2442 21 

06. Apr 85 5000 2120 2515 0,1 06. Apr 95 5200 2400 2662 

90 m mark mS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 75 m mark mS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 

13. Oct 105 68000 6800 960 2964 0,1 1 13. Oct 111 60000 6800 984 3100 0,1 0 

30. Oct 105 63000 7300 0,1 1 30. Oct 108 68000 7600 0 0 

16. Nov 80 34000 5900 0 2 16. Nov 90 41000 6600 0 1 

14. Dec 80 46000 6400 0,1 20,5 14. Dec 82 45000 5800 0,1 21 

31. Dec 87 26000 6700 0 19,5 31. Dec 105 43000 6400 0,1 20 

11. Jan 71 24000 4000 17,2 11. Jan 67,2 17 

29. Jan 81 20000 4700 17,8 29. Jan 86 20000 5800 17 

10. Feb 79 26000 5600 0,1 17 10. Feb 83 30000 5000 0,1 18 

10. Mar 89 45000 5200 2200 2100 0,2 20,2 10. Mar 91 50000 7100 2200 2393 21 

06. Apr 85 4700 2200 2615 0,1 06. Apr 95 54000 5400 2080 3200 

60 m mark mS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 45 m mark mS/cm Cl SO4 Ca Mg NO2 PO4 °C NH4 

13. Oct 116 60400 7900 1024 3448 0,1 0 13. Oct 120 73000 8600 1056 3610 0,1 1 

30. Oct 116 84000 10300 0,1 1 30. Oct 111 84000 9000 0,1 1 

16. Nov 82 39000 6300 0,1 2 16. Nov 93 42000 5500 0 2 

14. Dec 99 55000 7300 0,2 21,5 14. Dec 93 54000 6500 0,1 22 

31. Dec 112 45000 7100 20,7 31. Dec 102 36000 6100 21 

11. Jan 71 18 11. Jan 73 18 

29. Jan 83 20000 5200 1680 2030 17,2 29. Jan 81 18000 4200 1960 1950 18 

10. Feb 81 26000 5200 1960 1830 0,1 17,7 10. Feb 83 26000 5300 0,1 18 

10. Mar 93 51000 5500 2160 2295 0,1 21,4 10. Mar 93 47000 7600 2120 2344 22 

06. Apr 85 55000 4700 2480 3126 0 06. Apr 93 5000 2160 3126 

Tab. 5 Groundwater chemistry of mangrove transect (chapter 6.2.1.2) 

Cl- Dec Jan Feb Mar Apr °C Dec Jan Feb Mar Apr 

coast 16000 30000 32000 52000 65000 coast 24 16,8 19,7 22 25 

island 19000 30000 39000 64000 65000 island 22,5 17,4 16,6 19,6 23,5 

see 22000 38000 34000 50000 57000 see 24 20 19,6 31 

LF Dec Jan Feb Mar Apr Ca++ Dec Ca++ Feb Mar Apr 

coast 89,2 86,9 82,7 81 110 coast 1920 2100 1960 

island 76,2 100 96,6 101 104 island 2400 2760 

channel 79,8 81,5 88 88,4 89 see 2160 2040 

SO4-- Dec Jan Feb Mar Apr Mg++ Dec Mg++ Feb Mar Apr 

coast 6900 6300 5800 5600 9000 coast 1950 1953 2930 

island 5000 5100 6100 7100 12300 island 2442 3492 

see 4600 4650 4800 5900 10400 see 1929 3003 

258

Appendix 3 Chapter 6: 

Oil profiles of transects described in chapter 6.1.2 – 6.1.7 

Transect 6.1.2 

depth in cm 

depth in cm 

0 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

0 

-5 

-10 

-15 

-20 

-25 

15 

360 

30 

345 

45 

60 

75 

90 

105 

120 

135 

150 

165 

180 

195 

oil in burrows medium oiled heavily oiled well degraded oil residues 

330 

315 

300 

285 

270 

HWS HWN 

Transect 6.1.3 HWS HWN 

255 

240 

225 

210 

195 

180 



Transect 6.1.4 HWN 

HWS 

210 

165 

225 

150 

240 

135 

255 

120 

270 

105 

285 

90 

300 

75 

315 

60 

330 

45 

345 

30 

360 

15 

259

depth in cm 

0 

-2 

-4 

-6 

-8 

-10 

-12 

-14 

-16 

15 

30 

45 


depth in cm 

depth in cm 

0 

-5 

-10 

-15 

-20 

-25 

-30 

0 

-5 

-10 

-15 

-20 

-25 

-30 

-35 

0 

1035 

HWS 

15 

30 


990 

945 


60 

45 

900 

75 

60 

855 

90 

105 

120 

135 

150 

165 

180 

195 



75 

90 

105 

120 

135 

150 

165 

180 



810 

765 

720 

675 

630 

585 

540 

495 

210 

195 

450 

225 

210 

405 

240 

225 

360 

255 

240 

315 

270 

255 

270 

285 

270 

225 

300 

HWN 



180 

315 

135 

330 

90 

345 

HWS HWN 

HWS HWN 

45 

360 

0 

260

depth in cm 

0 

-5 

-10 

-15 

-20 

-25 

-30 

Appendix 4 

200 

190 

180 

170 

160 

150 

140 

130 

120 

110 

100 



Tab. 1 Soil texture of transects discussed in chapter 6.1.3 – 6.1.7 

6.1.3 > 2 0.63-2 0.2-0.63 0.063-0.2 < 0.063 6.1.5 > 2 0.63-2 0.2-0.63 0.063-0.2 < 0.063 

Sample mm mm mm mm mm Sample mm mm mm mm mm 

50 m -10 4 8 27 19 42 50 m -20 12 10 41 23 14 

50 m -15 8 17 30 15 30 100 m -10 1 3 20 41 35 

50 m -30 5 6 28 16 45 100 m -20 5 4 40 28 23 

90 m -10 3 5 24 19 49 100 m -30 13 19 38 18 12 

90 m -30 5 10 18 25 42 180 m -10 1 3 26 21 49 

140 m -10 9 15 31 12 33 180 m -12 6 11 33 12 38 

140 m -30 6 7 19 23 45 180 m -20 9 8 44 19 20 

240 m -10 4 8 27 18 43 250 m -2 1 9 24 11 55 

240 m -30 5 7 26 14 49 250 m -10 1 11 23 16 49 

260 m -10 8 16 29 16 31 250 m -20 10 16 31 17 26 

260 m -30 3 11 29 20 37 

6.1.6 > 2 0.63-2 0.2-0.63 0.063-0.2 < 0.063 

6.1.4 > 2 0.63-2 0.2-0.63 0.063-0.2 < 0.063 Sample mm mm mm mm mm 

Sample mm mm mm mm mm 0 m -10 3 10 25 18 44 

10 m -10 7 9 21 36 27 0 m -30 9 19 35 17 20 

10 m -35 11 12 42 17 18 85 m -5 4 9 20 12 55 

130 m -10 7 10 25 28 30 85 m -15 8 18 33 20 21 

130 m -30 5 9 29 30 27 85 m -20 2 5 34 18 41 

150 m -10 3 14 30 26 27 115 m -5 3 14 19 15 49 

150 m -20 5 12 45 20 17 115 m -20 6 9 23 11 51 

220 m -20 3 8 49 25 15 115 m -30 3 9 22 10 56 

300 m -10 5 16 38 21 20 205 m -30 1 6 24 12 57 

300 m -20 8 11 45 18 18 320 m -10 7 14 33 19 27 

340 m -10 3 12 47 22 16 320 m -20 5 11 18 15 51 

340 m -30 11 7 43 20 19 420 m -10 3 15 31 19 32 

420 m -25 6 16 45 19 14 

420 m -30 2 6 29 21 42 

420 m -50 1 4 20 13 62 

475 m -20 1 3 35 22 39 

475 m -30 3 7 24 19 47 

474 m -40 4 9 33 28 26 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

261

Tab. 2 Soil texture of low energy sand shore chapter 6.4.2 

6.4.2 

Sample > 2mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm CaCO3 colour 

0 m -10 0 3 80,4 16,7 0 6,6 2,5Y7/3 

0 m -40 8 21 54 15 2 8 

5 m -20 1 7 69 22,3 0,7 6,1 2,5Y6/3 

5 m -30 0,3 4,7 62,7 31 1,3 5,2 2,5Y5/2 

5 m -40 0,7 7,3 67,3 23,3 1,4 4,2 5Y5/1 

15 m -20 0 0,3 13,7 82 4 10,3 5Y4/1 

15 m -30 0,3 0 0,3 13,7 85,7 64,3 5Y7/1 

20 m -20 4,3 3,7 29 56,7 6,3 17,3 5Y5/1 

20 m -40 0,3 0,3 1,7 13,3 84,4 52,4 5Y8/1 

25 m -5 1 0,3 17,3 61,7 19,7 22,2 5Y5/1 

25 m -20 2,9 4,1 19,3 38 35,7 45,5 7,5Y6/1 

Appendix 5 

Tab. 1 Trace metal concentrations in 2001 (chapter 6.1.1) 

sample Nickel Vanadium Zinc Chromium Arsenic Cadmium Mercury Copper Lead 

135 m -5 6,05 4,92 6,4 3,36 3,85 0,025 0,05 4,17 1,92 

135 m -10 19,5 8,5 13,1 5,22 4,37 0,025 0,21 15,67 1,7 

135 m -20 4,73 2,55 2,47 2,67 0,92 0 0,11 1,98 0,85 

250 m -5 20,6 8,42 12,9 6,3 4,77 0,05 0,16 5,02 1,95 

250 m -10 20,4 9,85 5,57 6,1 3,12 0,025 0,18 4,57 1,27 

250 m -20 29 10,62 20 8,52 3,6 0,05 0,18 8,72 0,85 

350 m -5 13,9 6,77 6,87 4,6 3,17 0,75 0,14 2,82 2,55 

350 m -10 9,7 4,17 8,5 3,25 2,3 0,025 0,35 4,67 3,2 

350 m -20 9,47 4,4 11,6 4,4 2,6 0,025 0,17 355 1,82 

Appendix 6 

Soil temperatures in July in the upper eulittoral below a flat polygonally cracked cyanobacteria layer 

(chapter 6.1.1). 


45 

40 

35 

30 

25 

20 

15 

10 

1 

May 2001 

-5 cm -10 cm 

262



Temperautre in °C 

50 

45 

40 

35 

30 

25 

20 

15 

10 

1 

50 

45 

40 

35 

30 

25 

20 

15 

10 

1 

45 

40 

35 

30 

25 

20 

15 

10 

5 

1 

August 2001 

June 2001 

-5 cm -10 cm 

July 2001 

-5 cm -10 cm 


45 

40 

35 

30 

25 

20 

15 

10 

5 

1 

September 2001 

263


Temperature in ´°C 


45 

40 

35 

30 

25 

20 

15 

10 

5 

45 

40 

35 

30 

25 

20 

15 

10 

5 

45 

40 

35 

30 

25 

20 

15 

10 

1 

1 

5 

1 

Appendix 7 

October 2001 

December 2001 

February 2002 

Rapid assessment prints for chapters 6.1.1 – 6.1.7). 

6.1.1 




45 

40 

35 

30 

25 

20 

15 

10 

5 

45 

40 

35 

30 

25 

20 

15 

10 

1 

5 

1 

45 

40 

35 

30 

25 

20 

15 

10 

5 

1 

November 2001 

January 2002 

March 2002 

264

Sec. 12 –5 cm Sec. 10 –10cm Sec. 9 –5cm Sec. 7 –25cm Sec. 5 –10cm Sec. 5 –20cm 

17.8 g/kg 28.5 g/kg 34 g/kg 3.7 g/kg 24.6 g/kg 4.9 g/kg 

6.1.3 

50m – 5cm 140m –10cm 240m –5cm 240m –20cm 

16.5 g/kg 24.5 g/kg 19.3 g/kg 7.8 g/kg 

6.1.4 6.1.5 

Sec. 5 –30cm 150 m –10cm 340 m –3cm 220 m –5cm 260 m –5 cm 

0.8 g/kg 29.4 g/kg 64.5 g/kg 14.5 g/kg 15.9 g/kg 

6.1.5 


46.0 g/kg 22.3 g/kg 23.5 g/kg 10.3 g/kg 29 g/kg 2.2 g/kg 

6.1.6 



6.1.6 

265



6.1.7 


41.7 g/kg 

6.2.1 

53.3 g/kg 1.1 g/kg 28.1 g/kg 3.4 g/kg 34.4 g/kg 



6.4.2.1 


26.5 g/kg 35.1 g/kg 21.7 g/kg 28.9 g/kg 46.7 g/kg 15 g/kg 

Appendix 8 

Soil texture chapter 6.2 

Tab.1 Mangrove transect no.1. 

Sample > 2mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm CaCO3 Colour 

0 m -5 0,3 0,7 19,3 72,7 7 2,2 2,5Y6/3 

0 m -15 5,2 8,9 43,3 17 25,4 2,5Y6/3 

0 m -20 0,3 2,7 53 31,3 13 13,1 2,5Y7/2 

45 m -10 0,7 6,3 18,7 24,3 50 30,4 5Y7/2 

80 m -10 1,3 7,7 53,9 13,1 24 32,4 2,5Y8/1 

80 m -20 3,1 8 30,6 16 43,3 40,1 2,5Y8/1 

86 m -20 3,4 3,3 35,7 18,4 39,2 40,6 2,5Y8/2 

88 m -10 2 2,8 43,7 18,7 26,3 10,4 10YR8/2 

88 m -20 2,8 11,2 28 15,6 42,4 35,6 10Y6/1 

100 m -10 0,7 5,3 9,7 11,3 73 57,6 2,5Y8/2 

266

Tab.2 Mangrove transect no.2 Qurma island. 

Sample > 2mm 0.63-2 mm 0.2-0.63 mm 0.063-0.2 mm < 0.063 mm CaCO3 

0 m -3 4 11 37 16 32 

0 m -10 2 4 15 11 68 50,2 

0 m -15 0 5 19 15 61 

0 m -20 1 2 22 39 36 

0 m -30 5 13 42 19 21 

5 m -10 4 7 18 10 71 64,7 

5 m -30 9 12 34 22 23 

8 m -5 1 3 40 27 30 

8 m -15 2 2 14 13 69 

8 m -30 7 13 39 20 21 

11 m -30 0 1 23 24 51 

21 m -10 2 4 10 12 72 70,1 

Appendix 9 

GC spectra oil beneath cyanobacteria from Coast Guard transect (chapter 6.1.7, 6.1.9). 

Retention time 

267

268

Appendix 10 

Key species list for different shore types after Jones et al. (1995) and Kinzelbach et al. 

(1992): 

Rocky shores: 

Upper eulittoral: (gastropods) Nodolittorina subnodosa, Planaxis sulcatus, Trochus sp. 

(barnacles) Euraphia sp., Chthalamus malayensis, (bivalves) Ligia sp., Isognomon dentifera, 

(crabs) Metopograpsus messor 

Mid eulittoral: (gastropods) Cerithium scabridum, Clypeomorus bifasciata, Thais sp., 

(barnacles) Chthalamus malayensis, Balanus amphitrite, the serpulid worm Potamoleios 

kraussii, (crabs) Metopograpsus messor, (bivalves) Isognomon dentifera, 

Lower eulittoral: (barnacles) Balanus amphitrite, (gastropods) Cerithium scabridum, 

Clypeomorus bifasciata, (crabs) Metopograpsus messor, Hermit crabs Diogenes sp., 

(bivalves) Lunella coronatus 

Sandy shores: 

Littoral fringe: (crabs) Ocypode rotundata 

Upper eulittoral: (crabs) Scopiera crabicauda, (molluscs) Talorchestia martensii, Orchestia, 

Tylos, Dotilla blanfordi, Eurydice arabica, (gastropods) Pirinella conica, Mitrella blanda, 

(bivalves) Dosinia hepatica, 

Mid eulittoral: (gastropods) Cerithium scabridum, Cerithidae cingulata, Pirinella conica 

(barnacles) , (crabs) Ilyoplax frater, (bivalves) Macrocallista umbonella, Dosinia hepatica 

Lower eulittoral: (barnacles), (gastropods) Pirinella conica, Mitrella blanda, Cerithidae 

cingulata , (crabs) Macrophthalmus sp. , (bivalves) Macrocallista umbonella, Dosinia 

hepatica 

Muddy shores: 

Littoral fringe: (crabs) Cleistostoma dotilliforme 

Upper eulittoral: (crabs) Cleistostoma dotilliforme, Metopograpsus messor, Illyoplax sp. 

(barnacles) Euraphia sp., 

Mid eulittoral: (crabs), Macrophthalmus depressus, Illyoplax frater., (gastropods) Cerithidae 

cingulata, Pirinella conica, Mitrella blanda, (barnacles) , (bivalves) Macrocallista 

umbonella, Dosinia hepatica 

Lower eulittoral: (barnacles), (gastropods) Pirinella conica, Mitrella blanda, Cerithidae 

cingulata , (crabs) Macrophthalmus sp., Ilyoplax frater,, (bivalves) Macrocallista umbonella, 

Dosinia hepatica, Solen vagina 

269

The 1991 Gulf War Oil Spill

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