icolls - Sustainable Tourism CRC

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS
APPENDIX C: ALL ABSTRACTS SUBMITTED TO THE ICOLLS
SPECIAL SESSION AT THE ‘ESTUARIES AND CHANGE’
CONFERENCE
Title of paper: Trends in sediment and water quality in relation to riverine sediment loads to estuaries in south
Western Australia
Author: L.C. Radke, D. T. Heggie, I. Prosser, M. Robb, B. Brooke, D. Fredericks and J. Skemstad
Author's email: Lynda.Radke@ga.gov.au
Abstract: This paper examines trends in sediment geochemistry and water quality in relation to riverine
sediment loads to a suite of estuaries in south Western Australia. The surface sediment samples analysed are
from 12 wave-dominated estuaries, while sediment loads are derived from erosion and sediment transport
modelling for the catchments of these estuaries, conducted as part of the Australian National Land and Water
Resources Audit. As expected, sediment total nitrogen, phosphorus and organic carbon concentrations varied
inversely with sediment loads because mineral-bearing sediment dilutes organic matter concentrations. The
TOC:TS ratio of sediment is also negatively correlated with sediment loads, presumably because sulfate
reduction becomes more important for organic matter degradation as sediment loads increase. Significantly,
there is a pronounced curvilinear relationship between a weathering index for the estuarine sediment and
sediment load, with soil erosion explaining the rising phase of the curve at low to intermediate loads. Bedrock
erosion could explain the declining phase of the curve at higher sediment loads. The pattern of change for water
column total nutrients (nitrogen and phosphorus) with sediment loads is similar to that of the weathering index.
Most water quality problems occur in association with soil erosion, and at sediment loads that are intermediate
for the data set.
Title of paper: Nutrient distribution and behaviour in the Pichavaram Mangroves, India
Author: Ramanathan Alagappan
Author's email: alr0400@mail.jnu.ac.in, alrjnu@hotmail.com
Abstract: The coastal regions are where terrigenous materials are introduced to the ocean, where productive
wetlands have developed and the biogenic zones are the most productive regions of the oceans. The elevated
phytoplankton productivity of the neritic waters is in part due to the fertile input from rivers and the coastal
boundary currents promote primary productivity. The river dominated coastal margins are thus important both
for the regional enhancement of primary productivity and also for the biogeochemical changes occurring due to
changing sea levels. Pichavaram mangrove ecosystems have their center of distribution in the tropics and subtropics;
the global distribution of mangroves is likely to be most affected by temperature changes in the longer
term, shorter and medium term changes can be expected in individual mangrove communities as a consequence
of Changes to the physico-chemical environment and anthropogenic factors. In this paper, we focus on the
sources of energy to the mangroves; the nutrient input-export characteristics. The extensive spatial and temporal
measurements carried out in this study provide facts to highlight the extent of human intervention in the
mangrove ecosystems. Sampling of surface water was carried out throughout the year, on a monthly basis, at the
Pichavaram mangroves of south India. Surface water samples (1 litre) were collected in polyethylene bottles for
the determination of various physico-chemical and biological factors. The filtered samples were then analysed
for nutrients (NO3-NO2-, NH4+, PO4, Total Dissolved Phosphorus [TDP] and H4SiO4) using standard
procedures (APHA: Standard Methods for Water and Waste Water Analysis, 1985). In situ measurements of pH,
conductivity [EC], water temperature, total dissolved solids [TDS] and Biological Oxygen Demand (BOD) were
carried out using standard methods. In the Pichavaram mangroves, three different zones based on surface salinity
gradient and species diversity were identified for this study: i) the high salinity (>33‰); ii) intermediate salinity
(between 15 and 25‰) and iii) low salinity zone (60%) and a freshwater zone can be demarcated only during the monsoon. The maximum
depth of water in the Pichavaram mangrove area varies between 3 and 4 m near the main channel and the
minimum range is between 30 and 50 cm, with a mean depth of 1.5 m. Semi-diurnal tides flush this ecosystem,
with fluctuating tidal amplitude of 0.5 to 1 m. At each site four replicate samples of gas, water and soil were
collected and the water level from the sediment surface at the time of sampling was noted. Dissolved oxygen
(Winkler method), pH, and EC, were also measured in situ in the surface water using a portable field laboratory
kit. The nutrients distribution shows temporal and spatial variations. The nutrient budget using the LOICZ model
has predicted that input of nutrients is more than the out put. The N is the limiting factor. The Org. C is more in
the interior channel sediments and the DIC is very less in pre-monsoon seasons. The silt and sand fraction are
dominant here and the Clay mineral is dominated by montmorllionite and Kaolinite in the sediments. The Nitrate
and phosphate concentrations show the anthropogenic signature in the mangroves.
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