Lerotholi, S. et al - eWISA

BIOASSESSMENT OF A RIVER IN A SEMI-ARID,
AGRICULTURAL CATCHMENT, EASTERN CAPE
S. Lerotholi 1 , C.G. Palmer 1 and K. Rowntree 2
1
Unilever Centre for Environmental Water Quality, Institute for Water Research, Rhodes University,
PO Box 94, Grahamstown 6139.
2
Geography Department, Catchment Group, Rhodes University, Grahamstown. Corresponding Author:
Tel: (046) 622 2428 or 6224014. Fax: (046) 622 9427. E-mail: tally@iwr.ru.ac.za
ABSTRACT
The Kat River flows from a semi-arid agricultural catchment in the Eastern Cape. The river is
vulnerable to salinisation, owing to the type of climate and geology. The problem is exacerbated by
the predominance of citrus irrigation and sewage treatment plant effluent at Fort-Beaufort, the main
urban centre in the catchment. An assessment of the salinity in the Kat River catchment was
carried out using; historical water quality data, time series plots and an evaluation of the
relationship between flow and Total Dissolved Solids as a surrogate for salinity. An additional salt
load monitoring that included flow and electrical measurements was undertaken at the end of every
month to assess the magnitude of salt load transport in the catchment. Continuous salinity
measurements were taken at one of the DWAF weirs to monitor the relationship between flow and
salinity more closely. Bioassessments were also undertaken simultaneously so as to be able to
relate salinisation to ecological health. Different indices, SASS5 for macroinvertebrates, FAII for
fish, RVI for riparian vegetation and IHAS for the physical habitat were used. The role played by
salinity on the macroinvertebrate community structure is being investigated by relating instream
salinity, salinity tolerances and macroinvertebrate community composition.
INTRODUCTION
Salinisation has been identified as one of the main water quality concerns in South Africa
(1)(32)(33) and (14). Both natural and anthropogenic factors may contribute to this high salinity. A
number of natural processes are responsible for the high salt concentration in the country’s water
bodies. Evaporation can cause salts concentration to increase (32), as some of the water is lost in
the atmosphere as water vapour. This phenomenon is prevalent in arid and semi-arid
environments (9), where the annual rainfall is exceeded by the annual evaporation (4). In other
parts of the World, aerosol spray from the sea are a major source of salts to the land and running
water especially in areas that are in the proximity of the sea (4). Salinisation in water bodies may
also be caused by the geology in an area (16). Sedimentary rocks like shale that are easily
weathered are capable of adding more salt to the surface water environment, through base flow
(16).
However the input of salts in rivers, can also either be created or exacerbated by anthropogenic
activities that are prevalent in the catchment (9)(32) and (33). Irrigation has been identified as one
of the sources of salts in river systems. After irrigation, some of the water may evaporate, leaving
salt concentrates on the surface. These salts may end up in a river system through wash-off after a
storm (32). Irrigation also causes a build up of salts in the soil profile. During groundwater
recharge, these salts are leached out and ultimately end up in the surface water (4). Other
activities include mining, tree felling and waste disposal (32). Sewage treatment works usually
discharge their effluents back into the river (9) and (32).
These various processes result in increased salt levels in rivers, hence salinisation. The higher the
salt levels in the water, the higher the likelihood that it would be deemed unfit for its intended use
(3). It would therefore require the water to be treated before its intended use. This does not only
cost more money for water treatment, but agricultural production will surely decrease.
Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004
ISBN: 1-920-01728-3 Cape Town, South Africa
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Salinity also affects riverine aquatic ecosystems (2) and (32). Some of the goods and services that
are provided by the river ecosystem are, damaged at differing levels of severity (26), (17) and (12).
The National Water Act (No. 36 of 1998), recognises a need to provide for the ecological Reserve,
in order to sustain the ecosystems in a state that they can provide for different uses (8).
Traditional water quality monitoring (including salinity) programmes alone, cannot be used to
assess the impact of salt and other impacts on aquatic ecosystem (7) and (26). It is practically
impossible to monitor all the different water quality parameters over a long period of time (12). The
current monthly sampling frequency can miss important extreme events that may impact on the
aquatic ecosystem. Water resources management has evolved into incorporating chemical and
biological monitoring in monitoring programmes (7),(17) and (12). This employs the use of
components of the aquatic ecosystems as indicators because the ecological integrity cannot be
measured directly. Macroinvertebrates (10), (11) and (22), fish (5), (6) and (19), riparian vegetation
(25) and the physical habitat (23) and (28) can all be used to infer the ecological integrity. Different
indices and protocols have been implemented in different parts of the world to deal with the
biological assessments of rivers as a tool for water resources management. In South Africa, the
South African Scoring System version5 (SASS5) for macro invertebrates, Fish Assemblage
Integrity Index (FAII), Riparian Vegetation Index (RVI) and the Intergrated Habitat Assessment
System (IHAS) are being widely applied.
GEOGRAPHICAL SETTING OF THE STUDY AREA
The Kat is a tributary of the Great Fish River in the Eastern Cape of South Africa. It rises from the
Hogsback mountains on the North East and the Katberg in the North West. Balfour, Fairbairn and
Blinkwater streams, are the main tributaries entering the river below the Kat River dam. The dam
was commissioned in 1970 and the Department of Water Affairs and Forestry (DWAF) controls the
dam releases. The river extends for about 80 kilometres before it joins the Great Fish River. The
area is heavily used for both stock farming and citrus irrigation in the middle and lower reaches.
Several rural villages are found along the river, as it is the most important source of water in the
area.
The geology of the area is predominantly of sedimentary origin (4) with igneous intrusions. Shales
that are ubiquitous through the area have been associated with high salinity areas. The climate in
the area varies considerably; the upper catchment receives annual rainfall of about
1000mm/annum compared to only about 400mm/annum in the lower reaches (4). Prevalence of a
high evaporation rate means the lower reaches are highly vulnerable to salinity as in other semiarid
environments. This poses a threat to the use of the river as the main source of water supply in
the area. High salt levels can be detrimental to citrus trees (4), which are the main economic
activity in the area. In fact a drought in the early 1980’ s rendered a threat to citrus commercial
farming as the salt levels were regarded a threat to irrigation. As a result commercial farmers then
initiated a salinity-monitoring programme mainly in and around their citrus orchards. The data
collected by the farmers where spot salinity measurements as Electrical Conductivity. Water quality
is monitored at DWAF weirs at the Kat dam, on the Kat at Fort-Beaufort and on the Balfour and
Blinkwater rivers.
The salinity level in different parts of the catchment, can also depend on the flow in the river (15)
and (20). This highlights the importance of monitoring both flow and salinity level (14). Furthermore
the aerial extent of the monitoring needs to be expanded further beyond that carried out by DWAF.
As noted above, the level of salts in rivers can be affected by catchment-wide land and water use
as well as climate, topographic and geological characteristics. Salinity management depends on an
integrated, catchment-wide approach that incorporates knowledge of the effects of flow regime
alterations on the salt concentration (9). Alterations in the flow, can lead to changes in water quality
(20), (24) although such relationships are often complex (14) and (15). The direct results of which
are that the interaction between different factors and inputs from tributaries are difficult to manage
(30).

In the context of different management priorities, the objectives of this paper are to assess the
ecological integrity of the Kat river and its main tributaries. In addition it aims to describe the extent,
magnitude and significance of catchment scale assessment of salt loadings. Finally the role of
salinisation on the macroinvertebrate structure will be investigated.
MATERIALS AND METHODS
Salinity Sampling Sites
During the course of this study, a number of sites on the Kat River and tributaries were selected for
monthly salinity and discharge monitoring. The main aim of the exercise was to determine the salt
loads inputs from different reaches and tributaries. Sites on the Balfour and Blinkwater tributaries
were not monitored for salinity because flow and salinity data is already being collected by DWAF
every fortnight. At the selected site, flow was measured using the flow-area method (29). A tape
measure and a scientific instruments flow meter were used in taking average water speeds at the
0.6 depths (29). Electrical Conductivity readings were taken using a Cyber scan conductivity meter.
These readings were then later converted to Total Dissolved Solids by multiplying by a factor (16),
as shown in equation [1]
EC (mS/m) x 6.5 = TDS (mg/l) [1]
Salinity Modelling
Simple flow concentration models have been developed to aid in the predictions of salts at different
flow conditions (13) and (9). Other author’s have assessed the implications of dam releases on
water quality components in downstream reaches (30). The model by Malan (2003) is readily
available from the Water Research Commission, and was chosen to assess the relationship
between historical daily flows and salinity measurements from DWAF. The model makes use of
mean monthly flows and monthly salinity concentrations.
Salinity Logging
It has already been mentioned that the relationship between flow and concentration is not always a
straightforward one (20). A number of author’s have shown that the salt concentration at a
particular time depends on whether it was taken at the lowering or the rising limb of the hydrograph
(24). It therefore means that it is sometimes necessary to take continuous measurements of both
flow and salinity. The relationship is important because it will reveal the salt concentrations that the
river biota is being exposed to over time (2),(11) and (21). For this purpose a YSI 610 DM data
logger was installed at one of the weirs in Fort-Beaufort. Before the logging could begin, the DWAF
transducer and the data logger were synchronised.
Bioassessment Methods
Even without human impacts, resident biota in rivers (e.g. macroinvertebrates) varies from the
mountain stream to the mouth (1). This presents a challenge in assessing a change in aquatic
ecosystems due to water quality. In order to deal with the problem, the river was divided into
reaches according to the slope on the 1:50, 000 topographic map. The major assumption is that
reaches represent zones of aquatic ecosystems that are homogeneous in terms of the physical
habitat (17). Site selection involved visiting all potential sites and selecting at least a site in each
reach for comparisons (12) and (21). An attempt was made to select less impacted sites
(reference), which are upstream of citrus farming and monitoring sites downstream. Thus a paired
approach was used in site selection.
Sampling in the Kat River and its major tributaries, was undertaken to cover all the four seasons of
the year. The sampling design was such that the frequency of sampling varied for different indices.
SASS 5 sampling was undertaken in all the four seasons, since macroinvertebrates were being
used in evaluating salinity impacts on the aquatic ecosystem. The sampling was carried out
according to (10) and samples were preserved in 80% alcohol. These were later sorted in the lab,
where the individuals from each family were counted and further identification to morpho-species
may be carried out in the future. Limited water quality measurements were taken during the SASS5
sampling. Temperature, Ph, Dissolved Oxygen and Electrical Conductivity were recorded at every
site. A total SASS5 score for a particular site was derived from a summation of all family scores

esident at a site. With this, the Average Score Per Taxon (ASPT) was calculated by getting a
quotient between the total SASS5 score and number of families recorded at a site (10). An
assessment of habitat sampled and the general condition of a site were evaluated using the
Integrated Habitat Assessment System (IHAS) (28). Thus a habitat assessment was carried out
together with every SASS5 sampling.
Fish are the other component of aquatic ecosystem that can be used to infer the ecological
integrity or health (5),(6.),(18) and (19). Two FAII surveys were carried out during a year. An
electro-shocker was used to sample for fish in the available fish habitat at each site (6). On rare
occasions where the substrate was not made of cobbles, a seine net was used to sample. Most of
the fish were identified in the field with a few specimens conserved in 10% formalin and brought
back for verification with fish experts. In addition, the conditions of the riparian vegetation are to be
assessed later in the study. The Riparian Vegetation Index is to be used for this purpose.
RESULTS AND DISCUSSION
The results presented in this paper are those that were attained midway of the research work.
They include salt loads, SASS5, ASPT, IHAS and fish species that were caught for the FAII. The
main questions in the study are therefore not yet fully answered.
Table 1. Monthly salt loads measurements from July to December, 2003.
River Site Description
Fairbairn 4 Before it joins the
Kat
Kat 5 Downstream of
Confluence with
Fairbairn
Kat 9 Downstream of
Confluence with
Balfour
Kat 10 Downstream of
Citrus farming
Kat 12 Downstream of
Confluence with
Blinkwater
Kat 16 Downstream of
Sewage treatment
Works
Kat 17 Upstream of Citrus
farming
Kat 18 Downstream of
Citrus farming
Kat 19 Upstream before
Confluence with
Fish River
- means no measurements were taken due to the river being dry
Salt load (Kg/Sec)
Jul Aug Sep Oct Nov Dec
0.17 0.09 0.21 0.31 0.23 0.24
4.08 1.25 1.77 1.99 1.50 1.19
2.33 0.64 3.31 1.46 1.98 1.65
9.30 0.48 2.10 1.44 0.90 1.26
11.62 0.39 0.07 0.97 0.40 0.35
9.30 1.27 0.07 0.74 4.35 3.43
3.76 0.64 3.76 0.64 0.34 3.52
11.62 0.49 3.04 3.15 - -
2.15 1.02 4.47 4.12 - -

The monthly salinity loads results reveal that the Fairbairn tributary is contributing minimal salt into
the Kat river system (table1). This was however to be expected because of its low salinity level
(TDS, 77 to 114 mg/l) and the relatively low flows compared to the Kat River. From these
preliminary results, the Kat River transports most of the salts. However this data does not include
other tributaries, Balfour and Blinkwater Rivers. Salt loads for these rivers will be computed from
data sourced from the Department of Water Affairs and Forestry. High salt loads at site 16, may be
due to the sewage treatment plant effluent. In all the six months, TDS values have been the
highest compared to other sites. The salinity increases progressively as one move down the
catchment. However, the trend changes between sites 16,17,18 and 19. The reasoning behind has
not yet been established.
The following is the different results of SASS5, ASPT and IHAS scores obtained at different sites. It
appears that the habitat at different sites differed considerably during the different seasons. The
size of stones at site three were making it difficult to kick. At some of the sites not all
macroinvertebrate habitat was available. This makes the direct comparison of SASS scores to
suspect. A better approach might be to compare sites with regard to stones in current biotope, as
this is available at all the sampled sites. On the other hand the IHAS scores show a drop in Winter.
This can be associated with the low water levels that resulted in marginal vegetation at most sites,
not being sampled.
SASS Score
ASPT
200
180
160
140
120
100
80
60
40
20
0
9
8
7
6
5
4
3
2
1
0
Kat River Autumn,Winter and Spring SASS5 Scores
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Site Number
Kat River Autumn, Winter and Spring ASPT Scores
1 2 3 4 5 6 7 8 9 10
Sites
11 12 13 14 15 16 17 18 19
Autu
mn
Winte
r
Autumn
Winter
Spring

Figure 1. SASS5 scores for the three seasons range from 168 to 83, IHAS from 46 to 71 and
ASPT from 4.7 to 7.6.
Identified fish species at different sites were Barbus anoplus, Sandelia bainsii, Tilapia sparmanii,
Labeo umbretus, Glossogobius callidus and Anguilla bicolor bicolour. Barbus anoplus were caught
at all the sites except 17,18 and 19. Sandelia bainsii were caught in 2,4,5,9,10 and 16 whilst Labeo
umbretus were found at sites 10,11,17,18 and 19. Tilapia sparmanii were recorded at sites 10,14
and 15, Glossogobius callidus in sites 15 and 16, Anguilla bicolor bicolour at site 17. No fish
species were recorded at site 6. The average number of fish species caught at each site is low.
This is being identified as one of the problems of applying the FAII in the area. Furthermore, the
natural conditions have not yet been established. This means it is not yet possible to calculate the
FAII at different sites.
The RVI assessment will be conducted in the future. Available results are not sufficient for the
assessment of the ecological health. Reference conditions for both macroinvertebrates and fish
need to be defined. All SASS samples are being sorted, to get the actual numbers from different
sites. Primer 5, will then be used to compare the different sites. Monthly salinity and discharge
monitoring will be undertaken for 6 more months. Salinity and flow data from the different DWAF
weirs is being used to relate salinity and flow. The role of salinity on the macroinvertebrate
community structure will be assessed in the future. Instream salinity, salinity tolerances and
macroinvertebrate community composition are going to be used for this purpose.
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