BUFFALO RIVER, EASTERN CAPE
4.3 S TUDY SITE
4.4.1 Collection of test organisms and experimental medium
A preliminary investigation of the Buffalo River revealed that baetid nymphs were in abundance in an unimpacted area upstream of King William’s Town. Their absence in the polluted downstream section of the river could indicate their sensitivity to effluents released downstream. Although present throughout the year, the abundance of baetids appeared flow-related. Field investigation during winter months showed very few baetids present, probably related to reductions of flow. Reduced flow conditions can induce organisms to release their hold on the substrate and swim into the water column (Minshall and Winger, 1968 cited by Corkum, 1977). During some summer months, mayflies were swept away by heavy flows, which would be expected, as baetids rely on claws and swimming to resist currents (Hynes, 1960).
Baetid (Ephemeroptera) nymphs were collected from shallow, rocky, riffle areas in the Buffalo River downstream of the Rooikrantz Dam (Figures 4.3 and 4.4). This site was chosen as it was considered “unpolluted” and not impacted by any effluent or point source discharges. It is also one of the sites used by Palmer and O’Keeffe (1990a,b) during the Buffalo River Programme conducted at the IWR from 1986 to 1988. The nymphs of baetid mayflies were selected as test organisms because other researchers and institutions such as US EPA, American Standards of Testing Materials (ASTM) (Persoone and Janssen, 1993), and the IWR (Palmer et al., 1996;
Williams, 1996; Binder, 1999) used them routinely, and they were in abundance.
After collection from the test site (Figure 4.4), the test organisms were transported a distance of about 20 km to the Zwelitsha laboratory for sorting. As baetids are extremely sensitive to handling and can be easily damaged (Palmer et al., 1996;
Williams, 1996), handling was kept to a minimum. After sorting, about 30 to 40 organisms were placed in each artificial stream system. Since the baetids from the sampling site appeared to be a mixed population, and it is not possible to speciate baetids live, a great effort was made to select similar-looking organisms so as to increase the probability of using a greater percentage of the same species. The nymphs with wing-buds were not used, as they would probably emerge during the experiment.
Buffalo River water was collected in 25 litre plastic containers from the same site where the test organisms were collected. River water was used as test diluent as well as control medium. It was analyzed by IWQS before the start of the project to ascertain its suitability for use as test medium. Physico-chemical analysis results indicated good water quality (Section 4.5.1, Table 4.2).
Figure 4.4 Sampling and collection site in the Buffalo River during low flows.
The textile effluent used as the toxicant was collected from two points: i) the settling tanks before irrigation (i.e. General Textile Effluent), and ii) post-irrigation from the Tailwater Dam weir after irrigation. General effluent is therefore the effluent directly from the mill, excluding caustic effluent and sewage effluents. Post-Irrigation Textile Effluent is the seepage and run-off from the irrigated land that collects in a holding dam, the Tailwater Dam. The results of chemical analyses by IWQS are presented in Section 4.5.1, Table 4.2. Grab samples were taken in 25 litre plastic containers. Grab samples were preferred for acute toxicity testing since the effluent was highly variable (Burton et al., 1996).
130 4.4.2 Experimental approach
Laboratory design
Twelve recirculating artificial streams, the channels (Figure 2.1), were set up at the Zwelitsha Scientific Services laboratory near King William’s Town, which is under the control of the DWAF in the Eastern Cape region. Laboratory temperature was controlled with the use of a Panasonic room air-conditioner, Model CW-A90FN, and maintained between 16°C and 22°C (mean = 19.4°C, standard deviation ± 2.3°C).
Maintaining the laboratory temperature at a smaller range was difficult due to the fluctuation in ambient temperatures. Lighting was maintained at a 12:12 hour light:dark cycle with OSRAM biolux tubes providing wavelengths of light similar to sunlight (Palmer et al., 1996).
Experimental stream systems and experimental procedure
The channel stream systems used for toxicity tests are described in Chapter 2. After an acclimation period of 36 hrs, 96 hr acute and 7 day sub-chronic toxicity tests were conducted. The Buffalo River water was used as test water, the textile effluent as toxicant, and the baetids as test organisms. For general experimental procedure refer to Chapter 2. Test organisms in channels were exposed to increasing percentages of textile effluent (Table 4.1) in a regression design (Section 2.5), with one channel used as a control. During Experiment 7 (a 7 day sub-chronic toxicity test), the test medium was replaced with freshly prepared test medium after 96 hours to reduce the build-up of toxins and metabolites, such as ammonia, in the water (Coler and Rockwood, 1989). All the preserved test organisms were sent to the IWR at Rhodes University for identification by Mr. KM Soxujwa, as it was difficult to identify the organisms before the start of the experiment.
Water quality analyses
The whole effluent was chemically analysed by the IWQS at the start and finish of each experiment to provide information on chemical composition, and to determine the variability in the measured variables over time, and between individual experiments. Daily measurements of pH, temperature and EC were routinely taken in
each experimental channel. The Amel digital conductivity meter (model 160, graphite electrode model 193) was used for EC measurements, and the Knicks calimatic pH meter 601, for pH readings.
TABLE 4.1
PERCENTAGE CONCENTRATIONS OF TEXTILE EFFL UENT USED FOR ACUTE (96 HOUR) AND SUB- CHRONIC (7 DAY) TOXICITY TESTING WITH BUFFALO RIVER WATER AS DILUENT AND CONTROL.
Experi- ment number
Type of
Experiment Type of Effluent Effluent concentration (%) Starting date
1 1,3,5,10,20,30,40,50,60,75,100 24-11-1997
2 1,3,10,30,40,50,100 01-05-1998
3 1,3,10,15,20,25,30,50 07-05-1998
4 1,3,5,10,15,20,25,30,50 11–05-1998
5
Acute
General Textile Effluent (GTE)
0.5,1,3,5,10,15 15-05-1998
6 Acute 1,3,10,15,20,25,30,50 21-05-1998
7 Sub-chronic
Post-Irrigation Textile Effluent
(PITE) 1,3,5,10,20,30,50,60,75,100 02-06-1998
8 Acute
General Textile
Effluent (GTE) 1,3,5,10,15,20,25,30,50,100 11-11-1998
Data analysis
The experiments were set up using a regression design with one channel at each dilution, plus a control. The Probit and Trimmed Spearman-Karber methods were used to calculate LC50 values, as described in Chapter 2. The Probit method was preferred as it also provides LC1 and LC5 values. These values were used to derive the Acute Effect Values (AEV) (Section 2.9.4) (see DWAF (1996f) for methods). The AEV, LC1, LC5, and the associated 95% confidence limits were used to apply the hazard-based approach of Palmer and Scherman (in press). This approach links toxicity test results to river health classification (DWAF, 1999a; Kleynhans, 1999).
132 4.5 RESULTS
In this the study attention was paid to the toxicity of two textile effluents: (i) general textile effluent (GTE), and (ii) post-irrigation effluent (PITE). Six 96 hr acute tests were conducted using GTE, and 1 acute and sub-chronic test using PITE. The PITE effluent reaches the river via an overflow from the Tailwater Dam weir down the Mlakalaka stream.
4.5.1 Chemical composition of Buffalo River water and textile effluent