Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Runoff is generally regarded as one of the most important routes of nonpoint source pesticide pollution in agricultural surface waters. Of major concern is the fact that low, sub-lethal levels of pesticide exposure are responsible for negative ecotoxicological effects, stressing the need for methods capable of identifying problem areas where populations could be at risk. Predicted average losses of three pesticides in tributaries of nine sub-catchments of the Lourens River were calculated through use of a GIS-based runoff model. There was a significant (p < 0.005) positive correlation between the predicted average loss and mean measured concentrations of the insecticides both in water and suspended sediments (R2 between 0.75 and 0.9), indicating that the model could serve as a powerful tool for the risk assessment and management of surface waters in South African orchard areas. Based on field relevant exposure scenanos, the potential effects of azinphos-methyl on macroinvertebrate communities were evaluated in a combined microcosm and field approach. Microcosms were contaminated for 1 h with AZP (control, 0.2; 1,5and 20 ug/L; three replicates each) and acute effects on survival were evaluated 6 days after exposure. The sensitivity or tolerance of 12 core taxa was determined based on their response to the exposure scenarios and compared to field tolerance/sensitivity as was established by a field investigation at a control and contaminated site of the Lourens River. The sensitivity/tolerance of ten of the 12 taxa corresponded to that which was found in the field. Thus microcosm studies employing a field relevant design can be successfully linked to field studies and indicate that transient pesticide contamination affects the aquatic communities of the Lourens River. / AFRIKAANSE OPSOMMING Afloop word oor die algemeen beskou as een van die belangrikste roetes van niepuntbron pestisiedbesoedeling in landbou oppervlakwaters. Die feit dat lae, sub-letale vlakke van pestisiedblootstelling negatiewe ektoksikologiese gevolge kan hê, is van groot belang. Dit beklemtoon die behoefte aan metodes om probleemgebiede te kan identifiseer waar bevolkings aan risiko onderhewig is. 'n GIS-gebaseerde afloopmodel is gebruik om die gemidddelde verlies van drie pestisiede in die sytakke van nege sub-opvangsgebiede van die Lourensrivier te voorspel. Daar was 'n beduidende (p < 0.005) positiewe korrelasie tussen die voorspelde gemiddelde verlies en gemete konsentrasies van insektisiede in beide die water en sediment (R2 between 0.75 and 0.9) fases, wat aandui dat die model as 'n kragtige hulpmiddel vir risikobestuur van oppervlakwaters in Suid Afrikaanse boord-gebiede kan dien. Die potensiële gevolge van azinfos-rnetiel (AZP) op makroinvertebraat gemeenskappe is deur middel van 'n gekombineerde mikrokosmos (wat op veldrelevante blootstellings gebaseer is) en veldbenadering bepaal. Mikrokosmosse is vir 1 h met AZP gekontamineer (kontrole; 1; 0.2; 1; 5 en 20 ~g1L; drie replikate elk), en die akute gevolge op oorlewing is ge-evalueer na ses dae van blootstelling. Die sensitiwiteit of toleransie van 12 sleutel taksa is deur middel van hulle respons op die blootstellingsreeks bepaal, en met hulle veldtoleransie/sensitiwiteit vergelyk wat in 'n veldstudie by 'n kontrole- en gekontamineerde gebied in die Lourensrivier bepaal is. Die sensitiwiteit/toleransie van 10 van die 12 taksa in die mikrokosmos eksperimente het ooreengestem met die wat in die veld gevind is. Mikrokosmosstudies wat op 'n veldrelevante ontwerp gebaseer is, kan dus suksesvol aan veldstudies gekoppel word, en dui aan dat oorgedraagde pestisiedkontaminasie die akwatiese gemeenskap van die Lourensrivier beinvloed.

This study assesses the contribution of agricultural non-point source pollution, to poor water quality of the Vaal River within the Grootdraai dam catchment area. The study evaluates agricultural pollutants affecting the quality of water within the study area. The impact of agricultural non-point source pollution on the water quality of the Vaal River was evaluated by establishing a correlation between the quantity of polluted runoff reaching the River and the quantity of measured nitrates and phosphates in its waters. A questionnaire using random sampling was used to capture data from 15 commercial farmers 35 local residents and the Department of Water Affairs management. The results of the study show that agricultural nutrients are heavily impacting and compromising the water quality of the Grootdraai Dam. The mean concentrations of Nitrogen and Phosphorus were found to be well above the water quality guidelines there by promoting eutrophication. / Environmental Sciences / M. Sc. (Environmental Management)

This study assesses the contribution of agricultural non-point source pollution, to poor water quality of the Vaal River within the Grootdraai dam catchment area. The study evaluates agricultural pollutants affecting the quality of water within the study area. The impact of agricultural non-point source pollution on the water quality of the Vaal River was evaluated by establishing a correlation between the quantity of polluted runoff reaching the River and the quantity of measured nitrates and phosphates in its waters. A questionnaire using random sampling was used to capture data from 15 commercial farmers 35 local residents and the Department of Water Affairs management. The results of the study show that agricultural nutrients are heavily impacting and compromising the water quality of the Grootdraai Dam. The mean concentrations of Nitrogen and Phosphorus were found to be well above the water quality guidelines there by promoting eutrophication. / Environmental Sciences / M. Sc. (Environmental Management)

The Kat River is an agricultural catchment that drains salt rich geology. Potential salinity impacts on ecological condition of the river were investigated. Monthly salt concentrations and flow discharges were monitored at ten sites along the Kat River below the Kat Dam. Monthly salt loads were computed to relate salinity to land use and ionic data used to assess the toxicity of major salts using the TIMS model. Concentration duration curves for sodium chloride were derived from flow concentration relationships, representing sodium chloride concentrations to which the aquatic ecosystem had been exposed. The ecological condition was assessed at nineteen sites using SASS5 biotic index over four seasons. Finally, the modelled instream salt concentrations and bioasessments were evaluated in terms of the modelled level of species protection afforded at different salt concentrations. Species Sensitivity Distributions (SSDs) were used for this exercise. There was a general downstream increase in salinity with the minimum concentrations recorded at the Fairbain tributary (84 mg/L) and maximum levels at the sewage outfall in Fort Beaufort (1222 mg/L). There was evidence that citrus irrigation upstream of Fort Beaufort increased salinisation. Sodium chloride, and to a lesser extent magnesium sulphate, were the dominant salts in the Kat River catchment, with the latter being more toxic. However these had little or no impact on the aquatic ecosystem. Flow-derived sodium chloride concentrations showed that both the Balfour and Blinkwater tributaries were in a fair/ poor condition. However with regard to ecological condition, it was demonstrated that the river is generally in a good state except for the Blinkwater River and the lower catchment. Degraded habitat condition at the Blinkwater was responsible for poor ecological condition. Integrating SSD derived classes, sodium chloride classes and ecological condition indicated that sodium chloride is a driver of ecological condition at the sewage treatment works and the subsequent site (only two of nineteen biomonitoring sites).