Water quality of the Mooi River North-West Province : a supporting study for the determination of resource quality objectives
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South Africa, a semi-arid country, is currently facing an increasing water scarcity. Therefore a need exists for the management of water resources. A balance must however exist between the need to protect and maintain our water resources and the need to utilize it. As a means to ensure a desired level of protection, resource quality objectives (RQO) have to be determined for all significant water resources. The purpose of the RQO is to provide numerical and narrative descriptors of quality, quantity, habitat and biotic conditions as a basis from which management actions can be implemented for the sustainable use of all water resources. The Mooi River, located in the North West Province, is a significant water resource that forms part of the Upper Vaal catchment region. Potable water for the City of Potchefstroom is gathered from the Mooi River catchment, specifically the Boskop Dam, from where it is transported to the purification plant. During this study the water quality of the Mooi River were determined by means of algal indices, physico-chemical analyses and microbiological analyses. Samples were taken at eight sites along the Mooi River, including three reservoirs. The Mooi River, regularly form part of the news due to the Wes Rand mining activities and the impact thereof on the Mooi River via the Wonderfonteinspruit. The main uses of the Mooi River include abstraction for drinking water and irrigation, agricultural activities and recreation. The physico-chemical and microbiological data is therefor expected to exhibit results indicative of aforementioned activities. The variables for this study were chosen with these activities in mind in order to achieve the objectives set out for this study. Due to their high reproductive rates, algae respond rapidly to natural and/or anthropogenic changes in their environmental conditions. During this study four algal indices and the overall algal group abundance was used to aid in determining the water quality of the Mooi River. The Palmer index, indicative of organic pollution, the Shannon-Weaver index, indicative of inorganic pollution, and the Margalef- and Pielou index indicative of species richness and evenness respectively. The Palmer index showed that the Mooi River currently experiences high levels of organic pollution with index scores higher than 20. Possible sources of organic pollution include livestock, sewage effluent from informal settlements, agricultural runoff and abattoirs. The Palmer Index identified genera that contributed most to the high scores are Euglena spp, Scenedesmus spp and Chlamydomonas spp, present at all sites. On investigation the high species richness and diversity identified by the Margalef and Pielou indices, showed that it was contributed by mostly Palmer Index recognised species. It was found that the Mooi River water quality deteriorated from an oligotrophic state to a mesotrophic -eutrophic state in the current study. The trophic state is further confirmed as Mesotrophic by the mean nitrate and nitrite concentration of 0.877mg/l and the mean orthophosphate concentration of 0.163mg/l determined for the whole Mooi River. The abundance of the Cyanophyceae and Bacillariophyceae algal groups, characteristic of mesotrophic to eutrophic water, were found to have increased when compared to previous studies. This change is most probably brought on by the agricultural activities surrounding the Mooi River. Problematic Cyanophyceae genera identified at Site 2: KKD and Site 5: BKD were Microcystis sp. and Oscillatoria sp. Microcystis is known for producing cyanotoxins, which pose a health risk for both humans and animals. Oscillatoria is known to be a taste and odour causing culprit, and was also identified at Site 3: BWFS, Site 6: PD and Site 7: WWTP. The results obtained during the evaluation of the algal community corresponds to the class III classification of the Mooi River, stating that the river is heavily impacted on by human activity but is still ecologically sustainable. Significant differences in the levels of the physico-chemical parameters: electrical conductivity, magnesium, calcium, total dissolved solids and sulphate were seen, after the confluence of the Mooi River with the Wonderfonteinspruit. Highlighting the effect of the mining activities. The magnesium and calcium levels are most probably contributed by not only the dolomitic lithology of the region but also the West Rand mining activities via the Wonderfonteinspruit. The dissociation of the dolomitic lithology has a buffering effect and contributes to higher pH. A significant correlation, (p<0.05), exists between the sulphate concentration and the cell concentration of sulphate reducing bacteria in the Mooi River. Even though the sulphate levels are currently not a threat when considering the RQO, the activity of Sulphate Reducing bacteria may pose a threat due to the formation of H2S. This phenomenon once again highlights the impact of the mining activities on the electrical conductivity, magnesium-, calcium concentration and total dissolved solids on the river. During this study the need for RQOs to manage and improve the water quality of the Mooi River is evident. Compared to previous studies the uranium concentration decreased at Site 5: BKD where water is abstracted for drinking water purposes. The average E.coli counts determined for the Mooi River were 828cfu/100ml. The sites displaying high count were mainly Site 4: AWFS, where cattle grazing were evident, and Site 8: EBR, influenced by agricultural activities and the runoff from a piggery. Results for which the 95% percentile exceeded the set RQO for the Upper Vaal were pH, orthophosphate, magnesium and E.coli. Variables measured that were below the set ROQs for the Upper Vaal were: nitrate and nitrite, electrical conductivity, sulphate, dissolved manganese and dissolved uranium. Considering the physico-chemical, phytoplankton and biological levels measured it can be concluded that the Mooi River system has high levels of organic pollution with a high faecal pollution load. The nutrient pollution needs intervention as it is rapidly contributing to an eutrophic system. It is also found that the Mooi River is a productive system with high species diversity. Blooms of nuisance algae can however be expected. The implementation of resource quality objectives are thus of need and must be continuously reconsidered and monitored as the quality of the Mooi River changes.