| Summary: | M.Sc. (Aquatic Health) === Urban impoundments play both a recreational and functional role in the urban areas. From the recreational point of view these impoundments offer aesthetically pleasing environs as well as habitat for aquatic organisms in a built environment. The functional role of impoundments is related to attenuation of storm water run-off that is released into urban water courses. Storm water run-off can have adverse effects on the ecological integrity of aquatic ecosystems. Water quality will influence other physical and biological components of these systems. It is for this reason that the ecological health of impoundments is assessed from an ecotoxicological perspective, focusing on Westdene and Emmarentia dams in Johannesburg. It has become common practice to use aquatic biota to assess the impacts of human activities on aquatic ecosystems. This is because animals and plants can provide a long-term integrated reflection of water quality, quantity, habitat quality and other environmental conditions. Water and sediment quality were assessed by applying standard techniques and protocols. Fish were utilized as bioindicator organisms in order to quantify the concentrations of metals available in the dam. Abundance of the macro invertebrate community was also measured. Physico-chemical water analyses were done during each sampling period to assess the water quality against the South African Water Quality Guidelines. Ammonia, which can be toxic to aquatic life, remained high in both dams. High phosphate concentration during the low rainfall season in Westdene Dam could result in eutrophication related problems. The microbiological analysis of the water suggests that the main cause of faecal and total coliforms contamination of the impoundments possibly originates from dominant birds, African Sacred Ibis (Threskiornis v aethiopicus) and Egyptian Goose (Alopochen aegyptiaca ) in the dam and others water birds frequenting the dams. Abnormally high concentrations of the heavy metals Nickel and Chromium were found in the water body and fish (Clarias gariepinus and Tilapia sparmanii ) thus indicating bioavailabity of these metals resulting in bioaccumulation in fish. High concentration of Lead in sediment was recorded and may greatly impact benthic macroinvertebrates population and their habitat.
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