Abstract
Human activities such as mining, industry, agriculture, rural and urban settlements are some of the factors responsible for the ecological deterioration of freshwater ecosystems in South Africa and globally. Urban stormwater runoff transfers high concentrations of pollutants and contains a wide range of these pollutants such as bacteria, viruses, nutrients, heavy metals, pesticides and hydrocarbons. This study focuses on one particular urban impact on freshwater ecosystems – that of stormwater runoff. The aim of this study is to assess the effectiveness of wetland systems in improving the quality of stormwater runoff in urban environments, using the Jackson Dam and Rietvlei Farm wetland as a case study. Of particular interest was the role of the wetland in removing nutrients and other pollutants introduced into the system by stormwater inflow into the dam, which occurs upstream of the wetland. It was hypothesized that the measured indicators of water quality and ecosystem health would reflect an improvement with increasing distance downstream from the stormwater discharge point due to uptake by plants and settling out into sediments. To determine the water quality, the project focused on assessing the physicochemical and microbial parameters, as well as the macroinvertebrate samples to determine family abundance and richness at the six sampling points that run the length of the system. For analysing the water quality results, Kruskal-Wallis nonparametric ANOVA’s were conducted to test for differences in water quality variables between the stormwater inflow, dam and downstream wetland sites. Water quality results were compared against the South African Water Quality Guidelines (SAWQG) using the Target Water Quality Ranges (TWQR) for aquatic ecosystems. The hypothesis was generally supported by the data, although the water quality parameters often exceeded the TWQR for aquatic ecosystems, which raises concern. Most of the water quality variables showed significant improvement (reduction) downstream, with the key exceptions being nitrite and phosphate, which showed an inverse pattern. The improvement in water quality at the downstream sites shows the ability of wetlands plants in sequestering pollutants from contaminated water. The macroinvertebrate community showed a substantial and significant improvement from upstream to downstream in terms of species richness and abundance.
M.Sc. (Aquatic Health)