Abstract
The loss of wetlands in urban environments further exacerbates existing stressors on water resources, given that wetlands offer important ecological services such as water purification. In Gauteng, most wetlands are dominated by Phragmites reeds, which have the ability to remove nutrients and other chemical pollutants from water flowing through them. However, in highly urbanised environments wetlands may lose some of their ability to function effectively and may not cope with sequestering very high loads of organic pollutant runoff, thus reducing their ability to purify water. This study investigates whether wetlands consisting of Phragmites reeds are still able to function effectively in decreasing the organic pollutant load in a small perennial urban stream in the East Rand of Gauteng (Ekurhuleni Municipality). Ex situ laboratory analysis of organic nutrient compounds from water and sediment samples and in situ analysis of water quality parameters was performed for various sites along the stream, some of which were associated with wetlands and some not. Aquatic macroinvertebrates were also collected using the SASS5 bioassessment protocol. Given the known ability of wetlands to remove pollutants from water, it was expected that physico-chemical indicators of water quality and sediment pollution would show improvements in reaches of the stream that flow through wetlands compared to those reaches that are not associated with wetland habitats. It was further expected that macroinvertebrate assemblages would track the improvements in water quality as hypothesized for sections of the stream with extensive wetland habitat. Findings revealed that water quality improved clearly and consistently for sites within or immediately downstream of wetlands, but this trend was not consistent for the sediment analyses. The macroinvertebrate SASS5 index scores and analysis of assemblage composition did not reveal any clear differences in macroinvertebrate assemblages between wetland and non-wetland sites. Thus, the expectations of this study were partly met, being supported by the water quality results, but not the sediment or macroinvertebrate results. It is recommended that similar follow-up studies should include sampling in the wet season (summer) and should incorporate sampling of aquatic macroinvertebrates from a broader range of sites across wetland and non-wetland areas of the stream. Future studies on the functioning of wetlands on the Rietspruit (and other nearby streams) should incorporate sampling of heavy metals to better detect the impacts of mining-related activities (especially tailings) in the catchment.
M.Sc. (Aquatic Health)