Rehabilitating a wetland in the Zaalklapspruit Wetland system impacted by acid mine drainage
Acid mine drainage (AMD) is one of the biggest threats to water resources, human health and the environment in South Africa. In many cases, its impact is exacerbated by agricultural practices and other developments that disrupt the structure and flow of water bodies. The CSIR and partners designed and implemented interventions in the Zaalklapspruit Wetland that resulted in improved water quality and ecosystem functioning.
The South African mining sector is an important contributor to the South African economy. However, one of the negative effects of mining is the release of chemical contaminants into water resources, which can cause environmental damage and threaten the health and safety of people. CSIR water researchers assessed the entire upper Olifants River catchment to determine the different sources of pollution resulting from the various land use activities. This entailed the assessment of the quality of water emanating from sewerage works, mining, agriculture and industries.
A part of the Zaalklapspruit Wetland system was selected for rehabilitation. The CSIR, in collaboration with the South African National Biodiversity Institute and the Working for Wetlands programme of the Department of Environmental Affairs, devised several interventions to address the problem. The wetland was no longer acting as a sponge that diffused the energy of storm waters, but instead these waters carved gullies, leaving the floodplain dry. The rehabilitation process focused on lifting the floor of the stream, using structures to slow the waters and diffuse the energy. One such was constructing concrete structures, as well as earth berms and weirs, funded by Coaltech. Concrete structures were necessary due to the acidic and corrosive nature of incoming water, rather than the conventional gabion structures used in wetland rehabilitation. Gabion structures are rock-filled, wire basket-like structures that limit erosion, trap sediment and re-saturate drained wetland areas. The acidic water would corrode the wire used in these structures.
The Zaalklapspruit Wetland system showed an almost immediate improvement following the intervention, with decreased acidity and decreased levels of dissolved metals in the water flowing through the wetland. The rehabilitation resulted in improved water quality and ecosystem functioning, benefitting farmers, rural communities and other users downstream of the wetland.
Dr Paul Oberholster