The ecological and functional assessment of wetlands : case study of a constructed wetland, Dundee, KwaZulu-Natal.

Abstract

This dissertation focused on the constructed wetland at a disused coal mine in Dundee, KwaZulu-Natal. A sequence of 10 wetland cells was constructed by the Department of Water and Sanitation (DWS) to remediate seepage from the mine. The main aspects that this dissertation is focused on are the water quality and geochemistry of the wetland; the ability of the wetland in providing ecological goods and services, and the rehabilitation of the wetland system. The results of the water quality analysis revealed that the water in the system is of inferior quality. Several of the parameters exceeded South African water quality standards indicating that the water is detrimental to aquatic health and neither is it suitable for human consumption. The geochemical analysis revealed that whilst heavy metals are present in the sediments the enrichment factor (EF) values are low although certain elements may be bioavailable. This possibility is enhanced by the predominance of larger grained sediment which have low adsorption capacities, allowing for relatively easy remobilisation into the water column. PCA analysis indicated a predominance of some heavy metals in the wetland cells but that this was influenced by anthropogenic impacts via discard coal. The ability of the wetland system in providing ecosystem goods and services was found to be compromised due to the wetland being in a state of malfunction. The final part of this dissertation comprises of a proposed rehabilitation plan for the constructed wetland. The rehabilitation plan focuses on the causes of degradation of the system due to the prolonged lack of maintenance and monitoring resulting in dysfunctional connectivity of wetland cells; inhibition of wetland conditions; the proliferation of terrestrial and alien invasive plants and, the inappropriate original structural composition of the basal sediments used which initially would have worked counter to the original intention to reduce acidity of mine derived groundwater. The rehabilitation plan is intended to aid in the re-establishment of hydrological, geomorphological and ecological processes in the wetland system.