Impact of alluvial diamond mining on macroinvertebrate community structure in the lower Vaal River, Northern Cape Province

Abstract

Macroinvertebrates and physico-chemical parameters were assessed at four sites in the lower Vaal River. The primary aim of the study was to determine the impact that alluvial diamond mining activities have on aquatic macroinvertebrate community structure using the South African Scoring System version five (SASS 5), as an index of the river’s ecological status. The macroinvertebrates were sampled using the SASS5 method and the results were analysed together with selected physico-chemical water parameters and Integrated Habitat Assessment. The results indicated that habitat played a major role in the presence of macroinvertebrates. Macroinvertebrate diversity was calculated using the Shannon- Wiener Index. A total of 28,167 macroinvertebrates belonging to 36 families were recorded throughout the sampling seasons. The highest abundance was recorded at Site 4, the most impacted site, but in turn this site had the lowest diversity. Chironomidae was the most abundant family (2,588 individuals) and the least abundant were the Chlorocyphidae and Velidae, each having five individuals. High numbers of taxa were noted amongst the Simuliidae, Corbiculidae, Physidae, and Oligochaeta. Site 4 was the only site where the presence of livestock was seen, and construction trucks were observed driving over the biotopes crossing over banks of the river, further adding pressure on the existing alluvial diamond mining impacts that contributed to low presence of macroinvertebrates. Generally, the alluvial diamond mining activities had severe impacts on the riverbed and changed the river flow regime and water quality. The hypotheses that the water quality of the Vaal River is negatively impacted by the alluvial diamond mining practices, and that the mining activities negatively impacted on macroinvertebrate community structure were supported.