Effects of trace elements on benthic macroinvertebrate distribution in the sediments of two rivers in the Olifants River Basin, South Africa

Many freshwater ecosystems are facing ecological challenges such as influx of trace elements from human activities, and sediments behave as a sink for trace elements in these environments. Trace element contamination in river sediments is a major environmental concern due to its devastating effect on benthic organisms. The aim of this study was to assess the effect of trace elements in sediments on the distribution of benthic macroinvertebrates in the Blyde and Mohlapitsi rivers of the Olifants River Basin, South Africa. Sediment samples and benthic macroinvertebrates were collected from six sites along each river. The results showed variations in the concentration of the trace elements in the sediment and the distribution of benthic macroinvertebrates among the different sites and between the two rivers. Both rivers recorded high taxa richness and sensitive taxa were well represented in most parts of the rivers, an indication that the rivers are not highly disturbed. There were insignificant correlations between most of the trace elements and the abundance of the benthic macroinvertebrates, though some taxa showed significant correlations with the trace elements. Despite the low impact of the trace elements on the distribution and diversity of benthic macroinvertebrates, ecological health of the rivers and structural distribution of macroinvertebrates may be affected in the future due to increasing human activities in the catchments. It is therefore recommended that effluents from human activities should be controlled to prevent a further degradation of the rivers to protect macroinvertebrates and other aquatic biota.