Distribution of benthic macroinvertebrates in the Selati River of the Olifants River System, South Africa

The Ga-Selati River has been systemically impaired by increasing human activities in its catchment, resulting in contamination by mining, industrial and agricultural effluents and domestic waste, and as a result significantly impacting the water quality of the river. The study aimed at investigating the ecological state of the Ga-Selati River and the impact of water quality on the aquatic macroinvertebrate communities was conducted in 2014 and 2015. Five sites along the Ga-Selati River were selected for sampling macroinvertebrates. The family composition, based on abundance and diversity, was evaluated in relation to environmental variables. The levels of dissolved oxygen, conductivity, total dissolved solids, turbidity and nutrients affected the distribution of tolerant taxa. The number and diversity of macroinvertebrates were found to be higher at less degraded upstream sites compared to more degraded downstream sites. A canonical analysis clearly grouped the various macroinvertebrates with the physico-chemical parameters having an influence on their distribution. The relatively high influence of environmental factors in the abundance and distribution of the sensitive taxa highlights the importance of environmental variation on macroinvertebrate assemblages.