The impact of feedlot effluent on water quality and aquatic macroinvertebrate community structure in streams of the upper Vaal River catchment, South Africa

The impact of three intensive feedlots on aquatic macroinvertebrate community structure under high and low flows in the upper Vaal catchment was investigated. Water quality variables recorded upstream and downstream of feedlot activity include pH, dissolved oxygen, conductivity, temperature, turbidity, chloride, phosphate, sulphate, ammonium, nitrite, nitrate and chemical oxygen demand. Differences in water quality between upstream and downstream sites included nutrient concentrations, pH and conductivity. Alterations in family-level invertebrate community structures indicated a decline in abundances and species richness at sites situated downstream of feedlots. SIMPER analysis reflected invertebrate similarities for upstream and downstream sites for both low-flow and high-flow surveys. Downstream similarities of 59.03%, 69.26% and 63.92% were recorded. Some clear seasonal influences occurred. Redundancy analysis, using water quality variables and taxonomic orders, explained 80.3%, 81.3% and 86.0% of the variances recorded.