The Impact of Human Activities on Microbial Quality of Rivers in the Vhembe District, South Africa
The Modder River is a relatively small river which drains an area of 7 960 km, in the central region of the Free State Province, South Africa, and has a mean annual runoff of 184 x 10 m. Botshabelo is a city which was developed in the catchment area of the river and treated sewage is released into the Klein Modder River. This study determined seasonal and spatial patterns in the system as well as the continued influence that Botshabelo’s treated sewage outflow has on the water quality of the river. It was determined that the Modder River and Klein Modder River follow distinctive seasonal patterns in terms of algal growth and physical factors. There were periods when the waters of the Modder River and Klein Modder River are of acceptable quality; however, outflows from Botshabelo have a detrimental effect on the water quality, in terms of nutrient concentrations and algal biomass. The inflow of the Klein Modder River into the Modder River caused on average, 112% increase in phosphate-phosphorus (PO 4 -P), 171% increase in nitrate-nitrogen (NO 3 -N) and a 50% increase in chlorophyll-a concentration in the Modder River. The long-term detrimental effect of Botshabelo on the system can clearly be seen by comparing predicted nutrient increases with measured values.