The continued influence of organic pollution on the water quality of the turbid Modder River

Abstract

The Modder River is a relatively small river which drains an area of 7 960 km2, in the central region of the Free State Province, South Africa, and has a mean annual runoff of 184 x 106 m3. 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.

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