Investigation of self-purification and water quality index during dry and rainy seasons in the Khurumela Stream (Botswana)

Abstract

This study investigated the self-purification and predicted water quality index of a stream in Botswana, fed by a natural spring. The stream investigated is a tributary of Lotsane River which in turn drains into Limpopo River. The study was conducted through sampling and measuring of water quality variables (14) along the stream at different points during the dry and rainy seasons of the year. There were statistical significances observed between the dry and rainy seasons for temperature, electrical conductivity, salinity, total dissolved solids, dissolved oxygen (DO), and biochemical oxygen demand (BOD) with P values less than 0.05. No statistical significances were observed for turbidity, total suspended solids, and potential of hydrogen (pH). The water quality indices were mostly excellent during the rainy season and unacceptable during the dry season. The predicted BOD during the dry season was observed to increase, whereas DO concentrations were decreasing with distance. The deoxygenation rates during the dry and rainy seasons were 1.007 and 0.886 day−1 respectively. The predicted water quality indices were improving with distance during the dry season and constant during the rainy season. Negative correlation between water quality indices and water quality variables were observed during the dry season whereas positive correlations were observed during the rainy season. The study leverages advanced predictive algorithms to offer real-time insights and future projections. This methodology will be valuable for monitoring the main watercourse downstream, the Lotsane River, during the rainy season, to allow a better knowledge and define adequate strategies to safeguard water resources and ecosystems.