Water is essential for life processes of all species in the environment and for the socio-economic development of the human community. Without proper water quality, the life sustainability of many species is definitely doubtful. Pollutants from various sources enter river systems and cause serious river water pollution. In this situation, we need to understand how pollutants are transported along the water course, the types and sources of these pollutants and their effects on water quality. By

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... nderstanding the water pollution and self-cleaning capacity of a river system, one can make an appropriate decision for managing pollutant disposal. While a non-conservative pollutant enters a water course, depletion of dissolved oxygen (DO) takes place due to the consumption of oxygen in addition to advection and dispersion. At the same time, depending on the deficit of DO, re-aeration process takes place at a specific rate. There are many ways to solve DO and non-conservative pollutant relationships, such as the Streeter-Phelps model, many other concepts and experimental studies. The limitations of the previous studies on DO are that they are primarily based on the advection principle and first order decay only. In this study, considering first order decay along with advection and dispersion, DO concentration has been simulated by making use of mathematical mixing cells model incorporating de-oxygenation and re-aeration. In order for the validation, the results of the proposed model are compared with that of advection-dispersion based DO model. The spatial and temporal distribution of dissolved oxygen concentrations of Baynespruit stream in South Africa has been simulated having some input data and compared with large set of dissolved oxygen data at various locations of the stream.