Identification of critical source areas under present and projected land use for effective management of diffuse pollutants in an urbanized watershed

The land-use characteristics of a watershed determined the amount of pollution produced in it, which can be curtailed by implementation of best management practices (BMPs) in an identified critical source area (CSA). Present and future land-use scenarios of the watershed were produced, and the hydrological simulation program FORTRAN model was used to model the hydrology and in-stream pollutants' concentrations. The validated model was utilized to identify the CSA for diffuse total nitrogen, total phosphorus, sediment, and biochemical oxygen demand considering the two land-use scenarios. The results showed that CSA and the water quality index produced by the two land-use scenarios varied in each of the diffuse pollutants considered. It was observed that some portion of the identified CSA remains unchanged despite the changes in the land use and this was attributed to consistent urban development in these areas. The results in this study illustrate that BMPs can be included in the design and planning of future urban expansion based on the identified CSA derived from the expected future land-use changes. As anticipated, this approach will provide resilience on the effects of urbanization on the diffuse pollutants loads in a rapidly urbanized watershed.