Modelling the effects of urbanization on nutrients pollution for prospective management of a tropical watershed: a case study of Skudai river watershed

Nutrient pollution is considered as a primary factor of water quality deterioration in urban-dominated watersheds in which an informed decision on the management strategies are required to improve the water quality condition. The Hydrological Simulation Program Fortran (HSPF) model is used to evaluate the impacts of pollution by these nutrients using the Skudai River watershed in Malaysia as a case study. A developed land-use/land-cover (LU/LC) scenarios were used to evaluate these impacts. Statistical methods were employed to assess the extent of these impacts and their significance in shifting the trophic state of the rivers in the watershed. The study shows that when urban development increases from 18.2 to 49.2%, the total nitrogen (TN) and total phosphorus (TP) loads increase from 3.08 to 4.56 × 10 3 kg/yr and from 0.13 to 0.27 × 103 kg/yr, respectively. Streamflow and stream concentrations (NH3[sbnd]N, NO3[sbnd]N, and PO4-P) produce varying responses as the watershed land-use changes (from 1989 to 2039). As the rivers in the watershed shift their trophic state with respect to the level of anthropogenic disturbance within their catchments, the TN and TP concentrations at the estuaries are likely to change from oligotrophic to eutrophic state. This is an indication that the Johor Strait and the coastal rivers will be exposed to eutrophication, subsequently resulting in harmful algal bloom. This condition can be prevented by integrating water quality management alongside urban development because it is observed that a control of non-point source (NPS) pollutants from 1% of the urban development will decrease TN and TP concentration in Skudai River by 0.023 mg/L and 0.004 mg/L respectively