Predicting impact of fertilizer usage on water quality, Sutami reservoir, Indonesia

Nutrients are an important water quality concern in the Sutami reservoir basin, East Java, Indonesia, due to high reservoir eutrophication. Nitrogen and phosphorous are the two nutrients derived from intensive agriculture the upstream basin. This work investigates the effect of fertilizer application rates on nutrient transport to the reservoir. The ArcView Interface of Soil and Water Assessment Tool 2000 (A VSWA T) was used. It was calibrated using measured flow rates and nutrient concentrations between 1990-2002 and validated for 2003-2005. Model predictions generally performed well on both an annual and monthly basis. Four scenarios were used: no fertilizer application, normal application, and a 50 and 100 percent increase over normal. Results show the SWA T model can be efficiently used for identification of critical subbasins that have higher nutrient loads to develop apriority watershed management plan to reduce nutrient pollution losses.