Evaluating and estimating the effect of land used changed on water quality at Selorejo Reservoir, Indonesia

Nutrients are necessary for the survival of living organisms. The most important nutrient in aquatic ecosystem is typically Nitrogen (N) and Phosphorus (P). It was considered to be an important water quality concern in Konto River Basin due to a high water pollutant indication problem of reservoir Selorejo. Nitrogen and phosphorous are the two nutrients originating from inorganic and organic fertilizer that affect the reservoir water quality due to intensive agricultural farming. Increased N and P fertilizer application on the agriculture activity has larges N and P nutrient burdens to the reservoir through runoff and leaching. The aim of this study was to identify the sources of agriculture pollutants, to quantity the loads to reservoir Selorejo and to test the application of Soil and Water Assessment Tool Model. The model was calibrated using observed flow data of river collected during fieldwork. The nutrient concentration data obtained from water quality analysis in laboratory and during filed work. The annual Nitrogen and Phosphorous concentration comparison of measured and simulated on period 2000-2005, and than predicted of nitrogen and phosphorous at period 2006-2010. Result simulation was underestimate with correlation as indicated by R²=0,61 for Nutrient and R²=0,78 for Phosphorous. In general, the difference of land used in the watershed would be affected to increase runoff especially for nutrient loading on reservoir. The status of water quality at Selorejo reservoir is in accordance to the government water quality regulation.