Abstract
Pollutant runoff process of nutrients such as nitrogen and phosphorus in the Onga River watershed was studied on the basis of the relationship between the nutrients concentrations or pollutant load and flow rate. It is pointed out that the nutrients from the non-point sources i.e. agricultural land and urban area etc., have characteristic pollutant runoff process corresponding with the type of land use. The specific pollutant runoff process of nitrate nitrogen is dominated by leaching from the agricultural lands with runoff process of precipitation. On the other hands, municipal wastewater discharged from urban area is the main pollutant source of ammonium nitrogen and phosphatephosphorus in the Onga River watershed. One of serious water pollution problems in the estuary reservoir of Onga River is eutrophication due to nutrients from the non-point sources. Through water quality analysis on chlorophyll and nutrients, it is shown that nitrate nitrogen and phosphate-phosphorus are two limiting factors to algae growth in the reservoir.
