Assessment of NPS Pollutant Loadings from Rural Watersheds with Respect to Land Use

초록

Two small agricultural watersheds were monitored from March 1998 to December 1999 to measure runoff and the pollutant loads of selected NPS(Non-point Sources). Runoff was measured and water quality was analyzed every two weeks for SS, T-N, T-P and COD. Annual runoff coefficients ranged from 0.47 to 0.75 depending on rainfall amount and intensity. SS concentrations maintained most of the time the 1st grade water quality standard of 25 mg/L or less while T-N concentrations could not meet the lowest reservoir water quality (5th grade) standard of 1.5 mg/L all the time. It was analyzed that the constituents of T-N were mainly supplied from groundwater. T-P and COD concentrations were in between the first and the lowest water quality criteria. The importance of T-N control by means of nutrient management and rural wastewater treatment was emphasized. About 80 to 95% of the NPS pollutants were discharged during a short flooding period of 2 to 3 months. NPS pollutant load per unit area varied depending on daily rainfall. Patterns of pollutant discharges from the watersheds were different between rainy and normal seasons. It was recommended that the use of pollutant load per unit area must be applied very carefully, and the control strategies of NPS pollutants for rainy and normal seasons must be separately developed.

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