An agricultural ditch in headwater of Jinjin River, located at a small watershed in Changsha county, was selected as the study area, changes and losses of nitrogen, phosphorus in ditches and effects of ecological interception from rainfall runoff were analyzed. The results showed that the pollutants concentration and rainfall runoff increased gradually at their highest in preliminary stage of rainfall,however, they decreased gradually after the rainfall. The highest total nitrogen and total phosphorus content reached up to 4.67 mg/L and 0.38 mg/L during raining time respectively, ammonium and ...