Comparative Survey on Non-Point Source Pollution among Three Regions in Japan

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Rainfall runoff contains several types of pollutants and possibly causes deterioration of water quality in public water bodies. Recently many researchers have tried to evaluate non-point source (NPS) pollution quantitatively and to make clear the mechanism of pollutant runoff. But NPS depends so much on the regional characteristics that systematic research has not been done. The purpose of this study is to make clear the characteristics of NPS pollutant runoff from areas with different regional characteristics.In urban area like Funabashi City and Chiyoda City, road runoff is possibly the main NPS. Most of researches were conducted to investigate either sedimentation process or runoff process, because of the experimental difficulties. We tried to link the results obtained from each investigation together. Consequently, particle size and solubility were suggested to be the key factors in the mechanism of pollutant runoff.In Koriyama City, NPS pollutant runoff into Abukuma River and Miharu Lake caused by floods is major problem. Transportation mechanisms of pollutants during floods were investigated. Continuous observation revealed that the pollutant transportation characteristics were correlated with the regional properties. And mathematical model to express the phenomena, which were observed in this study, was developed. Sedimentation process, re-suspension process, and the correlation between river sediments and nutrients were also considered in the model.