A study on the water quality of runoff from forest

The important non-point sources in Japan are urban areas, rice paddy fields and forest. The forest area in river basins occupies about 70 per cent. Furthermore, Japanese forest is usually on steep mountains. Therefore, pollutant loads from the forest cannot be ignored in Japan. In this study, we discuss the seasonal variations of water quality of runoff from forest, and of component runoffs, inter-surface runoff and groundwater runoff, based on observations and on the results separated by a numerical filter. The seasonal variations of water quality and four types of relations between water quality and flow rates of component runoffs were noted.