Non-point pollution of Ishikari river, Hokkaido, Japan.

We researched the Ishikari river, Japan's second-longest river, to clarify the characteristics of non-point pollution by comparing flux characteristics of chemical components in three periods of one year: the snow melting period, the typhoon flooding period and the stable period. We found non-point pollutants present in great amounts because a large amount of suspended matter, which is contained in soil, flows into the river and concentrations of nutrients and organic matters do not decrease in a short time in the flooding period by rain and in the snow melting period.