Nonpoint Source Water Pollution in Rural Areas in the Upper Ayase River Basin of Saitama Prefecture in Japan

抄録

Nonpoint source pollution of water is an important environmental issue in Japan. In this study, water samples were collected from 12 selected sites and 4 different periods at the upper stretch of the Ayase River Basin located in Saitatma prefecture, and analyzed. The results revealed that the water in the study area was in eutrophic condition and the extent of pollution varied in different ranges depending on the sites’ ambient conditions. Moreover, the growing to harvesting period of crops (mainly mid-September to late-October) showed peak-values for nitrogen/phosphorus levels in water samples. The study recommends that either a strict policy needs to be incorporated or much more care should be taken to control pollution from agricultural runoffs.