Abstract
To conduct the water quality improvement properly, it is necessary to estimate the dynamics of pollutant loads at watershed scales. We have attempted to quantify the watershed information by GIS to estimate the relation between water quality and watershed imformation, and carried out the field observation and sample collection, and then we have analyzed the run-off of NO3-N in Chikuma Basin. As a result, it became clear that the land use of watershed had significant influence on NO3-N dynamics in the river. Since, the amount of NO3-N from the vegetable field changes, NO3-N in the river water changed seasonally. Also, nitrogen stable isotope ratio increased in downstream of the river, where N discharge from city area increase.
