Abstract
Enclosed and semi-enclosed water areas are subject to eutrophication due to influx of nitrogen and phosphorus. It has been pointed out that nitrogen dynamics in these water areas differ according to land use, soil properties, and soil types. In this study, we attempted to elucidate the nitrogen dynamics from land to water in Notsuke Bay, eastern Hokkaido, which has volcanic soil and has been turned into grassland by the development of dairy farming. Anthropogenic nitrogen input occurred due to grazing. In addition, as a result, the nitrate nitrogen concentration in the grassland increased, and the nitrate nitrogen concentration in the soil water runoff from the grassland also increased. On the other hand, the riparian forest soil between the grassland and the river tended to reduce the concentration of nitrate nitrogen discharged from the grassland. From these facts, when soil water passes through riparian forests and wilderness between grasslands and rivers, nitrate nitrogen may be absorbed or denitrified by trees and bamboo grass. As a result, the concentration of nitrate nitrogen in river water may be lower than that in soil water.
