抄録
Many streams on Kureha Hill, located in Toyama City, Japan, are believed to suffer from nitrogen saturation because of their high concentrations of nitrate. We tried to simulate the flow-path change and the nitrate dynamics within the soils of one of the watersheds by using a flow-path model in order to identify the factors regulating the nitrate concentration of the stream. The result from the model implied that the lateral flow containing extremely high concentration of nitrate from the sub-surface soil strongly affected the nitrate concentration of the stream water. The flow-path model also showed no seasonality in the nitrate concentration of the stream water after eliminating the effect of the flow-path change within the soils on the nitrate concentration of the stream water. This result well coincided with Stoddard's definition of nitrogen saturation in the respect that no seasonality would be found in the deep stage of nitrogen saturation.
