Verification of distributed rainfall-runoff model using a hydrogen isotopic ratio, and analysis of nitrate nitrogen transport to a stream (Joint research)

Tsuzuki, Katsunori  ; Matsunaga, Takeshi; Inoue, Takanobu*

The discharge of nitrate nitrogen from a forested catchment was analyzed using a distributed rainfall-runoff model. Observation in rainfall events were carried out in November, 2006 in the Ijira River. The distributed rainfall-runoff model carried out runoff simulation of ground water and rain water at the catchment. The model was verified by observed flow rate, and the hydrogen isotopic ratio of rain water and river water. The nitrate ion concentration in river water was shown as a function of the residence time of discharge water in the catchment calculated by the model. As a result, it was estimated that the nitric-acid ion in the river water was transported by the lateral flow of the rain water at the subsurface and the up-flow of ground water. Moreover, it was estimated that the residence time of the soil moisture influenced the discharge of nitrate nitrogen. This study was suggested that dynamic behavior of water in catchment was important when considering the balance of nitrate nitrogen in catchment.