Abstract
NO3-N pollution in groundwater is becoming an important issue in the Nasunogahara basin. The aim of the present study is to model the inflow process of the nitrogen load to unconfined aquifers. Based on the analysis of processes of the nitrogen load inflow to groundwater, a water quality tank model was constructed by adding the behavior of the nitrogen load to the existing tank model (Nasunogahara hydrologic model). For formulating the process of inflow of the nitrogen load, L-Q and dissolution types of formulations were considered. Considering the nature of water movement on/in the soil, the L-Q type was applied to the first of the non-paddy field tanks and the dissolution type was applied to the second of the non-paddy field tanks and to the paddy field tank. From this modeling, the trend of change in NO3-N and the response to precipitation were sufficiently well represented by the model simulation. Results of sensitivity analysis showed that changes in parameter values and conditions of the water quality tank model did not significantly affect calculated results of the change in NO3-N. On the contrary, slight changes in water movement and water balance in the hydrologic model were found to greatly influence calculated results of water quality. More adequate modeling of the hydrologic process is needed in the future to enable further improvement in the performance of the water quality tank model.
