Abstract
The previous researches about the Lake Kasumigaura have neglected the effect of groundwater on the water and nutrient budgets in the lake because they have believed that the effect of surface water is predominant. In this study, the National Institute for Environmental Studies (NIES) Integrated Catchment-based Eco-hydrology (NICE) model was expanded to include the interaction between the lake water and groundwater in this catchment. Although inflowing and outflowing streams are dominant in the annual hydrologic budget of the lake, the model shows that groundwater seepage plays a great role in the net water budget. Groundwater entering the lake from the north side is contaminated with high concentrations of nitrate and ammonia from intensive pig and cattle raising. This groundwater inflow plays an important role in the nutrient loading into the lake and consequently in the water quality and eutrophication.
