Point and non-point source nutrient loading simulation for the Takasaki River Basin, Chiba–Japan

Urbanization, agriculture, fertilization, livestock farming and unprecedented precipitations are presumed to cause augmented loadings of nitrogen (N) and phosphorus (P) to rivers and downstream reservoirs. At present, point source (PS) pollution in watersheds can easily be controlled, and it has been well-managed due to growing awareness and strict low enforcements. However, the control of pollutants from non-point sources (NPS) is still challenging and NPS have been identified as the main cause of water pollution and eutrophication in watersheds at present. Limitations in technical, human and financial resources impede efficient monitoring of those influents at watershed scale. At this end, process-based modelling approaches play an important role in analysis of nutrient loading effects quantitatively and qualitatively. Process-based water and energy processes (WEP) hydrological model with its updated version to couple nutrient loading through the implementation of N and P circulation processes was studied in this paper highlighting the application of the model to the Takasaki River, a tributary to the Inba-numa Lake basin, Chiba prefecture, Japan to understand the impacts of PS and NPS to the river water quality.