| Increasing concerns have been raised over the impacts on both regional and global environments due to the alterations in water and material cycles over the recent past. Anthropo-genic influences like land use changes due to urbanization, increased agricultural fertilization and natural phenomena like global climatic variations are presumed to cause aug-mented loadings of nitrogen (N) and phosphorus (P) to rivers and downstream reservoirs. Pollutants from nonpoint-sources have been identified as the major cause of water pollution or eutrophication (Campbell et al, 2004). Better insight into and monitoring of those influents at watershed scale is now cru-cial in the management of river basin environments. The field monitoring is impracticable in most cases due to vast scopes of areas and complexities involved and process-based modeling approaches play a crucial role in quantitative analysis of such effects and deriving best management practices. The process-based WEP (Water and Energy Processes) hydrologic model, initially developed at the Public Works Research Institute, Japan as a tool for extensive analysis of water and energy budgets at catchment scale (Jia et al, 2002), was later enhanced by incorporating N and P components (Kinouchi et al., 2004), mainly targeting dissolved nutrient dynamics. Additional process-based soil erosion-transport module was then coupled to WEP model to introduce sedi-ment-bound pollutant (N, P) and suspended solids (SS) com-ponents (Rajapakse et al., 2009), which are essentially important both in agricultural and urban land use scenarios. The present study elaborates application of the improved model in the semi-urbanized agricultural basin of the Yata River, Japan, targeting integrated river basin management approaches. |
