A cell-based distributed hydro-environmental model is developed which enables to analyze groundwater nitrate-nitrogen (N-N) contamination in rural areas, with well-coordinated incorporation of the water quality tank submodel for surface zone and the nitrate-nitrogen transport submodel for unconfined groundwater aquifer into the previously developed hydrologic model (Takeuchi et al., 2010). Cell-based building of all component submodels allows us to mesh the problem domain with unstructured cells of triangular shape, and therefore renders it possible to reflect in a refined fashion a variety of land-use practices in an analysis of the problem. The solutions based on reality, associated with groundwater flow and quality, can thus be obtained at a high (or field-plot-scale) resolution. It is also of great advantage that quantities of the hydro-environmental components of interest, such as surface water discharge, ground-water recharge, surface nitrogen discharge, and N-N leaching, can be obtained cell by cell or land-use by land-use. Application of the model to a real rural area having diverse terrains testifies to its satisfactory performance in a global sense. The simulated N-N concentrations of the groundwater vary in the ranges of the observed concentrations. The model also well reproduces the observed realities that the N-N concentration is high in upland areas such as alluvial fan and river terrace, while low in the lowland areas such as delta and valley floor, and is lowered in the irrigation season. It is thus considered that the model presently developed is useful for simulating and assessing the process and geographic distribution of groundwater N-N contamination in rural areas where fertilizing-induced groundwater contamination is a special concern.
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