Spatial and temporal analysis of soil water and nitrogen distribution in undulating landscapes using a GIS-based model

Spatially-explicit, deterministic landscape models, such as those used for predicting behavior of diffusely distributed pollutants, are powerful analysis tools to effective environmental management and decision-making, and to the advancement of our understanding of interactions between ecosystems in complex landscapes. A geographic information system (GIS) provides an environment for those simulations, within which data can be managed most efficiently. Based on this motivation, a distribution model is developed and embedded in a GIS GRASS. The model simulates the spatial-temporal dynamics of soil water and nitrogen in temperate multiple hilly landscapes at sloping areas where interflow transport is important. It is based on the mass conservation laws and uses only readily available input data, including topography, soil-type, landuse, and standard meteorological information.; The model is validated and applied in selected watersheds in upstate New York. The predications of stream flow and nitrate concentration agree well with observations. Several simulation experiments are then designed to study the related environmental problems. First, a time-index is proposed to estimate the response time of nitrate when an amount of nitrogen application is added into the system. The index measures relative importance among water transport, plant uptake, and bio-activities for the fate of nitrate.; Next, a scaling analysis is performed using both a factorial-type experiment and an information index function. The study probes the dominant factor that results in information loss due to data aggregation. The results show higher moisture content and less cumulated outflow in simulations at larger grid sizes. The spatial distribution is affected by the topography most, especially in the periods shortly after storm events or high rainfall seasons. The analysis makes recommendations on the best way to choose a grid size in a large-scale simulation.; Finally, an example of the model application is demonstrated by evaluating the effects of water diversion ditches on the water and nitrogen distribution in a watershed in the Catskill mountains. Simulations show that diversions that are currently installed have little effect in a wet period, but can greatly modify the water and nitrogen distribution in fields near the diversions in the dry season.