SCALE-DEPENDENCY OF SOLUTE TRANSPORT MODELING GIS APPLICATIONS/

The movement of water through the soil profile and the consequent disp lacement and transformation of chemicals dissolved in the water is a k ey concern in preventing water quality degradation, with its eventual impact on living systems, both human and otherwise. Predictions of the effect of a particular water and chemical management system at the so il surface will lead to more enlightened control of chemicals introduc ed into the environment as pesticides, fertilizers, or waste products. The use of geographic information systems (GIS) in concert with simul ation modeling of soil leaching processes is becoming more widespread as a procedure applied to environmental chemical fate issues. The use of GIS has brought to the forefront the spatial scale of such database s as soil survey, elevation, climate and land use, and their use in th e modeling process. An accompanying concern is the spatial scale at wh ich any simulation model is assumed to be accurate, and the spatial sc ale at which both model input and field-verification data should be ge nerated. Such modeling presently consists of a number of approaches, s ome useful at several spatial scales, and others more limited by the a ssumptions inherent in their development. This paper discusses these i ssues, and presents two case studies as examples.