ABSTRACT
Agricultural nonpoint source contamination of water resources by pesticides, fertilizers, animal wastes, and soil erosion is a major problem in much of the Laurentian Great Lakes Basin, located between the United States and Canada. Point source contaminations, such as combined sewerage overflows (CSOs), also add wastes to water flows. Soil erosion and sedimentation reduce soil fertility and agricultural productivity, decrease the service life of reservoirs and lakes, and increase flooding and costs for dredging harbors and treating wastewater. Improper management of fertilizers, pesticides, and animal and human wastes can cause increased levels of nitrogen, phosphorus, and toxic substances in both surface water and groundwater. Sediment, waste, pesticide, and nutrient loadings to surface and subsurface waters can result in oxygen depletion and eutrophication in receiving lakes, as well as secondary impacts such as harmful algal blooms and beach closings due to viral and bacterial and/or toxin delivery to affected sites. The U.S. Environmental Protection Agency (EPA) has identified contaminated sediments, urban runoff and storm sewers, and agriculture as the primary sources of pollutants causing impairment of Great Lakes shoreline waters (USEPA 2002). Prediction of various ecological system variables or consequences (such as beach closings), as well as effective management of pollution at the watershed scale, require estimation of both point and nonpoint source material transport through a watershed by hydrological processes. However, currently there are no integrated fine-resolution spatially distributed, physically based watershedscale hydrological/water quality models available to evaluate movement of materials (sediments, animal and human wastes, agricultural chemicals, nutrients, etc.) in both surface and subsurface waters in the Great Lakes watersheds.
