ABSTRACT
Nonpoint source pollution is the leading source of impairment of U.S. waters (U.S. Environmental Protection Agency [EPA] 2002). In the Great Lakes basin, contaminated sediments, urban runoff and combined sewer overflows (CSOs), and agriculture have been identified as the primary sources of impairments of the Great Lakes shoreline waters (U.S. EPA 2002). The problems caused by these pollutants include toxic and pathogen contamination of fisheries and wildlife, fish consumption advisories, drinking water closures, and recreational restrictions (U.S. EPA 2002). Management of these problems and rehabilitation of the impaired waters to fishable and swimmable states require identifying impaired waters that are unable to support fisheries and recreational activities and tracking sources of both point and nonpoint source material transport through a watershed by hydrological processes. Such sources include sediments, animal and human wastes, agricultural chemicals, nutrients, and industrial discharges, and so forth. While a number of simulation models have been developed to aid in the understanding and management of surface runoff, sediment, nutrient leaching, and pollutant transport processes such as ANSWERS (Areal Nonpoint Source Watershed Environment Simulation) (Beasley and Huggins 1980), CREAMS (Chemicals, Runoff and Erosion from Agricultural Management Systems) (Knisel 1980), GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) (Leonard et al. 1987), AGNPS (Agricultural Nonpoint Source Pollution Model) (Young et al. 1989), EPIC (Erosion Productivity Impact Calculator) (Sharpley and Williams 1990), and SWAT (Soil and Water Assessment Tool) (Arnold et al. 1998), to name a few, these models are either empirically based, or spatially lumped, or do not consider nonpoint sources from animal manure and combined sewer overflows (CSOs) and infectious diseases. To meet this need, the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL) and Western Michigan University are jointly developing a spatially distributed, physically based watershed-scale water quality model to estimate movement of materials through both point and nonpoint sources in both surface and subsurface waters to the Great Lakes watersheds. The water quality
model evolves from GLERL’s distributed large basin runoff model (DLBRM) (Croley and He 2005; Croley et al. 2005). It consists of moisture storages of upper soil zone, lower soil zone, groundwater zone, and surface, which are arranged as a serial and parallel cascade of “tanks” to coincide with the perceived basin storage structure. Water enters the snowpack, which supplies the basin surface (degree-day snowmelt). Infiltration is proportional to this supply and to saturation of the upper soil zone (partial-area infiltration). Excess supply is surface runoff. Flows from all tanks are proportional to their amounts (linear-reservoir flows). Mass conservation applies for the snow pack and tanks; energy conservation applies to evapotranspiration. The model allows surface and subsurface flows to interact both with each other and with adjacent-cell surface and subsurface storages. Currently, it is being modified to add materials runoff through each of the storage tanks routing from upper stream downstream to the watershed outlet (for details of the model, see the companion paper by Croley and He 2006). This paper describes procedures for estimating potential loadings of sediments, animal manure, and agricultural chemicals into surface water from multiple databases. These estimates will be used as input to the water quality model to quantify the combined loadings of agricultural sediment, animal manure, and fertilizers and pesticides to Great Lakes waters for identifying the critical risk areas for implementation of water management programs.
