A SWAT/Microbial Sub-Model for Predicting Pathogen Loadings in Surface and Groundwater at Watershed and Basin Scales

Despite the many potential sources of release of pathogenic organisms into the environment, agronomic practices that utilize animal manures contaminated with pathogenic or parasitic organisms appear to be the major contributors to watershed or basin contaminations. High rates of land-applied raw manure increase the risks of surface or ground water contamination, both from excess nutrients and pathogenic organisms. Unfortunately, current technologies are not adequate for handling large-scale treatment processes (e.g., composting, digestion, etc.) for stabilizing human pathogens in animal manures before application to agricultural lands. Therefore, there is a need for modeling capabilities to assess risks associated with individual and cumulative impacts of various pollutants and pollutant sources on watershed and basin impairment. The aim of this project is to extend Soil and Water Assessment Tool (SWAT) capability by incorporating a microbial sub-model for use at watershed or basin levels. The model formulations have been structured to be comprehensive, flexible, and at a minimum contain: 1) functional relationships for both the die-off and re-growth rates that are dynamic and, at best, cover a range of representative values from less persistent to more persistent pathogenic bacterial species; and 2) optional processes that can easily be adaptable to simulate both the release and transport of pathogenic organisms from various sources that have distinctly different biological and physical characteristics. Model performance has been tested for pasture and crop fields at one location. Preliminary results appear to portray the general patterns of the fate and transport of bacteria, for the three field sites examined.