A SWAT/MICROBIAL SUB-MODEL FOR PREDICTING PATHOGEN LOADINGS IN SURFACE AND GROUND WATER AT WATERSHEP AND BASIN SCALES

Authors: Sadeghi, Ali; Arnold, Jeffrey

Submitted to: Proceedings ASAE Conference Clean Water Clean Environment
Publication Type: Proceedings
Publication Acceptance Date: 3/8/2002
Publication Date: 3/15/2002
Citation: Sadeghi, A.M., Arnold, J.G. 2002. A swat/microbial sub-model for predicting pathogen loadings in surface and ground water at watershed and basin scales. Total Maximum Daily Load (TMDL), Environmental Regulations, ASAE Proceedings. p. 56-63.

Interpretive Summary: A number of individual models exist for assessing pathogen transport from animal manures applied to field crops and pastures to surface waters. These models, however, do not consider the influence of management practices and other important watershed parameters that can influence their transport from application sites to streams and surface water resources. Therefore, a more comprehensive model is needed that can incorporate most of these parameters and allow assessment of the risks associated with individual and cumulative impacts of various pollutants and pollutant sources on watershed and basin impairment. This work explains the incorporation of the bacterial sub-model into a well tested and validated watershed model called SWAT, Soil and water Assessment Tool. Preliminary testing of the resulting model has shown that it can evaluate simultaneously the potential risks associated with excess nutrients, sediment, and pathogens from animal manures for various agricultural management scenarios.

Technical Abstract: 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 major contributors to watershed or basin contaminations. High rates of land- applied raw manure can increase the risks of surface or ground water contamination due to both 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. A need exists for modeling capabilities that can assess risks associated with individual and cumulative impacts of various pollutants and pollutant sources on watershed and basin impairment. The aim of this study is to extend the 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.