Title: Bacteria modeling with SWAT for assessment and remediation studies – a review Authors
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 2010
Publication Date: June 29, 2010
Citation: Baffaut, C., Sadeghi, A.M. 2010. Bacteria modeling with SWAT for assessment and remediation studies – a review. Transactions of the ASABE. 53(5):1585-1594. Interpretive Summary: Simulating bacteria fate and movement in watersheds with computer models has started only recently. We reviewed 5 case studies, where applications in which the Soil and Water Assessment Tool (SWAT), an existing watershed-scale computer simulation model, was used to simulate bacteria fate and transport. The review highlights similarities between these applications in terms of sampling protocols and amounts of bacteria spread on the land. In brief, we compared the values of input parameters and how well the model simulated concentrations. In all case studies reviewed, direct bacteria inputs into streams appeared to have a major impact on the model results. Results from this review indicate the need for better stream sampling procedures that allow bacterial analysis of storm water samples and for additional field studies to revise and fine-tune the equations that simulate the transport of bacteria in surface runoff. The proposed improvements could enable the SWAT model to be a more reliable tool for predicting bacteria concentrations and allow water resource managers to evaluate the impact of different management scenarios on bacteria contributions to surface water resources. These results are useful for scientists who are planning research in this field and for model users who look for information on the model’s capabilities and limitations.
Technical Abstract: No longer limited to 25 lines. A module to simulate bacteria fate and transport in watersheds was first tested in SWAT 2000 and fully integrated to the SWAT2005 code. Since then, few investigators have utilized SWAT to model bacteria or pathogens fate and transport in spite of bacteria impairment being a major impairment of streams and rivers in the United States. In this paper, bacteria equations are briefly presented. Five modeling applications from Missouri, Kansas, and Georgia in the U.S. and from Brittany in France are reviewed, highlighting the modeling successes and the challenges. These applications include watersheds that range from 16 km2 in Georgia to 3,870 km2 in Missouri. In all cases, land use included agricultural (cropland and pastures) and forested land with a mix of point and nonpoint sources. Nonpoint sources included indirect (manure deposited on land) and direct contributions from cattle or wildlife to the streams. In some cases, urban and residential contributions were also taken into account. Strategies to represent the different sources, calibration methods, parameter sensitivity and goodness of fit were compared between the five applications. Overall, SWAT reasonably simulated the range and frequencies of bacteria concentrations. In all case studies reviewed, direct bacteria inputs into streams appeared to have a major impact on the model results. Results from this review also indicate that the model processes that simulate the release and transport of bacteria in surface runoff may need to be revisited and tested. This improvement could enable the SWAT model to be a more reliable tool for the prediction of bacteria concentrations and allow water resource managers to evaluate the impact of different management scenarios on bacteria contributions to surface water resources.