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Title: Enhancing the USDA-ARS Soil and Water Assessment Tool (SWAT) with the in-stream bacteria fate and transport module including sediment bacteria resuspension and settling

Author
item KIM, JUNG WOO
item Pachepsky, Yakov
item SHELTON, DANIEL
item COPPOCK, CARY

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 3/16/2009
Publication Date: 4/15/2009
Citation: Kim, J., Pachepsky, Y.A., Shelton, D.R., Coppock, C.R. 2009. Enhancing the USDA-ARS Soil and Water Assessment Tool (SWAT) with the in-stream bacteria fate and transport module including sediment bacteria resuspension and settling. BARC Poster Day, April 15, 2009.

Interpretive Summary:

Technical Abstract: Streambed sediments have been shown to serve as environmental reservoirs for bacteria, including pathogenic strains. Although the Soil and Water Assessment Tool (SWAT), a watershed-scale, physically-based and continuous-time model, has been augmented with bacteria transport subroutine in 2005, the bacteria die-off is the only in-stream fate and transport process considered in the current SWAT version. The purpose of this work was to improve the in-stream bacteria fate and transport module of SWAT by considering sediment-associated bacteria deposition and resuspension, and to evaluate the potential significance of bacteria resuspension for the SWAT bacterial water quality simulations. In the newly developed module, bacteria were fractionalized into free-floating and sediment-associated bacteria. Only sediment-associated bacteria were settled with depositing sediment, while both free-floating and sediment-associated bacteria were involved in sediment resuspension. Bacteria concentration in streambed sediments was simulated as a bell-shaped function of water temperature. The modified SWAT was applied to the Little Cove Creek watershed (Franklin Co., PA) with forestry dairy pastureland and field crops in land use. The streamflow, E. coli concentrations in water and sediment, and weather have been monitored for two years, and landowners were surveyed for management details. Hydraulic parameters were calibrated with the rainfall and stream flow data, and E. coli data in stream water were used to evaluate the module. The seasonal trends of bacteria concentrations in streambed sediments and stream water were similar. The simulated E. coli input into the stream water from the streambed sediments was comparable with or larger than the simulated E. coli input from the pastureland runoff. The contribution of sediment resuspension could explain the E. coli persistence in stream water after heavy rainfall during the cold seasons. Results of this work indicate the need in gathering experimental information on fate of pathogen and indicator bacteria in streambed sediments to improve predictions of bacterial water quality.