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Attachment Of Bacterial Indicators To Particulates In Runoff From Various Soils

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 29 March - 3 April 2008, Concepcion, Chile  701P0208cd.(doi:10.13031/2013.24345)
Authors:   Michelle L Soupir, Saied Mostaghimi, Elizabeth Alphin

Abstract: Association of E. coli and enterococci with particulates present in runoff from highly erodible soils has important implications for modeling the fate and transport of bacteria from agricultural sources and in the selection of management practices to reduce bacterial transport. A field study was conducted to examine the fate of E. coli and enterococci transport from three bare soil types receiving cowpat treatments and develop relationships between bacterial partitioning and phosphorous and carbon transport. Particles sizes to which cells preferentially associated were also identified. Soil boxes (100-cm 20-cm 7.5-cm) were packed with loamy fine sand, silty loam and silty clay loam soils to simulate runoff from poorly managed erosive soils or trampled streambanks. A rainfall simulation was conducted 24-hours after application of a standard cowpat, followed by a second rainfall simulation approximately 80 days later. Runoff samples were analyzed for E. coli, enterococci, TSS, phosphorous, organic phosphorous and organic carbon. E. coli and enterococci partitioning coefficient (PC) and particulate associated fraction (PAF) were calculated to compare fecal indicator attachment in runoff from the different soil types and between two pathogen indicators, E. coli and enterococci and fractional filtration followed by centrifugations identified particle sizes to which indicators preferentially attached. Regression analysis was conducted to examine potential relationships to utilize nutrient and TSS data to predict E. coli and enterococci PC and total concentration (TC). The attachment of E. coli and enterococci to particulates present in runoff from three soil types was examined by a screen filtration and centrifugation procedure. Partitioning varied by indicator and by soil type. In general, enterococci had a higher percent attached to the silty loam (49%) and silty clay loam (43%) soils while E. coli had a higher percent attached to the loamy fine sand soils (43%). At least 50% of all attached E. coli and enterococci were associated with sediment and organic particles retained by an 8m filter. Findings from this study suggest that high concentrations of total suspended solids in runoff leads to higher bacterial attachment than previously reported.

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