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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:10.13031/2013.24295)
Authors:   Michelle L Soupir, Saied Mostaghimi
Keywords:   Bacterial partitioning, indicator organisms, E coli, enterococci, nonpoint source pollution

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. 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. 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. 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%). 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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