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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Water Management and Systems Research » Research » Publications at this Location » Publication #381027
Research Project: Improving the Sustainability of Irrigated Farming Systems in Semi-Arid Regions

Location: Water Management and Systems Research

Title: Grazing effects on bovine-associated and background fecal indicator bacteria levels in edge-of-field runoff

Author
item WAGNER, KEVIN - Oklahoma State University
item GENTRY, TERRY - Texas A&M University
item Harmel, Daren
item POPE, EMILY - Natural Resources Conservation Service (NRCS, USDA)
item REDMON, LARRY - Texas A&M Agrilife

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2021
Publication Date: 3/29/2021
Citation: Wagner, K.L., Gentry, T.J., Harmel, R.D., Pope, E.C., Redmon, L.A. 2021. Grazing effects on bovine-associated and background fecal indicator bacteria levels in edge-of-field runoff. Water. 13(7). Article e928. https://doi.org/10.3390/w13070928.
DOI: https://doi.org/10.3390/w13070928

Interpretive Summary: Excessive levels of fecal indicator bacteria are a major cause of water quality impairment. Grazing and its management may significantly impact bacteria concentrations; however, other sources can contribute to water quality issues both in the presence and absence of cattle, thus confounding results. In this study, we utilize a marker (called Bacteroides) to evaluate bacteria loading from cattle versus background sources in runoff from rotationally grazed and ungrazed pastures and how grazing management, timing of runoff in relation to grazing events, and stocking rate effect marker levels and ratios and their relation to E. coli concentrations in runoff at the small watershed scale. Data suggest the all markers and bovine (cattle) marker level were not significantly impacted by grazing management or stocking rate; however, the timing of runoff events in relation to grazing events significantly impacted the levels of these markers found in runoff. Further, the marker ratios confirmed that fecal contamination present in runoff when sites were not stocked with cattle more than two weeks originated from sources other than cattle. Thus, the magnitude and proportion of cattle impacts on fecal indicator bacteria in edge-of-field runoff were dramatically reduced shortly after de-stocking. However, background sources continued contributing significant concentrations of E. coli bacteria.

Technical Abstract: Excessive levels of fecal indicator bacteria are a major cause of water quality impairment. Grazing and its management may significantly impact bacteria concentrations; however, other sources can contribute to water quality issues both in the presence and absence of cattle, thus confounding results. In this study, we utilize Bacteroides markers to evaluate bacteria loading from cattle versus background sources in runoff from rotationally grazed and ungrazed pastures and how grazing management, timing of runoff in relation to grazing events, and stocking rate effect Bacteroides marker (AllBac and BoBac) levels and ratios and their relation to E. coli concentrations in runoff at the small watershed scale. Data suggest the AllBac and BoBac levels were not significantly impacted by grazing management or stocking rate; however, the timing of runoff events in relation to grazing events significantly impacted the levels of these markers found in runoff. Further, the BoBac/AllBac ratio confirmed that fecal contamination present in runoff when sites were destocked more than two weeks originated from sources other than cattle. Thus, the magnitude and proportion of cattle impacts on fecal indicator bacteria in edge-of-field runoff were dramatically reduced shortly after de-stocking. However, background sources continued contributing significant concentrations of E. coli.