Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/1996
Publication Date: N/A
Interpretive Summary: Grazing cattle and manure applications to pasture can affect bacterial runoff. The objective of this study was to assess the effects of grazing, time of year, and runoff amounts on fecal coliform (FC) and fecal streptococcus (FS) concentrations. Runoff water from four fields in NW Arkansas was monitored for three years. All fields were grazed, but two were fertilized with inorganic fertilizer and two with animal manure. Although runoff amounts had no effect, the season of the year influenced concentrations, with higher numbers in warmer months. Runoff of FC exceeded amount safe to swim in 89% of the time. Cattle grazing did not appear to have an effect.
Technical Abstract: Agricultural practices such as cattle grazing and animal manure application can contribute to relatively high runoff concentrations of fecal coliform (FC) and fecal streptococcus (FS). Available information, however, is inconsistent with respect to effects of such practices as well as to measures that can discriminate among candidate sources of FC and FS. The objective of this study was to assess the effects of grazing, time of year and runoff amounts on FC and FS concentrations and to evaluate whether FC/FS concentration ratios are consistent with earlier values reported as characteristic of animal sources. Runoff from four Northwest Arkansas fields was sampled and analyzed for fecal coliform (FC) and fecal streptococcus (FS) for nearly three years (1991-1994). Each field was grazed and fertilized, with two fields receiving inorganic fertilizer and two receiving animal manure. Runoff amount had no effect on runoff concentrations of FC or FS. There were no consistent relationships betwee the presence of cattle and FC and FS runoff concentrations. Both FC and FS concentrations were affected by the season during which the runoff occurred. Higher concentrations were observed during warmer months. Runoff FC concentrations exceeded the primary contact standard of 200 cfu/100 mL during at least 89 percent of all runoff events and the secondary contact of 1000 cfu/100 mL during at least 70 percent of the events. Ratios of FC to FS concentrations varied widely (from near zero to more than 100), confirming earlier findings that FC/FS ratios are not a reliable indicator of the source of FC and FS.