Management of Microbial Contamination in Storm Runoff from California Coastal Dairy Pastures
Journal of Environmental Quality , 39 , 2010

Lewis, D.J., Atwill, E. R., Lennox, M.S., Pereira, M.D.G., Miller, W.A., Conrad, P.A., Tate, K. W.

A survey of storm runoff fecal coliform bacteria (FCB) from working farm and ranch pastures is presented in conjunction with a survey of FCB in manure management systems (MMS). h e cross-sectional survey of pasture runoff was conducted on 34 pastures on fi ve diff erent dairies over 2 yr under varying conditions of precipitation, slope, manure management, and use of conservation practices such as vegetative fi lter strips. h e MMS cross-sectional survey consisted of samples collected during 1 yr on nine diff erent dairies from six loafi ng barns, nine primary lagoons, 12 secondary lagoons, and six irrigation sample points. Pasture runoff samples were additionally analyzed for Cryptosporidium sp. and Giardia duodenalis, whereby detectable concentrations occurred sporadically at higher FCB concentrations resulting in poor correlations with FCB. Prevalence of both parasites was lower relative to high-use areas studied simultaneously on these same farms. Application of manure to pastures more than 2 wk in advance of stormassociated runoff was related to a ≥80% reduction in FCB concentration and load compared to applications within 2 wk before a runoff event. For every 10 m of buff er length, a 24% reduction in FCB concentration was documented. A one-half (75%), one (90%), and two (99%) log10 reduction in manure FCB concentration was observed for manure holding times in MMS of approximately 20, 66, and 133 d, respectively. h ese results suggest that there are several management and conservation practices for working farms that may result in reduced FCB fl uxes from agricultural operations