Effects of rotational beef cattle grazing on microbial parameters in Elk River, Humboldt County, CA

The addition of nutrients and fecal coliforms from grazing activities to stream systems has been of great concern to farmers, cattlemen, environmental agencies and advocates, and local citizens. The North Coast Regional Water Quality Board is in the process of developing Total Maximum Daily Loads (TMDLs) for the Elk River (Humboldt County, California), primarily focused on sediments, however, fecal coliforms may derive from rural septic systems, wildlife sources, and/or livestock grazing. Water samples were collected upstream, downstream, and at a stream crossing of the Westfall Mazzucchi Ranch, a rotational beef cattle grazing operation, over a period of 16 months. Particular attention was paid to wet and dry seasons and the presence or absence of cattle. An additional experiment was performed to characterize the attenuation of fecal coliforms and Salmonella in grazed paddock soils and bovine fecal pats over a period of about one month. An ANOVA revealed that there was no significant difference in fecal coliform concentrations in Elk River as a function of sampling location (p = 0.84). There was a significant difference in concentrations with regards to cattle presence or absence (p = 0.0007). The maximum colony forming unts (CFUs) per 100 mL (occurring June 10th, 2010) were 200, 213, and 285 at upstream, crossing, and downstream sampling sites, respectively. It was inferred that fecal coliform values were higher at the same time that cattle were present on the ranch and not that cattle were the sole contributors of bacteria, as this was an observational study. The maximum value per dry gram of bovine feces was 6.95 x 10 CFUs. Additional ANOVAs showed that there was a significant difference in fecal coliform values found within cowpats as a function of moisture content (p = 1.0 x 10-6). However, there was no statistical difference in fecal coliform concentrations of soils as a function of moisture content (p = 0.1248) or sampling location (p = 0.5036). It was concluded that the Westfall Mazzucchi Ranch utilizes management practices that reduce and/or eliminate microbial contributions made by cattle. However, further investigations would be needed to identify the magnitude of these contributions within the watershed as a whole and other possible sources of contamination.