Effects of Rotational Beef Cattle Grazing on Microbial Parameters In Elk River, Humboldt County (CA).

The North Coast Regional Water Quality Board (CA) initiated the scoping period for the development of the Elk River (CA) Total Maximum Daily Load (TMDL) process in 2009.  While impairment by sediment load is the primary concern, the addition of nutrients and fecal coliforms from grazing activities has been specified as a concern.  However, fecal coliforms may derive from rural septic systems, wildlife sources, and/or livestock grazing.  This study provides objective scientific data to inform the current TMDL process in the Elk River Watershed and will give valuable insights for other watersheds as well.  Our hypothesis is that there are no significant differences in water quality/microbial parameters as a function of a well-designed rotational grazing operation along the Elk River.  Water samples were collected upstream, downstream, and at a stream crossing of a rotational beef cattle operation for a period of 15 months, during wet and dry seasonal fluctuations and presence or absence of cattle.  Stream water samples were processed through 0.45 micron opening, 47 mm diameter membrane filter paper and enumerated using m-FC agar poured into 50 mm diameter micro-plates after filtration and incubation for 24 hours in a 44.5^o C water bath. Fecal coliform levels were found to be relatively constant, with numbers between 2 and 12 cfu’s / 10 mL, regardless of sampling location.  A drainage ditch running from a paved road in the area, entering Elk River between the upstream and stream crossing sampling locations, yielded much higher levels of coliform; between 22 to 36 cfu’s / 10 mL.  Additionally, soil and bovine fecal pats were sampled for fecal coliform and Salmonella for a period of approximately 1 month.  Soil samples were consistently low in fecal coliforms and Salmonella. Fecal coliform levels sampled from the bovine fecal pats initially increased within the first 3 days before gradually decreasing to less than 10% viability by the end of the sampling period. Our sampling was concurrent with independently collected regional water quality board sampling in response to citizen concerns about the impact of the grazing operation on water quality. A repeated-measures ANOVA will be used to test for statistical differences in microbial parameters as a function of land use management.