Surface waters were tested before and after the arrival of cattle to summer grazing allotments for pathogenic bacteria indicators E. coli, fecal coliform bacteria, and total coliform bacteria in the high elevation mountains of the Stanislaus National Forest, California, USA. Water samples were collected from one control/ungrazed stream site and at four grazed stream sites before cattle grazing began and during the time when livestock were present. All sample sites were higher than 1900 meters in elevation. Samples were transported within 6 hours to a water analysis laboratory, where they were analyzed following standardized lab methods. Results showed that individual and average concentrations of fecal coliform bacteria in surface waters were below regulatory thresholds at the ungrazed site and at the grazed sites before cattle arrived. Mean fecal coliform concentration increased from 9 to 350 CFU/100 mL, and mean E. coli increased from 8 to 240 CFU/100 mL, respectively, after grazing. The increase in mean concentration of fecal coliform at each grazed site was significant (p < 0.05). Total coliform bacteria and E. coli concentrations showed the same pattern. Cattle grazing in the sampled high elevation Sierra Nevada meadows resulted in a significant increase in indicator bacteria.

The impact of summer cattle grazing on water quality during three very different climatic years in the Sierra Nevada was investigated. Water year 2009 had near normal precipitation; 2010 had late precipitation and snowmelt; and 2011 had 150% above normal precipitation. Surface waters were tested for pathogenic bacteria indicators fecal coliform, E. coli, and total coliform before and after cattle were released onto summer grazing allotments. Water samples were collected from meadow stream sites up to 6 weeks before and up to 6 weeks after cattle grazing began. Streams passing through ungrazed meadow served as controls. Eight sample sites were between 1694 m and 2273 m in elevation; one site was lower at 1145 m in elevation. Samples were transported within 6 hours to a water analysis laboratory, where samples were analyzed following standardized laboratory methods. Results showed that individual site and total mean concentrations of E. coli in surface waters were within regulatory standards before cattle arrived during each of the 3 study years. After the beginning of grazing, mean E. coli counts increased as follows: 2009 from 8 to 240 CFU/100mL, 2010 from 7 to 561 CFU/10mL; 2011 from 7 to 657 CFU/100mL (p < 0.05 all years). Total coliform bacteria and fecal coliform concentrations showed the same pattern. This study shows that cattle grazing in the high elevation Sierra Nevada results in a significant increase in indicator bacteria. This impact on the watersheds occurs despite widely variable annual climatic conditions

Livestock presence in proximity to forest streams has been shown to contribute pathogenic bacteria in excess of water quality standards established to protect human health. However, the degree to which livestock fecal contamination in streams on national forest lands is either a limited or a potentially widespread occurrence is still debated. This study provides additional insight into the matter. We analyzed water in small streams near known cattle grazing areas within the Stanislaus National Forest in the Sierra Nevada, California from 2012 to 2016. Fourteen stream sites were sampled before and after cattle were released onto the forest (four of these sites were sampled across multiple years) to compare indicator bacteria concentrations (fecal coliform-FC, Escherichia coli-EC) to standards established for recreational contact for surface waters. One control site was also sampled. There were 194 water quality violations of either state or federal regulatory standards for recreational contact, all of which occurred once cattle were on the forest. Mean (max) FC and EC concentrations were on orders of magnitude higher after cattle were released onto the forest [FC 1307 (30,000) and EC 1033 (17,000) MPN/100 mL] than during the time period before cattle were on the forest [FC 19 (220) and EC 17 (220) MPN/100 mL; FC, F 1,210 = 105, p < 0.001; EC, F 1,210 = 85.5, p < 0.001]. In addition, the presence of cattle, visual evidence of recent cattle-related disturbances, and sampling week were important predictor variables of FC and EC. These findings support the link between cattle presence and increased levels of stream pathogenic bacteria, and also demonstrate that stream pathogenic bacteria pollution occurs widely across the forest. This research indicates the need to consider alternative range management practices to better protect water quality and human health.