"There's been a lot of concern about public lands and water quality, especially with cattle grazing," says lead author Leslie Roche, a postdoctoral scholar in the UC Davis Department of Plant Sciences.

"We're able to show that livestock grazing, public recreation and the provisioning of clean water can be compatible goals."

Roughly 1.8 million livestock graze on national forest lands in the western U.S. each year, the study says. In California, 500 active grazing allotments support 97,000 livestock across eight million acres on 17 national forests.

"With an annual recreating population of over 26 million, California's national forests are at the crossroad of a growing debate about the compatibility of livestock grazing with other activities dependent upon clean, safe water," the study's authors write.

"We often hear that livestock production isn't compatible with environmental goals," says principal investigator Kenneth Tate, a Cooperative Extension specialist in the UC Davis Department of Plant Sciences.

"This helps to show that's not absolutely true. There is no real evidence that we're creating hot spots of human health risk with livestock grazing in these areas."

The study was conducted in 2011, during the grazing and recreation season of June through November.

Nearly 40 UC Davis researchers, ranchers, U.S. Department of Agriculture Forest Service staff and environmental stakeholders went out by foot and on horseback, hiking across meadows, along campsites and down ravines to collect 743 water samples from 155 sites across five national forests in northern California.

These areas stretched from Klamath National Forest to Plumas, Tahoe, Stanislaus and Shasta-Trinity national forests. They included key cattle grazing areas, recreational lands and places where neither cattle nor humans tend to wander.

UC Davis researchers analyzed the water samples for microbial and nutrient pollution, including fecal indicator bacteria, fecal coliform, E. coli, nitrogen and phosphorous.

The scientists found that recreation sites were the cleanest, with the lowest levels of fecal indicator bacteria. They found no significant differences in fecal indicator bacteria between grazing lands and areas without recreation or grazing.

Overall, 83 percent of all sample sites and 95 percent of all water samples collected were below U.S. Environmental Protection Agency benchmarks for human health.

The study noted that several regional regulatory programs use different water quality standards for fecal bacteria. For instance, most of the study's sample sites would exceed levels set by a more restrictive standard based on fecal coliform concentrations.

However, the EPA states that E. coli are better indicators of fecal contamination and provide the most accurate assessment of water quality conditions and human health risks.

The study also found that all nutrient concentrations were at or below background levels, and no samples exceeded concentrations of ecological or human health concern.

The study was funded by the USDA Forest Service, Region 5. 

—From UC Davis News Service