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Scientists Work to Minimize Impact of High Sierra Grazing

September 13, 2010

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September 13, 2010

Does cattle grazing in the High Sierras affect water purity? If so, under what conditions and what can we do about it?

Answers to those pressing questions and more are the focus of a study under way by the University of California, the U.S. Forest Service and other agencies. Results from the study should help keep water in national forests safe for diverse public uses such as camping, fishing, swimming and more.

“Our goal is to evaluate the scope of the problem and come up with real solutions for how to fix it,” said UC Davis Cooperative Extension watershed specialist Ken Tate, the study’s principal investigator. His co-investigator is UC Davis Cooperative Extension specialist Rob Atwill, interim director of the Western Institute for Food Safety and Security.

Our national forests are home to a wide variety of activities and creatures, all of which both effect and rely upon clean water. Forest lands support a long list of uses - hiking, biking, horseback riding, swimming, fishing, camping, hunting, cattle grazing and driving off-road vehicles, just to name a few. Many of those activities along with wildlife and cabins with septic systems can contribute bacteria to waterways. Cattle grazing has received special attention lately as a potential source of water contamination.

“This study will be designed to provide a complete and accurate picture of the microbial risk of not just cattle grazing but all the activities and creatures found in our national forests,” says Tate, who, along with Atwill, has spent his entire 15-plus-year career studying rangeland watershed issues. “We will try to determine the level of risk, the sources of the risk and what management strategies can reduce the risk.”

Over the next several years, scientists will test water samples from forests across the state. This summer they are conducting pilot studies on the Stanislaus National Forest. They will check for levels of so-called indicator bacteria, such as fecal coliform and E. coli, at strategically selected locations – such as both above and below grazing sites, campgrounds and other select areas, the better to understand the source and risk of water impurities.

“We will also be looking at what happens to microbial counts when ranchers use herding and other mitigation measures to keep cattle from congregating near streams and in meadows,” Tate says.

As Atwill explains, “We want to focus on the practices that can move us forward so everyone can safely enjoy the national forest.”

Public input is vital to designing the comprehensive study. Environmental groups, ranchers and all interested parties are encouraged to participate in this project. .

“We’re at the preliminary stage,” said Scott Oneto, director and farm advisor for the UC Extension programs in Calaveras and Tuolume counties. “The flood gates are just now opening in terms of gathering information and we welcome input.”

To learn more about the study and provide input, go to

Read about other ecology studies undertaken by Atwill through Veterinary Medicine Extension.

Media contacts: Kenneth Tate, UC Davis Cooperative Extension specialist,, 530-754-8988

Rob Atwill, UC Davis Cooperative Extension specialist,, 530-754-2154

Scott Oneto, UC Extension farm advisor,, 209-533-5686

Diane Nelson, UC Davis Department of Plant Sciences senior writer,, 530-752-1969