title: Impact of summer cattle grazing on the Sierra Nevada watershed: aquatic algae and bacteria.
abstract: BACKGROUND
  We evaluated periphytic algal and microbial communities to assess the influence of human and cattle impact on Sierra water quality.
  
  
  METHODS
  64 sites (lakes and streams from Lake Tahoe to Sequoia National Park, California) were sampled for suspended indicator bacteria and algae following standardized procedures. The potential for nonpoint pollution was divided into three categories: cattle-grazing areas (C), recreation use areas (R), or remote wildlife areas (W).
  
  
  RESULTS
  Periphyton was found at 100% of C sites, 89% of R sites, but only 25% of W sites. Eleven species of periphytic algae were identified, including Zygnema, Ulothrix, Chlorella, Spirogyra, mixed Diatoms, and Cladophoria. Mean benthic algae coverage was 66% at C sites compared to 2% at W sites (P < 0.05). The prevalence of E. coli associated with periphyton was 100% at C sites, 25% of R sites, and 0% of W sites. Mean E. coli CFU/gm of algae detected was: C = 173,000, R = 700, W = 0. (P < 0.05). Analysis of neighboring water for E. coli bacteria >100 CFU/100 mL: C = 91%, R = 8%, W = 0 (P < 0.05).
  
  
  CONCLUSIONS
  Higher periphytic algal biomass and uniform presence of periphyton-attached E. coli corresponded to watersheds exposed to summer cattle grazing. These differences suggest cattle grazing compromises water quality.
authors.affiliation: Department of Environmental Science and Policy and the John Muir Institute of the Environment, University of California, Davis, CA 95616, USA. rwderlet@ucdavis.edu
authors.forename: Robert W
authors.initials: RW
authors.lastname: Derlet
authors.forename: John R
authors.initials: JR
authors.lastname: Richards
authors.forename: Lidia L
authors.initials: LL
authors.lastname: Tanaka
authors.forename: Curtis
authors.initials: C
authors.lastname: Hayden
authors.forename: K Ali
authors.initials: KA
authors.lastname: Ger
authors.forename: Charles R
authors.initials: CR
authors.lastname: Goldman
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification / Q000302:isolation & purification*; D018407:Bacterial Physiological Phenomena; D018533:Biomass; D002140:California; D002417:Cattle; D057946:Charophyceae / Q000145:classification / Q000502:physiology; D000460:Chlorophyta / Q000145:classification / Q000502:physiology; D017377:Diatoms / Q000145:classification / Q000502:physiology; D056890:Eukaryota / Q000145:classification* / Q000502:physiology*; D005618:Fresh Water / Q000382:microbiology*; D012621:Seasons; D014877:Water Pollution, Chemical / Q000009:adverse effects*