Impact of summer cattle grazing on the sierra nevada watershed: Aquatic algae and bacteria

Introduction. 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 >100CFU/100mL: C = 91, R = 8, W = 0 (P < 0.05). Conclusion. 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.