Masthead: Kaweah Range

Sierra Nature Notes, Volume 10, May 2011

Abstract: Comparison of Periphyton and Microbial communities in the High Sierra watershed of California: Cattle grazed versus non-grazed areas
Robert W. Derlet, Lidia L. Tanaka, Curtis Hayden, John R. Richards, K. Ali Ger, and Charles R. Goldman 
Department of Environmental Science and Policy,
Department of Medicine,
University of California, Davis

Correspondance: rwderlet@ucdavis.edu

Cows Stanislaus National Forest
Cattle grazing, Stanislaus National Forest, California.
Photo: Robert Derlet

Introduction: The Sierra Nevada alpine watershed is the most important source of surface water in California. Lack of significant topsoil and the short growing season limits the ecosystems capacity for resilience to common stressors such as nutrient pollution.  We evaluated the periphyton and microbial community structure across the landscape as indicators to assess the influence of land use on water quality and eutrophication.


Methods: A total of 64 sites, including both lakes and streams were accessed during the summer of 2010, and assigned land use categories of: 1) cattle grazing areas (C), 2) recreation use areas (R), or 3) remote wildlife areas (W). Analysis involved 12 C sites, 36 R sites, and 16 W sites. Collection sites ranged from 1,650 to 3,800 m elevation, scattered on either side of the Sierra Crest from Lake Tahoe to Sequoia National Park. Paired samples were collected from each site, which have been studied in previous years for suspended indicator bacteria and were accessed on foot from 1 to 30 km from the nearest trailhead. The first algal sample was scraped from benthic surfaces, placed in 5 ml of water and preserved with Lugol’s solution. An estimate of periphyton coverage of lake/stream bed was made (how?). A second algae sample, for attached microbes was placed in 5 ml of Kerry-Blair transport media. Additionally,water for Coliforms and E. coli was collected and transported to the laboratory; periphytic algae were then identified under a microscope. Algae preserved for attached microbes were centrifuged, and 10 µL plated onto a variety of 100 ml agar media and incubated at either 35° C or 44° C. Bacteria colonies were counted, and CFU/gm algae calculated after spun algae were weighed. Suspended aquatic indicator bacteria were analyzed as previously published.

 

Algae in Stream
Algae in surface water, Stanislaus National Forest, California
Photo: Robert Derlet

Results: Periphyton was found at 100% of C sites, 89% of R sites, and 25% of W sites. Most common periphytic algae included Zygnema, Ulothrix, Chlorella, Spirogyra, mixed Diatoms, and Cladophoria. However, only Zygnema and Ulothrix were identified in C areas. Benthic coverage (biomass estimate) of algae was highest in C areas compared to other areas (P<0.05).Mean bacterial CFU/gm of algae were: Heterotrophic: C = 2,014,000, R = 1,968,000, W = 335,000; Coliforms: C = 198,000, R = 150,000, W = 39,000; E. coli: C = 173,000, R = 700, W = 0. (P < 0.05 for E. coli at C sites vs. other site categories). Analysis of neighboring water for indicator bacteria > 100 CFU/100 ml as follows: Coliforms: C = 100%, R = 25%, W = 0; E. coli: C = 91%, R = 8%, W = 0. (P < 0.05 comparing C to other areas). Multi-variant analysis of data found no significant differences as a result of water temperature, latitude, or elevation.


Conclusion: Higher algal cover/biomass and lower community diversity corresponded to watersheds where summer cattle grazing occur. Results suggest that unrestricted summer cattle grazing in alpine watersheds may increase periphytic algal biomass and attached bacteria by an order of magnitude, indicating significantly deteriorating water quality within these source watersheds.

 

 



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Masthead Photo from:
Kaweahs From Trailcrest, Kings Canyon National Park
© 2009, Howard Weamer