Sierra Nevada Water: Is it safe to drink?
Some of us dream of the good old days…days when you could dip your sierra cup into the nearest mountain stream and take a long refreshing drink—sans filtering. Do you really need to filter your water? Maybe… maybe not. New research sheds some light one of the oldest debates in the sierra: is the water safe to drink? Three articles are featured here that address this question. Do your reading and make up your own mind!
Read the article below or click on the following links to access these:
Giardia Lamblia and Giardiasis: With Particular Attention to the Sierra Nevada
Analysis of Yosemite National Park Wilderness water for Coliform and Pathologic Bacteria
Robert W. Derlet, MD
Professor, University of California Davis, School of Medicine
James Carlson, Ph.D.
Associate Professor, Director of Medical Microbiology Lab
University of California Davis Medical Center
INTRODUCTION
The quality of water in wilderness streams and lakes in Yosemite National Park is important to multiple users. Yosemite water is utilized by summer backpackers, day hikers, fishermen, and other recreational users. Precipitation that collects as snow during the winter storm season provides continuous water for streams into late summer from snow runoff.1,2
Over the past 20 years, an emphasis has been placed on Giardia as the major harmful water microbial contaminant in wilderness areas.3-5 Although certain mammals such as beavers have been attributed as natural reservoirs of the infection, we believe the seriousness of exposure in the wilderness to Giardia has been over emphasized. The average concentration of less than ten cysts per 1,000 liters reported in studies of Sierra Nevada wilderness water poses minimal risk to humans.6- 7 In one study of Sierra Nevada backpackers who developed diarrhea, none had Giardia.6 Although portable water filters may remove Giardia and other protozoal organisms, they become easily clogged with sediment, and are of no use on extended trips. In addition, some water filters used by backpackers may be effective at filtering out Giardia, but not bacteria.8
We believe that bacteria, and not protozoa such as Giardia, pose a greater risk of causing water-borne disease in humans. This has also been suggested by others.9-11 Pathogenic bacteria may originate from “imported” sources such as pack animals and humans visiting wilderness areas or may be present from natural environmental sources. Manure may be swept into streams and rivers by both summer storms as well as annual snowmelt. Areas of high human use may result in contamination of waterways with pathogenic bacteria. Finally, other bacteria may originate from natural wild animal zoonotic reservoirs. Some of these zoonotic infections are a potential threat to humans. This includes Yersenia enterocolitica which has been previously cultured in parts of the Sierra and may have a natural reservoir in small mammals.15,16 Potentially Leptospirosis, Campylobacter, and other microorganisms may have a reservoir in wild animals.
METHODS
A) Field Site Collection: 23 streams or lakes were selected which statistically differentiate among environmental risk for different types of bacterial risk in Yosemite. Risk classifications included: a) high use by backpackers; b) high use of pack animals; c) natural sites (wild ecologies) not contaminated by humans or domesticated animals. Early season samples were taken in July 2003 and late season in September 2003.
B) Field Water Collection: Water was collected in a) sterile test tubes; and b) Millipore total coliform count samplers. Coliform counts were collected in duplicate and samples were cooled following standardized procedures and transported to UC Davis.17
C) Water Analysis: The quantitative analysis for coliform counts and total bacterial counts were obtained from incubated Millipore counting plate paddles. Bacterial colonies were harvested from counting plates and also transport tubes for qualitative analysis. Colonies were initially plated onto Sheep Blood and MacConkey agar. Further screening was done by subplating onto sorbitol-MacConkey agar, L.I.A. and TSI tubes. An additional qualitative analysis was done to confirm the presence of coliform bacteria and to identify other pathogenic bacteria using standardized automated laboratory procedures. Coliforms were also subjected to analysis to determine the presence of E-coli O157, utilizing standard laboratory procedures.
RESULTS
A total of 23 different sites in Yosemite were sampled. Three of these sites were sampled in both early and late season. The results are displayed in Table I. Water temperatures ranged from a low of 7ºC at some early season lakes to 19ºC during September in Pate Valley.
Coliform bacteria: Coliform bacteria was detected at 8 of the 23 sites. At three locations, low levels of coliforms were found: 50-100 colony-forming units per 100 mls. (CFU/100 ml). These sites include: 1) Booth Lake and 2) Tuolumne River early season in Tuolumne Meadows, and 3) Upper Yosemite Creek.
At five locations higher levels of coliforms were found: 1) Merced Lake (1,000 CFU/ml), 2) Tuolumne River at confluence of Cathedral Creek (500 CFU/ml); 3) Return Creek near confluence of the Tuolumne (200 CFU/ml); 4) Snow Creek below May Lake (1,000 CFU/ml) and 5) Kibby Creek (250 CFU/ml).
No coliform bacteria were found in 16 of the locations. These locations included those watersheds both highly and lightly used by livestock and backpackers. For example, many sites along the Tuolumne River were free of coliform bacteria.
Other bacteria: Aquatic bacteria ranged in concentration from 350 to 12,000 CFU/100 ml. Identification of these bacteria included 1) Enterobacter aerogenes, 2) Serratia spp., 3) Aeromonas hydrophila/caviae, and 4) Pseudomonas spp.
Three sampling sites were studied during both early and late season. Total bacterial counts were higher during late season in all these sites. Significant increases occurred, for example bacteria at Snow Creek increased from 350 CFU/ml to 12,000 CFU/ml. We did not detect other pathogenic bacteria in this study.
DISCUSSION
Most Yosemite lakes and streams do not contain E-coli and other coliforms. Of sites sampled, 35% contain some level of coliform presence. Six of eight positive sites have very low levels. These potentially could be part of the natural environment or ecosystem. Only two sites, Merced Lake and Upper Snow Creek, below May Lake contained moderate levels.
Coliform bacteria have been used as indicators of fecal pollution or contamination of waterways in the US. The coliform group of bacteria consist of several genera belonging to the family enteroeacteriaceae.17 These bacteria are gram negative non-spore forming rod shaped bacteria that ferment lactose when incubated at 35ºC. Most common species associated with human or animal fecal contamination include E-coli, Klebsiella, or Enterobacter.
It is generally accepted that E-coli and other coliform bacteria can survive in aquatic environments for at least several weeks depending on the nutriment availability, pH, and water temperature. The number of years that E-coli can survive in aquatic environments has been debated.18 A recent study on the beaches of Lake Michigan suggest that E-coli may sustain itself indefinitely in appropriate environmental situations.19 Indeed, we have found significant concentrations of E-coli below cattle grazed meadows in the Golden Trout Wilderness nine months after the last cattle grazing activity.20 Although less relevant in national park environments, range cattle are noted to carry E-coli strain O157:H7 at a rate of 1% potentially placing persons who drink untreated water below established cow pastures at risk for a very serious pathogenic disease.21 In addition, many non-O157 E-coli are capable of inducing serious disease in humans.22
It is difficult to interpret the higher coliform counts found at two locations in Yosemite. Ongoing studies need to be conducted to make this determination. Although it is possible to genetically differentiate human from animal/ecologic E-coli, these techniques are very expensive and only available in limited laboratories in the United States. The one finding of high levels of coliforms at Merced Lake and Upper Snow Creek should be considered as a single point sample only and would require confirmation with multiple samples taken over a summer season.
Total Bacterial Counts: Aquatic bacteria are expected to be found in all healthy lakes and streams. However, some sites contained higher levels of aquatic bacteria than normal for Sierra Nevada wilderness areas. Past studies of wilderness water have shown a correlation between total bacterial counts and usage by backpackers.20 Although late season total counts were higher in watersheds utilized by backpackers, we did not perform early samplings at these sites. We did not detect non-coliform pathogenic bacteria in this study. However, other studies of wilderness water have found Camplylobacteria, Salmonella, and Yersinia species.9,20,23 High water run-off from abundant snowfall as well as wilderness management practices may have contributed to not finding these bacteria.
Finally, of concern are some of the observations made during the study. Moderate levels of soap foam were noted at several locations along the Tuolumne River between Tuolumne River and Pate Valley in September. Some soaps are known to contain phosphates. In the Sierra Nevada phosphates are the rate limiting growth factor of algae whereas, nitrites from the air and air pollution provide a political source of nitrites for algae. The authors have concern that excessive use of soap in the wilderness environment may lead to an over abundance of phito plantcum and algae growth. While a limited amount of phito planctum are important for ecology and fish as well as zoo planctum, excessive algae in lakes and streams can be harmful.
CONCLUSION
The majority lakes and streams studied in Yosemite do not contain coliform bacteria. Very low levels were found in six of eight specimens. These low levels may be of a natural ecological environment, or may be secondary to contamination from humans, pack animals or natural wild animals. The two sites found to have moderate levels need confirmation as part of a longitudinal study. The lower Tuolumne River watershed has non-measurable or only natural background coliforms. Further studies would be necessary to delineate this question.
REFERENCES
1. Storer T, Usinger R. Sierra Nevada natural history. University of CA Press (Berkeley) 1963:1-355.
2. Farquhar F. History of the Sierra Nevada. University of CA Press (Berkeley) 1965:1-246.
3. Fraker LD, Gentile DA, Krivoy D, Condon M, Backer H. Giardia cyst inactivation by iodine. J Wild Med 3:351-357, 1992.
4. Gerba CP, Johnson DC, Hasan MN. Efficacy of iodine water purification against Cryptosporidium oocysts and Giardia cysts. Wild and Environ Med 8:96-100, 1997.
5. Backer H. Wilderness acquired diarrhea. J Wild Med 3:237-240, 1992.
6. Zell SC, Sorenson SK. Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe. J Wild Med 4:147-154, 1993.
7. Zell SC. Epidemiology of wilderness –acquired diarrhea: implications for prevention and treatment. J Wild Med 3:241-249, 1992.
8. Backer HD. Field Water Disinfection IN: Paul S. Auerbach, ed: Wilderness Medicine, 4th ed. St. Louis, 2001, 1186-1236, Mosby.
9. Taylor DN, McDermott KT, et al. Campylobacter enteritis from untreated water in the Rocky Mountains. Ann Intern Med 1:38-40, 1999.
10. Welch TP. Risk of giardiasis from consumption of wilderness water in North America: a systematic review of epidemiologic data. Int J Infect Dis 4(2):100-3, 2000.
11. Rockwell R. Wilderness water purity, especially in the High Sierra. The American Alpine News 11:(238) Summer 2002.
12. USDA Forest Service: Pacific Southwest Region. www.r5.fs.fed.us. Accessed 2-21-03.
13. Renter DG, Sargeant JM, et al. Diversity, frequency, and persistence of Escherichia coli O157 strains from range cattle environments. Appl Environ Microbiol 69(1):542-547, 2003.
14. Slutsker L, Ries AA, et al. Escherichia coli O157:H7 diarrhea in the United States: Clinical and epidemiologic features. Ann Intern Med 126(7):505-513, 1997.
15. Harvey S, Greenwood JR, Pickett MJ, Mah RA. Recovery of Yersinia enterocolitica from streams and lakes of California. Appl Environ Microbiol. 32:352-354, 1976.
16. Derlet RW, Carlson JR. An analysis of human pathogens found in horse/mule manure along the John Muir Trail in Kings Canyon and Sequoia and Yosemite National Parks. J Wild Med 13:113-118, 2002.
17. American Public Health Association. Microbiologic Examination, IN: Clesceri LS, Ed., Standard Methods for the Examination of Water and Wastewater, 20th ed., United Book Press, Inc., Baltimore, MD, 1998.
18. Winfield MD, Groisman EA. Role of nonhost environments in the lifestyles of Salmonella and Escherichia coli. Applied and Environmental Microbiology 2003, 69(7):3687-3694.
19. Whitman RL, Nevers MB. Foreshore sand as a source of Escherichia coli in nearshore water of a Lake Michigan Beach. Applied and Environmental Microbiology 2003, 69(9):5555-5562.
20. Derlet RW, Carlson JR. Incidence of fecal coliforms in fresh water from California wilderness areas. Abstract accepted by the American Society for Microbiology 2003 meeting, Washington, D.C.
21. Renter DG, Sargeant JM, Oberst RD, Samadpour M. Diversity, frequency, and persistence of Escherichia coli O157 strains from range cattle environments. Applied and Environmental Microbiology 2003, 69(1):542-547.
22. Khan A, Yamasaki S, Sato T, et al. Prevalence and genetic profiling of virulence determinants of non-O157 Shiga toxin-producing Escherichia coli isolated from cattle, beef, and humans, Calcutta, India. Emerging Infectious Diseases 8(1):54-62.
23. Schaffter N, Parriaux A. Pathogenic-bacterial water contamination in mountainous catchments. Water Res 2002, 36(1):131-139.
24. Wang GD, Doyle MP. Survival of enterohemorrhagic Escherichia coli O157:H7 in water. Journal of Food Protection 1998, 61(6):662-667.
STREAM/LAKE- EXACT LOCATION- ELEVATION- COLIFORM BACTERIA1 OTHER BACTERIA1
EARLY2 LATE2 EARLY2 LATE2
Flecher Lake Outlet 10,220 None * 500 *
Vogelsang Lake Outlet 10,341 None * 10,000 *
Bernice Lake Outlet 10,217 None * 500 *
Booth Lake East Shore 9,850 100 * 2,700 *
Emeric Lake East Shore 9,400 None * 2,800 *
Babcock Lake East Shore 8,983 None * 600 *
Washburn Lake Outlet 7,600 None * 1,200 *
Merced Lake North Shore 7,200 1,000 * 5,500 *
Rafferty Creek 100 yards above JMT crossing 8,790 None * 300 *
Dana Fork At Parker Pass Trail 9,500 None * 600 *
Tuolumne River Tuolumne Meadows 8,550 100 None 2,200 6,500
Tuolumne River JMT upper bridge (Glen Aulin) 8,330 * None * 11,000
Tuolumne River 200 yards below Glen Aulin bridge 7,800 * None * 5,700
Tuolumne River At Cathedral Creek confluence 5,600 * 500 * 4,400
Tuolumne River Just above Pate Valley 4,832 * None * 3,900
Return Creek At confluence of Tuolumne 6,200 * 200 * 4,000
Rogers Creek At confluence of Tuolumne 5,350 * None * 7,000
Piute Creek Pate Valley 4,365 * None * 5,800
Yosemite Creek ¼ mile above Highway 120 7,474 100 None 700 10,500
Snow Creek ¼ mile above Highway 120 8,430 None 1,000 350 12,000
Kibby Creek Trail Crossing above Lake 4,700 * 250 * 8,000
Chain of Lakes Outlet 8,900 None * 2,000 *
South Fork Merced River 1 mile west of Chain of Lakes 8,100 None * 800 *
1. = CFU/100ml
2. = Early = May/June; Late = August
- = Sample not taken
