Do Waterborne Coliform Bacteria Increase in Sierra Nevada Mountain Wilderness Area Lakes and Streams During Drought Periods?
Objectives.-Humans may acquire waterborne infections in remote wilderness environments. We hypothesize the risk of waterborne infection increases during drought years.
Methods.-Water was collected from wilderness area lakes and streams in the Sierra Nevada Mountains of California during summer 2007 and 2008, and results compared to a previously published data set from this laboratory. Precipitation during water years 2007 and 2008 was 45% and 55% of normal, respectively. Collection locations matched those from prior years in Yosemite, Kings Canyon-Sequoia (SEKI) National Parks and Forest Service Wilderness. Land use was categorized as predominate impact from either: 1) wildlife (W), 2) day-hike (DH), 3) backpackers (BP) only, or 4) pack animals (PA). Water was collected in sterile tubes and Millipore coliform samplers and analyzed at the University of California, Davis research laboratory, where bacteria were harvested, then subjected to analysis using standardized techniques. Coliforms were used as a marker of infection risk; samples showing ΟΎ100 CFU/100 mL were considered positive. Statistical analysis to compare among site categories was performed using Fisher exact test.
Results.-A total of 168 sites were sampled (84 each year) among the 3 types of wilderness. Prevalence of coliforms is listed by area and land use (% positive, raw number positive sites/total sites): Location Wild (W) Day-hike (DH) Backpack (BP) Pack animal (PA) Yosemite 35% (5/13) 10% (2/10) 20% (5/23) 78% (18/23) SEKI 0% (0/14) 14% (1/7) 17% (2/12) 68% (23/34) Forest wild 20% (1/5) 50% (1/2) 17% (1/6) 95% (18/19) Totals 19% (6/32) 21% (4/19) 20% (8/41) 75% (59/76)
No difference was found comparing 2007 to 2008; coliform prevalence was significantly higher in PA use areas when compared to either W, DH, or BP areas (P Υ
.05). Results were also compared to coliform prevalence from 364 samplings collected during 5 nondrought years (2002)(2003)(2004)(2005)(2006) previously reported as follows: W 9%, DH 12%, BP 18%, and PA 63%. Coliform prevalence was higher in the drought years compared to nondrought, in W, DH, and PA areas but only significant in PA areas (59/76 vs 70/111; P Ο½.05).
Conclusion.-During drought years, wilderness water coliform prevalence was significantly increased compared to nondrought years in those areas used by pack animals.