Waterborne disease outbreaks have been associated with dispersed sources of animal wastes, such as contamination from animal agriculture (Ferguson, Husman, Altavilla, Deere, & Ashbolt, 2003). Pathogens found in animal wastes may infect people following fecal contamination of drinking or recreational waters (Centers for Disease Control and Prevention [CDC], 1998). Dogs and other companion animals are a potential source of waterborne pathogens from feces (Maepherson, 2005). Canine-borne zoonoses include fecal salmonellosis (S. typhimurium), mycobacteria (M. bovis, M. tuburculosis), and protozoa including Giardia spp., Cryptosporidium parvum. Toxo-plasma gondii, and Leptospira (L. hardjo, L. ictero-haemorrhagiae) (Macpherson, 2005; Owen, 2005).
Zoonotic pathogens may affect human health, especially if they have environmentally resistant infective stages (Nithiuthai, Anantaphruti, Waikagul, & Gajadhar, 2004). These pathogens may be abundant in areas that have significant accumulations of fecal matter from infected animals. For example, approximately 36% of dogs in the United States are infected with helminths capable of causing human disease through contact with or ingestion of contaminated soils (CDC, 1995). Human enteric infections acquired from pets living in developed, urban communities are common (Croese, Loukas, Opdebeeck, Fairley, & Prociv, 1994). City parks and sidewalks used for dog exercise have been shown to have high accumulations of dog feces when owners do not collect and dispose of feces (Bonner & Agnew, 1983).
Frequently used dog parks with significant fecal loading could contaminate surface waters. Alta, Utah, cited this as a primary reason to limit the total number of dogs within town boundaries by restricting the number of licenses available (Foy, 2006). In 2004, the number of dog licenses in the California counties of Placer and Nevada alone led to an estimate of over 15,000 licenses in the Lake Tahoe basin watershed (Cobourn & Segale, 2004). Although some water quality monitoring efforts in the Lake Tahoe Basin have shown fecal coliform results ranging from 0 to 25,000 colony-forming units (CFU) per 100 ml (Tahoe Regional Planning Agency, 2007), little research has examined the sources or transport of these bacteria. This may be an important concern, especially in heavily used areas where residents and visitors exercise pets. The correlation between this type of fecal loading and microbial water quality, however, has not been explored.
This investigation examined fecal loading in a popular dog exercise area adjacent to a tributary (Burke Creek) to Lake Tahoe, Nevada (Figure 1). The intake for a public drinking water supply was approximately 200 meters offshore from the creek outlet. E. coli is a common fecal contamination indicator in water studies and monitoring efforts (Edberg, Rice, Karlin, & Allen, 2000) and was chosen as the microbial indicator for this study. Based on a statistically sufficient number of samples (not less than five samples equally spaced over a 30-day period), standards established by the U.S. Environmental Protection Agency (U.S. EPA) state that the geometric mean of E. coli should not exceed 126 CFU per 100 ml and no single sample should exceed 75% of a one-sided confidence limit if water is used for contact recreation (Emerson, 2003).
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The study consisted of site mapping with repeated fecal matter collection and water sampling. The goal of the study was to characterize spatial and seasonal trends in, as well as any possible correlation between, fecal accumulation and E. coli in surface waters.
The study area was within the U.S. Forest Service--managed Burke Creek Recreational Area (BCRA), located on the southeast side of Lake Tahoe (Figure 2). The BCRA lacked dog waste collection and disposal facilities and was heavily used by dog owners. A network of trails connected a parking lot and residential area to the lake through the BCRA. Burke Creek flows through the BCRA after descending through private and public lands from its origin near the Heavenly Mountain ski resort. At the study site, 0.75 miles (1.3 km) east of Lake Tahoe's south shore, the flow of Burke Creek was approximately 0.1 f[t.sup.3]/min (4x[10.sup.-3] [m.sup.3]/min). The creek flows through a 1 acre (0.4 hectare) constructed sedimentation pond and along a course with nearly a mile of meadow and riparian wetlands before reaching the lake. The predominant soils are alluvial tills, including loamy coarse sands with some gravel (Hanes, 1974). Plant cover included species common to arid alpine environments, such as cheatgrass, sagebrush, and rabbitbrush.
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The boundaries for the study site were based upon the trail systems and topography. The bounded area was a portion of the lower watershed for Burke Creek, extending from Route 50 to approximately 1310 feet (400 m) downstream (Figure 2). Route 50 served as the upstream limit of the study area and the downstream-most water sampling site was below a wetland at a pedestrian bridge and stream crossing.
Fecal Accumulation and E. coli Burden Characterization
Fifteen circular plots of 7 ft (2.1 m) radius were established to estimate distribution of dog feces over the 8.8 acre (3.6 hectare) study site (Figure 2). All feces within the plots were collected semimonthly for 14 consecutive months. The plots were sited adjacent to heavily used trails and in unused portions of the study area. Plot locations were recorded with a Trimble Explorer 3 and corrected using a local geopositioning reference station.
Prior to establishing sampling plots we noted that fecal...