Differentiating Sources of Fecal Contamination to Wilderness Waters Using Droplet Digital PCR and Fecal Indicator Bacteria Methods

Introduction: Human activity in wilderness areas has the potential to affect aquatic ecosystems, including through the introduction of microorganisms associated with fecal contamination. We examined fecal microorganism contamination in water sources (lake outlets, snowmelt streams) in the popular Absaroka Beartooth Wilderness in the United States. Although the region is remote, increasing human visitation has the potential to negatively affect water quality, with particular concern about human-derived microorganism fecal contaminants. Methods: We used standard fecal indicator bacterial assays that quantified total coliform bacteria and Escherichia coli concentrations, together with more specific polymerase chain reaction-based microbial assays that identified possible human sources of fecal microorganisms in these waters. Results: Total coliforms were detected at all lake outlets (21 of 21 sites), and E coli was detected at 11 of 21 sites. Droplet digital polymerase chain reaction assays revealed the presence of human feces-derived microorganisms, albeit at abundances below the limit of detection (<10 gene copies per milliliter of water) at all but 1 of the sampling sites. Conclusions: Our results suggest low prevalence of water-borne pathogens (specifically E coli and human-derived Bacteroides) in this popular wilderness area. However, widespread detection of total coliforms, Bacteroides, and E coli highlight the importance of purifying water sources in wilderness areas before consumption. Specific sources of total coliforms and E coli in these waters remain unknown but could derive from wild or domesticated animals that inhabit or visit the Absaroka Beartooth Wilderness. Hence, although contamination by human fecal microorganisms appears minimal, human visitation could indirectly influence fecal contamination through domesticated animals.