Microbial source tracking (MST) in Chattahoochee River National Recreation Area: Seasonal and precipitation trends in MST marker concentrations, and associations with E. coli levels, pathogenic marker presence, and land use

Abstract

Escherichia coli levels in recreational waters are often used to predict when fecal-associated pathogen levels are a human health risk. The reach of the Chattahoochee River that flows through the Chattahoochee River National Recreation Area (CRNRA), located in the Atlanta-metropolitan area, is a popular recreation area that frequently exceeds the U.S. Environmental Protection Agency beach action value (BAV) for E. coli . A BacteriALERT program has been implemented to provide real-time E. coli estimates in the reach and notify the public of potentially harmful levels of fecal-associated pathogens as indicated by surrogate models based on real-time turbidity measurements from continuous water quality monitoring stations. However, E. coli does not provide information about the sources of fecal contamination and its accuracy as a human health indicator is questionable when sources of contamination are non-human. The objectives of our study were to investigate, within the Park and surrounding watersheds, seasonal and precipitation-related patterns in microbial source tracking marker concentrations of possible sources (human, dog, and ruminant), assess correlations between source contamination levels and culturable E. coli levels, determine which sources best explained model-based E. coli estimates above the BAV and detection of esp2 (a marker for the esp gene associated with pathogenic strains of Enterococcus faecium and Enterococcus faecalis ), and investigate associations between source contamination levels and land use features. Three BacteriALERT sites on the Chattahoochee River were sampled six times per season in the winter and summer from December 2015 through September 2017, and 11 additional stream sites (synoptic sites) from the CRNRA watershed were sampled once per season. Samples were screened with microbial source tracking (MST) quantitative PCR (qPCR) markers for humans (HF183 Taqman), dogs (DogBact), and ruminants (Rum2Bac), the esp2 qPCR marker, and culturable E. coli . At the BacteriALERT sites, HF183 Taqman concentrations were higher under wet conditions DogBact concentrations were greater in the winter and under wet conditions, and Rum2Bac concentrations were comparatively low throughout the study with no difference across seasons or precipitation conditions. Concentrations of HF183 Taqman, DogBact, and Rum2Bac were positively correlated with culturable E. coli concentrations; however, DogBact had the largest R 2 value among the three markers, and the forward stepwise regression indicated it was the best predictor of culturable E. coli concentrations at the BacteriALERT sites. Recursive partitioning indicated that BAV exceedances of model-based E. coli estimates were best explained by Do...

Detection and quantification of enteric pathogens in aerosols near open wastewater canals in cities with poor sanitation

“…There were two Atlanta samples adjacent to the Chattahoochee River positive for adenovirus nucleic acid and one adjacent to Proctor Creek with Campylobacter coli nucleic acid, both above their respective 95% LODs (SI Table 2). The Chattahoochee commonly experiences levels of fecal indicator bacteria beyond EPA-recommended limits for recreational use, above 235 CFU per 100 mL 86,113,114 . To compare across cities, we normalized the collection volume to 2000 m 3 and calculated the expected number of positives based on measured values.…”

“…LODs (Table S2). The Chattahoochee commonly experiences levels of fecal indicator bacteria beyond EPA-recommended limits for recreational use, above 235 CFU per 100 mL 86,113,114 . To compare across cities, we normalized the collection volume to 2000 m 3 and calculated the expected number of positives based on measured values.…”

“…In past studies, this river system and its basin -eventually flowing into the Amazon -has been shown to contain a diverse and rich array of enteric microbes indicating high levels of fecal contamination 79,82,83 . As a reference site, Atlanta is characterized by having an established and maintained subsurface wastewater infrastructure, although urban surface waters in Atlanta's watershed experience elevated levels of fecal-associated pathogens [84][85][86] due to nonpoint source pollution and combined sewer overflows 87,88 . The city of Atlanta's population density is an estimated 1500 persons/km 2 89 , though sampling locations near impacted streams were in suburban locations at lower than mean population density.…”

Microbial and Viral Indicators of Pathogens and Human Health Risks from Recreational Exposure to Waters Impaired by Fecal Contamination

“…Microbial source tracking can be particularly helpful for determining sources of fecal contamination when FIB levels are high, but the likely source(s) is/are unknown, such as when the site is unaffected, or unlikely to be affected, by point sources of contamination. For example, McKee et al (2020) determined that E. coli levels were most strongly correlated with levels of a dog MST marker in the reach of the Chattahoochee River encompassed in the Chattahoochee River National Recreation Area in Georgia. McKee et al (2020) also found that samples with E. coli levels that exceeded the EPA beach action value of 235 most probable number (MPN) per 100 mL were best predicted by samples with dog MST marker concentrations of 300 gene copies per 100 mL or greater.…”

“…For example, McKee et al (2020) determined that E. coli levels were most strongly correlated with levels of a dog MST marker in the reach of the Chattahoochee River encompassed in the Chattahoochee River National Recreation Area in Georgia. McKee et al (2020) also found that samples with E. coli levels that exceeded the EPA beach action value of 235 most probable number (MPN) per 100 mL were best predicted by samples with dog MST marker concentrations of 300 gene copies per 100 mL or greater. Results from this study led to a joint effort between the National Park Service and a local nonprofit to install dog waste stations throughout the park.…”