Abstract
Fecal contamination of surface water has been associated with multiple enteric disease outbreaks and food recalls. Thus, it is important to understand factors associated with fecal contamination of agricultural water sources. Since fecal indicator bacteria (FIB) were used to monitor surface water for potential fecal contamination, the purpose of the present study was to characterize associations between environmental factors, and (i) FIB (E. coli, Enterococcus, and coliform) levels, and (ii) host-specific fecal marker detection. This study used data collected from 224 sites along 3 waterways, which spanned an urban-rural gradient around Syracuse, New York. Between 2008 and 2017, 2,816 water samples were collected, and E. coli, Enterococcus, and/or coliform concentrations were enumerated. Thirty-one samples were also tested for human and ruminant microbial source-tracking markers. Water quality (e.g., turbidity, nitrate) and weather data were also collected for each site. Univariable Bayesian regression was used to characterize the relationship between each microbial target and land use, water quality, and weather factor. For each model, probability of direction and region of practical equivalence overlap (ROPE) were calculated to characterize the association's direction and strength, respectively. While levels of different FIB were not correlated with each other, FIB levels were associated with environmental conditions. Specifically, FIB levels were also positively associated with temperature, nutrient and sediment levels. Log10 E. coli levels increased by 0.20 (CI = 0.11, 0.31) and log10 Enterococcus levels increased by 0.68 (CI = 0.08, 1.24) for each log10 increase in salinity and nitrate, respectively. These findings may indicate that similar processes drove microbial, sediment, and nutrient contamination of the sampled watersheds. While fecal contamination was strongly associated with land use, the direction of association varied between FIBs and the buffer distance used to calculate land use metrics. E. coli levels and human marker detection were positively associated with percent pasture cover within 122, 366, and 1,098 m of the sampling site, while Enterococcus and coliform levels were only associated with pasture cover within 1,098 m (not 122 or 366 m). Ruminant markers were positively associated with pasture cover within 122 m, but not 366 or 1,098 m. These findings highlight the importance of considering (i) adjacent land use (and associated non-point sources of contamination) when developing strategies for managing fecal hazards associated in agricultural and recreational water, and (ii) spatial scale (e.g., 122 vs. 1,098 m) when developing these strategies.
Highlights
Fecal contamination of surface water represents a public health hazard, and threatens the economic and recreational value of waterbodies (Rabinovici et al, 2004; Dwight et al, 2005; Given et al, 2006; DeFlorio-Barker et al, 2017; U.S Environmental Protection Agency SIM., 2018; Calderón-Arrieta et al, 2019)
While E. coli levels were associated with levels of other fecal indicator bacteria (FIB), land use and spatial factors, such as rurality, that were positively associated with fecal coliform and Enterococcus levels tended to be negatively associated with E. coli levels, and vice versa (Tables 1–3)
Given the pattern of land use associations observed here, our findings suggest that the sources of Enterococcus and fecal coliform contamination differ from sources of E. coli or MST markers, with the former coming from developed areas, and the latter from agricultural areas
Summary
Fecal contamination of surface water represents a public health hazard, and threatens the economic and recreational value of waterbodies (Rabinovici et al, 2004; Dwight et al, 2005; Given et al, 2006; DeFlorio-Barker et al, 2017; U.S Environmental Protection Agency SIM., 2018; Calderón-Arrieta et al, 2019). Fecal contamination of agricultural or recreational water has been identified as the probable cause of multiple enteric disease outbreaks (Ackers et al, 1998; Wachtel et al, 2002; Johnson, 2006; Greene et al, 2008; Barton Behravesh et al, 2011; Food Drug Administration, 2019, 2020). A 2008 multistate Salmonella outbreak in the United States was traced back to the use of contaminated water to irrigate hot peppers in 2008 While this outbreak caused 1,200 salmonellosis cases, it cost tomatoes growers $25 million in the US, as tomatoes were originally misidentified as the food vehicle, before hot peppers were eventually identified (Barton Behravesh et al, 2011; Ribera et al, 2012). Multiple studies have shown that stream sediments can act as inchannel stores for FIB, and that disturbance of these sediments (e.g., during storm events) can re-introduce the bacteria into the water column (Nagels et al, 2002; Muirhead et al, 2004)
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