POSTER: Using Chemical Tracers to Supplement Microbial Source Tracking in the Estero River
Research Mentor: Dr. Hidetoshi Urakawa
Additional Authors: Taylor L. Hancock, Haruka E. Urakawa, L. Donald Duke, and Serge Thomas
Abstract:
Detecting fecal pollution is a crucial component in water quality monitoring due to the human health risk involved. Fecal indicator bacteria (FIB), like Escherichia coli and enterococci, have been the primary analyte for human wastewater contamination in U.S water quality monitoring since the 1960s. The methods used to enumerate these bacteria are relatively cheap and quick to use, but researchers have recommended using other tracers in tandem with E. coli and enterococci. This is due to their presence in a variety of warm-blooded animal species as well as their extra-enteric environmental persistence. In this study, we used the chemical tracers, sucralose (a man-made sugar), and 15N/18O stable isotopes to help identify the source of FIB contamination in the Estero River via surface and groundwater sampling. The Estero River has had chronic exceedances of the Florida Department of Environmental Protection (FDEP) FIB standard for recreational waterways but monitoring efforts have not identified the main driver of these elevated FIB levels. There are multiple wastewater treatment plants (WWTPs) and septic tanks along the river, potentially leaching FIB and pathogens into the groundwater and eventually the river if not treated properly. Using tandem-tracing methods, we found that there was no significant correlation between any of the chemical tracer and FIB combinations. Groundwater FIB levels were below detection levels in the majority of samples but also had sucralose levels near the level of wastewater (>1000 ng/L). This result indicates that the residential WWTPs are eliminating FIB and potential human pathogens before entering the waterway and are not the primary cause of elevated FIB levels in the Estero River. E. coli correlated strongly with electric conductivity, which may be an indication that tidal resuspension is leading to elevated E. coli levels in the downstream portion of the Estero River. We also observed that poor correspondence between sucralose and 15N levels that is likely due to microbial transformation of nitrogen via denitrification and the fact that the majority of groundwater nitrogen came from fertilizer. Overall, we demonstrated the effectiveness of the use of sucralose and 15N/18O stable isotope signatures as chemical tracers to assist in identifying the source of FIB contamination.