Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 33, Pages 10419-10424Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1415836112
Keywords
Escherichia coli; Bacteroides thetaiotaomicron; baseflow; reference conditions; septic system
Categories
Funding
- National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory Grant Land Use Change and Agricultural Lands Indicators and Tipping Points
- Environmental Protection Agency [112013, 118539]
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Linking fecal indicator bacteria concentrations in large mixed-use watersheds back to diffuse human sources, such as septic systems, has met limited success. In this study, 64 rivers that drain 84% of Michigan's Lower Peninsula were sampled under baseflow conditions for Escherichia coli, Bacteroides thetaiotaomicron (a human source-tracking marker), landscape characteristics, and geochemical and hydrologic variables. E. coli and B. thetaiotaomicron were routinely detected in sampled rivers and an E. coli reference level was defined (1.4 log(10) most probable number.100mL(-1)). Using classification and regression tree analysis and demographic estimates of wastewater treatments per watershed, septic systems seem to be the primary driver of fecal bacteria levels. In particular, watersheds with more than 1,621 septic systems exhibited significantly higher concentrations of B. thetaiotaomicron. This information is vital for evaluating water quality and health implications, determining the impacts of septic systems on watersheds, and improving management decisions for locating, constructing, and maintaining on-site wastewater treatment systems.
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