title: Linking fecal bacteria in rivers to landscape, geochemical, and hydrologic factors and sources at the basin scale.
abstract: 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 log10 most probable number⋅100 mL(-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.
authors.affiliation: Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824; mverhougstraete@email.arizona.edu.
authors.forename: Marc P
authors.identifier: http://orcid.org/0000-0003-4154-7531
authors.initials: MP
authors.lastname: Verhougstraete
authors.affiliation: Department of Geological Sciences, Michigan State University, East Lansing, MI 48824.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Martin
authors.affiliation: Department of Geological Sciences, Michigan State University, East Lansing, MI 48824.
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Kendall
authors.affiliation: Department of Geological Sciences, Michigan State University, East Lansing, MI 48824.
authors.forename: David W
authors.initials: DW
authors.lastname: Hyndman
authors.affiliation: Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824;
authors.forename: Joan B
authors.initials: JB
authors.lastname: Rose
mesh_terms: D001439:Bacteroides / Q000302:isolation & purification; D004784:Environmental Monitoring / Q000379:methods; D004926:Escherichia coli / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D005844:Geology; D006863:Hydrogen-Ion Concentration; D008824:Michigan; D062065:Wastewater; D014867:Water / Q000032:analysis*; D014871:Water Microbiology; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D062065:Wastewater; D014867:Water; D014873:Water Pollutants
keywords: Bacteroides thetaiotaomicron; Escherichia coli; baseflow; reference conditions; septic system