title: Enrichment of stream water with fecal indicator organisms during baseflow periods.
abstract: Fecal indicator organisms (FIOs) are generally believed to be present in surface waters due solely to direct deposition of feces or through transport in runoff. However, emerging evidence points toward hyporheic exchange between sediment pore water and the overlying water column during baseflow periods as a source of FIOs is surface waters. The objective of this work was to (a) propose a mass balance-based technique for estimating changes of FIO concentrations in the same volume of water (or "slug") from the inlet to outlet of stream reaches in baseflow conditions and (b) to use such enumeration to estimate rate of the FIO release to stream water column. Concentrations of Escherichia coli (E. coli) and enterococci were measured in the slug while simultaneously monitoring the movement of a conservative tracer, Br that labeled the slug. Concentrations of E. coli in the slug were significantly larger (P = 0.035, P = 0.001, and P = 0.001, respectively) at the outlet reach in all three replications, while enterococci concentrations were significantly larger in two of three replications (P = 0.001, P < 0.001, and P = 0.602). When estimated without accounting for die-off in water column, FIO net release rates across replications ranged from 36 to 57 cells m-2s-1and 43 to 87 cells m-2s-1for E. coli and enterococci, respectively. These release rates were 5 to 20% higher when the die-off in water column was taken into account. No diurnal trends were observed in indicator concentrations. No FIO sources other than bottom sediment have been observed during the baseflow period. FIOs are released into stream water column through hyporheic exchange during baseflow periods.
authors.affiliation: USDA-ARS Environmental Microbial and Food Safety Laboratory, Beltsville, MD, USA. Yakov.Pachepsky@ars.usda.gov.
authors.forename: Yakov
authors.initials: Y
authors.lastname: Pachepsky
authors.affiliation: USDA-ARS Environmental Microbial and Food Safety Laboratory, Beltsville, MD, USA.|Oak Ridge Institute for Science and Education (ORISE), Oak Ridge, TN, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Stocker
authors.affiliation: Department of Environmental Sciences, University of Puerto Rico - Rio Piedras, San Juan, Puerto Rico.
authors.forename: Manuel Olmeda
authors.initials: MO
authors.lastname: Saldaña
authors.affiliation: USDA-ARS Environmental Microbial and Food Safety Laboratory, Beltsville, MD, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Shelton
mesh_terms: D016983:Enterococcus / Q000254:growth & development*; D004784:Environmental Monitoring; D004926:Escherichia coli / Q000254:growth & development*; D005243:Feces / Q000382:microbiology*; D019015:Geologic Sediments / Q000382:microbiology; D060587:Groundwater / Q000382:microbiology*; D045483:Rivers / Q000382:microbiology*; D014871:Water Microbiology; D014872:Water Movements; D060753:Water Quality
keywords: Enterococci; Escherichia coli; Microbial water quality; Release rate; Streambed sediment