TY - JOUR
T1 - Use of Nitrogen-15-Enriched Escherichia coli as a Bacterial Tracer in Karst Aquifers
AU - Ward, James W.
AU - Warden, John G.
AU - Bandy, Ashley M.
AU - Fryar, Alan E.
AU - Brion, Gail M.
AU - Macko, Stephen A.
AU - Romanek, Christopher S.
AU - Coyne, Mark S.
N1 - Publisher Copyright:
© 2016, National Ground Water Association.
PY - 2016/11/1
Y1 - 2016/11/1
N2 - Karst aquifers are susceptible to contamination by microorganisms, but relatively few studies have used bacteria as tracers. We demonstrate the utility of Escherichia coli enriched in the stable isotope nitrogen-15 (15N) as a novel bacterial tracer. Nonpathogenic E. coli from two springs in central Kentucky were grown on 15N-enriched media. Survival of E. coli and persistence of the isotopic signal were assessed in two sets of laboratory experiments conducted with sterilized spring water in dark microcosms at 14 °C. First, isotopically labeled bacteria survived for 130 d at concentrations within one log unit of the average initial value, and there was no significant difference in δ15N values from Day 1 to Day 130. Second, water samples with E. coli were inoculated with either of two different species of protozoa (Tetrahymena pyriformis or Colpoda steinii). During 7 d, δ15N values increased in T. pyriformis while bacterial populations decreased. In a field test, following a 2.1-cm rainfall, 15N-labeled E. coli, solutes (rhodamine WT dye and bromide), and latex microspheres were injected into a sinkhole approximately 530 m upgradient of a spring. Breakthrough of all tracers coincided, but microspheres were remobilized by subsequent storms, unlike other tracers. Enriched E. coli exhibited more tailing than solute tracers during the initial storm-flow recession. These results indicate that 15N-enriched E. coli is a viable tracer of bacterial transport in karst aquifers, although predation may attenuate the isotopic signal in systems that are not rapidly flushed.
AB - Karst aquifers are susceptible to contamination by microorganisms, but relatively few studies have used bacteria as tracers. We demonstrate the utility of Escherichia coli enriched in the stable isotope nitrogen-15 (15N) as a novel bacterial tracer. Nonpathogenic E. coli from two springs in central Kentucky were grown on 15N-enriched media. Survival of E. coli and persistence of the isotopic signal were assessed in two sets of laboratory experiments conducted with sterilized spring water in dark microcosms at 14 °C. First, isotopically labeled bacteria survived for 130 d at concentrations within one log unit of the average initial value, and there was no significant difference in δ15N values from Day 1 to Day 130. Second, water samples with E. coli were inoculated with either of two different species of protozoa (Tetrahymena pyriformis or Colpoda steinii). During 7 d, δ15N values increased in T. pyriformis while bacterial populations decreased. In a field test, following a 2.1-cm rainfall, 15N-labeled E. coli, solutes (rhodamine WT dye and bromide), and latex microspheres were injected into a sinkhole approximately 530 m upgradient of a spring. Breakthrough of all tracers coincided, but microspheres were remobilized by subsequent storms, unlike other tracers. Enriched E. coli exhibited more tailing than solute tracers during the initial storm-flow recession. These results indicate that 15N-enriched E. coli is a viable tracer of bacterial transport in karst aquifers, although predation may attenuate the isotopic signal in systems that are not rapidly flushed.
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U2 - 10.1111/gwat.12426
DO - 10.1111/gwat.12426
M3 - Article
C2 - 27089430
AN - SCOPUS:84963894031
SN - 0017-467X
VL - 54
SP - 830
EP - 839
JO - Groundwater
JF - Groundwater
IS - 6
ER -