Utilization of Tryptophan-like Fluorescence as a Proxy for E. coli Contamination in a Mixed-Land-Use Karst Basin

Ryan T. Dapkus, Alan E. Fryar, Benjamin W. Tobin, Diana M. Byrne, Shishir K. Sarker, Leonie Bettel, James F. Fox

Research output: Contribution to journalArticlepeer-review


Karst aquifers are susceptible to contamination by pathogenic microorganisms, such as those found in human and animal waste, because the surface and subsurface drainage are well integrated through dissolution features. Fecal contamination of water is commonly assessed by the concentration of thermotolerant coliform bacteria, especially E. coli. This method is time-consuming, taking ≥18 h between the start of incubation and subsequent enumeration, as well as the time required to collect and transport samples. We examined the utility of continuous monitoring of tryptophan-like fluorescence (TLF) as a real-time proxy for E. coli in a mixed-land-use karst basin in the Inner Bluegrass region of central Kentucky (USA). Two logging fluorometers were sequentially deployed at the outlet spring. During storm flow, TLF typically peaked after discharge, which suggests that TLF transport in the phreatic conduit is likely related to sediment transport. The ability of TLF and other parameters (48 h antecedent precipitation, turbidity, and air temperature) to predict E. coli concentrations was assessed using the Akaike information criterion (AIC) applied to linear regression models. Because both the models and baseline concentrations of TLF differed between fluorometers, TLF and instrument interaction were accounted for in the AIC. TLF was positively correlated with E. coli and, in conjunction with antecedent precipitation, was the best predictor of E. coli. However, a model that included air temperature and antecedent precipitation but not TLF predicted E. coli concentrations similarly well. Given the expense of the fluorometers and the performance of the alternate model, TLF may not be a cost-effective proxy for E. coli in this karst basin.

Original languageEnglish
Article number74
Issue number4
StatePublished - Apr 2023

Bibliographical note

Funding Information:
This material is based upon work supported, in part, by the U.S. Geological Survey under Grant/Cooperative Agreement No. G21AP10631 through an award to A.E.F., D.M.B. and R.T.D. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey. This work was funded in part by the Kentucky Senate Bill 271B Water Quality program and National Science Foundation awards #1632888 and #1933779 to J.F.F.; by the Kentucky Geological Survey through a Commonwealth Research Assistantship to R.T.D.; by the University of Kentucky College of Agriculture, Food and Environment through a Kerri Casner Fellowship to R.T.D.; and by the Karst Waters Institute through a William Wilson Scholarship to R.T.D.

Publisher Copyright:
© 2023 by the authors.


  • Kentucky
  • bacteria
  • fluorometer
  • karst
  • spring
  • tryptophan

ASJC Scopus subject areas

  • Oceanography
  • Water Science and Technology
  • Waste Management and Disposal
  • Earth-Surface Processes


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