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Title: Use of stable isotope-labeled Escherichia coli as a tracer in karst aquifers

item BANDY, ASHLEY - University Of Kentucky
item Cook, Kimberly - Kim
item MACKO, STEVE - University Of Virginia
item FRYAR, ALAN - University Of Kentucky

Submitted to: Geological Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/25/2014
Publication Date: 10/19/2014
Citation: Bandy, A., Cook, K.L., Macko, S., Fryar, A. 2014. Use of stable isotope-labeled Escherichia coli as a tracer in karst aquifers. Geological Society of America Annual Meeting. October 19-22, 2014. Vancouver, Canada.

Interpretive Summary:

Technical Abstract: Bacterial contamination of karst aquifers is a large concern across the globe, yet bacterial transport in karst aquifers is not currently well understood. Groundwater tracers typically used in karst systems include fluorescent dyes and latex microspheres. Not only can these tracers can be cost-prohibitive, depending on the karst system being studied, but these common tracers cannot accurately mimic the transport behaviors of bacteria and other potential pathogens, meaning they are not good proxies for risk assessment involving microorganisms. This study examines the movement and attenuation of two serotypes of Escherichia coli (E. coli) with differing attachment efficiencies compared to traditional tracers (Rhodamine WT dye and 1-µm diameter fluorescent microspheres). Study sites include epikarst above Cave Springs Cavern near Bowling Green, KY, and a karst aquifer that emerges at Royal Spring in Georgetown, KY. E. coli is enriched with either 13C or 15N and is injected into the karst area of interest (epikarst or aquifer conduit) along with dye and microspheres. Quantification of E. coli will be performed through molecular methods (qPCR) and isotope analysis on an IRMS (Isotope Ratio Mass Spectrometer). Preliminary findings suggest that the two methods may be complementary, having limitations across the range of isotopically enriched bacteria or number of gene copies they can detect. Based on prior research, it was hypothesized that the three tracers will exhibit differential transport times in the Cane Run/Royal Spring basin under base flow conditions, with microorganisms arriving at the spring prior to microspheres or conservative dyes. For the epikarst trace, the E. coli isolate exhibiting higher attachment efficiency and contains the iha gene is expected to have higher attenuation and emerge from the epikarst after the isolate that contains the kps gene. These two isolates of E. coli will have transport times differing from microspheres or dyes, with the potential for multiple storm events occurring before bacteria are flushed through the epikarst, with dye emerging from the epikarst prior to particulate tracers.