Mobility of Stable Isotope-Label Escherichia coli in Karst Terrains

Currently, bacterial transport in karst aquifers is not well understood. Bacterial contamination of karst aquifers is a large concern across the globe. Groundwater tracers typically used in karst systems include fluorescent dyes and latex microspheres. These tracers do not exhibit surface properties and transport behaviors mimicking those of bacteria and pathogens, and therefore are not good proxies for risk assessment involving microorganisms. The proposed project will expand upon a proof-of-concept study tagging nonpathogenic Escherichia coli (E. coli) with stable isotopes (15N and 13C) to use as a tracer in a karst basin. A trace will be conducted using labelled E. coli in conjunction with fluorescent dyes and latex microspheres in the Cane Run karst aquifer in central Kentucky and through epikarst above Cave Spring Caverns near Bowling Green, Kentucky. It is hypothesized that dyes, microspheres, and bacteria tracers will show differential transport times in the Cane Run/Royal Spring basin under normal flow conditions, with microorganisms arriving at the spring prior to microspheres or conservative dyes. For the epikarst trace above Cave Spring Caverns, the E. coli isolate that exhibits higher attachment efficiency in saturated granular columns is expected to have higher attenuation and emerge from the epikarst after the isolate that exhibits lower attachment efficiency. These two types of E. coli will have different transport times than microspheres or dyes and may take many storm events before they are flushed through the epikarst. Isotope analysis will be used in conjunction with genetic markers to monitor breakthrough of tracer bacteria.