Fate and Transport of E. coli Through Appalachian Karst Systems

Abstract

Karst waters serve as important water sources in rural Appalachia and are well-connected to surface waters, making them susceptible to anthropogenic contamination, including by fecal indicator bacteria which represent a public health risk. This work designed and implemented a watershed-scale monitoring program for a 26 km2 sinking stream system in southwest Virginia to determine the fate and transport of E. coli in the system. This hydrologically complex watershed is predominantly agricultural and includes multiple key surface water sinks that enter Smokehole Cave and emerge at Smokehole Spring. Field campaigns at surface sites and within Smokehole Cave included bacteriological sampling, hydrologic measurement, and dye tracing. Field data was synthesized to: 1) examine variations in E. coli concentrations in the watershed during varying flows/seasonal conditions; and 2) calculate E. coli growth/decay coefficients for the karst system during different flow/antecedent conditions. E. coli concentrations at Smokehole Spring consistently peaked days after peak hydrologic stage. Flow conditions and storm event response were the largest drivers of E. coli transport through the system. Dye trace results revealed that water from sinks can be stored or move slowly through the karst system, resurging during storm events. E. coli was calculated to decay within the karst system, with a half-life of about 5-120 days which is longer than the travel time of water through the cave of approximately 0.5-2 days. Findings indicate that E. coli transport in Appalachian karst systems is hydrologically driven, roadside spring water collection is not recommended, and bacterial treatment is encouraged if performed. Targeted land-management practices should be explored to decrease E. coli loadings in karst waters.