Transport and storage of trace metals in a karst aquifer: An example from Fort Campbell, Kentucky

This study addresses the release, transport and storage of contaminants in a karst aquifer. The project has two components: (1) temporal changes in spring water chemistry through storms and, (2) metal accumulation and speciation in spring sediments. The study was conducted on and near the Fort Campbell Army Base on the Kentucky-Tennessee border. The site is underlain Mississippian limestones and up to 30 meters of residuum.; The data demonstrate that spring water quality varies through storms but that the magnitude and direction of change depends on the specific chemical. As per many karst studies, the carbonate-derived constituents decreased in concentration during storms due to rapid recharge. A late-storm increase in CO₂ suggests that dispersed infiltration also contributed to recharge. The non-carbonate metals increased in concentration during storms and were transported in association with particulates. Although the trace metals had a variety of chemical properties, they exhibited similar behavior suggesting that the storm-induced transport of suspended sediments from the surface governed their fate. Other contaminants either had consistent concentrations through the storm (trichloroethene, chloroform) or decreased in concentration (nitrate), in a manner consistent with their inferred in-aquifer storage style.; Spring bed sediments were similar to the background soil and were ultimately controlled by the physical properties of transport, erosion, and deposition. Spring geomorphology was key because it determined sediment accumulation. Sediment redox condition were important for many metals and were regulated by sediment thickness and the presence of organic matter. Although the trace metals had different chemical properties, they were largely in the residual form. The metals with high concentrations in the suspended sediments also had high concentrations in the bed sediments implying that the soil-water surface chemistry of individual metals did not dictate their behavior.; Overall, the data indicated that physical, rather than chemical, processes controlled transport of metals and contaminants on a basin-wide scale. In contrast, chemical processes were more likely to be important on a local scale. Because spring water is heterogeneous temporally and sediments are heterogeneous spatially, contaminants in karst aquifers can contribute to both acute and chronic impacts to spring ecosystems and water supplies.