CA²⁺ AND MG²⁺ FLUXES WITHIN THE HORN HOLLOW KARST SYSTEM, CARTER CAVES STATE PARK, KY

The Horn Hollow karst system, located in a relatively pristine area of Carter Caves State Park, KY, is an ideal location to study Ca²⁺ and Mg²⁺ fluxes in karst valley waters. As these waters move down slope, they enter and exit the limestone subsurface several times before converging with Cave Branch, a tributary to the main stream in the area. This investigation was conducted to analyze the fluxes of Ca²⁺ and Mg²⁺ within these karst valley waters. Changes in the concentrations of these two elements can be used to identify the mixing of different waters, as well as calculating dissolution rates within the system. Major ion samples were collected and filtered at 15 locations within the Horn Hollow Valley at baseline flow conditions and after a precipitation event. Concentrations of Ca²⁺ and Mg²⁺ were analyzed in the lab using Inductive Coupled Plasma Emission Spectroscopy. Fluxes of both elements were observed as the karst waters entered and exited the subsurface. Water types are dominantly Ca-HCO₃ with two distinct subgroups based on major ion chemistry. The upstream portion of the system contains aggressive waters (Ca-Mg-HCO₃-SO₄) that are under-saturated with respect to Ca²⁺. This area includes Horn Hollow Cave and H₂O Cave. Less aggressive waters (Ca-HCO₃) are present in the downstream portion of the system, which includes Laurel Cave and Cave Branch, and are over-saturated with respect to Ca²⁺. In general, saturation indices show under-saturated waters from the northernmost Horn Hollow Cave inlet to the Laurel Cave inlet and super-saturated waters at the Laurel outlet. The increase in saturation with respect to Ca²⁺ through the system may be the result of limestone dissolution, a change in concentration of CO₂, or a change in temperatures as waters flow through the system. Mass flux calculations of Ca²⁺ and Mg²⁺ will be performed to determine dissolution rates within the upper Horn Hollow system. Our ultimate goal is to determine the sources and flow regime of these karst valley waters.