Assessing the Sensitivity of Water to Surface, Soil, Rock, and Cave Conditions in Fitton Cave, Northern Arkansas

Fitton Cave, located within the Buffalo National River in north-central Arkansas, offers a window into a relatively pristine portion of the Ozarks Plateaus. This region is one of the largest karst aquifers in the United States, providing more than 1.8 million people with drinking water. Understanding what happens to water as it moves from the surface to subsurface is requisite for utilization, management, and sustainability of karst aquifers as water resources. As population pressures increase, assessment of geochemical and hydrologic processes from pristine systems such as Fitton Cave will prove extremely valuable for providing baseline conditions. By integrating vascular plant biomarkers and GIS, along with traditional dye tracing and geochemical methods, we will constrain the sources of chemical changes to water as it interacts along flowpaths with soil, rock, and cave conditions in Fitton Cave.

Preliminary results indicate at least three distinct sources of water to the subsurface hydrology. Variability in electrical conductivity (EC), temperature, alkalinity, and the presence of vascular plant biomarkers demonstrates heterogeneity of flowpaths through soils, overlying strata, and host-rock. Elevated EC and alkalinity in one cave stream indicates more extensive water-host-rock interactions compared to an adjacent stream despite morphologic, stratigraphic, and hydrologic similarities. Aqueous sulfur content and localized gypsum deposits support geochemical contributions from overlying shale units. Observed direct flowpaths from sinking streams indicates strong influence of surface and rainwater inputs to the system without protracted reservoir storage. Despite the geochemical heterogeneity, we are able to delineate likely flow paths and provide critical information about how karst aquifers respond under near-natural conditions. This study has implications for the utility of vascular plant biomarker for delineating surface to subsurface connectivity, which may lead to their application as a novel paleoclimate proxy.