COUPLING POPULATION GENETICS AND TRACER HYDROLOGY TO CHARACTERIZE FLOW-PATH DYNAMICS IN A KARST SYSTEM

Karst systems are unique among groundwater systems because of the continual changes in permeability and flow-path organization that result from dissolution processes. These changes in flow-path connectivity over time provide a challenge in understanding the evolution of conduit networks in karst hydrogeology. Natural and artificial tracer techniques have long provided critical information for protecting karst aquifers and understanding potential impacts to ecosystems and human populations. Conventional tracer methods are useful in karst hydrogeologic studies for delineating flow paths and properties of recharge, storage, and discharge. However, these methods only provide a snapshot and do not provide sufficient information to understand the changes in interconnection or larger-scale evolution of flow paths in the aquifer over time.

To address this lack of temporal information, we combined the more traditional techniques with population genetic data to determine if these data can provide insight into seasonal or longer changes in connections between conduits. Dye traces from Fern Cave, a 15-mile-long, multilevel cave system in Nat Mountain, Alabama, identified two isolated flow paths within the cave that drain separate parts of the mountain. Major ion geochemistry showed a Ca/Mg-CO₃ water type, suggesting primary storage in the limestone rather than in overlying sandstone, and water isotope data suggest rapid recharge, with minimal evaporation. Hydrograph data show the system to be extremely flashy, with the lower section of the cave inundated by periodic floods of the nearby Paint Rock River. Population genetics data suggest that these two separate flow paths are connected during these floods because the downstream populations of both systems are similar. Although upstream populations show some similarities in genetics, hydrologic barriers, in the form of large waterfalls, likely separate populations within the same stream.