RIVERINE DISSOLVED INORGANIC CARBON ISOTOPE ORIGIN AND EXCHANGE DYNAMICS IN A KENTUCKY KARST LANDSCAPE

With the political, social and environmental debate on global climate change reaching newfound attention in recent years, carbon dioxide (CO₂) is receiving increased attention due to its profound ability to impact global climate and its associated dynamics within natural systems. Karst systems, like that of south-central Kentucky, are characterized by the dissolution of bedrock facilitated by the interaction of carbon dioxide in the atmosphere and water to create carbonic acid, which dissolves away the bedrock. Rivers represent the primary conduits of dissolved inorganic carbon (DIC) from terrestrial ecosystems to ocean basins. The amalgamation of internal cycling and external inputs are displayed in the concentrations of DIC, in addition to other chemical constituents. The riverine processes that influence total DIC flux are: (1) photosynthesis, (2) respiration, (3) water-air interchange of gases (CO₂­), (4) groundwater inputs, and (5) geochemical reactions including the precipitation/dissolution of carbonate minerals. This study aims to capture the long-term seasonal carbon dynamics of the Green River, a highly diverse tributary of the Ohio River that transects east-west through south-central Kentucky and serves as the hydrological base-level for the region. Two study sites represent the respective less karstified upstream and more karstified downstream reaches of the river. To track the sourcing and flux of the seasonal carbon cycle along the river’s reaches, stable carbon isotope (¹³C) samples, along with geochemical data, are being collected weekly at each site to monitor the inputs of soil water, groundwater, precipitation, and dissolved carbonate bedrock to the river. The isotopic data, combined with geochemical data and biological isotope data, present a complete picture of the carbon dynamics within the Green River system. Currently, we hypothesize that these changes are due to both seasonal and spatial variation within the river, and the dynamics of the karst inputs to the system.