CARBON DIOXIDE DYNAMICS IN THE CARBONATE CRITICAL ZONE, SAVOY EXPERIMENTAL WATERSHED, ARKANSAS, USA

Vital to understanding subsurface porosity and permeability development, carbon dioxide (CO₂) dynamics within the Earth’s critical zone drive the spatial and temporal distributions of dissolution and precipitation of carbonates. The Covington Research Group at the University of Arkansas explores these dynamics within a mantled karst terrain in Northwest Arkansas. Former group members developed a low-cost measurement and data logging system to monitor atmospheric, soil, and dissolved CO₂ variability in harsh conditions. They measured concentrations of dissolved CO₂ for several years at two karst springs at the Savoy Experimental Watershed (SEW) east of Fayetteville, Arkansas. Monitoring dissolved CO₂ concentrations and dissolution rates at SEW’s Basin 1 underflow (perennial), and overflow (high flow) springs helped shed light on the temporal variation in CO₂ within karst systems. However, we know little about spatial variation in CO₂ driving cave and karst forming processes in the carbonate critical zone.

This project aims to expand prior work to constrain patterns of production and transport of CO₂ within karst systems. We hypothesize that production sites and the advective transport of gases and water through the vadose zone influence spatial patterns of CO₂ in karst landscapes. To better constrain spatial variation in CO₂ and production and transport processes, we instrumented six additional sites at SEW’s Basin 1 that span a range of depths, including “deep” groundwater, “intermediate” vadose zone, and “shallow” soil zone wells. Using a weather station, we observe seasonal and daily temperature changes, storm events, and soil moisture and examine how these parameters impact CO₂ concentrations. Simultaneous CO₂ and oxygen (O₂) measurements allow us to explore how respiration or calcite dissolution and precipitation control CO₂ concentrations. The combination of CO₂ and O₂, weather, and soil data contribute to understanding spatial and temporal variability in CO₂ and karst’s role in the global carbon cycle. These data also help validate land-atmosphere modeling approaches.

This work is supported by the William L. Wilson and Diane C. Wilson Scholarship in Karst Science from the Karst Waters Institute (KWI) and NSF/GSA Graduate Student Geoscience Grant # 13449-22, which is funded by NSF Award # 1949901.