Date of Graduation
12-2024
Document Type
Thesis
Degree Name
Master of Science in Geography (MS)
Degree Level
Graduate
Department
Geosciences
Advisor/Mentor
Covington, Matthew D.
Committee Member
Blackstock, Joshua
Second Committee Member
Befus, Kevin M.
Keywords
Carbon Dioxide; Critical Zone; Geomorphology; Hydrogeology; Karst; Soil Respiration
Abstract
The dynamics of carbon dioxide (CO2) within the Earth’s critical zone (CZ) are essential for driving spatial and temporal variations of carbonate dissolution and precipitation, which are fundamental to subsurface porosity and permeability development. However, there is still a significant knowledge gap regarding the patterns of CO2 transport and production within the carbonate critical zone (CCZ). In this study, we investigated these dynamics within a mantled karst terrain at the Savoy Experimental Watershed (SEW) in Northwest Arkansas.
Previous monitoring of partial pressure of CO2 (PCO2) and dissolution rates at karst springs in SEW’s Basin 1 has provided valuable insights into the temporal variations in CO2 within a CCZ system. To improve our understanding of the mechanisms that govern CO2 production and transport in the SEW-CCZ system, we analyze the variability of CO2 in areas with high soil CO2 production and elevated concentrations along flow pathways, such as springs and groundwater. Our hypothesis suggests that in karst landscapes, CO2 is generated through biological processes in the vadose zone and is primarily transported by advective mechanisms, resulting in spatially variable distribution patterns. Alternatively, diffusive transport may produce a more gradual and widespread dispersal of CO2 in the karst CZ.
To gain a comprehensive understanding of the spatial and temporal dynamics of CO2 in the SEW-CCZ, we instrumented five PCO2 monitoring sites in SEW’s Basin 1 from 2022 – 2024. These monitoring stations span a range of subsurface depths, including “deep” groundwater (10 meters), the “intermediate” soil zone (1.8 meters), and the “shallow” soil zone (60 cm). Additionally, we monitored an epikarst spring and the main karst spring outlet of the basin, known as Langle Spring. Utilizing high-resolution PCO2 monitoring, we compared PCO2 data with hydrometeorological events and hydroclimatic parameters to identify controlling variables and examine their impact on CO2 production and transport in the SEW-CCZ system.
Additionally, this study employed simultaneous PCO2 and partial pressure of oxygen (PO2) measurements in the soil zone to further explore how coupled biotic (e.g., soil respiration) and abiotic (e.g., calcite dissolution and precipitation) processes control CO2 dynamics. The PCO2 at Langle Spring are closely linked to the PCO2 in the soil, indicating that soil respiration is the primary source of CO2 in the SEW-CCZ. This study illuminates the ways in which soil moisture and temperature impact root respiration, while also exploring how respiration affects daily, storm-related, and seasonal CO2 variations in CO2 concentrations within the SEW-CCZ.
Citation
Jones, M. D. (2024). Carbon Dioxide Dynamics in the Carbonate Critical Zone, Savoy Experimental Watershed, Arkansas, USA. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5594
