Date of Graduation

8-2018

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Covington, Matthew D.

Committee Member

Davis, Ralph K.

Second Committee Member

Suarez, Celina A.

Keywords

Arkansas; Carbon Cycling; Carbon Dioxide; Gas Transfer; Hydrogeology; Karst

Abstract

Prior work has shown that the concentration of carbon dioxide (CO2) within cave atmospheres is a function of cave airflow patterns. The dynamics of CO2 within karst systems are of increasing interest as they can control periods of precipitation or dissolution in speleothems and influence potential interpretations of paleoclimate records. Similarly, CO2 is an important driver of speleogenesis, and air-water CO2 dynamics can control patterns of cave passage evolution. Karst also plays an uncertain role in the global carbon cycle and understanding CO2 dynamics within karst systems will aid the development of carbon budgets. Here, a monitoring station was deployed to study the temporal variations of dissolved and gaseous CO2 concentrations in Blowing Springs Cave in Bella Vista, Arkansas. Results show fluctuations in CO2 concentrations are controlled by density driven chimney effect airflow. The chimney effect is driven by outside temperature changes, which influence the relative density of cave air and outside air. During the winter months, air is pulled into the lower, main entrance resulting in low CO2 concentrations within the cave. During the summer months, cool CO2 rich cave air from the cave flows out the entrance and CO2 levels in the cave rise. The CO2 concentration in the air is immediately affected by the reversals in airflow. However, in the water delayed responses were observed to changes in airflow direction. Airflow velocity and discharge are also being measured, so that CO2 fluxes within both the air and water can be quantified. Longitudinal profiles of gaseous and dissolved CO2 within the cave were constructed from spot measurements of CO2 during different seasons and airflow regimes. Ultimately, the observations are used to quantify CO2 fluxes, to examine the diurnal and seasonal changes in gaseous and dissolved CO2 and to quantify interactions between the air and water.

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