Publication details

The "breathing spots" in karst areas-the sites of advective exchange of gases between soils and adjacent underground cavities



Year of publication 2020
Type Article in Periodical
Magazine / Source Theoretical and Applied Climatology
MU Faculty or unit

Faculty of Science

Keywords carbon-dioxide; subterranean ventilation; CO2 concentrations; nullarbor plain; vadose zone; cave-air; flow; transport; buoyancy; efflux
Description Microclimatic processes were studied in the soil of the well-defined "breathing spot" named Pulhodina (BSP) in the Hranice Karst (Czech Republic). The results have indicated that air is exchanged between the external atmosphere and a supposed underground cavity under air-buoyancy control. Upward airflow ventilation mode (UAF mode) and downward airflow ventilation mode (DAF mode) were distinguished. The virtual temperature of switching between both modes was about 16.5 degrees C. At the UAF mode, the underground air is rising from the cavity through the BSP, warms soil, and carries out the underground CO2. At the DAF mode, the external air is sucked into the cavity through the BSP soil, promoting the advective flux of the soil-respired CO(2)deeper into the cavity. Whereas the warming of the soil is a dominant process in the UAF mode, the CO(2)advective flux into the cavity is the main process in the DAF mode. The simplified mathematical model was derived as a function of the external air temperature and the soil air temperature to simulate the time evolution of CO(2)concentration in the BSP. Despite simplifying assumptions, this model showed a good agreement with the collected data. The advective CO(2)flux from a breathing spot soil may significantly contribute to the total CO(2)flux into the adjacent underground cavity. Its total values may reach 4 x 10(-3) mol s(-1)or even more, based on the actual CO(2)concentration, the exchanged airflow magnitude (both controlled by external temperature), and the breathing spot area. This conclusion is important for karsologists studying the cave CO(2)budget, CO(2)sources, and the mechanisms of CO(2)transport into caves.

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