Study on vertical migration of CO₂ in a karst cave system

Abstract

CO 2 is an important driving force in karstification. Studying the variation characteristics of CO 2 in each zone of a karst cave system during different seasons might contribute to revealing its migration path and to further exploring CO 2 sources in caves. To this end, we monitored the soil, cave drip water, and cave air CO 2 in Mahuang Cave, SW China. We analyzed the vertical migration characteristics of CO 2 based on the carbonic acid equilibrium system theory and the stable isotopes of carbon through statistical analysis. The results show the following: (1) There are obvious seasonal changes in CO 2 in each zone of Mahuang Cave, generally indicating high rainy season and low dry season characteristics. (2) The CO 2 in Mahuang Cave is mainly supplied by the soil, bedrock, and the external atmosphere. The rainy season has plentiful rainfall, and the CO 2 in the cave is mainly derived from soil CO 2 . In the dry season, with lower temperature and little rain, cave CO 2 is mainly attributed to the external atmosphere, brought by the ventilation effect, and carbon in the bedrock. (3) Carbonate precipitation in Mahuang Cave is dominant throughout the year. The seepage migration process and carbonate precipitation are controlled by the soil "CO 2 effect" and drip water type.

Spatiotemporal Variation Characteristics and Influencing Factors of Karst Cave Microclimate Environments: A Case Study in Shuanghe Cave, Guizhou Province, China

“…Owing to the intermittent uplift in the area caused by tectonic stress in different directions (NE, NW, and SN), three groups of folded fault zones have formed, resulting in a relatively independent geological body that is slightly triangular in shape, mainly for the uppermiddle Cambrian series Loushanguan Group (∈ 2-3 ls) [39]. The cave area lithology is mainly dolomite and dolomitic limestone [40]. The groundwater type is primarily carbonatefractured water.…”

“…Cave relative humidity and cave air pressure had a negative correlation (r = −0.50) due to the increase in relative humidity in the cave, which increased the water vapor content in the air. Because the molecular weight of water vapor is smaller than that of air, the air density and pressure decreased, resulting in a negative correlation [40].…”