Study On Variation And Transmission Of Carbon Dioxide In Tourist Cave System

There is a growing concern about the global climate change in world-wide scenario, since recently happened extreme climates and meteorological disasters. It is conformed that the rising concentration of carbon dioxide to some extent attributes to the human activity, while some people questions that if there was an over estimate of human activity and ignorance of nature itself change. The key point to solve this contradiction is the research of long-term climate record and the record after human activity appeared. According to record of continuous meteorological variation and atmospheric CO2 concentration variation by instruments appeared shortly, the time span is not long enough to resolve the problem mentioned above. Therefore, geological record plays play an significant role in revealing the regularity of palaeoclimate, which recorded in speleothem. The cave system is widespread concerned for providing an opportunity to enter the karst aquifer to survey the relationship among water, gas and base rock in karst area and as the environment of speleothem. The transmission of CO2 is the driving force of degassing and carbonate deposition, so the research of this process could reveal the relation between speleothem and cave environment. Even more, the result would help the description of geological record in speleothem.The factors affecting concentration of cave air CO2 include underground river and drip degassing, air exchange between cave inside and outside, human respiration in tourist cave, etc. The changing pattern of cave air CO2 concentration will display different since the extent of factors is diversity. The dissimilar changing pattern of cave air CO2 in different time scales reveal the active phases of factors have diverse durations. Long-term factors (e.g. the transmission of CO2 between air and water) control the seasonal variation of cave air CO2, and short-term factors (e.g. respiration of tourist) control the high-frequency variation of air CO2 concentration. The changing pattern of cave air CO2 could be found in geological record in speleothem because of the Synchronization between degassing and deposit process.This issue aimed at analyzing the interaction between air CO2 and Pco2 in groundwater and the influence to speleothem deposition from cave air CO2 by researching variation of air CO2 concentration and the mechanism of CO2 transmission between water and rock. Based on prior's research and data, it took a whole hydrological year to run the monitoring work on cave environment, drip hydrochemistry, hydrology and hydrochemistry of groundwater. The result present as below:(1)The variation of Snow-Jade Cave air CO2 concentration is same as other caves in seasonal scale. It is controlled by strengthen of biological activities in recharge area and represented a high value in summer and low value in winter, respectively. The influence of Human activities was not significant contrast to groundwater degassing. However, when the scale is limited to a week or a day, human activities and self-purification ability is able to observe. For these reason, Air CO2 concentration monitoring need a continuous online monitoring device.(2)The deposition status of Underground River could not generalize as one status through the whole stream. The air CO2 has reaction to groundwater, although it comes from the water degassing in the beginning. And this phenomena is obviously amplified when the ventilation of cave is poor, which caused the air above the groundwater is different from site to site. For Snow-Jade Cave, the downstream has a trend to degas, and the upstream is opposite.(3)The distance between sample position and cave roof would influence the degassing process of drip water. However, the variation of partial pressure of CO2 in drip is same as the Underground River. For the smaller volume than the river, the influence from cave air is more significant to drip and drip sites have poorer self-purification ability. The frequency of drip and carbon isotope can reflect the difference of recharge route.(4)The cumulative effect and human activities are in charge of high concentration of Air CO2 in Snow-Jade Cave in summer. Underground River plays a role in balance the CO2 concentration between air and water and in buffering the extreme high CO2. Significant elevation of air CO2 concentration during March to May is caused by degassing enhanced by human activities. The decrease process need future survey and research.