Characteristics Of Water-Soil-Air CO₂ Concentration In Karst Cave System And Its Environmental Significance

The karst cave is one of the important geomorphological forms formed by the karst effect.Compared with the external environment of the cave,the cave environment is a relatively stable space.Cave water-soil-air environmental changes affect the stability of secondary sediments and cave environment in the cave,which is a key factor in the occurrence of karst.Therefore,it is important to study the water-soil-air environment characteristics of caves,and also to study the carbon conversion of karst dynamic systems.The paper uses Shuanghedong,Shuyang County,Guizhou Province as the research area.From January 2016 to December 2017,the soil environment of the cave,the atmospheric environment of the cave and the water environment of the cave are monitored monthly,and in 2017 and The“Eleventh Holiday”in 2018conducted seven days of continuous monitoring to analyze changes in CO₂concentrations on short-term scales?day and night?and long-term?seasonal?scales.Based on the characteristics of soil environment,cave atmosphere and cave water environment,the characteristics of each environmental index are analyzed based on GIS spatial interpolation analysis and linear fitting to study the water-soil-air CO₂characteristics and their deposition.Environmental impact.The main research conclusions are:?1?The CO₂ in the wind-blown cave,the CO₂ in the cave,and the CO₂ in the cave water show the change of summer and autumn seasons compared with the winter and spring seasons,with obvious seasonal characteristics.Specifically,soil CO₂ showed a small difference in CO₂ concentration between soils 1#,3#,and 4#,and soil 2#had higher CO₂ concentration due to the particularity of bamboo forest.The atmospheric CO₂ in the cave also shows the seasonal variation characteristics of summer>autumn>spring>winter,and the monitoring point near the hole.The CO₂ concentration is relatively low.With the deepening of the monitoring point,the CO₂ concentration gradually increases and gradually stabilizes the space.The law of change;and through the analysis of intensive monitoring data,it shows that the concentration of CO₂ in the cave shows the characteristics of diurnal variation of daylight,nighttime and low nighttime.The partial pressure of CO₂ in water(PCO_2?water?)is consistent with the change law of atmospheric CO₂ in the cave,and it also shows obvious seasonal variation law.From the spatial analysis,the average value of CO₂ partial pressure of each water point in Dafengdong is water point2#>Shuidian 1#>Shuidian 3#>Shuidian 4#,analysis is mainly affected by the structure of the tunnel.?2?According to the data analysis,there is a correlation between the water-soil-air CO₂ in the Dafengdong,indicating that there is a response relationship between the three.Through the linear fitting of soil CO₂ and CO₂ in the cave,it can be seen that the CO₂ concentration at different depths of soil 1#,soil 2#and soil 4#is correlated with the corresponding CO₂ concentration in the cave;soil3#different depth and DF10#Weak negative correlation.The data show that the atmospheric CO₂ concentration in summer caves is the highest in the year.The reason is that the summer precipitation is abundant.The rainwater infiltration will bring some soil CO₂ into the cave and release it,so that the cave CO₂ concentration reaches the highest value in the summer.This also explains the response relationship between CO₂ inside and outside the hole.Cave air CO₂ and cave water CO₂ are one of the important sources of each other,mainly depending on the concentration content between the two.When?P?water-air?>0,CO₂ in the water escapes,and the cave air CO₂ is replenished.Degassing deposition occurs;when?P?water-air?<0,the cave air CO₂ dissolves into the water,causing the concentration of CO₂ in the water to increase,resulting in inhalation erosion.Therefore,the cave air CO₂ is consistent with the change of CO₂ in the cave water,indicating that there is obvious water-air exchange between the cave water-air CO₂.?3?By analyzing the response relationship between cave water-soil-air CO₂,the significance of its indication to the cave environment is analyzed.The mineral saturation index of the cave water in Dafengdong is greater than 0,indicating that the cave water is still in the sedimentary state.By correlating SIc,SId with PCO_2?water?and?PCO₂,it is found that there is a significant correlation between SIc and SId and PCO_2?water?,indicating that CO₂ in water has obvious control effect on SI;but both and?PCO₂ The correlation is weak,indicating that air CO₂ has obvious interference to the partial pressure of CO₂ in the dripping water of the cave and has an important influence on the sediment deposition of the cave.