Study On Environmental Change Characteristics And Vertical Carbon Migration Mechanism Of Cave System In Liangfeng Cave Of Guilin

Along with global warming and extreme weather events,the carbon cycle and carbon sink effect closely related to the greenhouse effect have become the focus of current scientific research,and are closely related to the prosperity of the human destiny community.The open karst caves are widely distributed in the karst area,and there is a response relationship with the external environment.The vertical carbon migration mechanism of the cave system and the potential carbon sink potential research are less involved.Carbon migration is accompanied by the water cycle becoming an important part of the biogeochemical process,shaping the cave environment and indicating changes in the external ecological environment.From November 2017 to November 2018,this study took the open cave system of Guilin Liangfeng cave in the Maocun underground river basin as the research object,and carried out real-time monitoring of the atmospheric environment and cave environment in the field;measured the vertical direction of“atmosphere-soil-cave”The CO₂ concentration and?¹³C value in the main process of carbon migration were carried out in the field test strip dissolution test to estimate the carbon sink potential.The conclusions are as follows:?1?The main environmental parameters of the cave show the characteristics of seasonal variation with the long rainy season from March to October of this monitoring year.The abnormal weather phenomenon will lead to the extension and shortening of the features.The internal temperature of the cave slowly rises in spring and summer,and falls rapidly in autumn and winter.The pressure and humidity inside the cave are regulated by the temperature of the cave and the overlying CO₂.The cave structure is different,and the environmental parameters of the cave are different.The essence is the difference in the relative effect of air convection and overlying roof at each monitoring point.The drip type of the cave is Ca²⁺-HCO₃^-type water.The hydrogeochemical index of the drip of the cave has the same regularity with the external hydrothermal combined strength.The external environmental parameters match the anisotropy of the cave top over the three-dimensional scale.The differences in vertical biogeochemical processes at each observation point.?2?During the vertical carbon migration process of“atmosphere-soil-cave”,the soil respiration intensity of the karst surface zone determines the carbon migration of the cave system.Increased temperature enhances soil respiration,and the response of soil respiration to humidity is unclear.Correlation analysis showed that the R value of CO₂ concentration and atmospheric temperature at the 30 cm above the cave was 0.92,the value at 60 cm was 0.88,and the R value of CO₂ concentration and atmospheric temperature at the closed point was 0.77.?3?The dissolution experiments under the carbonate rock of the roof over the cave show that the soil erosion can weaken the soil carbon source.The dissolution rates of carbonates at 30 cm and 60 cm in soil are:0.23 mol/?m²·a?and 0.45 mol/?m²·a?,respectively.The difference in the dissolution of different layers in the vertical section of the soil is a reflection of the difference in soil respiration at different horizons.The amount of C in the LF-4,LF-5 and LF-9 drip points HCO₃^-from March to October in this monitoring year was:10887.54 mg,7529.28 mg and 8620.73 mg,respectively,the amount of C in the CO₂ released by degassing during this period.At 3.99,26.23 and17.21 times,the average dissolution rate of the internal test piece of the cave was0.039 mol/?m²·a?.Because of the wide space inside the cool wind tunnel system and the dense carbonate rock,the cave carbon sink has great potential.