Study On Inorganic Carbon Transport Process In Jiguan Cave Small Watershed,Henan Province

Global warming is an indisputable fact,resulting in frequent occurrence of extreme weather and climate events,which is one of the most serious challenges facing the world;Under this background,the resource and environmental problems in karst fragile areas are particularly prominent.Karst areas have a typical surface and underground two-layer karst hydrogeological structure,and karst caves are developed,making the structure of key areas of the earth clear in karst areas,which is helpful to solve and respond to the problems of resources,environment,and global change in karst areas.The theory of“karst dynamics”proposed by Academician Yuan Daoxian is the embodiment of earth system science in modern karst science.The latest development is the“karst critical zone”,which is a key zone where water,soil,gas,trace elements,and other biogenic elements can form and migrate,and life can generate and evolve.It is an excellent site for studying the carbon cycle.Continuous monitoring of modern processes in karst critical zone has potential significance for solving the problems of resource environmental mechanisms and carbon cycle mechanisms.In addition,studying the coupling mechanism between hydrological and biogeochemical cycles in watershed ecosystems on a larger scale is the most common research paradigm,which helps to understand the carbon cycle process of terrestrial ecosystems driven by hydrodynamic forces,and reveals the pathways of carbon migration and transformation.However,the research work on carbon transfer combining karst critical zone in caves with watersheds is still relatively lacking,and it is not yet in-depth to understand the carbon transfer process and control mechanism at the watershed scale,and clarify the ecological and environmental significance of karst carbon sinks.Based on previous studies,this paper expanded the scope of research to the two karst critical zones in caves and their respective source regions of the Yi River,exploring the transport mechanism of inorganic carbon in the karst critical zones at different time and space scales through 13 years of continuous monitoring（2010-2022）of the Jiguan Cave,a tourist cave located near the geographical north-south boundary of China that is sensitive to the impact of the Asian monsoon,and 6 years of continuous monitoring（2017-2022）of the Dongshiya Cave,a natural cave adjacent to it.Compare the vertical scale carbon migration process,carbon flux differences,and influencing factors between tourist caves（Jiguan Cave）and natural caves（Dongshiya Cave）,and explore the impact of human activities on carbon flux in tourist caves.At the same time,through sampling and analysis for nearly a hydrological year from the source of the Yi River（Mendunling Jinguoquan）to Jinniuling Reservoir,we preliminarily understand the hydrogeochemical process in the source area of the Yi River,and discuss the transfer process of inorganic carbon and stable isotopes from point to surface in the water body.Thereby providing theoretical basis and data accumulation for the work of karst carbon sink potential in the source area of the Yi River.The results show that:（1）At both annual and seasonal scales,the CO₂ levels in Jiguan Cave and Dongshiya Cave exhibit a higher level in summer and a lower level in winter.The differences between the two are mainly influenced by various factors such as cave overlying CO₂,cave ventilation,cave structure,and tourist activities.On a short-term day and night scale,high-resolution monitoring data indicates that the main source of CO₂ in the tourist cave Jiguan Cave is tourist activities,while the CO₂ in the natural cave Dongshiya Cave is mainly controlled by the soil CO₂ above the cave and is sensitive to response to rainfall events outside the cave.According to the formula,the total number of tourists to Jiguan Cave in 2022 was approximately 2.668×10⁷L of CO₂.（2）During the heavy rainfall event in July 2021,the magnitude of CO₂ changes in Jiguan Cave and Dongshiya Cave was not significant.The magnitude of changes in Jiguan Cave was about 100 ppmv,while the magnitude of changes in Dongshiya Cave was about 250 ppmv.However,during the rainfall event from the end of August to early September 2021,there was a change of approximately 1500 ppmv in CO₂ inside the Dongshiya Cave.Considering that some areas inside the Dongshiya Cave were submerged by water during the second strong rainfall process,the degassing effect of cave water and the soil CO₂ overlying the cave jointly affected the CO₂ inside the Dongshiya Cave.（3）The water body HCO₃^-in Jiguan Cave and Dongshiya Cave is generally higher in the dry season and lower in the rainy season.The comparison found that the HCO₃^-content of Jiguan Cave drip water（LYXS）and Dongshiya Cave drip water（DSY1）was higher than that of DSY2 in both dry and rainy seasons,and there were differences in seasonal changes.This is due to the different transport paths of dripping water.The process of inorganic carbon transport in Jiguan Cave and Dongshiya Cave is relatively consistent,which occurs during the process of inorganic carbon transport from soil,cave drip,cave underground river,δ¹³C_DIC gradually enriched and shifted towards negative at the outlet of the underground river.In addition,HCO₃^-in the water body of Jiguan Cave can obviously respond to the El Ni?o Southern Oscillation（ENSO）and the regional precipitation affected by it.This discovery has some new implications for the understanding of the impact of global change on the carbon cycle of the cave system.（4）The HCO₃^-of the Shilonggou River（SLGH）,which is supplied by the underground rivers of Jiguan Cave and Dongshiya Cave,is low in the rainy season and high in the dry season,δ¹³C_DIC tends to be negative during the rainy season and positive during the dry season.On a spatial scale,from the underground river outlet of Dongshiya Cave to the underground river outlet of Jiguan Cave,δ¹³C_DIC gradually enriched,HCO₃^-gradually increased,and the underground river of Jiguan Cave had a significant replenishment effect on the Shilonggou River.Theδ¹³C_DICof Yi River tends to be positive during the dry season and rainy season during normal water periods,and negative during the rainy season during high water periods,mainly related to its source of supply.According to the formula,the inorganic carbon flux of the Dongshiya Cave underground river in July 2022 is estimated to be approximately 797 kg/（km²·month）.The carbon flux of the Jiguan Cave underground river in the rainy season is significantly higher than in the dry season,ranging from 235.8 to 2314.8 kg/（km²·month）.The average annual inorganic carbon flux in the source area of the Yi River is 17.45×10⁴ t/（km²·a）。...