A Study On The Seepage Characteristics Of Cave Dripping Water In Vadose Zone Based On Stable Isotope

Cave dripping is the result of the combined action of gas-water-rock three-phase recharge of precipitation in the aeration zone.There are not only dissolved pores,micro-cracks and layers of diffusion flow media,but also dissolved large cracks and pipeline flow media.When the karst process guides the groundwater seepage along the recharge path to the discharge point,the choice of this path is hierarchical:the well connected large fissures and pipelines provide the main flow path,while the small fissures and pores with low karst development are the main space for groundwater storage and exchange.Because of the inhomogeneity of most karst strata and fractures and the variability of permeability,different hydrogeology is made there are many types of seepage process of cave dripping water in the aeration zone under conditions.The research on stable isotope characteristics of dripping water can directly or indirectly reflect the storage and seepage process of water in the aeration zone.In this paper,Huanglong Cave in Aziying,Kunming City,is selected as the tudy area,and the high-frequency recharge links of groundwater such as atmospheric precipitation,nine cave dripping water(hole pool water)and surface spring water are used to carry out continuous fixed-point monitoring of hydrogen and oxygen stable isotopes in water body for two hydrological years with a cycle of one week.The?¹⁸O values of precipitation and groundwater are analyzed by mathematical statistics to explore the source and temporal and spatial characteristics of karst water body.Secondly,time series autocorrelation analysis is used to determine the difference of migration path and average retention time of different types of dripping water and karst spring water in aeration zone(MRT).1.Local precipitation line(LMWL),?D=7.75?¹⁸O+3.78(R²=0.94),and showed obvious"precipitation effect"and anti-"temperature effect";cave dripping,pool water and karst spring water?¹⁸O values are distributed near the atmospheric precipitation line in the study area,indicating that the main source of water in the cave system of Laohuangdong is atmospheric precipitation,but because of the inhomogeneity of most karst strata and fissures in the aeration zone and the variability of infiltration,cave dripping water is applied to the local atmosphere the inheritance of precipitation is modified.2.The variation range of?¹⁸O values of cave dripping water,cave pool water nd karst spring water in two complete hydrological year is-12.36‰^-10.65‰?-11.56^-11.35‰and-12.85‰^-12.27‰.Moreover,it is much smaller than the range of?¹⁸O in local precipitation-16.60‰^-1.28‰.Because of the difference of air circulation,drip drop time,height and overlying aeration zone characteristics in the cave system,the?¹⁸O value of karst water body varies greatly:8^#has better air circulation and higher drop height(5 meters)relative to the opening of the cave,and 15^#and 16^#drop fall time is longer,which makes the?¹⁸O value more positive than other drop points.3.time series autocorrelation was used to analyze the dripping water in the hole.It was found that the fresh infiltration water in the recharge path of the hole dripping water was exchanged with the"stranded water"which did not flow through the passage and discharged to form different types of cave dripping water.(1,12 and 14)During the1-month period,a large amount of recharge water is stored in a well-drained fissure network;(MRT)slow-dropped water is stored in a well-drained fissure network4.Three caverns dripping water(1,12 and 14)adjacent to the same fissure are analyzed by Gaussian mixture model.The results show that the three drip points have common water resources storage in the aeration zone,but the No.12 drip supply transport channel has lower karst development than the other two points(1 and 14);In the rainy season,when the recharge speed of groundwater is greater than that of cave drip discharge,the recharge infiltration water will be stored in the microcracks and pores with lower karst development.The water body in the system is"stranded water"by the barrier of capillary water,and the water level in the system is formed with the end of rainy season.5.Use empirical formula to calculate the average retention time(MRT)of dripping water and karst spring water in the aeration zone,the longest retention time of No.16 dripping water is about 9.6 weeks;the retention time of adjacent three drip points 1,12 and 14 dripping water in the aeration zone is 3.7,5.8 and 3.7 weeks,respectively;the average retention time of karst spring water is about 2.8 weeks due to the existence of"fast preferential flow".