Analysis And Mechanism Of The Water-Rock Interaction In Karst Watershed

The complexity of the dual structure in the karst area and the difference in landform heights such as peak forest valley bottom and peak cluster depressions.In the complex water cycle of precipitation? surface water? groundwater?spring water?? surface water? water vapor,the surface water and groundwater is converted between each other,often accompanied by geological landform phenomena such as prone currents and sinkholes.Because of the conversion,the water chemistry of surface water and groundwater in the study area extremely complicated.Explore the characteristics of the water cycle in the basin,especially surface water and the conversion relationship of groundwater is a prerequisite for rational planning and accurate evaluation of the existing water resources in the basin.Therefore,in order to explore the hydrogeochemical processes of surface water and groundwater.Measurement of physical parameters?p H,T,TDS and EC?,major ions(Ca²⁺,Mg²⁺,Na⁺,K⁺,HCO₃^-,Cl^-,SO₄^2-and NO₃^-),and stable isotopes??18O and ?D?in 10 surface water and 10 groundwater were taken to understand the geochemical processes occurring in the Shuanghe Watershed of Guizhou province,southwestern China.From December 2018 to July 2019 during the three quarters of monitoring,through a detailed inspection of the surrounding environment of the monitoring point,the monitoring points are set up at the surface water,groundwater and intersections of places,in the Shuanghe Watershed.Using the PHREEQC 3.7 low-temperature hydrogeochemical analysis software,SPSS19.0 statistical software,Piper graphical analysis,Gibbs graphical analysis and many other analytical methods,the change characteristics of the main ions and the water-rock interaction are discussed in the Shuanghe Watershed,and draws the following important conclusions:?1?Ca²⁺ and Mg²⁺ were the dominant cation,HCO₃^-was the dominant anion for both surface water and groundwater,the dominant hydrochemical facies for the watershed were Ca²⁺·Mg²⁺-HCO₃^-type.Combined with Gibbs diagram and ion ratio method to make a preliminary judgment on the water chemistry control process in the study area,it can be shown that the surface water and groundwater,the water sample basically belongs to the rock weathering zone,which means that the chemical weathering of diagenetic minerals is the control study area The main factor of water chemistry.This may be due to the weathering of minerals such as carbonate.The dissolution process is dominated by limestone-dolomite,and the non-seasonal sulfate ions are extracted from the rocks with H₂S to participate in the reflection of carbonate rocks.?2?Comprehensive analysis of hydrogeochemical characteristics of different water seasons in the watershed by ion proportion method and isotope tracing method,based on the fractionation effect of hydrogen and oxygen isotopes,study the correlation trend line of groundwater and surface water in the watershed and local atmospheric precipitation line Closer,indicating that it is directly or mainly derived from atmospheric precipitation,there is less rainfall in the dry season,the groundwater supplied by the underground and the system is stored in karst fissures and pores,the flow of water is slower,and the water-rock-gas interaction time is longer The effect of silver due to weak evaporation is negative,the isotope of the water body is negative,and the recharge effect of groundwater on surface water is obvious.It also shows that groundwater is likely to be recharged by direct infiltration of rainwater.In July,the wet season is affected by the same period of rain and heat,and the evaporation is strong.Therefore,the water body is enriched with heavy isotopes,surface fissures and pores are developed,and the rainfall in the rainy season mostly recharges the underground river through karst formssuch as sinkholes,shafts and funnels.In March,groundwater recharged surface water accounted for 93% of the total recharge,rainfall recharge accounted for only 7%;while July groundwater recharged surface water accounted for 43% of the total recharge,rainfall recharge accounted for57%;?3?On the basis of different seasons and hydrogeochemical characteristics of water bodies,select representative monitoring points in different watersheds,based on the monitoring system of surface water and groundwater systems in Shuanghe Watershed,adopt reverse simulation analysis method from The output end simulates the input end,and uses PHREEQC to simulate and analyze the evolution process of water-rock interaction.Finally,it is concluded that the change of groundwater chemical composition is mainly caused by the dissolution of calcite and gypsum and the precipitation of salt rock and dolomite.