Variation Characteristics Of Karst Groundwater Quality And Its Mechanism In ATourist Attraction Of Subalpine Area

Karst groundwater is one of the crucial water resources to karst area.Karst groundwater system is sensitive to the environmental changes,even small variations of human activities and external environment can affect it.With the development of social economy,tourism activity has increasingly become a popular leisure activity.Tourism activities experience a relatively short time and high intensity when it occurs.Therefore,vulnerable karst hydrologic system must be influenced by unreasonable tourism activities.The study of tourism activities'impacts on karst groundwater plays a significant role in protecting against water contaminations and taking the countermeasures in time.To some extent,it will have both theoretical and practical significances.Shuifang spring,which is located in the core tourist attraction of the Jinfo Mountain,was selected to compare the variations of the mutual physicochemical parameter'concentrations in 2018 and 2016(including physical parameters such as water temperature,pH,DO,SpC and chenmical parameters such as HCO₃^-?Ca²⁺?Mg²⁺?K⁺?Na⁺?PO₄^3-?Cl^-?NO₃^-?SO₄^2-),and compare the variation characteristics of parameters that newly added in2016?including trace elements such Ba,Sr,Fe,Mn,Si and hydrogen and oxygen stable isotopes?.By the means of calculating the fluctuation percent and geochemical susceptivity of various parameters,groudwater quality evolution characteristics and its mechanismand are revealed.According to the research,the main results are shown as following:Large amounts of sewage bringing with tourism activities was conductive to reproduction of microorganisms,which increased the concentration of CO₂ of groundwater.CO₂ from microbial processes that tourism activities result in and the natural environment are all the sources of CO₂ of groundwater.From 2008 to 2016,the CO₂ concentration variation is the main factor of making rising concentrations of carbonate dissolution properties like HCO₃^-?Ca²⁺?Mg²⁺,and that accounts for 80%of the contribution.In addition,there are allogeneic acid in sewage bringing by tourism activities.The change of its concentration can cause the change of carbonate dissolution velocity,and it accounts for 18.85%of the contribution,far below CO₂.Unprocessed sewage from accommodations directly recharged the karst aquifer,increasing the concentrations of Cl^-,NO₃^-in 2016,and its concentration growth percentage for 80.53%and 64.93%respectively,deteriorating the groundwater quality.Hydrochemical types of Shuifang spring evolved from Ca-HCO₃ type to Ca-HCO₃·Cl·NO₃ type.Meanwhile,accommodation sewage was discharged into underground after precipitation and degradation of septic tank built in 2013,which made concentrations of K⁺,Na⁺,PO₄^3-reduced,and diminished this effect of tourism activities on Shuifang spring.Compared with 2008,the tourist numbers in peak and off-peak was narrowing in 2016,while the geochemical susceptivity indexes of chemical parameters in 2016 were generally lower than 2008,which shows the lower intensity of groundwater influenced by tourism activities,but the longer time.The geochemical susceptivity indexes of chemical parameters was largely consistent with normal concentrations in 2008,but was disorderly in 2016.It maybe indicates that the stability of groundwater systems in study area was gradually destroyed.The average concentrations of trace elements in dry season are lower than in rainy season,with obvious monthly and season variation.Water-rock interaction,soil leaching and dilution effect have an impact on the concentrations of trace elements in Shuifang spring.The water-rock interactive,having 51.8%'s variance ratio contribution,is the most important one.The distance between of various injection points in spring basin and spring is so close that groundwater can be rapidly recharged from atmospheric precipitation.The below-cloud secondary evaporation effect has little impact on hydrogen and oxygen stable isotopes of precipitation in cold weather,and isotopic information of precipitation can be totally remained to Shuifang spring when precipitation is of more than a certain degree.Combined with?¹⁸O-?D values of Shuifang spring at the peak of tourism activities,all values of the slope,intercept and correlation coefficient of?¹⁸O-?D in groundwater line(?D=3.09?¹⁸O-27.19,R²=0.3)are under both of the CMWL and groundwater line of jinfo mountain.Instead,excluding it,all values in groundwater line(?D=4.72?¹⁸O-13.10,R²=0.77)are above both.The study reveals that sewage at tourism activities peak dramatically changed the isotopic information of groundwater.