Study On The Hydrogeochemical Characteristics Of Karst Groundwater Under The Influence Of Tourism Activities

Carbonate rocks are widely distributed in the southwest of China.There is a large amount of karst groundwater,which has become one of the important sources of water for production and domestic use.It is of great significance for its economic development and ecological protection.The karst system is a unique system developed in the soluble rock aquifer,with the characteristics of double space structure of surface and underground,tightly linked between surface water and groundwater,sensitive to the external environment change.However,the karst aquifers are highly subjected to contamination due to uneven development of pipe,fast transformation between groundwater and surface water and low water purification capacity.The pollution once enter the pipeline flow of karst aquifer,will easy to cause the pollutant diffusion and deteriorate water quality.In particular,with the increasing influence of human behavior on the natural environment,untreated wastewater is discharged directly into the underground.The karst groundwater is facing serious water pollution risk at present.The tourism resources in karst areas are very rich.The development of tourism activities continuously threaten the quality of karst groundwater,which has an important influence on the hydrogeochemical characteristics of karst groundwater.In this study,Shuifang spring watershed,the core area of the world natural heritage site in Jinfo Mountain,Chongqing,was selected as the study object to study the hydrogeochemical characteristics of the Shuifang spring karst groundwater under the influence of tourism activities.From April 2016 to May 2017,this study carried out regular sampling monitoring and field tracer tests of groundwater,precipitation,soil water,sewage,tap water,and lake water in the basin;The high density online monitoring and automatic sampling of shuifang spring are conducted by online high resolution water quality meter and automatic sampler during the peak period of tourism;and a short-term high-resolution artificial labor on spring water and sewage during 2016May Day,the hydrogeochemical properties of karst groundwater during the key tourist season are studied.The main conclusions are as follows:（1）The tracer test showed that the recovery of uranine was as high as 90%or more,and the sewage of 1#sinkhole eventually flowed to Shuifangquan.The initial appearing time of uranine was 24.5 hours.After 42.8 hours,the mass concentration reached the peak.The maximum flow rate of groundwater from 1#sinkhole to the Shuifang section was 32.14m/h,and the average flow rate was 18.4m/h,indicating that the sewage from1#sinkhole reach to Shuifang spring at the speed of 24.5h.The double peak of BTCs shows that the water-bearing medium is uneven development in test section,and there are two parallel channels,which is main conduit parallel branch fissure without underground lakes.（2）Under strong rainfall conditions,the changes in hydrogeochemical characteristics of Shuifang Spring are very rapid in response to rainfall,and soil erosion occurs in the early rainfall period,causing spring water turbidity,ions of total Mn,total Fe,Ba²⁺,and Al³⁺rise rapidly;The Spc,Ca²⁺,Mg²⁺,and Sr²⁺also increased,and the water-rock effect was enhanced,showing a significant CO₂ effect;K⁺and Na⁺also increased,which may be related to leaching effect of pollutants of tourism activities during rainfall.Rainfall has obvious dilution effects on NH₄⁺-N and NO₃^-.The concentration of Cl^-fluctuates greatly,but it is also mainly due to human activities.Under the rainfall conditions,various indicators of spring water presented as soil erosion effect,piston effect,water-rock effect,dilution effect of rainwater and leaching effect of pollutants.These effects superimpose each other,so that the change of various hydrogeochemical indicators of spring water are more complicated.（3）During the Summer vacation,National Day and Snow festival,the main hydrogeochemical indices of Shuifang spring increase and decrease significantly.The water quality during the peak travel period presents obvious worsening trend.On the contrary,before and after the tourism peak,the water quality changes more stable and the water quality is better.During the peak of tourism,sewage is increased in large quantities and discharged into the ground.Dissolved oxygen and pH values decreased rapidly to low value areas,while K⁺,Na⁺,Ca²⁺,Sr²⁺,total Fe,total Mn,NO₃^-,NH₄⁺-N,HCO₃^-,PO₄^3-,Spc,and other indicators have rapidly risen to form high value regions.Ions of K⁺,Na⁺,Ca²⁺,Sr²⁺,total Fe,total Mn,NO₃^-,NH₄⁺-N,HCO₃^-,PO₄^3-and Spc are the main hydrogeochemical indexes of Shuifang spring,these indicators have a good response relationship with the 3 tourist peak periods,indicating that tourism activities have a very important impact on the quality of spring water,and karst groundwater is very sensitive to changes in the external environment.Sewage from human tourism activities is the source of major pollutants in spring water.During the Summer vacation,National Day and Snow festival,the maximum concentration of NO₃^-in Shuifang spring has exceeded the World Health Organization standard for drinking water（NO₃^--N≤10mg/L）and exceeded China’s Groundwater Quality Standard（GB/T 14848-2017）Type II water standards,and the maximum value of total Fe and total Mn has exceeded Groundwater Quality Standard（GB/T 14848-2017）TypeⅢwater standards.Spring water is no longer suitable for residents to drink directly,and there is health risk.（4）The monthly dynamic data of main hydrogeochemical indicators of Shuifang spring show three major fluctuations,which are consistent with the changes in water quality under high-density sampling monitoring.The fluctuation of hydrogeochemical index of spring responds to the three main tourist peak periods of the Summer vacation,National Day and Snow festival.Based on the PCA,the two principal components of the monthly dynamic changes in the hydrogeochemical characteristics of the Shuifang Spring during the monitoring period were determined.The contribution of the cumulative variance of the two components reached 75%,including most of the hydrogeochemical information.The first principal component is the influence of sewage generated by tourism activities,its variance contribution rate is 55.7%,while the second principal component is the water-rock effect and precipitation effect,and the variance contribution rate is 19.5%.The sewage generated by tourism activities has become a major factor affecting the monthly dynamic changes of main hydrogeochemical indicators of springs during the monitoring period.The tourism activities in the Jinfo Mountain area have a great impact on the groundwater.The management departments and personnel of the Jinfo Mountain should take measure to reduce the impact of the sewage generated by the tourism activities on the groundwater.