Hydrochemical Response Of Karst Underground River System To Tourism Disturbance

For a long time,the impact of human activities on the hydrochemistry of groundwater has been carried out in different regions of the world.Human activities such as change of land use,urban industry,commerce,and agriculture has been considered as the main causes.In recent years,the influence of tourism activities on groundwater caused by the unique tourism resources in the southwest karst mountains has gradually become the focus of researchers.However,there are few studies on the hydrochemical interference of underground river system caused by the periodic,intensive and abrupt high-intensity tourism activities driven by national major scientific and technological infrastructure such as FAST?Five-hundred-meter Aperture Spherical radio Telescope?.This article selects Daxiaojing underground river systems where FAST is located as the research object.During the May Day,continuous fixed-point monitoring of underground river entrances and exits,discuss the hydrochemical characteristics,influencing factors,changing process and reasons of karst underground river under the influence of human activities.In order to provide theoretical guidance for regional drinking water safety,tourism development planning and underground river pollution prevention.The main results obtained from the study are as follows:?1?The hydrochemical type of sewage in FAST was HCO₃-Ca before and after the May Day and HCO₃-Na·Ca during the May Day.The conductivity,ammonia nitrogen,Na⁺and other hydrochemical index concentrations of sewage increased first and then decreased with time,and the concentration after the May Day was significantly higher than before,the impact of tourism has a certain lag.The change of sewage chemistry by time is a good description of tourism.?2?The hydrochemical type of Dajing underground river was HCO₃-Ca during the monitoring period.Tourism have a certain impact on water quality,it is manifested by the significant fluctuations such as conductivity,ammonia nitrogen,and the obvious changes of anion and cation concentration in water in the early May Day and slow rise later.The hydrochemical type of Xiaojing underground river during the monitoring period was HCO₃-Ca,the water quality of Xiaojing underground river entrance is good,and the variation coefficients of ammonia nitrogen and total phosphorus are high,which may be affected by the domestic sewage discharged from the upstream towns or agricultural activities.?3?Dajing and xiaojing underground river outlets have experienced the same heavy rainfall processes twice during the monitoring period,and many indexes responded to precipitation very quickly,rainfall interfered with the pollution signal of tourism activities input at the entrance,it also bring the influence of agricultural activities at the same time,which caused the concentration and coefficient of variation of Mg²⁺and other indicators of underground river outlets significantly higher than those of underground river entrance.However,some indicators of Dajing underground river outlet have shown a large fluctuation before the rainfall,which inherits the changing characteristics of the underground river entrance,indicating that tourism activities have an impact on the water quality of Dajing underground river system.?4?The hydrochemistry of Dajing underground river has been comprehensively affected by natural water-rock processes,tourism activities and agricultural activities,mainly controlled by natural water-rock process.Ca²⁺,Mg²⁺and HCO₃^-in Daxiaojing underground river are controlled by the dissolution of calcite and dolomite.Tourism,agriculture and other human activities will also bring in ions such as Na⁺,Cl^-,Mg²⁺and SO₄^2-.?5?The?³⁴S-SO₄^2-values of underground rivers in Daxiaojing are quite different from the?³⁴S-SO₄^2-values of gypsum dissolution.The variation range of?³⁴S-SO₄^2-values of Daxiaojing underground river is-7.96‰?4.59‰,atmospheric precipitation are the main sources of SO₄^2-in underground rivers,and SO₄^2-may also come from sewage generated by tourism activities.The?¹⁸O and?D points of Daxiaojing underground river are roughly distributed near the atmospheric precipitation line of Guiyang,and the main source of groundwater is atmospheric precipitation.The deuterium excess of Daxiaojing underground river outlet is lower than entrance,the reason is due to the weakening of the isotope exchange degree and evaporation intensity of water-rock interaction during groundwater migration.