Study On Hydrogeochemical Processes Of Bare Karst Underground River System

Xiangshui Cave underground river in Kaiyang county is a typical bare karst underground river,which is vulnerable and sensitive,and is highly susceptible to local agricultural activities and resident lives.This study uses the field investigation and monitoring that combined with traditional water chemistry methods and isotope techniques,in order to study the hydrogeochemical processes of the Xiangshui Cave underground river system of in Kaiyang county,providing reliable reference information and Scientific basis for the rational development and utilization of water resources in the underground river.The research has mainly achieved the following results:?1?The groundwater in the study area is obviously controlled by atmospheric precipitation,and the flow dynamic curve of the total outlet?DT?exhibits a multi-peak shape,which has the characteristics of fast rise and fast decline.The?¹⁸O and?D data of groundwater and surface water in the study area indicate that the two are mainly derived from atmospheric precipitation,and the groundwater and surface water are closely related.Kaiyang County and Dongfeng Reservoir are the most important sources of groundwater recharge in the southwest of the study area,providing the underground river system.With 71.17%of water,groundwater recharge in the northern and southeastern parts of the system is dominated by atmospheric precipitation,which recharges accounting for 23.32%and 4%in the total system respectively.?2?The study area is located in the bare karst development zone.The groundwater hydrochemical type is mainly HCO₃-Ca·Mg type.The water-rock interaction contributes the most to the hydrochemical composition of the underground river system in the study area.The main source of Ca²⁺,Mg²⁺and HCO₃^-ions in the study area groundwater are mainly derived from the dissolution of carbonate minerals such as calcite and dolomite,and the presence of exogenous nitric acid and sulfuric acid exacerbates the dissolution of carbonate rocks.The influence of human activities makes the groundwater hydrochemical characteristics of the study area show regional spatial differences.The main controlling factor of groundwater chemical characteristics in the north is water-rock interaction.The water quality is obviously better than that of the south and southeast,and the groundwater chemical components in the south and southeast.Affected by human activities,and the southern part is more affected than the southeast.Agrochemicals and domestic sewage contribute more to the groundwater Na⁺,K⁺,Cl^-and NO₃^-plasmas,and these ions show a strong positive correlation.Most of them show strong geochemical sensitivities.The hydrogeochemical processes in the study area are the result of a combination of natural processes and human activities.?3?Through the sulfur isotope and nitrogen and oxygen isotope data,combined with the isotope mass balance model,it is judged that the sulfate in the underground river system of the study area mainly comes from domestic sewage?52%?,atmospheric precipitation?30%?and sulfide oxidation?18%?.Nitrate is mainly from organic fertilizers and domestic sewage?62%?,atmospheric precipitation and chemical fertilizers NH₄⁺?24%?and soil organic nitrogen?14%?.Groundwater sulphate and nitrate in the study area are significantly affected by humans.