Hydrogeochemical Characteristics And Simulation Analysis Of Oinglongtan Karst Groundwater In Dianyuan Town,Kunming City

Qinglongtan is an important water source for local residents’production and life,which outcrops in the north of Baiyi Basin and forms a cold river in the branch of Panlong River.The northern spring area is bounded by Devonian clastic rock,the eastern Permian basalt,and the western boundary is fault.The southern spring area is bounded by Quaternary sedimentary strata in the central basin and non-carbonate strata and karst aquifer boundary in the north-central basin.The spring area is 46.98km2.The recharge area is mainly composed of Devonian,Permian and Carboniferous carbonate rocks.The discharge area is located at the junction of carbonate and non-carbonate strata.The relative height difference between recharge area and discharge area is between 600 and 500 m.There are five spring points（I,II,III,IV and V）in Qinglongtan,among which spring points I and II are seasonal springs,dry season is short of water,and III,IV and V are pressure springs.The five spring points are relatively close,and hydrology and hydrochemistry show different characteristics.In this study,the hydrological and water cycle processes of five springs were studied.Through long-term hydrological observation,the spring water level data,main anion and cation data and hydrogen and oxygen stable isotope data(δ¹⁸O,δD)were obtained.The hydrogeochemical method was used to analyze the main anions and cations,and the groundwater types and hydrochemical changes of five springs in the spring area were discussed.According to the stable isotopes(δ¹⁸O,δD)of karst groundwater and precipitation in Baiyi Qinglongtan,the characteristics of hydrogen and oxygen stable isotopes of groundwater and the retention time of groundwater were analyzed by sine fitting method.The influence of different migration paths on karst hydrochemistry in the spring area was studied by using hydrogeochemical reverse simulation method.The main results include:（1）The influence of atmospheric precipitation on spring water level is remarkable.Springs I and II are seasonal springs and lack water in dry season.After rainy season,the water level began to rise in early and middle July,and the maximum water level was in August.The minimum water level of spring point III was in May,and the maximum water level appeared in September.The karst groundwater is discharged at a certain rate after receiving a large amount of precipitation supply in the rainy season.Due to the imbalance of storage and discharge,tand the peak time of spring water level is not necessarily.（2）The hydrogen and oxygen stable isotopes of karst groundwater in Qinglongtan spring region show similar variation characteristics,with different ranges and mean values.Affected by evaporation,humidity and temperature,the hydrogen and oxygen isotopes are positive in rainy season and negative in dry season.The average residence time of the four springs（I,III,IV and V）in Qinglongtan spring area was 38.2,31.3,26.1 and 33.9 days,respectively.（3）The difference of physical parameters and hydrochemical components between the five spring points is small,and the seasonal variation characteristics are obvious.The variation amplitude of rainy season is greater than that of dry season,and there is a downward trend in the early rainy season.The precipitation is more and the frequency is higher in the middle and late rainy season.The difference of hydrochemical components is greater than that in the early rainy season.The change of hydrochemical composition of karst groundwater has obvious response to rainfall,and it has dilution effect at the beginning of rainfall,and then a large amount of rainfall recharges groundwater,which promotes the water-rock interaction in aquifer.（4）The reverse simulation results show that the main mineral phase calcite in the simulation path has reached saturation state,and dolomite is in dissolution and precipitation state.With the increase of groundwater retention time,the precipitation of calcite increases,and the dissolution and precipitation of dolomite decreases.The shorter the groundwater retention time is,the more CO₂ is involved in the dissolution of carbonate rocks in the aquifer.The longer the groundwater retention time is,the more CO₂ degasses.The interaction between Ca-Mg and Ca-Na ions also exists in the simulation path.