Chemical Characteristics Of Spring Water In Baiyi Fault Basin

Karst fault basin is an Intermountain basin formed by differential subsidence and dissolution of fault blocks caused by fault activities arising from Cenozoic uplift of the plateau.The study on the hydrogeological characteristics of karst fault basin is of great significance to the protection of groundwater resources and the rational exploitation and utilization of groundwater resources.In this paper,the hydrochemical characteristics of recharging spring water in Baiyi fault depression basin is not clear,the type of recharging spring water is not clear,and the source of recharging spring water is not clear,etc.Based on these problems,this paper took the Baiyi fault basin in Kunming City as the research area,and 13 springs in the basin are selected according to the hydrogeological map and the difference of hydrochemical characteristics of springs.The continuous observation and analysis are carried out with a period of one week and a period of one hydrological year.The obtained data include pH,EC,T,Ca²⁺,HCO^3-,F^-,Cl^-,NO^3-,SO₄^2-,NO^2-,Br^-ion concentration data,and hydrogen and oxygen isotopes of?D and 6 ?¹⁸O,dissolved organic carbon DOC and dissolved inorganic carbon DIC data.By means of hydrochemical analysis and multivariate statistical analysis,the hydrochemical and hydrogeological characteristics of 13 springs in the study area were systematically studied.Research shows:1.According to the different spring water chemical characteristics of the selected spring of 13 points clustering analysis,it is judged that there are five main types of recharging springs in Baiyi fault basin:type one??,?,?,?,? GYQ,?,?,??,type two???,type three?GYQ+1?,type four???and type five???.2.The first type springs are elevated by quaternary sediments in the process of transmission.In rainy season,groundwater is discharged as confined springs in drainage areas.In dry season,there is not much groundwater.Some springs are reduced or even depleted,which belongs to weak confined pressure,so hydrochemistry has a strong response to precipitation.The second kind of spring is the shallow groundwater formed by the infiltration of atmospheric precipitation into karst aquifer,and finally the shallow karst spring emerged before reaching the aquifer.The third kind of spring water,deep groundwa.ter is discharged upward by karst fissure pipeline,and the exposed surface becomes low temperature hot spring.The fourth type of springs,the recharge path is that precipitation seeps down to the ground and seeps along the slope along the soil-rock interface under the action of gravity,and eventually emerge at the foot of the slope Because there is no contact with carbonate rocks in the process of infiltration,its hydrochemistry is characterized by low alkalinity,hardness and conductivity,and low anion content,so it is a non-karst spring.The fifth type of spring i,s mainly the atmospheric precipitation infiltrating into the surface karst zone,which has water-rock interaction with carbonate rocks in aquiferous media and forms the surface.It is a surface karst spring.3.The hydrochemical characteristics of five types of spring water are as follows:the seasonal variation of spring water chemistry is obvious,the variation range of spring water chemistry is larger in rainy season than in dry season,and there is a downward trend in the early rainy season,which indicates that the chemical change of spring water responds to rainfall,and rainfall has a dilution effect on it.Hydrogen and oxygen isotopes show obvious seasonal variation,and the variation range in dry season is smaller than that in rainy season.The main recharge source of all kinds of spring water is the local precipitation,but there are other recharge sources.In the same rainfall period,the peak time of the isotopes of ?D and ?¹⁸O in different types of springs is different,showing a certain lag.