Response And Evolution Of Karst Groundwater Hydrochemistry To Urbanization

Urbanization,a global trend,is one of the important indicators to measure the economic,social,cultural,technological and other development levels of a country or region;Groundwater is an important basic resource for maintaining social and economic development,human survival and environmental ecosystem balance,and an important basic condition for urban formation and development.It plays an irreplaceable role in supporting regional social stability and sustainable economic development.With the expansion of cities and the intensification of human activities,the impact on groundwater is deepening,causing widespread concern around the world.This study collected groundwater samples in the dry and wet seasons of Guiyang City and carried out a hydrological year monitoring of the Bailongdong underground river.The study identified the space-time distribution characteristics of groundwater ion content、DOC,total phosphorus,total nitrogen,ammonia nitrogen,and carbon isotope,using parallel factor analysis（PARAFAC）,Gibbs model,ion ratio,2D-COS analysis,HFE-D analysis Mantel test and Pearsor correlation analysis and other means are used to classify and analyze the response of karst groundwater hydrochemistry to urbanization and the response relationship between urbanization and evolution,providing scientific basis for identifying the evolution of karst groundwater system driven by urbanization,optimizing the prevention and control path of urban groundwater pollution and urbanization.The results show that:（1）The overall p H of groundwater in the study area is weakly alkaline.Affected by human activities,groundwater has the highest levels of temperature（T）,conductivity（EC）,TN,TP,and NH₃-N in urban areas;With the development of urbanization,the dissolved oxygen（DO）and conductivity（EC）TN of underground rivers have been increasing,and the relationship between groundwater and underground riversδ¹³C_DICis generally negative,and groundwater is abundant and dry differences inδ¹³C_DIC.（2）The hydrochemical types of groundwater are mainly Ca-HCO₃type,with a small amount of Ca-SO₄type.Ca²⁺、Mg²⁺and HCO₃^-show a trend of urban fringe area>urban area>suburban area,while K⁺、Na⁺、Cl^-、NO₃^-and SO₄^2-show a trend of urban area>urban fringe area>suburban area through human activities;The chemical types of groundwater are Ca-HCO₃and Ca-SO₄,with Ca²⁺、Na⁺、Mg²⁺、K⁺、SO₄^2-、NO₃^-and Cl^-increasing with time.（3）By parallel factor analysis（PARAFAC）,the DOM fluorescence component of karst groundwater in Guiyang City is divided into one kind of humus（C1）and two kinds of proteins（tryptophan like C2,tyrosine like C3）.The fluorescence components C1、C2、C3 and the total fluorescence intensity FT appear in the space of urban area>urban fringe area>suburban area,and the relative molecular weight,aromaticity and humification degree in wet season are greater than in dry season;Three fluorescent components were identified from the underground river:C1 marine humus,C2 protein（tryptophan）;C3 type humus（terrestrial humus）,the fluorescence intensity showed an increase first and then a decrease,the endogenous and exogenous combined,the size of DOM molecular weight increased with time.（4）Gibbs model、ion ratio and HFE-D indicate that the groundwater in the study area is affected by the external environment,and the degree of pollution in urban areas is greater than that in suburban areas.The groundwater system in suburban areas is affected by agricultural activity emissions,and the degree of pollution in high water periods is greater than that in low water periods;The underground river is influenced by human activities and urbanization development around it.（5）2D-COS analysis:Urban and suburban areas are sensitive to components related to human sources,while suburban areas are sensitive to components from natural sources.Underground rivers have differences in priority changes in different seasons.Correlation analysis:There is a strong correlation between various indicators of groundwater in urban areas,and fluorescent components have the potential to indicate water quality;Before the renovation and development of surrounding shantytowns,the material correlation of underground rivers was strong,but during the development and construction process,the correlation of various indicators decreased.