Hydrochemical characteristics and formation mechanism of karst water in Baotu Spring watershed
Karst groundwater is an important water source for human production and livelihood,but it faces the risk of pollution.The study of the hydrochemical formation mechanism of karst groundwater is an important research topic.However,due to the evident control of factors such as local hydrogeological conditions and the intensity and manner of human activities on karst groundwater,it is challenging for us to explore the hydrochemical formation mechanism of karst groundwater.The Baotu Spring watershed is a typical distribution area of karst in Northern China,which has faced water quality deterioration in recent years.However,there is a lack of comprehensive case studies that combine multiple mathematical and statistical methods with hydrochemical analysis in the study of spatial differences in the hydrochemical formation mechanism of groundwater in Baotu Spring watershed.This study collected three surface water samples,six pore water samples,47 karst groundwater samples,and four fracture water samples from the Baotu Spring watershed.Hydrochemical and multivariate statistical methods,such as Piper diagram,ion ratio,correlation analysis,factor analysis,and cluster analysis,were used.Additionally,ArcGIS geostatistical functionality was applied to investigate the hydrochemical formation mechanism and spatial differences of karst groundwater in the Baotu Spring watershed.The results indicate that the contents of Total Dissolved Solid(TDSs)in surface water samples ranged from 268.65 to 317.86 mg·L-1,with small spatial variations in different chemical parameters.The hydrochemical type was primarily HCO3·SO4-Ca,indicating good connectivity of surface water.The TDS contents in groundwater samples ranged from 191.65 to 948.69 mg·L-1,with large variations in all chemical parameters except for K+,indicating significant influences from local hydrogeological conditions or human activities on karst groundwater.The hydrochemical types of karst groundwater were mainly HCO3-Ca,HCO3·SO4-Ca and HCO3-Ca·Mg,with an increasing proportion of SO42-.The dominant cations in karst groundwater were Ca2+and Mg2+.For anion,in the indirect recharge zone and discharge zone,karst groundwater was mainly dominated by HCO3 and SO4-2,while in the direct recharge zone,the proportions of SO42-and Cl-in karst groundwater significantly increased.Correlation analysis and ion ratio analysis reveal that the hydrochemical composition of karst groundwater in the study area is mainly influenced by the dissolution/precipitation of minerals such as carbonate,sulfate,and halite.With an increase in the flow path,the interaction between water and rock became more thorough,leading to an increase in ion content in groundwater.Pollution caused by human activities increased the concentration of NO3 in groundwater,and the nitration process reduced the release of carbonates resulting from carbonate mineral dissolution.Therefore,human activities can directly pollute groundwate and affect the natural water-rock interaction mechanisms in groundwater.Overall,the degree of pollution in groundwater in the study area is not significant,with the hydrochemical composition being mainly influenced by water-rock interactions.However,human activities have also led to the contamination of Cl-and NO3-in groundwater,with the polluted groundwater primarily distributed in the central karst zone with strong leakage in the study area.The karst groundwater in the northwest area was polluted in a lower degree,mainly because the thickness of the Quaternary system may reduce the direct pollution of karst groundwater by human activities.This study explores the hydrochemical formation mechanisms of the Baotu Spring watershed and provides preliminary analysis of the spatial differences in the hydrochemical formation mechanism,which can support the protection of local groundwater environment.
Baotu Spring watershedgroundwater hydrochemistrymultivariate statisticsspatial distribution
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