Chemical Characteristics Of Karst Water And Its Chemical Significance In Caohai Area Of Guizhou Province

Guizhou Caohai area is densely populated with frequent agricultural activities,and karst groundwater is the main source of water for local residents' living and industrial and agricultural water use.With the development of local social economy,the impact of human activities on karst groundwater environment is more and more obvious.The chemical environment of primary karst groundwater changes under the influence of human activities and other factors,which are prone to karst groundwater pollution and other problems,which makes the regional karst The development and utilization of water resources are subject to certain constraints,affecting the local socio-economic development.The study of chemical characteristics of groundwater,the influencing factors of groundwater chemical characteristics,the formation and evolution of groundwater chemical composition and other aspects of the significance.If the study of the chemical characteristics of groundwater,the influencing factors of groundwater chemical characteristics,the formation and evolution of groundwater chemical composition and other aspects of the significance,on the one hand,it can accumulate the basic data for the study of rocky soil weathering,water-rock material transformation and migration,water system circulation,groundwater pollution and prevention,groundwater resources evaluation and protection,and ecological restoration and reconstruction.On the other hand,it provides theoretical basis and guidance for the rational development and utilization of local karst groundwater resources and the formulation of environmental protection policy,which has high scientific value and social significance.Based on the analysis of the geology and hydrogeological background of Caohai area,based on the basic theory of hydrogeochemistry,this paper studied the relationship between grassland and geo-geology based on the theory of mathematical statistics,stoichiometry,ion scale factor method and hydrogeochemical simulation regional karst groundwater chemical characteristics and to explore the significance of karst water chemistry,the following results:?1?The groundwater type in the study area is mainly composed of carbonate rock cave fissure water.The groundwater chemistry types are HCO₃-Ca,HCO₃-Ca·Mg,HCO₃·SO₄-Ca,HCO₃·SO₄-Ca·Mg,SO₄-Ca·Mg.(Ca²⁺?Mg²⁺)concentration in most groundwater components is higher than that of alkali metal elements?K⁺+Na⁺?,weak acid radical?HCO₃^-?is greater than that of strong acid radicals(Cl^-+SO₄^2-).?2?Ca²⁺ is the dominant cation in karst groundwater,and the order of cationic mean value is Ca²⁺>Mg²⁺>K⁺+Na⁺.Anions are HCO₃^-as the dominant anions,the mean from large to small order is HCO₃^->SO₄^2->Cl^-.The mean TDS of karst groundwater samples is 496.4 mg·L-1,which belongs to fresh water.PH value of 6.90,the overall was weak acid,part of the neutral or weak alkaline.Hardness average of 318.7 mg·L-1,most of which belong to hard water.TDS,pH,hardness,Ca²⁺,Mg²⁺,HCO₃^-coefficient of variation is relatively small,relatively stable in the regional groundwater.The coefficient of variation of K⁺+Na⁺,SO₄^2-and Cl^-is larger,and the content in groundwater is larger,which is a sensitive factor with the change of environmental factors.In general,the spatial distribution of the seven main anions and cations is generally different from the north and south sides of the Kongjia and Mengjiashan faults.?3?Using Gibbs diagram and principal component analysis to study the influencing factors of chemical composition of karst groundwater.The results of Gibbs show that the hydrochemical ions in the study area are affected by evaporation-enrichment and precipitation,and the water-rock interaction is the controlling factor of water chemical ions.The principal component analysis shows that the eigenvalues of the first principal component PC1 The total hardness,Ca²⁺,SO₄^2-,HCO₃^-,Cl^-,Mg²⁺,Na⁺,K⁺,which are closely related to PC1 are closely related to the lithology of the region,PC1 Reflecting the effect of water-rock on water chemistry.The second principal component PC2 has a characteristic value of 2.032 and a contribution rate of 18.474%.The PC2 is related to K⁺,Na⁺,NO₃^-,which are closely related to human activities,indicating that the effect of water-rock is reflected The impact of human activities.The third principal component PC3 has a characteristic value of 1.039 and a contribution rate of 9.445%.The pH is closely related to PC3,with a load of 0.735,suggesting that PC3 reflects the effect of atmospheric precipitation input.?4?Based on the analysis of hydrogeochemical system,the origin and formation characteristics of water chemical ions were studied by using mathematical statistics method,ion scale factor analysis method and stoichiometric method.The results show that the carbonate minerals mainly composed of calcite?CaCO₃?and dolomite?CaMg?CO₃?₂?are mainly composed of gypsum?CaSO₄·2H₂O?and anhydrite?CaSO₄?Alkaluminate minerals?feldspar,etc.?and clay minerals are the main source of groundwater ions.The role of the formation of regional water chemistry mainly includes the role of mineral filtration,de-dolomitization,cationic adsorption,mixing and synergistic effects.In addition,human activities have a certain impact on water ions,such as industrial and family life using salt?NaCl?residual infiltration will cause Na+ rise,the residual agricultural potash dissolved is one of the sources of K+.Agricultural manure,atmospheric,human and animal metabolites and bio-burning,etc.may be one of the main sources of NO₃^-.?5?Through the PHREEQC equilibrium calculation,the equilibrium state of the dissolution of the main minerals in the water-rock interaction process was determined.The calcite part is in the dissolved state,partly in the precipitation state;most of the dolomite in the dissolved state,a small part in the precipitation state;gypsum are not saturated,in a dissolved state.In general,the mineral saturation index is gradually increased from the supply area to the excretion area,and the saturation index increases with the growth of the runoff path.Its increasing speed decreases with the increase of runoff path.Indicating that the karst water dissolution capacity is weakened with the growth of the runoff path,and the decay rate of dissolution is decreased with the increase of the path.?6?The results of reverse modeling by PHREEQC show that there is some similarity and difference between the water-rock interaction and the excretion area in the recharge runoff area.Calcite,gypsum and rock salt are mostly dissolved in the unsaturated state;cation exchange is mainly Ca-Na ion exchange,along the groundwater runoff direction cation exchange effect The results show that the CO₂ is in the dissolved state and participates in the water-rock-gas effect,the reverse simulation results and the saturation index results,and the actual situation of the groundwater chemical analysis results is basically consistent.