Study On The Hydrochemical Characteristics Of Changhe River Basin And The Law Of SO₄^2- Migration In Shallow Groundwater

The arid and semi-arid region in northern China is one of the regions with the most shortage of water resources,and the economic development of China is severely restricted by water resources.In recent years,due to the influence of human activities such as drought climate,decreasing rainfall,increasing groundwater exploitation and coal mining,the water supply,diameter,discharge conditions,water quality and hydrochemical characteristics of water resources in the basin have changed significantly,leading to a series of environmental problems.Therefore,it is significant to analyze the water quality evolution characteristics and hydrogeochemical process in arid and semi-arid regions.This study by jincheng long river basin as the study area,combining with the hydrogeological conditions in the study area and the effects of coal mining,with shallow groundwater and river water chemical evolution relationship as the main line,is a typical with SO42-diffusion law,comprehensive,water chemical analysis and numerical simulation method using multivariate statistical methods,explore the study area,surface water and groundwater hydrogeochemical processThe aim is to reveal the hydrochemical characteristics and evolution law of the Changhe River Basin comprehensively.By clarifying the law of SO42-migration in shallow groundwater,the paper reveals the quantitative transformation relationship of SO42-in shallow groundwater in the study area,and provides a scientific basis for the protection of water resources in the study area.The main research contents and results are as follows:(1)Through the stationing sampling to test the water quality analysis in the study area,the results show that the period of large coal mines in the study area,surface water SO42-.concentration of ammonia nitrogen and heavy metal material will increase,at the same time,the plentiful water and under the influence of coal mining activities,large shallow groundwater in the soluble solid(TDS)and SO42-concentration showed a trend of rising;Single factor index method and PCA-RSR method were used to evaluate the water quality of surface water and shallow groundwater respectively.The surface water quality evaluation results were poor V,and all indexes exceeded the standard to a certain extent.The heavy metal content in the densely concentrated coal mining plant reaches seriously exceeded the standard.The water quality evaluation results of shallow groundwater are mainly III and Fe type water,while the water quality evaluation results of middle-upstream mining concentration area and downstream chemical plant distribution area are Aisu type water,and the main pollutants are TDS and sulfate.(2)Analyze the hydrogeochemical characteristics of surface water and groundwater from the perspective of time in three periods of abundant and low water:In surface water,pH and TDS showed a difference along the path.According to the correlation analysis,TDS had a significant positive correlation with Na-,K+,SO42-,HCO3-and Cl-,and the highest correlation was HCO3-and TDS,with the correlation coefficient up to 0.96,indicating that HCO3-was the main source of TDS in surface water.HCO3-is correlated with Na+ and K+ ions,indicating that HCO3-ions originate from carbonate.While SO42-is not related to Ca2+,gypsum is not the main source of SO42-,SO42-comes from the outside.According to the results of hydration analysis,the hydrochemical type of surface water is HCO3-Mg,which is mainly controlled by rock weathering.The content of TDS is lower than that of surface water,which is highly correlated with SO42-and is more deeply affected by coal mining.The hydrochemical type in each water stage is mainly HCO3·CO3-Mg·Ca,and the hydrochemical composition presents vertical differences.With the increase of the depth of the aquifer,the cation concentration increases while the anion concentration decreases,which is more affected by the water-rock interaction,and the dissolution of the sodium-containing silicate rock minerals is the main factor.(3)Based on the cluster analysis and principal component analysis of all water samples from surface water and groundwater,the collected water samples were divided into three categories.The results showed that the surface water in the upper reaches of the Changhe River Basin recharges groundwater,and the hydrochemical type is HCO3·CO3-Ca type,and the water body is mainly affected by the weathering and dissolution of carbonate rocks.The hydrochemical type of other regions in the upper reaches is HCO3·CO3-Ca·Na type,and the groundwater in this section recharges surface water.Groundwater in the middle reaches of the Yangtze River Basin resupplies surface water,and the hydrochemical type is HCO3·CO3-Ca,which is mainly influenced by weathering and dissolution of carbonate and silicate rocks.Surface water in the lower reaches of the Changhe River Basin replenished the groundwater,and the concentration of ionic components in the water was low.The results show that there are consistency and difference between surface water and groundwater.(4)Through the establishment of groundwater flow and SO42-migration and diffusion model,the prediction study on the change of water level and SO42-concentration of shallow groundwater in the study area was carried out,and the results showed that:In the next 10 years,the water level of shallow groundwater will decrease by about 10m,and in 5 years,it will drop more than the water level limit.The concentration of SO42-will spread 15 km from north to south along with the flow of shallow groundwater,and the polluted area will be 3.2 times of the original.Three different working conditions of SO42-3 were set according to the limit of chemical composition of shallow groundwater water.The results show that when the concentration of SO42-3 is higher than 15 mg/L,the content will accumulate continuously in the next 10 years.When the concentration of SO42-was 15 mg/L,the content of SO42-remained basically unchanged in the next 10 years.When the concentration of SO42-is less than 15 mg/L,the cumulative effect will decrease in the next 10 years.Therefore,appropriately reducing the coal mining amount will inhibit the cumulative effect to a certain extent.Combined with correlation analysis,it can be seen that SO42-in shallow groundwater and SO42-in surface water,dissolved solids,rainfall show a cubic function relationship,and the content of SO42-in shallow groundwater can be estimated by collecting data.