Hydrochemical Evolution Characteristics And Mechanism Of Groundwater Funnel Areas In The Eastern Hengshui City

The eatern funnel area of Hengshui is located in the center of the funnel area in the North China.The long-term and large-scale exploitation of groundwater has led to the changes in the groundwater recharge,runoff and drainage,which has a serious impact on the evolution of groundwater chemistry.Since the comprehensive control of overexploitation in North China in 2014,the recharge,runoff and drainage of groundwater had changed again.In view of this problem,the eastern funnel area of Hengshui was selected as the research area.The analysis of the chemical composition evolution and genetic mechanism of shallow and deep groundwater in the process of artificial control of groundwater funnel is of great significance to the management and protection of groundwater resources.Based on the monitoring data of shallow and deep groundwater quality and water level in the eastern funnel area of Hengshui from 2014 to 2020,the chemical evolution characteristics and influencing mechanisms of shallow and deep groundwater are studied by the methods of Piper diagram,geostatistical analysis,Gibbs diagram,chlor-alkali index and correlation analysis,etc.The results of the research are as follows:1.Groundwater savings and the changes of groundwater cycle.Gucheng County has the largest cumulative groundwater savings in the implementation of agricultural,forestry and hydraulic overdraft limit measures,which is148.0368 million m³.In the first half of the year,affected by spring ploughing and precipitation the groundwater level was buried deeper within the year,and in the year and annual changes of shallow and deep groundwater levels were similar.From 2019 to 2021,the groundwater level rose significantly with the highest recovery rate of 6.26m/a.The shallow groundwater flows from south to north before and after groundwater overdraft limit,and the deep groundwater flows from west to east.The funnel area is distributed in Zaoqiang and Jingxian counties.After groundwater overdraft limit,the central water level of the shallow groundwater funnel area increased by 4m,and the central water level of the deep groundwater funnel area decreased by 6m.2.Evolution characteristics of chemical composition of shallow and deep groundwater.The chemical composition changes of the shallow and deep groundwater were similar which chemical types tend to be diversified after groundwater overdraft limit and the fluctuation range of the components of the shallow groundwater is higher than that of the deep groundwater.The distribution of ion concentration in shallow and deep groundwater after groundwater overdraft limit was higher in the north and lower in the south,and the distribution of HCO₃^-was different from other ions.The area of the shallow groundwater freshwater area decreased and the TDS increased after the groundwater overdraft limit.The TDS of the deep groundwater decreased and the whole area is freshwater before and after groundwater overdraft limit.The ion distribution of the shallow and deep groundwater was greatly affected by the groundwater funnel,and the deep groundwater before groundwater overdraft limit was relatively less affected by the groundwater funnel.Na⁺,Cl^-,Mg²⁺,SO₄^2-,Ca²⁺in shallow and deep groundwater wera the main contribution indicators of TDS.3.Analysis of main controlling factors of chemical genesis of groundwater.Shallow groundwater is mainly affected by evaporation dominance and rock dominance,followed by human activities.Rock dissolution was mainly affected by silicate and evaporite rocks.Deep groundwater is mainly affected by human activities,followed by water-rock action.Rock dissolution was mainly evaporite and silicate rock dissolution.The dissolution of albite,anorthite,gypsum,fluorite,rock salt,and the precipitation of calcite and dolomite were the main sources of ions for shallow and deep groundwater.Alternate adsorption of cations existed in the both shallow and deep groundwater.4.Research on chemical mechanism of groundwater.Changes in the groundwater level depth,precipitation,human activities,and the shallow salt water had a greater impact on both shallow and deep groundwater hydrochemistry.In 2016 and 2020,the transfer amount of different minerals in shallow and deep groundwater changed significantly.The chemical composition of groundwater is affected by different minerals to different extents.Influenced by the amount of precipitation and extraction,the TDS and TH concentrations of shallow groundwater increased on the whole.Due to the reduction of deep groundwater exploitation,TDS and TH concentrations decreased with the influence of shallow groundwater was weakened.