Analysis On Water Chemistry Evolution Characteristics And Mechanism Of Shallow Groundwater In Hutuo River Alluvial Fan

In recent decades,increasing human activities in Hutuo River alluvial area have inevitably made the evolution of shallow groundwater environment complicated.The scientifically protection,development and utilization of groundwater resources were becoming more difficulty.The study of the characteristics and variations of groundwater quality could clarify the mechanism of groundwater quality evolution in this area.The results could provide reference for the groundwater development and utilization.This research was started from the evolutionary characteristics of groundwater hydrochemistry.Methods of hydrogeochemical,isotope and multivariate statistical techniques were used in studying the evolution of groundwater hydrochemical and its formation mechanism.The results clarified the formation mechanism of typical chemical components of groundwater driven by anthropogenic impacts.The process of water-rock interaction on typical water flow path was quantitatively analyzed by reverse hydrogeochemical simulation.Main achievements of the study are summarized as following:The groundwater chemistry type of Hutuo River alluvial fan has changed significantly.Shijiazhuang City,located in the Hutuo River alluvial fan,has been in rapid urbanization process period since 1980.The variations of groundwater environment were exacerbated.The HCO3-Ca(Ca·Mg)groundwater,which was widely distributed in the 1970s,has been reduced and gradually replaced by HCO3·SO4-Ca(Mg),HCO3·ClCa(Ca·Mg).The evolution of water chemistry was becoming complicated.The increase of Cl-,NO3-and Na+ in shallow groundwater of the study area was mainly controlled by anthropogenic input.Human factors were one of the important driving factors for the increase of SO42-.Ca2+,Mg2+,HCO3-were mainly controlled by water-rock interaction.Hardness was consistent with the temporal and spatial evolution of TDS.The dissolution of calcite,dolomite and gypsum was the main source of groundwater Ca2+ and Mg2+.The high values of Cl-mainly came from the infiltration of urban sewage and industrial waste water.The high values of SO42-were mainly controlled by the supply of upstream river water,sewage discharge and gypsum dissolving and precipitation reaction.The high nitrate area was mainly distributed in the concentrated area of human activities.In contrast,the nitrate content in the agricultural area was relatively low.Nitrogen isotope data showed that the high values of nitrogen were mainly from the sewage or feces.This trend was consistent with the Cl-distribution.In addition,the total hardness and the distribution of high values of nitrate,chloride and sodium ions were also consistent with the control of cationic alternating adsorption and nitrification.The 293 groundwater samples were divided into three categories by cluster analysis.The main chemical components of the first group of groundwater(39.2%)showed lower values.Most of these samples were distributed in the agricultural area,mainly controlled by the release of natural matter in the formation caused by the destruction of water-rock balance,and subject to less pollution.The second group of groundwater(48.1%)was medium content,mainly affected by the infiltration of Hutuo River water and tannery wastewater.The third group of groundwater(13.0%)was high content.On the one hand,over-exploitation of groundwater lead to various mechanisms of high hardness.On the other hand,industrial wastewater and domestic sewage were the main reasons for the high values of groundwater components in the third group.The results of flow path simulation showed that the dissolution and sedimentation trends of the main mineral facies in the top and middle of the alluvial fan were significantly different.At the top of the alluvial fan,the dissolution and precipitation of the main mineral facies were relatively complex:the calcite and dolomite were precipitated on the water flow path in the western upper funnel area.In the funnel area,two flow paths converging to the center of the funnel was characterized by the dissolution of calcite and dolomite.On the flow path east of the funnel area,the dissolution and precipitation trends of the main minerals were relatively consistent,showing the dissolution of calcite and the precipitation of dolomite and gypsum.