Characterisics Of Sediment Geocheimistry And Its Impacts On Groudwater Arsenic Near The Piedmont Plain From The Hetao Basin

The Hetao plain of Inner Monglia is a typical semi-arid inland basin,where high As groundwater is widely distributed and has caused a serious health problem on residents.Many studies have investigated groundwater genchemistry.However,aquifer sediment-based studies are scare to demonstrate sediment geochemistry and its impact on groundwater As.This study investigated the control of sediment geochemistry on groundwater As through spatial distributionss of sediment lithology,reflectance,and element contents,along with groundwater chemical characteristics,which is of theoretically and practically significance.The main findings of this study are shown as follows.?1?The sedimentary lithology varied from the pidemont to the plain.Coarse-grained size sediments like coarse sand are mainly distributed in the piedmont area,while fine-grained size sediments like clay and silty clay are mainly distributed in the plain with good stratification.Lithology and depth are the main factors controlling the sediment redox conditions.The coarse sand in the piedmont areas has high reflactence value,indicating the oxic conditions.In the plain,the fine-grained size sediments near the surface have higher reflactence values in relative to sediments in the deep aquifer.?2?Sediments in the study area are enriched in Al₂O₃,MgO,CaO,Fe₂O₃,As,Li,Cr,V,Ni,and Zn,but depleted in TiO₂ and Sr.Lithology has significant impact on spatial distribution of sediment components.Coarse-grained size sediments tend to be enriched in Si and Na,while fine-grained size sediments are enriched in Ca,Mg,Fe,Mn and As,Li,Cr,Co,Ni,Cu,Zn,As,Li,Cr,Co,Ni,Cu,and Zn.?3?Sediment As is associated with lithology and reducing conditions,where fine size sediments are generally enriched in As.Positive relationship is observed between As and Fe/Mn in sediments,indicating that As mainly exists as Fe/Mn oxide bound forms.?4?The major cation in groundwater is predominated by Na⁺,and the major anion varies in different wells.Concentrations of dissolved As,Fe,Mn,NH₄-N,and S^2-are lower in groundwater in the piedmont area than those in the plain.They show variation,indicating the impact of different hydrogeochemical process.?5?There are three factors affecting enrichment of groundwater As.High sediment As causes more As release to groundwater.Reducing conditions drive the release of As from sediments.Closed hydrogeological conditons are conducive to enrichment of groundwater As.