Study On Hydrogeochemical Characteristics In Faintly Acid Redox Environment

Redox reaction of water chemistry plays an important controlling role in evolution process,not only affects the degradationof organic matter and migration,but also plays a leading role in the geochemical process of inorganic matter.Based on the analysis of oxidation-reduction environmental hydrogeochemical characteristics,It can not only reveal the geochemical reaction and ion composition characteristics of different stages,but also find out distribution of the redox substances in the aquifer,thus it plays an important role in control and repair of nitrate and heavy metal.This study analyzed the characteristics of the hydrogeochemistry composition and distribution on the basis of field investigation,sampling and hydrogeochemistry data in the Wusuli River in Sanjiang plian.The spatial variability of groundwater redox environment were analyzed by using ArcGIS geostatistical module,the relationship between redox potential and redox sensitive materials was discussed,the control of redox environment on chemical composition of groundwater was revealed,and the change rule of the redox environment along the groundwater runoff sa well as the reaction characteristicsofwaterchemistrywereidentifiedbyreverse hydrogeochemical simulation.The followings are some main results:?1?The weak acidic environment of groundwater is continuous and stable in the study area,the shallow groundwater give first place to HCO₃?Cl-HCO₃and Cl-SO₄ with poor of soluble salt and brackish water.Deep groundwater is mainly composed of HCO₃ with low total dissoloved solid and desalination trend.Shallow groundwater and deep groundwater have obvious layering and taking 30m and 90m well depth as the boundary apart,the content of ions in groundwater has different variation trend.?2?The isotopic composition of groundwater in the basin is negative,which is located near the local atmospheric precipitation line and root in precipitation recharge.The composition of ions is controlled by weathering and human activities.Cl^-and NO₃^-show high spatial variability,which are easily affected and imported by human activities.?3?The shallow groundwater in a certain condition which are oxidizing environment,weak oxidizing environment and reducing environment with50¹00mV,100¹50mV change range of Eh.The Eh has no regularity change with the well depth,and the redox environment of aquifer is variable.The Eh of deep groundwater is mainly in the range of 0⁵0mV and<0mV,which is in the weak oxidizing environment and reducing environment and the redox environment of aquifer is stable.?4?The redox potential was significantly correlated with the redox sensitive substance.Eh,pH and DO control the redox environment of groundwater.The relationship between Eh and pH was negatively correlated,and Eh was positively correlated with DO.Both shallow groundwater and deep groundwater have experienced strong dissolved oxygen reduction,NO₃^-and NO₂^-reduction stages.The Fe reduction of deep groundwater is more significant,and migration and transformation process of Fe²⁺is controlled by redox conditions and the HCO₃^-of shallow water change more significant with Eh,which is negative.?5?The oxidation reduction reaction in shallow groundwater is marked.The nitrification and the oxidation of pyrite are mainly occurred in the condition of oxidation.Under the reducing condition,the denitrification,the dissolution of iron oxide and the sulfate reduction are mainly occurred.The change of redox conditions mainly caused the change of contents such as SO₄^2-,NO₃^-,NO₂^-and Fe²⁺,The contents of SO₄^2-and NO₃^-in the oxidizing environment were increased,and the contents of NO₂^-and Fe²⁺in the reducing environment were increased.The change of Ca²⁺,Mg²⁺,Na⁺and Cl^-in water is mainly controlled by water-rock interaction and cation exchange,and the effect of redox condition is small.HCO₃^-content is affected both by water-rock interaction and redox reaction.The oxidation and reduction environment of deep groundwater is stable,and its environmental change has little effect on the content of conventional water chemical ions,which mainly causes the change of Fe²⁺and Mn content.