| Shizihe area is located in the hinterland of Eurasia and belongs to a typical continental climate and one of the water resources deficient areas in the northwest inland of China.The groundwater resources are the main water source in this area as well as a keyelement of the local people’s living,production and ecological water utilization.The contradiction between supply and demand of water resources in this area has become increasingly prominent in recent years.The groundwater resources have been overexploited and polluted to various degrees,restricting local social and economic development.Therefore,it is also of great practical value to reveal the present situation of local groundwater quality,explore the occurrence mechanism of regional groundwater components,analyze and summarize the formation law of groundwater quality,which is also of practical value for ensuring the safety of local water supply and preventing endemic diseases.At the same time,it can also provide reference for the protection and utilization of groundwater resources and the realization of regional sustainable development in other arid areasThe paper selects Shizihe area as the study area.By investigating and sorting out the local geological and hydrological conditions and adopting principal component analysis,Q type cluster analysis,ionic ratio method,hydrochemical graphic method,hydrogeochemical reverse simulation and other methods,the hydrochemical characteristics of groundwater and the hydrogeochemical process of regional groundwater evolution are analyzed,and the sources and distribution characteristics of arsenic,fluorine and iodine that affect the safety of water use in the region are analyzed and the influence mechanism of its formation is studied.The main research achievements and innovations are as follows:(1)Hydrochemical types of groundwater and its evolution:From 2014 to 2017,the types of HCO3·SO4-Ca·Mg,HCO3·SO4-Na-Ca and HCO3·SO4-Ca were stable hydrochemical types of unconfined groundwater;the types of HCO3-Na·Ca,HCO3·SO4-Na·Ca an d HCO3·SO4-Ca were stable hydrochemical types of confined groundwater.(2)The evolution of chemical components of groundwater:In the plane direction,the content of major components showed the trend of decreasing from Shihezi city to the surrounding of the study area;in the vertical direction,the content of major components showed an overall decreasing trend from unconfined groundwater,shallow confined groundwater to deep confined groundwater;the TH and TDS decreased from the southern mountainous area to the northern plain area,and decreased obviously from the unconfined groundwater to the deep confined groundwater in the vertical direction(3)The process of the formation and evolution of groundwater quality:It was found that formation and evolution of groundwater quality were related to natural processes such as mineral dissolution,oxidation-reduction and so on,and also affected by human factors;the unconfined groundwater runoff was enhanced gradually along the axis of the alluvial-diluvial fan of Manasi River,but the runoff of shallow confined groundwater and deep confined groundwater gradually were weakend;the main sources of the constant component in groundwater were dissolution reactions of the halite,sodium minerals(albite,mirabilite,etc.),carbonate(dolomite,calcite)and sulfate(gypsum etc.);the formation and evolution of groundwater which was influenced not only by weathering and hydrolysis,evaporation and concentration,but also accompanied by cationic exchange,oxidation-reduction,etc(4)Trace inorganic component As:As in groundwater mainly came from the arsenic minerals in aquifers and the use of arsenic-containing pesticides;the content of As increased from south to north,from unconfined groundwater to confined grounowater;the hydrochemical types of high As groundwater in this area was mainly HCO3-Na and HCO3 Cl-Na;the alkaline,reduction environment was favorable to the concentration of As in groundwater in this area;the content of As in the groundwater was closely related to the oxidation-reduction sensitive component NO3-,NH4+,SO42-,HCO3-,iron oxide;according to different thermodynamic enthalpy of reaction,the reduction process of As dominated by the above oxidation-reduction sensitive components could be divided into three stages(the reduction dominant stage of NO3-,the reduction dominant stage of iron oxide and the reduction dominant stage of SO42-successively),which was consistent with the partition of As content in spatial distribution;the H AsO42-content in the occurrence form of As under the control of pH and Eh was absolutely dominant.(5)Trace inorganic component F-:The F-in groundwater mainly came from the weathering dissolution of fluorite and the discharge of industrial waste in the area;the content increased gradually from south to north,the hydrochemical type of fluorine rich groundwate were HCO3·Cl-Na,CI·SO4-Na and HCO3-Na;alkaline,reduction environment was favorable to the concentration of F-in groundwater in this area;there was no rule of high salinity,high hardness and high alkalinity accompanied by high fluorine in this area;dissolution and precipitation of fluorite and calcite,evaporation and concentration,cationic exchange had an affect on fluorite;the possible forms of F-in the groundwater of the study area were mainly F-,MgF+,CaF+,NaF,HF.(6)Trace inorganic component l-:Bioaccumulation in sediments,precipitation and irrigation water leaching promoted iodine into groundwater;its content gradually increased from south to north;the hydrochemical types of high iodine groundwater were mainly Cl·SO4-Na,HCO3-Na and HCO3·Cl-Na;alkaline,reduction environment was conducive to its enrichment;the contents of Na+ and Cl-increased,making more I-into groundwater.(7)Generality of trace inorganic components:The contents of As、F-、I in groundwater increased from south to north,which was related to the differences of hydrogeological environment and circulation velocity of groundwater between south and north in the study area;the hydrochemical types of groundwater that the three trace inorganic components exceeded the standard at the same time wereHCO3·Cl-Na,HCO3-Na and Cl·SO4-Na;the weak alkaline and alkaline,reduction environment was the common condition for their formation and enrichment;the simultaneous surpassing of the standard was more likely than that of the single component or two components at the same time.It was easier for deep confined groundwater than shallow confined groundwater to enrich them;TDS had certain promoting effect to the enrichment of As,F-and I-at the same time. |
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