Application Of Multivariate Statistics Method Into Research On Spatial Distribution Law Of Hydrochemistry In Dusituhe Groundwater System In Ordos Cretaceous Basin

Dusituhe River groundwater system in the Ordos Cretaceous Artesianbasin is located in the east of Asian continent, under the influence oftemperate zone continent monsoon, which leads to a climate therecharacterized by its low precipitation, intense evaporation and large seasonalvariations ofprecipitation.Thus,local surfacewateris deficient,besides,dueto the significant interannual change, utilization of surface water isineffective. However, groundwater resources are abundant in the region andhighly important for local water supply. In the groundwater resourcesdevelopment process, groundwater quality is the focused issue to beconcernedwith.Traditionally, researches on groundwater quality mainly aims at majoriron content, using methods such as mapping of hydrochemical componentsor hydrochemical types, piper trilinear diagram, and ritio coefficient of mainirons, etc., in which pH, TDS and electric conductivity that can reflect theformation law of groundwater chemical fields cannot be portrayedappropriately. As an effective method to extract useful information fromcomplicated data, multivariate statistics provides a means which isreasonable, effective and swift in the researches on groundwater chemistrycharacters. Formation of groundwater chemistry fields concerns with manyfactors involving dissolution, mixing effect and evaporation, and so forth.Employing multivariate statistics in the abstraction of information from themain irons and non-iron components in groundwater gives a promisingprospects of the identification of the chief factors that affects thegroundwaterchemicalfields.In this thesis, the geological and hydrogeological settings of DusituRiver groundwater system were studied firstly and the distribution of theaquifers and the groundwater recharge, runoff and drainage Conditions werefound out. Based on that, traditional methods were used to investigate thehorizontal and vertical distribution of the main hydrochemical componentsand hydrochemical types of the rock groups with water content in DusituRiver groundwater system. The results showed that the hydrochemicalfeature has an apparent horizontal zonal characteristic in shallow, middle anddeep groundwater, particular in shallow and middle groundwater. The mainirons in the groundwater are SO₄^2-,Cl^-,K⁺ + Na⁺,Ca²⁺ and Mg²⁺,whoseconcentration are increased from the east(northeast) to the west(southwest).The hydrochemical type presents a similar characteristic of variation, fromthe recharge area to the discharge area, it evolves from HCO3-type toHCO3-SO4–type,andfinallySO4-Cl-type.Then, factor analysis and cluster analysis were applied, conclusions arethat Q model cluster analysis can gather samples with similar characteristicseffectively, and separate out the hydrochemical samples sampled along therecharge area, runoff area and discharge area, reflecting the difference andthe distribution characteristic of different hydrochemical samples. Not onlycan factor analysis reduce the number of variable effectively, but alsoabstract the main factors affecting the hydrochemical componentssuccessfully. The main factors in shallow and middle groundwater aredissolution, the dissolution of gypsum, carbonate evolution andalkality-acidity evolution, while dissolution, dissolution of mineral includingmagnesium and the dissolution equilibrium of CaCO₃.At the end, it reveals that the shallow groundwater accepts verticalrecharge, during which low salinity groundwater of HCO₃-type is formed bydissolution at first, further dissolution in the runoff and discharge areachanges the hydrochemical type into HCO₃-SO₄-type, HCO₃-SO₄-Cl-typeand SO₄-Cl-type, in the region where evaporation is violent, high salinitygroundwaterofSO₄-Cl-typeisformed.Due to the mixing with the shallow groundwater, the middlegroundwater in the recharge area is of HCO₃-type. Along the flow path, asynthetic effect of dissolution, mixing effect and occasional cation exchangereaction alters the hydrochemical type from HCO₃-type to HCO₃-SO₄–typeandHCO₃-SO₄-Cl-typehorizontally.The deep groundwater in subjiective Dusituhe River groundwatersystem influenced bydissolution, mixingeffect and cation exchange reactionformedgroundwaterevolvesfromHCO₃-SO₄-Cl-typetoHCO₃-SO₄-typeandfinally SO₄-type.The renewal rate of the groundwater in Shanghaimiao andYanchi subjiective system is low, dissolution and occasional cation exchangereaction change the hydrochemical type of the groundwater fromHCO₃-Cl-typeintoHCO₃-SO₄-typeandfinallySO₄-Cl-type.