【作者】 姜凌；

【导师】 李佩成；

【作者基本信息】 长安大学 ， 地质工程， 2009， 博士

【摘要】 地下水资源是干旱区绿洲生存与发展的重要水源。随着人口的增长和社会经济的快速发展，对水的需求量增大，加之对地下水资源的不合理开采，导致许多绿洲地下水水位不断下降，地下水水质出现恶化，可利用地下水资源日趋减少，引发了一系列相关的水资源—环境问题，严重威胁着绿洲的可持续发展。在这样的背景下，长安大学国际干旱半干旱地区水资源与环境研究培训中心承担了《阿拉善盟腰坝绿洲地下水资源承载力及可持续利用》的研究任务，以典型干旱区绿洲——内蒙古阿拉善腰坝绿洲为研究对象，对其水资源开发利用现状和水资源开发过程中出现的环境地质问题进行研究，确定地下水资源允许开采量及承载力，为该地区可持续发展提供水资源保证，并为进一步开展其他绿洲的同类研究创造经验。本文作者承担了总项目中的子课题“阿拉善盟腰坝绿洲地下水水质评价”的研究工作，并结合研究课题，开展博士论文的研究，重点对腰坝绿洲地下水水化学成分形成及演化机制进行了研究。揭示了人类长期生活生产影响下的水化学场时空演化规律，借助水化学信息全面系统的认识干旱区绿洲地下水系统，对于评价区域地下水可持续开发利用，制定合理的地下水开发模式，促使绿洲自然与人类和谐发展具有重要意义。本文综合应用水文地质学、水文地球化学、同位素水文学的理论与方法，对干旱区绿洲地下水水化学成分的时空变异特征与演变规律进行了深入的研究，明确了地下水水化学成分演化规律及其演化过程中发生的主要地球化学作用，揭示了地下水与环境的相互作用机制，验证了地下水补给来源、径流途径、排泄方式。论文的主要研究成果如下：（1）腰坝绿洲不同农灌季节地下水主要水化学指标的统计分析结果表明：季节变化对水化学空间变异性影响较小。但潜水水文化学性质空间变异性较大，主要受含水层介质、地形地貌、水文气象条件和人类活动等因素的影响大，尤其Na⁺、Cl^-、SO₄^2-空间变异性较大，是决定潜水盐化作用的主要变量。承压水受外界因素干扰较少，盐化作用弱。（2）地下水水化学成分的实测分析结果表明：地下水化学类型和总溶解固体（TDS）在空间上的分布特征表现为：在垂直方向上，由上到下表现为TDS由高变低，水化学类型由复杂变简单的反向地球化学分带特征。在水平方向上，地下水的水化学分布特征为东北部的TDS较低，水化学类型主要为HCO₃-SO₄型水；西南部TDS大部分较高，水质较差，水化学类型主要为Cl-SO₄型水。且TDS含量和水化学类型随季节变化明显，非开采期较开采期TDS含量整体增大，硫酸型和氯型水的分布面积较开采期扩大。（3）地下水离子比例系数(γ_Cl^-／γ_Ca²⁺、γ_Mg²⁺／γ_Ca²⁺、γ_Na⁺)／γ_Mg²⁺、γ_Cl^-／γ_HCO3^2-、γ_Cl^-)／γ_SO4^2--、γ_Na⁺)／γ_Cl^-)的研究表明：研究区地下水流动系统中的水化学成分总体上受水动力条件和地下水在径流途径上的沿程累积作用影响，表现为自东北向西南随着水动力条件逐渐变差，Cl^-、Mg²⁺、Na⁺离子等高盐分离子逐渐富集，易溶盐逐渐累积，水体总体向咸化方向发展。（4）以1968～2006年的地下水水化学资料为基础研究地下水水化学场随时间的演化规律，得出：腰坝绿洲自开采以来地下水TDS总体上呈增加趋势，平均每年增加40mg／L以上，但随年际和位置的不同增加幅度并不均匀，南部TDS增加速率比中部和北部大。水化学类型已由原来以HCO₃-Ca·Mg型为主要转为现在Cl·SO₄-Na．Mg型为主，Ca²⁺、Mg²⁺离子基本达到饱和，HCO₃^-虽有增加，但相对含量在减少，Na⁺、SO₄^2-、Cl^-离子含量显著增加。表明天然水化学场正在向盐化和碱化以及地下水化学类型趋于复杂化、水质变差的方向演化。（5）腰坝绿洲地下水的δ¹⁸O、δD值都集中沿同位素雨水线分布，标志着绿洲地下水为大气降水补给成因。而且地下水的δ¹⁸O和δD值呈现出东北区大于西南区的分布特点，指示着两区地下水具有不同的水循环意义，即西南区地下水更多地保存着较冷气候补给环境下的地下水；而东北区，水循环比较积极，为较暖气候环境下补给的地下水。垂向上，氢氧同位素含量十分相近，表明垂向上各层地下水水力联系密切。（6）根据腰坝绿洲及其周边地区地下水中氚含量的测定结果证实：腰坝绿洲地下水的的主要补给来源是东部山前台地裂隙孔隙水、北部孔隙水和西部沙漠潜水的侧向径流补给，及山区洪水的垂直渗漏补给。径流特征主要表现为：在天然条件下，由东北向西南方向径流，陶苏湖则是腰坝绿洲范围内的局部排泄区；在大规模开发以后，绿洲地下水径流交替严格受到人为开采及开采时段的影响。在开采期内，由于区域降落漏斗的形成，地下水的径流主要是绿洲周边地下水向漏斗中心运移。在非开采期内，地下水位以恢复为主，此时，区内地下水的径流方向则主要是由北、西北、西南向绿洲内径流。西南陶苏湖方向的上层咸水向其东北方向运移，源源不断地补给绿洲地下水。（7）研究区第四系孔隙潜水水文地球化学模拟结果表明：混合作用是控制区域北部和西南部孔隙潜水水化学状况的最主要因素，但混合过程并非是单纯的机械混合，在北部伴随着孔隙潜水、洪水、沙漠潜水三种补给水源的混合，还发生了方解石、白云石的沉淀，石膏和二氧化碳的溶解，以及钙离子的吸附和钠离子解析；在西南陶苏湖区伴随着沙漠潜水和洪水两种补给水源的混合，还发生了白云石和方解石沉淀，盐岩、石膏、萤石和二氧化碳的溶解，以及钙离子的吸附和钠离子解析。东部山前台地下水系统与腰坝绿洲地下水系统水力联系紧密，是研究区地下水的主要补给水源。在地下水径流过程中发生了方解石和白云石的沉淀，石膏、岩盐和萤石的溶解，以及钙离子的吸附和钠离子解析。（8）影响和决定研究区地下水水化学成分形成及演化规律的因素主要包括：水-岩相互作用、人类活动因素的影响和土壤易溶盐含量的影响。①溶解／沉淀作用、阳离子交换吸附作用、蒸发浓缩作用和混合作用共同决定了研究区地下水水化学成分的形成特征；②人类的生产活动，改变了地下水的原始环境，破坏了水化学场的原有模型。③土壤中的易溶盐的溶解及离子交换作用，造成区内地下水SAR值增高，TDS增大。更多还原

【Abstract】 Groundwater resources has become an extremely significant water sources for oasissurvival and development. However, with the growth of population and rapid development ofsocio-economy, irrational utilization of groundwater resources has triggered to a series ofwater resources and environmental issues, such as the decline ceaselessly of groundwaterlevel, deterioration continuously of groundwater quality, and diminution increasingly ofavailable groundwater quantity. These problems seriously threat to the sustainabledevelopment of oasis. Therefore, it has a great significance to carry out study onhydrochemical composition formation and evolution mechanisms of the groundwater in oasisof arid areas, reveal spatial and temporal evolution laws of gourdwater chemical compositionunder the long-term influence of the human farming, and use water chemistry information tounderstand comprehensively and systematically groundwater systems of arid Oasis. All ofthese play an important role to evaluate sustainable exploitation of groundwater resources,formulate rational exploitation model of groundwater, and promote harmonious developmentof nature and mankind.Under the guidance of system theory, the paper takes a typical arid area oasis, namelyYaoba Oasis in Alashan as the research object.. By applying all kinds of integratedinformation, such as groundwater chemical compositions, isotope, hydrogeology etc studiesthe temporal and spatial variations and evolution laws of the groundwater hydrochemistry. Onthe basis of these studies, the interaction mechanisms between groundwater and theenvironment is revealed, and the information of the recharge sources, recharge methods,runoff channels, excretion ways and the main geochemical roles in the groundwater is derivedquantitatively or semi-quantitatively. These study results provides an effective way forunderstanding groundwater system correctly. The main research results are that:（1） The paper also conducts statistical analysis on some major hydrochemical indicatorsof groundwater among different irrigation seasons over Yaoba Oasis. The results indicate thatregardless of the exploitation or non-exploitation period, the variation trend of major ioncompositions of phreatic water are in accordance with that of artesian water basically. Theconlusion could be acquired that seasonal change has little effect on hydrochemical spatialvariability. In addition, the hydrological and chemical characteristics of phreatic water is moresusceptible to spatial variation than those of artesian water, which is mainly affected byaquifer media, topography, hydro-meteorological conditions and human activity and so on.Among those water chemical characteristics, Na⁺, Cl^- and SO₄^2- has more spatial variability,which are the main variables determining salinization. Confined water is less suffuring fromexternal interference, therefore, the salinization is weak.（2） The analysis of groundwater chemical compositions measure display that thedistribution of groundwater chemical types and Total Dissolved Solids （TDS） with spacepresents the following features:①In vertical direction, from up to down, TDS varies fromhigh to low, and water chemical types range from complex to easy, which is a reversegeochemical zonation characteristics.②In horizontal direction, for the northeastern, TDS islower and water chemical type is HCO₃-SO₄. The hydrochemical characteristics of southwestern are high TDS, poor water quality and Cl-SO₄ type water; furthermore, it isobvious that TDS varies with season and TDS in non-mining period is higher than miningstage at overall production, while the change of water chemical types with season is notobvious.（3） The study on all kinds of ions ratio coefficients of groundwater (e.g.γ_Cl^-/γ_Ca²⁺、γ_Mg²⁺/γ_Ca²⁺、γ_Na⁺/γ_Mg²⁺、γ_Cl^-/γ_HCO2^2-、γ_Cl^-/γ_SO4^2-、γ_Na⁺/γ_Cl^-show the results as below:generally speaking, in research area, water chemical compositions of groundwater flowsystem is affected by hydraulic condition and groundwater accumulative action with runoffflowing, becoming poor from northeast to southwest with hydraulic condition, andassembling high saline ions like Cl^-, Mg²⁺ and Na⁺. The increasing of various salt densityprovides a good environment for salitation.（4） According to the data of groundwater chemistry in research area, the evolutionchateristics of hydrogeochemical compositions with time could be obtained. Sincegroundwater was exploited by human being, the TDS has been keeping on an increasing trendat speed of 40mg/L per year in overall. However, with the difference of years and locations,the raising extents are not even. Southern has higher increasing rate than middle part andnorthern. The hydrochemical type has changed from the original type of HCO₃-Ca·Mg toCl·SO₄-Na·Mg. The amount of Ca²⁺ and Mg²⁺ in groundwater has reached saturation statebasically. The amount of HCO₃^- is increasing, but the ratio of HCO₃^-to total ions is reducing.Groundwater contains more Na⁺, SO₄^-, and Cl^- than before. All those reveal that waterchemical field changes toward salination and alkalization, water chemical type developstoward complex, and water quality is becoming poor gradually.（5） Theδ¹⁸O,δD values of groundwater concentrating along the rainfall distribution line,marks that groundwater is recharged by precipitation in Yaoba Oasis. Furthermore, thedistribution feature that theδ¹⁸0 andδD values of northeastern are bigger than those ofsouthwestern, indicates the two regions have different groundwater cycles. Namely, thegroundwater of southwest area is almost kept in a colder climate environment; while in theNortheast area, due to water cycle is more positive for the environment, the groundwaterrecharge is in a warmer climate environment. Vertically, the hydrogen and oxygen isotopecontent are very similar with each other, indicating that all layers of the groundwater keepclose hydraulic contact in vertical direction.（6） The measured value of tritium in its surrounding areas groundwater approve that: inYao Oasis area, the Quaternary pore groundwater originated from precipitation, whichbasically is recharged vertically by precipitation Unit preserved by storage accumulationrather than modern atmospheric precipitation and surface water. but recharge. There is littlegroundwater recharge of the Quaternary groundwater in the Oasis’s east mountain valley tothe study area. The pore phreatic water of north part and surface floods are the main rechargesource of Oasis’s groundwater. The diving of Western desert is another source of supply.（7） The results of shallow groundwater hydrogeochemical simulation in study area showthat: the mixing action plays a crutial role in the formation of current water chemistry condition of shallow groundwater. However, the process is not simple mechanical mixing; inthe north, along with the mixture of three supply sources （shallow groundwater, floods, desertdiving）, some reaction occurred involving calcite dissolution, dolomite and gypsumprecipitation, carbon dioxide escape, calcium ion parsing and sodium ion adsorption; in TaoSuLakes region of the southwest, along with two types of recharges （shallow groundwater andflood） mixing, the precipitation of dolomite, gypsum and rock salt, the dissolution of calcite,fluorite and dissolved carbon dioxide, as well as Absorption of calcium and sodium ions alsotake place. Analysis of deep groundwater hydrogeochemical simulation results interpret that:in the process of deep groundwater flowing, water-rock interaction occurred refering to manyreactions. Dolomite, gypsum, rock salt, potassium salt dissolved into groundwater, and theirtransfer capacity changed from small and large, which caused calcite precipitation. At thesame time, cations undertook exchange between Na+, Ca2+ on the flowing path. In theprocess, Ca2+ entried into the water, and Na+ was adsorbed to the surface of the aquiferparticles. This reaction caused a significant change of water chemical compositions for theflow in the northern part, showing the water chemistry characteristics from recharge to runoffzone.（8） The factors affecting and determining the groundwater chemical characteristics of theOasis and their evolution laws include physical chemistry action, soluble salt content insurface soil as well as man-made acitivity.更多还原