阿拉善沙漠湿沙层水分来源同位素示踪

为弄清阿拉善沙漠湿沙层的水分来源,在该地区进行了人工模拟降水入渗的示踪试验。模拟单次降水量为59 mm,观察剖面最大入渗深度仅为46 cm,这一结果表明该地区的降水几乎不能通过沙层入渗到地下水中。对4个沙丘湿沙层剖面中不同深度的含水率、Cl-、δD与δ18O进行了分析,数据显示在蒸发能力极强的阿拉善地区,地下水是以薄膜水的形式,通过蒸发、凝结向地表运动,最终蒸发排泄。泉水、井水、湖水与土壤水中的同位素特征表明具有相同的补给源,均来自于地下水。推断横穿阿拉善地块的杂多-雅布赖断裂带与狼山-日喀则断裂带中可能存在地下水深循环通道,青藏高原河流、湖泊的渗漏水可能是阿拉善地下水的主要补给源。     

应用~2H、~(18)O同位素示踪华北平原石家庄包气带土壤水入渗补给及年补给量确定

采集2个不同深度包气带土壤水2 H、18 O同位素剖面ZK1,ZK2,应用天然稳定同位素2 H、18 O示踪的方法,研究了华北山前冲积平原石家庄地区包气带土壤水入渗补给的历史演化特征。结果显示,研究区内,以0.05m为取样间隔,δ2 H、δ18 O值可以明显指示出大气降水及灌溉水入渗补给时间—剖面深度位置的年际对应关系。ZK2的δ2 H、δ18 O值随着埋深的增大出现周期性的波动,具有分层现象的岩性差异并不明显,说明ZK2剖面以活塞流的入渗方式补给地下水。在0~3.90m深度,δ2 H、δ18 O值显示降水和灌溉水的入渗补给时间为2011年10月至2001年11月。18 O峰值位移法计算补给量的结果显示,降水、灌溉水通过包气带补给地下水的垂向运移速度为38.5~65.0cm/a,年均入渗补给量为131.3~185.3mm。同时,对比2003年及2005-2007年降水量数据,说明少雨年份农业灌溉用水量的大小对当地地下水的入渗补给量起着关键性作用。     

深循环地下水维系黄土高原风尘颗粒连续沉积

黄土高原地区的降水入渗试验表明,降水在入渗过程中受到了蒸发作用,并未入渗到潜水,土壤水中的氘氧同位素与地下水相近,这表明土壤水主要来自于地下水。外源水是黄土高原发源的河流、湖泊的主要补给源,当地的降水仅在汛期补给河流与湖泊。鄂尔多斯盆地黄土地区地下水的分水岭与基底断裂带的分布基本上重合,这暗示着地下水可能来自于基底断裂带,通过基底断裂带上涌的深循环地下水将风尘颗粒粘滞成颗粒团,形成了连续的风尘堆积,深循环的地下水成为维系风尘颗粒在黄土高原连续沉积的必要条件。分析黄土中CaCO3的物质不平衡和钙结核内部无生长层理以及碳氧同位素表现出高度均一性特征,得出黄土中的次生碳酸盐矿物也是由上涌地下水携带来的,并非大气降水入渗造成。调查发现,黄土塬规模的大小与塬轴对称中心钻孔的涌水量成正比关系,表明黄土塬风尘颗粒以对称形式沿着断裂连续地堆积,涌水量越大,所粘聚的风尘颗粒越多,塬的面积也越大,涌水量较小的断裂只能形成墚或峁结构。     

内蒙古鄂尔多斯西北土壤水流动示踪实验及自流井群补给源讨论

降水模拟实验证明,鄂尔多斯北部沙土层单次降水入渗最大深度小于1 m,降水在土壤中受到蒸发后排泄到大气中。实验证实,只有当土壤含水率达到最大田间持水率,吸附在土颗粒表面的薄膜水才能克服电磁引力转化为重力水,在重力的作用下继续下渗。鄂尔多斯北部的年降水量小而蒸发量大,降水入渗土壤不能形成累积效应,无法形成连续下渗的重力水流。同位素示踪分析表明,土壤水主要来源于地下潜水,结合土壤含水率与TDS分析证实,地下水是通过薄膜水与蒸发-凝结方式补给到土壤水中,薄膜水从高温区向低温区流动,对于等温的薄膜水而言,薄膜水从厚层向薄层流动。同位素分析表明,都思兔河流域的河水、泉水、井水、湖泊、土壤水接受相同的外源水补给。鄂尔多斯盆地降水比地表水与地下水明显富集重同位素,不符合补给区降水同位素特征。鄂尔多斯盆地地下水分水岭与基底断裂带重合,据此推断,外源水以深循环方式通过基底断裂带补给鄂尔多斯盆地,在干旱地区形成自流井群。     

基于氢氧同位素的华北平原降水入渗过程

华北平原地下水浅埋区水循环主要以垂直方向上的入渗、蒸发和蒸腾的方式存在,同位素可以作为一种有效"示踪剂"揭示降水入渗补给地下水的过程。选择华北平原中、东部地下水浅埋区的衡水和沧州为典型实验点,研究不同降水特征、土壤质地和植被条件下入渗过程的差异性。结果表明,土壤非均质条件下(沧州),降水入渗补给过程中伴随着蒸发、植被蒸腾作用以及与土壤前期水分的强烈混合作用,活塞流入渗的同时土壤100 cm深度可能还存在大孔隙优先流;土壤均质条件下(衡水),降水向下均匀入渗,入渗速度较快,土壤水运动以新水基本代替老水的活塞流为主要形式,并经过强烈的蒸发浓缩作用补给地下水。     

黄土丘陵区降水-土壤水-地下水转化实验研究

通过对黄土丘陵区燕沟流域2005~2007年雨季的多次降水、0~400 cm土层土壤水、沟道地表水、地下水(泉水、井水)水样中D和18O采样分析,研究了该区降水、土壤水、地表水、地下水的转化关系.结果认为:燕沟流域的降水线与中国、世界的降水线有明显区别,斜率和截距偏小;降水、地表水、土壤水、地下水逐渐富集δD和δ18O,且δ18O富集速度高于δD,由D和18O的蒸发分馏差异所致,可利用各类水体的δD和δ18O变化情况甄别水体之间的水量转化;土壤水δD和δ18O剖面在200 cm深度处出现低值区,应是降水补给到达该深度且土壤蒸发影响逐渐衰减共同作用的结果,其在200 cm以下逐渐升高则因为降水补给影响逐渐降低、土壤水本底同位素影响增强所致.由于380~400 cm深层土壤水的δD和δ18O对降水事件的响应存在,因此认为降水-地下水的转化存在,降水补给泉水的滞后期小于35 d.而对井水的补给滞后时间以及土壤水对地下水的补给量还需进一步研究.     

锡林河流域地表水和浅层地下水的稳定同位素研究

2006年4—9月,在从锡林河源头沿河流进行地表水和地下水同位素样品采集和分析的基础上,利用全球降水同位素监测网(GNIP)包头站的大气降水稳定同位素资料,结合锡林河流域的气象和水文资料,对锡林河流域大气降水、地表水和地下水稳定同位素进行了研究.结果表明:地下水中δ18O和δD值分别集中在-11.7‰～-14.9‰和-80‰～-89.5‰范围内,δ18O沿地下水流向有增加的趋势,大部分地下水中δ18O的季节波动性不大;河流干流δ18O和δD的年算术平均值从源区的-12.8‰和-94.5‰到入锡林河水库处的-10.0‰和-79.3‰,差值分别约为3‰和15‰.河水中的δ18O值沿流程增加而增大的现象可归结为受含有较高δ18O值的地下水补给作用和河水的蒸发作用的共同影响,其中对δ18O蒸发富集的研究显示,蒸发引起δ18O富集值为1‰.通过地下水线(GWL)和地表水线(SWL)及区域大气降水线(LMWL)的对比分析发现,在径流季节,降水对地表水的贡献小,地下水是地表水主要的补给源,地表径流基本是地下水的排泄.     

格尔木河流域平原区地下水同位素及水化学特征

通过对格尔木河流域天然水中H、O同位素的系统分析,根据地球水化学组分循环演化规律所对应流域不同类型水体的同位素组成的研究,结果表明流域地下水化学组分随流程增加溶滤作用增强,地下水中HCO3-逐渐减少,Cl-则增加。运用δD、δ18O和3H值建立了流域大气降水线方程,确定了山区河水非当年降水补给,河水以地下水补给为主、其次是冰雪融水和大气降水补给。山区降水δD、δ18O均值低于平原区,表明平原区降水受蒸发作用影响水中富重同位素。平原区地下水中的δD、δ18O值与河水基本一致,说明平原区地下水主要受河水出山后入渗补给。承压自流水δD和δ18O值与潜水基本一致,根据地下水的3H值确定早于潜水年龄,且随埋深增加δD、δ18O值减少的趋势,其年龄亦由新变老。     

新疆焉耆盆地水环境氢氧同位素特征及其指示作用

根据焉耆盆地开都河水及其两岸地下水中的氢氧稳定同位素资料及氘过量参数(d)值,分析了焉耆盆地内不同水体的δ(D)、δ(18O)和d值的分布规律,并得到地下水的主要补给来源及其与开都河水的相互作用关系;地下水的δ(D)在-87.60‰～-61.82‰间,δ(18O)在-10.90‰～-9.73‰间;开都河水的δ(D)在-71.95‰～-58.58‰间,δ(18O)在-9.57‰～-8.64‰间。结果表明:焉耆盆地内地下水和地表水同源于山区的降水和冰雪融水,且经历了较强的蒸发作用;地下水与地表水之间的直接水力联系较弱,深层地下水主要接受开都河水在洪积扇区的入渗补给,浅层地下水主要接受河流引水灌溉入渗;不同深度地下水之间的水力联系较为密切,为统一的地下水系统。     

降水量与地下水补给量的关系分析

降水入渗补给是地下水的主要补给源，研究降水与地下水的关系，主要是分析由于降水垂直入渗引起的地下水位的变化。本文主要通过对降水入渗机理、影响水入渗的因素、降水入渗补给量计算的研究，分析降水量与地下水补给量的关系。     

Relationships between precipitation,soil water and groundwater at Chongling catchment with the typical vegetation cover in the Taihang mountainous region,China

Vegetation cover plays an important role in the process of evaporation and infiltration. To explore the relationships between precipitation, soil water and groundwater in Taihang mountainous region, China, precipitation, soil water and water table were observed from 2004 to 2006, and precipitation, soil water and groundwater were sampled in 2004 and 2005 for oxygen-18 and deuterium analysis at Chongling catchment. The soil water was sampled at three sites covered by grass (Carex humilis and Carex lanceolata), acacia and arborvitae respectively. Precipitation is mainly concentrated in rainy seasons and has no significant spatial variance in study area. The stable isotopic compositions are enriched in precipitation and soil water due to the evaporation. The analysis of soil water potential and isotopic profiles shows that evaporation of soil water under arborvitae cover is weaker than under grass and acacia, while soil water evaporation under grass and acacia showed no significant difference. Both δ¹⁸O profiles and soil water potential dynamics reveal that the soil under acacia allows the most rapid infiltration rate, which may be related to preferential flow. In the process of infiltration after a rainstorm, antecedent water still takes up over 30% of water in the topsoil. The soil water between depths of 0–115 cm under grass has a residence time of about 20 days in the rainy season. Groundwater recharge from precipitation mainly occurs in the rainy season, especially when rainstorms or successive heavy rain events happen.     

Preliminary research on hydrogen and oxygen stable isotope characteristics of different water bodies in the Qilian Mountains,northwestern Tibetan Plateau

Hydrogen and oxygen stable isotope in water bodies is a widely used tracer in hydrological process studies. In order to provide a basis for stable isotopic characteristics in different water bodies at the high mountainous area of northwestern Tibetan Plateau, samples for river water, groundwater, soil water, and plant water were collected from 10 sites in the Qilian Mountains during July and August 2015, and then analyzed for δ¹⁸O and δD, respectively. Results indicated that the stable isotope values of soil water were mostly plotted below the global meteoric water line (GMWL), which suggested that evaporation made heavy isotope in soil water enriched. The stable isotope values of soil water were quite different in the top soil layer, but tended to be uniform in the deep soil layer. Furthermore, the stable isotope difference of plant water is related to climatic conditions, water isotopes utilized by plant, plant species, growing season, and so on. Additionally, the variation of δ¹⁸O values for river water and groundwater relatively coincided with each other, and this showed the recharge sources of above two water bodies may be consistent. The stable isotope values of river water and groundwater were mainly plotted on the upper left of GMWL, and the lower level of isotopic fractionation due to weak evaporation may accountable for this.     

Isotopes (δD and δ18O) in precipitation, groundwater and surface water in the Ordos Plateau, China: implications with respect to groundwater recharge and circulation

The characteristics of δD and δ¹⁸O in precipitation, groundwater and surface water have been used to understand the groundwater flow system in the Ordos Plateau, north-central China. The slope of the local meteoric water line (LMWL) is smaller than that of the global meteoric water line (GMWL), which signifies secondary evaporation during rainfall. The distribution of stable isotopes of precipitation is influenced by temperature and the amount of precipitation. The lake water is enriched isotopically due to evaporation and its isotopic composition is closely related to the source of recharge and location in the groundwater flow systems. River water is enriched isotopically, indicating that it suffers evaporation. The deep groundwater (more than 150?m) is depleted in heavy isotopes relative to the shallow groundwater (less than 150?m), suggesting that deep groundwater may have been recharged during the late Pleistocene and early Holocene, when the climate was wetter and colder than at present. All groundwater samples plot around the LMWL, implying groundwater is of meteoric origin. Shallow groundwater has undergone evaporation and the average evaporation loss is 53%. There are two recharge mechanisms: preferential flow, and the mixture of evaporated soil moisture and subsequent rain.     

Isotopic and hydrochemical data to restrict the origin of the groundwater in the Badain Jaran Desert,Northern China

Despite its extreme aridity, the Badain Jaran Desert is rich in groundwater. In the southeastern part of the desert, it is characterized by coexistence of high megadunes and a great number of lakes. Deuterium and oxygen 18 isotope compositions as well as hydrochemistry of groundwater, lake water, soil water and river water were investigated in detail to gain an insight into their relationships and the origin of the ground-water. The results show that the groundwater and the lake water are genetically related, but unrelated to local precipitation and the leakage of Heine River at northern slope of Qilian mountain. δD and δ¹⁸O values of deep soil water (lower than 40 cm) and groundwater plot on the same evaporation line E11, which shows that they have the same recharge source. The point of intersection between E11 and LMWL suggests that the groundwater originates from the water resource which has a weighted mean value that is lighter by some 6‰ δ¹⁸O than the local precipitation in Badain Jaran Desert. ³H data of water samples shows that the groundwater in Badain Jaran Desert originates from the water recharged after the nuclear test. The deep fault zone underground maybe the water circulation channel based on Helium analysis of groundwater. The result has guiding significance to rational exploitation and utilization of the local groundwater.     

Comparison of diurnal dynamics in evaporation rate between bare soil and moss-crusted soil within a revegetated desert ecosystem of northwestern China

Effects of biological soil crusts (BSCs) on soil evaporation is quite controversial in literature, being either facilitative or inhibitive, and therein few studies have actually conducted direct evaporation measurements. Continuous field measurements of soil water evaporation were conducted on two microlysimeters, i.e., one with sand soil collected from bare sand dune area and the other with moss-crusted soil collected from an area that was revegetated in 1956, from field capacity to dry, at the southeastern edge of the Tengger Desert. We mainly aimed to quantify the diurnal variations of evaporation rate from two soils, and further comparatively discuss the effects of BSCs on soil evaporation after revegetation. Results showed that in clear days with high soil water content (Day 1 and 2), the diurnal variation of soil evaporation rate followed the typical convex upward parabolic curve, reaching its peak around mid-day. Diurnal evaporation rate and the accumulated evaporation amount of moss-crusted soil were lower (an average of 0.90 times) than that of sand soil in this stage. However, as soil water content decreased to a moderately low level (Day 3 and 4), the diurnal evaporation rate from moss-crusted soil was pronouncedly higher (an average of 3.91 times) than that of sand soil, prolonging the duration of this higher evaporation rate stage; it was slightly higher in the final stage (Day 5 and 6) when soil moisture was very low. We conclude that the effects of moss crusts on soil evaporation vary with different evaporation stages, which is closely related to soil water content, and the variation and transition of evaporation rate between bare soil and moss-crusted soil are expected to be predicted by soil water content.     

断陷盆地高原面典型岩溶洼地旱季土壤水氢氧同位素时空差异特征

以云南省蒙自断陷盆地东山山区典型岩溶洼地为研究区,通过野外采集土壤样品与实验室测试分析相结合的方法,运用稳定同位素技术研究旱季不同深度土壤水氢氧同位素组成,揭示区内土壤水氢氧同位素时空变化特征,为进一步研究云南断陷盆地山区土壤水分运移机制和当地农业合理利用和管理水资源提供科学依据。结果表明:(1)土壤水δD、δ18O同位素值的变化范围分别为-128.3‰~-27.6‰和-17.5‰~2.5‰,平均值分别为-96.1‰±20.7‰和-12.3‰±3.7‰,降雨转化为土壤水和水分在土壤中重新分布时发生一定程度的氢氧同位素分馏。(2)旱季两个月份土壤水氢氧同位素组成发生变化,4月份土壤水δD、δ18O同位素平均值分别为-86.3‰±23.83‰和-10.6‰±4.3‰,显著高于2月份(δD:-106.1‰±9.5‰;δ18O:-14.1‰±1.6‰)(p<0.05),主要和4月份土壤水的蒸发作用强烈有关。(3)在空间上,坡地与洼地之间土壤水氢氧同位素组成存在差异,2月份坡地与洼地之间土壤水δD、δ18O值差异显著(p<0.05),洼地土壤水δD、δ18O比坡地偏轻;4月份坡地与洼地之间土壤水δD、δ18O值差异不显著(p>0.05)。(4)土壤垂直剖面方向上土壤水δD、δ18O值随着土壤深度的增加而减小,浅层土壤水δ18O和深层土壤水δ18O存在显著差异,2月份浅层土壤水δ18O比深层土壤水δ18O偏正2.8‰,4月份浅层土壤水δ18O比深层土壤水δ18O偏正10.5‰。      

巴丹吉林高大沙山表层孔隙水现象的疑义

1997-2003年对巴丹吉林沙漠中不同位置共7个高大沙山和1个流动沙丘表层2m内的孔隙水情况用常规方法作了观测,每年均在相近日期进行。孔隙水量随深度而增大,历年观测期间2m附近的体积含水量约3%,达到相应实测最大持水量的约65%或更高,25cm至1m孔隙水δ18O的正值表明它经过了反复补给-蒸发过程。观测了雨后入渗深度及其在沙丘120m坡面上的分布,另由历年短期能量平衡测验获得沙山陆面蒸发和凝结概念。认为当地年降水量和凝结量不足以对沙山2m表层内的孔隙水现象作出解释,疑另有与大尺度地下水系统相关的补给源。     

Application of HYDRUS-1D in understanding soil water movement at two typical sites in the North China Plain

Recharge and discharge, such as rainfall infiltration and evapotranspiration in vertical direction, are major processes of water cycle in the shallow groundwater area of the North China Plain. During these processes, soil water movement in the unsaturated zone plays an important role in the transformation from rainfall infiltration to groundwater. The soil water movement models were developed by using HYDRUS-1D software at two typical experimental sites in Cangzhou (CZ) and Hengshui (HS) with different soil, vegetation and similar climate conditions. As shown in the results, the comparison in precipitation infiltration features between the two sites is distinct. The soil water experiences strong evaporation after precipitation infiltration, which accounts for 63% of the total infiltration at the HS site where the soil is homogenous. It is this strong evaporation effect that leads to slight increase of soil water storage. At the CZ site, where the soil is heterogeneous, the evaporation effect exists from July to October of the simulation period. The total evaporation accounts for 33% of the total infiltration, and the evaporation rate is slow. At the end of the simulation period, the soil water storage increases and the water table decreases, indicating a strong storage capacity at this site.     

乌兰布和沙漠北部地下水资源的环境同位素探讨

工作范围在乌兰布和沙漠北部,面积共约4200km2.年平均降水量85～140mm,由西南向东递增,降水同位素组成δD～δ18O恰与Craig线一致,并与阿拉善地区相同.测得地下水中同位素含量范围,δ18O为-74‰～121‰,氚为0～190TU,14C为17～97pMC.由地下水同位素组成区别出与降水线平行或相交的6种类型.从所有地下水水点,以及可能有补给关系的其它水点的各类同位素关系,包括δ18O,T,δ13C和pMC,识别出两类承压水的各3个补给源和潜水的3个补给源,并区别出一组氚含量极低的潜水,对不同位置的承压水和潜水,由其同位素关系估算出了各补给源的组成和变幅.