洞庭湖湖区降水-地表水-地下水同位素特征

为探明洞庭湖湖区水体稳定同位素时间和空间上的变化规律,弄清各水体间的相互关系,分别在2012年4月和8月对区域内具有代表性的采样点进行了地表水和地下水的采样。通过对样品进行D、18O同位素分析,结合全球大气降水同位素监测网（GNIP）公布的1988—1992年间长沙降水同位素数据,发现湖区年内受不同盛行风影响,降水及地表水的同位素存在较大的季节性差异,4月份同位素富集,8月份贫化。此外,河水、湖水同位素也呈现明显的空间差异。两个时期地表水的水线斜率均小于当地降水线,地表水在两个时期均存在蒸发作用。虽然地表水和地下水的来源均为大气降水,但与地表水相比,地下水同位素季节变化较小,地下水接受地表水补给是一个较为长期的过程。     

Variographic analysis of water table data from the Oued-Souf phreatic aquifer, northeastern part of the Algerian Sahara

Phreatic aquifers present many serious problems for local public authorities, and they have done so especially for the water resources managers in Oued-Souf, Algeria, since 1980. Recently, a perturbation in piezometric level was observed in Oued-Souf. The spatial distribution of piezometric level data was analyzed by applying geostatistical methods, which provide an indication of the uncertainty of the estimation using the computer software VARIOWIN 2.2. In this paper, the evolution of the piezometric level by referring to other research campaigns was studied. Campaigns were conducted from March 1993 to April 2002. In the beginning, elementary statistics has been carried out to understand the statistical distribution and performed an analysis of variance so that two campaigns could be chosen for comparison. Geostatistics for modeling and cartography were applied. The results show that piezometric levels admit power model that the direction of groundwater flow is from south to north and that, due to the return of irrigation water (there is no drainage system), water levels increase in places like Foulia (1.35 m), northwest of Oued-Souf (1.43 m), Kouinine (4.58 m), and Ouzitene (3.01 m). The water levels also decrease in places like Guemar, Dmitha, Rhamra, and Djeldida, from between −2 and −6 m, due to excessive pumping of groundwater.     

Recharge and sustainability of a coastal aquifer in northern Albania

The River Mati in Albania has formed a coastal plain with Holocene and Pleistocene sediments. The outer portion of the plain is clay, with three underlying aquifers that are connected to an alluvial fan at the entry of the river into the plain. The aquifers supply water for 240,000 people. Close to the sea the aquifers are brackish. The brackish water is often artesian and found to be thousands of years old. Furthermore, the salinity, supported by δ¹⁸O results, does not seem to be due to mixing with old seawater but due to diffusion from intercalated clay layers. Heavy metals from mines in the upstream section of River Mati are not an immediate threat, as the pH buffering of the river water is good. Moreover, the heavy metals are predominantly found in suspended and colloidal phases. Two sulphur isotope signatures, one mirroring seawater sulphate in the brackish groundwater (δ³⁴S >21 ‰) and one showing the influence of sulphide in the river and the fresh groundwater (δ³⁴S <10 ‰), indicate that the groundwater in the largest well field is recharged from the river. The most serious threat is gravel extraction in the alluvial fan, decreasing the hydraulic head necessary for recharge and causing clogging of sediments.     

水化学—稳定同位素技术在岩溶水文地质研究中的应用

水化学—稳定同位素技术在岩溶水系统分析中得到了广泛的应用,尤其是在指示岩溶水文地球化学过程、识别岩溶水补给循环途径、溶质溯源及岩溶水污染监测防控等方面显示了独特的优势,产生了丰富的成果。本文着重阐述了环境稳定同位素δD、δ18O、87Sr/86Sr的工作原理,及水化学—稳定同位素技术在岩溶水文地质研究中的应用。此外,论文还以娘子关泉域和北京西山岩溶水系统为例,介绍了运用水化学—稳定同位素技术分析岩溶水系统补给的思路和方法,展望了该技术在岩溶水文地质和岩溶生态环境领域中的应用前景。     

The Tunisian Jurassic aquifer in the North African Sahara aquifer system: information derived from two-dimensional seismic reflection and well logs

Southern Tunisia is an arid area where socio-economic activities are dependent on groundwater resources. The presented study aims to better characterize the Jurassic aquifer based on geological and geophysical data, with a view to develop a rational exploitation program. Well logs are used to precisely determine the position and composition of the known Jurassic aquifer layers and to identify others able to produce good quality water. The logs show that limestones, sandstones and dolomites of the Krachoua, Techout and Foum Tataouine formations are the main Jurassic aquifers. Sixty-eight seismic-reflection sections are integrated within this study. The interpolation between the interpreted sections leads to the construction of isochronous isopach maps and geoseismic sections, and their analysis finds that compressive and extensive tectonic deformations have influenced the Jurassic aquifer geometry. The Hercynian orogeny phase manifestation is remarkable in that there are several stratigraphic gaps in the Jurassic sequence. The E–W, NW–SE, and NNW–SSE accidents, reactivated in normal faults since the Permian to Lower Cretaceous epochs, have generated the structures found in the Jurassic series, such as subsided and raised blocks. Their syn-sedimentary activity has controlled the thickness and facies of these series. The Cretaceous, Tortonian and Post-Villafranchian compressions are responsible for the Jurassic-deposits folding in some localities. The highlighted tectonic and sedimentary events have an important impact on the Jurassic aquifer function by favoring the Jurassic aquifer interconnections and their connections with the Triassic and Cretaceous permeable series.     

Moisture source in the Hyblean Mountains region (south-eastern Sicily, Italy): Evidence from stable isotopes signature

Here the authors present results of an isotope study on precipitation collected during a 2-a period from a rain-gauge network consisting of 6 stations located at different elevations in the Hyblean Mountains (HM) region, in south-eastern Sicily. The slope of the local meteoric water line (δD = 6.50 δ¹⁸O + 9.87) obtained for the region suggests that precipitation is affected by evaporation during rainfall events. The main variations in rainwater isotope composition are due to seasonal effects and elevation. An average ²H excess value of +21.2‰ was found for precipitation events less affected by evaporation (i.e. when the rainfall was >65 mm/month). The spatial distribution of O isotope composition of precipitation shows a negative gradient from east and south to the inner areas. The depositional rate of Cl, used as a tracer of the origin of air masses, is highest at the coastal rain-gauges (SR and MRG stations) and lowest on the northern flank of the HM region (SC station). Based on these findings, a model is proposed for the origin of precipitation in the HM region, which assumes that a Mediterranean-derived component is the main source of moisture in the studied area. D/H and ¹⁸O/¹⁶O ratios of inferred meteoric recharge waters were also compared with the isotope composition of waters collected from the main local springs and wells. The best linear fit of the δ¹⁸O vs δD relationship for Hyblean groundwater is δD = 4.85 δ¹⁸O–2.01. The enrichment of heavy isotopes in Hyblean groundwater is probably due to evaporation occurring after precipitation events or to a recharging contribution from surface waters (lakes or rivers) enriched in heavy isotopes.     

Nitrate contamination in a shallow urban aquifer in East Ukraine: evidence from hydrochemical,stable isotopes of nitrate and land use analysis

A combined hydrochemical and stable isotope approach was used to investigate the origin of nitrate in the shallow unconfined groundwater of Kharkiv city, Eastern Ukraine. The contamination was investigated in the context of land use within the catchment area. The observed enrichment of sulfate, chloride and nitrate suggests significant groundwater contamination in the shallow urban aquifer, which is widely used as drinking water source for the urban population. Characteristic nitrate/chloride ratios as well as stable isotope ratios (N and O) of nitrate in the most contaminated springs confirmed that septic waste from leaky sewer systems was the main source of nitrate contamination in the groundwater. Nitrate contamination is linked to the type of land use and sewage treatment regime in the catchment area. It is also modulated by the regional hydrogeology, which determines the susceptibility of a given aquifer toward groundwater pollution. A more quantitative assessment of nitrate sources based on the nitrate isotope analysis alone is rather difficult. However, our study confirms that the combination of hydrochemical tracers, robust land-use analysis and nitrate stable isotope measurements represents a valuable approach to identify the origin of the nitrate contamination.     

南水北调中线河南省受水区浅层地下水水位演化规律

南水北调中线工程供水后对河南省受水区浅层地下水位、用水结构等产生了重要影响。首先回顾了河南省平原区以往地下水位埋深变化,并通过收集、统计2008—2018年河南省受水区浅层地下水位的监测成果,基于ArcGIS软件,针对南水北调中线供水前后河南省受水区浅层地下水位变化进行量化分区;结合降水量、地下水资源量、供水量等资料对供水前后河南省受水区用水结构变化等进行分析。结果表明:自20世纪60年代至2008年,河南省平原区浅层地下水位平均埋深整体逐渐增加;河南省受水区地下水资源量随降水量增加呈线性增加趋势;南水北调中线一期供水后,2015—2018年平均地下水供水量在地下水资源量中的占比较2008—2014年减少9.55%;受水区浅层地下水位有所回升,且主要体现在埋深 > 8~12 m范围向埋深 > 4~8 m及≤4 m范围的转变,埋深 > 12~16 m及 > 16~20 m范围在受水前后基本保持不变,埋深 > 20 m的区域范围有所减少;2008—2014年各监测点分布县区的浅层地下水位呈下降趋势,2015—2018年供水期间有2/3以上县区浅层地下水位逐渐恢复;农林渔业用水和工业用水占比在供水后均有所减小,城乡生活、环境综合用水占比增加明显。研究结果表明南水北调中线工程对河南省受水区浅层地下水位恢复及缓解供水矛盾问题等产生积极有效的影响。      

Alleviating drought and water scarcity in the Mediterranean region through managed aquifer recharge

Drought and water scarcity can significantly impair the sustainable development of groundwater resources, a scenario commonly found in aquifers in the Mediterranean region. Water management measures to address these drivers of groundwater depletion are highly relevant, especially considering the increasing severity of droughts under climate change. This study evaluates the potential of managed aquifer recharge (MAR) to offset the adverse effects of drought and water scarcity on groundwater storage. Los Arenales aquifer (central Spain), which was unsustainably exploited for irrigation in the second half of the twentieth century, is employed as a case study. Two neighbouring zones within this aquifer are contrasted, namely, Los Arenales (LA) and Medina del Campo (MC). The primary difference between them in terms of water resources management is the wide-scale implementation of MAR systems in LA since the early 2000s. Several groundwater statistical methods are used. Groundwater-level trend analysis and average piezometric levels show in LA a faster recovery of aquifer storage and less susceptibility to drought compared to MC. On the other hand, standardised precipitation indexes and standardised groundwater level indexes of detrended groundwater-level time series, which do not include the effects of MAR, show that LA can be more negatively affected by drought and groundwater abstraction. The sharper recovery of piezometric levels in LA when considering MAR, and bigger drought impacts observed when the effects of this measure are removed, demonstrate that MAR can effectively alleviate the impacts of water scarcity and drought, providing an adaptation solution to climate change worldwide.

     

Biogeochemistry of the stable hydrogen isotopes

The fractionation of H isotopes between the water in the growth medium and the organically bonded H from microalgae cultured under conditions, where light intensity and wavelength, temperature, nutrient availability, and the H isotope ratio of the water were controlled, is reproducible and light dependant. All studies were based either on the H isotope ratios of the total organic H or on the lipids, where most of the H is firmly bonded to C. H bonded into other macromolecules, proteins, carbohydrates and nucleic acids, does not exchange with water, when algae are incubated in water enriched with deuterium. Only after the destruction of quaternary H bonds are labile hydrogens in macromolecules free to exchange with water. By growing algae (18 strains), including blue-green algae, green algae and diatoms, in continuous light, the isotope fractionations in photosynthesis were reproducibly ?93 to ?178 %. depending on the organism tested. This fractionation was not temperature dependent. Microalgae grown in total darkness with an organic substrate did not show the isotope fractionation seen in cells grown in light. In both light- and dark-grown algae, however, additional depletion of deuterium (?30 to ?60%.) in cellular organic matter occurs during the metabolism of carbohydrates to form lipids. Plants from several natural populations also fractionated isotopes during photosynthesis by an average of ?90 to ?110%. In addition, the organically bonded H in nonsaponifiable lipids was further fractionated by ?80%. from that in saponifiable lipids, isolated from two geographically distinct populations of marsh plants. This difference between H isotope ratios of these two groups of lipids provides an endogenous isotopic marker.     

藏南岗巴地区上白垩统海相碳酸盐岩碳稳定同位素研究

本文对藏南岗巴地区上白垩统海相碳酸盐岩的碳稳定同位素组成特征及变化趋势进行了研究,对比分析了藏南其它地区及欧洲同时代地层,认为岗巴地层的碳稳定同位素的记录很好地响应了白垩纪期间全球性的缺氧事件。通过对岗巴地区岩石地层学及区域环境的分析说明,全球性的海平面升降及板块运动造成了大洋溶解氧含量的波动是碳稳定同位素δ¹³C值偏移的根本原因。     

Salinisation origin and hydrogeochemical behaviour of the Djerid oasis water table aquifer (southern Tunisia)

The shallow Plio-Quaternary (PQ) water table, present over almost the whole Djerid and Chott El Gharsa basins (southern Tunisia), is used as a complement of oases irrigation, especially in summer season. The simplicity of the Plio-Quaternary lithology is confronted to the complexity of the mineralisation mechanisms and the water origin in this aquifer. An approach combining the use of water-dissolved chemical species and isotopic contents has been used to better understand the PQ behaviour under severe increasing exploitation and to determinate the origin of its different water bodies. In southern Tunisia, the aquifer system is composed of the upper unconfined PQ aquifer, the intermediate semi-confined/confined Complexe Terminal (CT) and the deeper confined Continental Intercalaire (CI). Chemical analyses highlighted an origin of mineralisation in close relationship to the dissolution of both sulphated salts (MgSO₄ and Na₂SO₄) and chlorinated salts (NaCl and MgCl) abundant in the surface and subsurface gypsum crust. Positive correlations between gypsum anhydrite, mirabilite, thenardite and halite saturation indexes with respective mineral species, confirm evaporites dissolutions. Isotopic data showed that in addition of sporadic rainfall events, there is a contribution from the CI and the CT Saharan groundwaters, recharging the PQ aquifer in the study area. Return flow irrigation is partly affected by evaporation, before recharging the shallow aquifer, in oases limits.     

Recharge estimation from discrete water-table datasets in a coastal shallow aquifer in a humid subtropical climate

A time-series approach to the estimation of recharge rate in unconfined aquifers of highly variable water level is proposed. The approach, which is based on the water-table fluctuation method (WTF), utilizes discrete water-level measurements. Other similar techniques require continuous measurements, which makes them impossible to apply in cases where no data from automatic loggers are available. The procedure is deployed at the Ressacada Farm site, southern Brazil, on a coastal shallow aquifer located in a humid subtropical climate where diurnal water-level variations of up to 1 m can follow a precipitation event. The effect of tidal fluctuations on the groundwater levels is analyzed using a harmonic component builder, while a time-variable drainage term is evaluated through an independent analysis and included in the assessment. The estimated recharge values are compared with those obtained from the continuous measurements showing a good agreement with the approaches for discrete dataset intervals of up to 15 days. Subsequently, the estimated recharge rates are incorporated into a transient groundwater-flow model and the water levels are compared showing a good match. Henceforth, the approach extends the applicability of WTF to noncontinuous water-level datasets in groundwater recharge studies.     

蒸发皿中水面蒸发氢氧同位素分馏的实验研究

气象要素与蒸发密切相关,通过室内外不同气象条件下的器皿水蒸发实验,获得了水面蒸发氢氧稳定同位素分馏因子与气象要素的关系。实验结果表明,随着蒸发的进行,剩余水体中逐渐富集重同位素;自由水体蒸发同位素分馏在垂线上有分层现象,表层水体同位素值比垂线平均的同位素值略富集;不同温度条件下的室内蒸发实验中,温度越高,液-气间分馏系数越小,相应于同一剩余水体体积比,剩余水体稳定同位素值则越低。室外器皿水自由蒸发实验中得出的蒸发线方程斜率较大地偏离了当地降水线,表明实验期间水体蒸发分馏作用较明显。该研究为进一步揭示水体蒸发分馏规律提供了可靠的实验依据。     

多年冻土区风火山流域降水河水稳定同位素特征分析

由于多年冻土区流域土壤冻融过程对水循环影响的复杂性,水循环物理过程观测存在困难和不足,而利用稳定同位素方法可以有效地解决该问题。因此,基于2009年长江源风火山流域夏季定点降水和河水δD和δ¹⁸O,对研究区降水河水稳定同位素特征进行分析。结果表明,研究区夏季降水δD和δ¹⁸O受到降水量和温度的双重影响,即受海洋性和大陆局地气团的交替影响。河水氢氧同位素的季节变化和空间差异与壤中流、地下水补给河流的季节差异和植被覆盖的空间差异有关。随着地温升高和土壤冻融锋面的迁移,河水补给来源和同位素特征发生改变,表明土壤冻融变化对多年冻土流域径流过程起到重要作用。此外,蒸发分馏作用是研究区河水同位素的重要影响因素。     

大陆俯冲带流体活动:超高压变质岩矿物水含量和稳定同位素制约

对超高压变质岩中含水矿物和名义上无水矿物的地球化学研究,极大地深化了我们对大陆碰撞带地壳俯冲和折返过程中流体体制的认识。就流体体制和化学地球动力学来说,有关研究在大别-苏鲁造山带进行的最为详细,因此已经成为研究大陆俯冲带变质的典型地区。本文以大别-苏鲁造山带为对象,从矿物水含量的角度,结合稳定同位素论述了大陆俯冲带流体活动。超高压变质岩中名义上无水矿物含有大量的水,以结构羟基和分子水形式存在。名义上无水矿物中结构羟基和分子水出溶与含水矿物分解共同构成了折返过程中退变质流体的主要来源。名义上无水矿物所释放的水以富集轻的氢氧同位素为特征,而含水矿物分解则提供了富集D的流体来源。折返过程中,名义上无水矿物降压脱水存在亏损D的分子水的优先丢失和不同形式水之间的相互转化。不同岩性的水含量差异导致了它们在折返过程中不同的流体活动行为。大陆板块俯冲和折返过程中,在不同矿物、不同岩性以及板片不同部位之间存在水的再分配;板片的一部分作为富水流体的源,而另一部分可能作为汇。     

Evaluation of the groundwaters from the Stripa mine using stable chlorine isotopes

Groundwater samples and a rock leachate sample from the Stripa mine and south central Sweden have been analysed for their δ³⁷Cl values. Results reveal that the salinity found at depth in the groundwater is most likely derived form water–rock interaction. The overall distribution is one of δ³⁷Cl enrichment with depth and with chloride concentration. This trend is comparable to other sites in the Fennoscandian Shield where it is believed that deep groundwaters derive their δ³⁷Cl values from the local bedrock.     

Variations of stable hydrogen isotopes in plankton from a freshwater lake

The isotopic composition of the organically bonded hydrogen in micro plankton and zoo-plankton samples collected monthly from Lake Kinneret during 1972 and 1973 ranges between ?90 and ?130%. The temporal variations which have been observed in the deuterium content of the plankton samples, seem to be controlled by metabolic processes and not by variations in the temperature and in the deuterium content of the lake water. The organic material of the Zooplankton is consistently enriched in deuterium, by about 20%., as compared to that of the phytoplankton.     

Evaluation of nitrate source in surface water of southwestern China based on stable isotopes

Stable isotope tracing and analysis play an important role in interpretation of hydrological and ecological processes at the watershed scale and can provide information regarding the flow path, water source, nutrient loss and biogeochemical cycles of a system. In this study, environmental isotopes (δ¹⁸O-H₂O, δD, δ¹⁵N-NO₃ ^?, δ¹⁸O-NO₃ ^?) and chemical compositions of surface water in Guizhou Province, China, were measured to evaluate the primary sources of nitrate and characterize the processes affecting nitrate as well as its correlation with vegetation cover in karstic areas. The δ¹⁵N and δ¹⁸O-NO₃ ^? levels ranged from +1.3 to +9.8 ‰ and +4.7 to +16.9 ‰, respectively, which indicated that nitrate in water from the investigated area primarily originated from nitrification of soil organic matter during the sampling period. There was also a wide range of isotopes in the water and high contents of nitrate in karstic areas with poor vegetation cover, indicating that water and nutrient loss were serious problems hindering plant growth in the study areas. For example, there was a positive relationship between isotopic composition and nitrate content in the natural forest and negative relationship in Libo County nearby, which suggested that the nitrate fate was affected by land use and human disturbance.