The deep Cretaceous aquifer in the Aleppo and Steppe basins of Syria: assessment of the meteoric origin and geographic source of the groundwater

A drilling project was carried out in Syria to assess the potential of the deep groundwater resources of the Cretaceous aquifer, composed of Cenomanian-Turonian limestones and dolomites. In this context, isotope (¹⁴C, ³H, δ¹³C, δ¹⁸O, δ²H) and hydrochemical analyses were performed on wells in and around the Aleppo and Steppe basins. The interpretation includes complementary results from published and unpublished literature. The results provide evidence that many new wells pump mixed groundwater from the Cretaceous aquifer and the overlying Paleogene aquifer. Radiocarbon measurements confirmed dominating Pleistocene groundwater in the Cretaceous aquifer and mainly Holocene groundwater in the Paleogene aquifer. Most groundwater in the Cretaceous aquifer seems to be recharged in the western limestone ridges, stretching from Jebel az Zawiyah (south of Idlep) via Jebel Samane (south of Afrin and A’zaz) to the region north of Aleppo, and in the Northern Palmyrides mountain belt. Some recharge also occurs around the basalt plateau of the Jebel al Hass, south east of Aleppo. It is concluded that the Taurus Mountains and the Euphrates River do not recharge the Cretaceous aquifer. The sources of recharge seem to be occasionally occurring intensive winter storms that approach from Siberia.     

Use of the subsurface thermal regime as a groundwater-flow tracer in the semi-arid western Nile Delta,Egypt

Temperature profiles from 25 boreholes were used to understand the spatial and vertical groundwater flow systems in the Western Nile Delta region of Egypt, as a case study of a semi-arid region. The study area is located between the Nile River and Wadi El Natrun. The recharge areas, which are located in the northeastern and the northwestern parts of the study area, have low subsurface temperatures. The discharge areas, which are located in the western (Wadi El Natrun) and southern (Moghra aquifer) parts of the study area, have higher subsurface temperatures. In the deeper zones, the effects of faults and the recharge area in the northeastern direction disappear at 80 m below sea level. For that depth, one main recharge and one main discharge area are recognized. The recharge area is located to the north in the Quaternary aquifer, and the discharge area is located to the south in the Miocene aquifer. Two-dimensional groundwater-flow and heat-transport models reveal that the sealing faults are the major factor disturbing the regional subsurface thermal regime in the study area. Besides the main recharge and discharge areas, the low permeability of the faults creates local discharge areas in its up-throw side and local recharge areas in its down-throw side. The estimated average linear groundwater velocity in the recharge area is 0.9 mm/day to the eastern direction and 14 mm/day to the northwest. The average linear groundwater discharge velocities range from 0.4 to 0.9 mm/day in the southern part.     

Stable isotope geochemistry of dissolved chloride in relation to hydrogeology of the strongly exploited Quaternary aquifers,North China Plain

Deep Quaternary groundwater is the main source for industrial, domestic, and agricultural water supply in the North China Plain (NCP). There is currently a regional decline of groundwater levels, deterioration of water quality and environmental geological problems induced by increasing exploitation of the NCP Quaternary aquifer system. To trace sources and transport processes of dissolved Cl⁻ in a regional aquifer system and to reveal hydrogeological characteristics of Quaternary complexes, δ³⁷Cl, δ¹⁸O and δD, and chemical compositions (including F⁻, Cl⁻, Br⁻) of the deep groundwater sampled from the northern flow system of the NCP were measured along the west–east groundwater flow paths. The measured δ³⁷Cl values decreased from 0.39‰ to −2.22‰ (SMOC) along the groundwater flow direction, with increasing Cl⁻ concentrations. Marine aerosol input via rainfall is the main source of Cl⁻ in the deep groundwater near the recharge areas, and subsequent evaporation/evapotranspiration appears to be responsible for Cl⁻ accumulation. Mixing of recharge water with water of high-Cl⁻ and low-δ³⁷Cl accounts for the pattern of δ³⁷Cl and Cl⁻ concentration observed in Aquifer-3 along the west–east transect. The water with high-Cl and low-δ³⁷Cl is likely from pore water released from compacted clays induced by over-exploitation of deep groundwater, suggesting that clay is a dominant subsurface source of Cl⁻ for groundwater where a regional depression cone is present in the Quaternary aquifers. The groundwater of Aquifer-4 in the Huang-Hua depression is potentially mixed with an upward flux of Cl⁻ from the Neogene aquifer through subvertical faults. Diffusion and ion filtration are two mechanisms invoked to explain the highly negative δ³⁷Cl data for groundwater of Aquifer-4 in the Yanshan–Haixing areas, which provides new insight into solute migration and the hydraulic relationship in the strongly exploited groundwater system. This study using the conservative solute Cl⁻ provides additional important information for further investigations of the geochemistry of a wide range of reactive solutes in the Quaternary aquifer system, so guiding water resource management.     

Identifying the recharge sources and age of groundwater in the Songnen Plain (Northeast China) using environmental isotopes

The recharge sources and groundwater age in the Songnen Plain, Northeast China, were confirmed using environmental isotopes. The isotopic signatures of the unconfined aquifers in the southeast elevated plain and the north and west piedmont, cluster along local meteoric water lines (LMWLs) with a slope of about 5. The signature of source water was obtained by the intersection of these LMWLs with the regional meteoric water line (RMWL). This finding provides evidence that the recharge water for these areas originate from the Changbai Mountains and the Low and High Hingan Mountains, respectively. Groundwater in the unconfined aquifer in the low plain yields a LMWL with a slope of 4.4; its nitrate concentration indicates the admixture of irrigation return flow. The δ-values of the unconfined aquifer in the east elevated plain plot along the RMWL, reflecting recharge by local precipitation. The mean residence time of groundwater in these aquifers is less than 50?years. However, the ¹⁴C age of the groundwater in the confined Quaternary aquifer ranges from modern to 19,500?years, and in the Tertiary confined aquifer from 3,100 to 24,900?years. Modern groundwater is mainly recharged to the Quaternary confined aquifer on the piedmont by local precipitation and lateral subsurface flow.     

A geochemical study of the impact of irrigation and aquifer lithology on groundwater in the Upper Yakima River Basin,Washington, USA

The Yakima River, a major tributary of the Columbia River, is currently overallocated in its surface water usage in part because of large agricultural water use. As a result, groundwater availability and surface water/groundwater interactions have become an important issue in this area. In several sub-basins, the Yakima River water is diverted and applied liberally to fields in the summer creating artificial recharge of shallow groundwater. Major ion, trace element, and stable isotope geochemistry of samples from 26 groundwater wells from a transect across the Yakima River and 24 surface waters in the Kittitas sub-basin were used to delineate waters with similar geochemical signatures and to identify surface water influence on groundwater. Major ion chemistry and stable isotope signatures combined with principal component analysis revealed four major hydrochemical groups. One of these groups, collected from shallow wells within the sedimentary basin fill, displays temporal variations in NO₃ and SO₄ along with high δ¹⁸O and δD values, indicating significant contribution from Yakima River and/or irrigation water. Two other major hydrochemical groups reflect interaction with the main aquifer lithologies in the basin: the Columbia River basalts (high-Na groundwaters), and the volcaniclastic rocks of the Ellensburg Formation (Ca–Mg–HCO₃ type waters). The fourth major group has interacted with the volcaniclastic rocks and is influenced to a lesser degree by surface waters. The geochemical groupings constrain a conceptual model for groundwater flow that includes movement of water between underlying Columbia River basalt and deeper sedimentary basin fill and seasonal input of irrigation water.     

Characterization of surface water and groundwater in the Damascus Ghotta basin: hydrochemical and environmental isotopes approaches

The hydrochemistry of major ions and environmental isotope compositions (¹⁸O, ²H and tritium) of water samples have been used to investigate the characteristics of rainfalls, surface water and groundwater in the Damascus Ghotta basin. The groundwater salinity in the Damascus Ghotta basin gradually increases, as the groundwater moves from western to south-eastern and north-eastern parts of the basin. A strong relationship exists between the Barada river and the surrounded groundwaters, mainly in terms of recharge by infiltration of surface waters. The groundwater quality in the Adra region has clearly become less saline as a result of establishment of the sewage-water-treatment station in this area since 1997. The uncommon depleted stable isotope concentrations in the vicinity of Al-Ateibeh Lake and Adra valley could be interpreted as a result of sub-flow recharge from the Cenomanian–Turonian aquifer, mostly prolonged along the Damascus Fault, which forms direct contact between this complex and the Quaternary alluvium aquifers. The extensive exploitation of water from the Cenomanian–Turonian aquifer for drinking water supply would shortly be reflected by a gradual decline of the groundwater table in the Damascus Ghotta basin. Amelioration of water quality in the Damascus basin still requires further management strategies and efforts to be taken within the forthcoming years.     

Recharge rate estimation in the Mountain karst aquifer system of Figeh spring, Syria

Figeh watershed spring is one of the important groundwater aquifer, which is considered a major source for drinking waters of Damascus city and countryside. The origin identification and recharge estimates of groundwater are significant components of sustainable groundwater development in this Mountain karst aquifer of Figeh spring. During the period 2001–2009, monthly groundwater and precipitation samples were taken and the isotopic compositions of δ¹⁸O, δ²H, and chloride contents were analyzed to identify groundwater origins and to estimate recharge rates. The δ¹⁸O, δ²H of the groundwater show that the groundwater recharge is of meteoric origin. The chloride mass balance (CMB) method was used to quantify recharge rates of groundwater in the Mountain karst aquifer of Figeh spring. The recharge rate varies from 192 to 826 mm/year, which corresponds to 43 and 67% of the total annual rainfall. Recharge rates estimated by CMB were compared with values obtained from other methods and were found to be in good agreement. This study can be used to develop effective programs for groundwater management and development.     

Recharge into Southern High Plains aquifer—possible mechanisms,unresolved questions

The High Plains aquifer in the Southern High Plains (Texas and New Mexico), consisting of Tertiary, Cretaceous, and Triassic formations, has traditionally been considered to be recharged by its uppermost water-bearing unit, the Tertiary Ogallala aquifer. This article provides hydrologic, chemical, and isotopic evidence that in the Southern High Plains: (1) Cretaceous rocks actually contain independent recharge sources; (2) Triassic rocks cannot currently be recharged by the Ogallala aquifer in significant quantities; and (3) in places, both Cretaceous and Triassic aquifers recharge the overlying Ogallala aquifer. On the basis of chemical and isotopic data, playa lakes seem to act as the predominant recharge source of the Ogallala aquifer, suggesting recharge rates greater than 30 mm/yr, as opposed to the much lower rates reported by others. The Cretaceous aquifers are being recharged by cross-formational flow from the Ogallala aquifer but also from overlying Quaternary sands and the underlying Triassic aquifer in eastern New Mexico. Current recharge into the Triassic aquifer may be insignificant.     

云应盆地东北部含水层结构特征及地下水转化模式

云应盆地东北部属鄂北贫水地区,赋存于古近系—第四系含水层中的地下水是当地生产、生活用水的主要来源,亟需查明含水层的结构、含水层间地下水的转化关系等基本条件,为研究区内合理开发利用地下水提供依据。本研究通过野外水文地质调查、水文地质钻探工作,将研究区划分为单层含水层与双层含水层结构两个亚区（6个小区）。并通过地下水水位动态长期监测,获取了区内不同含水层的水位动态变化特征,分析各含水层之间的水力联系,建立了区域地下水转化的概念模式,即:研究区地下水以接受山前降雨入渗及风化裂隙水侧向径流补给为主,主要以水平径流的形式经古近系孔隙-裂隙含水层及第四系孔隙承压含水层往澴水方向运移,而后进入第四系孔隙潜水含水层。地下水和地表水在不同季节补排模式不同,雨季地表水（澴水）补给地下水,旱季地下水向地表水（澴水）排泄。古近系孔隙-裂隙水与上覆第四系孔隙水联系密切互为补给,共同构成具有统一水力联系的垂向多层结构的含水系统。独特的含水层结构决定了区内地下水接受降水补给的条件较差,地下水可开采资源量总体较贫乏,建议重点利用区域地表水资源,适度开发地下水资源,推进农业节水灌溉工程,实现水资源可持续利用。     

Using geochemical indicators to investigate groundwater mixing and residence time in the aquifer system of Djeffara of Medenine (southeastern Tunisia)

Stable isotopes (??²H, ??¹⁸O and ??¹³C) and radiocarbon (¹⁴C) have been used in conjunction with chemical data to evaluate recharge mechanisms and groundwater residence time, and to identify inter-aquifer mixing in the Djeffara multi-aquifer in semi-arid southeastern Tunisia. The southern part of this basin, the Djeffara of Medenine aquifer system, is comprised of two main aquifers of Triassic and Miocene sandstone. The Triassic aquifer presents two compartments; the first one (west of the Medenine fault system) is unconfined with a well-defined isotope fingerprint; the second compartment is deeper and confined. Multi-tracer results show groundwater of different origins, ages and salinities, and that tectonic features control groundwater flows. Fresh and brackish groundwater from the unconfined part of the Triassic aquifer was mostly recharged during the Holocene. The recharge rates of this aquifer, inferred by ¹⁴C ages, are variable and could reach 3.5?mm/year. Brackish water of the deep confined part of the Triassic aquifer has stable isotope composition and ¹⁴C content that indicates earlier recharge during late Pleistocene cold periods. Brackish to saline water of the Miocene aquifer presents variable isotope composition. Groundwater flowing through the Medenine fault system is mainly feeding the Miocene aquifer rather than the deep confined part of the Triassic aquifer.     

Geochemical indicators of interbasin groundwater flow within the southern Rio Grande Valley, southwestern USA

Increased groundwater withdrawals for the growing population in the Rio Grande Valley and likely alteration of recharge to local aquifers with climate change necessitates an understanding of the groundwater connection between the Jornada del Muerto Basin and the adjoining and more heavily used aquifer in the Mesilla Basin. Separating the Jornada and Mesilla aquifers is a buried bedrock high from Tertiary intrusions. This bedrock high or divide restricts and/or retards interbasin flow from the Jornada aquifer into the Mesilla aquifer. The potentiometric surface of the southern Jornada aquifer near part of the bedrock high indicates a flow direction away from the divide because of a previously identified damming effect, but a groundwater outlet from the southern Jornada aquifer is necessary to balance inputs from the overall Jornada aquifer. Differences in geochemical constituents (major ions, δD, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr) indicate a deeper connection between the two aquifers through the Tertiary intrusions where Jornada water is geochemically altered because of a geothermal influence. Jornada groundwater likely is migrating through the bedrock high in deeper pathways formed by faults of the Jornada Fault Zone, in addition to Jornada water that overtops the bedrock high as previously identified as the only connection between the two aquifers. Increased groundwater withdrawals and lowering of the potentiometric surface of the Jornada aquifer may alter this contribution ratio with less overtopping of the bedrock high and a continued deeper flowpath contribution that could potentially increase salinity values in the Mesilla Basin near the divide.     

Hydrogeology of the Ordos Basin,China

The Ordos Basin is located in the east of NW China that is composed of different aquifer systems. Karst groundwater is stored in the Carmbrian-Ordovician carbonates along the margins of the basin. Fissured-pore water is present in the Cretaceous strata in the central-western basin and pore water is stored in the overlying Quaternary deposits discontinuously. The main origin of groundwater in the basin is direct or indirect infiltration of precipitation. Groundwater flows from recharge areas to adjacent local discharge areas. Besides evaporation and abstraction, groundwater feeds springs and rivers, such as the Yellow River and its tributaries. According to the karst aquifer lithologic structure, the features of karst development and circulation, the karst aquifer is divided into three structural and circulation patterns. Based on the control of Cretaceous sedimentary environment, lithologic structure, lithofacies, and palaeogeographic characteristics, the Cretaceous system is divided into the northern desert simple plateau aquifer system and the southern loess plateau aquifer system. PACKER was used to obtain temperature, hydrogeochemical and isotope data at specific depths. Groundwater circulation is studied using hydrodynamic fields, temperature fields, isotopes, hydrogeochemical data and numerical simulations. According to the result, it is divided into local, intermediate and regional systems.     

涞源北盆地地下水氢氧同位素特征及北海泉形成模式

拒马源泉群作为拒马河的源头,受到了较多专家和学者的关注。但这些研究多集中在地下水的水化学、水位动态、泉流量等特征上,对地下水氢氧同位素特征的分析几乎没有,且对北海泉的成因解释多为粗略的定性概述。为了说明涞源北盆地地下水的氢氧同位素特征,详细揭示北海泉的形成模式,首次系统地采集了不同含水岩组的地下水样品,测定了水样的氢氧同位素组分。结果表明:样品点δD和δ18O值均落在区域大气降水线上或附近,大气降水是研究区地下水的主要补给来源;白云岩、灰岩含水岩组高程效应较明显,径流途径长,松散含水层径流途径短,受蒸发作用较强;白云岩、灰岩含水岩组和松散含水层氘盈余d值分别为6.0‰～11.6‰、4.2‰～11.2‰、3.8‰～8.0‰,较大气降水大部分偏小,表明岩溶水和松散孔隙水经历了不同的流动过程;白云岩、灰岩含水岩组从补给区向排泄区各自流动过程中,在小西庄、香炉屯村附近断裂带发生沟通混合,然后在向盆地中心径流过程中受断层阻水上升,上升过程中又接受了松散孔隙水的补给,最后在松散岩层中出露成泉,形成北海泉。在孔隙水混入前,两者的平均补给比例大约为48.4%～57.6%和42.4%～51.6%。     

Pollution vulnerability of the Quaternary aquifer near Cairo, Egypt, as indicated by isotopes and hydrochemistry

The present study was conducted to delineate the pollution vulnerability of the Quaternary aquifer in two areas, Imbaba and Shobra El-Khima, near Cairo, Egypt. Environmental isotopes combined with hydrochemistry were used for this purpose. The groundwater in the Imbaba area (average total dissolved solids about 900 mg/L; sodium/chloride, sulfate, and bicarbonate water types) is more mineralized than groundwater in the Shobra El-Khima area (average total dissolved solids 500 mg/L; calcium and sodium/bicarbonate water type). A high nitrate content and significant mineralization in the groundwater are probably due to contamination of recharge to the aquifer by irrigation drainage, deteriorated sewage networks, and septic tanks. The deuterium and oxygen-18 compositions of the groundwater are depleted compared to Nile River water, which is the main source of aquifer recharge. This less isotopically enriched water probably represents older Nile water recharge that flooded the region before construction of the Aswan High Dam in 1963, or it is a mixture of a young water and originally deposited paleowater that was in deeper horizons at a time of cooler and more humid climate. Intensive pumping has moved the paleowater higher in the aquifer. Groundwater in the Shobra El-Khima area has higher residence time, based on the tritium concentration, than groundwater in the Imbaba area. The percentage of the isotopically depleted water equals 75% in the Shobra El-Khima and 35% in Imbaba, and the thickness of the clay cap above the aquifer is 38 m in Shobra El-Khima and 20 m in Imbaba. These factors are indicative of the rate of recharge to the aquifer and were used to evaluate the pollution vulnerability in the two areas. Electronic Publication     

Impact of rock-water interactions and recharge on water resources quality of the Agadir-Essaouira basin,southwestern Morocco

The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of δ¹⁸O and δ²H suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units.     

Groundwater recharge in suburban areas of Hanoi,Vietnam: effect of decreasing surface-water bodies and land-use change

Over-exploited groundwater is expected to remain the predominant source of domestic water in suburban areas of Hanoi, Vietnam. In order to evaluate the effect on groundwater recharge, of decreasing surface-water bodies and land-use change caused by urbanization, the relevant groundwater systems and recharge pathways must be characterized in detail. To this end, water levels and water quality were monitored for 3 years regarding groundwater and adjacent surface-water bodies, at two typical suburban sites in Hanoi. Stable isotope (δ¹⁸O, δD of water) analysis and hydrochemical analysis showed that the water from both aquifers and aquitards, including the groundwater obtained from both the monitoring wells and the neighboring household tubewells, was largely derived from evaporation-affected surface-water bodies (e.g., ponds, irrigated farmlands) rather than from rivers. The water-level monitoring results suggested distinct local-scale flow systems for both a Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). That is, in the case of the HUA, lateral recharge through the aquifer from neighboring ponds and/or irrigated farmlands appeared to be dominant, rather than recharge by vertical rainwater infiltration. In the case of the PCA, recharge by the above-lying HUA, through areas where the aquitard separating the two aquifers was relatively thin or nonexistent, was suggested. As the decrease in the local surface-water bodies will likely reduce the groundwater recharge, maintaining and enhancing this recharge (through preservation of the surface-water bodies) is considered as essential for the sustainable use of groundwater in the area.

     

The origin of groundwater in Zhangye Basin,northwestern China,using isotopic signature

Zhangye Basin, in arid northwestern China, has recently been repeatedly flooded by rising groundwater. Isotope signatures of sampled waters gained insight into the recharge source of the groundwater. The summer Heihe River water and most of the spring water in Zhangye and Yongchang basins plotted above the global meteoric water line (GMWL) on the δ¹⁸O-δD plot. The spring water had R/Ra ratio >1, low TDS and high tritium, which indicates origin from Qilian Mountain glacier meltwater. The groundwater of Qilian Mountains was transported to the Hexi Corridor (in which Zhangye Basin is located) through underground fault zones. Additionally, some of the groundwater in the alluvial plain, and all spring water surrounding Zhangye Basin, plotted below the GMWL on the δ¹⁸O-δD plot along an evaporation line, and had R/Ra ratio?<?1 and high TDS. It is proposed that the Tibetan rivers or lakes source the Hexi Corridor groundwater through either the NE-trending or NW-trending buried fault zones. The isotopic signatures presented as part of this study rule out the conventional viewpoint that groundwater of the Zhangye Basin was recharged by local precipitation and infiltration of Heihe River water on the alluvial plain.     

The fate and transport of nitrate in shallow groundwater in northwestern Mississippi, USA

Agricultural contamination of groundwater in northwestern Mississippi, USA, has not been studied extensively, and subsurface fluxes of agricultural chemicals have been presumed minimal. To determine the factors controlling transport of nitrate-N into the Mississippi River Valley alluvial aquifer, a study was conducted from 2006 to 2008 to estimate fluxes of water and solutes for a site in the Bogue Phalia basin (1,250 km²). Water-quality data were collected from a shallow water-table well, a vertical profile of temporary sampling points, and a nearby irrigation well. Nitrate was detected within 4.4 m of the water table but was absent in deeper waters with evidence of reducing conditions and denitrification. Recharge estimates from 6.2 to 10.9 cm/year were quantified using water-table fluctuations, a Cl^– tracer method, and atmospheric age-tracers. A mathematical advection-reaction model predicted similar recharge to the aquifer, and also predicted that 15% of applied nitrogen is leached into the saturated zone. With current denitrification and application rates, the nitrate-N front is expected to remain in shallow groundwater, less than 6–9 m deep. Increasing application rates resulting from intensifying agricultural demands may advance the nitrate-N front to 16–23 m, within the zone of groundwater pumping.     

Groundwater flow dynamics in the complex aquifer system of Gidabo River Basin (Ethiopian Rift): a multi-proxy approach

Hydrochemical and isotope data in conjunction with hydraulic head and spring discharge observations were used to characterize the regional groundwater flow dynamics and the role of the tectonic setting in the Gidabo River Basin, Ethiopian Rift. Both groundwater levels and hydrochemical and isotopic data indicate groundwater flow from the major recharge area in the highland and escarpment into deep rift floor aquifers, suggesting a deep regional flow system can be distinguished from the shallow local aquifers. The δ¹⁸O and δ²H values of deep thermal (≥30 °C) groundwater are depleted relative to the shallow (<60 m below ground level) groundwater in the rift floor. Based on the δ¹⁸O values, the thermal groundwater is found to be recharged in the highland around 2,600 m a.s.l. and on average mixed with a proportion of 30 % shallow groundwater. While most groundwater samples display diluted solutions, δ¹³C data of dissolved inorganic carbon reveal that locally the thermal groundwater near fault zones is loaded with mantle CO₂, which enhances silicate weathering and leads to anomalously high total dissolved solids (2,000–2,320 mg/l) and fluoride concentrations (6–15 mg/l) exceeding the recommended guideline value. The faults are generally found to act as complex conduit leaky barrier systems favoring vertical mixing processes. Normal faults dipping to the west appear to facilitate movement of groundwater into deeper aquifers and towards the rift floor, whereas those dipping to the east tend to act as leaky barriers perpendicular to the fault but enable preferential flow parallel to the fault plane.     

环境同位素在北京平谷盆地山前侧向补给研究中的应用

利用地下水水化学和同位素测试分析成果,结合区域地质、水文地质条件研究了平谷北山山区侧向补给情况和中桥水源地地区第四系松散孔隙水和下伏岩溶水关系。结果表明：研究区第四系松散孔隙水和基岩岩溶地下水均来源于大气降水,地下水化学类型均为HCO-3-Ca2+?Mg2+ 型;平谷北山山前基岩岩溶水侧向补给平原区第四系松散孔隙水和下伏岩溶地下水;通过D值估算得到中桥水源地第四系浅层地下水的山区岩溶水侧向补给和垂向降水入渗补给比例为57：43;中桥水源地基岩岩溶水接受山区岩溶水侧向补给和第四系孔隙水垂向越流补给比例为87：13。研究成果为平谷地区地下水资源量评价和地下水动力场数值模型的建设提供了关键参数,为区域地下水的合理开采和有序回补涵养提供了科学依据。