Distinguishing groundwater flow paths in different fractured-rock aquifers using groundwater chemistry: Dandenong Ranges, southeast Australia

Major ion geochemistry is used to qualitatively interpret groundwater residence times within an aquifer, and the extent of mixing between aquifers with distinctive mineralogy. In conjunction with hydraulic heads and stable isotope geochemistry, flow paths and inter-aquifer exchange are defined in a fractured-rock aquifer system in the Dandenong Ranges, southeast Australia. Stable isotopes indicate modern seasonal recharge throughout the system. At high elevations in the sub-catchment, which includes both marine Silurian-Devonian sedimentary and Tertiary basalt aquifers, Cl is derived primarily from cyclic salts, and differences in mineralogy result in groundwater from the basalt aquifer having higher TDS contents (123–262 mg/L) and (Ca+Mg)/Na ratios (0.9–1.3) than groundwater from the sedimentary aquifer (TDS: 55–79 mg/L; (Ca+Mg)/Na: 0.1–0.2). At low elevations, in areas of local groundwater discharge, the more regional flow system in the Silurian-Devonian sediments contains additional Cl from water–rock interaction and has distinctly higher TDS contents (517–537 mg/L). Differences in groundwater chemistry between the aquifers and between shallower and deeper flow systems highlights areas of inter-aquifer mixing. This is particularly important for aquifer vulnerability where groundwater quality in the deeper aquifer may be impacted by surface activities.

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Resumen Se ha utilizado geoquímica de iones mayores para interpretar cualitativamente los tiempos de residencia del agua subterránea dentro de un acuífero, y el grado de mezcla entre acuíferos con mineralogía característica. De manera conjunta con presiones hidráulicas y geoquímica de isótopos estables, se han definido trayectorias de flujo e intercambio entre acuíferos en un sistema de acuífero de roca fracturada en las Sierras Dandenong, sureste de Australia. Los isótopos estables indican recarga estacional moderada a través del sistema. A elevaciones altas en la sub-cuenca que incluye acuíferos sedimentarios Silúrico-Devónicos y acuíferos basálticos Terciarios, Cl se deriva principalmente de sales cíclicas. Las diferencias en mineralogía resultan en agua subterránea del acuífero basáltico que tiene mayores contenidos TDS (123–262 mg/L) y mayor relación (Ca+Mg)/Na (0.9–1.3) que el agua subterránea de los acuíferos sedimentarios (TDS:55–79 mg/L; (Ca+Mg)/Na: 0.1–0.2). A elevaciones bajas, en áreas de recarga local de agua subterránea, el sistema de flujo más regional en los sedimentos Silúrico-Devónicos contiene Cl adicional que se deriva de la interacción roca-agua y típico contenido TDS más alto (517–537 mg L). Las diferencias en la química del agua subterránea entre los acuíferos y entre los sistemas de flujo más profundo y más somero resalta áreas de mezcla entre acuíferos. Esto es particularmente importante para la vulnerabilidad del acuífero donde la calidad del agua subterránea en el acuífero más profundo puede ser impactada por las actividades superficiales.

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Résumé Les ions majeurs sont utilisés pour interpréter quantitativement les temps de résidence des eaux souterraines dans les aquifères, et létendue des zones de mélange entre les aquifères de différentes minéralogies. En regard de la répartition des charges hydrauliques et des informations données par les isotopes stables, les écoulements et les échanges inter-aquifères sont définis dans un aquifère fracturé dans le Dandenong Ranges, SE de lAustralie. Les isotopes stables indiquent des recharges modernes et saisonnières à travers le système aquifère. A haute altitude dans le sous-bassin versant, qui inclut des sédiments du Siluro-Dévonien et des basaltes du Tertiaire, le chlore est dabord dérivé des sels cycliques, et des différences minéralogiques dans les eaux souterraines sont observées selon laquifère : basalte tertiaire (TDS: 123–262 mg/L; Ca+Mg/Ca: 0.9 à 1.3) et sédiments primaires (TDS: 55–79 mg/L; Ca+Mg/Ca: 0.1–0.2). Aux basses altitudes, dans les zones locales de décharge des eaux souterraines, les écoulements les plus régionaux possèdent des teneurs plus élevées en Chlore en provenance des interactions eau—roche, et des TDS plus élevées (515–537 mg/L). Des différences dans la chimie des eaux souterraines entre les aquifères et entre les systèmes découlement de surface et les écoulements profonds mettent en lumière les zones de mélange inter-aquifère. Ceci est particulièrement important pour la définition de la vulnérabilité où la qualité des eaux souterraines en profondeur peuvent subir les impacts des activités de surface.

     

Deep reaching fluid flow in the North East German Basin: origin and processes of groundwater salinisation

Major element chemistry, rare-earth element distribution, and H and O isotopes are conjointly used to study the sources of salinisation and interaquifer flow of saline groundwater in the North East German Basin. Chemical analyses from hydrocarbon exploration campaigns showed evidence of the existence of two different groups of brines: halite and halite Ca–Cl brines. Residual brines and leachates are identified by Br^?/Cl^? ratios. Most of the brines are dissolution brines of Permian evaporites. New analyses show that the pattern of rare-earth elements and yttrium (REY) are closely linked to H and O isotope distribution. Thermal brines from deep wells and artesian wells indicate isotopically evaporated brines, which chemically interacted with their aquifer environment. Isotopes and rare-earth element patterns prove that cross flow exists, especially in the post-Rupelian aquifer. However, even at depths exceeding 2,000 m, interaquifer flow takes place. The rare-earth element pattern and H and O isotopes identify locally ascending brines. A large-scale lateral groundwater flow has to be assumed because all pre-Rupelian aquifer systems to a depth of at least 500 m are isotopically characterised by Recent or Pleistocene recharge conditions.     

Hydrogeochemical processes,mixing and isotope tracing in hard rock aquifers and surface waters from the Subarnarekha River Basin, (east Singhbhum District,Jharkhand State,India)

Geochemical observations, including major ion and trace element analysis, and isotopic tracing have been carried out in the Subarnarekha River system (northeastern India) during a surface-water- and groundwater-monitoring program aimed at evaluating impacts of mining. The aquifer is of fracture type. Groundwater flow conditions and pollutant transfer were observed through a network of 69 wells. δ¹⁸O and δ²H results suggest that transfer from rainfall towards groundwater storage through soils and the unsaturated zone is fast, without any major transformation like evaporation. The scatter of ⁸⁷Sr/⁸⁶Sr signatures in surface water and groundwater are explained by three end-members. One is compatible with rainwater inputs. The most mineralised end-member represents anthropogenic inputs (agricultural practices and ore processing). The third end-member, characterised by a high ⁸⁷Sr/⁸⁶Sr signature, is believed to be controlled by natural geochemical processes, although affected by human activities (e.g. drainage of mine waste). Potential flow paths, investigated north of the area, reveal that all groundwater types seem to evolve more in pockets than along a flow path. The limited extent of transfer and the predominance of natural phenomena help to explain the moderate level of groundwater contamination and the characteristics of surface water contamination by mining and the metallurgy industry.     

Groundwater origin and flow along selected transects in Ethiopian rift volcanic aquifers

The disruption of lithologies by cross-cutting faults and the variability in volcanic structures make the hydrogeology of the rifted volcanic terrain in Ethiopia very complex. Along two transects, selected due to their hydrogeologic characteristics, groundwater flow, depth of circulation and geochemical evolution have been conceptualized. The groundwater flow continuity between the high rainfall plateau bounding the rift and the rift valley aquifers depends principally on the nature of the bounding faults. Up to 50% of recharge to the rift aquifers comes from the plateau as groundwater inflow where the rift is cross cut by transverse fault zones. Recharge from the mountains is found to be insignificant where the rift is bounded by marginal grabens; channel loss and local precipitation are the principal sources of recharge to the rift aquifers in such cases. At a regional scale, there is a clear zonation in the geochemical compositions of groundwaters, the result of aquifer matrix composition differences. The environmental isotope results show that the majority of the aquifers contain modern groundwaters. In a few localities, particularly in thermal groundwaters representing deeper circulation, palaeo-groundwaters have been identified. Deeper groundwaters in the rift floor have a uniform ¹⁴C age ranging between 2,300 and 3,000 years.     

Hydrochemistry and isotope geochemistry as tools for groundwater hydrodynamic investigation in multilayer aquifers: a case study from Lomellina, Po plain, South-Western Lombardy, Italy

A multicriteria approach in studying hydrodynamics of a multilayer aquifer system has been used in the Lomellina region (Northern Italy). It involves the reconstruction of the hydrogeological framework coupled to the definition of the hydrochemical and isotopic features of the aquifers. A shallow phreatic aquifer, reaching depths of about 60–80 m from the surface, and deeper aquifers containing confined groundwater, were distinguished. Groundwater generally shows mineralisation decreasing with depth; dissolved ions depict calcium-bicarbonate hydrochemical facies and stable isotopes define the recharge mechanisms, the origin of groundwater, and the hydraulic confinement of deep aquifers. The phreatic aquifer is fed by local infiltration and by streams and irrigation channels. Tritium and Carbon-14 groundwater dating indicate long residence times (on the order of thousands of years) for confined aquifers. The confined aquifers show essentially passive hydrodynamic conditions and maintain a higher piezometric level than the phreatic aquifer. This inhibits the possibility of recent water penetrating far below the surface. The hydrogeological setting of the Lomellina region displays features which are common to other sectors of the Po plain. As a consequence, the results of this study, although conducted on a restricted area, are highly illustrative of groundwater hydrodynamics in large sedimentary aquifers.     

Hydrogeologic controls on groundwater recharge and salinization: a geochemical analysis of the northern Hueco Bolson aquifer, Texas, USA

Identification of hydrogeologic controls on groundwater flowpaths, recharge, and salinization is often critical to the management of limited arid groundwater resources. One approach to identifying these mechanisms is a combined analysis of hydrogeologic and hydrochemical data to develop a comprehensive conceptual model of a groundwater basin. To demonstrate this technique, water samples were collected from 33 discrete vertical zone test holes in the Hueco Bolson aquifer, located within the Trans-Pecos Texas region and the primary water resource for El Paso, Texas, USA and Juárez, Mexico. These samples were analyzed for a suite of geochemical tracers and the data evaluated in light of basin hydrogeology. On the basis of δ²H and δ¹⁸O data, two regional recharge sources were recognized, one originating from western mountain-fronts and one from through-flow of the adjacent Tularosa aquifer. Chloride concentrations were strongly correlated with lithologic formations and both Cl/Br and ³⁶Cl ratios suggested the primary chloride source is halite dissolution within a specific lithologic unit. In contrast, sulfur isotopes indicated that most sulfate originates from Tularosa basin Permian gypsum sources. These results yielded a more comprehensive conceptual model of the basin, which suggested that chloride salinization of wells is the result of upconing of waters from the Fort Hancock formation.     

Hydrogeology of thermal waters in Viterbo area, central Italy

A conceptual hydrogeological model of the Viterbo thermal area (central Italy) has been developed. Though numerous studies have been conducted on its geological, geochemical and geothermal features, there is no generalized picture defining the origin and yield of the hydrothermal system. These latter aspects have therefore become the objectives of this research, which is based on new hydrogeological and geochemical investigations. The geological setting results in the coexistence of overlapped interacting aquifers. The shallow volcanic aquifer, characterized by fresh waters, is fed from the area around the Cimini Mountains and is limited at its base by the semiconfining marly-calcareous-arenaceous complex and low-permeability clays. To the west of Viterbo, vertical upflows of thermal waters of the sulphate-chloride-alkaline-earth type with higher gas contents, are due to the locally uplifted carbonate reservoir, the reduced thickness of the semiconfining layer and the high local geothermal gradient. The hot waters (30–60°C) are the result of deep circulation within the carbonate rocks (0.5–1.8 km) and have the same recharge area as the volcanic aquifer. The upward flow in the Viterbo thermal area is at least 0.1 m³/s. This flow feeds springs and deep wells, also recharging the volcanic aquifer from below.     

Hydrochemical tracers in the middle Rio Grande Basin,USA: 1. Conceptualization of groundwater flow

Chemical and isotopic data for groundwater from throughout the Middle Rio Grande Basin, central New Mexico, USA, were used to identify and map groundwater flow from 12 sources of water to the basin, evaluate radiocarbon ages, and refine the conceptual model of the Santa Fe Group aquifer system.Hydrochemical zones, representing groundwater flow over thousands to tens of thousands of years, can be traced over large distances through the primarily siliciclastic aquifer system. The locations of the hydrochemical zones mostly reflect the modern predevelopment hydraulic-head distribution, but are inconsistent with a trough in predevelopment water levels in the west-central part of the basin, indicating that this trough is a transient rather than a long-term feature of the aquifer system. Radiocarbon ages adjusted for geochemical reactions, mixing, and evapotranspiration/dilution processes in the aquifer system were nearly identical to the unadjusted radiocarbon ages, and ranged from modern to more than 30 ka. Age gradients from piezometer nests ranged from 0.1 to 2 year cm^–1 and indicate a recharge rate of about 3 cm year^–1 for recharge along the eastern mountain front and infiltration from the Rio Grande near Albuquerque. There has been appreciably less recharge along the eastern mountain front north and south of Albuquerque.

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Resumen Se utilizaron datos químicos e isotópicos de agua subterránea a lo largo de la cuenca central del río Grande, Nuevo México, EEUU, para identificar y mapear el flujo de agua subterránea de 12 fuentes de agua a la cuenca para evaluar edades por medio de radio carbon y para refinar el modelo conceptual del sistema acuífero del Grupo Santa Fé. Se puede establecer zonas hidrotérmicas que representan el flujo de agua subterránea a lo largo de miles a miles de decenas de años en grandes distancias a través del sistema acuífero principalmente siliclástico. Las ubicaciones de las zonas hidroquímicas mayormente reflejan la distribucion de la cabeza hidráulica pre-desarollo moderna pero son inconsistentes con una depresión en los niveles de agua pre-desarollo en la zona central oeste de la cuenca. Esto indica que esta depresión es un rasgo transitorio y no un rasgo de largo plazo del sistema acuífero. Las edades de radio carbon ajustadas para los procesos de reaciones geoquímicas, de mezclado y de evapotranspiración-dilución son casi idénticas a los edades de radio carbon no ajustadas oscilan en un rango desde la modernidad a 30 mil años. Las gradientes de edad de nidos de piezometros van de 0.1 a 2 años cm^–1 e indican un sitio de recarga de aproximadamente 3 cm/yr para la recarga a lo largo del frente montañoso oriental e infiltración del río Grande cerca de Albuquerque. Se aprecia una recarga menor a lo largo del frente oriental de montañas al norte y al sur de Albuquerque.

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Résumé Des données sur les éléments chimiques et les isotopes présents dans leau souterraine prélevée à divers endroits dans le bassin moyen du Rio Grande, au centre du Nouveau-Mexique (É-U), ont permis de déterminer lexistence et létendue de douze sources deau régionales dans le bassin, dévaluer les âges radiocarbones et de raffiner le modèle conceptuel du système aquifère du groupe de Santa Fe. Des zones hydro-chimiques qui représentent lécoulement de leau souterraine depuis des dizaines de milliers dannées peuvent être suivies sur de longues distances à travers laquifère principalement siliclastique. La position des zones hydro-chimiques reflète principalement la distribution moderne des charges hydrauliques mais est incohérente avec une dépression dans le niveau deau dans la partie centre-ouest du bassin, ce qui indique que cette dépression est un élément transitoire du système aquifère plutôt quun élément à long terme. Les âges radiocarbones ajustés aux réactions géochimiques et aux processus de mélange et dévapotranspiration/dilution qui ont lieu dans laquifère sont presque identiques aux âges non ajustés et varient de la période moderne jusquà 30 ka. Les gradients dâge établis à partir des nids de piézomètres sétendent de 0.1 à 2 a cm^–1 et suggèrent un taux de recharge denviron 3 cm a^–1 le long du front des montagnes à lest et pour linfiltration provenant du Rio Grande près dAlbuquerque. Il y a eu substantiellement moins de recharge le long du front des montagnes à lest, au nord et au sud dAlbuquerque.

     

Hydrogeochemistry and isotope analyses used to determine groundwater recharge and flow in low-gradient catchments of the province of Buenos Aires,Argentina

The region known as Pampa Plain, in Argentina, is a vast area characterized by slopes of less than 0.05%. The surface sediment is silty sand, mainly Aeolian, referred to as Pampean Loess, which is a phreatic aquifer unit of utmost importance for the water supply of the region. On account of the slight gradient, hydrogeological analyses using only hydraulic measurements are difficult to perform, often leading to confusing results. Thus, the study presented relies on hydrochemical modeling and isotopic determinations as well. The study area comprises three catchments in the inter-mountainous area corresponding to El Moro, Tamangueyú and Seco creeks, and covering 2,570 km² in the province of Buenos Aires. Measurements of piezometric levels and samples of groundwater, surface water and rainwater were carried out between January and March 2005. Major ion results were analyzed by means of hydrochemical graphs and hydrogeochemical modelling using NETPATH. The resulting data show that it is possible to identify local changes in recharge, flow direction and stream/groundwater relationship by using hydrochemical and isotopic information, which may become a useful and more precise tool for the study of particularly flat landscapes.     

Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO₃ type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ¹⁸O of − 8.3‰, δD of − 48.2‰,δ¹¹B of 1.5‰, and ⁸⁷Sr/⁸⁶Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO₄ type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ¹⁸O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ¹¹B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and ⁸⁷Sr/⁸⁶Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO₄ type water with the highest TDS (249.1 g/l, brine) and has δ¹⁸O of − 2.8‰, δD of − 45.8‰,δ¹¹B of 21.2‰, and ⁸⁷Sr/⁸⁶Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ¹¹B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.     

Use of hydrogeochemistry and environmental isotopes for evaluation of groundwater in Qingshuihe Basin,northwestern China

Hydrogeochemistry and environmental isotope data were utilized to understand origin, geochemical evolution, hydraulic interconnection, and renewability of groundwater in Qingshuihe Basin, northwestern China. There are four types of groundwater: (1) shallow groundwater in the mountain front pluvial fans, originating from recent recharge by precipitation, (2) deep paleo-groundwater of the lower alluvial plains, which was formed long ago, (3) shallow groundwater in the lower alluvial plains, which has undergone evaporation during the recharge process, and (4) mixed groundwater (shallow and deep groundwater in the plain). The main water types are Na–HCO₃, which dominates type (1), and Na–SO₄, which dominates types (2) and (3). Geochemical evolution in the upper pluvial fans is mainly the result of CO₂ gas dissolution, silicates weathering and cation exchange; in the lower alluvial plains, it is related to mineral dissolution. The evaporative enrichment only produces significant salinity increases in the shallow groundwater of the lower alluvial plains. Shallow groundwater age in the upper plain is 10 years or so, showing a strong renewability. Deep groundwater ages in the lower plain are more than 200 years, showing poor renewability. In the exploitation areas, the renewability of groundwater evidently increases and the circulation period is 70–100 years.     

Hydrochemistry of urban groundwater in Seoul, South Korea: effects of land-use and pollutant recharge

The ionic and isotopic compositions (δD, δ¹⁸O, and ³H) of urban groundwaters have been monitored in Seoul to examine the water quality in relation to land-use. High tritium contents (6.1–12.0 TU) and the absence of spatial/seasonal change of O–H isotope data indicate that groundwaters are well mixed within aquifers with recently recharged waters of high contamination susceptibility. Statistical analyses show a spatial variation of major ions in relation to land-use type. The major ion concentrations tend to increase with anthropogenic contamination, due to the local pollutants recharge. The TDS concentration appears to be a useful contamination indicator, as it generally increases by the order of forested green zone (average 151 mg/l), agricultural area, residential area, traffic area, and industrialized area (average 585 mg/l). With the increased anthropogenic contamination, the groundwater chemistry changes from a Ca–HCO₃ type toward a Ca–Cl(+NO₃) type. The source and behavior of major ions are discussed and the hydrochemical backgrounds are proposed as the basis of a groundwater management plan.     

A conceptual model for water resources circulation patterns in Andarokh-Kardeh region (NE,Iran)

Andarokh-Kardeh region is located northeast of Iran and provides notable part of potable water of Mashhad, the second most populated city of Iran with over 3 million inhabitants. Stable isotopes (¹⁸O, ²H and ¹³C), hydrodynamic, and hydrochemical indicators have been applied to evaluate water resources quality comprehensively and to present a hydrogeological conceptual model for the Andarokh-Kardeh region. Hydrochemical studies indicate that chemical rock weathering and ion exchange are the main factors controlling the quality of water in the region, while atmospheric (precipitation) as well as anthropogenic sources have no notable effect. Stable isotopes (¹⁸O and ²H) studies in surface and groundwater samples demonstrate enriched values in Kardeh Dam Reservoir (KDR) due to evaporation and also demonstrate that the interaction between KDR and downstream groundwater resources is negligible. The δ¹³C isotope and DIC and DOC concentrations indicate role of carbonate mineral dissolution from Mozdooran Formation, atmospheric and soil CO₂ and also the domination of C3 vegetation coverage in the study region. The developed conceptual model for Andarokh-Kardeh demonstrates different hydrogeological conditions during wet and dry periods, and highlights the main process which affect hydrogeology of the region. Water quality studies and the developed conceptual model demonstrate the main factors controlling water quality and the main hydrogeological characteristic of Andarokh-Kardeh region which can be used by water resources scientists for the future water management programmes.     

Measurement of rates of surface lowering of limestone in the southern Pennines: an example in the Wye catchment,Derbyshire, UK

Measurement of the differential denudation between chert and limestone in a Carboniferous limestone sequence that was cut during excavations for a railway tunnel (in 1865) has provided a means of assessing limestone dissolution rates in a valley side setting in the southern Pennines over the last ∼150 years. Dissolution rates of 0.031 mm/annum have been determined. This rate falls within the range of previously determined limestone dissolution rates in the UK, which have been described in the context of different methods of measurement and the difference in denudations rates over time.     

Stable isotope study of cave percolation waters in subtropical Brazil: Implications for paleoclimate inferences from speleothems

We analyze the interannual monthly variability of oxygen isotope ratios in data from IAEA stations along the Atlantic coast of South America between 23° and 34° S to evaluate the influence of parameters such as temperature, rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical Brazil. In addition, a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the Santana Cave System (24°31′ S; 48°43′ W), is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water δ¹⁸O.

Interannual monthly variations in δ¹⁸O of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer (negative values of δ¹⁸O) to a more extratropical regime in winter (positive values of δ¹⁸O). Variations in groundwater δ¹⁸O indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters, regardless of location of collection in the cave. In addition, the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs. Significant perturbations in the groundwater composition, characterized by more positive values of δ¹⁸O, are probably connected to an increased Atlantic moisture contribution associated with extratropical precipitation. This implies that the δ¹⁸O of speleothems from caves in this region may be a suitable proxy for studying tropical–extratropical interactions over South America, a feature that is intrinsically related to the global atmospheric circulation.     

Evaluation of groundwater in a three-aquifer system in Ramtha area, Jordan: recharge mechanisms, hydraulic relationship and geochemical evolution

The groundwater wells in the Ramtha region of Jordan are tapping three aquifers: the upper, intermediate and deep aquifers. The upper aquifer groundwater is tritiated and its stable isotopic composition varies over a wide range. This signifies short residence times and local recharge from an elevation around 600 m above sea level. The groundwater of the upper aquifer has an elevated level of , which is attributed to anthropogenic sources. The intermediate and deep aquifers are untritiated and have long residence times. The stable isotope results signify a recharge elevation for the intermediate aquifer higher than that for the upper aquifer. Stable isotopes in groundwater from both aquifers clustered along the eastern meteoric water line and demonstrate association with the dominant climate of Jordan. The groundwater of the intermediate aquifer is classified as Ca²⁺- , which reflects circulation through a carbonate aquifer. There is evidence that leakage from the upper aquifer has influenced the isotopic and chemical makeup of the groundwater in an intermediate aquifer well. The groundwater of the deep aquifer has the highest temperature in the basin and its isotopic composition is much more depleted than both the upper and intermediate aquifers and plots on the global meteoric water line.

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Résumé  Les puits de la région de Ramtha en Jordanie captent trois aquifères : les aquifères supérieur, intermédiaire et profond. L’eau de l’aquifère supérieur est tritiée et sa composition en isotopes stables varie dans un large intervalle. Ceci signifie des temps de séjour courts et une recharge locale à une altitude d’environ 600 mètres au-dessus du niveau de la mer. L’eau de l’aquifère supérieur a une teneur en élevée, qui est attribuée à des origines anthropiques. Les aquifères intermédiaire et profond ne sont pas tritiés et ont des temps de séjour longs. Les valeurs des isotopes stables indiquent une altitude de recharge pour l’aquifère intermédiaire plus élevée que pour l’aquifère supérieur. Les isotopes stables de l’eau des deux aquifères groupés le long de la droite des eaux météoriques orientale démontrent une relation avec le climat prédominant en Jordanie. L’eau de l’aquifère intermédiaire est de type Ca²⁺-, ce qui traduit une circulation dans un aquifère carbonaté. Il est évident qu’un apport de l’aquifère supérieur a influencé la composition isotopique et chimique da l’eau d’un puits dans l’aquifère intermédiaire. L’eau de l’aquifère profond a la température la plus élevée dans le bassin et sa composition isotopique est bien plus déprimée que dans les deux aquifères supérieur et intermédiaire et se situe sur la droite globale de l’eau météorique.

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Resumen  Las perforaciones en la región de Ramtha de Jordania atraviesan tres acuíferos: los acuíferos superior, intermedio y profundo. El agua del acuífero superior contiene tritio y su composición isotópica varía en un rango amplio. Esto se interpreta como aguas de corto período de residencia recargadas localmente en una zona elevada a unos 600 m sobre el nivel del mar. El agua del acuífero superior posee elevadas concentraciones de , de origen antropogénico. Las aguas de los acuíferos intermedio y profundo no contienen tritio y su período de residencia es largo. Los resultados de las concentraciones de isótopos estables sugieren que la recarga del acuífero intermedio proviene de alturas mayores que las correspondientes al acuífero superior. Los datos de isótopos estables de ambos acuíferos se agrupan a lo largo de la Línea Meteórica Este, y demuestra su asociación con el clima predominante en Jordania. El agua subterránea del acuífero intermedio se clasifica como Ca²⁺-, lo que refleja su circulación a través de un acuífero carbonático. Hay evidencias que las filtraciones desde el acuífero superior han influenciado las características químicas e isotópicas del acuífero intermedio. Las aguas del acuífero profundo son las de mayor temperatura en la cuenca, su composición isotópica es más reducida que aquella de los acuíferos superior e intermedio, y su posición gráfica se aproxima a la Línea Meteórica Mundial.

     

The hydrochemical characteristics and evolution of groundwater and surface water in the Heihe River Basin, northwest China

A combination of isotopic and chemical indicators has been used to characterize rainfall, surface water and groundwater in the Heihe River Basin, China. Surface- vs. groundwater chemistry data enabled geographical zones and chemical types to be differentiated. The dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite determine Na⁺, Cl^?, Mg²⁺, Ca²⁺, $ {\text{SO}}^{{2 - }}_{4} A combination of isotopic and chemical indicators has been used to characterize rainfall, surface water and groundwater in the Heihe River Basin, China. Surface- vs. groundwater chemistry data enabled geographical zones and chemical types to be differentiated. The dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite determine Na⁺, Cl⁻, Mg²⁺, Ca²⁺, and chemistry, but other processes such as evaporation, ion exchange, and deposition also influence the water composition. The majority of deep confined groundwaters are tritium-free and less mineralized than in the shallow aquifer. Radiocarbon values in the deeper groundwaters range from 18.8 to 38.9 pmc, and 80 pmc probably represents the upper limit of initial ¹⁴C activity; this yields ages of approximately 5,960–11,971 years BP, which is about 3,000 years older than those calculated by models in previous work. The shallow aquifer exhibits fairly high and variable tritium activities (4–75 TU), evidence of recent recharge and low residence time (<60 years), which is in line with estimates from previous work. Isotopic signatures indicate formation of deeper groundwaters in a colder and wetter climate during the late Pleistocene and Holocene. The results suggested that significant changes are urgently needed in water-use strategy to achieve sustainable development.

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Résumé Une combinaison de plusieurs indicateurs isotopiques et chimiques a été utilisée dans le but de caractériser les précipitations, les eaux de surface et les eaux souterraines dans le Bassin de la Rivière Heihe, en Chine. La confrontation des chimies des eaux souterraines et de surface a permis de différentier plusieurs secteurs géographiques et faciès chimiques. Les compositions chimiques en Na⁺, Cl⁻, Mg²⁺, Ca²⁺, et sont déterminées par la dissolution de la halite, du sel de Glauber, du gypse, de la dolomite et de la calcite, mais d’autres processus peuvent également avoir une influence, comme l’évaporation, les échanges de bases et la sédimentation. La majorité des eaux souterraines captives profondes ne contiennent pas de tritium, et sont moins minéralisées que dans l’aquifère superficiel. Les valeurs de carbone 14 dans l’aquifère le plus profond sont comprises entre 18.8 et 38.9 pcm, pour une valeur maximum probable d’activité initiale de 80 pcm; les ages estimés correspondants sont compris entre 5,960 et 11,971 ans, soit environ 3,000 ans de plus que ceux calculés auparavant par les modèles. L’aquifère superficiel présente des activités tritium plut?t élevées et variables (4 à 75 UT), démontrant l’existence d’une alimentation récente et d’un temps de résidence faible (<60 ans), ce qui concorde avec les études antérieures. Les signatures isotopiques indiquent une alimentation des eaux souterraines les plus profondes au cours d’épisodes climatiques plus froids et plus humides qu’actuellement, à la fin du Pléistocène et à l’Holocène. Les résultats suggèrent que des changements significatifs dans la planification des usages de l’eau sont nécessaires et urgents dans des perspectives d’exploitation durable.

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Resumen Se ha utilizado una combinación de indicadores isotópicos y químicos para caracterizar la precipitación, el agua superficial y el agua subterránea en la Cuenca del Río Heihe, China. Los datos químicos de aguas superficiales frente a las subterráneas no permiten diferenciar zonas geográficas y tipos químicos. La disolución de halita, sal de Glauber, yeso, dolomita y calcita determina la química de Na⁺, Cl⁻, Mg²⁺, Ca²⁺, y , pero otros procesos, como evaporación, intercambio de iones y precipitación influyen también en la composición del agua. La mayoría de las aguas subterráneas profundas confinadas no tienen Tritio y están menos mineralizados que el acuífero superficial. Los valores de radiocarbono en las aguas subterráneas más profundas oscilan entre 18.8 y 38.9 pmc, y el valor de 80 pmc representa probablemente el límite superior de la actividad inicial de ¹⁴C; proporcionando edades de aproximadamente 5,960–11,971 a?os BP, que son unos 3,000 a?os más antiguas de las calculadas mediante modelización en trabajos previos. El acuífero superficial tiene actividades de tritio bastante más altas y variables (4–75 UT), evidenciando una recarga reciente y unos tiempos de residencia bajos (<60 a?os), lo cual está en la línea de lo estimado en trabajos previos. Los datos isotópicos apuntan a la formación de aguas subterráneas más profundas en un clima más frío y húmedo durante el Pleistoceno superior y el Holoceno. Los resultados sugieren que se necesita hacer cambios significativos en la estrategia de uso del agua para alcanzar un desarrollo sostenible.

     

Utilising seasonal variations in hydrogeochemistry and excitation-emission fluorescence to develop a conceptual groundwater flow model with implications for subsidence hazards: an example from Co. Durham, UK

Groundwaters were sampled from four research boreholes, a private supply well and a natural karst resurgence in southern County Durham, England. Time series data sets of piezometric levels, groundwater major ions, and fluorescence of dissolved organic matter (DOM) were interpreted in the light of new geological mapping to assess the movement of groundwater and its potential for the dissolution of gypsum. Three distinct groundwater facies were identified representing contact with gypsiferous strata, dolomitic limestone and Quaternary Till. Piezometric data indicated time varying transverse flow across the gypsifeorus strata, which was confirmed from gradational mixing of groundwater types and cation ratios. Fluorescence of dissolved DOM identified variations in protein and fulvic-like acid fluorescence. The former was taken to represent surface derived, short-lived material. Spatial and temporal variations in protein fluorescence offered a means to trace groundwater movement along the regional groundwater gradient and indicated rapid lateral movement of groundwater. It was concluded that gypsum dissolution is occurring beneath the town of Darlington, however, the presence of a thick deposit of Quaternary till effectively confines the small head differences of approximately 1 m, across the gypsum strata beneath the town. Further to the south, the lowering of the ground surface results in a greater upwards flow of water across the gypsum and is used to explain the presence of historic collapse sinkholes.     

Environmental tracers as indicators of karst conduits in groundwater in South Dakota,USA

Environmental tracers sampled from the carbonate Madison aquifer on the eastern flank of the Black Hills, South Dakota, USA indicated the approximate locations of four major karst conduits. Contamination issues are a major concern because these conduits are characterized by direct connections to sinking streams, high groundwater velocities, and proximity to public water supplies. Objectives of the study were to estimate approximate conduit locations and assess possible anthropogenic influences associated with conduits. Anomalies of young groundwater based on chlorofluorocarbons (CFCs), tritium, and electrical conductivity (EC) indicated fast moving, focused flow and thus the likely presence of conduits. δ¹⁸O was useful for determining sources of recharge for each conduit, and nitrate was a useful tracer for assessing flow paths for anthropogenic influences. Two of the four conduits terminate at or near a large spring complex. CFC apparent ages ranged from 15 years near conduits to >50 years in other areas. Nitrate-N concentrations >0.4 mg/L in groundwater were associated with each of the four conduits compared with concentrations ranging from <0.1 to 0.4 mg/L in other areas. These higher nitrate-N concentrations probably do not result from sinking streams but rather from other areas of infiltration.     

Weathering processes in the Indus River Basin: implications from riverine carbon, sulfur, oxygen, and strontium isotopes

This study deals with the major ions and isotope systematics for C, O, S, and Sr in the Indus River Basin (IRB). Major ion chemistry of the Indus, and most of its headwater tributaries, follow the order Ca²⁺>Mg²⁺>(Na⁺+K⁺) and HCO₃⁻>(SO₄²⁻+Cl⁻)>Si. In the lowland tributaries and in some of the Punjab rivers, however, (Na⁺+K⁺) and (SO₄²⁻+Cl⁻) predominate. Cyclic salts, important locally for Na⁺ in dilute headwater tributaries, constitute about 5% of the annual solutes transported by the Indus. Weathering of two lithologies, sedimentary carbonates and crystalline rocks, controls the dissolved inorganic carbon (DIC) concentrations and its carbon isotope systematics throughout the Indus, but turbulent flow and lower temperatures in the headwaters, and storage in reservoirs in the middle and lower Indus promote some equlibration with atmospheric carbon dioxide. Combined evidence from sulfur and oxygen isotopic composition of sulfates refutes the proposition that dissolution of these minerals plays a significant role in the IRB hydrochemistry and suggests that any dissolved sulfates were derived by oxidation of sulfide minerals.

In the upper Indus, silicate weathering contributes as much as 75% (or even higher in some tributaries) of the total Na⁺ and K⁺, declining to less than 40% as the Indus exits the orogen. In contrast, about two-thirds of Ca²⁺ and Mg²⁺ in the upper Indus (over 70% in some tributaries) and three-fourth in the lower Indus, are derived from sedimentary carbonates. The ⁸⁷Sr/⁸⁶Sr ratios tend to rise with increasing proportions of silicate derived cations in the headwater tributaries and in the upper and middle Indus, but are out of phase or reversed in the lower Indus. Finally, close to the river mouth, the discharge weighted average contribution of silicate derived Ca²⁺+Mg²⁺ and silicate derived Na⁺+K⁺ are, respectively, about one-fourth and two-thirds of their total concentrations.