Karst groundwater: a challenge for new resources

Karst aquifers have complex and original characteristics which make them very different from other aquifers: high heterogeneity created and organised by groundwater flow; large voids, high flow velocities up to several hundreds of m/h, high flow rate springs up to some tens of m³/s. Different conceptual models, known from the literature, attempt to take into account all these particularities. The study methods used in classical hydrogeology—bore hole, pumping test and distributed models—are generally invalid and unsuccessful in karst aquifers, because the results cannot be extended to the whole aquifer nor to some parts, as is done in non-karst aquifers. Presently, karst hydrogeologists use a specific investigation methodology (described here), which is comparable to that used in surface hydrology.Important points remain unsolved. Some of them are related to fundamental aspects such as the void structure – only a conduit network, or a conduit network plus a porous matrix –, the functioning – threshold effects and non-linearities –, the modeling of the functioning – double or triple porosity, or viscous flow in conduits – and of karst genesis. Some other points deal with practical aspects, such as the assessment of aquifer storage capacity or vulnerability, or the prediction of the location of highly productive zones.

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Resumen Los acuíferos kársticos tienen características originales y complejas que los hacen muy diferentes de otros acuíferos: alta heterogeneidad creada y organizada por el flujo de agua subterránea, espacios grandes, velocidades altas de flujo de hasta varios cientos de m/h, manantiales con ritmo alto de flujo de hasta algunas decenas de m3/s. Diferentes modelos conceptuales que se conocen en la literatura tratan de tomar en cuenta todas estas particularidades. Los métodos de estudio usados en hidrogeología clásica- pozos, pruebas de bombeo y modelos distribuidos- son generalmente inválidos y no exitosos en acuíferos kársticos, debido a que los resultados no pueden extenderse a todo el acuífero ni a alguna de sus partes, como se hace en acuíferos no kársticos. Actualmente los hidrogeólogos kársticos usan una metodología de investigación específica, que se des cribe aquí, la cual es comparable con la que se utiliza en hidrología superficial. Puntos importantes permanecen sin resolverse. Algunos de ellos se relacionan con aspectos fundamentales tal como la estructura de espacios- solo una red de conductos, o una red de conductos más una matriz porosa-, el funcionamiento-efectos threshold y no-linealidades-, el modelizado del funcionamiento-porosidad doble o triple, o flujo viscoso en conductos- y génesis del karst. Algunos otros puntos se relacionan con aspectos prácticos, tal como la evaluación de la capacidad de almacenamiento del acuífero o la vulnerabilidad, o la predicción de la localización de zonas altamente productivas.

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Résumé Les aquifères karstiques présentent des caractères originaux complexes qui les distinguent profondément de tous les autres milieux aquifères : forte hétérogénéité créée et organisée par les écoulements souterrains eux-mêmes, vides de très grandes dimensions, vitesses découlement pouvant atteindre quelques centaines de mètres par heure, sources à débit pouvant atteindre quelques dizaines de m³/s. Différents modèles conceptuels tentent de prendre en compte ces particularités. Les méthodes détude de lhydrogéologie classique—forage, essai de pompage et modèles maillés – ne sont en général pas adaptés aux aquifères karstiques, parce que les résultats obtenus ne peuvent pas être étendus à laquifère tout entier, ou à certaines de ses parties, comme cela est fait pour les aquifères non karstiques. Actuellement les hydrogéologues du karst ont recours à une méthodologie détude spécifique décrite ici, comparable à celle utilisée en hydrologie de surface.Des points importants restent à résoudre. Certains concernent des aspects fondamentaux, comme la structure des vides – réseau de conduits uniquement, ou bien réseau de conduits et matrice poreuse –, le fonctionnement – problèmes de seuil et plus généralement les non-linéarités –, la modélisation du fonctionnement – double porosité ou écoulement visqueux en conduits – et de la genèse du karst. Dautres points portent sur des aspects pratiques, comme lévaluation de la capacité de stockage ou de la vulnérabilité de laquifère, et la prédiction des zones à haute productivité.

     

Karst groundwater vulnerability mapping: application of a new method in the Swabian Alb, Germany

Groundwater from karst aquifers is an important drinking water resource, which is, however, particularly vulnerable to contamination. Karst aquifers consequently need special protection. This paper discusses the concept of groundwater vulnerability mapping and the special characteristics of karst aquifers that are relevant in this context. On this basis, a new method of groundwater vulnerability mapping is proposed—the PI method. It can be applied for all types of aquifers, but provides special tools for karst. Vulnerability is assessed as the product of two factors: protective cover (P) and infiltration conditions (I). The method was first applied and compared with two other methods (EPIK and the German method) in a test site in the Swabian Alb, Germany. The results obtained with the different methods are discussed and an outlook on the role of vulnerability maps within an overall groundwater protections scheme is given.

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Resumen Las aguas subterráneas en medios kársticos suponen un recurso importante para uso de boca, pero es particularmente vulnerable a la contaminación, por lo que los acuíferos kársticos requieren una protección especial. Este artículo discute el concepto de cartografía de vulnerabilidad de las aguas subterráneas y las características propias de los acuíferos kársticos que son relevantes en este contexto. Con esta base, se propone un nuevo método para cartografiar la vulnerabilidad de las aguas subterráneas, denominado "PI". Puede ser aplicado a todo tipo de acuíferos, pero proporciona herramientas especiales en medios kársticos. Se establece la vulnerabilidad como resultado de dos factores: la cubierta protectora y las condiciones de infiltración. El método ha sido aplicado por vez primera y comparado con otros dos enfoques (EPIK y el método alemán) en un emplazamiento ubicado en Swabian Alb (Alemania). Se discute los resultados obtenidos con estos métodos y se incide en cuál es el papel que desempeñan los mapas de vulnerabilidad en el contexto de los esquemas generales de protección de las aguas subterráneas.

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Résumé L'eau souterraine des karsts est une importante ressource d'eau potable, cependant particulièrement vulnérable à la pollution. C'est pourquoi les aquifères karstiques nécessitent une protection particulière. Ce papier discute le concept de cartographie de la vulnérabilité de l'eau souterraine et les caractéristiques particulières des aquifères karstiques qui sont concernés dans ce contexte. Sur cette base, une nouvelle méthode de cartographie de la vulnérabilité de l'eau souterraine est proposée: la méthode PI. Elle peut être appliquée à tous les types d'aquifères, mais fournit des outils spécifiques au karst. La vulnérabilité est évaluée comme étant le produit de deux facteurs: les conditions de couverture protectrice (P) et d'infiltration (I). La méthode a été mise en oeuvre pour la première fois et comparée à deux autres méthodes (EPIK et la méthode allemande) sur un site test du Jura souabe (Allemagne). Les résultats obtenus avec les différentes méthodes sont discutés et le rôle des cartes de vulnérabilité dans un schéma général de protection des eaux souterraines est passé en revue.

     

Karst flash flooding in a Mediterranean karst, the example of Fontaine de Nîmes

Karst flash flooding, identified as one of the hazards in karst terrains, is directly linked to the structure and hydraulic properties of karst aquifers. Due to the characteristics of flow within karst aquifers, characterized by a dual flow – diffuse flow within fissured limestone and conduit flow within karst conduits networks – flash flooding may be important in volume and dynamics. Such phenomenon may cause serious damages including loss of lives, as it occurred on 3rd October 1988 in Nîmes (Gard, South France). Flash floods there have been considered to be the result of very intensive rainfall events conjugated to runoff due to the geomorphologic context of the city located down hill. However, preliminary results of recent studies of the hydrologic behaviour of groundwater and surface water for a specific event (September 2005) show that the karst plays an important role in the flood genesis. The main characteristics of the Nîmes karst system leading to karst flash flooding are presented in this paper. A methodology comprising modelling of the karst system allowed proposing simple warning thresholds for various part of the karst (water level threshold for the karst conduits and cumulative rainfall threshold for the overflowing fissured karst). These thresholds can be included in the flash flood warning system of the Nîmes city.     

Karst morphology and groundwater vulnerability of high alpine karst plateaus

High alpine karst plateaus are recharge areas for major drinking water resources in the Alps and many other regions. Well-established methods for the vulnerability mapping of groundwater to contamination have not been applied to such areas yet. The paper characterises this karst type and shows that two common vulnerability assessment methods (COP and PI) classify most of the areas with high vulnerability classes. In the test site on the Hochschwab plateau (Northern Calcareous Alps, Austria), overlying layers are mostly absent, not protective or even enhance point recharge, where they have aquiclude character. The COP method classifies 82% of the area as highly or extremely vulnerable. The resulting maps are reasonable, but do not differentiate vulnerabilities to the extent that the results can be used for protective measures. An extension for the upper end of the vulnerability scale is presented that allows identifying ultra vulnerable areas. The proposed enhancement of the conventional approach points out that infiltration conditions are of key importance for vulnerability. The method accounts for karst genetical and hydrologic processes using qualitative and quantitative properties of karst depressions and sinking streams including parameters calculated from digital elevations models. The method is tested on the Hochschwab plateau where 1.7% of the area is delineated as ultra vulnerable. This differentiation could not be reached by the COP and PI methods. The resulting vulnerability map highlights spots of maximum vulnerability and the combination with a hazard map enables protective measures for a manageable area and number of sites.     

The effect of the Messinian Deep Stage on karst development around the Mediterranean Sea. Examples from Southern France

It is difficult to explain the position and behaviour of the main karst springs of southern France without calling on a drop in the water table below those encountered at the lowest levels of Pleistocene glacio-eustatic fluctuations. The principal karst features around the Mediterranean are probably inherited from the Messinian period (“Salinity crisis”) when sea level dropped dramatically due to the closing of the Straight of Gibraltar and desiccation of the Mediterranean Sea. Important deep karst systems were formed because the regional ground water dropped and the main valleys were entrenched as canyons. Sea level rise during the Pliocene caused sedimentation in the Messinian canyons and water, under a low hydraulic head, entered the upper cave levels.

The powerful submarine spring of Port-Miou is located south of Marseille in a drowned canyon of the Calanques massif. The main water flow comes from a vertical shaft that extends to a depth of more than 147 m bsl. The close shelf margin comprises a submarine karst plateau cut by a deep canyon whose bottom reaches 1,000 m bsl. The canyon ends upstream in a pocket valley without relation to any important continental valley. This canyon was probably excavated by the underground paleoriver of Port-Miou during the Messinian Salinity Crisis. Currently, seawater mixes with karst water at depth. The crisis also affected inland karst aquifers. The famous spring of Fontaine de Vaucluse was explored by a ROV (remote observation vehicle) to a depth of 308 m, 224 m below current sea level. Flutes observed on the wall of the shaft indicate the spring was formerly an air-filled shaft connected to a deep underground river flowing towards a deep valley. Outcroppings and seismic data confirm the presence of deep paleo-valleys filled with Pliocene sediments in the current Rhône and Durance valleys. In the Ardèche, several vauclusian springs may also be related to the Messinian Rhône canyon, located at about 200 m below present sea level. A Pliocene base level rise resulted in horizontal dry cave levels. In the hinterland of Gulf of Lion, the Cévennes karst margin was drained toward the hydrologic window opened by the Messinian erosional surface on the continental shelf.     

Dynamics and contribution of karst groundwater to surface flow during Mediterranean flood

This paper describes the role of groundwater contribution to surface flow at the Causse d’Aumelas, a karst system near Montpellier (France), which is traversed by an intermittent river, the Coulazou. A first hydrologic model integrating a digital terrain model shows the inability of a standard rainfall-runoff model to replicate recorded flood hydrographs. While the flood peaks are routed through the karstic system along the Coulazou without a phase lag, the peak magnitude is somewhat modified. These results indicate an initial karst system recharge followed by a significant contribution to surface flow. A hydrodynamic analysis of ground-water flow confirms these results: the karst system first absorbs part of the rainfall, which induces a general water table rise within the aquifer, and then contributes to surface flow in the Coulazou.     

Interpretation for technical requirements of mapping regional groundwater resources

Under the organization of China Geological Survey, relevant departments have made industry specifications and technical requirements based on hydrogeological survey data collection at the scale of 1:50 000. Among them, groundwater resource map is a must. According to nationally unified technical requirements of mapping groundwater resources put forward in 2018, this paper mainly interprets relevant principles, content, methods, diagrams as well as legend, and further to point out future directions: Higher precision will equal to higher demand of application, so that is there any more effective way to further interpret application aspect rather than only rules?     

The groundwater discharge in the Mediterranean karst coastal zones and freshwater tapping: set problems and adopted solutions. Case studies

In the karstic regions of the Mediterranean coastal zones the groundwater discharge and its outcrops—the coastal and submarine springs—represent the most typical natural phenomena of littoral karst, the economic potential of which is significant. The case studies discussed in this paper concern the problems of freshwater tapping in karst coastal zones along the Mediterranean littoral. Owing to the geological and hydrogeological approach, the set problems and adopted solutions involve two most important tasks: (1) the regulation of groundwater flow in the tapping facilities and (2) the control system of saltwater encroachment in a larger protection zone, between the coast and the site of tapping facilities.     

Climate change and groundwater resources in Cambodia

Climate change has become a major global concern and threatens the security of natural environmental resources, including groundwater, especially for Cambodia. In this study, literature reviews related to climate change and groundwater resources in Cambodia were evaluated to address the impact of climate change on the groundwater environment. In Cambodia, global climate change will likely affect available water resources by driving changes in the groundwater recharge and usage pattern. Despite a general increase in the mean annual rainfall, a reduction in rainfall is anticipated during the dry season, which could lead to shortages of fresh water during the dry season. The impact of climate change on water resource environments can significantly affect national economic development. Thus, strategic management plansfor groundwater in response to climate change should be established to ensure the security of water resources in Cambodia.     

Fluoride contamination in groundwater resources of Alleppey,southern India

Alleppey is one of the thickly populated coastal towns of the Kerala state in southern India.Groundwater is the main source of drinking water for the 240,991 people living in this region.The groundwater is being extracted from a multi-layer aquifer system of unconsolidated to semi-consolidated sedimentary formations,which range in age from Recent to Tertiary.The public water distribution system uses dug and tube wells.Though there were reports on fluoride contamination,this study reports for the first time excess fluoride and excess salinity in the drinking water of the region.The quality parameters,like Electrical Conductivity(EC) ranges from 266 to 3900 μs/cm,the fluoride content ranges from 0.68 to2.88 mg/L,and the chloride ranges between the 5.7 to 1253 mg/L.The main water types are Na-HC03,NaCO_3 and Na-Cl.The aqueous concentrations of F~- and CO_3~(2-) show positive correlation whereas F~- and Ca~(2+) show negative correlation.The source of fluoride in the groundwater could be from dissolution of fluorapatite,which is a common mineral in the Tertiary sediments of the area.Long residence time,sediment-groundwater interaction and facies changes(Ca-HCO_3 to Na-HCO_3) during groundwater flow regime are the major factors responsible for the high fluoride content in the groundwater of the area.High strontium content and high EC in some of the wells indicate saline water intrusion that could be due to the excess pumping from the deeper aquifers of the area.The water quality index computation has revealed that 62%of groundwater belongs to poor quality and is not suitable for domestic purposes as per BIS and WHO standards.Since the groundwater is the only source of drinking water in the area,proper treatment strategies and regulating the groundwater extraction are required as the quality deterioration poses serious threat to human health.     

The protection of karst water resources: the example of the Larzac karst plateau (south of France)

Wide karst plateaus extend in the carbonate rocks of the Grands Causses area, north of Montpellier (south of France). They are surrounded by a hard rock base that feeds important rivers, such as the Tarn River and tributaries, and crosses the plateaus creating deep gorges. The Larzac plateau, the most southern, makes a link with the Mediterranean region. It is traversed by one of the main national roads and another main road under construction from Clermont-Ferrand to Montpellier and Spain. The karst water resource of the plateau, from springs, is used as a water supply for the Millau area (30,000 inhabitants); but it also recharges surface rivers, mainly during the summer and fall when the water level is low, in a region that is well known for water recreation activities, for fish farming and, above all, for sheep farming and Roquefort cheese production. The fundamental question was should the karst and its water resource be fully protected by strict regulations (for example as a nature reservation) in land-use management of the plateau based upon the knowledge of its hydrogeological functioning and its karst structure? Decisions, concerning the ～500-km² area were elaborated from detailed hydrogeological studies, which included natural and artificial tracing, analysis of karst aquifer functioning, landscape analysis, and risk assessment and mapping. Recommendations were proposed to local and regional decision makers to define what were the preferences in terms of water resource protection and water quality restoration. Following such an approach in a karst area is not easy for hydrogeologists or for decision makers. In non-karstic regions, protection zones currently extend over small areas of a few square kilometers, which can be easily placed under the control of a small municipality. In the present example, the main water supplies are two springs that recharge areas that extend respectively over 100 and 110?km². Included are several municipalities, some of which use them for their water supply, whereas others are concerned with pollution risks and land management projects. The recent French Water Act, which considers water as a common heritage, allows for general management by all the users, and it deals with the water and the terrain in which it flows. The regulation tools seem very well suited to karst region management. However, time is needed to educate users and decision makers, and with the help of karst scientists, to work together in a framework that is larger than the usual municipal limits.     

A local-scale groundwater flow model for groundwater resources management in Dakhla Oasis,SW Egypt

Dakhla Oasis is located in the Western Desert of Egypt. Groundwater exploited from the Nubian Sandstone aquifer is the only available water resource in this area. This resource has been heavily exploited since 1960, which has led to a substantial decline in the potentiometric surface of the aquifer. A regional numerical groundwater flow model, calibrated under unsteady-state conditions, has been developed and used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifer. To account for local details and to allow a precise analysis of pumping and the resulting drawdown in Dakhla Oasis, a local-scale model was developed by refining the grid cells in the calibrated regional model. The local-scale model gave a detailed picture about the expected drawdown due to the different groundwater management options in the next 100 years. The simulated results indicated that the planned increase in groundwater extraction will have a major impact on groundwater flow patterns in the whole area located southwest of Dakhla Oasis.

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Resumen El oasis Dakhla está situado en el gran desierto occidental de Egipto. El agua subterránea que se extrae del acuífero de roca arenosa nubia es la única fuente de agua disponible en esta área. Este recurso ha sido explotado en medida considerable desde 1960. Este hecho he causado una disminución sustancial en la superficie potenciométrica del acuífero. Se ha desarollado un modelo de flujo de agua subterránea numérico regional calibrado bajo condiciones de estado variable. Este modelo se ha utilizado para investigar el impacto hidrodinámico que diferentes opciones de manejo de aguas subterráneas tienen sobre la potenciometría del acuífero. Se desarolló un modelo de escala local mediante el refinamiento de las células de malla en el modelo regional calibrado con el objecto de involucrar los detalles locales y de permitir un análisis preciso del bombeo y disminución del nivel de aqua resultante en el oasis Dakhla. El modelo de escala local proporcionó un imagen detallada de la disminución de nivel esperada según las diferentes opciones de manejo de agua subterranea en los próximos 100 años. Los resultados simulados indican que el incremento de extración planificado en la agua subterránea tendrá un gran impacto en el patrón de flujo de agua subterranea en toda el area ubicada al suroeste del oasis de Dakhla.

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Résumé Loasis de Dakhla est située dans la partie occidentale du désert dÉgypte. La seule source deau disponible dans la région provient de lexploitation de laquifère gréseux de Nubian. Cette ressource a largement été exploitée depuis 1960, résultant en la diminution significative de la surface piézométrique de laquifère. Un modèle numérique découlement régional de leau souterraine, calibré en régime transitoire, a été développé et utilisé afin détudier les impacts hydrodynamiques de différents scénarios de gestion de laquifère sur la surface piézométrique. Afin dinclure les particularités locales et de réaliser une analyse précise du pompage et du rabattement qui y est associé dans lOasis de Dakhla, un modèle local découlement a été développé en raffinant le maillage dans le modèle régional préalablement calibré. Le modèle local découlement fournit une image détaillée du rabattement prévu pour les cent prochaines années selon les différents scénarios de gestion de laquifère. Les résultats obtenus par simulation numérique indiquent que laugmentation prévue dans lexploitation de leau souterraine aura un impact majeur sur les patrons découlement de leau souterraine dans toute la région située au sud-ouest de loasis de Dakhla.

     

Karst groundwater protection in the Kupa River catchment area and sustainable development

One of the most significant water resources in the Republic of Croatia is the catchment area of the Kupa River, located in the region bordering the Republic of Slovenia. About 88% of the total amount of water in this catchment originates in Croatia and just 12% from Slovenia; therefore, the largest part of the catchment area (about 1000 km²) is on the Croatian side of the border. It is a typical karst area of the Dinarides with aquifers characterized by a relatively rapid water exchange, high groundwater flow velocities and aquifers open to human impact from the surface. Consequently, the aquifers are highly vulnerable and at risk. Due to the availability of large quantities of high-quality spring water (about 6 m³/s), the entire area has a strategic importance within the context of any future development strategy pertaining to the western part of Croatia. The catchment area on the Croatian side was investigated using a wide range of research methods that included a classical hydrogeological approach, the detailed hydrologic calculation of water balance to the hydrogeochemical analyses and modelling. The objective was to determine protection zones and protection measures for the whole area. The difficulties are increased due to the fact that the karst catchment area is crossed by major traffic corridors, oil pipelines and a railway and that many settlements and a highly developed wood industry are present. The combination of protecting water resources with adequate prevention measures and necessary remedial activities that should satisfy the very strict requirements necessary for the protection of the karst aquifers while still allowing for present and future human activities is difficult – but not impossible – to achieve. One good example is the present highway with a closed dewatering system and waste water treatment before the water passes into the karst underground system.     

Climate change and groundwater resources in Lao PDR

The national economy of Lao PDR is highly dependent on water resources. Consequently, the sustainable management of groundwater and successful adaptations to future climate change are major concerns. Climate projections for Lao PDR predict increased rainfall and hot weather, with more intense rainfall events and more frequent and severe droughts and floods. Under climate change, reductions in the amount and quality of groundwater are two critical problems. Reductions of the groundwater level will restrict the access of local people to groundwater resources, thereby posing a threat to food security and livelihoods. Lao PDR suffers from a limited number of human resources with the requisite skills to perform groundwater investigations and provide sustainable management. For the successful implementation of groundwater management plans, limitations associated with funding and technology should be resolved via support from the government and international cooperation. Advanced action plans for capacity building and training courses should be established to strengthen administrative and individual capacities. Technical measures, such as groundwater monitoring, aquifer characterizations, and water treatment systems, should be implemented to manage future climate change and water resource security.     

Interpretation for technical requirements of mapping regional groundwater resources

Under the organization of China Geological Survey,relevant departments have made industry specifications and technical requirements based on hydrogeological survey data collection at the scale of 1:50 000.Among them,groundwater resource map is a must.According to nationally unified technical requirements of mapping groundwater resources put forward in 2018,this paper mainly interprets relevant principles,content,methods,diagrams as well as legend,and further to point out future directions:Higher precision will equal to higher demand of application,so that is there any more effective way to further interpret application aspect rather than only rules?     

Groundwater protection in Mediterranean countries after the European water framework directive

The European Water Framework Directive (WFD) has driven the protection of groundwater and characterization of water bodies. Development of appropriate and efficient approaches which consider the special features of the hydrologic regime is essential. The results of different projects that have been carried out to integrate characterization and protection of water bodies are summarized herein. In the Les eaux de la Mediterranée (AQUAMED) Project, applicability to the Mediterranean Region of guidelines provided by the European Commission to facilitate the WFD implementation has been verified. The Background criteria for the identification of groundwater thresholds (BRIDGE) Project developed a methodology to establish threshold values of pollutants contributing to the chemical status of groundwater bodies. This method has been applied to pollutants used to classify groundwater bodies as at risk of not achieving objectives of the WFD. Selected features of protection areas for drinking water and safeguard zones are analyzed, as well as the possibility of using wellhead protection areas.     

Stable chlorine isotopic signatures and fractionation mechanism of groundwater in Anyang,China

The present work provides an online Bench II-IRMS technique for the measurement of stable chlorine isotope ratio, which is used to measure the δ³⁷Cl of 38 groundwater samples from the Karst and Quaternary aquifers in Anyang area. The regional distribution and signature of δ³⁷Cl value are characterized on the base of isotopic data. The results suggest that the δ³⁷Cl value of Quaternary groundwater decreases with increasing Cl^? concentration, and has no correlation with δ¹⁸O and δD values, but closely correlates with the depth to water table. The fractionation mechanism of the chlorine isotope is expounded according to the type of groundwater. The δ³⁷Cl value of karst water is generally positive, which is relevant to the dissolution of evaporite (gypsum mine), and may be caused by the mixing of groundwater and precipitation. The groundwater of Quaternary unconfined aquifer is mainly recharged by precipitation, and the δ³⁷Cl value of groundwater is generally negative. The δ³⁷Cl value of groundwater in Quaternary confined aquifer is more negative with increasing the depth to water level and elevated Cl^? concentration, which is possible to result from the isotope fractionation of ion filtration. The groundwater with inorganic pollutants in Quaternary unconfined aquifer has generally a positive δ³⁷Cl value.     

Climate change and groundwater resources in China

Water resources play an important role in supporting the economic and social development of China. The impact of climate change on water resources has become a bottleneck in this process, especially for major projects, with surface water and groundwater systems experiencing considerable impacts. The annual natural recharge of fresh groundwater is 8 840×10~8 m~3, which accounts for approximately 31% of the water resources. Groundwater is the most significant water source for many cities and energy bases, and it is also the main source acting as a buffer against extreme climate events caused by climate change. However, most of the groundwater in China buried deeply and unevenly, which increases the difficulty of investigating and exploiting this resource.This paper illustrates the general conditions of China water resources and hydrogeological hazards, such as karst sinkholes, surface subsidence, and soil salinization, caused by climate change, El Nino, La Nina, other climate events and human activities and presents the regulatory measures enacted to mitigate these issues in China.The China Geological Survey(CGS) has organized professional teams to investigate and evaluate groundwater resources and the environment since 1999. Based on these investigations, the total quantity, expected exploitable quantity and current exploited quantity of groundwater in whole China have been evaluated. In addition, an evaluation of the groundwater pollution caused by climate change throughout China and key areas has been conducted. At present, the CGS is conducting national groundwater monitoring projects and establishing regional engineering and technical measures for water resource exploitation and utilization.