Recharge Elevation Research Articles

Deep groundwater recharge mechanism in the sedimentary and crystalline terrains of Sri Lanka: A study based on environmental isotope and chemical signatures

Springs discharge groundwater that travels along flow paths of different spatial and time domains. In many instances, it is difficult to describe its involved groundwater movement, availability as well as geochemical evolution due to its hidden nature. The present study has assessed the deep groundwater in the form of thermal and non-thermal springs in the Palavi and Vanathavillu basins of sedimentary terrain as well as the Southern, Eastern, and Eastern-North Central lowlands of the crystalline terrain of Sri Lanka, using isotope and geochemical approaches. The results revealed that cation exchange in the sedimentary aquifers, whereas rock-water interaction in hard rock and fairly deep aquifers, are the important factors that control the groundwater chemistry. Artesian wells in the sedimentary terrain are mainly recharged by meteoric water, moving through fractured basement rocks at elevations from 100 to 200m above sea level, and have a long residence time. Despite its proximity to the West coast, the data acquired do not indicate that there is seawater mixing. Mixing of percolated water through an unconsolidated geological matrix appears to promote an increase in the salinity of groundwater. Non-mixed, non-evaporated, and young groundwater with a recharge elevation of more than 1000 m above mean sea level can be found in the Southern lowlands of the crystalline terrain. In the Eastern North Central lowlands, groundwater is lowland originated, fast replanished and significantly mixed with evaporated surface water. Thermal waters do not contain tritium and therefore are older than 50 years and have deeply percolated. Artesian water in the Eastern region is high altitude originated and intensely rock-water interacted. Some hot springs in the same area emerging through weathered overburden have water significantly mixed with recent precipitation. Thermal springs that emerge through quartzite bedrock have a non-mixed, non-evaporated, and less rock-water interacted nature. Both thermal and non-thermal water with artesian conditions have clearly indicated that they originate from a common recharge source but with different flow paths, penetration depths, and travel distances, resulting in different chemical characteristics. Non-thermal springs are recharged by recent precipitation and have percolated only to shallow depths.

Miocene to modern hydrothermal circulation and high topography during synconvergent extension in the Cordillera Blanca, Peru

AbstractThe Cordillera Blanca detachment in the highest elevations of the Peruvian Andes has been accommodating synconvergent extension since the late Miocene. Stable isotope analysis of synkinematic mica from its exhumed footwall shear zone provides new constraints on deep meteoric-hydrothermal circulation during ductile deformation and regional paleoelevation. Muscovite and biotite that deformed and/or grew synkinematically in the shear zone have δ2H values of −131‰ to −58‰ and −149‰ to −98‰ (versus Vienna standard mean ocean water, VSMOW), respectively. The δ2H value difference between coexisting muscovite and biotite is consistent with equilibrium fractionation of the same fluid at the same temperature. Calculated δ2H values of water (−107‰ to −78‰) in equilibrium with these micas are indistinguishable from those of present-day, deeply circulated (9–11 km) hot spring waters emanating from the fault. Such low-δ2H fluids indicate circulation of meteoric water to the depths of the brittle-ductile transition that cannot be explained by other mechanisms. Average recharge paleoelevation for water entering the shear zone based on hydrogen isotopes was 3400 + 500/–700 m (1σ). This is near, but ~500 m below, the present-day mean elevation of the catchments feeding modern hot springs of 3965 ± 880 m, and ~700 m below the 4200 + 700/–900 m mean recharge elevation derived from δ2H values of modern surface and thermal water. The consistency between modern and ancient fault-assisted hydrothermal systems and elevation suggests that high topography, steep relief, and meteoric-hydrothermal circulation have persisted throughout the history of the Cordillera Blanca detachment system.

Stable isotopes changes in groundwater: a case study in Mudal and Clapar springs, West Progo

Hydroisotope studies were carried out on Mudal and Clapar springs located in the central part of the West Progo Dome. The research was conducted by taking samples of groundwater in each spring for three periods, representing the rainy (2016), dry (2017), and rainy (2018) seasons. Data on stable isotope content of 18O and D were analyzed to see the hydroisotope characteristics of groundwater and their relationship to climate change. The results show that the stable isotope content of groundwater in both springs was relatively stable, with insignificant changes over time and season. Mudal springs tend to show light isotopes, indicating deep aquifer or high elevation recharge, less affected by the season. Clapar spring shows heavy isotopes, which may be sourced from a shallow aquifer with mixing/evaporation processes and are more influenced by the season. Meanwhile, the range value of δD in the two springs shows slightly - totally changes, indicating that the D content also changes due to seasons, although it is small. The δD enrichment shows the medium-large change in both spring springs, but uncertainty in Mudal. However, the D-excess value shows that the dry and rainy season conditions, which may be related to temperature or precipitation, are not much different.

Karst Recharge Areas Identified by Combined Application of Isotopes and Hydrogeological Budget

The identification of recharge areas in karst aquifers allows us to perform sustainable management of these groundwater resources. Stable isotopes (δ18O and δ2H) have been largely used to provide information about recharge elevation in many mountainous regions. In this paper, an improved version of a recent “isotope-driven model”, for the identification of recharge areas, was applied to Capodacqua di Spigno Spring (south of the Latium region). The model upgrade consists of a preliminary check procedure to estimate the degree of influence of the rainfall’s isotopic variability on the spring water. This additional procedure gives us an indication of the reliability of the model and its applicability conditions. Moreover, the dataset of the spring was updated to analyze the degree of reliability of the isotope-driven model. The purpose of this study was to combine the previously mentioned isotope-driven model with hydrogeological tools. A quantitative study of the basin, based on the estimation of the average monthly infiltration volume, was performed by using the inverse hydrogeological water budget. In this way, the qualitative model for the recharge areas’ estimation was validated by a quantitative hydrogeological tool. Both models show that, for karst mountain basins, the recharge areas decrease as the average recharge elevations increase, including areas at high altitudes.

Investigation of meteoric water and parent fluid mixing in a two-phase geothermal reservoir system using strontium isotope analysis: A case study from Southern Bandung, West Java, Indonesia

Determinations of the recharge area and recharge mechanism in geothermal systems are essential for reservoir management and a sustainable resource use. To address this problem, studies aplenty have aimed to identify the recharge elevation using stable water isotopes, δ2H and δ18O. Nevertheless, the physical and chemical processes involved in the generation of a reservoir fluid from a deeply infiltrated recharge flow remain poorly understood. This study aims to clarify this process using strontium (Sr) concentrations and isotope composition from water and well rock samples by selecting a geothermal field with a two-phase reservoir system in Southern Bandung, West Java, Indonesia. The water samples are characterized by variable Sr isotopic compositions (87Sr/86Sr) (0.70450–0.70725) and low Sr concentrations (0.01–0.72 ppm). The 87Sr/86Sr of the well rocks is also variable (0.70400–0.70827) with particularly high Sr concentrations (9.1–53 ppm). Three types of domain that are the combinations of the reservoir fluid mixing with groundwater are identified. The first two types are shallow and deep groundwater composed of 90 % meteoric water and 10 % upflow fluids with Sr concentration 0.01 to 0.11 ppm and the 87Sr/86Sr from 0.7055 to 0.70725. The shallow groundwater may possibly carry a 87Sr/86Sr anomaly (higher than 87Sr/86Sr of plagioclase: 0.7065) from the anthropogenic activities through the pathways created by the intersection of the NW-SE and NE-SW inferred regional faults in the west part of the field, hosted by the Wayang Windu Formation. The deep groundwater type is also a mixture of 10 % parent fluid hosted by the deeper aquifer rocks Malabar Formation, with lower strontium isotopes ratio than the first aquifer (87Sr/86Sr 0.7045–0.7055). The third groundwater refers to the perched aquifer with mixture of 30 %–70 % parent fluid that has undergone condensation and mixing processes in Pangalengan Formation (87Sr/86Sr 0.70452–0.7052). This groundwater is thought to be the source of mostly hot springs in the study area.

The Zhacang thermal field, Qinghai Province, China: its geology, geophysics, chemistry, and conceptual model

The Zhacang thermal field has the highest temperature and the most typical characteristics among the 84 geothermal anomalies discovered in Qinghai Province, China. It is located 15 km southwest of Guide County and has a total area of 8.4 km2, where two geothermal wells have been drilled since 2011. This paper summarises the geological conditions, drilling data, geophysical exploration data, and hydrochemical characteristics of the Guide–Zhacang geothermal field. The Zhacang geothermal field has a high geothermal flow value and is rich in geothermal resources with high thermal conductivity (2.910 W/(m•K)) and high geothermal flow value (87–117 mW/m2). The main strata are made up of Neogene mudstone, Triassic sand slate, and Indosinian granite and granodiorite, which provide a good thermally insulating cover layer and storage zone. The Zhacang and Reguang faults are deep, which helps the deep heat source and underground hot water move upward. The source of borehole hot water and hot spring water in the Zhacang geothermal field is atmospheric precipitation with a recharge elevation of 3320–3470 m, and the circulation depth is −2888.6 m. The results of explorations and surveys are integrated to propose a new conceptual model of the Zhacang geothermal reservoir.

Multiple fluid-mineral equilibria approach to constrain the evolution of thermal waters in the Hisaralan geothermal field, Simav Graben, western Turkey

In this study seasonal changes in the geochemical and stable isotope compositions of Hisaralan thermal waters in Simav Graben, western Turkey, were investigated with regards to a variety of mineral-water interactions and mixing processes. The Hisaralan and Emendere geothermal waters, with temperatures of up to 99 °C, were mostly of Na-HCO3 and Ca-HCO3 types. The δ18O and δ2H values of the Hisaralan waters ranged from -9.32‰ to -8.73‰ and -65.02‰ to -61.10‰, with maximum seasonal differences of 0.3‰ and 1.8‰. The Emendere waters were represented by a more positive range of δ2H values (-54.95‰ to -54.61‰), while their δ18O compositions (-9.04 to -8.41‰) were very similar to those of the Hisaralan waters. The stable isotope compositions of the Hisaralan thermal waters were consistent with those of the global meteoric water line, whereas the Emendere waters closely resembled those of the Marmara meteoric water line. The δ13C of the dissolved inorganic carbon varied from -4.33‰ to -2.77‰ for the thermal waters and from -13.84‰ to -12.51‰ for the cold waters. These values indicated a marine carbonate origin for the former and an organic source for the latter. Sulfur isotope systematics of dissolved sulfate in the Hisaralan geothermal waters indicated that the sulfate was most likely derived from the dissolution of marine carbonates and terrestrial evaporites. Chemical geothermometers applied to the Hisaralan thermal waters yielded average reservoir temperatures of 123 to 152 °C, which were rather consistent with those estimated using the silica-enthalpy (146 to 154 °C) and chloride-enthalpy (142 to 178 °C) mixing models. The recharge elevations of the thermal waters that were computed from the δ2H compositions were between 1060 and 1330 m.

Groundwater Recharge Area Based on Hydrochemical and Environmental Isotopes Analysis in the South Bandung Volcanic Area

The determination of recharge areas needs to support the groundwater conservation in the southern volcanic Bandung area. This study aims to determine the recharge area based on environmental isotopes and hydrochemical. A sampling of 26 groundwater was carried out at springs, dug wells, and drilling wells. The variation in groundwater chemistry principally is controlled by a combination of ion exchange, silicate weathering, calcite, and dolomite dissolution of minerals. The hydrochemical facies were CaCl, CaMgCl, CaMgHCO3, CaHCO3, and NaKHCO3. The CaHCO3 facies describe moderate groundwater flows. The NaKHCO3 facies shows the mixing of shallow and deep groundwater. The recharge area in the central, proximal, and medial facies zone consists of 3 groups. Group I is considered water originating from local rainwater infiltration; Group II is considered the infiltration elevation which ranges from 980–1230 m asl; Group III estimated to be derived from the recharge elevation between 750–970 m asl, Group IV are more likely to show symptoms of evaporation or interaction with surface water. The discharge area is characterized by less active groundwater circulation, with dominant HCO3– and TDS value in the distal facies zone. Hydrochemical variation helped the identification of recharge areas in the volcanic facies.

Isotopic temporal and spatial variations of tropical rivers in Thailand reflect monsoon precipitation signals

AbstractStable isotopic compositions (δ18O andd‐excess) from 25 rivers in Thailand were analysed monthly during 2013–2015. Results indicated that monsoon precipitation fundamentally influences the river isotopes. The overland flow supplied from monsoon precipitation and human‐altered flow regimes produces considerable isotopic variability. Spatial and temporal variations were observed among four principal geographical regions. The seasonality of monsoon precipitation in mountainous Thailand produced large variations in isotopic compositions because most rainfall occurred during the southwest monsoon, and dry conditions prevailed during the northeast monsoon. The northern and northeastern regions are mountainous, highland areas. Low δ18O values were found in these regions, likely because of altitude effects on precipitation. Conversely, monsoonal precipitation continually supplies rivers in southern Thailand all year round, producing higher and more consistent δ18O values than in the other regions. The Chao Phraya plain in the central region experienced enrichment of δ18O river runoff related to evaporation in irrigation systems. Larger catchment areas and longer residence times resulted in more pronounced evaporation effects, producing lower values ofd‐excess and local river water line slopes compared with precipitation. The isotopic differences between river waters and precipitation were utilized to determine river recharge elevations and water transit time. The methods presented here can be used to explore hydrological interactions in other tropical river basins.

A Mountain‐Front Recharge Component Characterization Approach Combining Groundwater Age Distributions, Noble Gas Thermometry, and Fluid and Energy Transport Modeling

AbstractMountain‐front recharge (MFR), or all inflow to a basin‐fill aquifer with its source in the mountain block, is an important component of recharge to basin‐fill aquifer systems. Distinguishing and quantifying the surface from subsurface components of MFR is necessary for water resource planning and management, particularly as climate change may impact these components in distinct ways. This study tests the hypothesis that MFR components can be distinguished in long‐screened, basin‐fill production wells by (1) groundwater age and (2) the median elevation of recharge. We developed an MFR characterization approach by combining age distributions in six wells using tritium, krypton‐85, argon‐39, and radiocarbon, and median recharge elevations from noble gas thermometry combined with numerical experiments to determine recharge temperature lapse rates using flow and energy transport modeling. We found that groundwater age distributions provided valuable information for characterizing the dominant flow system behavior captured by the basin‐fill production wells. Tracers indicated the presence of old (i.e., no detectable tritium) water in a well completed in weathered bedrock located close to the mountain front. Two production wells exhibited age distributions of binary mixing between modern and a small fraction of old water, whereas the remaining wells captured predominantly modern flow paths. Noble gas thermometry provided important complementary information to the age distributions; however, assuming constant recharge temperature lapse rates produced improbable recharge elevations. Numerical experiments suggest that surface MFR, if derived from snowmelt, can locally suppress water table temperatures in the basin‐fill aquifer, with implications for recharge elevations estimated from noble gas thermometry.

Evaluation of recharge areas of Arusha Aquifer, Northern Tanzania: application of water isotope tracers

Abstract In Arusha urban, northern Tanzania, groundwater contributes about 80% of the water supply. However, elevated fluoride levels and evidence of anthropogenic pollution have been reported in the groundwater around Mount Meru which is a water source for Arusha urban. This study aims at understanding the recharge areas and flow pathways of groundwater in what has been a poorly monitored area. The study uses the isotopic ratio of oxygen and hydrogen to estimate the groundwater recharge area and flow pathway. The results show the recharge elevation of groundwater is between 1,800 and 3,500 m above mean sea level on the slopes of Mount Meru. The average fluoride contents in the study area are 5.3 ± 0.4 mg/L greater than the limits of 1.5 mg/L set by the World Health Organization (WHO) and Tanzania. The nitrate concentration of 83.9 mg/L at the lower elevation areas (<1,400 m above mean sea level) exceeds the 50 mg/L WHO limit. The relationship of F− with δ18O and NO3− suggests the leaching of fluoride in high altitudes and dilution in lower altitudes.

Geochemical insights into groundwater movement in alpine karst, Bear River Range, Utah, USA

Alpine karst aquifers control the availability and longevity of some water resources, but are not well understood. A conceptual model of the alpine karst aquifer system in the Bear River Range of northern Utah (USA) has been developed by geochemical analysis (major ions, δ18O, δ2H and δ13C values) of seasonal water samples from seven perennial springs, and residence-time assessment (3H and CFCs) of two low- and two high-discharge springs. All spring data can be explained by reaction paths dominated by the dissolution of calcian dolomite. The δ13C values align well with reaction paths for open-system dissolution. Saturation indices and low Ca:Mg molar ratios indicate that incongruent dissolution exerts a strong control on water–rock interactions, complicating interpretation of natural solute tracers. Values of δ18O and δ2H in springs follow the Utah meteoric water line. Snow δ18O values correlate with elevation, but not with increasing rainout distance, providing qualitative estimates of recharge elevation that generally align with previous dye-traces to five of the seven springs. Concentrations of 3H and CFCs likely are best described by binary mixing of subannual recharge with 60–65-year-old groundwater, suggesting that the alpine karst aquifer system in the Bear River Range is best represented by a double-porosity model. Subannual recharge documented by dye traces implies that caverns are the primary flowpaths to the springs, but the presence of decadal-age water may indicate that lower permeability flowpaths dominate during baseflow. No evidence was found for a longer-residing flow component, suggesting high sensitivity to future climate variability.

Bayesian estimates of the mean recharge elevations of water sources in the Central America region using stable water isotopes

Study regionCentral America Study focusKnowledge of the mean recharge elevation (MRE) of water resources is important where water resources are vulnerable. The purpose of this study was to develop and apply a Bayesian approach which incorporates isotopic uncertainties and evaporative effects on isotopic compositions to determine the MRE of 680 surface water sources from Central America. Differences were assessed between results from our approach and those from other isotope-based methods that do not account for these factors. New hydrological insights for the regionDifferent MRE patterns were identified for Pacific and Caribbean basins, which were characterized by distinct isotopic signatures: 1) the Pacific slope had recharge occurring at higher elevations relative to the source mean catchment elevation (MCE) and 2) the Caribbean slope had recharge largely occurring at elevations lower than the MCE. These relationships were quantified: MREP = 1.072 (MCE) + 45.65 (Pacific: r2 = 0.93, error = 144 m); MREC = 0.9493 (MCE) – 28.24 (Caribbean: r2 = 0.83, error = 190 m). The MRE, surface water site elevation (SWSE), and MRE-SWSE differences were generally greater on the Pacific slope, which hosts most of the region’s population. Bayesian MRE estimates were on average lower than MREs obtained using other methods and may better approximate the actual (recharge-weighed) MRE, suggesting that the inclusion of isotopic uncertainties, evaporative corrections, and recharge likelihoods all positively effect MRE estimations.

Fluid geochemistry in a low-enthalpy geothermal field along a sector of southern Apennines chain (Italy)

The chemical and isotopic features of the fluids (water and gases) in the Lucane thermal area (southern Italy) have been investigated in order to verify their origin, water temperature in the geothermal reservoir, and to recognize the main natural processes concerning the water composition during ascent towards the surface. The Lucane geothermal system is placed in the southern sector of the Apennines chains, a seismically active area, close to the southern base of the Mt. Alpi carbonate massif. Along the study area, two main sets of high-angle faults form an almost orthogonal fault system that, as suggested by local structural geology, acts as a preferential pathway for uprising deep fluids. Here, we recognized two different types of waters: (i) cold shallow waters having a meteoritic origin and interacting with carbonate rocks (dolomite and calcite), whose dissolved gases show a dominant atmospheric contribution and (ii) hypothermal waters (average temperature of 21 °C), having a meteoritic origin and interacting with both carbonate rocks and inter-bedded evaporitic deposit. Geochemical data allow estimating a geothermal reservoir temperature between 30 °C and 60 °C, according to silica and Ca/Mg geothermometers, respectively. A heat discharge related to hypothermal groundwater flow between 7.75E+06 and 2.00E+07 J/s was computed. δ18O and δ2Η data allowed recognizing a meteoric origin for hypothermal (hereafter TL) waters, with mean recharge (infiltration) elevations between 1300 and 1700 m a.s.l. These waters are gas-rich (e.g., CO2 and He), which amounts are higher than those in air-saturated water (ASW). Carbon and helium isotope signature in the TL waters indicate their mainly crustal origin and involve a tectonic control on fluid migration through the crust. Furthermore, we observe that the He isotopic signature in gases dissolved in TL waters is stable over time and its monitoring could be a powerful tool to assess the seismogenetic processes since their preparatory phases.

The Hydrochemical and Isotopic Evolution of the Surface Water and Groundwater for Impoundment in the Xiluodu Reservoir, Jinsha River, China

The construction of a large reservoir with a high dam may cause irreversible changes in the water flow system and even affect the original environmental balance. Xiluodu reservoir, as a representative of the high arch dam reservoirs in China, clearly has this potential issue. Based on the monitoring data of the hydrochemistry and stable isotopes of the water (δD, δ18O) in the Xiluodu reservoir, this study presents the evolution of the hydrochemical and isotopic characteristics of the surface water and groundwater in the reservoir before and after impoundment using cluster analysis and saturation index analysis. The main cations in the reservoir water and groundwater change from Ca2+ and Mg2+ to Ca2+ and Na+, respectively, while the ratio of HCO 3 - to the total anions dropped from 0.86 to 0.7 as the main anion. The cluster analysis results show the high correlation between the groundwater and surface water before and after water impoundment. The calculation of saturation indices indicates that the hydrogeochemical process of the groundwater includes a different trend of the dissolution of minerals. The study of deuterium excess shows that the evaporation of the groundwater near the reservoir decreased after impoundment. Based on the above results and the recharge elevation, this research concludes that the interaction between the surface water and groundwater before and after impoundment is prominent and different. The groundwater replenished the river water before impoundment, while this relationship reversed after impoundment. This evolution process is caused by reservoir storage, and the drainage system and other conditions make this evolution possible. In addition, the influence of interaction evolution on the regional water decreases continuously along the dam site, and some areas even have irreversible changes.

Headwaters drive streamflow and lowland tracer export in a large‐scale humid tropical catchment

AbstractHeadwaters are generally assumed to contribute the majority of water to downstream users, but how much water, of what quality and where it is generated are rarely known in the humid tropics. Here, using monthly monitoring in the data scarce (2,370 km2) San Carlos catchment in northeastern Costa Rica, we determined runoff‐area relationships linked to geochemical and isotope tracers. We established 46 monitoring sites covering the full range of climatic, land use and geological gradients in the catchment. Regression and cluster analysis revealed unique spatial patterns and hydrologically functional landscape units. These units were used for seasonal and annual Bayesian tracer mixing models to assess spatial water source contributions to the outlet. Generally, the Bayesian mixing analysis showed that the chemical and isotopic imprint at the outlet is throughout the year dominated by the adjacent lowland catchments (68%) with much less tracer influence from the headwaters. However, the headwater catchments contributed the bulk of water and tracers to the outlet during the dry season (>50%) despite covering less than half of the total catchment area. Additionally, flow volumes seemed to be linearly scaled by area maintaining a link between the headwaters and the outlet particularly during high flows of the rainy season. Stable isotopes indicated mean recharge elevations above the mean catchment altitude, which further supports that headwaters were the primary source of downstream water. Our spatially detailed “snap‐shot” sampling enabled a viable alternative source of large‐scale hydrological process knowledge in the humid tropics with limited data availability.

Future water resource shifts in the high desert Southwest of Northern New Mexico, USA

Study RegionThis study focuses on the headwaters of the Upper Rio Grande basin, the Pajarito Plateau, northern New Mexico, USA. Study FocusOur work examines 2050s water balance changes using the INFIL hydrologic model run under different downscaled earth system model (ESM) projections to simulate impacts on runoff, infiltration, and overall water regime shifts. New Hydrological Insights for the RegionClimate change is shifting the water balance in the high desert of the US Southwest. Across the Pajarito Plateau, increases in temperature and changing precipitation form and delivery result in increased rain during winter, spring and fall, and decreased snow during winter (47 % less snow is projected to fall). ESM projections of summer rainfall vary, with increases and decreases possible. High elevation recharge zones exhibit increased runoff and infiltration, but across the region aridity also increases due to warmer temperatures. This dichotomy illustrates the complexities in regional responses that occur across time and space, and require a firm understanding to mitigate impacts on the region’s ability to sustainably manage water resources within the next 30 years.

Exploring the hydrogeochemical evolution of cold and thermal waters in the Sarein-Nir area, Iran using stable isotopes (δ18O and δD), geothermometry and multivariate statistical approaches

In recent years, water management in Iran has mostly focused on monitoring, understanding and mitigating issues of water quality. To understand the processes that can affect water quality, this study carried out a geochemical study on cold (5 well water samples and 6 cold springs) and thermal (9 hot springs) waters in the Sarein-Nir area in Iran. A total of 20 water samples were collected in July 2016, and physicochemical variables such as pH, electrical conductivity (EC) and major, minor and trace element concentrations were determined. Using multivariate statistics, the main geochemical processes and possible origin of selected trace elements were investigated. The maturity and mixing processes of the waters were investigated using stable isotope (δ18O and δD) and geothermometry techniques. It was found that water-rock interaction was the predominant process, and that denitrification and ion exchange processes also took place in the groundwater system of the area. Thermal waters had an elevated EC, whereas cold waters showed elevated pH and NO3 values, indicating the impact of anthropogenic activities on water quality. Alkalinity and temperature were recognized as the most important variables that control the release of trace elements into the groundwater. Most thermal water samples were immature and belonged to peripheral water types, indicating that these samples came in part from deep circulation. Geothermometry of the thermal waters showed that the springs of the Sarein region had high temperatures compared to the springs of the Nir region. Considering that the Sarein spring waters had lower deuterium ratios than spring waters in the Nir region, it was concluded that the recharge elevation of the Sarein springs was higher than that of the Nir springs.

Changes of groundwater flow systems after the 2016 Mw 7.0 Kumamoto earthquake deduced by stable isotopic and CFC-12 compositions of natural springs

Large earthquakes change the hydrogeological properties of aquifer systems, such as permeability, and cause changes that impact groundwater flow. To understand these changes in mountain aquifer systems, we analyzed stable isotopic ratios of water molecular (δD and δ18O) of H2O and chlorofluorocarbons (CFCs) concentrations of natural spring waters and compared these values between before (2009) and after (2017) the 2016 Kumamoto crustal earthquake sequence in Kumamoto-Aso area, southern Japan. Stable isotope ratios were used to identify the spring source characteristics that reflected recharge elevations, whereas CFC age tracers were applied to evaluate the contribution of earthquake-induced additional waters from different pathways (shorter or longer) and/or CFC-enriched (contaminated) surface waters. In general, spring waters after the earthquake became more depleted in water isotopic compositions than those before the earthquake, suggesting an increased contribution of waters recharged from higher elevations across the area. In addition, changes observed in CFC-12 concentrations were classified into several increasing/decreasing patterns defined by the contribution of additional waters from different flow paths, such as older groundwater with longer flow paths, younger groundwater from shorter flow paths, and CFC-enriched (contaminated) water released from shallow aquifers and soils. These isotopic and chemical features, when combined with previously documented seismotectonic surface rupture distributions, demonstrated the occurrence of coseismic mountain water release due to enhanced permeability. These findings enabled us to document how groundwater flow changes in mountain aquifers. Although CFC age markers have rarely been applied as a tool to investigate coseismic hydrological changes, our study exemplifies their usefulness—in combination with stable isotope ratios—in such investigations.

Hydrogeological research in the Ordesa and Monte Perdido National Park (Huesca, Spain)

The National Park of Ordesa and Monte Perdido (PNOMP) is the largest mountainous limestone massif of Western Europe. It has the highest altitude karst of the whole Europe. Groundwater is essential for the genesis, development and evolution of the park. The spatial distribution of recharge infiltration capacity is obtained by using the APLIS method. Additionally, a preliminary estimation of recharge is obtained by using the HBV and Visual Balan codes. The values of average surface runoff, evapotranspiration and recharge for the whole Paleocene-Eocene aquifer in the park are respectively about 160, 360 and 1227 mm/yr, or 10, 20 and 70% of yearly precipitation. Average recharge ranges between 72 and 77% of yearly average precipitation. This highlights the high vulnerability of water resources of PNOMP to possible climate and global change, according to surface and deep karstification and the snow cover during several months a year. Water is mainly of the calcium bicarbonate and calcium-magnesium bicarbonate types. There is a dominant process of calcite dissolution, which is consistent with the carbonate nature of the most abundant materials in the park (Upper Cretaceous and Lower Paleocene Eocene). Other observed hydrogeochemical processes are anhydrite and/or gypsum dissolution, as well as a possible incongruent dissolution of dolomite in the Ordesa Valley. Water stable isotopes show that the fronts that produce the greatest precipitations come from the Atlantic Ocean. In autumn, winter and spring there is a deuterium excess in the recharge water which is assumed to be related with diurnal snow sublimation and night water vapour condensation over the snow pack. The recharge elevation zone is located between 1950 and 2600 m asl, and most of the sampled springs show short transit times, between 1 and 4 years, although one of the springs (Fuen dero Baño) shows the influence of a slowly changing regional groundwater flow system.