Isotopic Characteristics Of Groundwater Research Articles

Effect of CO2 and H2SO4 on the dissolution of a carbonate basement and alteration of silicates in a volcano-sedimentary system in central Mexico

This study explores the hydrogeochemical and isotopic characteristics of groundwater in the Irapuato Valley and Celaya Valley Aquifers in central Mexico, specifically focusing on the role of CO2 in mineral alteration during water-rock interaction. The study is grounded in the principles of hydrogeochemistry and stable isotope geochemistry, analyzing the impact of CO2 and H2SO4 on the weathering of carbonates and silicates. Hydrogeochemical analysis, including Piper diagrams, and isotopic measurements (δ13C, δ18O, δ2H), were conducted on water samples from wells in four municipalities (Irapuato, Salamanca, Villagrán, and Juventino Rosas). The data was statistically evaluated using Shapiro-Wilk tests to assess normality, skewness, and kurtosis, ensuring the reliability of the findings. The results indicate that HCO3− dominates the groundwater composition, with CO2 and H2SO4 significantly influencing mineral alteration processes. The isotopic data suggest that CO2 is primarily released from carbonate rock degassing, with slight isotopic enrichment in δ13C due to water-carbonate interaction. Hydrothermal fluids contribute to the geochemical evolution of the aquifer, leading to the formation of minerals such as tridymite, alunite, and kaolinite. Additionally, some groundwater samples exhibit evidence of thermalism and water-rock interactions, influencing their isotopic signatures and temperatures. These findings underscore the importance of CO2 in groundwater chemistry and highlight the need for further studies to understand regional flow dynamics and the potential impact of geothermal systems on water quality.

Temperature-induced arsenic accumulation in groundwater from Pliocene aquifers of a semiarid continental basin

Contributions of geothermal reservoir and aquifer rock weathering to dissolved arsenic (As) concentrations remain poorly understood. This study investigated geochemical and isotopic characteristics of groundwater from the Quaternary aquifer (Quaternary-GW) and groundwater from the middle-Pliocene aquifer (Pliocene-GW) to reveal As enrichment mechanisms in geothermal groundwater. The results showed that As concentrations in Pliocene-GW were higher than in Quaternary-GW. δ7Li values varied in a wider range in Quaternary-GW than those in Pliocene-GW, and δ11B values were generally lower in Pliocene-GW than those in Quaternary-GW. Normally, δ7Li values in Pliocene-GW showed a negative correlation with the ratio of Li to Na+, and increased along the flow path, which indicated that the prolonged residence time was responsible for high δ7Li. Negative correlations between δ11B and HCO3–, CO32– and B in Pliocene-GW revealed the processes of B desorption and silicate weathering in the middle-Pliocene aquifer. The processes of B desorption and silicate weathering were enhanced by geothermal reservoir, which was evidenced from the negative correlation between δ11B and calculated reservoir temperature. Arsenic concentration increased with increasing δ7Li along the groundwater flow path in the middle-Pliocene aquifer, indicating that prolonged residence time of Pliocene-GW promoted As enrichment. Meanwhile, As concentrations were negatively correlated with δ11B in Pliocene-GW, illustrating that silicate weathering and desorption driven by geothermal conduction were important processes for As mobilization. In samples of Pliocene-GW with similar δ7Li and relatively low δ11B, As was mainly released from the original groundwater-rock interactions, especially desorption and silicate weathering facilitated by geothermal conduction. This study provides quantitative insights into As enrichment mechanisms in geothermal groundwater.

Mantellic degassing of helium in an extensional active tectonic setting at the front of a magmatic arc (central Mexico)

Abstract The physicochemical and isotopic characteristics of groundwater and dissolved gas of central Mexico provide valuable information about the geologic and tectonic context of the area. Low–high-enthalpy manifestations (up to 98 °C in springs and more than 100 °C in geothermal wells) are distributed within the San Juan del Río, Querétaro, and Celaya hydrologic basins, located at the boundary between the current Mexican magmatic arc and an extensional continental area with intraplate volcanism called Mesa Central Province. Groundwaters in the study area represent a mixture between the cold water end-member with a Ca2+-Mg2+-HCO3-composition and a hydrothermal end-member enriched in Na+, K+, SO42−, and Cl-. Cold and hot groundwaters δ2H and δ18O plot along the same evaporation lines and do not exhibit a magmatic input. Dissolved and free gas do not show a typical volcanic composition signature. He and Ne isotope composition provide evidence of an important contribution of non-atmospheric noble gases. Although helium composition mainly has a crustal origin (21–83%), the mantellic contribution (1–39%) is higher than expected for an area lacking recent volcanism. A volatilerich magma aging at depth was discarded as the source of this mantellic helium signature but points out a recent mantellic contribution. Thus, we propose that mantellic helium comes from the sublithospheric mantle into the shallow crust through the highly permeable tectonic boundaries between the geologic provinces, namely the N−S Taxco−San Miguel de Allende and Chapala-Tula fault systems. Mantellic helium flow rates through these fault systems were estimated to have values ranging from 0.1 m/yr to 2.9 m/yr. This He flux range implies that aside from subduction, mantle volatile degassing enhanced by crustal fault systems is the main degassing process in the region studied.

Hydrochemical and isotopic characteristics of groundwater in the Continental Intercalaire aquifer system: Insights from Mzab Ridge and surrounding regions, North of the Algerian Sahara

Study regionNorth of Sahara, Algeria. Study focusThe effects of water/rock interactions and hydrodynamic conditions on the characteristics of groundwater in the Continental Intercalaire aquifer (CI) are demonstrated using hydrochemical and isotopic data from the Mzab Ridge. New hydrological insightsThe results confirm that CI groundwater in the oriental basin is highly mineralized (1010 > EC > 3500 μS/cm) and is of the SO4-Cl-Na type. However, it is poorly mineralized (340 > EC > 960) in the occidental basin and predominantly belongs to the HCO3-Ca type. The important contribution of evaporite minerals has been deduced using saturation indices and minor element ratios of Sr/Ca and Br/Cl. This is explained by lithological heterogeneities within the CI aquifer and corroborates the observations from regional piezometric features which suggest a groundwater divide located between 31.55° and 31.57 °N latitude. δ18O-NO3 and δ15N-NO3 analyses show that NO3 has a predominantly natural origin, which is soil nitrification even for the high concentrations exceeding 50 mg/L. CI groundwaters are highly depleted in both δ18O and δ2H compared to modern rainfall isotopic signatures. The most depleted ones are those situated in the Great Oriental Erg sub-basin. Isotopic values as low as δ18O=−6‰ can be taken as the limit for groundwater that is typically old. In the El Golea region, isotopic enrichment seems to indicate mixing between old groundwater and evaporation-affected groundwater infiltrating through the dunes of the Great Occidental Erg.

Hydrochemical and Isotopic Characterization of the Waters of the Manglaralto River Basin (Ecuador) to Contribute to the Management of the Coastal Aquifer

Coastal aquifers are strategic and fundamental in the development of touristic areas. The coastal aquifer within the Manglaralto River Basin in Ecuador is essential, as it is the only source of water supply for a large part of the northern part of the Santa Elena province. It is a semi-arid region where high volumes of water are pumped from the aquifer, causing a significant drawdown of groundwater levels, thus affecting the water quality. This work aims to characterize the characteristics of groundwater in the coastal aquifer using hydrochemistry and stable isotopes to propose a hydrogeological conceptual model. The methodology for determining the chemical and isotopic characteristics of groundwater follows the following scheme: (i) studies of ionic concentrations using the Piper diagram, (ii) assessment of the origin of salinity through the Cl/Br ratio, the presence of seawater intrusion through the Hydrochemical Facies Evolution Diagram HFE-D, (iii) characterization of precipitation events using stable isotopes (18O and 2H), and, (iv) development of a hydrogeological conceptual model of the study area. The results indicate that in the basin there are mixing processes of the existing water in the aquifer with recharge water, direct cation exchange processes in the freshening process during recharge, and evaporation in the unsaturated zone. A conceptual model of the flow system in the basin is built, based on the mentioned processes. The main conclusions are: seawater intrusion is present in the areas of the wells located closest to the coast, urban activity through septic tanks is affecting the quality of the aquifer, and rainfall is highly relevant in the different hydrochemical and isotopic processes that operate in the basin.

Statistical analysis of hydrochemistry and isotopic characterization of groundwater from the Parecis Basin

ABSTRACT Knowledge of mechanism controlling the hydrochemistry of groundwater are crucial requirement to understand the hydrochemical evolution and evaluate the water quality of subsurficial water resources. Thus, to understand the process governing the hydrochemistry variability and flow dynamics of the Parecis and Ronuro Aquifers, the use of statistical analysis and isotopic characterization were combined. In the correlation matrix it was found that the highest correlation coefficient was observed for HCO3-, Ca2+, Mg2+, Sr2+, SO42-, and F-, which suggested that these parameters are derived from the same source, most likely from rock–water interactions. Additionally, we noticed moderate to high correlation among NO3-, Cl-, Na+, K+, and Ba2+, which collectively are indicative of domestic sewage contamination. Finally, a principal component analysis (PCA) identified that the most variance in hydrochemistry from the evaluated samples was controlled by HCO3-, Ca2+ and Mg2+, which is associated with rock–water interaction. Regarding the 18O and 2H isotope values, it could be observed that the aquifer recharges were of meteoric origin and that the Ronuro Aquifer samples were more enriched than the PAS samples. This work reinforces the capability of multivariate statistics to discern the main process that controls the variability of groundwater hydrochemistry.

Hydrochemical and isotopic characteristics of groundwater in the Jiuquan East Basin, China

To investigate the hydrochemical characteristics and evolution of groundwater in the Jiuquan East Basin, 133 groundwater samples were collected and tested. Statistical analysis, Piper diagram, Gibbs plot, ion ratio and isotope techniques were used to analyse the samples. Our results suggest that both shallow and deep groundwater generally consist of weakly alkaline freshwater, with SO42− and HCO3− as the main anions, and Mg2+ and Na+ as the cations. The shallow groundwater has gradually evolved from the HCO3·SO4–Mg·Ca type in the southern part of the basin (the groundwater recharge runoff area) to the SO4·Cl–Na·Mg type in the northern part of the basin (the groundwater discharge area). Similarly, deep groundwater has progressively evolved from the HCO3·SO4–Mg·Ca type to the SO4·HCO3–Na·Mg type. In the groundwater recharge-runoff area, the chemical components in the shallow and the deep groundwater are mainly originated from the silicate rock weathering, the evaporite rock dissolution and the carbonate weathering. From the groundwater recharge-runoff area to the discharge area, the evaporation concentration, the cation exchange and the adsorption gradually become the main controlling factors of the shallow groundwater hydrochemical composition. The deep groundwater mainly undergoes the leaching, the cation exchange and the adsorption, during the runoff. Furthermore, based on isotope analysis, ice-snow melt water and atmospheric precipitation are identified as the main recharge sources of the shallow and deep groundwater in the area. This paper is great significance for the further protection of water resources and ecological environment, in the area.

Identifying locations and sources of groundwater discharge into Poyang Lake (eastern China) using radium and stable isotopes (deuterium and oxygen-18)

Knowledge of groundwater discharge (location and sources) into Poyang Lake is needed for water resources management and ecological security. In this study, hydrochemical and stable (δD and δ18O) and radium (223Ra, 224Ra, 226Ra, and 228Ra) isotopic approaches were employed to study the hydrochemical and isotopic characteristics of groundwater and surface water (river water and lake water) to identify the places where groundwater discharged into Poyang Lake and the groundwater discharge sources. The results showed that the groundwater discharge area was extensive during the dry season. The locations of predominant groundwater discharge were indicated by the evolution of radium and stable isotopes in lake water along two water flow profiles. At the confluence of Ganjiang and Xiushui rivers, groundwater with more negative δ18O value than that of the lake water discharged into this area, and the estimated groundwater discharge proportion in this area was close to that of the river water input. The main sources of groundwater input for Poyang Lake were inferred to originate from clastic rock pore-fissure aquifer and bedrock fissured aquifer around this lake. This study also found that groundwater affected by the anthropogenic activities may have discharged into Poyang Lake. Future studies are required to focus on groundwater discharge into Poyang Lake for its management and protection.

Geochemical and isotopic characterization of groundwater and identification of hydrogeochemical processes in the Berrechid aquifer of central Morocco

The hydrogeochemical characteristics and processes affecting the groundwater chemistry of the Berrechid Basin, central Morocco, were determined using chemical and isotopic data from 71 groundwater and six surface water samples. Chemical data shows a wide variation in mineralization, notably exceeding the permissible level of potability. Unlike the northern area, which seems to be separate from the main system, the salinity profile demonstrates a rising trend from the intake area in the south to the downstream area in the east and west, where the groundwater becomes more saline. Three basic hydrogeochemical facies are distinguished: Na–Cl, Na–Mg–Ca–Cl, and Ca–Mg–HCO3–Cl. A trend was also noticed for the last two types toward Na–Cl. Chemical composition of the groundwater is mainly determined by the influence of evaporation, cation exchange, rock weathering, salt dissolution, and anthropogenic activities. The dolomitization process has also been put forward as an explanation for groundwater saturation with respect to the carbonate minerals, particularly in the eastern and western parts. The groundwater is enriched with 2H and 18O, which independently, as well as with Cl− and NO3−, strengthens the findings from the chemical data by affirming the dominant effects of evaporation, the dissolution of minerals, and anthropogenic activities in assessing the geochemical evolution of the groundwater. Furthermore, this allows a twofold identification of recharge sources in the Berrechid aquifer: a lateral flow from the Phosphate Plateau, mainly along the southern part of the basin, and a vertical downward movement of evaporated water from rainfall, rivers, and the return of irrigation flow.

Geochemical and isotopic characterization of groundwater in the alluvial aquifer of Guelma (north-eastern Algeria)

This study aims at determining the factors and the processes controlling groundwater quality, origin, and chemistry in the alluvial aquifer of Guelma northeastern of Algeria. Hydrochemical and isotopic investigations were carried out on 21 points, including boreholes, wells, springs, and surface waters in June 2016. A thorough hydrogeological investigation has revealed that groundwater is Ca–Mg/SO4–Cl facies. The combined use of geochemical tools and multivariate statistical analysis indicates that groundwater composition is largely governed by water-rock interactions, particularly the dissolution of evaporitic minerals as well as ion exchange processes. This study reports for the first time the isotopic contents (δ18O, δ2H) of the alluvial aquifer and the surface water. The stable isotope composition for the ground- and surfacewater samples has shown a homogeneous isotopic signature and reveals non-evaporated waters in the northern and central parts of the aquifer. This is the indication of the presence of a significant recharge by modern rainfall. Evaporated waters that are characterized by relatively enriched δ18O and δ2H contents are located in the western part of the plain. This suggests the occurrence of partial evaporation at the surface prior to, during, or after infiltration through the unsaturated zone.

Hydrochemical and Isotopic Evolution of Groundwater Flowing Downstream of the Daqing River (Liaodong Bay, China)

Guo, Q.; Zhang, J.; Hu, Z., and Zhou, Z., 2020. Hydrochemical and isotopic evolution of groundwater flowing downstream of the Daqing River (Liaodong Bay, China). Journal of Coastal Research, 36(3), 608–618. Coconut Creek (Florida), ISSN 0749-0208.Hydrochemistry and specific environmental isotope ratios (δD, δ17O, and δ18O) were employed to investigate the hydrochemical and isotopic characteristics of groundwater in the downstream coastal plain of the Daqing River, China. The relative abundance of the major cations and anions of groundwater along the Daqing River changed from Ca2+, Mg2+ to Na+, Ca2+ and from to Cl–, respectively. The samples, divided into different groups on the basis of correlation coefficients, showed that the chemical composition of the groundwater samples near the Daqing River is approximately consistent with that of the Daqing River. The saturation indices calculated by PHREEQC software indicated that the main hydrogeochemical processes are evaporation and concentration along groundwater flow paths from the upper zone to the middle zone of the Daqing River basin. However, in the down zone, calcite, anhydrite, and dolomite become supersaturated. Isotopic data reveal that the groundwater is affected by the strong evaporation along the Daqing River. In the down zone of the Daqing River, the groundwater is polluted by the seawater.

Hydrogeochemical and isotopic characteristics of groundwater in Xinchang preselected site and their implications.

The safety disposal of high-level radioactive waste (HLW) has become an important issue for nuclear energy and environmental protection. Water chemistry and environmental isotope are accepted as feasible ways to trace groundwater circulation; it can effectively reveal the conversion relationship between different groundwater of the disposal site. Geochemical and isotopic tracers were used to constrain origins and chemical evolution of groundwater in the arid fissure system of the Xinchang preselected site for high-level radioactive waste geological disposal in China. Groundwater level, water temperature, and water chemistry information at different depths were obtained by multi-layer groundwater monitoring. The results show that the chemical and isotopic composition of groundwater in this fissure system is mainly controlled by evaporation, the water chemistry type of the shallow groundwater is mainly Na-Cl-SO4 or Na-Ca-Cl-SO4, and the deep groundwater is mainly Na-Cl-SO4. Based on the values of monitoring data in deep borehole, the fluctuation of groundwater level is less than 0.40m with weak hydrodynamic condition, and the geothermal gradient is 1.91°C/100m. The isotope analyses indicate that the groundwater in the system recharged by local atmospheric precipitation, and the deep groundwater recharged capacity of the site is weak and with no deep cycle.

Physical, chemical and isotopic characteristics of groundwater and surface water in the Lake Chilwa Basin, Malawi

We measured the physical, chemical and isotopic properties of groundwater and surface water from streams and Lake Chilwa in the Lake Chilwa Basin in southern Malawi. The study objective was to assess water quality and determine the cause of water quality deterioration. Groundwater from 16 boreholes, 5 stream samples and 3 samples from Lake Chilwa were investigated for temperature, pH, electrical conductivity, total dissolved solids (TDS), major ions and stable isotopes of hydrogen and oxygen. Groundwater and water from Lake Chilwa had higher ionic concentrations (e.g., Cl−, HCO3−, Na+, Ca2+, Mg2+) than stream water. Ionic evolution models indicate weathering of silicate minerals as the major control of the ionic concentrations in groundwater. The chemistry of water in Lake Chilwa is markedly affected by evaporation. The concentrations of the TDS, HCO3−, F− and NO3− in groundwater at several locations were above the recommended limits prescribed for drinking water by the World Health Organization. The results of this study show that poor groundwater quality for drinking and domestic use is due to natural water-rock interactions (TDS, HCO3−, F−) and anthropogenic pollution (NO3−). Because stream water is of good quality, and streamflow is supported by baseflow from fresh groundwater, efforts should be made to map fresh groundwater aquifers for domestic, agricultural and industrial use.

Hydrochemical and isotopic characterization of groundwater in the southeastern part of the Plateaux Region, Togo

ABSTRACTHydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO3 associated with Ca/Mg-Cl, Na-HCO3 and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution.

Hydrochemical and isotopic characterization of groundwater in the Ghis-Nekor plain (northern Morocco)

The coastal aquifer of Ghis-Nekor (Morocco) was studied to identify the major processes causing salinization of groundwater. In fact, a geochemical approach multi tracer (general chemistry and isotopes - δ2H, δ18O-H2O, δ34S, δ18O-SO4) was utilized, with the hydrodynamics to explain the processes responsible for the salinization of groundwater, and for identttifying areas most vulnerable to seawater intrusion. The recharge of the aquifer is mainly by the Al-Khattabi dam, the Nekor River and the Ghis River, on the eastern border of the plain. The water that feeds the aquifer shows a relatively high level of salinity and for this reason, the majority of sampled wells indicate high values of electric conductivity and total salinity which arrives at 7.5 g L−1. The plot of the geochemical results analyzes of groundwater in the Piper diagram shows two distinct chemical facies; sodium chloride-facies and chlorinated calcium and magnesium sulfated facies. The concentrations of 18O range between −4.15‰ and −5.73‰, while the values of 2H range between −28.4‰ and −41.7‰. The Nekor river water is depleted in heavy isotopes, and the isotopic compositions are in the order on −6‰ for 18O and −40.5‰ for deuterium. Most of the wells have a slope <8 indicating a slight evaporation before infiltration. The data show low and variable d-excess values (range from −0.02‰ to 11.6‰), reflect recharge during different climatic conditions. The isotopic concentrations of 18O-SO4 vary between 4.35‰ and 8.60‰, while the 34S isotope values range from −4.3‰ to 9.9‰. For Ghis River, these values are between −4.4‰ and 4.95‰, respectively, for sulfur and oxygen. The interpretation of the chemical and isotopic results suggesting the intrusion of seawater to increase salinity of groundwater in the region is low. However, only the NE area shows probable contamination of seawater. In contrast, wells are saline independent of seawater intrusion, the origin of the high salinity can be related to: 1- the accumulation of rivers fluid intake and water dam rich dissolved salts and sulphates, 2- the anthropogenic pollution (domestic sewage, agricultural inputs, septic uses).

Hydrochemical and isotopic characteristics of groundwater in the northeastern Tennger Desert, northern China

Groundwater is typically the only water source in arid regions, and its circulation processes should be better understood for rational resource exploitation. Stable isotopes and major ions were investigated in the northeastern Tengger Desert, northern China, to gain insights into groundwater recharge and evolution. In the northern mountains, Quaternary unconsolidated sediments, exposed only in valleys between hills, form the main aquifer, which is mainly made of aeolian sand and gravel. Most of the mountain groundwater samples plot along the local meteoric water line (LMWL), with a more depleted signature compared to summer precipitation, suggesting that mountain groundwater was recharged by local precipitation during winter. Most of the groundwater was fresh, with total dissolved solids less than 1 g/L; dominant ions are Na+, SO4 2− and Cl−, and all mineral saturation indices are less than zero. Evaporation, dissolution and cation exchange are the major hydrogeochemical processes. In the southern plains, however, the main aquifers are sandstone. The linear regression line of δD and δ 18O of groundwater parallels the LMWL but the intercept is lower, indicating that groundwater in the plains has been recharged by ancient precipitation rather than modern. Both calcite and dolomite phases in the plains groundwater are close to saturation, while gypsum and halite can still be dissolved into the groundwater. Different recharge mechanisms occur in the northern mountains and the southern plains, and the hydraulic connection between them is weak. Because of the limited recharge, groundwater exploitation should be limited as much as possible.

Geochemical and Isotopic Characterization of Groundwater in Tecate, Baja California, Mexico

Environmental isotopes and hydrochemistry are useful tools for the study of groundwater flow systems. Groundwater from Tecate area in Peninsula of Northern Baja California, Mexico, was sampled for chemical and stable isotopes analyses. Four groundwater types were identified, predominating the Mixed-HCO3 facie. A tendency of calcium to the sodium and bicarbonates to sulphates is noted. The Na+/Cl− and (Ca+2 + Mg+2)/(SO42− + HCO3−) ratios reveal an input of sodium to the system which can be related to water-rock interaction and Na–Ca exchange. The δ2H vs δ18O plot shows that evaporation has occurred during recharge, indicating that groundwater is derived from modern precipitation that is subjected to evaporation during its passage through the soil and unsaturated zone to reach the water table. In general, there is a trend of groundwater chemistry to be modified by anthropogenic processes towards the western portion.

The effects of water use on Tothian flow systems in the Mexico City conurbation determined from the geochemical and isotopic characteristics of groundwater

Groundwater flow systems have been differentiated in the metropolitan zone of Mexico City based on their chemical composition and stable isotope contents. The existing hydrogeological framework for the region provided a reference for such differentiation. Local flows (Flow-system I) represent the youngest and shallowest groundwater flow identified in boreholes on the hills. Intermediate flows (Flow-system II) in boreholes on the plain represent a mixture of inflows travelling horizontally, and vertically upwards (Flow-system IV) and downwards (overlaying aquitard leakage) to extraction boreholes. Flow-system III identified in boreholes on the plain is an intermediate flow system which extends deeper than Flow-system II. Flow-system IV, which is classified as a regional system, is related to a former thermal spring site. Groundwater travelling times, and their regional distribution and the thickness of related rock formations suggest extensive inflow supporting Flow-system IV. Future climate condition evolution (i.e. drought) will only have a limited impact on Flow-system IV as compared to Flow-system I which have relatively rapid and short flow paths. The identification of the hierarchy of the flow systems is of paramount importance in achieving adequate groundwater management in any region where the aquifer units are several thousand metres thick.

Hydrogeochemical and isotopic characterization of groundwater at Žitný Island (SW Slovakia)

Hydrogeochemical investigations and spatial variations studies on the distribution of water isotopes and radiocarbon in the groundwater of Žitný Island (Rye Island) were carried out. Žitný Island represents the largest groundwater reservoir in Central Europe (about 10 Gm3). The chemical composition of the groundwater of Žitný Island depends mainly on the chemical composition of Danube water, as well as on the length of its infiltration from the Danube River. The groundwater is characterized by potamogenic mineralization, and its chemical composition is influenced by anthropogenic contamination. Sub-surface water profiles showed enriched δ18O levels up to around 20 m water depth, and depleted values for deeper waters. The observed isotopic composition of the groundwater is similar to Danube water, suggesting that the Danube River is the main source of the Žitný Island groundwater. The core of the sub-surface 14C profile represents contemporary groundwater with 14C values above 80 pMC.

Hydrogeochemical and isotopic characteristics of groundwater in the salt chemical industrial base of Guyuan City, northwestern China

The salt chemical industrial base of Guyuan is located in the south of Ningxia, northwestern China. Guyuan had been not only an important but also a challenging area for the state’s poverty alleviation and development work for a long time. In addition, the overexploitation of groundwater for agriculture activities in recent decades had led to the decline of the water table and the degradation of the water quality. In this study, environmental isotope data for different water sources are presented and discussed to identify the hydrochemical character of the aquifer systems and to investigate the geochemical processes controlling groundwater mineralization. Piper trilinear diagrams indicate that shallow groundwater in the western mountainous area is characterized by three water types (i.e., SO4–HCO3, HCO3–SO4, and SO4) while deep groundwater is characterized by two water types (i.e., SO4 and SO4–Cl). Furthermore, hydrochemical tracers show that the groundwater in the Qingshuihe plain is of the (1) HCO3–SO4 and HCO3 types in the southern piedmont recharge zone, (2) SO4 type in the southwestern recharge zone, (3) SO4–HCO3 and HCO3–SO4 types in the midwestern recharge zone, (4) SO4–HCO3 and SO4–Cl–HCO3 types in the northwestern recharge zone, and (5) SO4–HCO3, HCO3–SO4, and SO4 types in the runoff and discharge zone. Dissolution of soluble salts is the principal contributor to the water geochemistry in the western mountainous area within the study region. However, water geochemistry in the Qingshuihe plain is primarily controlled by mixing processes and by the recharge of highly mineralized surface water and groundwater in the southwestern and northwestern piedmont areas. In the conventional δD and δ 18O diagram, the distribution of data points indicates that the groundwater is of meteoric origin and has been affected by evaporation before or during underground transit. The deep groundwater in the western mountainous area is recharged under conditions that are different from currently prevailing conditions.