Genesis and evolution of high-pCO2 groundwaters of the Mukhen spa (Russian Far East)

We present the chemical and isotope compositions of the water and gas phases of the unique Mukhen cold high-pCO₂ spa. Estimated 5¹⁸O, 5D, and 5¹³C_tic values and data on geology and hydrogeology of the studied area indicate that the source of the groundwaters is meteoric waters, whereas carbon dioxide is of deep genesis and numerous regional faults are gas-feeding channels. Calculations of equilibrium reactions in the water-rock system show that the upper-aquifer waters (HCO₃-Ca-Mg) with low TDS are undersaturated with carbonate minerals, montmorillonites, and aluminosilicates but are oversaturated with kaolinite, whereas the lower-aquifer waters (HCO3-Na) with high TDS are oversaturated with calcite, dolomite, and clay minerals but are undersaturated with main aluminosilicates. We propose a new concept of the formation of these groundwaters, demonstrating that long interaction between rocks and groundwaters in the presence of CO₂ and considerable precipitation of secondary minerals are responsible for the high TDS of the lower-aquifer waters (up to 14 g/L) and their geochemical type (HCO₃-Na) and unusual isotope composition (5¹⁸O = -25.2%c, 5D = -69.0%c).     

Isotopic evidence of the origin of mineralized waters from the Central Carpathian Synclinorium,SE Poland

Stable isotopes of hydrogen and oxygen were determined in 45 samples of water (27 samples of oil-associated waters, 17 samples of mineral waters used by spas, 1 sample of surface river water) from the Central Carpathian Synclinorium, covering a stratigraphic range of flysch sediments from Upper Cretaceous to Oligocene. Moreover, oxygen isotope compositions of authigenic calcite (vein and cement) from core samples of four boreholes were made to evaluate isotopic equilibrium between waters and diagenetic carbonates as a function of temperature. The saline and brackish waters (TDS from1 g/l to 48.9 g/l) considered here, generally belong to four hydrogeochemical classes: Na-Cl, Cl-HCO₃-Na, HCO₃-Cl-Na and HCO₃-Na. Their isotopic composition causes them to fall to the right of Global Meteoric Water Line (GMWL) showing enrichment in ¹⁸O and ²H. On the other hand, relative to Standard Mean Ocean Water (SMOW) they are depleted in ²H and both depleted and enriched in ¹⁸O. The observed isotopic composition can be explained by the three-component mixing of surface water, diagenetically modified sea water (kind of connate water) and metamorphic water. The mixing is accompanied by an exchange of oxygen isotopes between water and carbonate cements causes ¹⁸O enrichment of interstitial waters. The contribution of isotopic exchange between water and clay minerals in shales was evaluated only theoretically basing of the literature.     

The origin of thermal waters in the northeastern part of the Eger Rift,Czech Republic

An investigation of the thermal waters in the Ústí nad Labem area in the northeastern part of the Eger Rift has been carried out, with the principal objective of determining their origin. Waters from geothermal reservoirs in the aquifers of the Bohemian Cretaceous Basin (BCB) from depths of 240 to 616 m are exploited here. For comparison, thermal waters of the adjacent Teplice Spa area were also incorporated into the study. Results based on water chemistry and isotopes indicate mixing of groundwater from aquifers of the BCB with groundwater derived from underlying crystalline rocks of the Erzgebirge Mts. Unlike thermal waters in Dě?ín, which are of Ca–HCO₃ type, there are two types of thermal waters in Ústí nad Labem, Na–HCO₃–Cl–SO₄ type with high TDS values and Na–Ca–HCO₃–SO₄ type with low TDS values. Carbon isotope data, speciation calculations, and inverse geochemical modeling suggest a significant input of endogenous CO₂ at Ústí nad Labem in the case of high TDS groundwaters. Besides CO₂ input, both silicate dissolution and cation exchange coupled with dissolution of carbonates may explain the origin of high TDS thermal waters equally well. This is a consequence of similar δ¹³C and ¹⁴C values in endogenous CO₂ and carbonates (both sources have ¹⁴C of 0 pmc, endogenous CO₂ δ¹³C around −3‰, carbonates in the range from −5‰ to +3‰ V-PDB). The source of Cl⁻ seems to be relict brine formed in Tertiary lakes, which infiltrated into the deep rift zone and is being flushed out. The difference between high and low TDS groundwaters in Ústí nad Labem is caused by location of the high mineralization groundwater wells in CO₂ emanation centers linked to channel-like conduits. This results in high dissolution rates of minerals and in different δ¹³C(DIC) and ¹⁴C(DIC) fingerprints. A combined δ³⁴S and δ¹⁸O study of dissolved SO₄ indicates multiple SO₄ sources, involving SO₄ from relict brines and oxidation of H₂S. The study clearly demonstrates potential problems encountered at sites with multiple sources of C, where several evolutionary groundwater scenarios are possible.     

Carbon isotopes and geochemical processes in CO2-rich cold mineral water,N-Portugal

This paper summarizes a new outlook on the conceptual model of Melgaço–Messegães CO₂-rich cold (≈18 °C) mineral water systems, issuing in N of Portugal, based on their isotopic (²H, ³H, ¹³C, ¹⁴C and ¹⁸O) and geochemical features. Stable isotopes indicate the meteoric origin of these CO₂-rich mineral waters. Based on the isotopic fractionation with the altitude, a recharge altitude between 513 up to 740 m a.s.l. was estimated, corroborating the tritium results. The lowest ³H content (0 TU) is found in the groundwater samples with the highest mineralization. The mineral waters circulation are mainly related to a granitic and granodioritic environment inducing two different groundwater types (Ca/Na–HCO₃ and Na/Ca–HCO₃), indicating different underground flow paths. Calcium dissolution is controlled by hydrolysis of rock-matrix silicate minerals (e.g. Ca-plagioclases) and not associated to anthropogenic sources. The shallow dilute groundwaters exhibit signatures of anthropogenic origins (e.g. NO₃) and higher Na/Ca ratios. The stable isotopes together with the geochemistry provided no indication of mixing between the regional shallow cold dilute groundwater and mineral water systems. The heavy isotopic signatures identified in the δ¹³C data (δ¹³C = 4.7 ‰, performed on the total dissolved inorganic carbon (TDIC) of CO₂-rich mineral waters) could be derived from a deep-seated (upper mantle) source or associated to methanogenesis (CH₄ source). The negligible ¹⁴C content (≈2 pmC) determined in the TDIC of the mineral waters, corroborates the hypothesis of a mantle-derived carbon source to the mineral groundwater systems or dissolution of carbonate layers at depth.     

Groundwater recharge,circulation and geochemical evolution in the source region of the Blue Nile River,Ethiopia

Geochemical and environmental isotope data were used to gain the first regional picture of groundwater recharge, circulation and its hydrochemical evolution in the upper Blue Nile River basin of Ethiopia. Q-mode statistical cluster analysis (HCA) was used to classify water into objective groups and to conduct inverse geochemical modeling among the groups. Two major structurally deformed regions with distinct groundwater circulation and evolution history were identified. These are the Lake Tana Graben (LTG) and the Yerer Tullu Wellel Volcanic Lineament Zone (YTVL). Silicate hydrolysis accompanied by CO₂ influx from deeper sources plays a major role in groundwater chemical evolution of the high TDS Na–HCO₃ type thermal groundwaters of these two regions. In the basaltic plateau outside these two zones, groundwater recharge takes place rapidly through fractured basalts, groundwater flow paths are short and they are characterized by low TDS and are Ca–Mg–HCO₃ type waters. Despite the high altitude (mean altitude ∼2500 masl) and the relatively low mean annual air temperature (18 °C) of the region compared to Sahelian Africa, there is no commensurate depletion in δ¹⁸O compositions of groundwaters of the Ethiopian Plateau. Generally the highland areas north and east of the basin are characterized by relatively depleted δ¹⁸O groundwaters. Altitudinal depletion of δ¹⁸O is 0.1‰/100 m. The meteoric waters of the Blue Nile River basin have higher d-excess compared to the meteoric waters of the Ethiopian Rift and that of its White Nile sister basin which emerges from the equatorial lakes region. The geochemically evolved groundwaters of the YTVL and LTG are relatively isotopically depleted when compared to the present day meteoric waters reflecting recharge under colder climate and their high altitude.     

Groundwater quality on the territory of Kikinda municipality (Vojvodina,Serbia)

This paper provides insight into the quality of groundwater used for public water supply on the territory of Kikinda municipality (Vojvodina, Serbia) and main processes which control it. The following parameters were measured: color, turbidity, pH, KMnO₄ consumption, TDS, EC, NH₄ ⁺, Cl^?, NO₂ ^?, NO₃ ^?, Fe, Mn, total hardness, Ca²⁺, Mg²⁺, SO₄ ²⁺, HCO₃ ^?, K⁺, Na⁺, As. The correlations and ratios among parameters that define the chemical composition were determined aiming to identify main processes that control the formation of the chemical composition of the analyzed waters. Groundwater from 11 analyzed sources is Na–HCO₃ type. Intense color and elevated organic matter content of these waters originate from humic substances. The importance of organic matter decay is assumed by positive correlation between organic matter content and TDS, HCO₃ content. There is no evidence that groundwater chemistry is determined by the depth of captured aquifer interval. The main processes that control the chemistry of all analyzed water are cation exchange and feldspar weathering.     

Isotopic and Chemical Constraints on the Biogeochemistry of Dissolved Inorganic Carbon and Chemical Weathering in the Karst Watershed of Krka River (Slovenia)

The hydrogeochemical and carbon isotope characteristics of the Krka River, Slovenia, were investigated to estimate the carbon transfer from the land ecosystem in the watershed. During the 3-year sampling period (2008–2010), temperature, pH, electrical conductivity, major ion content, dissolved inorganic carbon (DIC) and dissolved organic carbon content, and the isotopic composition of DIC (δ¹³C_DIC) were monitored in the main stream of the Krka River and its tributaries. The major solute composition of analysed waters is dominated by an input of HCO₃ ^?, Ca²⁺ and Mg²⁺ originating from carbonate dissolution. The Mg²⁺/Ca²⁺ and Mg²⁺/HCO₃ ^? molar ratio values ranging from 0.24 to 0.71 and 0.05 to 0.30, respectively, indicate a high degree of dolomite dissolution relative to calcite. Dissolved CO₂ concentrations in the river were up to tenfold supersaturated relative to the atmosphere, resulting in supersaturation with respect to calcite and degassing of CO₂ downstream. The δ¹³C values in river water range from ?15.6 to ?9.4 ‰ and are controlled by the input of tributaries, exchange with atmospheric CO₂, degradation of organic matter, and dissolution of carbonates. The mass balance calculations for riverine DIC suggest that the contribution from carbonate dissolution and degradation of organic matter have major influence, whereas the exchange with atmospheric CO₂ has minor influence on the inorganic carbon pool in the Krka River.     

Nature and role of CO2 in some hot and cold HCO3/Na/CO2-rich Portuguese mineral waters: a review and reinterpretation

 At the northern part of the Portuguese mainland, the upflow zone of several hot and cold HCO₃/Na/CO₂-rich mineral waters is mainly associated with important NNE–SSW faults. Several geochemical studies have been carried out on thermal and non-thermal hydromineral manifestations that occur along or near these long tectonic alignments. The slight chemical differences that exist between these meteoric hot and cold HCO₃/Na/CO₂-rich mineral waters seem to be mainly caused by CO₂. δ¹³C_(TIDC) values observed in these groundwaters range between –6.00 and –1.00‰ versus V-PDB (V denotes Vienna, the site of the International Atomic Energy Agency; PDB originates from the CaCO₃ of the rostrum of a Cretaceous belemnite, Belemnitella americana, collected in the Peedee formation of South Carolina, USA) indicating a deep-seated (mantle) origin for most of the CO₂. Nevertheless, in the case of the heavier δ¹³C_(TIDC) values, the contribution of metamorphic CO₂ or the dissolution of carbonate rock levels at depth cannot be excluded. Concerning the hot waters, the lack of a positive ¹⁸O-shift should be attributed to water-rock interaction in a low temperature environment, rather than to the isotopic influence of CO₂ on the δ¹⁸O-value of the waters. Received: 9 August 1999 · Accepted: 8 March 2000     

Geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district,Andhra Pradesh,India

A survey on quality of groundwater was carried out for assessing the geochemical characteristics and controlling factors of chemical composition of groundwater in a part of Guntur district, Andhra Pradesh, India, where the area is underlain by Peninsular Gneissic Complex. The results of the groundwater chemistry show a variation in pH, EC, TDS, Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^? and F^?. The chemical composition of groundwater is mainly characterized by Na⁺?HCO₃ ^? facies. Hydrogeochemical type transits from Na⁺–Cl^?–HCO₃ ^? to Na⁺–HCO₃ ^?–Cl^? along the flow path. Graphical and binary diagrams, correlation coefficients and saturation indices clearly explain that the chemical composition of groundwater is mainly controlled by geogenic processes (rock weathering, mineral dissolution, ion exchange and evaporation) and anthropogenic sources (irrigation return flow, wastewater, agrochemicals and constructional activities). The principal component (PC) analysis transforms the chemical variables into four PCs, which account for 87% of the total variance of the groundwater chemistry. The PC I has high positive loadings of pH, HCO₃ ^?, NO₃ ^?, K⁺, Mg²⁺ and F^?, attributing to mineral weathering and dissolution, and agrochemicals (nitrogen, phosphate and potash fertilizers). The PC II loadings are highly positive for Na⁺, TDS, Cl^? and F^?, representing the rock weathering, mineral dissolution, ion exchange, evaporation, irrigation return flow and phosphate fertilizers. The PC III shows high loading of Ca²⁺, which is caused by mineral weathering and dissolution, and constructional activities. The PC IV has high positive loading of Mg²⁺ and SO₄ ^2?, measuring the mineral weathering and dissolution, and soil amendments. The spatial distribution of PC scores explains that the geogenic processes are the primary contributors and man-made activities are the secondary factors responsible for modifications of groundwater chemistry. Further, geochemical modeling of groundwater also clearly confirms the water–rock interactions with respect to the phases of calcite, dolomite, fluorite, halite, gypsum, K-feldspar, albite and CO₂, which are the prime factors controlling the chemistry of groundwater, while the rate of reaction and intensity are influenced by climate and anthropogenic activities. The study helps as baseline information to assess the sources of factors controlling the chemical composition of groundwater and also in enhancing the groundwater quality management.     

Diagenetic and other highly mineralized waters in the Polish Carpathians

Highly mineralized waters of different chemical types and origin occur in the flysch formations and their bedrocks in the western part of the Polish Carpathians. The marine sedimentation water of the flysch formations is not preserved, as the most mineralized and the heaviest isotopic values of flysch waters are characterized by δ¹⁸O and δ²H values in the ranges of 5–7‰ and −(20–30)‰, respectively. Their origin is related to the dehydration of clay minerals during burial diagenesis, with molecules of marine water completely removed by molecules of released bound water. They are relatively enriched in Na⁺ in respect to the marine water, supposedly due to the release of Na⁺ during the illitization of smectites and preferable incorporation of other cations from the primary brine into newly formed minerals. In some parts of younger formations, i.e. in the Badenian sediments, brines occur with isotopic composition close to SMOW and Cl⁻ contents greatly exceeding the typical marine value of about 19.6 g/L, supposedly due to ultrafiltration. Most probably, the marine water of the flysch formations was similarly enriched chemically in its initial burial stages. Final Cl⁻ contents in diagenetic waters depend on different Cl⁻ contents in the primary brines and on relationships between diagenetic and further ultrafiltration processes. In some areas, diagenetic waters migrate to the surface along fault zones and mix with young local meteoric waters becoming diluted, with the isotope composition scattering along typical mixing lines. In areas with independent CO₂ flow from great depths, they form chloride CO₂-rich waters. Common CO₂-rich waters are formed in areas without near-surface occurrences of diagenetic waters. They change from the HCO₃–Ca type for modern waters to HCO₃–Mg–Ca, HCO₃–Na–Ca and other types with elevated TDS, Mg²⁺ and/or Na⁻ contents for old waters reaching even those of glacial age. Bedrocks of the flysch are represented by Mesozoic and Paleozoic mudstones, sandstones and carbonates, and in some areas by Badenian sediments. Brines of the Mesozoic and Paleozoic bedrocks are usually significantly enriched in Ca²⁺ and Mg²⁺ in comparison with the Badenian brines. By analogy to the deepest brines in the adjacent Upper Silesian Coal Basin, they are supposed to originate from paleometeoric waters of a hot climate.     

Geochemistry of the thermal waters of Sikhote Alin

This paper reports new geochemical data on the low temperature nitric thermal waters of Sikhote Alin. The studied alkaline waters belong to the HCO₃-Na type with significant trace element variations. The waters demonstrate an increase in temperature and TDS from the south northward of Sikhote Alin. The oxygen and hydrogen isotopic data suggest their infiltration origin. The chemical composition of these waters was formed by water-rock interaction.     

Rare earth elements,neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central,France

Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO₂-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l⁻¹. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO²⁻₃ complexes dominate (>80%) over the free metal, F⁻, SO²⁻₄ and HCO⁻₃ complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO₂-rich and pH neutral fluids is due essentially to the predominance of the CO²⁻₃ complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵ_Nd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵ_Nd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.     

Ion chemistry of groundwater and the possible controls within Lhasa River Basin,SW Tibetan Plateau

In order to study the major ion chemistry and controls of groundwater, 65 groundwater samples were collected and their major ions measured from wells within Lhasa River Basin. Groundwater has the characteristics of slightly alkaline and moderate total dissolved solid (TDS). TDS concentration ranged from 122.0 to 489.9 mg/L with a median value of 271.2 mg/L. Almost all the groundwater samples suited for drinking and irrigation. The major cations of groundwater are Ca²⁺ and Mg²⁺, accounting for 59.6 and 31.3% of the cations, respectively. Meanwhile, HCO₃^? and SO₄^2? constituted about 56.7 and 36.9% of the anions, respectively, in Lhasa River Basin. The hydrochemical type of groundwater is HCO₃-SO₄-Ca-Mg. The chemical composition of groundwater samples located in the middle of Gibbs model, which indicates that the major chemical process of groundwater is controlled by rock weathering. Carbonate weathering was the dominant hydro-geochemical process controlling the concentration of major ions in groundwater within Lhasa River Basin, but silicate weathering also plays an important role.     

Hydrochemical,isotopic, and reservoir characterization of the Pasinler (Erzurum) geothermal field,eastern Turkey

The reservoir temperature and conceptual model of the Pasinler geothermal area, which is one of the most important geothermal areas in Eastern Anatolia, are determined by considering its hydrogeochemical and isotope properties. The geothermal waters have a temperature of 51 °C in the geothermal wells and are of Na–Cl–HCO₃ type. The isotope contents of geothermal waters indicate that they are of meteoric origin and that they recharge on higher elevations than cold waters. The geothermal waters are of immature water class and their reservoir temperatures are calculated as 122–155 °C, and their cold water mixture rate is calculated as 32%. According to the δ¹³C_VPDB values, the carbon in the geothermal waters originated from the dissolved carbon in the groundwaters and mantle-based CO₂ gases. According to the δ³⁴S_CDT values, the sources of sulfur in the geothermal waters are volcanic sulfur, oil and coal, and limestones. The sources of the major ions (Na⁺, Ca²⁺, Mg²⁺, Cl^?, and HCO₃ ^?) in the geothermal waters are ion exchange and plagioclase and silicate weathering. It is determined that the volcanic rocks in the area have effects on the water chemistry and elements like Zn, Rb, Sr, and Ba originated from the rhyolite, rhyolitic tuff, and basalts. The rare earth element (REE) content of the geothermal waters is low, and according to the normalized REE diagrams, the light REE are getting depleted and heavy REE are getting enriched. The positive Eu and negative Ce anomalies of waters indicate oxygen-rich environments.     

Assessment of mixing between shallow and thermal waters using geochemical and environmental isotope tracers (N Portugal): a review and reinterpretation

Caldas de Moledo thermal (27–46 °C) spring and borehole waters issue in the region of the famous Port Wine vineyards, in the Douro River valley (Northern Portugal). The most abundant lithotypes are lower Cambrian metasedimentary rocks, Variscan granitoids and aplite-pegmatitic veins. The thermal waters are characterised by pH ≈ 9.0, TDS ranging from 200 to 350 mg/L, and belong to the HCO₃–Na facies indicating that the reservoir rock should be mainly granite. Since the local Spa is strongly dependent on water quality, the effects of mixing between local shallow cold groundwaters and deep thermal waters have been properly investigated. In the SO₄ ^2? (mg/L) versus δ¹⁸O (‰ vs. V-SMOW) diagram we can observe that some of the thermal springs show evidences of mixing (higher SO₄ ^2? concentrations) with local meteoric waters infiltrated at lower altitude sites (enriched δ¹⁸O signatures), showing the “altitude effect” in the isotopic composition of the recharge waters. Similar trends can be found in the K⁺, NO₃ ^?, Ca²⁺ and Na⁺ (mg/L) versus δ¹⁸O (‰ vs. V-SMOW) diagrams. It should be stated that SO₄ ^2?, K⁺ and Ca²⁺ are present in the fertilizers and fungicides used in the vineyards in the northern part of the country. Up to now, the thermal waters from boreholes used in the local Spa do not show evidences of mixing with shallow groundwaters contaminated with agrochemicals. The results obtained so far indicate that in the near future, special attention should be put on the possible occurrence of diffuse agricultural contamination (related to the Port Wine vineyards) in the thermal spring waters.     

Hydrogeochemical characterization and groundwater quality assessment in Al-Hasa,Saudi Arabia

Fifty groundwater samples were collected from Al-Hasa to analyze the pH, electrical conductivity (EC, dS m^?1), total dissolved solids (TDS), major anions (HCO₃^?, CO₃^2?, Cl^?, SO₄^2?, and NO₃^?), major cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺), and total hardness. The analyzed data plotted in the Piper, Gibbs, and Durov diagrams, and water quality index (WQI) were calculated to evaluate the groundwater geochemistry and its water quality. The results reveal that most of the investigated samples are Ca²⁺, Mg²⁺, SO₄^2?, Cl^? and Na⁺, and HCO₃^? water types using the Piper diagram. Na⁺?>?Ca²⁺?>?Mg²⁺ are the dominant cations, while Cl^??>?HCO₃^??>?SO₄^2??>?CO₃^2? are the dominant anions. Sodium adsorption ratio (SAR) values varied from 0.79 to 10; however, the Kelly ratio (KR) ranged between 0.1 and 2.2. The permeability index (PI) showed that well water is suitable for irrigation purposes with 75% or more of maximum permeability. The US salinity diagram revealed that the water quality classes of studied waters were CIII-SI, CIII-SII, and CIV-SII, representing height hazards of salinity and medium- to low-sodium hazard. The water quality index (WQI) results indicated that total dissolved solids are out of the drinking water standard limits in Saudi Arabia. The WQI revealed that 38% of the studied wells were considered as poor water (class III), 52% are found as very poor water class (IV), and 10% are unsuitable water for drinking class (V).     

Chemical and isotopic characteristics of fluids along the Cameroon Volcanic Line, Cameroon

Results of the chemical and isotopic analysis of the water and gases discharged from volcanic crater lakes and soda springs located along the Cameroon Volcanic Line were used to characterize and infer their genetic relationships. Variations in the solute compositions of the waters indicate the dominant influence of silicate hydrolysis. Na⁺ (40–95%) constitutes the major cation in the springs while Fe²⁺ + Mg²⁺ (70%) dominate in the CO₂-rich lakes. The principal anion is HCO₃ (>90%), except in the coastal springs where Cl-predominates. Lakes Nyos and Monoun have FeMgCaHCO₃⁻ type signatures; the soda springs are essentially NaHCO₃⁻ type, while all other lakes show similar ionic compositions to dilute surface waters. Dissolved gases show essentially CO₂ (>90%), with small amounts of Ar and N₂, while CH₄ constitutes the principal component in the non-gassy lakes. Active volcanic gases are generally absent, except in the Lobe spring with detectable H₂S. Stable isotope ratio evidence indicates that the bicarbonate waters are essentially of meteoric origin. CO₂ (δ¹³C = −2 to −8%₀ and He (³He/⁴He = 1 to 5.6R_a) infer a mantle contribution to the total CO₂. CH₄ has a biogenic source, while Ar and N₂ are essentially atmospheric in origin, but mixing is quite common.     

Origins of high pH mineral waters from ultramafic rocks, Central Portugal

This paper reviews the geochemical, isotopic (²H, ¹⁸O, ¹³C, ³H and ¹⁴C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO₃ type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ²H and δ¹⁸O suggest a common meteoric origin and that the Mg–HCO₃ type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO₃ to Mg–HCO₃ waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO₂ (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of ¹⁴C and ¹³C values, which is in agreement with the ³H concentrations being below the detection limit.     

Fluid mixing in carbonate aquifers near Rapolano (central Italy): chemical and isotopic constraints

Chemical (major and trace elements) and isotopic compositions (δD and δ¹⁸O in waters and δ¹³C in CO₂ and ³He/⁴He in gases) of natural thermal (11) and cold (39) fluids (spring waters and gases) discharging from a tectonic window of Mesozoic limestones in central Italy, have proved to be the result of mixing processes inside the limestone formations. The limestones provide a preferential route for subsurface fluid migration and they gather both descending cold, Ca-HCO₃, B-depleted groundwaters and rising convective Ca-SO₄(HCO₃), CO₂-saturated, B-rich thermal waters. Atmospherically-derived descending gas components (N₂, Ne, He), dissolved in rainfall that infiltrates the limestone system mix with N₂, Ne, He-depleted hot rising waters. Boron in the liquid phase and N₂ and Ne in the gas phase are the most useful elements to trace the mixing process. The deeper gas samples recognised in the area are associated with the hotter waters emerging in the area. In spite of being depleted in Ne and He and light hydrocarbons they have the higher measured ³He/⁴He ratios, suggesting a contribution of mantle ³He to the gas phase. This contrasts with deep circulation in the crust which would lead to increased concentration of ⁴He in the deeper gases. Paradoxically, there is more relative concentration of ⁴He in the more air-contaminated gas samples than in the deeper gas samples. A similar paradox exists when the δ¹³C of CO₂ in the deeper gas samples is considered. The shallower air-contaminated gas samples, although they should be affected by the addition of soil-¹³C depleted organic C, have δ¹³C in CO₂ more positive than the deeper gas samples recognized. Since any deep hydrothermal source of CO₂ should generate CO₂ with more positive values of δ¹³C than those measured at surface, a multiple (single) calcite precipitation process from hydrothermal solutions, with C isotopic fractionation along the rising path inside the Mesozoic limestone formations, is proposed.     

Hydrochemistry and isotopic studies to identify Ganges River and riverbank groundwater interaction, southern Bangladesh

The Ganges River water and riverbank shallow groundwater were studied during a single wet season using the hydrochemical and isotopic composition of its dissolved load. The dissolved concentrations of major ions (Cl^?, SO₄ ^2?, NO₃ ^?, HCO₃ ^?, Ca²⁺, Na⁺, Mg²⁺, and K⁺), trace elements (barium (Ba) and strontium (Sr)) and stable isotopes (O and D) were determined on samples collected from the Ganges River and its riverbank shallow aquifers. In the present study, the shallow groundwater differs significantly from the Ganges River water; it shows distinct high concentrations of Ca²⁺, Mg²⁺, HCO₃ ^?, Ba, and Sr due to water–rock interaction and this in particular suggests that the Ganges River may not contribute significantly to the riverbank shallow aquifers during wet season. Besides, the sum of the total cationic charge (∑⁺, in milliequivalents per liter) in the groundwater shows high values (2.48 to 13.91 meq/L, average 9.12 meq/L), which is much higher than the sum of the cations observed in the Ganges water (1.36 to 3.10 meq/L, average 1.94 meq/L). Finally, the more depleted stable isotopic (δ ¹⁸O and δ ²H) compositions of the Ganges River water are in contrast to those of the riverbank aquifer having enriched stable isotopic values during the wet season and the riverbank groundwater thus has a purely local origin from precipitation.