HCO3 SO4 Research Articles

Влияние факторов водной среды на минерализацию цианобактерий и зеленых водорослей (Республика Коми)

This article describes crystallization formed in the exogenous mucous sheath of phototrophic microorganisms living in the surface waters of the south area of the Komi Republic. The mineralization of colonies of cyanobacteria of the Gloeotrichia sp. and green algae Chaetophora elegans was studied. The waters of rivers in the Northern Dvina basin have been studied as habitats for the microorganisms. They have a different composition: HCO3 Ca–Mg, typical for the taiga zone of a temperate continental climate; SO4–HCO3 Ca–Mg and Cl–Na (in the zone of technogenic pollution). Using the example of these neutral — weakly alkaline ultrafresh — salty (0.2—2.8 g/L) waters, it is shown that the geochemistry of the aquatic environment is one of the most important factors influencing the minerogenesis. Calcite, vaterite, quartz and halite were identified in dried colonies of microorganisms within the extracellular polymeric substance using the methods of X-ray diffractometry, electron microscopy, microprobe analysis and IR spectroscopy. The morphological features of microminerals are presented depending on the type of microorganisms. Calcium carbonate crystals and aggregates are formed within the exogenous mucous sheath of algae and cyanophytes. The carbon isotope composition of carbonates (13C –7.5 and –3.8 ‰ PDB) indicates their organic nature. The formation of minerals, morphological features of crystals and the degree of biomineralisation of colonies of phototrophic microorganisms are conditioned by the physicochemical parameters of the aquatic environment. The possibilities of chemogenic precipitation of carbonates from the studied natural waters were assessed.

Evaluation of river water quality using multivariate statistics and water quality indices: A case of Göynük canyon (Turkey)

Natural and anthropogenic water pollution caused by heavy metals has become a major problem worldwide. As a result of these processes, many harmful heavy metals are mixed into the water and endanger the environment and human health. Therefore, this study aimed to investigate the hydrogeochemical properties of the stream waters of Göynük Canyon (Göynük Stream), which is located in southern Turkey, an important touristic region of Antalya. A total of 44 water samples were retained to evaluate the geochemical type, heavy metal contamination level, and suitability for drinking and irrigation of Göynük Canyon Stream waters. All samples were analysed by inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF), and multi-parameter portable water quality assessment.Analysed water samples were found to be of classes II and III in terms of overall water quality. The average hardness level is above the limit values. The results of geochemical analyses showed that the common water types in the region are Mg–Ca–HCO3, Ca–Mg–HCO3, Ca–Mg–HCO3–SO4, and Ca–Mg–HCO3–Cl-water facies. Most of the samples belong to the "rock weathering dominated" region represented in the Gibbs diagram. The hydrogen ion concentration (pH), electrical conductivity (EC), and total dissolved solids (TDS) values vary between respectively 6.5–7.9; 230.4–720.8 μS/cm, and 149–468 mg/L. Cations and anions followed the order Ca2+ > Mg2+ > Na+ > K+ and HCO3− > SO42− > Cl− > F− > NO3−. Heavy metal anomalies in water followed an increasing order: Cu < As < Pb < Ni < Ba < Fe < Cr < Mn < Zn < Sr. These heavy metals showed high index values (Poseidon index (PoS), contamination factor (CF), enrichment factor (EF), geochemical index (Igeo), heavy metals pollution index (HPI), contamination degree (Cd), in some water samples. There is a spatial anomaly in these locations related to limestone and ophiolite. This water can be used for irrigation purposes according to Wilcox, the United States salinity laboratory diagram (USSL), permeability index (PI), Kelly's ratio (KR), and Residual Sodium Carbonate (RSC).

Hydrogeochemical characterization of groundwater in mountainous catchment and its suitability for drinking purposes in Irob, Tigray, Northern Ethiopia

Abstract The primary source of drinking water in Ethiopia's semi-arid mountainous regions is groundwater. The present study aims to assess the hydrogeochemical characteristics of low-grade basement rocks dominated by mountainous catchments. Moreover, it examines the suitability of the groundwater quality for drinking purposes in Irob, Tigray, northern Ethiopia. However, relatively little is known about the water chemistry and groundwater quality of the resources in the area. Fifteen samples of groundwater were collected and examined for ions according to standard procedures. The outcomes were assessed against the World Health Organization (WHO) drinking water quality criteria. To identify the source of dissolved ions and the process involved, graphic interpretations were applied. The results show that Ca–Mg–SO4–HCO3 and Ca–SO4–HCO3 were the dominant water types. Gibbs plots and ionic ratios reveal that silicate weathering, carbonate dissolution and ion exchange control water chemistry. Furthermore, the findings reveal that 60, 80, 46.67, 46.67, 60, 6.67, 60 and 53.33% of samples are above the safe limits of the WHO for hardness, alkalinity, total dissolved solids, electrical conductivity, calcium (Ca2+), potassium (K+), bicarbonate (HCO3-) and sulfate (SO42-), respectively. Consequently, the groundwater quality assessment demonstrates that the water sources in lower parts of the catchment are unsuitable for drinking.

Geochemistry of nitric thermal springs from Khoja-Obi-Garm thermal area (Pamir-Tien Shan region)

This paper presents data on the composition of the low-enthalpy thermal waters from the unique Khoja-Obi-Garm field located at the central part of the southern slope of the Gissar Range, in the gorge of the Khoja- Obi-Garm River, at an altitude of 1740-1960 meters. In this place, the eponymous SPA-center was built. Groundwaters from springs and boreholes of Khoja-Obi-Garm thermal area have temperatures from 57 to 93 °C, high pH (up to 8), and low TDS (less than 0.5 g/l). These waters belong to Na–SO4–HCO3 type with high content of H2SiO3 (~140 mg/l), F (up to 18 mg/l), and Rn (up to 814 Bq/l). The specific feature of these thermal waters is a predominance of N2 in the gas phase (up to 83-98 vol.%), while other gases (O2, CO2, Ar, Кr, Хe, Нe, and Ne) are nonessential. Gas content at Khoja-Obi-Garm spa waters is usually not high, does not exceed 30 ml/l. We prove that N2 and O2 are atmospheric gases, but CO2 is biogenic gas (δ13CTIC -30‰ – -22 ‰). The estimated subsurface temperature is 193-197 °C based on the silica and K/Na geothermometer. Thermodynamic speciations indicate that these groundwaters are supersaturated with clay minerals and lowtemperature zeolites and undersaturated with carbonate and aluminosilicate minerals.

Sulfur-oxygen isotope analysis of SO42− sources in cave dripwater and their influence on the karst carbon cycle

Sulfuric acid is involved in carbonate rock dissolution in karst areas and affects regional hydrogeochemical and carbon cycling processes. Sulfate sources and carbonate weathering at dripwater points of different hydrological types also differ significantly. Therefore, in this paper, three dripwater points (SQ2#, PB and MH6#) of different hydrological types in Dafeng Cave and Mahuang Cave were selected and systematically analyzed. The results show that: (1) ions in the cave dripwater mainly originated from rock weathering, and the water chemistry types were HCO3·Ca–Mg and HCO3–SO4·Ca–Mg. (2) Sulfur and oxygen isotopes reveal that sulfate in the cave water of Shuanghe Cave mainly came from a mixture of soil sulfate and chemical fertilizers. (3) The Simmr model shows that the main sources of sulfate at each dripwater point were natural sources, such as soil sulfate and gypsum dissolution. The natural sources contributed more than 80% of the sulfate in the cave water and were less affected by anthropogenic activities. (4) Carbonate weathering by sulfuric acid (CSW) can accelerate rock weathering and the prior calcite precipitation effect, involving regional CO2 exchange through fissure pipes. The forward model results show that CSW reduced the karst carbon sinks at SQ2#, PB and MH6# by about 19.44%, 23.88% and 12.74%, respectively. Therefore, the impact cannot be ignored in assessing carbon source and sink processes in karst areas.

Water–Rock Interactions, Genesis Mechanism, and Mineral Scaling of Geothermal Waters in Northwestern Sichuan, SW China

Geothermal resources are the vital renewable energy for resolving energy crisis and environmental deterioration. Understanding hydrogeochemical processes, genesis mechanisms and scaling trends is crucial for securing the sustainable utilization of geothermal resources. In this study, fourteen geothermal waters were collected for hydrochemical and δ2H–δ18O isotopic analyses in northwestern Sichuan, SW China to clarify hydrogeochemical processes, genesis mechanisms, and scaling trends. Geothermal waters were recharged via atmospheric precipitation. Three different types of geothermal waters were identified using a piper diagram. Class 1 geothermal water with HCO3–Na and HCO3–SO4–Na types formed in the contact zone with Yanshanian intrusions and heated by residual radioactive heat. The hydrochemical processes were sodium/potassium silicate dissolution and positive cation–exchange. Class 2 geothermal water with HCO3–Ca and HCO3–Ca–Mg type was carbonate–type and heated by geothermal gradient. The dissolution of carbonate minerals dominated the hydrochemical process. Class 3 geothermal water with the SO4–Ca–Mg type was determined within deep faults. The dissolution of carbonatite and gypsum minerals and the oxidation of sulfides played a vital role in the hydrochemical process. The reservoir temperatures of geothermal waters followed the orders of Class 1 (74.9–137.6 °C) &gt; Class 3 (85.9–100 °C) &gt; Class 2 (38.7–93.5 °C). Calcium carbonate scaling should be paid attention to in Class1 and Class 3 geothermal water, and calcium sulfate scaling merely occurs in Class 3 geothermal water. This study provides vital information for geothermal exploitation in western Sichuan and other similar areas.

Impacts of River Bank Filtration on Groundwater Hydrogeochemistry in the Upper of Hutuo River Alluvial Plain, North China

River bank filtration (RBF) under human supervision has been applied for groundwater recharge. This study clarified the characteristics of water composition and its origins during the reservoir water recharge RBF. The groundwater samples were collected during four periods: pre-recharge (June 2018), early recharge (November 2018), intermediate recharge (May 2019), and late recharge (October 2019). Hydrogeochemical methods (Piper diagram, chlor-alkali index, and ion correlation) and principal component analysis (PCA) were used to analyze the chemical evolution of groundwater in the aforementioned periods. TDS concentration tended to increase in the later stage due to the aggravation of carbonate rock dissolution and cation exchange adsorption. Results demonstrated a small, temporary influence of reservoir water on groundwater, characterized as the Ca–Mg–HCO3–SO4 and Ca–Mg–SO4–HCO3 types, both before and after the recharge. The research on water chemistry changes under different mixing ratios depicts that the continuation of the recharge process promotes mineral dissolution. Rock dissolution was the primary environmental control factor of groundwater components during the recharge period. This strengthened the water–rock reaction and caused potential risk impacts such as the increase of nitrate.

Hydrogeochemical characterization of groundwater resources in Wadi Araba Basin, Southern Jordan

Groundwater quality is an important factor that determines its usage for drinking and irrigational use. This study was carried out along the quaternary alluvial aquifer which extends along Wadi Araba groundwater basins, in southern Jordan. Chemical and physical parameters were measured and analyzed for thirty-seven groundwater samples collected from twenty-one wells in the study area during two periods in the year 2019; the spring season (April–May) was represented by fourteen samples and the autumn season (August–September) represented by twenty-three samples were collected to determine its suitability for drinking and irrigational purposes. The groundwater in the study area is generally of low alkalinity with an average pH value of less than 8 for both spring and autumn seasons. The water of the area is excessively mineralized due to salinity, and the increase in water salinity of the southern Wadi Araba basin is less expressed than in the northern part. The hydrochemical characterization shows that most wells of the study area are characterized by HCO3–Ca–Mg and HCO3–SO4–Ca–Mg types in the eastern escarpments of Wadi Araba (i.e., recharge area) and Cl–SO4–Na and Cl–Na types in the discharge area. There is no substantial change in the hydrochemical composition during the two seasons. Based on the Piper diagram, most of the groundwater samples (91.8%) belong to class “E” as “earth alkaline water with increased portions of alkalis with prevailing sulfate and chloride.” The Durov diagram reveals that most groundwater samples (62.2%) lay in the water genesis “field 6” which indicates that the water may be related to the reverse ion exchange of Na–Cl. The chemical composition of the water samples was compared with the drinking water standards of the World Health Organization and the Jordanian Standard. Groundwater from this area was not suitable to be a source for direct drinking based on total hardness and total dissolved solids. The dominant cation is sodium, while the dominant anion is chloride. The calculations of saturation indices for the two sampling campaigns for different minerals showed negative values of (SI) for carbonates minerals (anhydrite, gypsum, sylvite, and halite). This suggests that the groundwater in the alluvial aquifer is undersaturated with respect to these minerals in most of the study area. This is indicative of the fact that these minerals are undergoing the process of dissolution. The mineral saturation indices suggest that the dominating hydrochemical processes were dissolutions of evaporite minerals (halite and gypsum), carbonate minerals (such as calcite, dolomite, and rhodochrosite), the manganese oxide minerals (such as jarosite-K, hausmannite, pyrochroite, and pyrolusite) and reverse ion exchange.

Radon-rich waters of the Tulinka aquifers, Novosibirsk, Russia

The first integrated isotope and chemical data on radon-rich waters of the Tulinka aquifers (Novosibirsk, West Siberia) are presented. The Tulinka radon waters are fresh, with neutral to moderately alkaline рН (7.3–7.7), SO4–HCO3 Na–Mg–Ca major-ion chemistry. The amount of total dissolved solids is 720–910 mg/L, Si content 6.41–9.02 mg/L. Eh is within +169.1 – +250.0 mV, corresponding to oxidized conditions. The concentration of dissolved oxygen is 2.86–7.37 mg/L. Radon activity (222Rn) varies from 173 to 276 Bq/L. The concentrations of U, Th, and Ra isotopes are 0.015–0.017 mg/L238U, 9.59∙10−7 to 1.58∙10−5232Th, and up to 4.93∙10−10226Ra; the 232Th/238U ratio is in the range 5.81∙10−5 to 9.42∙10−4. Total α activity is not higher than 891 mBq/L, and β activity is 80 mBq/L. The compositions of stable isotopes are −15.4 to −15.1‰ δ18O, −114.2 to −112.8‰ δD, and −13.9 to −9.9‰ δ13C. The isotope signatures and recharge patterns of the Tulinka waters are insensitive to seasonal effects, which suggests the slow water exchange. Substantial seasonal variations of the content of dissolved inorganic carbon (DIC) are detected. The range of δ13CDIC in the analyzed samples (from −14.3 to −9.0‰) corresponds to a mixed CO2 origin: diffusion of soil CO2 approaching the atmospheric δ13CCO2 values, and biogenic CO2 released by decaying plant residues. The measured isotope characteristics provide evidence that the waters recharge by infiltration from meteoric sources. The approximate radiocarbon age of DIC in the Tulinka waters, determined for the first time, is 2663 ± 144 years. However, this age may be underestimated due to groundwater mixing with the present-day surface waters.

Hydrogeochemical assessment and groundwater quality in a shallow aquifer: A case study of San Luis Potosí Valley, Mexico

The chemical composition of groundwater is the product of the evolution and incorporation of major ions, the product of natural hydrogeochemical processes or human interference that occurs in an aquifer. To establish the hydrogeochemical groundwater characteristics and suitability, 47 samples were collected from shallow wells in the study area. The objective was to determine the hydrogeochemical assessment of the groundwater in the shallow aquifer and establish the water quality and pollution associated with the dissolved organic matter in the San Luis Potosí sub-basin. The water quality assessment has been carried out by evaluating the physicochemical parameters such as temperature, pH, EC, TDS, and the main ions, which present the following trend: Ca2+>Na+>K+>Mg2+, HCO3− > SO42− > Cl− > NO3. The type of water in the area is mainly of four types: Ca–Na–HCO3–Cl (32%), Ca–Na–SO4–HCO3 (19%), Na–Ca–HCO3–Cl (13%), Ca–Na–HCO3–SO4 (11%). The content of NO3− (4.0–50.0 mg L−1), NH4+ (0.03–40.0 mg L−1), SO42− (20.0–276.0 mg L−1) y PO43− (0.01–45.5 mg L−1) indicate contamination that may come from inorganic and organic matter. Organic matter of anthropogenic origin was identified by 3D fluorescence. The results of this study demonstrate that the main processes that affect and control the chemical composition of the water in the shallow aquifer of SLP are silicate weathering, albite weathering, and reversible ion exchange.

Geochemical evolution and the processes controlling groundwater chemistry using ionic ratios, geochemical modelling and chemometric analysis in uMhlathuze catchment, KwaZulu-Natal, South Africa

The sources of chemical constituents of groundwater and its associated hydrogeochemical processes in the part of Mhlathuze catchment was identified. Groundwater of the area is classified into soft to very hard and the nature is identified as acidic to alkaline. The overall electrical conductivity is < 3000 μS/cm except in three wells. The predominant water type is NaCl (69% of samples) and CaMgCl facies. Gibbs plots, mCa/Mg ratio, mNa/Cl ratio, Ca + Mg vs HCO3+SO4 plot, Na + K vs HCO3 plot, Ca/Na vs HCO3/Na, Chloroalkaline indices (CAI 1, CAI 2) and Ca + Mg–HCO3–SO4 vs Na + K–Cl plots confirm the impact of silicate, carbonate mineral weathering and ion exchange reaction in this aquifer. However, few wells are influenced by the evaporation process. Groundwater is highly undersaturated with sulphate, chloride minerals and saturated with carbonate minerals. CA revealed that Cl and SO4 are derived from anthropogenic sources and a significant positive correlation between HCO3 and Cl reveals that wastewater recharge has most likely simulated the mineral weathering in the vadose zone, which could have further enhanced HCO3 and Cl in the aquifer. PCA resulted in three factors. Factor 1 defines the influence of geogenic and anthropogenic processes while Factors 2 and 3 imply the mineral weathering and nitrification processes. Hierarchical cluster analysis defines that evaporation, anthropogenic input, silicate and carbonate weathering and nitrification process are the sources of chemical constituents of groundwater in this aquifer.

Hydrogeochemical processes in aquifers of volcano-sedimentary origin using inverse modeling

The study area is located in the Trans-Mexican Neovolcanic Belt. A complex hydrogeological system was approached, composed of metamorphic rocks, covered by sedimentary rocks of marine origin and folded, covered by tertiary clastic rocks and a volcanic sequence of Quaternary age. The main objective of this research was to carry out a hydrogeochemical characterization to identify hydrogeochemical processes. The interaction with different geological units and anthropogenic activities produces different water types (facie Ca–Mg–Na–HCO3–SO4 in the urban area, Ca–Na–Mg–HCO3 agricultural area). It was determined that the local flow contributes 55%, the intermediate 26%, and the regional 19% with ternary mixtures model. With speciation diagrams, the conditions of chemical equilibrium in the aquifer are determined. Given this scenario, inverse modeling was applied in a cross-section to identify water interaction with the different types of geological materials through which it circulates and anthropogenic activities. The inverse modeling in cross-section 71-61, from the Pico de Orizaba recharge zone, indicates that the main processes present are altering silicates and clays (albite, illite, Ca-montmorillonite, gibbsite; dolomite, halite and gypsum dissolution; calcite and kaolinite formation). In cross-section 61-51, the model shows albite, gibbsite, Ca-montmorillonite alteration; dolomite and halite dissolution; also, calcite, gypsum, kaolinite, and illite formation. In cross-section 51-53, the modeling indicates albite, gibbsite, illite, Ca-montmorillonite alteration; halite and dolomite dissolution; also, gypsum, calcite, kaolinite, formation; NH3 (g), NH4, N (2) (g), ion exchange of NaX. The organic matter plays an essential role in REDOX conditions due to anthropogenic activities of the study area.

Hydrogeochemical characteristics and sources of mirabilite in the high saline system of Sabkha Oum El Khialate, Southern Tunisia

Using hydrogeochemical approaches and geochemical modeling, integrated with data from 83 samples, including brines and fresh water, the main factors controlling the evolution of brine in the Sabkha Oum El Khialate catchment area in southeastern Tunisia are determined. Samples with high total dissolved solids (TDS), in the continental saline depression, are consistently dominated by Na–SO4 and Na–SO4–Cl water types while Ca–SO4–HCO3 and Ca–HCO3–SO4–Cl are the dominated facies in the catchment area of the sabkha. The PHREEQC geochemical modeling using PITZER database shows that most samples of the saline depression are oversaturated with respect to (sulfate minerals) thenardite, bloedite, glauberite, gypsum, and mirabilite and undersaturated with respect to calcite, halite, and dolomite. The most important hydrogeochemical processes that affect brine evolution in the Sabkha along the flow path are evaporation, gypsum dissolution, and the cationic exchange on clay minerals.

Geothermal Fluid Characterisics based on Geochemical Analysis of Hot Water in The Wawolesea Area, North Konawe Regency Southeast Sulawesi Province

North Konawe Regency is an area with interesting geothermal potential to be studied. The observed geothermal potential manifestation is located in the Wawolesea area through the collection and analysis of three hot spring samples. This study aims to determine the characteristics of geothermal fluids, namely the type and origin of the fluid by conducting geochemical analysis on samples of hot springs in the study area which further shows the content of elements and chemical compounds and their respective concentrations. The analysis in this research is Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) to obtain B and Li concentrations, conductivity meter to obtain Cl concentration, visible spectroscopy method for SO4 concentration and HCO3 concentration measured by acid-base titration. The results showed that the type of hot springs in the study area was included in the Chloride type with a percentage of 81.8156%-83.3976% with a pH value of 6.7-7.4 and a hot spring temperature of 50-54°C then plotted into trilinear diagram. The Cl-Li-B Ternanry diagram shows that the source of the fluid is in a reservoir that has the same rock structure and comes from the old hydrothermal system. Based on the results of the analysis of fluid characteristics obtained from the research, it can be concluded that the hot springs of the Wawolesea Region are an indicator of the presence of geothermal sources and further research is needed on the magnitude of the geothermal potential.

Silica geothermometry and multi indices approach to characterize groundwater from Midyan region in Northwestern Saudi Arabia

This research was performed in the northwestern part of Saudi Arabia, where physico-chemical parameters obtained from 81 groundwater samples were interpreted. High heat flow granites underlie the study area, and their weathering and erosion cause the accumulation of radioactive elements in sediments surrounding these granites, resulting in a high temperature of the circulating water. The chalcedony (no steam loss) temperature of the circulating groundwater was determined using the dissolved silica values in the samples. Based on the obtained chalcedony temperature, the samples were categorized into two groups. The first group contained 63 samples with chalcedony temperatures less than 50 °C, and the second group contained 18 samples with temperatures above 50 °C. The Cl–SO4–HCO3 ternary diagram showed that the samples with higher temperatures were chloride type and plotted close to the mature water. The silica concentration showed a strong correlation with chloride, indicating that Cl was mostly obtained from mineral dissolution, although the wide variation in Cl and TDS for a narrow range of silica values indicated groundwater mixing or anthropogenic influence. According to the Piper plot, the (Ca + Mg)-(SO4+Cl), (Ca + Mg)-(HCO3+CO3), and (Na + K)–(SO4–Cl) types are the three key groundwater facies in the area. The TDS levels in water with chalcedony temperatures above 50 °C were high (over 5000 mg/L), with chloride dominating the composition. Pollution indices of the samples in terms of heavy metals and major ions were also calculated to determine the suitability of the groundwater for human consumption. The heavy metal pollution index, heavy metal evaluation index, and heavy metal contamination index indicated no HM pollution. However, the water quality index, which uses major ions to determine drinking water quality, showed that approximately 50% of the examined samples were unfit for consumption without any primary treatment.

Hydrochemical Characteristics of Arsenic in Shallow Groundwater in Various Unconsolided Sediment Aquifers: A Case Study in Hetao Basin in Inner Mongolia, China

This study focused on the entire Hetao Basin, which can fall into four hydrogeological units, the Houtao Plain, Sanhuhe Plain, Hubao Plain, and South Bank Plain of the Yellow River, all of which are under different geological and environmental conditions. To systematically investigate the hydrochemical characteristics and spatial distribution of high-As groundwater (As &gt; 10 μg/L), 974 samples were collected from shallow groundwater. As indicated from the results, high-As groundwater had an extensive distribution, and its spatial distribution in the four hydrogeological units exhibited significant variability. Three concentrated distribution areas were reported with high-As groundwater, which were all in the discharge areas of groundwater, and the arsenic contents in the groundwater were found to exceed 50 μg/L. The hydrochemical types of high-As groundwater in the HT Plain and the SHH Plain consisted of HCO3 SO4·Cl for anions and Na for cations, while those in the other two plains included HCO3 for anions as well as Na·Mg·Ca for cations. According to the pH values, the groundwater was weakly alkaline in the areas with high-As groundwater, and arsenic primarily existed as arsenite. Furthermore, high-As groundwater in the Hetao Basin was characterized by high contents of Fe (mean value of 2.77 mg/L) and HCO3− (mean value of 460 mg/L) and a low relative concentration of SO42− (average value of 310 mg/L). This study did not identify any significant correlation between groundwater arsenic and other ions (e.g., Fe2+, Fe3+, HCO3−, SO42−, NO2− and NO3−) in the entire Hetao Basin over a wide range of hydrogeological units. The results remained unchanged after the four hydrogeological units were analyzed. The special sedimentary environment evolution of the Hetao Basin was found as the prerequisite for the formation of high-arsenic groundwater. Furthermore, groundwater runoff conditions and hydrogeochemical processes in the basin were indicated as the factors controlling the formation of high-arsenic groundwater.

Origin and Evolution of Saline Spring Water in North and Central Laos Based on Hydrochemistry and Stable Isotopes (δD, δ18O, δ11B, and δ37Cl)

This paper discusses the origin and evolution of saline springs in north and central Laos, based on chemical and stable isotopes (δD, δ18O, δ11B, and δ37Cl). All the saline springs in this study are of the Na–Cl geochemical type. The geochemical and water isotope values suggest that the saline springs in this study are mainly derived from meteoric water and/or ice and snow melt from the surrounding mountains and that they also experienced strong evaporation and intense rock–water interactions. The ionic ratios, characteristic coefficients, ternary Ca–SO4–HCO3 phase diagrams, and saturation indices of minerals show that the dissolution of halite, sulfate, and carbonate rocks may be the solute sources for saline springs in this study, whereas the underground brines in the Thakhek potash mining area are geochemically influenced by the dissolution of carnallite and sylvite. The global geothermal δ11B–Cl/B relationship and δ11B values (5.50 to 36.01‰) of saline springs suggest a continental origin of B. This B is most likely derived from marine carbonate rocks and marine evaporates (gypsum and halite) of the late Cretaceous, which is similar to the saline springs of the Nangqen–Qamdo–Simao Salt Basin. The δ37Cl value (−0.12 to +0.79) and the Cl/Br ratio (4076 to 9853) show that dissolution of late cretaceous marine halite layers, atmospheric precipitation, and water–rock interactions between volcanic rocks, mudstones, and sandstone can restrict the δ37Cl values in saline springs. Results from silica geothermometry and multi–mineral equilibrium diagrams indicate that the reservoir temperatures for the saline springs range from 87–137 °C and experience deep circulation. Hydrochemical characteristic coefficients suggest that saline springs in the Muang Say basin may have leached sylvinite and carnallite and that the potash exploration prospect in this area is relatively good.

Hydrogeochemical characteristics and geothermometry of hot springs in the Altai region, Mongolia

This study determines the properties of hot spring waters and associated rocks, calculates reservoir temperatures and depths in the Mongolian Altai region, and constructs a conceptual model for geothermal water based on these results. The hot springs consist of HCO 3 –Na, SO 4 –Na, and HCO 3 –SO 4 –Na mixed waters. They exhibit alkaline pH levels and temperatures in the range 21.3–35°C. X-ray diffraction analyses of outcrop rocks reveal silicate and carbonate-type minerals such as quartz, albite, orthoclase, dolomite, mica and actinolite, while correlation analysis indicates that the chemical composition of the hot spring water is directly related to rock mineral composition, where dissolution of albite, orthoclase and dolomite minerals has played an important role. Reservoir water circulation depths are 2615–3410 m according to quartz and chalcedony geothermometry. The results indicate that the spring water in the Mongolian Altai region comprises a low mineral content with alkaline pH levels and that the reservoir temperature can reach up to 106°C. We also propose a conceptual model for geothermal water in the Chikhertei hot spring. The geothermal water in the Mongolian Altai region has the potential for use in heating systems. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Monitoring of radionuclides in the natural waters of Novosibirsk, Russia

Results of the investigation of 238U, 232Th, 226Ra and 222Rn content in the natural waters of Novosibirsk city and adjacent territories are presented for the first time. Hydraulic interrelations between the aquifer systems of Quaternary, Neogene and Paleogene sediments, Upper Devonian – Lower Carboniferous sediments and Upper Paleozoic granites predetermined the features of hydrogeological structure. Twenty-five chemical types of water were established, with the domination of HCO3 Mg–Ca, HCO3 Na–Mg–Ca and SO4–HCO3 Na–Mg–Ca. The amount of total dissolved solids varies from 127 to 1848 mg l−1, pH from neutral to alkaline (6.9–9.5). The values of Eh vary from reductive −157 mV (O2dissolved = 0.3 mg l−1) to oxidative +280 mV (O2dissolved = 19.4 mg l−1). Silicon content varies from 0,14 to 11,77 mg l−1. The ranges within which the concentrations of radioactive elements vary in natural waters are: radon (222Rn) 0–1216 Bq.l−1, uranium (238U) 9.75∙10−8 – 0.098 mg l−1, thorium (232Th) 2.2∙10−7 – 2.1∙10−3 and radium (226Ra) 1.6∙10−12 – 3,5∙10−7 mg l−1. The maximal content of these elements in the waters of boundary territories reach 222Rn – 43,764 Bq.l−1, 238U–6.5 mg l−1 and 226Ra – 3.7∙10−7 mg l−1. The 232Th/238U ratio is 4.20∙10−5 – 2.96. The concentrations of uranium and thorium in the geological objects of Novosibirsk vary within the ranges (mg.kg−1): 238U = 1.6–3.6 and 232Th = 5.55–13.6 for sedimentary rocks, and 238U = 0.2–47.2 and 232Th = 0.8–44.1 in intrusive formations. It is established that waters with high radon content relate to the aquiferous zones of Upper Devonian - Lower Carboniferous shale rocks and hornfels, as well as Upper Paleozoic granites. The highest concentrations of radionuclides are characteristic of the aqueous scattering halos of the uranium ore deposit.

Geochemical influences on methanogenic groundwater from a low rank coal seam gas reservoir: Walloon Subgroup, Surat Basin

Hydrochemical data responds at a much slower rate to changes in groundwater conditions than does the propagation of hydraulic pressure, and therefore may provide more insight to groundwater flow paths. In low rank coal measures, where gas is biogenic, it is important to understand the fluid-rock and microbial interactions that affect the spatial and temporal distribution of groundwater composition. Pressure data may not reflect true groundwater conditions pre-anthropogenic influence, nor does it provide information on the main drivers of groundwater composition, actual aquifer behaviour or even prove groundwater flow.This study uses a process-based approach to interpret a combination of tracer (36Cl, 14C, 87Sr/86Sr, 18O/16O) and hydrochemical data obtained from coal seam gas production wells to identify the main geochemical processes and thus controls on the groundwater composition in different coal seam producing areas of the Walloon Subgroup, Surat Basin, Australia. This is arguably one of the largest coal seam gas producing regions in the world. Tracer data measured in this study show that the Walloon Subgroup behaves as a stagnant aquitard, as indicated by the almost total loss of cosmogenic tracers over relatively short groundwater flow distances (~15 km), suggestive of very low ground water flow velocities. The range of 36Cl is 9.0 to 23.8 (x 10−15) while the 36Cl values across the Undulla anticline in the eastern edge of the basin, are essentially the same (12.2–14.7) within analytical error. It is argued that these isotopic values represent secular equilibrium for the Walloon Subgroup. Radiometric carbon (14C) levels across all three production areas (Roma, Undulla Nose, Kogan Nose) are also too low (range = 0.12–1.95 pMC) for viable field interpretation largely owing to the long residence time of the groundwater and the local activity of methanogens. Groundwater flow velocity was estimated to be <0.1 m/y, which is significantly less than the 0.7 m/y recently reported for the underlying Hutton Sandstone.As a result of the low groundwater flow velocities, trends in geochemistry are visible only in production regions proximal to the subcrop. At flow distances greater than 10–15 km from subcrop, several low-temperature interactions (cation exchange, silicate weathering, matrix diffusion and hyperfiltration) start to influence groundwater composition. Shallow subsurface chemical and microbial reactions may initially dominate the geochemical composition of the meteoric groundwater, but this is then overprinted by the actions of sulfate reducers and methanogens, resulting in groundwater with the typical geochemical characteristics similar to other coal bed methane groundwater in basins across the world (low SO4, Ca, Mg and high HCO3, Na, Cl). As distance and depth increase further, low temperature fluid-rock interactions then begin to influence the groundwater composition.This holistic, process-based approach applied to a combination of cosmogenic and stable isotopes, and standard hydrochemical data interpreted against basin lithology has enabled a more comprehensive picture on the behaviour of the groundwater of the Walloon Subgroup and is applicable to the study of other sedimentary basins.