Dissolution Of Evaporites Research Articles

Fluoride enrichment mechanisms and related health risks of groundwater in the transition zone of geomorphic units, northern China

Although groundwater is the primary drinking water source in northern of China, little is known about generation mechanisms and related health risks of high fluoride groundwater at the geomorphic transition zones. Thus, 419 groundwater samples were collected from Zhangjiakou region, where is a typically geomorphic transition zone of the North China Plain and the Inner Mongolia Plateau, to conduct the hydrochemical analysis, geochemical modeling, multivariate statistical analysis, and health risks assessment. From the results, F− concentration in groundwater had a range of 0.05–9.71 mg L−1. About 37.1% and 26.2% of groundwater samples from Bashang region (BSR) and Baxia region (BXR), respectively, were over the 1.50 mg L−1, which were mainly distributed in the groundwater flow retardation area and/or evaporation discharge area. Thermodynamic simulations demonstrated that F-bearing minerals dissolution and Ca2+/Mg2+ removal via calcite/dolomite precipitation primarily governed high-F- groundwater formation in the whole study area. Competitive adsorption, evaporation, evaporites dissolution and salt-effect also affected F− enrichment in BSR. Desorption in alkaline environment, ion exchange and human activities played a vital role in F− enrichment at BXR. The multivariate statistical analysis revealed that the origin of F− contamination was geogenic in BSR; whereas, it was geogenic and anthropogenic in BXR. Besides, more than 71.8%, 51.0%, 36.1% and 25.5% of the study area exceeded the acceptable level (health index>1) for infants, children, adult males, and females, respectively. The health risks for different groups of people varied significantly and ranked: infants > children > males > females, suggesting that younger people were more susceptible to fluoride contamination. Meanwhile, females were more resistant to fluoride contamination than males. These findings are vital to providing insights on high-F- groundwater formation, investigate the situation of health risks, and conduct the integrated management for high fluoride groundwater in geomorphic transition zones at northern China.

Responses of the biogeochemical sulfur cycle to Early Permian tectonic and climatic events

The late Paleozoic was characterized by a series of continental collisions and ice ages. Despite the drastic environmental changes, sparse sulfur isotope data hinder our understanding of the late Paleozoic biogeochemical sulfur cycle, especially during the Early Permian. To overcome this potential bias, we present a high-resolution sulfur isotope record of carbonate-associated sulfate (CAS) and pyrite from the Carboniferous-Permian successions of the Svalbard archipelago. Throughout the Carboniferous, our results are largely consistent with the global trend, although the development of restricted environments resulted in a regionally observed δ34SCAS peak of +20‰ during the Gzhelian. The Early Permian δ34SCAS data in Svalbard bridge the gap in the existing record, showing a steady increase contemporaneous with the closure of the Ural Seaway and Gondwana glaciation, albeit superimposed by short-term oscillations. The enhanced incorporation of diagenetic sulfate into authigenic carbonates may have caused small-scale oscillations during the regional regression in the Artinskian, but the long-term increasing trend of δ34SCAS and its relation to known geological events can be best explained by the enhanced pyrite burial flux driven by a major shift in the locus of organic carbon burial from the continent to the ocean, with a lesser contribution from the dissolution of epicontinental seaway evaporites. Since the onset of the Middle Carboniferous Bashkirian δ34SCAS excursion also corresponds in timing to the major glaciation event and the closure of the Rheic Seaway, the sulfur isotope record in the course of the consolidation of Pangea is apparently punctuated by the episodes of increased pyrite burial and evaporite sulfate weathering, delineating the links between paleogeography, paleoclimate, and biogeochemical cycles.

Hydrogeochemical processes controlling the water composition in a hyperarid environment: New insights from Li, B, and Sr isotopes in the Salar de Atacama

Northern Chile, NW Argentina, and SW Bolivia, (“the lithium triangle”), represent a world class reservoir of lithium, but this extraordinary enrichment is still controversial, and different processes have been invoked over the years, including, geothermal waters associated with active volcanism, leaching of soluble salts from volcanic rocks and leaching of lithium-rich clays. The Salar de Atacama (SDA) represents one of the richest reservoirs of Li in northern Chile and has been extensively studied during the past years. Most of the studies have been focused in the southern and southeastern portions, where the highest lithium concentrations have been reported. However, a comprehensive model of water recharge at SDA is still imprecise. We used a combination of isotopic methods, including δ7Li, δ11B and 87Sr/86Sr ratios, with their chemical composition of a set of water samples from salt lakes, geothermal manifestations, groundwaters and surficial diluted waters (rivers and streams with low salinity). This study explores the hydrogeochemical processes controlling the water composition and solute distribution of the SDA. Our data confirm that weathering of the ignimbrites constitutes one of the most important processes in relation of solute origin in the region, where deep water-rock interactions would operate at high temperature, enhancing leaching of Li and other solutes. We determine that groundwater flow entering the SDA has undergone pre-enrichment processes (e.g., leak from Altiplano salt lakes; evaporite dissolution, among others) associated with salt inputs in the Western Cordillera. Our results provide a step forward to a comprehensive understanding of the processes that govern brine formation and lithium enrichment in a hyperarid environment, contributing to a sustainable exploration and exploitation of lithium in these environments.

Influence of permafrost and hydrogeology on seasonal and spatial variations in water chemistry of an alpine river in the northeastern Qinghai-Tibet Plateau, China

Known as the third pole of the world, the Qinghai-Tibet Plateau has been experiencing rapid permafrost warming and thawing over the last few decades. However, the impact of permafrost distribution and hydrogeology on river hydrochemistry in alpine areas remains unclear. This study conducted four sampling campaigns to reveal the temporal and spatial variations in and factors driving river hydrochemistry in the upper reaches of the Heihe River, the northeastern Qinghai-Tibet Plateau. We found that the concentrations of major ions and total dissolved solids (TDS) in river water showed substantial seasonal variations; the concentrations were generally lower during the initial thawing and thawed periods than during the initial freezing period. However, solute fluxes during the thawed period were much higher than those during the frozen period. The concentrations of major ions and TDS gradually decreased to a minimum from the permafrost meander (PM) section to the seasonal frost meander (SFM) section and then increased the seasonal frost canyon section. Using the revised forward model, we found that river solutes were contributed by carbonate weathering (mean 38.9%) > sulfide oxidation (22.9%) > evaporite dissolution (20.2%) > atmospheric precipitation (8.7%) > silicate weathering (5.0%) > glacial meltwater (4.3%). The higher TDS, Na+, Cl−, Ca2+, Mg2+, and SO42− concentrations in the PM section reflected the influence of freeze-out fractionation. The concentrations of major ions and TDS were lowest in the SFM section, indicating that the riparian porous aquifer was essential in regulating river hydrochemistry, thus reducing its spatiotemporal variations in the alpine area. In the mountain glacier–hillslope–riparian porous aquifer–river system, the river was mainly recharged by groundwater with insufficient water–rock interactions due to the rapid flow owing to the high elevation difference and high permeability of the riparian quaternary porous aquifers. Our findings provide insights into the construction of hydrogeochemical models in alpine areas and are practically important for the scientific management of water resources in the Qinghai-Tibet Plateau.

Spatial variations on the hydrochemistry, controls, and solute sources of surface water in the Weihe River Basin, China.

The Weihe River Basin (WRB), the largest tributary of the Yellow River Basin (YRB), is located in the northwest of China. As the "mother river" of the Guanzhong Plain, it plays an important role in the development of Guanzhong City Group. Based on pH, electric conductivity (EC), total dissolved solids (TDS), and major ionic concentrations of 227 samples collected from the main stream (MS), northern tributaries (NT), and southern tributaries (ST) of the WRB, we explored spatial differential characteristics of hydrochemistry and their controlling factors, solute sources, and water quality of surface water. The results revealed mildly alkaline pH and much higher TDS values than the global average with mean values of 7.9 and 1037.7mgL-1, respectively. Except NO3-, the concentrations of major ions in the MS and NT were higher than those of the ST, with similar spatial distribution patterns of Ca2+, Na+, Mg2+, SO42-, and Cl-. Na+ and SO42- were the most dominant cation and anion in the MS and NT controlled by both rock weathering and evaporation-crystallization processes. Ca2+ and HCO3- were the most dominant cation and anion in the ST mainly controlled by rock weathering process. Evaporite dissolution contributed the most to dissolved solutes in the MS and NT, while carbonate weathering dominated dissolved solutes in the ST. These findings were confirmed by the results of correlation matrix, principal component analysis (PCA), stoichiometric plots, and different water types identified as Na-SO4·Cl in the MS and NT, and Ca-HCO3 in the ST. Atmospheric and anthropogenic inputs had a minor effect on the surface water chemistry. However, human activities could not be ignored in the ST accounting for 10.9% of the total dissolved solutes, mainly because of the fertilizer application. And the surface water of the ST was more suitable for irrigation and drinking purposes than that of the MS and NT. Knowledge of our findings could contribute new insights to the solute geochemistry and sustainable management of water resources in the lithologically distinct segments of the WRB and other similar areas.

Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin, Colorado Plateau, USA

AbstractThe Paradox Basin in the Colorado Plateau (USA) has some of the most iconic records of paleofluid flow, including sandstone bleaching and ore mineralization, and hydrocarbon, CO2, and He reservoirs, yet the sources of fluids responsible for these extensive fluid-rock reactions are highly debated. This study, for the first time, characterizes fluids within the basin to constrain the sources and emergent behavior of paleofluid flow resulting in the iconic rock records. Major ion and isotopic (δ18Owater; δDwater; δ18OSO4; δ34SSO4; δ34SH2S; 87Sr/86Sr) signatures of formation waters were used to evaluate the distribution and sources of fluids and water-rock interactions by comparison with the rock record. There are two sources of salinity in basinal fluids: (1) diagenetically altered highly evaporated paleo-seawater-derived brines associated with the Pennsylvanian Paradox Formation evaporites; and (2) dissolution of evaporites by topographically driven meteoric circulation. Fresh to brackish groundwater in the shallow Cretaceous Burro Canyon Formation contains low Cu and high SO4 concentrations and shows oxidation of sulfides by meteoric water, while U concentrations are higher than within other formation waters. Deeper brines in the Pennsylvanian Honaker Trail Formation were derived from evaporated paleo-seawater mixed with meteoric water that oxidized sulfides and dissolved gypsum and have high 87Sr/86Sr indicating interaction with radiogenic siliciclastic minerals. Upward migration of reduced (hydrocarbon- and H2S-bearing) saline fluids from the Pennsylvanian Paradox Formation along faults likely bleached sandstones in shallower sediments and provided a reduced trap for later Cu and U deposition. The distribution of existing fluids in the Paradox Basin provides important constraints to understand the rock record over geological time.

Multiple stable isotopes and geochemical approaches to elucidate groundwater salinity and contamination in the critical coastal zone: A case from the Bou-areg and Gareb aquifers (North-Eastern Morocco)

Mediterranean areas are characterized by complex hydrogeological systems, where water resources are faced with several issues such as salinity and pollution. Fifty-one water samples were gathered from the Bou-areg coastal and the Gareb aquifers to evaluate the source of water salinity and to reveal the processes of the different sources of pollution using a variety of chemical and isotopic indicators (δ2H–H2O, δ18O–H2O, δ34S–SO4, and δ18O–SO4). The results of the hydrochemical analysis of water samples show that the order of dominated elements is Cl− > HCO3− > SO42- > NO3− and Na+ > Ca2+ > Mg2+ > K+ and evidenced extremely high salinity levels (EC up to 22000 μS/cm). All samples exceeded the WHO drinking water guidelines, making them unfit for human consumption. Ion ratio diagrams, isotopic results, and graphical comparing indicate that the mineralization of groundwater in the area, is controlled by carbonate dissolution, evaporite dissolution, ion exchange, and sewage invasion. The return of irrigation water plays a significant role as well in the groundwater recharge and its mineralization by fertilizers mainly. Evaporites (Gypsum), sewage, and fertilizers constitute the main sources of sulfates in the investigated water resources. These scientific results will be an added value for decision-makers to more improve the sustainable management of groundwater in water-stressed regions. The use of chemical and isotopic tracers once again shows their relevance in such zones where systematic monitoring is lacking.

Geochemical modeling and isotopic approach for delineating water resources evolution in El Fayoum depression, Egypt

In this study, an attempt was made to understand the hydrogeochemical processes controlling water resources (surface and groundwater) evolution in El Fayoum depression, Egypt. Hydrochemical, inverse geochemical modeling integrated with environmental isotopes was applied. Forty-three surface and groundwater samples were collected and analyzed for major chemistry (cations, anions) and environmental stable isotopes (δ18O, δD). The ionic sequence based on relative molar proportions for cations was Na+ > Ca2+ > Mg2+ > K+ and Na+ > Mg2+ > Ca2+ > K+ for surface and groundwater, respectively and for anions was HCO3− > Cl− > SO42− for all water samples. δ18O and δD relationship plot on a typical evaporation line, enhance potential evaporation of recharging water prior to infiltration. Saturation index estimation revealed that water resources were affected by carbonate and evaporites minerals dissolution and supersaturated with Goethite, Gibbsite and Barite minerals. Inverse geochemical modeling using PHREEQC was used to identify water resources evolution in the study area through two flow paths A, B. The inverse model was constrained so the primary mineral phase including calcite, Aragonite, Anhydrite and Gypsum with Carbon dioxide (gas) are constrained to dissolve until they reach saturation, Whereas H2(g), hydrogen sulphide (gas) and O2(g) are constrained to out gas in all models for flow path (A). For flow path (B), Dolomite, Anhydrite and Gypsum are tend to dissolve with carbon dioxide (gas), H2(g) and O2(g) gases tend to outgassed. Finally, two processes controlling water resource evolution; carbonate and evaporites dissolution and development of cation exchange process through the aquifer system.

Reservoir NO3- pollution and chemical weathering: by dual isotopes of δ15N-NO3-, δ18O-NO3- and geochemical constraints.

Reservoir dams alter the nutrient composition and biogeochemical cycle. Thus, dual isotopes of δ18O-NO3- and δ15N-NO-3 and geochemical signatures were employed to study the NO3- pollution and chemical weathering in the Three Gorges Reservoir (TGR), China. This study found that the TGR dam alters the δ15N-NO3- composition and is enriched in the recharge period. Values of δ15N-NO3- varied from 4.5 to 12.9‰ with an average of 9.8‰ in the recharge period, while discharge period δ15N-NO3- ranged from 3.2 to 12.5‰, with an average of 9.3‰. δ18O-NO3- varies (1.2-11.3‰) with an average of 6.5‰ and (2.4-12.4‰) with an average of 7.5‰, in the recharge and discharge periods, respectively. Stable isotopic values sharply decreased fromupstream to downstream, indicating thedamming effects. δ18O-NO3- and δ15N NO3- confirm that sewage effluents, nitrification of soil organic material, and NH4+ fertilizers were the primary sources of NO3- in the reservoir. Carbonate weathering mainly provides ions to the reservoir. HCO3- + SO42- and Ca2+ + Mg2+ represent 90% of major ions in theTGR. Downstream sampling sites showed low solute concentration during the recharge period, indicating the dam effect on solute concentration. Ca-Mg-Cl-, Ca-HCO3- and Ca-Cl- were the main water types in theTGR. The average percentage of solutes contribution revealed the carbonate weathering, evaporites dissolution, silicate weathering, and atmospheric input were 51.9%, 41%, 7.8%, and 1.7% for the recharge period. In contrast, the discharge period contributed 66.4%, 29.2%, 10%, and 4.3%, respectively. TGR water is moderately suitable for irrigation, and hardness is high in drinking water. This study provides new insight into the dual isotopic approach and geochemical signatures to interpret the NO3- cycle and chemical weathering process under dam effects in the TGR. However, this isotopic application has some limitations in source identification, isotope fractionation, and transformation mechanisms of nitrate. Thus, further studies need to be done on these topicsfor a better undestanding.

Hydrogeochemical controls on As and B enrichment in the aqueous environment from the Western Tibetan Plateau: A case study from the Singe Tsangpo River Basin

Although enrichment of As and B has been extensively observed in major rivers within the Tibetan Plateau, the mechanisms regulating natural enrichment of As and B in the river basins remain poorly understood. To evaluate the hydrogeochemical controls on the As and B enrichment in the aqueous environment in the western Tibetan Plateau, samples of river waters, river sediments, and groundwater were collected within the Singe Tsangpo River basin. The results revealed significant enrichment of As and B in river water (up to 104 μg L−1 for As and 3.2 mg/L for B), river sediment (up to 141 mg/kg for As and 79.4 mg/kg for B), and groundwater (up to 73 μg /L for As and 2.5 mg/L for B). Moreover, the decreases in the molar ratios from the Ca2+ /(Na++K+) in river water and the chemical index of alteration (CIA) in the sediments accompanied with the enrichment of heavier δ18O values along the river flow path suggested that, carbonate and silicate weathering were more substantial at the upper reaches, and the dissolution of evaporites was enhanced at the lower reaches. The As and B enrichment in the river waters primarily resulted from the discharge of geothermal springs, while the carbonate weathering has facilitated the B enrichment through providing HCO3− for the competitive adsorption with H3BO3 or B(OH)4− . In addition, the recharge of surface water into groundwater resulted in elevated As and B concentrations in the alluvial aquifers at the lower reaches of the Singe Tsangpo River. The present study highlighted that variations in the weathering processes within the river basin could significantly contribute to the enrichment of As and B, which can improve our understanding of hydrogeochemical controls on the transport and enrichment of trace elements at the catchment scale worldwide.

Exploration of Hydrogeochemical Characterization and Assessment of Organic Pollution Characteristics of Shallow Groundwater near a Chemical Plant That Discharged Sewage Illegally

Groundwater plays a significant role in domestic use and agricultural irrigation in rural areas of northern China. The untreated wastewater from the chemical plant was directly discharged into a seepage well, resulting in the pollution of groundwater. Assessing characteristics of groundwater organic pollution and identifying evolutionary mechanisms of hydrogeochemistry are beneficial for groundwater protection and sustainable management. Statistical methods (correlation analysis (CA) and principal component analysis (PCA)) combined with hydrogeochemical methods including Piper, Gibbs, Gaillardet, and ions binary diagrams and the chloride alkalinity index were employed to explore hydrogeochemical characteristics and evolutionary mechanisms. The results showed that cations were predominantly located at the Ca2+ end and anions were mostly close to the SO42− and Cl− end. The ion concentrations of groundwater were mainly affected by water–rock interactions. The weathering or dissolution of silicate (i.e., aluminosilicate minerals), evaporite (i.e., halite and gypsum), carbonate minerals (i.e., calcite and dolomite), cation exchange, and anthropogenic activities contribute to the chemical compositions of groundwater. Based on CA and PCA, the dissolution of halide minerals and the use of pesticides and fertilizers were the main factors controlling water chemistry. Additionally, the dissolution of sulfur-bearing minerals and gypsum was the key factor controlling the concentrations of Ca2+ and Mg2+. Application of mathematical statistical methods characterized that the exceedance rate of seven organic compounds with high detection rates were as follows: carbon tetrachloride (39.83%) > 1,1,2-trichloroethane (28.81%) > chloroform (10.17%) > trichloroethene (6.78%) > 1,1,2,2-tetrachloroethane (5.93%) > perchloroethylene (5.08%) > trichlorofluoromethane (0.85%). Simultaneously, pollution under the influence of volatilization and diffusion was significantly less than that in the direction of groundwater runoff.

Hydrochemistry and source apportionment of boron, sulfate, and nitrate in the Fen River, a typical loess covered area in the eastern Chinese Loess Plateau

Fen River Basin (FRB) is water-deficient and strongly influenced by human activities in the eastern Chinese Loess Plateau. The spatio-temporal variation and controlling factors of hyrochemistry and quality, sources of high boron, sulfate, and nitrate of surface waters in FRB were unclear. Major ions, δ11B, δ15N, and δ18O in surface waters in dry season and wet season of FRB were analyzed and correlation analysis (CA), principal component analysis (PCA), self-organizing map (SOM), forward model, and Bayesian isotope mixing model (MixSIAR) were used to solve above problems. Results showed that average riverine δ11B, δ15N, and δ18O of FRB was 7.8‰, 11.2‰, and 1.3‰ (1SD), respectively. Dissolved solutes ranked midstream > downstream > upstream with water type of Na +-Cl-, Ca2+-Mg2+-Cl-, and Ca2+-HCO3-, respectively. Low dissolved solutes were in forest areas while high values were in cropland and city areas. SOM analysis indicated that hydrochemistry was both influenced by natural (upstream) and pollutional input (midstream and downstream) and variation between dry season and wet season was minor. The abnormally high boron concentrations were mainly from silicate weathering (43%) and evaporites dissolution of loess (32%), urban and industrial input contributed 15% of riverine boron. High SO42− (207 ± 267 mg/L, 1SD) was mainly from sulfates. δ15N and δ18O analysis indicated that nitrification was the primary N cycling process. Further, MixSIAR showed that NO3− was mainly from municipal sewage (∼67%) and the total contribution of chemical fertilizer and soil nitrogen was ∼30% with slightly higher values in upstream and wet season. Influenced by land-use types, evaporite dissolution, and anthropogenic input, water quality below midstream was worse and strict sewage reduction policies must be developed. This study highlights the significant influence of evaporite dissolution of loess and anthropogenic input (urban and industrial input for B and sewage for NO3−) on hydrochemistry and water quality.

The abyssal giant sinkholes of the Blake Bahama Escarpment: evidence of focused deep-ocean carbonate dissolution

This study reports the discovery of abyssal giant depressions located at the toe of the Bahamian carbonate platform, along the Blake Bahama structurally-controlled Escarpment (BBE) that exhibits up to 4 km of submarine elevation above the San Salvador Abyssal Plain (SSAP). Analysis of seismic reflection and bathymetric data collected during the CARAMBAR 2 cruise revealed the presence of 29 submarine depressions; their water depths range from 4584 m to 4967 m whereas their negative reliefs are elliptical in shape, range in diameter from 255 m to 1819 m, and in depth from 30 m to 185 m. The depression alignment trends are parallel to the BBE as well as to structural lineaments of the area, exclusively between 2200 and 5000 m from its toe, and overlies a buried carbonate bench in which a high-amplitude seismic anomaly has been detected. The depression density interestingly increases where the recognized structural lineaments intersect the BBE. Based on their physical attributes (i.e. location, jagged morphologies, water depths), we interpret these depressions as collapse sinkholes rather than pockmarks or plunge pools. The aforementioned observations suggest an atypical relationship between the spatial occurrence of the giant abyssal sinkholes, the carbonate platform tectonic structures, the buried carbonate bench that underlies the hemipelagites in the SSAP and the geomorphology of the area. According to the wider literature that reports fluid seepages along submarine carbonate escarpments, we propose that the ground water entrance during low sea-level stands, the dissolution of evaporites by meteoric water, the platform-scale thermal convection and the seawater entrance at the platform edge most probably collectively act in concert to favor the circulation of brines and therefore the corrosion within the Bahamian carbonate platform. These mechanisms are particularly efficient along the structural heterogeneities (e.g. the Sunniland Fracture Zone, SFZ) which act as fluid conduits localizing the dissolution and control the physiography of the area by maintaining the location of the sedimentary pathways. The dense fluids would migrate along the faults towards the BBE free edge and are subsequently trapped into the buried carbonate bench that laterally disappears below the low-permeability deep-sea hemipelagites of the SSAP. In consequence, the trapped corrosive fluids dissolve the carbonates preferentially along the tectonic structures such as the SFZ. They are this way at the origin of the BBE curvature and generate collapse-structures in the overlying fine-grained deposits finally resulting in the formation of giant abyssal sinkholes. This structurally-directed process of dissolution seems efficient to provide a brines density head to move out down to >4.5 km of water depth and is believed to have played a major role in the BBE 5–6 km erosional retreat.

A Strontium and Hydro-Geochemical Perspective on Human Impacted Tributary of the Mekong River Basin: Sources Identification, Fluxes, and CO2 Consumption

As the largest and most representative tributary of the Mekong River, the Mun River Basin (MRB) provides critical understanding of regional hydro-geochemical features and rock weathering processes on a basin scale. The present study measured strontium (Sr) isotopes with hydro-geochemistry data of 56 water samples in detail in the MRB in northeast Thailand. The dissolved Sr contents and 87Sr/86Sr isotopic ratios were reported to be 8.7–344.6 μg/L (average 126.9 μg/L) and 0.7085–0.7281 (average 0.7156), respectively. The concentrations of dissolved Sr in the mainstream slightly decreased from upstream to downstream, while the variation trend of 87Sr/86Sr was on the contrary. Correlation analysis showed that Na+ strongly correlated with Cl− (0.995, p < 0.01), while Ca2+ exhibited weak relationships with SO42− (0.356, p < 0.01). Samples of the MRB exhibited lower Mg2+/Na+, Ca2+/Na+, HCO3−/Na+ and 1000Sr/Na ratios, and gathered around the end-member of evaporite dissolution, with slight shift to silicate weathering end-member, demonstrating the dominant contribution of evaporite dissolution and silicate weathering on dissolved loads. Comparing with data of major world rivers from previous research, our results remained consistency with rivers draining through similar geological conditions. The dissolved Sr flux to the adjacent Mekong River was estimated to be 20.7 tons/year. In accordance with the forward model, silicate weathering rate and CO2 consumption rate during dry season were calculated to be 0.73 tons/km2/year and 1.94 × 104 mol/km2/year, and may get underestimated due to intense water consumption by extensive agricultural activities. The superimposed effect of anthropogenic impacts on the water environment could enhance chemical weathering, and thus should be taken into account in regional ion cycles and carbon budgets. These findings highlight the coupling analysis of Sr isotopes and hydro-geochemistry in Earth surface processes and provide basic investigation for sustainable regional water treatment mechanisms in the pan basin of the Mekong River.

Potassium and its isotope behaviour during chemical weathering in a tropical catchment affected by evaporite dissolution

This work presents the systematic investigation of K contents and stable K isotopic compositions of surface waters, groundwater, wastewaters, suspended particles, bed sediments, and fertilizers in the Upper Mun Rive catchment, northeast Thailand. This area is of particular interest because its abundant potash deposits and intensive agricultural activities and urbanization, therefore this will improve our understanding whether the K isotope is robust enough to resist evaporite dissolution and anthropogenic disturbances on tracing silicate weathering in the highly weathered tropical region. The dissolved loads in surface waters and shallow groundwater display the large variation in δ41Kdiss values from −0.54‰ to +0.09‰ relative to suspended particles (−0.60‰ to −0.41‰), river bed sediments (−0.54‰ to −0.47‰), the upper continental crust (UCC, −0.44 ± 0.05‰), which agrees with the fact that 39K is preferentially retained in weathering products during silicate weathering. The wet and dry seasons difference ranging from −0.05‰ to +0.10‰ δ41K, which is slightly greater than our long-term analytical uncertainty of ±0.06‰. There is likely a limited K input from evaporites dissolution due to weak correlation between δ41Kdiss values and Cl concentrations or Cl/K ratios in the UMR and world rivers, while a major tributary Takhong River is clearly influenced by the contribution of domestic sewage with lower δ41K and higher δ15N values. Based on a mass balance of K budge, the dissolved K in the UMR is mostly (>90%) derived from silicate weathering in the unpolluted area, this is consistent with previous studies of large river basins, and the evaporite dissolution and other non-silicate sources may not strongly influence dissolved K and δ41Kdiss values in rivers, even in evaporite-rich catchment. Therefore, K isotopes cannot be used as lithological tracers in catchments, rather the K isotopic fractionation mainly occurs during silicate weathering, such as the formation of secondary minerals which favor light isotope. Hence, the mechanism of K isotopic fractionation linked to secondary minerals K uptake needs further consideration. Overall, these results clearly show that K isotopes could be an ideal indicator to constrain silicate weathering processes and anthropogenic inputs at catchment scale.

Sources and behaviors of dissolved sulfate in the Jinan karst spring catchment in northern China identified by using environmental stable isotopes and a Bayesian isotope-mixing model

In recent decades, surface water and groundwater in the Jinan spring catchment have become increasingly contaminated by sulfate due to the expansion of urbanization and the increasing intensity of anthropogenic activities. In this study, ten surface water samples and forty-three groundwater samples were collected in the catchment from June to September 2019, and their hydrochemistry and stable isotopes (δ34SSO4, δ18OSO4, δDH2O and δ18OH2O) combined with a Bayesian isotope mixing model were used to identify sources and transformations and to quantitatively evaluate the contribution of sulfate from multiple potential sources of pollution. The dual isotopes of sulfate and the isotope mixing model showed that sulfate in the surface water was mainly derived from evaporite dissolution (32.6%), sewage (18.8%), soil sulfate (15.4%) and sulfide oxidation (10.2%), while that in the groundwater was mainly derived from soil sulfate (32.4%) and sewage (30.6%). In groundwater, the proportions of sewage and evaporite dissolution increased from the indirect recharge area to the discharge area, while the contribution of soil sulfate and sulfide oxidation decreased. In regard to surface waters, the contribution proportion of evaporite dissolution to SO42− in June was 40.9%, which was significantly higher than 24.2% in September, but the proportion of sewage, soil sulfate and sulfide oxidation was lower in June (13.7, 12.9 and 9.5%, respectively) than in September (23.8, 17.8 and 10.8%, respectively). There was no significant correlation between the ratio of SO42−/Cl− and δ34SSO4 and δ18OSO4 in surface water and groundwater, indicating that bacterial sulfate reduction did not play a major role. This study can provide a reference for the development of effective pollution management strategies for water resources in karst areas of northern China.

Assessment of Shallow Groundwater Quality Using Water Quality Index and Human Risk Assessment in the Vogan-Attitogon Plateau, Southeastern (Togo)

The shallow Continental Terminal aquifer constitutes the primary water resource for drinking purpose in the coastal sedimentary basin of Togo, facing population growth, mining development, industrialization, and intensive agriculture. This study aims to assess groundwater quality and associated human health risks, to ensure the sustainable water supply in the basin. Major chemical parameters, and trace elements of forty-two samples of shallow groundwater and eight samples of surface water collected during march 2019 were analysed using AFNOR methods. The dataset obtained was used to evaluate drinking water quality and safety. The results showed that groundwater was slightly acid (4.83 + > Ca2+ > Mg2+ > K+ and Cl- > SO42- > HCO3-> NO3-. Thus, water samples were predominantly Na - Cl water type (~88 %). The water quality index score based on major ions indicated that 93% of the groundwater samples were classified as excellent and good for drinking. The non-carcinogenic risk ranged from 3.887 to 17.650 for children, from 2.272 to 10.135 for adult females, and from 1.785 to 8.104 for adult males and was related principally to manganese, nitrate, arsenic, fluoride and cadmium. The carcinogenic risk ranged from 0.004 to 0.006 for children, 0.003 to 0.004 for adult females, and from 0.002 to 0.003 for adult males and was caused by arsenic and cadmium. The water quality is affected by seawater intrusion, evaporite dissolution and anthropogenic contamination. The consumption of groundwater may cause health effect on human.

Impacts of chemical weathering and human perturbations on dissolved loads of the Wei River, the Yellow River catchment

As the largest tributary of the Yellow River, the Wei River drains a basin mainly comprising two different geological settings, i.e., the Chinese Loess Plateau (CLP) in the north covered by Quaternary loess and the Qinling Mountains area in the south. Exploring the influence of natural weathering processes and human activities on river chemistry has high significance in understanding chemical transport from the Wei River to the Yellow River. The geochemical characteristics of the Wei River mainstream and its tributaries as well as chemical weathering were determined using a geochemistry and isotope dataset of high spatial resolution. The mainstream clearly exhibited a mixture of major elements and stable isotopes from tributaries on both the north and south banks, with values within the range of those of the tributaries. North-bank tributaries draining thick loess deposits showed higher contents of major elements and the enrichment of stable isotopes, reflecting the influence of geological setting on river chemistry. The dominant processes accounting for the water chemistry of the mainstream are evaporite (39–75%) and carbonate weathering (21–54%). Within the watershed, evaporite dissolution and silicate weathering are higher in the northern CLP area, whereas carbonate weathering is higher in the southern Qinling Mountain area. The CO2 consumption by the Wei River is 19.9 × 109 mol/yr, accounting for 32.5% of the total CO2 consumption by the middle reaches of the Yellow River. During the high-flow period, the chemical weathering flux of the Wei River was found to be within the range of northern rivers in China, while the chemical weathering rate was relatively high in the semi-arid region. This suggests that chemical denudation is a significant factor for the river chemistry of the CLP at least in the high-flow period.

A multi-isotopic evaluation of groundwater in a rapidly developing area and implications for water management in hyper-arid regions

Management of water resources in hyper-arid areas faces vital challenges in a global climate change context. Consequently, understanding the effects on groundwater sources can help mitigating the problem of water scarcity and the negative impact of human intervention on the environment. A case study area in the hyper-arid climate of the United Arab Emirates, was tackled here with the focus on applying stable isotopes as tools for evaluating groundwater sources and quality assessment. The results of major ions indicate variable increase in groundwater salinity moving away from Al Hajar Mountains recharge areas to the discharge areas (Arabian Gulf coast). The data of stable isotopes (δ18OH2O, δ2HH2O, δ18ONO3, δ15NNO3, δ18OSO4, δ34SSO4, δ11B) suggest impact of paleo-groundwater in the abstractions of the wells nearest to the coast. Nitrate isotopes indicate farming activities sources that can be masked due to the contribution from the nitrate-poor paleo-groundwater. Nitrate reduction processes are expected near to the recharge front. Sulphate and boron isotopes further suggest that influence of ancient evaporite dissolution in salinization. Management efforts should be focused on the diffuse sources of quality mitigations that can be vital in fingerprinting local and regional (transboundary) effects.

Chemical and isotopic composition of CO2-rich magnesium-sodium-bicarbonate-sulphate-type mineral waters from volcanoclastic aquifer in Rogaška Slatina, Slovenia.

Bottled natural mineral waters from an andesitic aquifer in Slovenia are enriched in magnesium (1.1 g/l), sulphate (2.2 g/l) and dissolved inorganic carbon (204 g/l). We analysed major ions, trace elements, tritium activity, 14C, δ18OH2O, δ2HH2O, δ13CDIC, gas composition and noble gases in six wells. In addition, 87Sr//86Sr, δ34SSO4 and δ11B were analysed here for the first time. Stable isotopes with δ18O = −11.97 to −10.30‰ and δ2H = −77.3 to −63.8 confirm meteoric origin. CO2 degassing is evident at three wells, causing the oxygen shift of about −1.3‰. Tritium activity was detectable only in the shallowest well, where the freshwater component was dated to the 1960s. δ13CDIC in five waters is −1.78 to + 1.33‰, typical of carbonate dissolution. Radiocarbon is low, 1.03–5.16 pMC. Chemical correction with bicarbonate concentration and δ13C correction methods gave best mean residence times, slightly longer than previously published. Sulphate has δ34S 26.6–28.9‰ and δ18O 8.9–11.1‰ due to dissolution of evaporites in carbonate rocks. Boron at concentrations of 1.2–6.1 mg/l has two origins: δ11B = 11.3–16.4‰ from hydrothermal alteration and δ11B = 26.6–31.7‰ from carbonate dissolution. Strontium at concentrations of 0.5–22.0 mg/l has 87Sr//86Sr, indicating three sources: 0.7106 for Miocene clastic rocks, 0.7082 for Triassic carbonates and 0.7070 for Lower Oligocene andesitic rocks. CO2 represents the majority of the dissolved (> 98.84 vol%) and separated gas (> 95.23 vol%). Methane is only found in two wells with a max. of 0.30 vol%. All waters show excess helium and 16–97% of mantle-derived helium. Since all show subsurface degassing, the paleo-infiltration temperature could not be calculated.