Search Results (99)

This study characterizes the hydrochemistry and geochemical signature of the Upper Cretaceous geothermal aquifer in the Zharkunak zone (Eastern Ili Depression, SE Kazakhstan) using certified analytical datasets from five deep wells (5539, 1-RT, 3-T, 1-TP, and 2-TP). The waters are hyperthermal (89–103 °C), alkaline (pH 8.1–9.0), and weakly mineralized (TDS 0.3–1.0 g/L), with sodium-dominated facies ranging from Na–HCO₃–SO₄ to Na–SO₄–Cl. Hydrochemical analysis indicates that water–rock interaction and cation exchange are the primary controls on fluid evolution, with limited influence from evaporation or external salinity sources. Elevated fluoride (up to ~10 mg/L) and dissolved silica (H₂SiO₃, often >50 mg/L) reflect prolonged high-temperature interaction with silicate-rich lithologies under low Ca²⁺ conditions. Trace elements and radon activity (up to 0.32 nCi/L) further support deep, fault-controlled circulation pathways. PHREEQC modeling indicates near-equilibrium to slight supersaturation with respect to silica phases, suggesting a potential risk of silica scaling during cooling, while carbonate scaling remains limited. Although the dataset is based on discharge conditions from a limited number of wells, the results demonstrate that the Zharkunak system has strong geothermal utilization potential, with management considerations related to fluoride, radon, and silica scaling. Future work should focus on integrating isotopic analyses and reactive transport modeling to better constrain subsurface processes and long-term system behavior. Full article

Groundwater nitrate (NO₃⁻) pollution, caused by anthropogenic activities, poses a global threat to water security. The mixing of multiple nitrate pollution sources and the associated biogeochemical reactions may create a complex chemical background, which renders traditional hydrochemical methods and single δ¹⁵N isotope analysis approaches limited in accurately identifying pollution sources and quantifying their contribution ratios. Accordingly, we adopted an integrated framework incorporating hydrochemistry, isotopes, and the MixSIAR model. Within this framework, results from different components mutually validate each other, helping to achieve more accurate source identification and contribution quantification. Results revealed severe nitrate contamination with striking spatial heterogeneity: concentrations were significantly higher in the eastern region (9.3–1890.7 mg·L⁻¹, Mean: 472.8 mg·L⁻¹) than in the western region (8.5–204.1 mg·L⁻¹, Mean: 52.0 mg·L⁻¹). Hydrochemical and δ¹⁸O-NO₃⁻ evidence identified nitrification as the dominant nitrogen transformation process. Critically, the MixSIAR model quantified drastically different source contributions between the two regions. In the eastern industrial zone, industrial wastewater was the predominant source (61.3%), followed by manure and sewage (18.5%). In contrast, in the western agricultural area, natural and agricultural sources dominated, with soil nitrogen contributing 43.9% and chemical fertilizer 31.7%. The findings pinpoint specific pollution drivers for each region, offering a robust scientific basis for formulating differentiated and effective nitrate pollution control strategies. Full article

Monitoring the hydrochemistry of groundwater and the H-O isotopes in the Jingpo Lake volcanic area, China, is fundamental to studying the mechanisms of volcanic and seismic events, as well as the associated hazards. To study the hydrogeochemistry of fluids in the Jingpo Lake volcanic area, water samples from seven sites were tested for hydrogeochemistry, H-O isotopes, and radon (Rn) content. The genesis and evolution of the groundwater system were elucidated through an integrated approach employing Gibbs diagrams, ionic ratio analyses, reservoir temperature estimation (silica–enthalpy method), and inverse geochemical modeling with PHREEQC. The results showed that the dominant water chemistry type was HCO₃⁻, primarily influenced by volcanic rock weathering and deep hydrothermal activity. Spring and well water were influenced by cation exchange, adsorption, and rock weathering dissolution. The H-O isotope composition and radon content indicate that atmospheric precipitation is the main source of supply, while well water is influenced by deep fluids. According to the Na-K-Mg triangle diagram, most of the groundwater was shallow and immature, whereas the well water was partially balanced. The temperature of the geothermal water was controlled by the geothermal gradient, depending on its occurrence and circulation depth. Additionally, the equilibrium temperature of the thermal reservoir was calculated using the silica–enthalpy equation method, with the concentrations of dissolved components in the water taken into account. The temperature of the thermal reservoir of the well water and the depth of groundwater circulation were estimated. The original reservoir temperature in the study area was calculated to range from 108 °C to 156 °C, with a geothermal water-to-shallow groundwater mixing ratio of between 71% and 85%. The estimated shallow temperature ranged from 64.9 °C to 74.9 °C. These hydrogeochemical signatures reflect active water–rock interactions and the contribution of deep-seated geothermal fluids, providing robust evidence for ongoing geothermal activity in the Jingpo Lake volcanic system. The findings enhance our understanding of the recent geological evolution and present-day hydrothermal processes of this potentially active volcanic field, which establishes a crucial hydrogeochemical baseline for future monitoring and hazard assessment studies. Full article

Lake Van (Eastern Turkey), the world’s largest soda lake, represents a unique geochemical environment characterized by high alkalinity (pH about 9.7) and a complex hydrochemistry, driven by deep hydrothermal input and extreme evaporative processes. This article evaluates mineralogy, minor elements, and Rare Earth Element (REE) geochemistry of coastal stromatolites from 11 sites, to discriminate between endogenous chemical signals and terrigenous contamination. Results identify two distinct lithological groups: a chemically pure authigenic end-member (CaCO₃ > 85%), overprinted by a significant siliciclastic detrital contribution, rich in SiO₂, Al₂O₃, and Fe₂O₃. Authigenic samples successfully preserve the primary hydrothermal signature, exhibiting marked Heavy Rare Earth Element (HREE) enrichment and superchondritic Y/Ho ratios (=35), inherited from the stability of dissolved dicarbonate complexes, such as [REE(CO₃)₂]⁻, which favor HREE solubility and uptake into the carbonate lattice. Conversely, the significant detrital contribution is highlighted by a robust correlation between REE and lithogenic proxies (Al-Si-Fe). Furthermore, the non-CHARAC behavior observed in Y/Ho and Zr/Hf twin pairs effectively distinguishes biogenic-chemical precipitation from detrital inputs. These results highlight the effectiveness of REE geochemistry as a proxy to filter out lithogenic overprints and accurately isolate the primary hydrochemical record of carbonate stromatolites. Full article

Integrating an end member catchment offers a mechanistic foundation for interpreting large basin hydrology. This critical aspect is rarely evident in Malawi’s river basin studies. This study characterizes the hydrochemistry of surface and groundwater and stable isotopes of water to gain a regional picture of how the Ruo River Transboundary Catchment (RRC) influences the Shire–Zambezi River Basin. Hydrochemistry (2013 to 2024) and stable isotope (2020 to 2022) data are used. Both Gibbs and Piper diagrams were used to interpret surface and groundwater facies and hydrogeochemical processes controlling mineralization of water. SI biplots were used to trace water sources, mixing signals, and evaporation trends. Low to moderate mineralization is noted in surface and groundwater sources, and electrical conductivity varied between 19 and 622 µS/cm and 31 and 1930 µS/cm for surface (12 sites) and groundwater (151 boreholes), respectively. Piper diagram analysis reveals a Ca-Mg-HCO₃ water type dominance. Gibbs plots suggested dissolution of silicate minerals and interaction of surface and groundwater. Stable oxygen (δ¹⁸O) and hydrogen (δ²H) isotope ratios in precipitation, surface, and groundwater exhibit a similar pattern, indicating a common meteoric input, variability in moisture source, and significant interaction of surface water and groundwater. SI plots indicate mixing of precipitation, surface, and groundwater of RRC. Finally, the Ruo River at flood stage reverses the flow of the Shire River sub catchments, impacting the water quality and quantity of the Zambezi, and, therefore, should be considered an important mixing end member in the Lower Shire Basin. Full article

Groundwater contamination in chemical industrial parks (CIPs) is a significant threat to global water security due to spills, leaks, and discharges, as well as the complexity of concealing a diverse range of industrial pollutants. In this article, we collected 30 groundwater samples from zones of presumed influence across a CIP, including upstream background, within-park, periphery, and downstream, located in Luxian County, Sichuan, China. We employed excitation–emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) coupled with comprehensive hydrochemical analysis to deconvolve the dissolved organic matter (DOM) signature and statistically link its fluorescent components to specific hydrogeochemical processes and anthropogenic sources. Results revealed that industrial activities have transformed the groundwater to Ca-HCO₃·Cl and Ca·Na-HCO₃·Cl types from the hydrochemical facies comprising Ca-HCO₃ and Ca·Mg-HCO₃ types. Hydrogeology and groundwater chemistry depend primarily on weathering and atmospheric precipitation, but industrial effluents and evaporation concentration also significantly affect them. EEM-PARAFAC identified three dominant fluorescent components: fulvic-like (C1), humic-like (C2), and tryptophan-like (C3), with the latter serving as a sensitive indicator of recent anthropogenic inputs. The spatial distribution of these components, particularly the enrichment of C3, is primarily governed by anthropogenic inputs (e.g., sewage leakage), modulated by local hydrological conditions. This work demonstrates the integration of optical spectroscopy with conventional hydrochemistry for source apportionment in complex industrial settings. It provides a mechanistic understanding of pollution propagation and a practical, rapid diagnostic tool for targeted groundwater protection in CIPs. Full article

Karst aquifers provide critical water resources in the Mediterranean region, yet climate change threatens their sustainability. This study integrates stable isotope analysis (δ²H, δ¹⁸O), hydrochemistry, and hydrological time series to characterize precipitation–groundwater dynamics in the Mt. Učka karst system (Croatia). Precipitation samples collected across an altitudinal gradient of approximately 1400 m and groundwater from three major groundwater sources were analyzed over a 2.5-year period. Precipitation exhibits pronounced isotopic variability with d-excess values indicating mixed Atlantic–Mediterranean moisture sources. Groundwater is primarily recharged by precipitation from the cold part of the hydrological year. It exhibits substantial attenuation of isotopic signals, which indicates extensive mixing processes but prevents quantitative estimation of mean residence time. Groundwater is predominantly recharged from elevations above 900 m a.s.l., with one spring showing evidence of higher-elevation recharge. Analysis confirms the system’s dual porosity: a rapid, conduit-dominated response indicates high vulnerability to surface contamination, while a sustained, matrix-dominated response provides greater buffering capacity. These findings highlight the vulnerability of karst systems to projected reductions in autumn precipitation, the critical recharge season, and demonstrate the necessity of multi-tracer approaches for comprehensive aquifer characterization. Full article

The Upper Olifants River Catchment in the Mpumalanga Province has experienced water contamination in the past few decades due to existing land use and land cover. This study employed hydrochemical and environmental isotopes to investigate the water quality and understand the sources of contaminants within tertiary catchments B11F and B11G of the Upper Olifants River Catchment. The hydrochemistry results indicate that the shallow weathered aquifers are more susceptible to contamination with major pollutants being TDS, SO₄, Ca, Mg, Fe, and Mn, which can be associated with the geology and coal mining activities in the area. Additionally, the environmental isotopes suggest that the climate, fractionation, and elevation play a major role in the evolution of the water. The correlation of major ion ratios suggests that processes such as silicate and carbonate weathering and cation exchange reactions play a significant role in making the water vulnerable to pollution. In general, the overall water quality index of the study area indicates poor water quality falling within the range of 0 < WQI ≤ 44, making it undesirable for domestic use. Furthermore, approximately 35% of the samples are not suitable for irrigation purposes based on the SAR and PI. Full article

The Cuitzeo Groundwater Flow System, located in central Mexico within a volcanic rock region, encompasses two of the largest lakes in the country: Lake Cuitzeo and Lake Pátzcuaro. These lakes are sustained by both surface water and groundwater discharge, playing a critical role in local ecosystems and the surrounding population. Groundwater is particularly important for maintaining the lakes’ existence. However, the behavior of the groundwater flow system in this region has not been previously described. This study compiles historical data from 170 groundwater sites within the system from different years and includes temperature (°C), pH, total dissolved solids (TDS), major ions, and geology in detail. The historical data provide a spatial analysis and initial characterization to study the hydrochemistry of the system, identify recharge and discharge zones, assess water-rock interaction processes, and trace the evolution of groundwater. The results highlight distinct chemical behaviors across the different zones of the study area, with the most notable being ion exchange consistent with the weathering of volcanic silicates and interaction with lacustrine sediments. This study is crucial as it offers valuable insights into the hydrochemistry and water levels of the groundwater flow system and highlights areas where additional data are needed to better understand its dynamics. Full article

Groundwater in the Nansi Lake Basin, a key reservoir of the South-to-North Water Diversion Project, supports domestic, agricultural, and ecological needs but faces pressure from overexploitation and pollution. This study clarifies the hydrochemical characteristics, controlling processes, environmental quality, and source contributions of shallow groundwater in the basin. Hydrochemical data from 67 wells were interpreted using Piper and Schukalev diagrams, Gibbs and ion-ratio plots, the entropy-weight water quality index (EWQI), and an absolute principal component scores–multiple linear regression (APCS-MLR) model. Groundwater shows high mineralization and hardness, with 35.82% and 55.22% of samples exceeding standard limits for total dissolved solids and total hardness, respectively. The dominant facies are HCO₃-Ca, HCO₃-Ca·Mg, and HCO₃·Cl-Na·Ca, indicating dissolution and ion exchange involving carbonate and silicate rocks. Gibbs and ion-ratio analyses demonstrate that rock–water interaction is the main control, with secondary influence from evaporation. EWQI results indicate generally good groundwater quality (68.66% Class I, 20.90% Class II). APCS-MLR identifies natural, agricultural, ion-exchange, and anthropogenic sources, contributing 53.34%, 22.71%, 4.79% and 19.14%, respectively. These findings show that protection should focus on pollution control in northern agricultural and mining zones while conserving high-quality groundwater elsewhere in the basin. Full article

The Puebla Metropolitan Area, one of the most industrialized regions in Mexico, shows severe contamination of both surface and groundwater. In this study a multi-tracer approach combining hydrochemistry with environmental isotopes (δ²H, δ¹⁸O, ³H) was applied to evaluate groundwater–surface water (GW–SW) interactions and their role in water quality degradation. Elevated concentrations of aluminum, iron, zinc, and lead were detected in the Alseseca and Atoyac Rivers, exceeding national standards, while arsenic, manganese, and lead in groundwater surpassed Mexican and WHO drinking water limits. The main sources of contamination include volcanic inputs from Popocatepetl activity (e.g., arsenic) and untreated discharges from industrial parks (e.g., lead), which together introduce significant loads of Potentially Toxic Elements (PTEs) into surface and groundwater. Isotopic analysis identified three sources for aquifer recharge: (1) recharge from high-altitude meteoric water, (2) mixed GW–SW water recharged at intermediate elevations with heavy metal presence, and (3) recharge from lower altitudes (evaporate water). Tritium confirmed both modern and old recharge, while isotope-based mixing models indicated surface water contributions to groundwater ranging from 18% to 72%. These interpretations were derived from the integrated analysis of hydrochemical and isotopic data, allowing the quantification of recharge sources, residence times, and mixing processes. The results demonstrate that hydraulic connectivity, enhanced by fractures and faults, facilitates contaminant transfer from polluted rivers into the aquifer. Full article

Groundwater serves as a vital water resource for agricultural irrigation and domestic use in farmland areas. Its chemical composition is jointly influenced by agricultural fertilization, land use practices, and natural geological processes. However, research on the controlling factors and spatial distribution characteristics of groundwater hydrochemistry in agricultural regions remains insufficient. In this study, 56 groundwater samples were collected from the central-eastern plain of Henan Province, China. A combination of hierarchical cluster analysis, ionic ratio methods, principal component analysis, and kriging interpolation was employed to investigate the hydrochemical characteristics, spatial patterns, and primary controlling factors of regional groundwater. The results indicate that the first group of samples is characterized by high total dissolved solids (TDS), elevated Na⁺ and Cl⁻ concentrations, predominantly controlled by evaporation and concentration processes. The second group exhibits high pH and low Ca²⁺ concentrations, mainly influenced by silicate weathering, with reverse cation exchange acting as a secondary controlling process. The third group is characterized by elevated concentrations of Ca²⁺ and NO₃⁻, primarily controlled by carbonate weathering and agricultural activities. The western part of the study area serves as the main groundwater recharge zone and has the highest NO₃⁻ and Ca²⁺ concentrations. In the central area, most ion concentrations are relatively high, forming a distinct gradient with surrounding regions. Meanwhile, the eastern area displays elevated concentrations of HCO₃⁻, TDS, Na⁺, and Cl⁻, highlighting pronounced spatial heterogeneity. Overall, the hydrochemical composition of groundwater in the study area is shaped by both natural processes and anthropogenic activities, exhibiting significant spatial heterogeneity. Notably, the spatial variation of NO₃⁻ concentrations is substantial, indicating that certain localities have already been affected by agricultural non-point source pollution. Full article

The Sahel Transboundary Taoudéni Basin, covering about 20% of Burkina Faso, hosts vital aquifers critical for water security and development. Effective groundwater monitoring is essential for sustainable resource management. In the Kou sub-basin, groundwater quality assessment is increasingly important. This study integrates hydrochemistry, water stable isotopes (δ¹⁸O, δ²H), GIS, and multivariate statistics to understand subsurface geochemical processes. A total of 48 samples—43 groundwater and 5 surface water—were analyzed for 19 hydrochemical parameters and isotopes. In surface water, δ¹⁸O ranged from −5.96‰ to −5.09‰, and δ²H from −37.65‰ to −29.15‰. In groundwater, δ¹⁸O ranged from −5.93‰ to −4.39‰, and δ²H from −34.62‰ to −25.05‰. The spatial distribution of δ¹⁸O and δ²H was mapped using inverse distance weighted (IDW) interpolation in ArcGIS 10.8. A δ²H vs. δ¹⁸O plot showed groundwater values clustered near the Global Meteoric Water Line, indicating minimal evaporation during recharge. Groundwater chemistry was dominated by Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > NO₃⁻ > Cl⁻ > SO₄²⁻. Key hydrogeochemical processes include water–rock interaction (leaching, weathering, ion exchange) and anthropogenic pollution. Isotopic signatures reveal heterogeneous recharge sources and aquifer connectivity. These findings enhance the understanding of water sources and geochemical processes in the Kou basin, supporting informed groundwater resource management. Full article

Underground brine as a liquid mineral resource available for development and utilization has attracted widespread attention. However, how the mining process affects the hydrochemical characteristics and evolution of underground brine has yet to be fully understood. Herein, 207 underground brine samples were collected from the Luobei mining area of the Lop Nur region during pre-exploitation (2006), exploitation (2019), and late exploitation (2023) to explore the dynamic change characteristics and evolution mechanisms of the underground brine hydrochemistry using the combination of statistical analysis, spatial interpolation, correlation analysis, and ion ratio analysis. The results indicated that Na⁺ and Cl⁻ were the dominant ionic components in the brine, and their concentrations remained relatively stable throughout the mining process. However, the content of Mg²⁺ increased gradually during the mining process (increased by 45.08% in the middle stage and 3.09% in the later stage). The elevation in Mg²⁺ concentration during the mining process could be attributed to the dissolution of Mg-bearing minerals, reverse cation exchange, and mixed recharge. This research furnishes a scientific foundation for a more in-depth comprehension of the disturbance mechanism of brine-mining activities on the groundwater chemical system in the mining area and for the sustainable exploitation of brine resources. Full article

Sulfate as a potential pollution source in the water environment of the basin, identifying sulfate sources and migration mechanisms is essential for protecting the water environment and ensuring sustainable water management. Liuyang River is a primary tributary of the Xiangjiang River. It has experienced progressively intensifying anthropogenic influences in recent decades, manifested by sustained sulfate concentration increases. However, the sulfate sources and their contributions were not clear. This study used hydrochemistry and multi-isotopes methods combined with Simmr model to study the hydrochemical characteristics, sulfate sources, and migration–transformation processes of surface water and groundwater. The results showed that the hydrochemical types of surface water were HCO₃-Ca and HCO₃·SO₄-Ca·Mg, and groundwater were HCO₃-Ca, HCO₃-Ca·Mg, and HCO₃·SO₄-Ca. Ions in the water primarily originated from carbonate and silicate rocks dissolution and sulfide oxidation, augmented by mining operations, sewage discharge, and chemical production. The analyses of hydrochemistry, isotopes, and Simmr model revealed that surface water sulfate originated from soil sulfate (35.70%), sulfide oxidation (26.56%), sewage (16.58%), and atmospheric precipitation (12.45%). Groundwater sulfate was derived predominantly from sewage (34.96%), followed by soil sulfate (28.09%), atmospheric precipitation (17.35%), and sulfide oxidation (12.25%). Sulfate migration and transformation were controlled by the natural environment and anthropogenic impacts. When unaffected by human activities, sulfate mainly originated from soil and atmospheric precipitation, relating to topography, geological conditions, agricultural activities, and precipitation intensity. However, in regions with intense human activities, contributions from sewage and sulfide oxidation significantly increased due to the influences of mining and industrial activities. Full article