Search

The Arabian Desert is characterised by very low rainfall and high evaporation, yet over 210 springs are on its northeastern edge in central Iraq along the Abu Jir lineament, which represents the western depositional margin of a foreland basin infilled by the floodplain sediments of the Tigris and Euphrates Rivers; there is little evidence of faulting. The springs discharge from gently east-dipping Paleocene–Eocene limestones, either where groundwater flowpaths intersect the ground surface or where groundwater flow is forced to the surface by confining aquitards. Calculated annual recharge to the aquifer system across the Arabian Desert plateau (130–500 million m3) is significant, largely due to rapid infiltration through karst dolines, such that karst porosity is the primary enabler of groundwater recharge. The recharge is enough to maintain flow at the Abu Jir springs, but active management of groundwater extraction for agriculture is required for their long-term sustainability. The hydrochemistry of the springs is determined by evaporation, rainfall composition (high SO4 concentrations are due to the dissolution of wind-blown gypsum in rainfall), and plant uptake of Ca and K (despite the sparse vegetation). Limestone dissolution has relatively little impact; many of the springs are undersaturated with respect to calcite and lack tufa/travertine deposits. The springs at Hit-Kubaysa contain tar and high levels of H2S that probably seeped upwards along subvertical faults from underlying oil reservoirs; this is the only location along the Abu Jir lineament where deep-seated faults penetrate to the surface. The presence of hydrocarbons reduces the Hit-Kubaysa spring water and converts the dissolved SO4 to H2S.

Due to extensive groundwater exploitation, a groundwater funnel has persisted in the Hutuo River alluvial fan in Shijiazhuang since the 1980s, lasting nearly 40 years and significantly impacting the groundwater chemical characteristics. In this study, based on the groundwater level and chemistry data, the hydrochemical evolution processes and mechanisms of the groundwater during the 1980 groundwater funnel period and the post-2015 artificial governance period were investigated using traditional hydrogeochemical methods and inverse hydrogeochemical simulations. The results show the following: (1) The ion concentrations gradually increased along the groundwater flow path, where they displayed a pattern of lower levels in the northwest and higher levels in the southeast. From 1980 to 2021, the concentrations of major ions were increased. (2) In 1980s, the groundwater hydrochemical type predominantly exhibited HCO3—Ca. From 1980 to 2015, the hydrochemical types diversified into HCO3·Cl—Ca, HCO3—Ca·Mg, and HCO3·SO4—Ca types. Following the artificial governance, the groundwater level rise led to an increase in the concentrations of SO42− and Mg2+. Post-2015, the prevailing hydrochemical type changed to HCO3·SO4—Ca·Mg. (3) The changes in the groundwater level and ion concentrations were quantitatively strongly correlated and exhibited spatial similarity. (4) In the 1980s, the groundwater hydrochemical composition was primarily controlled by the dissolution of albite, dolomite, halite, and quartz; reverse cation exchange; and groundwater exploitation. Since 2015, the hydrochemical composition has mainly been influenced by the dissolution of albite, calcite, and quartz; positive cation exchange; river–groundwater mixing; and industrial activities, with increasing intensities of both water–rock interactions and human activities.

This study investigates the Batha endorheic basin in Chad, situated east of the Lake Chad basin in the arid to semi-arid Sahelian zone. This region has not yet undergone comprehensive geological and hydrogeological studies. More broadly, the transition zone between semi-arid and arid climates has been minimally explored. This research aims to evaluate the resources and dynamics of this multi-layered system using a combined geology-hydrogeology-hydrochemistry-isotopes approach. The multilayer system includes sedimentary layers (Quaternary, Pliocene, and Eocene) over a crystalline basement. A piezometric investigation of the system shows a general SE–NW groundwater, indicating an interconnection between all layers. Hydrochemical analyses identifies four main facies (calcium-bicarbonate, sodium-bicarbonate, sulphate-sodium, and mixed), primarily controlled by water–rock interaction with secondary influences from base-exchange and evaporation. Saturation indices indicate that these waters are close to equilibrium with the calcite-Mg phases, gaylussite and gypsum. Stable isotopes (oxygen-18 and deuterium) categorize groundwater into three groups: ancient water, recent and older meteoric water mixtures affected by evaporation, and mixtures more heavily impacted by evaporation. Tritium contents reveal three groups: current rainwater, modern water, and sub-modern water. These results indicate that ionic and isotopic differentiations cannot be strictly linked to specific layers, confirming the interconnected nature of the Batha system. The observed heterogeneity is mainly influenced by lithological and climatic variations. This study, though still limited, enhances significantly the understanding of the basin’s functioning and supports the rational exploitation of its vital resources for the Batha area’s development. Future investigations to complete the present study are highlighted.

This study provides an in-depth analysis of the hydrochemical characteristics and their controlling factors in the lower reaches of the Yellow River. Through water quality sampling and analysis over two hydrological periods within a year, combined with hydrochemical methods and machine learning techniques, the study reveals the joint impact of natural factors and human activities on the spatiotemporal variations in hydrochemical constituents. The findings indicate that the water in the lower reaches of the Yellow River exhibits weak alkalinity (the pH is between 7 and 8), with the primary hydrochemical type being HCO3·SO4—Ca·Na·Mg. The temporal variation in the hydrochemical constituents is mainly influenced by rainfall, where nitrate levels are higher during the flood season due to the flushing effect of rainfall, whereas other hydrochemical constituents show an opposite temporal pattern due to the dilution effect of rainfall. The spatial variation in the Yellow River’s hydrochemistry is primarily controlled by a combination of human activities and rainfall. Using Gibbs diagram analysis, it is identified that rock weathering is the main source of ionic constituents, while agricultural fertilization, industrial emissions, and domestic wastewater discharge have significant impacts on the hydrochemical constituents. Compared to other rivers worldwide, the concentration of hydrochemical constituents in the lower reaches of the Yellow River is relatively high, especially nitrate and sulfate, which is closely related to the geological characteristics of the Yellow River basin and intense human activities in the middle and lower reaches. Principal component analysis reveals that the main controlling factors for hydrochemical constituents during the dry season in the lower reaches of the Yellow River are rock weathering dissolution and industrial activities, followed by domestic wastewater; during the flood season, the main controlling factors are rock weathering dissolution and industrial activities, followed by agricultural activities and domestic wastewater. The research findings provide theoretical support for water resource management and water quality protection in the lower reaches of the Yellow River.

Hydrochemical analysis is crucial for understanding soil and water composition dynamics in coastal aquifers. This study presents a novel framework for the comprehensive assessment of groundwater quality, integrating multivariate analysis and hydrochemical techniques. It comprises seven stages aimed at characterizing physicochemical properties, identifying water constituents, elucidating dominant mechanisms in water composition, evaluating ion exchange processes, analyzing spatial distribution of components, identifying impacting processes, and assessing drinking water quality. The framework was applied to the coastal unconfined Arroyo Grande aquifer in Cartagena, Colombia. Fifteen points were sampled, assessing physicochemical parameters such as total hardness, alkalinity, pH, temperature, electrical conductivity, anions, cations, among others. Findings reveal the presence of dominant anions including bicarbonate, chloride, and sulfate, with relevant variations observed between the dry and wet season, with manganese and iron surpassing WHO drinking water standards. The prevalence of these constituents has been attributed to mineral dissolution, ion exchange, salinization due to seawater intrusion, and anthropogenic contamination. Over 50% of samples in both seasons fail to meet freshwater drinking standards due to elevated dissolved mineral concentrations in groundwater. These findings provide insights for sustainable management and mitigation strategies, and the systematic approach enables researchers to identify key factors influencing water composition.

The water level of Lake Hulun has changed dramatically in recent years. The interannual interaction between groundwater and lake water is an important factor affecting Lake Hulun’s water level. Vertical recharge between groundwater and the lake is particularly important. Based on an analysis of differences between the hydrogeochemical and water quality characteristics of the spring water, the lake water, and the surrounding groundwater, the source and recharge mechanism of the spring water in the vertical recharge lake are determined. The results show that spring water is exposed at the bottom of Lake Hulun, and there are obvious differences between spring water and lake water in lake ice thickness, ion characteristics, and water quality characteristics. For example, the ice thickness at the spring site is only 6.8% of the average ice thickness of the lake, and there is a triangular area directly above the spring water area that is not covered by ice; the ion contents of the spring water at the lake bottom were less than 50% of those in the lake water; and the NH4+-N content of the spring water at the lake bottom was only 3.0% of the mean content of the lake water. In addition, the total nitrogen (TN), dissolved oxygen (DO), and NH4+-N contents of the spring water at the lake bottom all fall outside the range of contents of the surrounding groundwater. In general, the source of the spring water at the lake bottom is not recharged by the infiltration recharge of the phreatic aquifer but by the vertical recharge of the confined aquifer. Additionally, the Lake Hulun basin may be supplied with confined water through basalt channels while it is frozen. The vertical groundwater recharge mechanism may be that spring water at the lake bottom is first supplied by the deep, confined aquifer flowing through the fault zone to the loose-sediment phreatic aquifer under the lake, and finally interacts with the lake water through the phreatic aquifer.

As the medium of geological information, groundwater provides an indirect method to solve the secondary disasters of mining activities. Identifying the groundwater regime of overburden aquifers induced by the mining disturbance is significant in mining safety and geological environment protection. This study proposes the novel data-driven algorithm based on the combination of machine learning methods and hydrochemical analyses to predict anomalous changes in groundwater levels within the mine and its neighboring areas induced after mining activities accurately. The hydrochemistry analysis reveals that the dissolution of carbonate and evaporite and the cation exchange function are the main hydrochemical process for controlling the groundwater environment. The anomalous change in the hydrochemistry characteristic in different aquifers reveals that the hydraulic connection between different aquifers is enhanced by mining activities. The continuous wavelet coherence is used to reveal the nonlinear relationship between the groundwater level change and external influencing factors. Based on the above analysis, the groundwater level, precipitation, mine water inflow, and unit goal area could be considered as the input variables of the hydrological model. Two different data-driven algorithms, the Decision Tree and the Long Short-Term Memory (LSTM) neural network, are introduced to construct the hydrological prediction model. Four error metrics (MAPE, RMSE, NSE and R2) are applied for evaluating the performance of hydrological model. For the NSE value, the predictive accuracy of the hydrological model constructed using LSTM is 8% higher than that of Decision Tree algorithm. Accurately predicting the anomalous change in groundwater level caused by the mining activities could ensure the safety of coal mining and prevent the secondary disaster of mining activities.

The Woka-Cuona rift zone on the southeastern side of the Qinghai-Tibet Plateau is characterized by complex geological background conditions, comprising three independent or semi-grabens that traverse from south to north across the Himalayan and Gangdise terranes. Conducting research on the distribution patterns and genesis mechanisms of geothermal resources within the Woka-Cuona rift zone has certain guiding significance for understanding the genesis mechanisms of the geothermal system in the southern Tibetan rift and its exploitation. This paper utilized methods such as data collection, ground investigations, and geochemical analyses to analyze the distribution characteristics and evolutionary processes of geothermal waters in the Cuona rift area based on the geological background conditions of the study area. The research findings demonstrate a significant correlation between the occurrence of geothermal waters in the Cuona rift zone and geological structures, with most geothermal waters primarily distributed near intersections of graben boundary faults and east–west-trending faults. Different regions exhibit variations in the intensity of geothermal activity and geochemical characteristics, with the genesis of geothermal waters associated with deep magmatic activity, characterized by Na+ and K+ as the primary cations and Cl− as the primary anions. Geothermal waters mainly originate from atmospheric precipitation and snowmelt water from surrounding mountainous areas, with recharge elevations ranging from 4500 to 6200 m and an average elevation of 5400 m.

Contamination in coastal regions attributed to fluoride and nitrate cannot be disregarded, given the substantial environmental and public health issues they present worldwide. For effective decontamination, it is pivotal to identify regional pollution hotspots. This comprehensive study was performed to assess the spatial as well as indexical water quality, identify contamination sources, hotspots, and evaluate associated health risks pertaining to nitrate and fluoride in the Al-Hassa region, KSA. The physicochemical results revealed a pervasive pollution of the overall groundwater. The dominant water type was Na-Cl, indicating saltwater intrusion and reverse ion exchange impact. Spatiotemporal variations in physicochemical properties suggest diverse hydrochemical mechanisms, with geogenic factors primarily influencing groundwater chemistry. The groundwater pollution index varied between 0.8426 and 4.7172, classifying samples as moderately to very highly polluted. Similarly, the synthetic pollution index (in the range of 0.5021–4.0715) revealed that none of the samples had excellent water quality, with various degrees of pollution categories. Nitrate health quotient (HQ) values indicated chronic human health risks ranging from low to severe, with infants being the most vulnerable. Household use of nitrate-rich groundwater for showering and cleaning did not pose significant health risks. Fluoride HQ decreased with age, and children faced the highest risk of fluorosis. The hazard index (HI) yielded moderate- to high-risk values. Nitrate risks were 1.21 times higher than fluoride risks, as per average HI assessment. All samples fell into the vulnerable category based on the total hazard index (THI), with 88.89% classified as very high risk. This research provides valuable insights into groundwater quality, guiding water authorities, inhabitants, and researchers in identifying safe water sources, vulnerable regions, and human populations. The results highlight the need for appropriate treatment techniques and long-term coastal groundwater management plans.

The concentrations of chemicals in the groundwater chemical values in the Piedmont Po Plain (NW Italy) show significant temporal variability and need to be characterised due to the lack of regional-scale assessments. The aim of this study was to analyse the trends (period 2000–2020) in the main physicochemical parameters and main ions in 227 wells in the shallow aquifer and to identify the potential causes. The identification of change points (points of sudden change) and comparisons with groundwater level variations were also performed. Results highlight general increasing trends for Na, Cl and HCO3, decreasing trends for SO4 and NO3, stationary conditions for pH and heterogeneous behaviours for electrolytic conductivity, Ca and Mg. Change points occurred in at least 50% of the monitoring wells, mainly during the 2008–2011 period. The comparison between groundwater levels and chemistry highlights a direct proportionality. Superimposed processes that induce an absence of proportionality are shown. The comparison of results with those of previous studies conducted under similar conditions revealed similar variations.. In conclusion, the potential responsible factors (e.g., road-salt dissolution and agricultural practices) and the relevant role of groundwater level variation were identified.

One of the crucial challenges of our time is climate change. The consequences of rising sea levels and drought greatly impact water resources, potentially worsening seawater intrusion. Characterizing coastal aquifers is an essential step in devising strategies to address these phenomena. Seawater intrusion poses a critical socio-economic and environmental issue in the coastal plain of Muravera, southeastern Sardinia (Italy). This coastal plain is an important agricultural area in Sardinia, and the health of the crops is compromised by the increasing salinization of shallow groundwater. To enhance our understanding of the hydrogeological conceptual model, which is essential for a sustainable resource management system, hydrogeological investigations were conducted and complemented by the chemical and multi-isotopic analyses of groundwater. The main objectives of this study were to identify groundwater recharge areas, understand salinization mechanisms and trace the evolution of water chemistry. Within this framework, a monthly survey monitoring piezometric level and electrical conductivity was carried out for one year. This survey was integrated with chemical and isotope analyses, including δ18OH2O and δ2HH2O, δ11B, δ18OSO4, δ34SSO4, and 87Sr/86Sr. Hydrochemistry analysis results revealed the occurrence of seawater–freshwater mixing, extending up to 4 km inland. H2O isotope analysis confirmed the mixing processes and indicated the meteoric origin of recharge waters for both shallow and semi-confined aquifers. The strontium isotopes ratio facilitated the identification of four main groundwater flow paths, confirmed by the SIAR model. The results of this combined hydrogeological–geochemical–isotopic survey provide essential elements for the future implementation of an integrated and sustainable management system. These findings enable interventions to slow the process of seawater intrusion and meet the economic needs for the development of local communities.

A hydrochemical and mineral study of groundwaters and damaged rocks from the Tíscar and Larva fault zones (Betic Cordillera, Iberian Peninsula) was carried out in order to (a) describe the physical and chemical properties of the groundwaters; (b) recognize significant locations with deep-origin fluids related to active tectonics; (c) and to describe the water–rock interaction and the neoformation of clay mineral processes and their importance in the seismicity of the faults. A sampling campaign was completed between November 2012 and November 2013, during which data were obtained from 23 different groundwater sites in the fault areas. Two main groups of waters were distinguished: (a) Ca2+-Mg2+-HCO3− facies characterized by poor conductivity and salinity; and (b) saline waters (up to 30 meq/L) rich in Ca2+-Mg2+-SO4-Cl− and with an elevated conductivity (frequently > 1000 μS/cm). In addition, a minor group of saline and warm waters (T > 16.5 °C) was found to be Na+-rich and show moderately high B values (>0.33 ppm), and which mig ht be hosted in aquifers deeper than the two main groups. This group of deep-origin waters is oversaturated in clay minerals and is in equilibrium for Ca-Mg carbonate minerals. X-ray diffraction and scanning and transmission electron microscopy data corroborate the crystallization forecast of authigenic smectite, which appears as thin films coating carbonate fragments. The origin of smectite is related to the fragile strain and thermal–fluid–mineral interactions in fault rocks. Smectite could lubricate carbonate rocks, which favor creep deformation versus seismic slip. This work provides locations where groundwater physico-chemical properties and composition suggest tectonic fault activity.

Intense anthropogenic activities in arid regions remarkably affect groundwater by causing phreatic decline and water environmental deterioration. A systematic understanding of groundwater hydrochemical evolution and recharge is critical to regional water, ecological and agricultural security in arid regions, but is not well known in arid oasis–deserts. This research identified groundwater recharge processes and assessed the impact of anthropogenic activities on groundwater hydrochemical evolution in a representative oasis–desert in Central Asia using stable isotopic indicators (δ2H and δ18O) and hydrochemical data. Results indicated that the normalized difference vegetation index (NDVI) and cultivated land area exhibited a significant increasing trend during 2000 to 2020. Stable water isotopes and the ionic composition of both groundwater and surface water exhibited obviously spatial heterogeneity and seasonal variation. Generally, the spatial distribution pattern of major dissolved ions for shallow groundwater was consistent and increased along the groundwater flow direction from midstream to downstream. Surface water and groundwater were both characterized by higher δ18O and total dissolved solids (TDS) in the non-flood season than those in the flood season. Shallow groundwater had a larger seasonal variation in δ18O and TDS than other water components. Groundwater level in monitored wells generally presented a decreasing trend from 2018 to 2021, accompanied by a decrease in phreatic water TDS and NDVI in the desert area. Gypsum dissolution and weathering of silicate and halite had an important role in forming groundwater hydrochemistry. Anthropogenic activities significantly affected groundwater hydrochemistry and recharge. Shallow groundwater received its primary recharge from surface water and lateral groundwater flow, constituting 73% and 27% of the total recharge, respectively. Agricultural activities and groundwater overexploitation were the main factors for variations in groundwater level and quality in the oasis area, and directly affected groundwater and natural vegetation in the desert area. The results would be helpful to deeply understand groundwater hydrochemical evolution and cycling, and beneficial for groundwater efficient utilization and desert ecosystem restoration in the arid areas.

Geothermal water is the product of deep circulation within the crust, and the understanding of its hydrogeochemical process can provide effective information for integrated research on its circulation pattern and formation mechanism. Based on the geothermal geological conditions of the Yanggao geothermal field, this study analyzed water samples from thermal springs and geothermal wells in the geothermal field, ascertaining their hydrochemical components, along with their hydrogen and oxygen isotopes. Using methods like piper diagrams, ionic component ratio characterization, Na–K–Mg equilibrium diagrams, and reverse path simulations, this study elucidated the recharge source of geothermal water in the study area, revealed the water–rock interactions the geothermal water experienced, and evaluated the geothermal reservoir temperatures. The results show that the geothermal water has hydrochemical types of Na–Cl–HCO3 and Na–HCO3–Cl, and is primarily recharged by the atmospheric precipitation in the northern mountainous area. The geothermal water has experienced extended water runoff and deep thermal circulation, and its hydrochemical composition primarily results from the weathering and dissolution of silicate rocks and evaporites. The major hydrogeochemical processes of the geothermal water involve the dissolution of calcite, dolomite, gypsum, and kaolinite. In addition, the canon-exchange also changes the chemical component of the geothermal water. The SiO2 Geothermometer, a multimineral equilibrium diagram, and the silica–enthalpy model reveal the presence of deep and shallow geothermal reservoirs in the study area, which exhibit temperatures of 73 °C and ranging from 125 to 150 °C, respectively. The open geothermal reservoir environment results in the mixing of geothermal water and cold water, with shallow and deep geothermal water mixing with cold water at ratios of 57% and 76%, respectively.

The Hutuo River Drinking Water Source Area is an important water source of Shijiazhuang (North China Plain). Knowing the characteristics of groundwater chemistry/quality is essential for the protection and management of water resources. However, there are few studies focused on the groundwater chemistry evolution over the drinking water area. In this study, total of 160 groundwater samples were collected in November 2021, and the spatial distribution of groundwater chemistry and related controlling factors were analyzed using hydrological and multivariate analysis. The entropy-weighted water quality index (EWQI) was introduced to assess the groundwater quality. The results show that the hydrogeochemical types of groundwater are Ca-HCO3 (78.1%), mixed Ca-Mg-Cl (20%), and Ca-Cl (1.9%) in the area. Graphical and binary diagrams indicate that groundwater hydrochemistry is mainly controlled by water–rock interaction (i.e., rock weathering, mineral dissolution, and ion exchange). Five principal components separated from the principal component analysis represent the rock–water interaction and agricultural return, redox environment, geogenic sources, the utilization of agricultural fertilizer, the weathering of aluminum silicates, and dissolution of carbonates, respectively. More than 70% of the samples are not recommended for irrigation due to the presence of high salt content in groundwater. EWQI assessment demonstrates that the quality of the groundwater is good. The outcomes of this study are significant for understanding the geochemical status of the groundwater in the Hutuo River Drinking Water Source Area, and helping policymakers to protect and manage the groundwater.

The geochemical characterization and evolution of shallow groundwater in the Zihe River source area is a key issue that needs to be addressed. In this study, a combination of traditional geochemical techniques and geochemical modeling was used to explain the geochemical processes and major ion sources in the chemical evolution of shallow groundwater in the Zihe River source area, Northeast China. Fifty-seven water samples were collected in June 2020 for chemical analysis, and the results showed that the main groundwater chemistry types in the three major aquifers are HCO3·SO4-Ca·Mg-type pore water from loose quaternary rocks, HCO3·SO4-Ca·Mg-type karstic fissure water from carbonate rocks, and HCO3·SO4-Ca-type weathered fissure water from massive rocks. Water–rock interactions in alkaline environments were the main causes of changes in groundwater chemistry. Rock weathering dominated the geochemical evolution of each aquifer. The analysis of ion concentration ratios and modeling revealed that the aquifer’s chemical components are mainly derived from the dissolution of dolomite and calcite and partly from the infiltration of pollutants containing Cl− and NO3−, as well as from the dissolution of quartz. Mg2+ is derived from the dissolution of dolomite. HCO3− is primarily derived from the co-dissolution of calcite and dolomite, and to a lesser extent, its content is also influenced by the recharge of rainfall. SO42− has two sources: it mainly originates from the dissolution of gypsum and the anhydrite layer, followed by atmospheric precipitation. The synthesis showed that the groundwater quality in the source area of Zihe River is good, all the indices reached the standard of class III groundwater quality, and the overall degree of human pollution is low. The results of this research will provide a scientific basis for the local authorities to delineate karst groundwater protection zones in the Zihe River source area and to formulate resource management strategies for the development, utilization, and protection of karst groundwater.

Rivers are an important source of water in humid regions, but their availability is greatly limited by water chemistry. In order to accurately identify the changes in river water chemical composition, the compositional analysis method (CoDA) is proposed from the perspective of compositional data analysis theory, which considers the geochemical riverine system as a whole and detects the compositional changes of the entire watershed. The basic data analysis is carried out by traditional analysis methods, and the results show that the hydrochemical characteristics of different sections of the basin have significant features. The water chemistry of Dongxi River is of the HCO3− Ca type. The water of the Xixi River shows a gradual evolution from the HCO3-Ca type and high SO42− content in the upper reaches to the Cl-Ca type in the lower reaches. The hydrochemistry of river water in the watershed is mainly affected by rock weathering leaching (PC1) and agricultural and domestic pollutant discharge (PC2), with a contribution rate of 48.4% and 19.7%, respectively. Rock weathering, mining, and agricultural pollution are the main factors affecting the chemical composition of river water in different regions. The spatial composition of a single sample at different scales is monitored by the Mahalanobis distance approach in an iterative manner to minimize the influence of a single anomaly on the composition center. The results show that the main reasons for the change in river water chemical composition along the Xixi River are attributed to mine pollution, domestic pollution, and tea plantation and that along the Dongxi River is caused by domestic pollution. The hydrochemical composition changes after the confluence of the Xixi River and Dongxi River are mainly affected by human activities and seawater in urban areas. This research could provide new perspectives and methods for detecting the influences of human and natural factors on the hydrochemistry of river water in humid regions worldwide.

In the context of climate change, precipitation and runoff in the arid inland basins of northwest China have undergone significant changes. The Qaidam Basin (QB) is a typical highland arid inland area. Understanding the spatial and temporal variations in surface water and groundwater chemistry and isotopes, as well as their causes, is crucial for future water resource management and ecological protection. Samples of river, lake, and groundwater, as well as others, were collected and tested in five typical watersheds in the summer and winter. The hydrochemistry and isotopic spatiotemporal differences in various water bodies were studied using the significant difference method, water vapor flux models, hydrochemistry, isotopes, and other methods for cause analyses. The results indicate the following: (1) There are differences in hydrochemistry between the southern and northern basins because the southern basin is more influenced by the dissolution of salt rocks and evaporation, whereas the northern basin is mainly affected by carbonate weathering. (2) The enrichment of δD and δ18O in the northern basin gradually increases from west to east, while in the southern basin, it is the opposite. This is because the southern basin receives a larger contribution of water vapor from the mid-latitude westerlies, while the northern basin primarily relies on local evaporation as its water vapor source. (3) Significant differences are observed in the total dissolved solids (TDS) and hydrochemical types of river water and groundwater between the summer and winter due to higher rates of rock weathering and evaporation in the summer. (4) The more pronounced seasonal differences in hydrogen and oxygen stable isotopes in the southern basin are due to higher rates of internal water vapor circulation in the summer. (5) The similarity in characteristics between river water and groundwater is the result of strong exchanges between river water and groundwater from piedmonts to terminals. The spatiotemporal heterogeneity of terminal lakes is attributed to the accumulation of salts and groundwater replenishment from other sources.

To reduce downstream ecological damage, it is crucial to analyze water and salt sources in saline–alkali farmland drainage and optimize soil salt discharge. This study employs statistical, hydrochemical, and isotope methods to identify controlling factors and characteristics in water bodies during winter irrigation. The results show average TDS values of 0.59, 6.40, and 4.14 g/L for irrigation, phreatic, and drainage water. Irrigation and phreatic water mainly belong to the HCO3-Ca·Mg·Na and Cl·SO4-Na·Mg types. Na+/(Na+ + Ca2+) and Cl−/(Cl− + HCO3−) values suggest the rock–water interaction and evaporation influences in irrigation water, while evaporation primarily controls phreatic water. The main salt types include NaCl, MgSO4, Na2CO3, and CaCO3 for irrigation water and NaCl, MgSO4, Na2SO4, and CaCO3 for phreatic water. These findings lay a research basis for analyzing water and salt sources in farmland drainage during winter irrigation in saline–alkali land.

In order to achieve the rational development and utilization of underground water resources in the Dongsheng mining area under coal mining conditions, we selected the upstream area of Beiniuchuan River as a typical region. Through field investigations, sampling tests, and the application of hydrochemical and isotope techniques, we traced the groundwater circulation mechanism in the Dongsheng mining area. The results indicate that the majority of the Quaternary alluvial and Salawusu Formation groundwater is of the HCO3-Ca type, with a TDS content below 300 mg/L. However, in some areas, the hydrochemical type becomes complex due to anthropogenic contamination. The shallow-buried Yan’an Formation groundwater is either of the HCO3-Ca·Mg type or the HCO3·SO4-Ca·Mg type, with TDS content ranging from 200 to 750 mg/L. The Yan’an Formation at depths greater than 40 m exhibits complex water chemistry, with a TDS content higher than 500 mg/L, and it belongs to the Cl-Na type, with TDS around 700 mg/L. The hydrogen and oxygen isotope results indicate that the local groundwater is primarily recharged via atmospheric precipitation. The 3H and 14C results show that the Quaternary alluvial and shallow-buried Yan’an Formation groundwater has a fast turnover rate, while the deep-buried Yan’an Formation and Yan’chang Formation groundwater have a slower turnover rate. The regional groundwater circulation can be generalized into three flow systems: shallow, intermediate, and deep. Under the influence of coal mining activities, the water circulation conditions in the study area have undergone significant changes. The sealing integrity of the Yan’an Formation has been compromised, and precipitation and shallow groundwater have enhanced the vertical infiltration capacity of the formation, increasing the proportion of groundwater participating in the intermediate flow system. As a result, the river runoff mainly dependent on the discharge from the shallow flow system has drastically decreased.

The Perrot Spring (1300 m a.s.l.), located to the right of the Chalamy valley in the Monte Avic Natural Park (Valle d’Aosta, Italy), is an important source of drinking water for the municipality of Champdepraz. This spring is located on a large slope characterised by the presence of a Quaternary cover of various origins (glacial, glaciolacustrine, and landslide) above the bedrock (essentially serpentinite referred to the Zermatt–Saas Zone, Penninic Domain). Water emerges at the contact between the landslide bodies and impermeable or semi-permeable glaciolacustrine deposits. The aim of this study is to define the processes and recharge zones of this spring. The analysis of the data revealed the presence of two contributions to the Perrot Spring input: a spring thaw contribution defined by a small increase in flow and an autumn contribution from rainwater infiltration. The low average temperature and low variation of the annual temperature (4.8–6.5 °C) suggest a sufficiently deep flow circuit. Chemical analyses showed a groundwater chemistry consistent with the regional geology: the hydrochemical facies is calcium–magnesium bicarbonate and isotopic analyses (δ2H and δ18O) of rainfall and spring water suggested a recharge altitude of about 2100 m a.s.l. In conclusion, this study makes it possible to recognize the water inputs to the spring discharge and to delineate its recharge area, which can be proposed to implement strategies to protect the resource.

The Laizhou Bay area contains a large amount of Quaternary brine resources, which have been gradually depleted by long-term high-intensity mining. The local brine genesis is still controversial, and the dominant theory of the evaporation of brine formation limits the exploration of brine resources to the land area, while the confirmation of freezing brine formation would greatly expand the brine storage range. In this research paper, the genesis of underground brines was analyzed based on the major ion concentrations of 62 samples of underground brines at different depths at 24 stations along the south coast of Laizhou Bay. The results show that the underground brines originated from seawater; however, their chemical components were changed during the evolution process after formation. The hydrogeochemical modeling results show that the mixing of seawater and fresh groundwater also affects the chemical composition of brines. The large-scale exploitation of brine resources in recent decades has also led to significant changes in the chemical composition of the underground brine in Laizhou Bay compared with the earlier period. The special geographic environment and the development of the brine chemical industry have led to the evolution of underground brines in Laizhou Bay being affected by a variety of factors, which makes the traditional analysis of brine genesis in this region not applicable. Furthermore, although evaporation and concentration are the dominant factors in the formation of brine, there is still a lack of evidence to rule out the existence of the freezing pathway.

The purpose of this research was to understand the hydrogeochemical characteristics and assess the quality of phreatic and confined groundwater in southern Hebei Province. A total of 107 groundwater samples were collected, representing different aquifer conditions over the study area. Multivariate statistical analysis, hydrochemical maps, ionic ratio coefficients, geographic information system (GIS) and geochemical simulation were comprehensively and systematically used to reveal the hydrochemical characteristics of groundwater and its controlling mechanism. The results revealed that both phreatic (pH = 7.02–9.08) and confined groundwater (pH = 7.00–10.60) were slightly alkaline. The hydrochemical types were mainly present as the HCO3-Ca-Mg type in the western premontane area and mixed Ca-Mg-SO4-Cl and Na-Cl-SO4 types in the eastern plains. The hydrochemical composition was dominated by water–rock interactions of natural processes, including silicate weathering, dissolution of sulfate minerals (gypsum, anhydrite), and cation-exchange adsorption. Anthropogenic activities were the main factor causing NO3− content in some groundwater samples to exceed the geochemical baseline. The hydrogeochemistry of groundwater in different aquifers was significantly varied. The average contents of TH, TDS, Na+, Ca2+, Mg2+, Cl− and SO42− in phreatic aquifers were significantly higher than those in confined aquifers. The Entropy Weighted Water Quality Index (EWQI) results revealed that 17.78% of phreatic and 50% of confined water samples were meeting the purpose of drinking water. The groundwater samples with EWQI values exceeding 100 were mainly situated in the Handan urban area and the eastern region of Xingtai City, which should be avoided for direct utilization and needs to be improved through protection and management measures, to enhance the quality of groundwater. Correlation analysis showed that groundwater quality was significantly dominated by TH, TDS, Na+, Mg2+, Cl− and SO42− concentrations.

Ionic strength (I; mol·L−1) acts as one of the most important parameters of natural waters. It is indispensable for obtaining ion activities and thus is crucial for describing chemical processes in water solutions. Limnology, I, has many applications, but calculating the partial pressure of CO2 (pCO2) and the carbonate saturation index (SI) are among the most important examples. The determination of I requires the full ion composition of water to be recognized, and when the concentration of some major ion(s) is/are missing altogether, the I value remains unknown. Because historical and monitoring data are often incomplete, it seems useful to provide a method for the indirect assessment of I. In this paper, we developed and tested an empirical model to estimate I on the basis of electric conductivity at 25 °C (EC). Our model consists of two linear equations: (i) Imod = 15.231 × 10−6·EC − 79.191 × 10−6 and (ii) Imod = 10.647 × 10−6·EC + 26.373 × 10−4 for EC < 592.6 μS·cm−1 and for EC > 592.6 μS·cm−1, respectively. We showed that model performance was better than the hitherto used EC–I relationships. We also demonstrated that the model provided an effective tool for limnological monitoring with special emphasis on the assessment of CO2 emissions from lakes.

Coastal areas have made substantial contributions to global economic development but are plagued by challenges such as groundwater salinization. Groundwater serves as the primary source for drinking, industrial, and domestic purposes in these coastal areas. Therefore, understanding the causes and processes of groundwater salinization holds paramount significance for effective groundwater management. The coastal area of Laizhou Bay in northern China serves as a quintessential example of such a scenario. With substantial groundwater extraction and severe groundwater salinization issues, it exacerbates the disparity between water-resource supply and demand. Currently, our understanding of the processes and influencing factors related to groundwater salinization in this region remains limited. In this study, employing hydrochemical and stable chlorine isotope analyses on 35 groundwater and seawater samples, an in-depth investigation into the complex mechanisms underlying groundwater salinization in the Quaternary aquifers of the eastern coastal plain of Laizhou Bay was conducted. The test results of the samples indicate that brine and saline groundwater are primarily of the Na-Cl type, exhibiting a hydrochemical composition similar to that of seawater. Brackish groundwater exhibits a diverse hydrochemical composition. The hydrogen and oxygen isotope characteristics of brackish and fresh groundwater resemble atmospheric precipitation, while brine, seawater, and saline groundwater show hydrogen and oxygen isotope depletion. Compared to seawater, brine exhibits significant δ37Cl depletion. The analysis of the test results reveals that the formation of brine aquifers results from a complex interplay of climate change, tectonic movements, and sea–land evolution, involving lagoon development during seawater regression, salt concentration through evaporation, and subsequent water–rock interactions. The genesis of saline groundwater involves a complex interplay of brine–seawater mixing, significant evaporation, and potential input of fresh groundwater from atmospheric precipitation and river sources. The formation of brackish groundwater is predominantly influenced by atmospheric precipitation, and agricultural activities, with significant variations in NO3− concentrations attributed to varying intensities of fertilizer application in the northern plain area. These insights contribute to a deeper understanding of the origins of groundwater and can inform the development of policies for groundwater protection in this area.

Wastewaters are valuable sources of metals and metalloids and can serve as essential resources for their recovery. Characterizing and understanding the occurrence of metals and other compounds, along with identifying the most effective recovery methods, are key steps in unlocking the potential for reusing these resources. The present study focused on analyzing waters from various mining dams in the Iron Quadrangle (IQ) region of Brazil, which contained metals such as Au, Cu, Ni, Zn, and sulfates resulting from the metallurgical treatment of Au. The results revealed a range of metal concentrations in the neutral zone in three tailings. Additionally, a 3D map was created, and a statistical analysis and an exploration of the processes governing mobility and partitioning were conducted to assess the potential for reuse. Notably, the study identified a high potential for Au recovery, particularly through the utilization of sustainable and cost-effective methods such as nanofibers with biosorbents. Overall, this research contributes to the understanding and exploration of potential reuse procedures for strategic metals in various industrial applications.

Accurate identification of nitrate (NO3−) sources is critical to addressing groundwater pollution, especially in highly vulnerable karst aquifers. The groundwater hydrochemistry and δ15NNO3 and δ18ONO3 isotopes were analyzed in samples taken from the Jinan Spring Catchment, which has been affected by urbanization and agricultural activities. The study highlighted the use of hydrochemistry, environmental isotopes, and a multisource linear mixed model for NO3− source identification and apportionment. The results showed that, controlled by carbonate rocks, the hydrochemical types in both rainy and dry seasons were highly consistent, and HCO3·SO4−Ca was the dominant type, accounting for 60%. Except for Ca2+, Mg2+ and HCO3−, the coefficients of variation of other ions were all greater than 0.5 in rainy and dry seasons. The chemical composition of groundwater was mainly controlled by water–rock interaction. Ca2+ and HCO3− were mainly derived from carbonate rock dissolution; K+, Na+, SO42−, NO3− and Cl− were partially derived from atmospheric precipitation. The IsoSource model quantitatively revealed that the majority of the groundwater and surface water was influenced by manure and sewage (M&S) contributing 39.3% and 52.3% in the rainy season, and 37.1% and 56.9% in the dry season, respectively. The NO3− source fraction rates were in the order M&S > SON > AF > CF > AD. In addition, nitrate pollution control measures and suggestions for different areas are put forward. In rural residential areas, the free discharge of livestock manure and sewage should be strictly controlled. In agricultural planting areas, chemical fertilizers and pesticides should be used rationally to prevent non-point source pollution. In urban areas, the centralized treatment of industrial and residential sewage should be strengthened to prevent point source pollution.

Groundwater is vital to local human life and agricultural irrigation, and the quality of the water is critical to human health. As a result, it is critical to investigate the hydrochemical evolution and water quality of groundwater in the Sanjiang Plain. There were 259 samples obtained. Furthermore, hydrogeochemical simulation was performed to highlight groundwater’s hydrochemical features, evolution process, and water quality. The analytical results show that the groundwater in the study area is somewhat alkaline with a mean TDS of 285.94 mgL−1 and the primary contributing ions being Ca2+ and HCO3−. The closer the concentration of TDS and NO3− is to the city, the higher the concentration, indicating that the chemical composition of the water body has been affected by certain human activities. The Piper diagram, Gibbs diagram, and correlation analysis results demonstrate that the chemical type of groundwater is mostly HCO3-Ca and the hydrochemistry is primarily regulated by weathering and carbonate and silicate dissolution. According to the entropy-weighted water quality index, the groundwater quality in this location is pretty acceptable. This study could help strengthen groundwater quality monitoring based on local conditions, identify the source of nitrate, provide data support for the safe use of local water resources, and serve as a reference for global water chemical evolution and water quality evaluation in cold regions.

Water for irrigation use plays a critical role in agriculture via supporting crop growth and maintaining food production worldwide. Irrigation water quality evaluations provide useful information for sustainable water practices in many agricultural regions. In Brunei Darussalam, the quality of irrigation water is still poorly understood. The present study aims to investigate the hydrochemical characteristics of water resources in Brunei Darussalam and evaluate their quality and suitability for irrigation use. A total of fifteen sampling locations were chosen from selected ground and surface water sources found in all four Brunei districts. The water samples’ physicochemical properties, including pH, EC, and major cations and anions, were measured and compared with FAO standards. Hydrochemical classification based on the Piper diagram revealed that water mainly belongs to the calcium-, magnesium-, and bicarbonate-type, or Type IV water class. The evaluation of heavy metals (Fe, Zn, Cu, Cr, As, and Cd) showed concentrations within the FAO’s permissible limits. In this regard, iron showed the highest concentration among the investigated metals. Established water quality indices such as SAR, Na%, RSC, MAR, KR, PS, and IWQI were used to evaluate and classify the water’s suitability for irrigation use. Overall, our findings revealed that almost all of the analysed water samples in the study area have low salinity and sodicity risks. However, only 27% of the samples passed the magnesium hazard assessment, and one sample showed a very poor IWQI result. Thus, additional testing and treatment are recommended for these cases. This study provides valuable insights on water quality for present and future utilisation, aiming to contribute to the protection of water resources in Brunei Darussalam.

Groundwater pollution has emerged as a significant water crisis in various regions around the globe. Groundwater serves as a crucial source of water for human consumption and agricultural activities in the Sichuan Basin where groundwater quality has yet to be concentrated. A total of 41 groundwater samples were collected from domestic wells in Suining city of the Sichuan Basin, which were used for analyzing the hydrogeochemical processes and suitability for irrigation and drinking purposes. In the study area, groundwater samples belonged to the HCO3-Ca type. Hydrochemical compositions were dominated by carbonate and silicate mineral dissolution with positive cation exchange. Agricultural activities and urban sewage were the primary sources of NO3− pollution. The irrigation water quality index (IWQI) was calculated using electronic conductivity (EC), Na+, Cl−, HCO3−, and sodium adsorption ratio (SAR). The IWQI values showed that the suitability of groundwater irrigation was generally good and presented the decreasing trend southeastwardly. According to the entropy-weighted water quality index (EWQI), the groundwater quality for drinking purposes was generally good. However, there were some local areas with poor water quality concentrated in the southeast part. According to the human health risk (HHR) model, the groundwater was deemed safe for adults and children. However, for infants, the nitrate level in the groundwater remained high and posed potential health risks. The combined IWQI and EWQI evaluation served as a valuable reference for the utilization of the groundwater resource in the Sichuan Basin, as well as other comparable regions worldwide.

Water inrush caused by mining below the seafloor seriously affects the safety and production of mines. Identifying the end element of mine inrush and accurately calculating the mixing ratios of end elements are the basis for a reasonable evaluation of water inrush risk. Based on hydrogeochemical and stable isotope indexes, combined with the spatial distribution characteristics of brine, the classification of brine in the study area was preliminarily determined as follows: shallow brine, middle brine, and deep brine (while previous studies have only classified bedrock brine as one category). Hierarchical multi-index analysis was used to identify the inrush end elements in the different sublevels, and an end-element mixed model was determined according to the analysis results of the four pairs of evaluation indexes (Cl−–δ18 O, Cl−–Ca2+, Cl−–Mg2+, and Cl−–Na+). Through a comparison with the deviation analysis results of previous studies, it was shown that this method is suitable for mine-water-source identification when under complex hydrogeology conditions. According to the calculation results of the mixing ratio, the seawater ratio shows, within the mining process, a trend of first increasing, then decreasing, and finally stabilizing. This trend is controlled by disturbance stress, self-weight stress, and tectonic stress. The vertical zonation of the seawater proportions indicates that seawater mainly recharges mine water through vertical fractures. The difference in the proportion of seawater at the water inrush points of the −600 m sublevels indicates that the F3 fault and the northwest water-conducting fracture zone may be the preferred flow channels for seawater to recharge mine water. The research results are of great significance to promote the safe mining of coastal mines around the world.

The Heuningnes Catchment in the Republic of South Africa was used as a case study in this research to describe the application of saltwater fraction/quantification and hydrogeochemistry methods to evaluate the extent of saline intrusion in the coastal aquifers. The argument of the research is that the presence of seawater incursion may be conclusively determined by combining the examination of the major ions, seawater fraction, stable isotopes of water, bromide, and geochemical modeling. Using stable isotopes of oxygen (18O) and deuterium (2H), major ions chemistry, seawater composition, and geochemical modeling, the genesis of salinity and mixing of different water masses were examined. Twenty-nine (29) samples of groundwater were examined. All samples showed water facies of the Na-Cl type, indicating a seawater-related origin. The significance of mixing in coastal aquifers under natural conditions was shown by the hydrogeochemical characteristics of key ions derived from ionic ratios, which demonstrated substantial adherence to mixing lines among endmembers for freshwater as well as saltwater (seawater). The quantification of seawater contribution in groundwater percentages varied from 0.01 to 43%, with three samples having concentrations of seawater above 50%. It was clear from the hydrogeochemical analysis and determination of the proportion of saltwater that the seawater intrusion impacted the coastal fresh groundwater. In addition, the chloride concentration in the groundwater ranged from 81.5 to 26,557.5 mg/L, with the corresponding δ18O values ranging from −5.5‰ to −0.9‰, which suggested that freshwater and saltwater were mixing. The Br−/Cl− ratios showed that evaporation had played a part in elevating groundwater salinity as well. Since saturation indices were below zero, the mineral dissolution could also contribute to the salinization of groundwater. Further proof of seawater incursion in the investigated catchment was supplied by geochemical modeling and bromide. Even though such tools were not verified in multiple coastal aquifers for widespread generalization, the study offered a scientifically significant understanding of the application of such tools on seawater intrusion in coastal aquifers and has useful recommendations for the aquifer setting of similar environments.

Phreatic groundwater hydrochemistry is important for sustainable water utilization and ecological stability in arid regions. Based on the test data from collected water samples, this study explored the phreatic groundwater recharge, hydrochemical evolution, and quality of the Sugan Lake Basin using hydrogeochemical, isotopic, and multivariate statistical analyses. The stable isotopic results showed that the phreatic groundwater in the alluvial fan, plain, and wetland areas of the basin generally originated from modern water, and the phreatic groundwater in the piedmont was mainly recharged by paleowater under low-temperature conditions. Carbonate is the dominant mineral in the regional rock weathering process. Phreatic groundwater in the piedmont is controlled by mineral dissolution and cation exchange; however, phreatic groundwater in other areas of the basin is significantly affected by river infiltration. This indicates that the hydrochemical regime of phreatic groundwater is sensitive to natural river flow without disturbing human activity. Class I–V groundwater samples accounted for 2.86%, 25.71%, 34.29%, 14.29%, and 22.86%, respectively. Total dissolved solids, total hardness, sulfate, chloride, nitrite, Na, Fe, Hg, and Cr VI are important factors that determine groundwater quality. This study deepens the understanding of phreatic groundwater hydrochemical characteristics and hydrologic cycles in the Sugan Lake Basin and provides background values of hydrochemistry without human interference for further study in arid inland basins.

Groundwater plays a crucial role in triggering and reactivating deep-seated landslides. However, classical hydrogeological investigations have limitations in their applicability to deep-seated landslides due to anisotropic and heterogeneous media. The Huangtupo landslide in the Three Gorges Reservoir area has garnered significant attention due to its high hazard potential. Of particular interest is the NO.1 Riverside Sliding Mass (HTP-1), which has shown notable deformation and has become the primary focus of landslide research. The study aims to investigate the sources of water in the HTP-1 landslide through hydrochemical analysis. This was achieved by monitoring the major ion content in the groundwater within the landslide for one year. Furthermore, stable isotope investigations were conducted on the groundwater in and around the landslide area, and an analysis of the mineral composition of the landslide soil was also performed. The results indicate that the groundwater in the landslide area (LGW) is a mixture of karst groundwater (KGW) from the adjacent upslope and local precipitation (LP). The karst groundwater is a major contributor to the recharge of the landslide groundwater system, causing a high component of groundwater that can easily exceed the critical level that causes landside failure during heavy rainfall events. Furthermore, prior to the relocation of residents from the Huangtupo landslide, the landslide groundwater was also impacted by human sewage, which not only affected the chemical composition of groundwater, but also had potential implications for slope stability. These findings provide a more scientific basis for the design and implementation of interception and drainage measures for the Huangtupo landslide and other large-scale landslides with similar geological conditions in the Three Gorges Reservoir area.

Groundwater and surface water, though thought to be different entities in the past, are connected throughout the different landforms of the world. Despite being studied for quite some time, the interaction between groundwater and surface water (GW–SW) has received attention recently because of the heavy exploitation of both of these resources. This interaction is responsible for a phenomenon like contaminant transport, and understanding it helps to estimate the effects of climate change, land use on chemical behavior, and the nature of water. Hence, knowledge of GW–SW interactions is required for hydrologists to optimize resources and analyze the related processes. In this review article, different aspects of the interaction are discussed. Starting from the basics of the phenomenon, this work highlights the importance of GW–SW interactions in the hydrological cycle. Different mechanisms of GW–SW interactions are briefly examined to describe the phenomenon. The scales of interaction are also elucidated where the classification is addressed along with a brief introduction to the large scale and sediment reach scales. The study then moves on to the investigation methodologies used for the process of SW–GW interaction and their classifications based on whether they are field methods or modeling techniques. Various literature is then explored in terms of research approaches. Finally, we highlight the applicability of the methods for different scenarios. This work is aimed to summarize advances made in the field, finding research gaps and suggest the way forward, which would be helpful for hydrologists, policymakers and practicing engineers for planning water resources development and management.

The water-level fluctuation zone of the lower Jinsha River Basin is a fragile ecosystem with limited water resources in the southwest of China. Soil water is critical for maintaining ecological balance and promoting the healthy development of animals and plants in this region. In this study, eight typical soil profiles were monitored for hydrochemistry in soil-soluble salt from upstream to downstream of the lower Jinsha River Basin. The results show that the soil water content was low and had a negative correlation coefficient with major ions in the soil-soluble phase. The soil-soluble salt is slightly alkaline, and Ca2+, Na+, SO42−, and HCO3− are important components for ions in a soluble phase. Major ions in soluble salt originate from various sources, including precipitation, anthropogenic input, silicate weathering, and carbonate weathering, and the contribution rates from each end member were 0.7%, 45.1%, 25.2%, and 29%, respectively. The ion composition in surface soil soluble salt is mainly influenced by precipitation and human activities, while the ions in the 0–50 cm soil layer originate from the precipitation input and water-rock interaction. In addition, rock weathering is a vital process for releasing ions into soil-soluble salt from 50 to 100 cm soil layer. Our findings provide important references for ion sources and the eco-hydrological process in limited water resources in the water-level fluctuation zone of the lower Jinsha River Basin.

In this study, groundwater, stream water, and stream sediment samples were collected from a coal mine area in Dazhu, Southwestern China, and hydrogeochemical, multivariate, and X-ray analyses were conducted to examine the effects of coal mine pollution. The groundwater and stream samples were slightly acidic to alkaline (6.7 to 8.2). Typically, the water samples were dominated by Ca2+ + Mg2+–HCO3− and Ca2+ + Mg2+–Cl−. SO42− originates from gypsum dissolution and pyrite oxidation, and Ca2+ and Mg2+ may be related to the dissolution of carbonate. According to the Chinese standard and World Health Organization guidelines, the water in the coal mine area is of good quality in terms of its physical and chemical properties, except for the concentration of Mn and Fe, with values of 1925.14 μg/L and 12,872.88 μg/L, respectively. A principal component analysis revealed two groups in which the concentration of metals and metalloids in stream sediments are affected by the coal mine drainage. The Mn and Fe average concentration in the downstream Kongjiagou drain sediment samples was 2035.1 ppm and 6%, respectively. These values were higher than the average Mn and Fe concentration in Xiaojiagou at 453.1 ppm and 2.9%, respectively. Both the Mn and Fe concentration were higher than the background values (640 ppm and 4.4%).

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.

Underground reservoir technology can mitigate water shortage and pollution problems in water shortage coal mining areas and has a good application prospect. While still a new technology, the theory and method of underground reservoirs need to be improved. This research focused on the hydrochemical characteristics of mine water and their significance for the site selection of underground reservoirs. With the Shendong coal mining area as a case study, the hydrochemical major ions, toxicological indexes, and stable isotopes of hydrogen and oxygen were tested for the mine water samples, and the water quality was quantitatively evaluated and the origins of over-limit variables were investigated by hydrogeochemical numerical simulation and ionic ratio analysis. The influencing factors of water quality were analyzed and the significance of mine water quality for the site selection of underground reservoirs was discussed. The results show that the main over-standard variables are Na+, F−, SO42−, TDS, and sodium ion adsorption ratio (SAR), and a strong positive correlation exists between F− and SAR and a negative correlation exists between F− and Ca2+. Na+ in mine water originates from the dissolution of halite and silicate rocks, as well as reverse cation exchange. F− originates from reverse cation exchange and the displacement between OH− in alkaline water and F− adsorbed on the surface of minerals. On the whole, the mine water quality is better on the east than on the west of the WL River. The water–rock interactions in goaf increase the concentrations of F− and Ca2+ and SAR. The areas where the mine water samples have low concentrations of Na+, F−, and low SAR values, such as the shallow coal seams at the SGT, DLT, and WL mines, are favorable sites for the underground reservoir. The outcomes may benefit the reasonable site selection of underground reservoirs in similar coal mining areas with water shortage.

Groundwater is an important source of drinking water, particularly in arid regions. In this study, a total of 66 groundwater samples were collected from the phreatic aquifer in the Shizuishan area, a traditional irrigation region of Ningxia. The results showed that the TDS values were above the drinking water standards for nearly 50% of the groundwater samples. The ions followed the order of Na+ > Ca2+ > Mg2+ > K+ and SO42− > Cl− > HCO3− in the groundwater. There were four dominant factors in controlling groundwater chemistry based on principal component analysis: the salinity factor, alkalinity factor, carbonate factor, and pollution factor. The high concentration of NH4-N in groundwater was attributed to agricultural activities, but the high NO3-N levels were mainly due to sewage or wastewater. F and As were derived from geogenic sources. Based on the result of the WQI assessment, about 40% of the samples in the central part of the study region showed unacceptable water quality for drinking, which was mainly associated with high NH4-N, TDS, and As concentrations. The total non-carcinogenic risks of drinking the groundwater were 0.05–10.62 for adults and 0.09–20.65 for children, respectively. The order of pollutants in the groundwater in terms of their hazard to residents was: As > F− > NO3-N > NH4-N. The carcinogenic risk values of As through oral ingestion for children and adults were 0–7.37 × 10−4 and 0–1.89 × 10−4, respectively. Chronic exposure by oral ingestion presented as the main source of susceptibility to exposure to groundwater contaminants for children.

On the edge of sedimentary basins, karst aquifers can be fed by several water sources from both autogenic and allogenic recharge. In some cases, assessing water origins can be hard and cause some difficulties for water resource management. The main goal of this study is to show the implementation of the mobile sources mixing model approach. More precisely, this research develops how a monitoring method using a multi-proxy approach can be used to quantify waters sources contributions from several origins at the outlets of a karst system. The study site is the Ouysse karst system, located in western France. The site offers the opportunity to understand the mixing processes between allogenic and autogenic water recharges. The karst system covers a 650 km² watershed, and is fed by three different chemical facies: (i) Autogenic water from the direct infiltration on the karstified limestones with high HCO3− values (median: 436 mg.L−1); (ii) Water coming from sinking rivers fed by spring coming from igneous rocks with low mineralization but relatively higher K+ values (median: 4.2 mg.L−1); (iii) Highly mineralized water coming from deep evaporitic layers and feeding another sinking river with very high sulfate concentrations (median: 400 mg.L−1). Sliding window cross-correlation analyses and hydrochemical analyses during a flood event are performed to implement a mobile source mixing model approach. This approach shows significant differences with a simple fixed source mixing model and appears more reliable but requires more time and money to carry out. The results and conclusion of this study will be used for forecasting and managing operational actions for resource management.

Thermal waters from deep circulation systems are mixed with cold shallow system components during their ascent to drainage zones. In the current research, classic chemical geothermometers and geothermometric modeling using the GeoT app were employed to determine the temperatures of geothermal reservoirs in the Sudetic region. Moreover, models of primary deep components mixed with cold shallow circulation system components were used to determine their proportions, particularly water deposits. In the studied geothermal systems, the proportion of the cold component ranged from c. 46% to c. 75%. Classic cation thermometers (Na-K, Na-K-Ca) indicated a very wide temperature range and they proved rather unreliable. The reservoir temperatures estimated with silica thermometers ranged from 52 °C to 141 °C and they can be deemed more reliable. The temperatures obtained from modeling (54.5 ± 3–120 ± 4) were adopted as temperatures of waters pre-cooled conductively and then mixed with cold components. The temperatures of primary deep waters (74–225 °C) were adopted as geothermal system temperatures.

The Mangkang geothermal field, distributed in the Mediterranean–Himalayas geothermal belt, hosts abundant hot springs whose geneses remain unclear. To determine the hydrochemical characteristics, reservoir temperature, circulation and recharge depths, and water–rock interactions of the geothermal water in the geothermal field, this study analyzed hydrochemical compositions and isotopes (2H, 3H, and 18O), conducted a PHREEQC simulation, and established a conceptual model to illustrate the genesis of geothermal resources in the Mangkang field. Based on the study of hot springs in Meipu, Qvzika, and Zulongpu villages and Rumei town, the following results are reported: The orifice temperatures of these hot springs vary between 18 °C and 67.5 °C. The hydrochemical composition analysis results indicate that the geothermal water in the hot springs is of hydrochemical type HCO3-Ca·Mg. Moreover, the geothermal water has high HBO2 and Na+ concentrations, suggesting protracted water runoff and strong water–rock interactions during its evolution. According to the mineral–water solubility equilibrium and silica geothermometers, it is estimated that the reservoir temperature of the Zulongpu hot spring is 47 °C and other hot springs have much higher reservoir temperatures of 116–130 °C. As indicated by geothermal gradients, annual temperatures, and reservoir temperatures, the geothermal water in Meipu and Qvzika villages has the greatest circulation depth, up to 3600–4300 m, followed by that in Rumei town (3700–4000 m) and Zulongpu village (~1500 m). The 2H-18O isotopic analysis of the geothermal surface water revealed that the geothermal water originates from meteoric water. The recharge elevation was inferred to be ~4700–4900 m. Moreover, the low 3H values (2 during migration and storage.

In Tibet, water resource has been less studied due to remote and harsh conditions. In this study, hydrochemistry and stable isotopes (δ2H, δ18O and 87Sr/86Sr) were employed to investigate the major factors affecting the hydrochemical process of groundwater and surface water in the lower reaches of the Yarlung-Zangbo River, southern Tibet. Groundwater and surface water were weakly alkaline and very soft to moderately hard water. The hydrochemical type of surface water is mainly Ca-HCO3 (mainstream) and Ca-SO4-HCO3 (tributary), while the hydrochemical type of groundwater was mainly Ca-SO4-HCO3. Multivariate statistical analysis and Gibbs analysis proposed hydrochemical components were dominated by water-rock interaction. Ion ratio, saturation index, and Sr isotope revealed calcite dissolution and silicate weathering with local sulfide oxidation were involved in water–rock interaction. D-O isotopes indicated the recharge source was mainly derived from atmosphere precipitation. The entropy-weighted water quality index indicated surface water and groundwater reach the standard of drinking purpose in the lower reaches of the Yarlung-Zangbo River. The hydrochemical type varied regularly along the Yarlung-Zangbo River. The dissolution of carbonate rocks and local silicate weather and evaporate dissolution are the primary hydrochemical process along the Yarlung-Zangbo River. This study would provide a preliminary insight for hydrochemical process in the Yarlung-Zangbo River.

Hydrochemical research and identification of nitrate contamination are of great significant for the endorheic basin, and the Northern Huangqihai Basin (a typical endorheic basin) was comprehensively researched. The results showed that the main hydrochemical facies were HCO3–Mg·Ca and HCO3–Ca·Mg. Spatial variation coefficients of most indices were greater than 60%, which was probably caused by human activities. The hydrochemical evolution was mainly affected by rock weathering and also by cation exchange. The D–18O relationship of groundwater was δD = 5.93δ18O − 19.18, and the d–excess range was −1.60–+6.01‰, indicating that groundwater was mainly derived from precipitation and that contaminants were very likely to enter groundwater along with precipitation infiltration. The NO3(N) contents in groundwater exceeded the standard. Hydrochemical analyses indicated that precipitation, industrial activities and synthetic NO3 were unlikely to be the main sources of nitrate contamination in the study area. No obvious denitrification occurred in the transformation process of nitrate. The δ15N(NO3) values ranged from +0.29‰ to +14.39‰, and the δ18O(NO3) values ranged from −6.47‰ to +1.24‰. Based on the δ15N(NO3) – δ18O(NO3) dual isotope technique and hydrochemical methods, manure, sewage and NH4 fertilizers were identified to be the main sources of nitrate contamination. This study highlights the effectiveness of the integration of hydrochemical and isotopic data for nitrate source identification, and is significant for fully understanding groundwater hydrochemistry in endorheic basins and scientifically managing and protecting groundwater.

The Xiong’an New Area is one of the areas with the richest geothermal resources in the east-central part of China. However, the genesis of the geothermal water in Jixianian carbonate reservoirs in this area is still unclear. This study conducted systematical geochemical and isotopic analyses of the geothermal water in the Jixianian carbonate reservoirs in the Rongcheng geothermal field and summed up the genetic mechanisms of geothermal fluids in deep geothermal reservoirs. The results are as follows: the geothermal water in the study area has a hydrochemical type of Cl·HCO3-Na and originates from meteoric water in the Taihang Mountains. The age of the geothermal water increases from 22 ka in the west to 45 ka in the east, and its transport rate is approximately 1.02 m/a. The Sr concentration and 87Sr/86Sr ratio of the geothermal fluids increase along their runoff direction and are related to the dissolution and filtration of minerals such as dolomite and gypsum and the decay of 87Rb in the Earth’s crust. The geothermal water is involved in deep circulation and occurs in a closed system. These results are consistent with those obtained using the PHREEQC inverse model. The reverse hydrogeochemical simulation results exhibited the precipitation of gypsum and halite, the dissolution of anorthite and quartz, and desulfurization. The geothermal reservoir temperatures were estimated to be 92–113 °C using a SiO2 geothermometer, and the thermal groundwater may have undergone deep circulation, with a prolonged retention time. Moreover, the groundwater occurs in a closed environment, strong water-rock interactions occur between the groundwater and related minerals, and the groundwater absorbs the heat from the deep heat source, thus forming geothermal water.

Changbai Mountain is the source region of the Songhua, Tumen, and Yalu Rivers. It is a famous concentrated distribution area of high-quality mineral water in China, which has a great economic value. Antu County is one of the main distribution areas of basalt and mineral water in Changbai Mountain. The distribution of mineral water has a strong hydraulic relationship with surface water, which constitutes abundant recharge reserves. It is important to study the hydrochemical characteristics and the relationship between surface water and mineral water to provide a theoretical basis for further discussion on the formation process and rational utilization of mineral water resources in Changbai Mountain. A total of 18 water samples in the period of abundant and dry water were collected, including rainwater, mineral water, and surface water. Geostatistics was utilized to analyze the hydrochemical characteristics. Hydrochemical component tracing and stable environmental isotope technology with end-number calculation reveals the transformation relationship between mineral and surface water. The results indicate that: (1) The hydrochemical type is mainly HCO3-Ca-Na and HCO3-Ca-Mg type. The average content of H2SiO3 is 50.78 mg/L, which reach the standard of high quality metasilicate mineral water. (2) The mineral water formation process is dominated by the water-rock interaction in silicate mineral weathering. Metasilicate came from hydrolytic reaction of silicate and aluminosilicate under acidic conditions. (3) Atmospheric precipitation is the main recharge source, and the recharge area locates in the south nature reserve of the study area. The average retention time of mineral water is 35.5 years, and the recharge ratio of mineral water to surface water is up to 83.7%. This study will provide a theory guide for the protection and rational utilization of groundwater resources in study area and a reference for mineral spring formation study in basalt mountain area.

A survey of the hydrochemistry and isotopes of the Quaternary aquifer on the southern coast of Laizhou Bay provides new insights into the hydrodynamic and geochemical relationships between freshwater, seawater, and brine at different depths in coastal sediments. This study used a combination of groundwater level analysis, hydrochemistry, and isotopic methods to study the chemical characteristics of groundwater and the origin of groundwater recharge and salinity. Because the sedimentary structure of the area and the formation background of saltwater were important factors controlling the distribution of groundwater, we analyzed the distribution of groundwater in Holocene and Late Pleistocene sediments. The variation of groundwater levels in the Holocene and Late Pleistocene sediments in the saline–freshwater transition zone over time showed that the Holocene and Late Pleistocene groundwater flow directions differed in the saltwater–freshwater transition zone. From south to north in the study area, the hydrochemical types of groundwater in the Holocene and Late Pleistocene sediments were as follows: HCO3-Ca (freshwater), SO4-Mg and HCO3-Ca (brackish water), Cl-Na·Mg (saltwater), and Cl-Na (brine). The results of the hydrochemical and isotopic studies indicated that the saltwater in the Holocene and Late Pleistocene sediments and the brine in the Late Pleistocene sediments were the result of evaporation. The salinity of freshwater in the Holocene sediments was produced by rock weathering, while the salinity of freshwater in the Late Pleistocene sediments was not only derived from rock weathering, but was also affected by evaporation and precipitation. The salinity of brackish water in the Holocene and Late Pleistocene sediments was derived from evaporation and precipitation. Ultimately, the origin of groundwater recharge in the Holocene and Late Pleistocene sediments was atmospheric precipitation.

This study aims to evaluate the hydro-chemical characteristics of Ouargla, Algeria basin groundwaters harvested from the Mio Pliocene aquifer. The study covered 70 samples; the physical parameters, potential of hydrogen (pH), and electrical conductivity EC μS.cm−1 were determined in situ, using a multiparameter; the laboratory analysis included dry residuals DR (mg/L), calcium Ca2+ (mg/L), magnesium Mg2+ (mg/L), sodium Na+ (mg/L), potassium K+ (mg/L), bicarbonates HCO3− (mg/L), sulfates SO42− (mg/L), and chloride Cl− (mg/L). The piper diagram shows that the Ouargla basin ground waters divided into two facies, sodic chlorinated in 93% and sodic sulphated in 7% of samples. The United States Salinity Laboratory Staff (USSL) diagram was used to detect the suitability of groundwater in irrigation where the results show that the groundwater was classed into two classes, poor water (C4 S4) and bad water (C4 S4). Furthermore, indices such as the Kelly index (KI), sodium adsorption ratio (SAR), sodium solubility percentage (Na%), and magnesium hazards (MH) confirm the negative effect of groundwater on soil permeability in 96%, 80%, 89%, and 53% of samples. The permeability index (PI) shows that the analyzed samples were considered as doubtful (71%) and safe (29%), otherwise there is no risk related to residual sodium carbonate (RSC). The geo-spatial distribution of deferent indices shows that all the study area has poor groundwater for irrigation, except the south-west part, where the groundwaters of this sub-area do not form a problem related to RSC.

The Middle East is located in a semiarid and arid region and is faced with an intense water shortage crisis. Therefore, studying the hydrochemical characteristics of precipitation as a main part of the water cycle has great importance in this region. The hydrochemical analyses showed that the quality of precipitation was mainly affected by dust particles originating from terrestrial environments, while marine and anthropogenic sources had a minor role. The statistical studies showed that the dissolution of evaporative and carbonate minerals mainly controlled the hydrochemistry of precipitation. Precipitation had an acidic nature in some stations and a nonacidic nature in others. Ca2+ was the major acid-neutralizing cation in the Middle East precipitation. Various machine learning methods were also used to simulate the TDS values in precipitation. The accuracy of the developed models was validated, showing that the model developed by the Gboost method was more accurate than those developed by other machine learning techniques due to its higher R2 values. To conclude, the hydrochemistry of precipitation showed significant variations across the Middle East. The dissolution of particles with terrestrial origins dominantly controlled the hydrochemistry of precipitation, while marine and anthropogenic sources had minor roles.