Groundwater Processes Research Articles

Integrating MODFLOW and LSTM models for enhanced groundwater management in the coastal plains of Lattakia Governorate

ABSTRACT Effective groundwater management is vital for ensuring the sustainability of water resources, particularly in regions with significant agricultural and residential demands. This study focuses on the coastal plain of Lattakia Governorate, a 140-km2 area southeast of Lattakia city, bounded by the Mediterranean Sea, the Al-Kabir Al-Shamali River, and the Al-Sanobar River. The objective was to evaluate the performance of the MODFLOW model, within the Groundwater Modeling System (GMS), for simulating groundwater levels and to assess the predictive capabilities of Long Short-Term Memory (LSTM) networks for forecasting temporal changes in groundwater levels. The methodology involved data collection from thirty observation wells, preprocessing for model calibration, and the integration of MODFLOW and LSTM outputs to create a hybrid framework. Findings indicate that MODFLOW effectively simulates physical groundwater processes, while LSTM captures nonlinear and temporal dynamics. The integration of these models reduced prediction errors by up to 20% compared to standalone approaches, enhancing prediction accuracy and reliability. This study provides a novel approach to groundwater management, offering actionable insights for sustainable agricultural practices, residential water security, and pollution mitigation. The proposed framework demonstrates scalability and adaptability to similar hydrological settings globally, contributing to the advancement of integrated groundwater management strategies.

Measurements of groundwater, hydrodynamics, and sand characteristics at a dissipative sea turtle nesting beach

Beach groundwater and nearshore hydrodynamic data were collected during a field experiment along two dissipative beach transects on Galveston Island, Texas, in the fall of 2023. The monitored beaches serve as nesting habitat for the critically endangered Kemp’s ridley sea turtle. Conditions ranged from calm to stormy, with two storms occurring during the experiment, inundating the entire beach up to the dune toe. Collected hydrodynamic data include readings from pressure loggers submerged in the foreshore and mounted in groundwater wells in the backshore, data from two wave buoys about 1.5 km offshore, and GoPro timestacks of the instantaneous waterline (wave runup). Other collected data include bathymetry and topography surveys, subsurface temperature and moisture content readings, and sediment characteristics. This comprehensive dataset can be used to (1) study relevant beach inundation and groundwater processes, including their effect on the local ecosystem (e.g., repeated flooding of sea turtle nests), (2) study the propagation of nearshore hydrodynamic processes into the beach matrix and groundwater table, and (3) validate existing beach groundwater models.

Hydrogeochemical and Stable Isotope Processes of Groundwater in Laayoune-Dakhla (Southern Sahara, Morocco)

Hydrogeochemical and Stable Isotope Processes of Groundwater in Laayoune-Dakhla (Southern Sahara, Morocco)

Understanding Hydrological Dynamics in Andean Basins: An Isotope‐Based Study in Arid North‐Central Chile

ABSTRACTMountain ranges cover approximately 24% of the Earth’s land mass. These environments have a special relevance in terms of global water supply. However, historically mountain groundwater processes have been generally overlooked or poorly understood, especially in the Andes cordillera. With this in mind, this work aimed to study hydrological processes in four Andean, semi‐arid headwater river basins. Along with monthly stable isotope data collection, we carried out a synoptic surface water sampling programme in each river on four specific dates for 3H analysis. The latter indicated water of similar age in the rivers of three sub‐basins (Derecho, Cochiguaz, Incaguaz), but much older in the fourth (Toro). We assessed different possible explanations for these differences such as effects of past mining activities (El Indio mine), physiographic factors and snow accumulation and glacier related factors, but none of these were satisfactory. Instead, our findings point to the activation of faults in response to seismic activity, which induces pumping of fluids (water) from deeper zones, facilitating exfiltration processes in the Toro River sub‐basin. This explains the presence of surface waters older than those associated with current meteoric processes. Such geological process should be assessed and eventually accounted for when studying mountain hydrogeological processes, especially in high fractured areas with direct or indirect evidence of geothermal activity.

Hydrogeochemical Characteristics and Genesis of Hot Springs in Da Qaidam Area, Northern Qaidam Margin of the Qaidam Basin

Hydrogeochemical research on fluids is an effective method to understand the formation mechanism, occurrence environment, and circulation process of groundwater. The groundwater sampling sites are located in the town of Dachaidan on the northeastern edge of the Tibetan Plateau, which was selected as the study object. Samples were collected from hot and cold springs and surface water in the area. This study is based on the analysis of water chemistry and isotopes, and aims (1) to discuss the chemical characteristics of groundwater in Da Qaidam, (2) to estimate the deep reservoir temperatures, recharge elevation and circulation depth of geothermal waters, and (3) to figure out the heat source beneath the geothermal area and its genetic mechanism. The result showed the following: The hydrochemical type of the hot spring is Cl·SO4-Na and Cl-Na, and the hydrochemical type of cold spring is SO4·HCO3-Na·Ca and Cl·HCO3·SO4-Ca·Na. The main source of groundwater recharge is snow and ice melt water. The recharge elevation ranges from 4666.8 m to 5755.9 m. The geothermal reservoir temperature is about 119.15–126.6 °C. Ice and snow melt water infiltrate into the high mountainous areas on the north side of Da Qaidam and circulate underground through the developed deep and large fractures. Part of the groundwater migrates upwards under the water conduction of the Da Qaidam fault fracture zone to form cold springs, while another part is heated by deep circulation and exposed to the surface in the form of medium to low temperature tectonic hot springs. The research results can provide a scientific basis for geothermal resource exploitation and utilization in Qinghai Province.

Integrated impacts of mariculture on nitrogen cycling processes in the coastal groundwater of Beihai, southern China

Groundwater nitrogen (N) contamination in coastal zones is becoming an increasingly serious global issue. Mariculture, as a major anthropogenic activity, has profound impacts on coastal groundwater and constitutes an important source of coastal N contamination. However, a comprehensive understanding of the impact of mariculture on N cycling (especially N removal) is still lacking. Taking the Daguansha mariculture region in southern China as the study area, we aimed to investigate the environmental impact of mariculture on coastal groundwater and identify N cycling processes influenced by mariculture using hydrogeochemistry, multiple isotopes, coupled with 16S rRNA gene sequencing, and the quantitative polymerase chain reaction (qPCR) experiments. The results showed that the combined effects of seawater intrusion and seepage from land-based mariculture ponds have led to localized groundwater salinization in the region. Meanwhile, mariculture promotes nitrification and anammox processes in groundwater. The dominance of ammonia-oxidizing and anammox bacteria in the upper aquifer is attributable to local salinization, N and organic carbon input, as well as anoxic to suboxic conditions induced by seepage from aquaculture ponds. In addition, the gene abundances of ammonia oxidation (dominated by AOA) and denitrification were positively correlated, indicating their cooperative interaction. This study provides deeper insight into N cycling in coastal groundwater systems affected by extensive mariculture.

Formation of an Active Giant Nonsulfide Zinc System, Jinding, China: Relationships Among Tectonics, Climate, and Supergene Metal Remobilization

Abstract The oxidized portion of the giant Jinding Zn-Pb deposit, Yunnan, China, accounts for about 40% of the original metal resource, indicating a nonsulfide zinc component of 80 to 90 million tonnes (Mt), making it among the largest nonsulfide zinc concentrations known. The presence of the Jinding deposit within a rugged topographic upland undergoing active weathering and erosion suggests that the nonsulfide zinc supergene system was active at the time of discovery. The ore-bearing strata cropped out at ~2800 m elevation, and strong oxidation effects are present to at least 200 m below the premining surface. The exhumation of the late Oligocene Jinding primary ores and exposure to groundwater modification may have been initiated by late Miocene uplift that coincides with the onset of the Southeast Asia monsoonal climate. The abundance of calcium carbonate in the Jinding host strata and primary ore results in the preserved nonsulfide zinc ores being dominated by smithsonite crusts of a variety of compositions, along with a diverse assemblage of supergene Zn-Pb and other minerals reflecting the primary ore composition. Complex microstratigraphic banding in smithsonite at scales of ≤20 µm is revealed by luminescent microscopy, likely recording groundwater-related annual precipitation events. Jinding smithsonites from the Beichang and Jaiyashan ore zones have δ18OV-SMOW values (in which V-SMOW = Vienna-standard mean ocean water) that vary between 18.6 and 21.5‰, which are unusually low compared with most supergene smithsonites. These values are consistent with the cold conditions of the Jinding area (11°C mean annual temperature) and are compatible with local cold springs and travertines. The δ13CV-PDB values (in which V-PDB = Vienna-Pee Dee Belemnite) of the Jinding smithsonites range between –10.1 and –3.6‰ and are distinct from calcites formed by local hot springs and from low-18O smithsonites from other nonsulfide zinc deposits. The light carbon isotope composition of Jinding smithsonites suggests a major contribution of organic carbon and only minor, if any, contributions from local Triassic marine limestone and atmospheric CO2. The 13C-depleted carbon likely was derived from soils with C3 plant-dominated organic matter, from oxidation of hydrocarbons in the primary ore, or from dissolution of isotopically light sandstone cements or ore calcites. Reaction path models show that the reaction of descending, cool, oxidizing, meteorically derived groundwater with calcite, CO2, and primary sulfide minerals can account for much of the observed supergene mineral assemblage. The Jinding nonsulfide zinc mineralization reflects the interrelationships among tectonic, climatic, and groundwater processes in high elevation and/or latitude settings, notably related to cold groundwater. Although the preservation of thick nonsulfide zinc concentrations was impeded by the dynamic regional tectonic and climatic conditions that resulted in high precipitation and erosion rates, the size of the primary ore zone and focused groundwater transport resulted in the development of a giant nonsulfide zinc mineralization system.

Groundwater geochemistry using modified integrated water quality index (IWQI) and health indices with special emphasis on nitrates and heavy metals in southern parts of Tirupati, South India.

Groundwater is particularly vulnerable to pollution in places with a high population density and extensive human usage of the land, especially in southern parts of Tirupati, India. To assess this, 60 bore-well samples were obtained and assessed for physical specifications, ion chemistry, and heavy metals during the pre- and post-monsoon seasons 2022. The current investigation employed a modified integrated water quality index (IWQI), conventional graphical and human health risk assessment (HHRA) of nitrates and heavy metals to know the groundwater chemistry and its detrimental health effects on humans. The major ions were analyzed using American public health association (APHA)standards, whereas heavy metals were analyzed using inductively coupled plasma optical emission spectrometry(ICP-OES). Additionally, pH Redox Equilibrium and C (PHREEQC),a geochemical model written in C programming language was employed to determine the saturation indices of mineral facies and ArcGIS 10.3.1 was used for spatial distribution patterns of IWQI. Then, the HHRA of nitrates and heavy metals was performed using United States environmental protection agency (USEPA)guidelines. The noteworthy outcomes include elevated levels of Ca2+, Mg2+, Cl-, NO3-, Cu,Fe, Mn, and Pb, demonstrating rock-water interaction, silicate weathering, Ca-Mg-HCO3 followed by mixed water facies, dissolution/precipitation, reverse exchange, and anthropogenic contamination are the major controlling processes in groundwater of southern Tirupati, India. The modified IWQI reveals that most groundwater samples (38%) fall under the bad quality class, with (47%) in the poor quality class and only (15%) classified as medium qualityclass in pre- and post-monsoon seasons. Elevated IWQI were observed in all directions except in the east, which is suitable for drinking. Moreover, the major hazard quotient (HQ) and hazard index (HI)for nitrates (NO3-) and heavy metals like copper(Cu), iron (Fe), manganese (Mn), lead (Pb) and zinc (Zn) are above the critical value of 1, revealing potential risk to humans, especially infants, followed by children and adults, entailing the instantaneous implementation of proper remedial measures and stringent policies to reduce the risk associated with groundwater pollution in the southern parts of Tirupati.

Identifying Groundwater Recharge Sources and Mechanisms using Hydrochemistry and Environmental Stable Isotopes in High Arsenic Holocene Aquifers of Bangladesh

Und erstanding the sources and mechanisms of aquifer recharge is critical for water resource management. So far, this is the first comprehensive study to explore the sources and mechanisms of groundwater recharge applying stable environmental isotopes and hydrogeochemical properties in Southwestern Bangladesh. Water samples from the different sources (groundwater, surface (pond), river and rain water) of high arsenic (As) Holocene aquifers were used to investigate the chemical tracers and environmental stable isotopes (δ18O and δ2H) to explore the hydrogeological features, groundwater recharge sources, mechanisms and processes. The analytical results showed high As concentration in water samples observed 590.7 μg/L. High As groundwater was identified by a low pH value, medium HCO3- and TDS with low concentration of NO3- and SO42-. However, depleted δ2H and δ18O signatures indicated that local vertical rainfall is the key source to recharge groundwater in study area. The recharge process from pond seepage and irrigation return flow also contribute in groundwater recharge. Isotopic signatures suggested the vertical connectivity amongst the aquifers and significant vertical recharge. The reduced heavier isotope reveals extra recharging from floods of mountains and high altitude. Due to the heterogeneous and anisotropic structure of the aquifer system the spatial variability of δ2H and δ18O shows limited lateral connectivity. The combined analyses of δ2H isotope and Cl- ion showed that evaporation is the primary cause for groundwater discharge. Based on the spatial and vertical recharge processes of groundwater, present study provides a crucial baseline knowledge for establishing a sustainable groundwater management strategy. The findings from this study can guide the development of targeted groundwater management strategies and improvement of understanding the groundwater recharge sources and processes.

Isotope characterisation of groundwater resources in uranium impacted Fazilka, Punjab

AbstractGroundwater is the most reliable source for freshwater supplies in India and abroad. Population rise has affected the groundwater resources both in terms of quality and quantity. Punjab, being an agrarian state, is highly dependent on groundwater resources for both irrigation and drinking purposes. Recent studies have indicated presence of uranium in groundwater especially in southwestern parts of Punjab. In this research, water samples were collected from Fazilka district of Punjab for evaluating the water quality focussing uranium and identifying source and recharge processes of groundwater. Uranium concentration was found in both shallow and deep groundwater samples. Inter-ionic correlations signify that alkalinity and electrical conductivity of the water samples control the uranium mobilization from the aquifer matrix. Isotopic systematics demonstrate that groundwater recharge is mainly through rainwater infiltration.

Modeling of Filtration and Heat and Mass Transfer Processes in Groundwater

Purpose. The method of mathematical modeling is an important tool for solving complex problems involving the analysis of groundwater dynamics and heat and mass transfer processes in them when studying their contamination from various anthropogenic sources in the event of accidental spills of chemically hazardous substances, etc. The main purpose of the article is to develop a set of mathematical models for calculating the process of filtration of non-pressure groundwater, mass transfer of impurities and the process of heat transfer in groundwater. Methodology. The two-dimensional Boussinesq equation of filtration was used to predict the dynamics of groundwater. The two-dimensional equation of convective-diffusive transport of impurities was used to model the processes of mass transfer in groundwater. The process of freezing of individual sections of the groundwater flow is modeled using the Laplace equation for the velocity potential (calculation of the flow velocity field in a time-varying geometry) and the two-dimensional equation of heat transfer in groundwater. Finite difference schemes were used to solve the modeling equations of groundwater dynamics and heat and mass transfer. Findings. A set of mathematical models has been developed to calculate the process of filtration of non-pressure groundwater and its chemical contamination. The experiment has confirmed the adequacy of the constructed numerical model of filtration of a non-pressure groundwater flow. An effective mathematical model was developed that allows determining the temperature fields in groundwater during the operation of a well used to freeze certain sections of the flow. The results of computer modeling indicate the effectiveness of the developed mathematical models. Originality. Effective mathematical models for predicting the level of chemical contamination of groundwater, its dynamics and thermal regime are proposed. The constructed mathematical models make it possible to determine the dynamics of changes in the temperature regime of groundwater during the operation of wells through which refrigerant is supplied to freeze individual areas. A computer program has been developed that allows for a comprehensive assessment of groundwater conditions. Practical value. A set of computer programs has been developed to conduct a computational experiment to study the processes of filtration, chemical contamination of groundwater and heat transfer processes in them. This set of programs can be used for the scientific substantiation of engineering solutions aimed at protecting groundwater.

Hydrochemical Characteristics, Controlling Factors and Groundwater Sources of Zaozigou Gold Mine

The Zaozigou gold deposit is recognized as one of the largest and most significant independent gold deposits in northwest China, representing a colossal orogenic gold-antimony deposit. It is imperative to delve into the hydrochemical characteristics and controlling factors within the mining area to unveil the groundwater circulation evolution process and enhance water resource management. In 2018, a comprehensive collection of 50 groups of groundwater samples was conducted, alongside 17 groups of surface water and underground mine water samples in 2023. Compositional descriptive analysis, correlation analysis, Piper three-plot, Gibbs map, ion ratio method, hydrogeochemical simulation and PCA methods were employed to reveal the chemical characteristics and evolution process of groundwater in the Zaozigou gold mine. Furthermore, employing water isotopes theory allowed for the identification of recharge sources and circulation conditions within the Zaozigou Gold Mine. The findings indicated a transition from HCO3-Na·Ca type polluted water in 2018 to primarily the SO4-Ca·Mg type and HCO3·SO4-Na·Ca·Mg type groundwater hydrochemistry types by 2023. The hydrochemical characteristics of the study area are closely related to the mining depth and time. The chemical characteristics are influenced by various factors such as rock weathering, mineral dissolution, cation exchange processes, atmospheric precipitation as well as human activities related to pollution from industrial mining activities.

Influence of submarine groundwater discharge on the nutrient dynamics of a fringing-reef lagoon

Study regionThis study investigates nutrient distribution and flux dynamics in a coral reef lagoon in Quintana Roo, Mexico, located on a permeable limestone coast of the Mesoamerican Barrier Reef System. Study FocusEmphasis is placed on submarine groundwater discharge (SGD) as a crucial contributor to nutrient pathways, including ammonium (NH4+), nitrate and nitrite (NOx-), hydrogen silicate (HSiO3-), hydrogen phosphate (HPO42-), and urea. Inputs vary with SGD magnitudes and sources and by proximity to active spring discharges. Groundwater multi-tracer analysis and multiple linear regression identify 226Ra as explaining NH4+ variability due to long-term groundwater processes, while 223Ra predicts NOx-, HSiO3-, and urea due to short-term inputs. No significant relationship was found between HPO42- and any radium isotope, indicating complex behavior in coastal karst aquifers. New hydrological insights for the regionThe findings highlight complex nutrient dynamics in coastal karst settings, with SGD-derived fluxes primarily consisting of dissolved inorganic nitrogen (DIN) and HSiO3-. Although lower in concentration, HPO42- and urea fluxes are significant compared to other karst environments. Radium isotopes distinguish between short-term and long-term, as well as new and recycled nutrient inputs. Groundwater inputs transport fresh nutrients to healthier reefs, whereas processed, recycled inputs were detected near degraded reefs. These insights are essential for understanding global nutrient cycles and coral health, particularly in the context of global change and anthropogenic disturbances affecting coral reef ecosystems.

Spatial distribution and hydrogeochemical processes of high iodine groundwater in the Hetao Basin, China

To understand the genesis and spatial distribution of high iodine groundwater in the Hetao Basin, 540 groundwater samples were analyzed for the chemistry and isotope. Total iodine concentrations in groundwater range from 1.32 to 2897 μg/L, with a mean value of 159.2 μg/L. The groundwater environment was mainly characterized by the weakly alkaline and reducing conditions, with the iodide as the main species of groundwater iodine. High iodine groundwater (I > 100 μg/L) was mainly distributed in shallow aquifers (< 30 m) of Hangjinhouqi near the Langshan Mountain and the discharge areas along the main drainage channels. The δ18O and δ2H values ranged from −12.09 ‰ to −3.99 ‰ and − 91.58 ‰ to −52.80 ‰, respectively, and the correlation between groundwater iodine and isotopes indicates the dominant role of evapotranspiration in the enrichment of iodine in the shallow groundwater with depth <30 m. It was further evidenced by the correlation between groundwater iodine and Cl/Br molar ratio, and significant contributions of climate factors identified from the random forest and XGBoost. Moreover, irrigation practices contribute to high iodine levels, with surface water used for irrigation containing up to 537.8 μg/L of iodine, which can be introduced into shallow aquifer directly. The iodine in irrigation water can be retained in the soil or shallow sediment, and later leach into groundwater under favorable conditions.

Hydro Geochemical Characteristics and Mineralization Process of Groundwater in the Phosphatic Basin of Gafsa, Southwestern Tunisia

The present study examines the water quality in the Quaternary Mio-Plio-Quaternary aquifer of the mining basin of Gafsa using a hydrochemical approach and multivariate statistical methods, to assess groundwater mineralization processes. Results from the analysis of groundwater quality collected during the winter (January 2020) and summer (June 2021) seasons reveal a pronounced stability in geochemical parameters, emphasizing a noteworthy consistency in water composition between the two seasons, with the dominance of the Na-Ca-Mg-SO4-Cl facies, in addition to the fact that all year round these concentrations are beyond their respective WHO limits. Despite the intensive extractive and transformation phosphate industry, the prolonged interaction of water with geological formations is the primary factor controlling their high mineralization. This results from the dissolution of carbonates (calcite, dolomite), gypsum, and halite. The results of the PCA represent two correlation classes. Class 1 comprises major elements sulfate, chloride, sodium, magnesium, and calcium strongly correlated with electrical conductivity (EC) and total dissolved solids (TDS). This correlation is indicative of the water mineralization process. Class 2 includes major elements nitrate and potassium weakly correlated with (TDS) and (EC) As regards heavy metals, their concentrations fall consistently below their respective potability standards established by the WHO across all water sampling points. Meanwhile, fluoride (F-) concentrations exhibited values ranging from (1.6 mg·L−1 to 2.9 mg·L−1) in the winter of January 2020 and (1 to 2.9 mg·L−1) in the summer of June 2021, surpassing its WHO limit (1.5 mg·L−1) in almost all water samples. These findings allow us to conclude that the high mineralization of these waters is acquired due to the dissolution of carbonates (calcite, dolomite), gypsum, and halite due to their prolonged interaction with the geological formations. The deterioration of groundwater quality in the Gafsa mining basin associated with phosphate extraction and processing activities appears to be primarily due to the intensive exploitation of deep-water resources.

Hydrogeochemical characteristics and agricultural suitability of shallow groundwater quality in a concentrated coalfield area of Huaibei Plain, China.

Groundwater is one of the chief water sources for agricultural activities in an aggregation of coal mines surrounded by agricultural areas in the Huaibei Plain. However, there have been few reports on whether mining-affected groundwater can be adopted for agricultural irrigation. We attempted to address this question through collecting 71 shallow groundwater samples from 12 coal mining locations. The Piper trilinear chart, the Gibbs diagram, the proportional coefficient of major ions, and principal component analysis were examined to characterize the source, origin, and formation process of groundwater chemical composition. The suitability for agricultural irrigation was evaluated by a final zonation map that establishes a comprehensive weighting model based on analytic hierarchy process and criteria importance though the intercriteria correlation (AHP-CRITIC). The results revealed that the groundwater was classified as marginally alkaline water with a predominant cation of HCO3- and anion of Na+. Total hardness, total dissolved solids, sulfate (SO42-), sodium (Na+), and fluoride (F-) were the primary ions that exceeded the standard. The results also indicated that the dominant hydrochemical facies were Ca-HCO3 and Na-Cl. The dissolution of carbonate, silicate, sulfate minerals, along with cation exchange, were the main natural drivers controlling the hydrogeochemical process of groundwater. The zonation map suggested that 43.17%, 18.85%, and 37.98% of the study area were high, mediate, and low suitability zones, respectively. These results from this study can support policymakers for better managing groundwater associated with a concentration of underground coal mines.

Factors influencing residual air saturation during consecutive imbibition processes in an air-water two-phase fine sandy medium – A laboratory-scale experimental study

The residual air saturation plays a crucial role in modeling hydrological processes of groundwater and the migration and distribution of contaminants in subsurface environments. However, the influence of factors such as media properties, displacement history, and hydrodynamic conditions on the residual air saturation is not consistent across different displacement scenarios. We conducted consecutive drainage-imbibition cycles in sand-packed columns under hydraulic conditions resembling natural subsurface environments, to investigate the impact of wetting flow rate, initial fluid state, and number of imbibition rounds (NIR) on residual air saturation. The results indicate that residual air saturation changes throughout the imbibition process, with variations separated into three distinct stages, namely, unstable residual air saturation (Sgr-u), momentary residual air saturation (Sgr-m), and stable residual air saturation (Sgr). The results also suggest that the transition from Sgr-u to Sgr is driven by changes in hydraulic pressure and gradient; the calculated values followed the following trend: Sgr > Sgr-u > Sgr-m. An increase in capillary number, which ranged from 1.46 × 10−7 to 3.07 × 10−6, increased Sgr-u and Sgr-m in some columns. The increase in Sgr ranged from 0.034 to 0.117 across all the experimental columns; this consistent increase can be explained by water film expansion at the primary wetting front along with a strengthening of the hydraulic gradient during water injection. Both the pre-covered water film on the sand grain surface and a pore-to-throat aspect ratio of up to 4.42 were identified as important factors for the increased residual air saturation observed during the imbibition process. Initial air saturation (Sai) positively influenced all three types of residual air saturation, while initial capillary pressure (Pci) exhibited a more pronounced inhibitory effect on residual air saturation, as it can partly characterized the initial connectivity of the air phase generated under different drying flow rates. Under identical wetting flow rate conditions, Sgr was higher during the second imbibition than during the first imbibition due to variations in initial fluid state, involving both fluid distribution and the concentration of dissolved air in the pore water. In contrast, NIR did not have an obvious effect on the three types of residual air saturation. This work aims to provide empirical evidences and offer further insights into the capture of non-wetting phases in groundwater environments, as well as to put forward some potential suggestion for future investigations on the retention and migration of contaminants that involves multiphase interface interactions in subsurface environments.

Hydrogeochemical Characteristics and Formation Processes of Ordovician Limestone Groundwater in Zhuozishan Coalfield, Northwest China

A comprehensive understanding of the characteristics and formation mechanisms of groundwater in mining areas is essential for the effective prevention of coal mine water and the rational management of groundwater resources. The objective of this study was to examine the hydrogeochemical characteristics and evolution of Ordovician groundwater in the Zhuozishan coal mine, located in the northwest region of China. A total of 34 groundwater samples were collected for hydrogeochemical analyses and the investigation of their evolution processes, with the aid of a piper trilinear diagram, a Gibbs diagram, and an ion ratio diagram. The results indicate that the concentration of sodium (Na+), potassium (K+), bicarbonate (HCO3−), chloride (Cl−), sulphate (SO42−), total dissolved solids (TDS), and pH increases from the recharge area to the discharge area, whereas the concentration of calcium (Ca2+) and magnesium (Mg2+) decreases. The hydrogeochemical characteristics of the runoff from Zhuozishan to Gongdeer coalfield and further southward display a notable north–south directional change. The groundwater process is primarily controlled by rock weathering action and cation exchange, with Na+ and K+ deriving primarily from cation exchange and only to a minor extent from halite dissolution. In conclusion, the northern part of the coalfield is characterised by a geological structure that creates a retention area with groundwater, resulting in an unordered runoff process with a complex formation mechanism. The middle region is devoid of geological constraints that would alter the flow direction, thus simplifying the process of groundwater formation. In contrast, the southern area experiences an increase in strata depth and fault blocking, which creates a retention zone, thereby rendering the groundwater formation process more complex. This research contributes to the effective management of groundwater resources in this coalfield and other mining sites.

Hydrochemical Evolution Process and Mechanism of Groundwater in the Hutuo River Alluvial Fan, North China

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.

Deciphering chemical and physical processes that give rise to natronization in a shallow aquifer in an arid zone

Groundwater provides a reliable and stable alternative to surface water resources in arid and semiarid regions to meet human and environmental needs. However, excessive exploitation in the last decades has led to significant salinization of groundwater and soils in many parts of the world. In the highlands of central-north Mexico, a number of agriculturally used aquifers show increasing salinization effects. Tierra Nueva is a case where salt precipitations in recent years have made land mostly unsuitable for agriculture. It is assumed that the intensive irrigation under dry climatic conditions, together with the presence of argillaceous horizons at shallow depth and the alteration of Na-rich volcanic rocks, determine the occurrence of specific salinization processes producing evaporite minerals in excess. This investigation provides physical and chemical evidence of groundwater processes explaining the accumulation of solutes in groundwater and soils. It shows that the principal evolutionary processes in the studied aquifer were water-rock interactions and evaporation, while ionic exchange processes dominated the water circulating through the clay-sandy materials of the valley. Geochemical models show that recharging water dissolved CO2 from the unsaturated zone, and reacted with silicates (i.e. hydrolysis of albite, K-feldspar, and biotite), underwent cation exchange, and precipitated kaolinite. In the discharge area, the mineral natron was dissolved, while thermonatrite, natrolite (Na-natrolite), nontronite (Ca-nontronite, K-nontronite, Mg-nontronite, Na-nontronite) were formed, among other reactions. This salinization process eventually leads to soils which are unsuitable for agricultural activities. The study of this phenomenon represents an important contribution to the understanding of the implications of the expansion of arid and semiarid lands.