Search Results (173)

Seawater intrusion (SWI) increasingly threatens coastal aquifers that serve growing communities, emphasizing the need for generalizable, process-based diagnostics. We evaluate SWI in a multilayer coastal aquifer system in southern Alabama, USA, by integrating three groundwater sampling campaigns during spring–early summer 2025 (March, April, and June), hydrogeochemical–isotopic analyses, and variable-density SEAWAT modeling. This study couples HFE–Gibbs–isotope diagnostics with hydraulic-head-constrained SEAWAT modeling to characterize seawater intrusion extent and process state in a multilayer coastal setting. Groundwater major ions and δ¹⁸O/δ²H indicate dominantly meteoric, rock-weathering waters (Ca–HCO₃ inland) with localized Na–Cl near the coast; most samples plot in the rock dominance field, and stable isotope values cluster near the meteoric water line. A 3-D SEAWAT model (seven layers, 150 × 150 m cells), calibrated to available groundwater head observations using PEST, indicates that modeled intrusion is concentrated at depth in confined Miocene units, whereas shallow groundwater sampled from the unconfined zone remains largely fresh based on hydrogeochemical and isotopic evidence. Because chloride observations were used primarily for interpretation rather than direct transport calibration, the modeled deep salinity distribution is treated as a process-based estimate rather than a uniquely calibrated chloride field. To quantify exposure and process state, we introduce two indicators: a Depth-Weighted Intrusion Index (DWII) integrating the extent and intensity of the transition zone across layers, and an Ion-Exchange Departure Index (IEDI) capturing normalized Na–Cl departures from conservative mixing due to cation exchange. Predominantly negative IEDI values indicate reverse exchange with weaker intensity during spring freshening and only localized forward exchange episodes. Beyond the site-specific findings, the DWII and IEDI introduced in this study provide practical tools for detecting and quantifying subtle seawater intrusion in low-salinity coastal aquifers and may be applicable to other coastal aquifer systems with similar hydrogeological settings. Full article

Groundwater is a principal irrigation water source worldwide; however, its quality is increasingly diminished by rapid urbanization, improper agricultural practices, and accelerating industrial activities. Groundwater management is especially important in areas where soil salinization and erosion are more probable, such as arid and semi-arid zones. In view of this, the Armavir region of the Republic of Armenia was selected as the study area, being an intensively cultivated agricultural zone. The objective of this study was to assess and map the quality of groundwater for irrigation using advanced methods, taking into account both climatic conditions and anthropogenic influences. A total of 72 groundwater samples were collected during the irrigation season from 41 unconfined and 31 confined aquifer wells. Key hydrochemical parameters (pH, EC, TDS, Cl⁻, HCO₃⁻, CO₃²⁻, Na⁺, K⁺, Ca²⁺ and Mg²⁺), irrigation indices (SAR, Na%, MH, RSC and PI), and graphical methods (Gibbs, USSL and Wilcox diagrams) were applied to assess groundwater quality. An integrated assessment was performed using the Irrigation Water Quality Index (IWQI), and spatial distribution was evaluated through geostatistical analysis and GIS mapping. Although certain individual hydrochemical parameters indicated limitations for irrigation in localized areas, particularly within the unconfined aquifer, the integrated IWQI assessment revealed that groundwater predominantly falls within the good to excellent categories across the study area, with more favorable conditions observed in the confined aquifer. These findings constitute an essential prerequisite for counteracting soil salinization and promoting sustainable agricultural development. Full article

Overexploitation of groundwater resources poses a critical challenge in major agricultural regions worldwide, yet how confined and unconfined aquifers respond differentially to governance interventions remains poorly understood. This study presents a comparative assessment of hydrochemical evolution and nitrate contamination dynamics in the Weishan Irrigation District, Shandong Province, China, contrasting pre-governance conditions (2011) with post-governance status (2022–2023) following comprehensive overexploitation control. By integrating hydrochemical characterization with stable isotope tracers (δ¹⁸O, δD, δ¹⁵N-NO₃⁻, δ¹⁸O-NO₃⁻) and Bayesian mixing models (MixSIAR), we reveal fundamentally contrasting aquifer responses to regulation. The unconfined aquifer exhibited continued degradation under persistent agricultural influence, characterized by elevated sodium, nitrate, and bicarbonate concentrations. In sharp contrast, the confined aquifer demonstrated substantial recovery, with major ion concentrations declining markedly, hydrochemical facies restored toward a pristine state, and overall water quality improving significantly to achieve full compliance with the highest-quality standards by 2023. These divergent trajectories indicate that regulatory interventions effectively restored aquitard barrier integrity, thereby shielding the confined aquifer from surface contamination, whereas the unconfined aquifer remained vulnerable to agricultural pollution. Isotope-constrained Bayesian modeling identified soil organic nitrogen, chemical fertilizers, manure/sewage, and industrial wastewater as dominant nitrate sources, with isotopic evidence confirming that the unconfined aquifer receives mixed recharge from Yellow River water and precipitation under contemporary contamination, while the confined aquifer maintains independent, pollution-free recharge. These findings demonstrate that overexploitation control can effectively rehabilitate confined aquifer systems by reestablishing natural hydrogeological barriers, but unconfined aquifers require targeted agricultural pollution mitigation. The contrasting responses highlight the necessity of aquifer-specific management strategies in irrigation-dependent regions, advancing theoretical understanding of how regulatory measures differentially affect multi-layered groundwater systems and providing a scientific basis for precision groundwater governance. Full article

Global population growth and numerous anthropogenic activities are putting increasing pressure on island aquifers. This situation is exacerbated in popular tourist destinations where seasonal population fluctuations increase water consumption. Most island aquifers are threatened by overexploitation, contamination, and seawater intrusion (SWI), which threaten these resources’ sustainability. In this study, the vulnerability of the Bozcaada Island (Türkiye) to SWI during peak seasons (summer) was assessed using the GALDIT approach. The GALDIT index takes into account six key hydrogeological characteristics, including groundwater occurrence (G), which represents the type of aquifer (confined, unconfined, or semi-confined) and influences the interface between freshwater and saline water; aquifer hydraulic conductivity (A), where higher conductivity increases the risk of SWI and determines how easily water flows; groundwater level above mean sea level (L), which indicates hydraulic pressure against SWI; distance from the coast (D), which implies higher SWI risk when close to the coast; existing intrusion status (I), which takes into account current SWI detections based on the ratio of chloride ions to bicarbonate ions in a groundwater sample; and aquifer thickness (T). Bozcaada Island hosts a large number of tourists during the summer months, when agricultural production is at its peak, with a high demand for irrigation. This significantly increases the demand for groundwater and leads to saltwater intrusion. Based on the results of the GALDIT index, the island’s groundwater reserves are heavily used throughout the summer. The GALDIT index for the summer shows that this increased groundwater abstraction intensifies the SWI problem. In summer, the island is vulnerable with 6.11 km² of extremely high SWI, 7.88 km² of high SWI, 7.34 km² of moderate SWI, 7.40 km² of low SWI and 8.50 km² of very low SWI. This study emphasizes how urgently Bozcaada Island needs sustainable water management techniques. Full article

Numerical simulations quantify the transient impacts of implementing green infrastructure (GI) grass swales on unconfined aquifer storage and groundwater-surface water interactions around the Red Butte Creek (RBC) of Utah, USA. The Red Butte Creek Watershed (RBCW) transitions from undeveloped mountainous National Forest land to downstream urbanized areas within Salt Lake Valley (SLV). This reconnaissance-level study demonstrates that increasing stormwater infiltration in urbanized areas during the rainy months (April-June) can, until at least the subsequent March, (a) enhance aquifer recharge and support sustainable groundwater yields; and (b) improve surface water availability. Simulations predict hydrologic impacts of aquifer recharge resulting from hypothetical grass-swale implementation within a 704-acre area located around RBC. The employed model, HyperRBC, is an adaptation of a United States Geological Survey (USGS) transient numerical flow, MODFLOW, model implementation for SLV. Adaptations involved (a) uniformly refined horizontal discretization of seven aquifer layers within a sub-area encompassing parts of RBCW and an adjacent watershed; (b) updated input data; and (c) MODFLOW’s Streamflow-Routing (SFR) package to simulate RBC flow and aquifer-stream seepage. Model predictions indicated that by the end of next March: (a) about 3% of the GI-induced recharge would remain within the unconfined aquifer in the HyperRBC area; (b) 66.6% of the recharge would flow northward into the downgradient continuation of the unconfined aquifer; and (c) 30.3% would discharge to nearby stream and river. In summary, predicted hydrologic changes due to the short-term GI-induced recharge highlight increased groundwater availability within and outside the study area for at least the subsequent 12 months, including high-water-demand summer. These findings show the importance of GI in interim environmental management and in enhancing the effective use of water resources. Full article

Subsurface freshwater in oceanic islands is typically shaped like a thin lens due to limited land area and recharge, often the primary freshwater source for local communities and highly vulnerable to seawater intrusion (SWI). Freshwater injection (FI) is considered as a feasible strategy for mitigating SWI in coastal aquifers. However, its transient effectiveness for freshwater lens (FWL) development and SWI mitigation in island aquifers and how the design parameters like FI depth, intensity, duration and injectant concentration affect its performance remain poorly understood. To address this, this study employs a two-dimensional, variable-density island groundwater model to simulate the transient responses of FWL development and SWI mitigation to various FI patterns. Five indicators are developed for comprehensive evaluation, including (1) freshwater recovery efficiency (FRE), and the relative changes in (2) average water table elevation (WTE), (3) FWL depth, (4) FWL volume, and (5) total aquifer salt mass. Results reveal FI universally raises average WTE, expands FWL dimensions, and promotes aquifer desalinization. Injection intensity is the primary driver of WTE rises and salt mass reduction, with higher intensities consistently yielding greater WTE rises and salt mass reductions. Deeper injection within the mixing zone increases FWL depth, but reduces the net gain in FWL volume. Moreover, early-stage FI is highly efficient for expanding FWL volume, often yielding FRE values above 100%, but FRE converges toward zero over time as the system moves toward a new hydrodynamic equilibrium, returning diminishing marginal benefits for long-term FI. Full article

Subsurface freshwater in oceanic islands is typically shaped like a thin lens due to limited land area and recharge, often the primary freshwater source for local communities and highly vulnerable to seawater intrusion (SWI). Saltwater abstraction (SA) is considered as a feasible strategy for mitigating SWI. However, its transient effectiveness for freshwater lens (FWL) development and SWI mitigation in island aquifers, and how the design parameters like SA depth, intensity, and duration affect its performance, remain poorly understood. Therefore, this study employs a two-dimensional, variable-density island groundwater model to simulate the transient responses of FWL development and SWI mitigation to various SA patterns. Six indicators are developed for comprehensive evaluation, including: (1) freshwater recovery efficiency, and the relative changes in (2) average water table elevation (WTE), (3) WTE at the SA well, (4) FWL depth, (5) fresh groundwater volume, and (6) total aquifer salt mass. Simulation results highlight SA depth as the primary determinant of its effectiveness, characterized by critical thresholds that dictate whether SA imposes net positive or negative effects on FWL depth, volume, and aquifer desalinization, with SA intensity and duration serving as scaling factors that amplify the magnitude of these responses. Moreover, while SA can effectively expand FWL volume and shift it toward a more favorable hydrodynamic equilibrium, the diminishing marginal benefits over time cause the FRE to approach zero, indicating SA is a potent short-term restoration strategy rather than a long-term solution from a cost–benefit perspective. Full article

Groundwater-dependent communities such as De Aar require a better understanding of groundwater systems to ensure sustainable allocation. This study aims to trace recharge sources in unconfined and confined aquifers and identify processes controlling groundwater quality using hydrogeochemistry and environmental tracers. It argues that aquifer delineation and hydraulic parameters alone cannot fully identify recharge sources or geochemical processes; integrating them with hydrogeochemistry and environmental tracers provides stronger evidence to support groundwater allocation. To validate the argument, the study integrated hydrogeochemical analysis, stable isotopes, tritium, radon-222, and statistical methods supported by depth-specific groundwater sampling. The results, interpreted using Piper and Gibbs diagrams, PHREEQC modelling, and scatter plots, show that groundwater evolution is mainly controlled by rock–water interaction, ion exchange, evaporation, and mixing processes. Ca–HCO₃ water indicates recent recharge, while Na–Cl water reflects evaporation effects in both unconfined and confined aquifers, with halite dissolution contributing to Na and Cl enrichment. Isotope results indicate that unconfined aquifer water is isotopically enriched and linked to recent recharge, whereas confined aquifer and spring waters are depleted, suggesting recharge from higher elevations through fractured zones. Tritium dating reveals young (<30 years), intermediate (30–50 years), and old groundwater (60–109 years), while radon results indicate active groundwater flow path, particularly along fractures. These findings demonstrate that groundwater recharge is derived from both local meteoric sources and regional contributions, resulting in predominantly fresh groundwater; however, localized quality concerns should be considered for improved water allocation. Full article

Sea-level rise (SLR) and regional precipitation pattern change cause island subsurface freshwater, typically shaped like a thin lens, to be at higher risk of contamination from seawater intrusion (SWI). Installing a cutoff wall is considered a feasible strategy for protecting coastal fresh groundwater from SWI. However, the performance of the cutoff wall in managing freshwater lens (FWL) development and mitigating SWI into island aquifers under SLR and aquifer recharge (RCH) fluctuations remains inadequately quantified. This study investigates how water table elevation (WTE), FWL depth, thickness, and SWI extent, measured by aquifer salt mass and freshwater volume, in an island aquifer equipped with cutoff walls, respond to SLR and RCH fluctuations. It focuses on a two-dimensional, variable-density island groundwater simulation model based on hydrogeological conditions of San Salvador Island, Bahamas. The results demonstrate that RCH critically influences cutoff wall effectiveness for FWL development and SWI mitigation, with higher RCH amplifying gains in WTE, FWL metrics, freshwater storage, and aquifer salt removal, but this influence diminishes with wall depth increasing. SLR elevates WTE in a stable manner associated with its magnitude but negligibly affects the cutoff wall performance in FWL enhancement and SWI mitigation. Under simultaneous SLR and RCH fluctuations, SLR can offset the WTE reduction caused by reduced RCH, but the joint effects of SLR and RCH on FWL metrics, freshwater storage and aquifer salt removal align with their individual impacts. Moreover, cutoff walls are more efficient in low-RCH settings, yielding greater relative improvements in FWL development and SWI mitigation per unit wall depth increase. Full article

Unconfined coastal karst aquifers are highly susceptible to contamination from anthropogenic activities, particularly in regions lacking adequate wastewater treatment. Their open hydrological structure facilitates the input and dispersion of contaminants from both point and non-point sources. Furthermore, groundwater exerts a significant influence on coastal water quality through submarine discharge that could impact vulnerable ecosystems like seagrasses, mangroves, and coral reefs. Seasonal hydrological variability—especially between dry and rainy periods—affects contaminant transport, with increased groundwater flux potentially enhancing spatial dispersion. Additionally, the balance between the contributions from the coastal karst aquifer and the hydrodynamics of the coastal zone determines the extent and degree of salinization occurring at the interface between these two systems, which in turn influences aquifer water quality. This study presents a five-year dataset of metal and nutrient concentrations measured during dry and rainy seasons in surface waters (0.5 m depth) from 24 cenotes within the Ring of Cenotes (RC), Yucatán Peninsula, Mexico. The RC functions as a preferential groundwater flow path from inland to the coast via underwater conduits and submarine groundwater discharge (SGD), transporting contaminants present in groundwater into highly vulnerable coastal ecosystems. While most parameters remained below regulatory thresholds, concentrations of total Al, Cr, Pb, and N-NH₃ exceeded limits established by NOM-127-SSA1-2021 at several sites measured within the RC. Spatial heterogeneity was observed across seasons and years, driven by groundwater flux dynamics, land use, and individual sinkhole characteristics. Notably, N-NH₃ concentrations were higher during the dry season, particularly near agricultural and peri-urban zones. These findings underscore the need for mandatory wastewater treatment and integrated coastal karstic aquifer management to protect the region’s sole freshwater resource and the vulnerable ecosystems in the coastal area. Full article

Snowmelt recharge critically affects water table fluctuations in cold-region unconfined aquifers, where it serves as a primary source of groundwater. This study investigates the temporal and spatial variations in water table responses to snowmelt events in the Oakes Aquifer, North Dakota. Climatic data, including winter snowfall and temperature, were collected from the North Dakota Agricultural Weather Network (NDAWN), as well as the National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) stations. Observation well data (1991–2023) were analyzed, and Inverse Distance Weighting (IDW) interpolation in ArcGIS Pro 3.6 was used to generate continuous spatial maps of groundwater level rises during spring. Results indicate that snowmelt significantly drives water table fluctuations, with higher snowfall associated with larger rises. Spatial variability in responses reflects differences in soil permeability, and land cover, with high-permeability soils showing more pronounced increases. Temperature strongly influenced the magnitude of snowmelt-induced groundwater rise, with warmer winters generally associated with greater recharge, while colder periods limited infiltration, likely due to frozen soil effects. These findings underscore the role of snowmelt as a key recharge source in cold-region unconfined aquifers, with variations controlled by local hydrogeological and climatic conditions. Understanding these dynamics is critical for groundwater management, particularly under changing climate scenarios. Future studies should focus on long-term monitoring, climate modeling, and cross-regional comparisons to improve predictions of snowmelt-driven recharge. Full article

In recent decades, increasing anthropogenic pressure and climate change have made the protection and sustainable management of groundwater resources essential. In this context, the identification of aquifer recharge zones, especially those characterized by rapid groundwater flow and high vulnerability to surface pollution sources, becomes a priority for the protection of underground resources. In the Po Plain (northern Italy), based on the lithological, geometric, hydraulic, and hydrodynamic characteristics of the aquifers, the recharge areas are mainly located in the alluvial fans of the Alpine and Apennine foothills. Due to the high hydraulic conductivity of the aquifer, the shallow depth of the water table and the agricultural activities, groundwater resources are vulnerable to nitrate (NO₃⁻) contamination. Given this background, the present study introduces a novel methodological approach based on the geochemical signature of groundwater, indicated by the presence of bicarbonate (HCO₃⁻) and NO₃⁻ ions, aimed at identifying aquifer recharge areas. Specifically, by analyzing time series of NO₃⁻ and HCO₃⁻ concentrations for the period 2012–2023, and applying criteria of an HCO₃⁻/NO₃⁻ ratio < 10 and NO₃⁻ > 30 mg/L, it was possible to identify areas where aquifer recharge processes are clearly evident. These recharge processes are rapid, as confirmed by the hydraulic gradient, the high hydraulic conductivity of the aquifers, and further supported by the isotopic composition of groundwater, especially tritium concentrations. Furthermore, due to the hydrogeological characteristics of the surveyed region, which resemble those of alluvial basins in close proximity to mountain ranges, the methodology and findings of this study can be used as an unconventional and expedited method for similar research conducted globally, offering hope for the future of groundwater research. Full article

Arid regions in Central Asia face persistent and increasing water scarcity, with groundwater serving as the primary source for drinking water, irrigation, and industry. The effective exploration and management of groundwater resources are critical, but are constrained by limited monitoring infrastructure and complex hydrogeological settings. This study investigates the Akbakay aquifer, a representative area within Central Asia with challenging hydrogeological conditions, to delineate potential zones for fresh groundwater exploration. A multi-criteria decision analysis was conducted by integrating the Analytical Hierarchy Process (AHP) with Geographic Information Systems (GIS), supported by remote sensing datasets. To address the subjectivity of weight assignment, the AHP results were further validated using Monte Carlo simulations and fuzzy logic aggregation (Fuzzy Gamma). The integrated approach revealed stable high-suitability groundwater zones that consistently stand out across deterministic, probabilistic, and fuzzy assessments, thereby improving the reliability of the groundwater potential mapping. The findings demonstrate the applicability of combined AHP–GIS methods enhanced with uncertainty analysis for sustainable groundwater resource management in data-scarce arid regions of Central Asia. Full article

Southern Kazakhstan, particularly the Zhambyl Region, is facing increasing groundwater stress due to climate change, degradation of irrigation infrastructure, and unsustainable water use. Despite substantial renewable groundwater reserves (8.33 km³/year), irrigation still relies on ephemeral surface flow. This study delineates priority zones for Managed Aquifer Recharge (MAR) using a GIS-based Multi-Criteria Decision Analysis framework integrated with the Analytic Hierarchy Process (AHP). Nine hydrogeological criteria were incorporated: shallow aquifer depth, groundwater salinity, precipitation, terrain slope, soil texture, land use/land cover, Normalized Difference Vegetation Index (NDVI), drainage density, and lineament density. Each parameter was normalized to a five-class suitability scale and weighted through expert-informed pairwise comparisons. The MAR suitability map identifies about 19% of the region (27,060 km²) as highly favorable for implementation. Field investigations at eleven groundwater sites in 2024 corroborate model results, providing aquifer depth, quality, and infiltration data. The most suitable areas are concentrated on Quaternary alluvial–proluvial fans near the Kyrgyz Alatau foothills and the Talas-Assa interfluve. Three hydrostratigraphic settings were identified: unconfined alluvial aquifers, Neogene–Quaternary unconsolidated sediments, and fractured Carboniferous carbonates. Recommended MAR methods include infiltration galleries, check dams, and injection wells. The proposed approach, validated through consistency analysis (Consistency Ratio ≤ 0.1), demonstrates the applicability of integrated geospatial and field methods for site-specific MAR planning. Strategic MAR deployment could restore productivity to 37,500 ha of degraded irrigated lands and improve groundwater resilience. These findings provide a practical framework for policymakers and water management authorities to optimize groundwater use and enhance agricultural sustainability under changing climatic conditions. Full article

A managed aquifer recharge (MAR) project utilizing reclaimed water has been operated for over 10 years in northeastern Beijing, China, with the goal of restoring the long-dried Chaobai River and replenishing the region’s depleted groundwater resources. To ensure the safe implementation of the project, we quantitatively assessed the impact of river water recharge on the multi-layered groundwater system by investigating the hydrochemical compositions of the reclaimed water, river water, and groundwater. Results show that river water is characterized by higher concentrations of Na⁺, Cl⁻, and SO₄²⁻ than found in groundwater, and that river water recharge has altered the groundwater types in the 30 m-depth unconfined layer, changing them from Ca-Mg-HCO₃ and Ca-HCO₃ types to Na-Ca-HCO₃-Cl and Ca-Mg-Na-HCO₃ types. End-member mixing analyses of river water samples indicate that three end-members are needed to represent the seasonal and spatial variations in river water. A five-end-member mixing model is then developed to quantify fractions of river water (f_R) in different aquifer layers. The estimated f_R values vary from 18.4% to 100%, with an average of 67.6% in the 30 m-depth layer, while f_R values in the 80 m-depth confined layer are mainly below 30%, with an average of 13.3%, which corresponds well to the known site geology. Overall, combining hydrochemical analysis with the end-member mixing approach is useful for assessing the impact of river recharge on groundwater. This study also highlights the need for high-resolution characterization of subsurface heterogeneity in MAR sites. Full article