Search Results (414)

Surface water–groundwater interactions play a critical role in regulating hydrological fluxes and sustaining water availability, yet they remain poorly understood in hydrogeologically complex terrains. This study employed an integrated modeling approach combining SWAT+ and MODFLOW to quantify water balance components, groundwater flow dynamics, and river–aquifer exchanges in the Chemoga watershed, a representative headwater system of the Upper Blue Nile Basin characterized by strong environmental and geological contrasts. Model results revealed substantial spatial heterogeneity in hydrological partitioning, with annual groundwater recharge ranging from 105 to 711 mm (mean = 296 mm; 24% of annual rainfall). Simulated groundwater flow exhibited a pronounced topographic control, with hydraulic heads declining from highland recharge zones toward deeply incised lowland gorges. River–aquifer interactions showed marked spatial variability, with the Chemoga river predominantly acting as a gaining stream in the highland and nick-point gorge sections (up to 2867 m³ d⁻¹), while transitioning to a losing stream in the midland floodplains and lowland gorge areas, with leakage reaching up to 75.0 m³ d⁻¹. These findings highlight the value of integrated, process-based modeling for resolving complex hydrological interactions, advancing understanding of groundwater flow regimes and supporting sustainable groundwater management in the Ethiopian highlands and other similar regions worldwide. Full article

Accurate estimation of actual evapotranspiration (ETa) is essential for understanding hydrological processes and managing water resources, especially in regions characterized by intensive agriculture and complex groundwater–surface interactions. This study intercompares three independent satellite-based ETa estimation approaches applied over Northeast Italy. The first two methods correspond to the classical MODIS algorithm (MOD16), which is based on a simplified Penman–Monteith approach, and to the more recent Sen-ET modelling framework, which relies on a surface energy balance principle. The outputs of these methods are compared to those produced by a water balance algorithm, NDVI-Cws, which predicts ETa through the combination of conventional ancillary data and MODIS NDVI imagery. The results obtained show that, while the MODIS algorithm yields ETa estimates which are generally lower than those of Sen-ET and NDVI-Cws, the latter methods produce similar predictions for most cover types examined. The same two methods are potentially capable of providing higher spatial resolution daily ETa estimates depending on the satellite inputs used; out of them, however, only NDVI-Cws can yield spatially complete and temporally continuous datasets. The analysis therefore provides insights into the reliability and usability of different remote sensing approaches for regional-scale water resource monitoring. Full article

Computational models have gained recognition as effective tools for estimation of urban water balance. Beyond personal skills, the selection of an appropriate model requires an understanding of the city’s water system, the capabilities of the model and data requirements. Kabul represents a rapidly urbanizing city with limited water and sanitation infrastructure. To analyze the urban water balance of Kabul, ten prominent open-source and commercial hydrological models were evaluated. The characteristics of the models along with their data requirements, calibration parameters, and applications are assessed through a review of previous studies and user manuals. The study demonstrates that assessing Kabul’s urban water balance requires explicit consideration of processes such as snowmelt, groundwater abstraction, surface water–groundwater interaction and irrigation. The urban water balance of Kabul and cities with similar conditions can be effectively modeled using tools such as MIKE SHE, SWAT, and WEAP. The flexibility of the MIKE SHE model and its ability to use time-varying raster data make it a viable option for analyzing water balance under changing land cover and climatic conditions. Lumped models account for limited spatial variability and rely on empirical fitting. In contrast, physically based models reduce reliance on empirical calibration. However, they are more data-intensive and complex than simpler conceptual models. Full article

This study investigates the structure–performance relationship of Fe³⁺- and Zr⁴⁺-modified layered double hydroxides (LDHs) for fluoride removal from water. Mg–Al LDHs with different metal loadings (Zr0.05, Zr0.1, Fe0.8, and Fe1) were synthesized via ultrasound-assisted coprecipitation and characterized using XRD, SEM–EDS, FTIR, XPS, and N₂ physisorption. Among the synthesized materials, Zr0.05-LDH exhibited the highest adsorption performance. Response surface methodology identified adsorbent dosage as the most influential parameter, achieving a maximum fluoride removal efficiency of 98.17% under optimal conditions (pH ≈ 5, adsorbent dose of 0.88 g/L, and initial fluoride concentration of 12.6 mg/L). Zr0.05-LDH showed the largest specific surface area (261 m²/g) and a maximum adsorption capacity of 137 mg/g, as described by the Langmuir isotherm model. Kinetic studies indicated rapid adsorption, with equilibrium reached at approximately 180 min. Fluoride removal was governed primarily by inner-sphere complexation at Zr⁴⁺ and Fe³⁺ sites, accompanied by anion exchange and electrostatic interactions. The adsorbent retained 89% of its capacity after five regeneration cycles. Groundwater tests from Durango, Mexico, demonstrated effective fluoride reduction below Mexican and WHO guideline limits despite competing anions. These results demonstrate the potential of modified LDHs for fluoride-contaminated groundwater treatment. Full article

A one-pot strategy was developed for preparing a chitosan/Mg–Fe layered double hydroxide (LDH) composite by alkaline coprecipitation from an acidic chitosan solution containing Mg(II) and Fe(III) precursors, avoiding separate LDH synthesis and subsequent incorporation into chitosan. X-ray diffraction confirmed LDH formation within the chitosan matrix, and ICP analysis indicated an LDH-equivalent content of approximately 4.1 wt.% on an anhydrous basis. The composite exhibited enhanced chromate adsorption compared with both starting components. The experimental plateau adsorption capacity reached 137.4 mg/g, exceeding those of chitosan (92.2 mg/g) and Mg–Fe LDH (53.5 mg/g). Nonlinear isotherm fitting showed that Mg–Fe LDH was better described by the Freundlich model, whereas chitosan and the composite were better described by the Langmuir model. The kinetic behavior followed the pseudo-second-order equation, while Weber–Morris analysis indicated multistep uptake involving surface interaction and diffusion-related processes. In simulated groundwater containing chloride, bicarbonate, and sulfate, the composite removed 82% of Cr(VI) at 1.0 g/L. It also retained complete chromate uptake over five sorption/desorption cycles, although desorption efficiency decreased from 97.3% to 90.3%. A limitation of this study is that performance was evaluated mainly in batch systems and simplified simulated groundwater; validation with real contaminated waters and dynamic flow conditions is still required. 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

The Xianglaqu River Basin, a major recharge area of the Xiagacuo endorheic lake basin on the Tibetan Plateau, provides an ideal setting for investigating hydrochemical evolution in alpine arid closed basins. In this study, 27 groundwater, spring-water, and surface-water samples collected from June to August 2023 were analyzed using correlation analysis, Piper diagrams, Gibbs diagrams, and ion-ratio methods. The results show that groundwater, spring water, and most surface water are predominantly of the HCO₃⁻–Ca·Mg type, indicating overall hydrochemical consistency across the basin. However, marked spatial differentiation occurs along the flow system: upstream waters are relatively simple and stable, whereas downstream and terminal surface waters show pronounced increases in Na⁺, Cl⁻, SO₄²⁻, and TDS, and some samples exhibit a tendency toward HCO₃⁻–Na facies. These patterns reflect progressive solute accumulation and terminal enrichment in the closed basin. Hydrochemical evolution is controlled mainly by water–rock interaction, with carbonate weathering as the dominant source of major ions, while silicate weathering, minor local saline-mineral dissolution, cation exchange, and evaporation concentration further influence water chemistry. Overall, the basin is characterized by local weathering release, along-path solute accumulation, and terminal evaporative enrichment. Full article

Transboundary basins in arid and semi-arid regions are increasingly stressed by groundwater depletion, drought, and competing upstream water-management policies. Quantifying surface–groundwater interactions in such systems remains challenging due to sparse hydroclimatic observations. This study develops and applies a fully coupled SWAT–MODFLOW model to the Tigris–Euphrates River Basin (TERB; ~900,000 km²), the largest transboundary basin in the Middle East, to evaluate spatiotemporal stream–aquifer interactions and basin-scale water balance. The model integrates SWAT 2012 with MODFLOW-NWT at daily and monthly time steps and was calibrated and validated against monthly streamflow records from 23 gauges and groundwater levels from four wells over 1981–2002, with a 1976–1980 warm-up period. A multi-stage calibration strategy was adopted, including standalone SWAT calibration using SUFI-2, standalone MODFLOW calibration using PEST, and subsequent coupled refinement. Model performance was satisfactory, with Nash–Sutcliffe efficiencies exceeding 0.5 for streamflow and strong agreement between simulated and observed groundwater levels (R² = 0.92). Basin-integrated total water storage anomalies showed reasonable agreement with GRACE-derived estimates for 2002–2013 (R² ≈ 0.72). The basin-averaged net stream–aquifer exchange was estimated at −7.08 × 10⁶ m³ yr⁻¹, indicating net river leakage to aquifers, with a marked intensification after 1987 consistent with major upstream reservoir developments. Recharge patterns were highest over permeable foothill formations and lowest over consolidated northern highlands. The integrated use of streamflow, groundwater, and GRACE observations within a fully coupled framework provides a transferable approach for water-resources assessment in data-scarce transboundary basins. Full article

Groundwater–surface water interactions in volcanic hydrogeological systems represent a key process in river dynamics and were preliminarily investigated along a river draining the southern sector of the Sabatini Mountains (central Italy) using an integrated hydrogeological and geochemical approach. Serial discharge measurements, combined with physico-chemical parameters, major ions, stable oxygen isotopes, and radon analyses, reveal marked spatial variability in river–aquifer exchanges along distinct river reaches. The Arrone River exhibits clear differences between upstream, intermediate, and downstream sections, reflecting the relative influence of localized anthropogenic inputs, diffuse groundwater discharge from the volcanic aquifer, and subsurface flow contributions. Upstream reaches are characterized by pronounced modifications in discharge and chemistry, whereas intermediate and downstream reaches show progressive groundwater influence, resulting in distinct geochemical signatures and changes in water quality. Correlation and cluster analyses identify reach-specific processes controlling water composition and support the recognition of gaining and mixed river conditions under varying hydrological regimes. These results constrain a conceptual model in which river behavior is governed by spatially heterogeneous groundwater inflows, modulated by seasonal discharge dynamics and local human pressures. This study highlights the importance of reach-scale investigations for understanding SW–GW interactions in volcanic settings and provides transferable insights relevant to groundwater-dependent river systems. Full article

Hydrogeochemistry is a practical and low-impact tool for mineral exploration that relies primarily on groundwater as sampling media. It is particularly valuable for blind or deeply buried deposits where surface geochemical methods are ineffective, as groundwater acts as a natural integrator of geochemical signals from depth. This study presents a PRISMA 2020-compliant systematic review of hydrogeochemical exploration practices published between 1946 and 2025, synthesizing 118 empirically screened case studies from diverse geological and climatic settings. The review evaluates the geochemical processes governing aqueous dispersion halos, including sulphide oxidation, water–rock interaction, redox controls, and physicochemical speciation, and assesses how these processes influence pathfinder behaviour and anomaly expression. Quantitative synthesis highlights consistent patterns in hydrogeochemical footprints across major mineral systems and demonstrates the effectiveness of thermodynamically informed and multivariate interpretation strategies over simple concentration-based approaches. Emerging trends identified include the growing application of non-traditional stable isotope fractionation, nanoparticle geochemistry using single-particle ICP-MS, and integration of hydrogeochemical datasets with GIS, geophysics, and machine learning-based prospectivity modelling. Unlike recent narrative reviews, this study provides a fully reproducible, structured evaluation of the global evidence base and formalizes a standardized end-to-end workflow. Full article

Large-scale photovoltaic (PV) deployment in arid deserts may alter land–atmosphere interactions and influence groundwater systems, yet such impacts remain poorly quantified due to limited high-resolution observations. To overcome the coarse spatial resolution of GRACE data, this study develops a CNN-LSTM-Attention deep learning framework to downscale terrestrial water storage anomalies (TWSA) from 0.25° × 0.25° to 0.1° × 0.1° over the Huadian PV base in the Tengger Desert, China, during 2004–2024. Groundwater storage anomalies (GWSA) were derived using a water-balance approach, and piecewise linear regression was applied to detect trend shifts associated with PV development. Results show a persistent decline in TWSA and GWSA before 2022, followed by short-term recovery signals afterward. Groundwater responses exhibit greater magnitude and delayed behavior relative to soil moisture. Spatial analysis reveals stronger variability and more frequent deficits in the western subregion, indicating intra-base heterogeneity. A seasonal phase analysis identifies an approximately six-month lag between soil moisture and groundwater, highlighting constraints from deep vadose-zone processes. The findings suggest that groundwater dynamics reflect the combined effects of climate variability, infiltration lag, and PV-related land surface modification rather than a single driver. This study demonstrates the potential of deep-learning-based GRACE downscaling for groundwater monitoring in human-modified arid regions and provides insights for sustainable water management under renewable energy development. Full article

Surface water–groundwater interactions within oasis–desert ecotones of arid regions play a pivotal role in sustaining regional water security and ecological stability. Taking the Niya River Basin in Xinjiang, Northwest China, as a representative inland watershed, this study systematically elucidates the mechanisms and seasonal dynamics of surface water–groundwater coupling under the combined influences of natural processes and anthropogenic activities. A total of 68 surface water and groundwater samples were collected during the dry, normal, and wet hydrological periods. Integrated hydrochemical characterization, mineral saturation index analysis, and stable isotope (δ²H and δ¹⁸O) mass balance modeling were employed to quantify recharge contributions and unravel hydrogeochemical evolution pathways. Results indicate that the waters in the study area are predominantly brackish to saline, with consistent dominant ionic assemblages (SO₄²⁻ and Na⁺) across all hydrological periods, highlighting evaporite dissolution as the primary control on solute composition. Hydrochemical evolution is jointly regulated by evaporation concentration, water–rock interactions, and cation exchange processes. Surface water chemistry reflects the combined effects of silicate weathering and evaporite dissolution, whereas groundwater chemistry is mainly governed by evaporite dissolution coupled with pronounced cation exchange. Stable isotope signatures reveal substantial secondary evaporation of regional precipitation prior to recharge. Frequent bidirectional recharge between surface water and groundwater was observed, exhibiting distinct seasonal transitions. During the dry period, groundwater provides significant baseflow support to surface water (48.6% in the oasis zone and 54.3% in the desert zone). In the normal period, recharge direction reverses, with surface water becoming the dominant source of groundwater recharge (99.0% in the oasis zone and 76.6% in the desert zone). In the wet period, spatial heterogeneity becomes evident: surface water continues to dominate groundwater recharge in the oasis zone (92.7%), whereas groundwater recharge to surface water prevails in the desert zone (50.5%). This study identifies a seasonally dynamic “discharge–infiltration–zonal regulation” bidirectional recharge pattern in arid inland river systems. The findings advance the mechanistic understanding of hydrological connectivity reconstruction within oasis–desert ecotones and provide a scientific basis for optimized regional water resource allocation and groundwater salinization risk mitigation. Full article

The Aksu River Basin, the main headwater of the Tarim River, contributes more than 70% of the main stream’s runoff and is therefore critical in maintaining hydrological stability in this arid river system. In recent decades, rapid oasis expansion and growing agricultural water withdrawals have intensified competition for surface and groundwater, posing increasing ecological risks to the downstream Tarim River Basin. To quantitatively characterize river–groundwater hydrological responses under intensive water use, we combined statistical analysis, field observations, and distributed hydrological modeling within a basin-scale conceptual framework. Multiple lines of evidence—water level monitoring, hydrochemical tracers, stable isotopes, and the integrated surface–groundwater model MIKE SHE—were used to identify river–groundwater interaction mechanisms in the Aksu alluvial plain. Results reveal a typical three-stage spatial exchange pattern: river recharge to groundwater in the upstream reach, groundwater discharge to the river in the midstream, and renewed river infiltration to groundwater downstream. The patterns inferred from water levels, hydrochemistry, and isotopes are broadly consistent, while water-level data better resolve left–right bank asymmetry. The MIKE SHE model supports the seasonal bidirectional exchange dynamics and reproduces runoff behavior with acceptable performance (RMSE and residual standard deviation within 20% of observed means and R² > 0.7 during both calibration (2010–2017) and validation (2018–2021)). The proposed multi-evidence framework captures the spatio-temporal variability of river–groundwater interactions in arid regions and provides spatially differentiated guidance for conjunctive surface–groundwater regulation and integrated water resources management in the Tarim River Basin. Full article

Dissolved-air flotation (DAF) is widely used for surface-water pretreatment but remains insufficiently explored for chemically complex groundwater. This study develops a thermodynamic and bubble-dynamics modeling framework to evaluate the feasibility of DAF pretreatment for groundwater containing elevated arsenic, natural organic matter (NOM), and color. The study is theoretical and model-based; no experimental dissolved-air flotation tests were performed. Air solubility was calculated at pressures of 4–6 bar and temperatures of 13–17 °C, while microbubble size, rise velocity, and bubble–floc interaction efficiencies were estimated using established physical models. Laboratory coagulation–flocculation jar tests with FeCl₃ and FeCl₃/PAC were used to define realistic floc properties prior to flotation modeling. No experimental dissolved-air flotation tests were conducted; all flotation-related results presented in this study are derived from thermodynamic and hydrodynamic modeling. Results show that a temperature decrease from 17 to 13 °C increases effective gas supersaturation by ~15% and shifts predicted microbubble diameters from ~60–90 µm to ~35–60 µm under identical operating conditions. The qualitative consistency between modeled flotation-relevant parameters and previously observed coagulation–flocculation trends for color, total organic carbon, and arsenic removal supports the proposed mechanistic framework. The study demonstrates how coupling coagulation chemistry with thermodynamically optimized air dissolution can enhance DAF applicability for arsenic- and NOM-rich groundwater. Full article

Understanding nitrogen distribution in spring-fed karst rivers is important for interpreting ecosystem responses in populated Mediterranean landscapes. Nitrogen, in its various forms, is a key physicochemical quality element influencing biological communities and ecological quality of freshwater ecosystems. Elevated nitrogen availability may trigger eutrophication and other processes associated with biodiversity loss, posing risks to both aquatic ecosystem integrity and drinking water quality. However, translating nitrogen measurements into effective monitoring and management strategies remains challenging. Monitoring programs are often resource-intensive and require site-specific adaptation, particularly in heterogeneous systems such as karst catchments. General guideline values may not fully capture local hydrological variability, groundwater–surface water interactions, or combined stressors, including nutrient mixtures and salinity intrusion. These factors introduce uncertainty and complicate the interpretation of nitrogen dynamics. This pilot-scale exploratory study assessed total nitrogen (TN) across four environmental matrices—water and sediments, as well as tissue TN in aquatic bryophytes, and in benthic macroinvertebrates—at four spring-fed sites within the Koiliaris River Basin (Crete, Greece). The Koiliaris Critical Zone Observatory (CZO) is a representative karst watershed with highly permeable carbonate geology and long-term human pressures. TN concentrations were low in water (0.9–1.4 mg/L) and sediments (0.2–1.1 g/kg) but substantially higher in biotic compartments, particularly in macroinvertebrates (29.8–47.1 g/kg), while moss tissue TN ranged between 16.9 and 20.4 g/kg. Spatial variability among sites was observed, with consistently higher TN values at the coastal spring influenced by seawater intrusion. Although the limited sample size precluded formal statistical inference, exploratory analyses indicated positive associations between water TN and tissue TN in mosses and macroinvertebrates. These preliminary findings suggest that dissolved nitrogen may represent an important pathway of nitrogen availability to aquatic biota in this karst system. The study provides an exploratory framework for integrating abiotic and biotic nitrogen measurements and may inform the design of future, larger-scale investigations in Mediterranean spring-fed rivers. Full article