Water doi: 10.3390/w18202568

Authors: Sayat Alimkulov Lyazzat Makhmudova Mikhail Tskhay Marina Li Tursun Ibrayev Elmira Talipova Lyazzat Birimbayeva Makpal Dautaliyeva Oirat Alzhanov Azamat Akhmetay

In the context of increasing climate variability, the assessment of risks to irrigated agriculture requires a combined consideration of climatic and water management factors. The aim of this study is to develop an Integrated Climate and Water Stress Index (ICWSI) and to assess its potential applicability in index-based insurance. The study was conducted for the Shu-Talas Water Management Basin in Kazakhstan for the period 2000–2024. The ICWSI combines the Standardized Precipitation and Evapotranspiration Index (SPEI) with the actual annual Water Abstraction Index (WAI) for regular irrigation. Correlation analysis, RMSE, MAE, LOOCV cross-validation, ROC analysis and basis risk metrics were used to evaluate the index. It was found that the relationship between climatic drought and agricultural productivity was weak, whilst annual water abstraction was characterized by a more pronounced statistical relationship with its interannual variability. ICWSI values ranged from −1.64 to +1.70, reflecting differences in the combination of climatic and water management conditions. The results of the insurance validation revealed a trade-off between the completeness of identifying years with reduced productivity and the frequency of false positives. The Area Under the Curve (AUC) values obtained indicate that the indices under consideration have limited discriminatory power. The proposed approach enables the joint characterization of climatic and hydrological conditions in a regulated transboundary catchment. Its application as a standalone insurance trigger requires further validation using a dataset of independent data and refinement of the threshold values.

Water doi: 10.3390/w18202569

Authors: Xintong Du Xiangtong Zhou Yuntao Zhu Shuang Zhang Xu Wang Lu Han Hui Xu Bo Zhang Chundu Wu

Aeration dominates energy use in biological wastewater treatment, but aggressive energy-saving control risks violating dissolved oxygen (DO) safety margins. We present a guardrail-enforced tabular Q-learning controller for a pilot biofilm anoxic/oxic (A/O) system (2 × 4.86 m3) treating piggery wastewater, compared online against always-on aeration and a hysteresis rule. A first-order-plus-deadtime DO model (R2 = 0.973) identified from pseudo-random excitation was used to pre-train a 108-state policy balancing energy, DO-band keeping, and switching wear, deployed as a 5 min decision loop nested inside a 1 min hard-guardrail monitor with command readback verification. In 24 h online campaigns, the RL controller cut metered aeration energy by 44.3% versus always-on (26.05 vs. 46.8 kWh·d−1; 95% CI 43.2–45.4%) with zero guardrail interventions and day-to-day reproducibility within 1%; the cheaper hysteresis rule (−55.2%) required 9–12 hard-guardrail interventions per day. Effluent COD and NH4+-N remained far below the enterprise discharge requirement under all controllers throughout the 24 h campaign horizons, with no detectable short-term effluent penalty, and a manual actuator-override incident was contained autonomously by the guardrail layer. Because the hydraulic retention time (≈17 d) far exceeds the campaign length, longer-horizon effluent effects remain open and are stated as a limitation. A deliberately simple, auditable tabular policy thus captures most of the achievable aeration savings on small decentralised systems while its safety case rests on hard guardrails that bound the worst case independently of what the learned policy outputs.

Water doi: 10.3390/w18202567

Authors: Zhiyuan Bao Hongyan Shen Zhaoxing Han Jie Liu Jingye Wang Dezhi Sun Fei Qi

Slow-flowing water bodies formed after the cutoff and straightening of large canals have low flow velocity and weak water exchange, allowing nitrogen and phosphorus to accumulate and induce eutrophication. To enhance canal ecological restoration, a hybrid constructed wetland (HCW) system was established in the ecological conservation area of the Pinglu Canal. The system consisted of a grass swale, surface-flow constructed wetland (CW), subsurface-flow CW, and filter, and its performance under different hydraulic conditions and hydraulic retention time (HRT) was evaluated based on the removal of chemical oxygen demand (COD), NH3-N, total nitrogen (TN), and total phosphorus (TP). In the operating-condition comparison, removal rates of all four pollutants were highest during the planted normal-water-level stage. Pollutant removal responses to HRT varied among pollutants and operating conditions and were not consistently monotonic. Considering the observed multi-pollutant removal performance and hydraulic throughput, 48 h was considered a practically suitable HRT under planted normal-water-level conditions within the tested range. Unit contributions varied among pollutants and operating conditions. The subsurface-flow CW mainly contributed to COD removal, the surface-flow CW contributed most to TP removal, and the four units presented functional complementarity. Under the recommended practical conditions (normal-water-level, vegetation, HRT 48 h), removal rates of COD, NH3-N, TN, and TP reached 33%, 91%, 68%, and 58%, respectively. These findings provide preliminary evidence for further evaluation of the tested HCW at the Pinglu Canal study site.

Water doi: 10.3390/w18202566

Authors: Hongfei Yang Ziwei Zhao Ke Li Kuandi Zhang Yanqi Zhang Jiani Zhao Mingwang Zhang

Runoff and sediment regimes in highly erodible watersheds are increasingly affected by concurrent changes in climate and land use. However, runoff and sediment do not necessarily respond synchronously, making future sediment evolution and erosion-control planning difficult to assess. This study integrated Coupled Model Intercomparison Project Phase 6 (CMIP6) projections, the Patch-generating Land Use Simulation (PLUS) model, and the Soil and Water Assessment Tool (SWAT) to investigate historical and future runoff–sediment dynamics in the Wuding River Basin on the Loess Plateau. Meteorological, land-use, runoff, and sediment records for 1961–2021 were used for historical diagnosis and model development. Future simulations for 2022–2045 considered three Shared Socioeconomic Pathway (SSP) climate pathways and four land-use scenarios, including natural development, farmland protection, ecological protection, and urban development. Historical analysis identified asynchronous regime shifts, with runoff changing markedly in 1996 and sediment transport in 2002, respectively. Future runoff and sediment responses also varied among climate pathways. Mean annual runoff changes by +0.15, +0.34, and −0.65 × 108 m3 under SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively, while the corresponding sediment changes are −0.01, +0.04, and −0.06 × 108 t, showing that increased runoff does not necessarily lead to increased sediment export. Ecological protection and urban development produce the largest streamflow increases, whereas all land-use scenarios reduce sediment export relative to the 2020 baseline. Strong seasonal concentration persists, with July–October contributing more than 40% of annual runoff and June–September accounting for over 70% of annual sediment transport. These findings provide a quantitative basis for adaptive water resources management and ecological restoration in erosion-prone watersheds.

Water doi: 10.3390/w18202565

Authors: Filip Gamoń Paulina Sowik Dawid Zych Katarzyna Kowalska

Antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) are widespread in wastewater treatment plants (WWTPs), but their occurrence in high-solids matrices remains less characterized. This study used high-throughput quantitative PCR (HT-qPCR) to investigate ARG and MGE diversity, relative abundance, resistance mechanisms, and co-occurrence patterns in raw influent (IN), activated sludge (BR), and anaerobic digestate (AD) from a full-scale municipal WWTP. Among the 306 assays targeting ARGs, 197 were detected in at least one of the investigated matrices, with the highest number of detected targets observed in IN (189), followed by BR (132) and AD (120). Aminoglycoside, multidrug resistance (MDR), macrolide–lincosamide–streptogramin B (MLSB), tetracycline, and β-lactam resistance genes were the most diverse groups. Antibiotic deactivation was the dominant resistance mechanism (47.4%), followed by efflux (26.5%) and cellular protection (20.8%). Among 48 MGE assays and four integron-associated targets, 29 MGEs and all integron markers were detected. Co-occurrence analysis identified 56 connected ARGs/MGEs nodes distributed across nine modules. Overall, the results revealed distinct ARG and MGE profiles across the investigated wastewater treatment matrices, with lower numbers of detectable ARG targets in activated sludge and anaerobic digestate than in raw influent. Nevertheless, numerous resistance-associated genetic determinants remained detectable in both sludge-associated matrices, highlighting the importance of including these compartments in wastewater resistome surveillance.

Water doi: 10.3390/w18202564

Authors: Piotr Szmytkiewicz Joanna Borysiak Magdalena Stella-Bogusz Michał Bojan Małgorzata Bielecka Maria Rucińska Angelika Szmytkiewicz Wei-Po Huang

Large-scale beach nourishment projects constructed adjacent to port breakwaters may produce spatially contrasting shoreline responses because wave transformation, sediment redistribution, and structural effects act simultaneously. This study presents an empirical analysis of short-term shoreline evolution at a large artificially nourished beach constructed next to the eastern breakwater of the Vistula Spit Channel in the South Baltic Sea. The analysis combines historical orthophotomaps, monthly Real-Time Kinematic Global Positioning System (RTK-GPS) shoreline surveys, drone-based elevation data, hourly wave records, and tide-gauge observations collected between February 2024 and March 2025. The objective was to quantify the spatial and temporal variability of shoreline change and to interpret the observed erosion and accretion in relation to wave conditions, sea-level variability, the presence of the breakwater, and post-nourishment sediment redistribution. Historical shoreline changes were assessed at fixed coastal mileage locations. Monthly shoreline changes were quantified using a polygon-based on Geographic Information System (GIS) procedure, with gross erosion, gross accretion, and net area change calculated for successive survey intervals. Two characteristic 250 m coastal sectors were also compared: the area adjacent to the breakwater and the eastern boundary of the monitored beach. Approximately 55,550 m2 of erosion and 57,851 m2 of accretion were identified during the monitoring period, resulting in a net positive balance of approximately 2301 m2. The small net value masks substantially larger opposing changes in different parts of the study area. The sector adjacent to the breakwater showed a predominantly negative cumulative surface balance, whereas the eastern sector showed a predominantly positive balance. The May–June interval was not uniformly stable, despite generally moderate offshore wave conditions, because a net loss of approximately 9626 m2 was recorded. The results indicate that shoreline evolution was controlled by the combined effects of offshore wave forcing, sea-level variability, wave transformation near the breakwater, initial nourishment geometry, and natural post-nourishment sediment redistribution. Offshore wave parameters were not treated as direct nearshore forcing because refraction, shoaling, diffraction, breaking, and energy dissipation may modify the wave field before it reaches the shoreline. The study provides an empirical description of short-term shoreline adjustment rather than a validated predictive model.

Water doi: 10.3390/w18202562

Authors: Shirong Geng Jie Wei Wen Zhao Dongguo Song Xin Li Tingting Guo Wenke Liu Jiatai Pan Xiaoke Li

In northern deep-water drinking-water reservoirs, determining whether the taxonomic and functional structures of zooplankton respond consistently to environmental gradients is important for understanding seasonal community variation and evaluating the complementary ecological information provided by taxonomic and functional-group metrics. Seasonal surveys were conducted in Guanyinge Reservoir across four seasons, different horizontal regions, and water layers. Using community-structure analysis, functional-group classification, Mantel test, Pearson permutation correlation analysis, and redundancy analysis (RDA), we examined the spatiotemporal patterns of zooplankton communities and functional groups and their associations with environmental variables. Both aquatic environmental variables and zooplankton community characteristics exhibited stronger seasonal than spatial differentiation, and the reservoir remained within the mesotrophic range during the four seasonal surveys. A total of 98 zooplankton species were identified, belonging to 68 genera across five taxonomic groups. Species richness peaked in autumn and was the lowest in spring, whereas zooplankton abundance and biomass reached their maximum values in summer and minimum values in winter. This asynchronous variation indicated that seasonal changes in species richness did not parallel those in zooplankton abundance and biomass. Abundance- and biomass-based patterns also differed at both the dominant-species and functional-group levels. Specifically, relative abundance was dominated by PF, RF, and PC, whereas LCF, SCF, RC, and RF accounted for most of the relative biomass, indicating that numerical dominance did not correspond to biomass contribution. Further environmental response analysis revealed that water temperature (WT) and total nitrogen (TN) were strongly correlated with the overall characteristics of zooplankton communities. Nitrate nitrogen (NO3−-N) showed significant independent explanatory effects across the abundance- and biomass-based dominant-species and major functional-group RDA analyses and was the most consistent nitrogen-related explanatory variable across these analytical levels. In contrast, water temperature (WT), nitrite nitrogen (NO2−-N), transparency (SD), and total phosphorus (TP) showed level-specific associations with different components of zooplankton structure. Overall, the spatiotemporal variation in zooplankton communities in Guanyinge Reservoir was primarily associated with seasonal environmental variation. Moreover, taxonomic and functional-group structures, as well as abundance- and biomass-based patterns, showed non-congruent associations with environmental gradients. Combining taxonomic metrics with abundance- and biomass-based functional-group metrics can more comprehensively characterize seasonal community variation and environmental associations in northern deep-water reservoirs. This study provides complementary ecological information for ecological monitoring, protection, and ecological status assessment of drinking-water source reservoirs.

Water doi: 10.3390/w18202563

Authors: Samuel Agustín Limón Rico Leonardo Tenorio-Fernandez Joel Artemio Morales Viscaya Marco Antonio Castro Liera Iliana Castro Liera

This work proposes a methodology for sea level time series imputation based on separating the observed signal into an astronomical tidal component (via harmonic analysis using T-TIDE) and a residual non-tidal component, which is then modeled using a multilayer perceptron (MLP) with meteorological variables (wind, pressure, sea surface temperature) from ERA5 and cyclical temporal features (sine/cosine encoding). The main contribution consists in separating the observed signal into two physically meaningful components: (i) the tidal astronomical component, obtained through classical harmonic analysis, and (ii) the residual component, which captures non-tidal variability. Subsequently, the residual component is modeled using a multilayer perceptron (MLP) with meteorological variables from ERA5 and time data as the feature vector. The method is evaluated at four NOAA tide gauge stations along the California coast (San Diego, La Jolla, Los Angeles, and San Francisco), using hourly records spanning from 1 January 1950 to 30 June 2025, with station-dependent missing data fractions. The harmonic plus MLP approach achieves a coefficient of determination (R2) of 0.9955 and a root mean square error (RMSE) of 0.03475 across the four stations, representing an average reduction of 52% in the RMSE compared to classical harmonic analysis alone.

Water doi: 10.3390/w18202561

Authors: Easton G. Hopkins Robert B. Sowby Brian McPherson

A reliable water supply is essential for balancing hydrologic, operational, and institutional constraints and is intensified by the water demands of emerging carbon-removal technologies. This study applies a reliable water-supply framework to Castle Valley, Utah, USA, a region with favorable geologic conditions for carbon storage. Existing municipal, agricultural, and industrial water demands and surface-water, groundwater, and water-rights-based supply were quantified using publicly available datasets. Scenarios were then evaluated to test how a proposed 1 Mt/yr direct air capture (DAC) facility would affect the regional water balance. Results indicate that the existing supply–demand balance in Castle Valley is approximately in equilibrium, and that a 1 Mt/yr DAC facility would require an estimated 7–18% of total municipal water demand, disrupting the balance under several supply scenarios, particularly where supply is based on water rights rather than actual conditions. Retrofitting existing coal-fired power plants with carbon capture and storage (CCS) could double their water consumption. Non-potable water sources, such as brine water, may be necessary to support DAC development without compromising existing water users. The findings suggest that regional water-balance frameworks can help identify where carbon-removal infrastructure is feasible without exacerbating water scarcity, and that similar assessments should precede DAC siting decisions in other water-limited regions.

Water doi: 10.3390/w18202560

Authors: Vesna Vasić Dragana Lukić Teodora Subić Nenad Popov Jelena Lubura Stošić Oskar Bera Ivana Čabarkapa

The increasing contamination of aquatic environments by heavy metals and the need for sustainable management of invasive aquatic species have stimulated interest in low-cost biosorbents derived from biological waste. In this study, minimally processed shells of the invasive crayfish Faxonius limosus were evaluated for Zn(II) and Cd(II) removal from aqueous solutions. FTIR, SEM, and BET/BJH analyses revealed an organic-mineral material containing amino, hydroxyl, amide, and carbonate functional groups with a predominantly mesoporous structure. Batch experiments showed rapid metal uptake, with equilibrium reached within approximately 60 min. The pseudo-second-order model provided the best fit to the kinetic data, while equilibrium behavior was best described by the Temkin model for Zn(II) and the Langmuir model for Cd(II). Langmuir maximum adsorption capacities were 70.69 mg/g for Zn(II) and 302.12 mg/g for Cd(II). Metal removal was influenced by both initial pH and biosorbent dose, with 2.5 g/L providing high removal efficiencies for both metals. Calcium-release experiments showed increased Ca concentrations in the presence of Zn(II) and Cd(II), supporting the involvement of the Ca-rich mineral fraction in metal removal. Overall, F. limosus shell waste represents a promising low-cost biosorbent and a sustainable valorization route for invasive biomass.

Water doi: 10.3390/w18202559

Authors: Nishtha Sharnagat Anupam Kumar Nema Prabhash Kumar Mishra Rituraj Shukla Rahul Kumar K. C. Patel

Sustainable management of river basins requires land and water to be understood as a single interacting system, yet the land-use datasets most widely used in basin planning primarily represent physical land cover and rarely distinguish hydrologically distinct land uses, grouping hydrologically distinct pixels (e.g., rainfed and irrigated cropland, or natural and engineered water bodies) into a single undifferentiated class. The Water Accounting Land Use (WALU) classification of the Water Accounting Plus (WA+) framework was designed to close this gap, but its conventional implementation has typically been implemented as a desktop workflow that loads complete rasters into local memory, which limits its efficiency for large basins and fine-resolution inputs. This study addresses that constraint by re-engineering the WA+ WALU workflow as a cloud-native, server-side classification on Google Earth Engine, integrating nine geospatial input layers through a hierarchical rule-based fusion that implements the original WA+ classification rules, each checked against the desktop implementation, while avoiding the need to load complete raster datasets into local memory and providing a scripted workflow that can be re-run by other users. The 24-class, pixel-level WALU map of the 97,366 km2 Narmada River Basin reveals that the human-modified land uses Modified Land Use (MLU) and Managed Water Use (MWU) (51.5%) marginally exceed the natural and semi-natural land uses Protected Land Use (PLU) and Utilized Land Use (ULU) (48.5%). Irrigated cereals (MWU3; 32.21%) form the largest WALU class, exceeding closed deciduous forest (23.41%), which indicates a strong dependence of agricultural production on irrigation and increased engineered water regime. The classification also maps wasteland over 9.91% of the basin, providing a spatially explicit basis for prioritizing land-restoration assessments, and shows marked sub-basin and district-scale differences in land use, with irrigated cropland concentrated in about ten districts within the major reservoir command areas against a periphery of rainfed and degraded land. A two-level accuracy assessment, combining a stratified confusion-matrix analysis (86.4% area-weighted accuracy; Kappa = 0.82) with a Sentinel-2 NDVI (Normalized Difference Vegetation Index) phenological validation of the rainfed-irrigated split (Cohen’s d = 1.27), indicates that the map is suitable as a land-use input for basin-scale WA+ accounting at the aggregated class level. The framework can be adapted for WALU mapping across other data-scarce basins.

Water doi: 10.3390/w18202558

Authors: Mohamed Amine Bailiche Hamza Kheddar Mounir Bouhedda Redha Mazari

Aquaponic systems require reliable forecasting of water quality parameters to support proactive monitoring and maintain suitable conditions for aquatic organisms. This study investigates Transformer-based deep learning for multi-step, multi-target water quality forecasting using multivariate sensor measurements from aquaponic fish ponds. A leakage-safe time-series framework is developed in which historical observations are used to simultaneously forecast pH, temperature, and dissolved oxygen over multiple future time steps. The Transformer is systematically compared with CNN, LSTM, GRU, and their attention-enhanced variants under identical experimental conditions. Among the learned models, the Transformer achieves the best overall performance, attaining an MAE of 1.3908, RMSE of 2.1103, R2 of 0.7534, and sMAPE of 21.09%. Statistical analysis further demonstrates significant improvements over several competing architectures, while horizon-based evaluation investigates forecasting behavior as the prediction range increases. The Transformer remains computationally lightweight, requiring approximately 0.91 MB and achieving a mean inference latency of 14.55 ms, supporting real-time deployment. Cross-pond validation and controlled noise experiments further assess generalization and robustness under challenging conditions. The findings demonstrate the potential of Transformer-based temporal modeling for efficient and proactive water quality forecasting in intelligent aquaponic monitoring systems.

Water doi: 10.3390/w18202557

Authors: Alexsandro dos Santos Reis Carlos Henrique Medeiros de Abreu Ilana Syanne Martins Uchôa Taís Silva Sousa Orleno Marques da Silva Helenilza Ferreira Albuquerque Cunha Alan Cavalcanti da Cunha

Over the past fifteen years, the lower Araguari River drainage system has undergone profound hydrogeological reconfiguration, disconnecting its mouth from the Atlantic Ocean and forming two new channels. This study experimentally quantified the impacts of these changes on hydrodynamics and water quality, considering anthropogenic drivers (upstream dam construction) and natural drivers (hyperdynamic erosional processes, Te, downstream). The methodology integrated spatial and seasonal landscape analysis via remote sensing and in situ observations; seasonal quantification of discharge and water quality parameters across semidiurnal tidal cycles; statistical correlation between hydrodynamic variables and water quality indicators; and hypothesis testing to assess the significance of hydrogeomorphological impacts. The results showed significant seasonal variation in turbidity, pH, color, total dissolved solids (TDS), suspended solids, electrical conductivity, nitrate, and instantaneous discharge (Qinst), while temperature, total coliforms, and Escherichia coli showed no significant seasonal difference (p > 0.05). Spatially, TDS and E. coli did not vary significantly, but electrical conductivity showed marked marine influence, increasing up to twenty-twofold during the dry season (p < 0.05). Water balance analysis revealed significant seasonal fluctuations in both liquid discharge (Qliq) and Qinst (p < 0.05), underscoring Te’s critical role in shaping the new channels and reflecting their proximity to the Amazon River and Atlantic Ocean. Maximum discharge (Qmax) correlated significantly with erosional processes (p < 0.05), confirming that Te has measurably impacted basin hydrodynamics and water quality.

Water doi: 10.3390/w18202556

Authors: Jiayu Yang Yang Huang Wanying Pu Rui Xu Yibing Jiang Dunqiu Wang Mingrong Wei Kun Dong

Municipal sludge anaerobic digestion (AD) is often constrained by limited substrate accessibility due to extracellular polymeric substances (EPSs), microbial cell walls, and compact floc structures. This review integrates pretreatment technologies and EPS characteristics through a five-dimensional conceptual framework: cell disruption, EPS solubilization, particle-size reduction, soluble chemical oxygen demand (SCOD) release, and enhanced biodegradability. The framework connects structural changes with substrate accessibility and digestion performance. Physical, chemical, and biological pretreatment methods are critically compared using study-specific evidence and descriptive numerical ranges rather than pooled estimates. Thermal hydrolysis promotes cell disruption and organic matter solubilization, while other methods offer complementary mechanisms with distinct operational constraints. However, increased SCOD does not necessarily translate into improved biodegradability or methane recovery. Similarly, improvements in laboratory-scale biochemical methane potential (BMP) cannot be directly extrapolated to full-scale digesters. Pretreatment effectiveness should therefore be evaluated by considering biodegradability, net methane gain, energy and chemical inputs, and downstream environmental impacts. This framework supports the interpretation of heterogeneous evidence and the selection of context-specific pretreatment strategies.

Water doi: 10.3390/w18202555

Authors: Sang-Bo Sim Hyung-Jun Kim

Coupled sewer–surface flood simulations are computationally demanding. We evaluated twelve surface-flow and exchange-discharge precision combinations in a graphics processing unit (GPU)-accelerated urban flood model for Jinju, Korea, using rain-on-grid (RoG) and rain-on-subcatchment (RoS) inputs. In 6 h hydraulic tests with 64-bit double-precision (FP64) exchange calculations, reduced-precision surface settings gave final water-depth root mean square errors (RMSEs) of 0.172–1.187 mm for RoG and 0.746–2.867 mm for RoS relative to the full-FP64 reference. Using 32-bit single precision (FP32) in selected exchange operations gave a maximum within-setting RMSE of 11.347 mm relative to FP64 exchange in the 48 h test. In a separate performance experiment, ten repeated 1 h runs per condition kept coupling data in GPU memory. Using FP32 for state storage and all targeted surface-flow operations, with FP64 exchange, achieved median speed-ups relative to the full-FP64 configuration of 1.883 (95% interval from repeated sampling: 1.876–1.887) for RoG and 1.205 (1.199–1.212) for RoS. The results identified this combination as an efficient candidate for the tested catchment. Local water-depth and exchange-volume differences should be assessed when applying it.

Water doi: 10.3390/w18202554

Authors: Yen-Wei Pan Jun-Yi Lee Tse-Yang Teng Ching-Li Yen Chi-Cheng Chiu Tsung-Yu Lee Chia-Jeng Chen

Accurate precipitation inputs are essential for watershed hydrological modeling, yet different precipitation datasets may produce similar streamflow performance through different calibrated parameter combinations and hydrological process representations. This study evaluated the effects of gauge-based and Taiwan Climate Change Projection Information and Adaptation Knowledge Platform (TCCIP) gridded precipitation on SWAT+ simulations for two mountainous watersheds in southern Taiwan using the NSGA-II multi-objective optimization algorithm for calibration. Differences in Pareto-optimal parameter distributions, parameter convergence, and hydrological partitioning were compared between precipitation inputs. Although simulations driven by both precipitation datasets achieved comparable streamflow performance, they produced distinct calibrated parameter sets and, therefore, gauge-based and gridded precipitation resulted in substantially different hydrological partitioning. TCCIP gridded precipitation was approximately 11% and 22% lower than gauge-based precipitation in the ZW and LN watersheds, respectively. Correspondingly, the runoff coefficient decreased from 67.98% to 64.13% in ZW and from 62.13% to 53.18% in LN, while the evapotranspiration-to-precipitation ratio increased from 32.38% to 35.80% and from 37.72% to 45.06%, respectively. The findings indicate that calibrated parameter sets are precipitation-source dependent and should not be transferred directly between different precipitation datasets. Instead, independent model calibration is recommended whenever precipitation inputs are changed. More broadly, this study highlights the importance of complementing conventional streamflow-based evaluation with process-based diagnostics to improve the physical reliability of watershed simulations and water resource assessments.

Water doi: 10.3390/w18202552

Authors: Temel Temiz Mücahit Opan

Reservoirs can alter river responses to climatic water deficits, but distinguishing regulation-associated differences from hydroclimatic variability remains difficult. We use a large-sample matched-basin design to compare full-record meteorological–soil-moisture and meteorological–streamflow coupling between highly regulated basins and hydroclimatically similar near-natural references, with event-based drought propagation examined separately. GRDC-Caravan hydroclimatic records were combined with Global Dam Watch reservoir information, with reservoir exposure represented by a static, basin-level storage-to-discharge proxy. The main analysis retained 394 matched basin pairs for 2002–2018 (17 calendar years) with at least 80% streamflow completeness. The primary metric was zero-lag Pearson coupling computed from pairwise-complete monthly standardized anomaly series across the full analysis period; decoupling was defined as 1 − r0. Event-based metrics were evaluated separately in eligible pairs. Streamflow showed a modest regulation-associated shift: the median regulated-minus-reference decoupling difference was 0.023 (95% bootstrap CI [0.008, 0.037]), with 57.4% of pairs positive. Soil moisture showed an opposite-sign shift (median ΔDc = −0.017), indicating a compartment contrast rather than a common positive decoupling response. The streamflow signal remained positive under stricter completeness filtering, an extended analysis period, exclusion of the poorest matches, and without-replacement matching, with a complementary sign-flip sensitivity check. Country- and GRDC-subregion cluster bootstraps retained positive intervals, whereas coarse WMO-region clustering and the separate 1991–2020 eligible-subset sensitivity had intervals including zero. Storage-to-discharge intensity was positively but modestly associated with streamflow decoupling (Spearman ρ = 0.241). These results indicate that reservoir regulation is associated with weaker contemporaneous meteorological–streamflow coupling in the sampled basins and support reservoir-aware interpretation of drought signals, while residual geographic and other human water-use confounding, together with unobserved reservoir operation, preclude strict causal attribution.

Water doi: 10.3390/w18202553

Authors: James H. MacDonald Thomas M. Missimer Zoie R. Kassis Senthil Balaji Girimurugan Ju Chou Rachel R. Rotz Isabella Wollney

Aquifer storage and recovery (ASR) wells along northern Lake Okeechobee, Florida, have been proposed as part of the Comprehensive Everglades Restoration Plan. However, researchers have linked elevated concentrations of As, Hg and transition metals in groundwater because of ASR in carbonate rocks. This study presents portable X-ray fluorescence (pXRF) analyses of four continuous cores (C38S, C59, L63N, and L63S) recovered from the Floridan Aquifer System north of Lake Okeechobee, Florida. A total of 5078 pXRF measurements were collected at approximately 30.5 cm along the four cores. Measurements along the cores included the Intermediate Confining Unit, Upper Floridan Aquifer (UFA), Avon Park Permeable Zones (APPZ), and portions of the Lower Floridan Aquifer (LFA). Emphasis was placed on the concentrations of mercury (Hg), arsenic (As), molybdenum (Mo), chromium (Cr), and nickel (Ni), which have been identified as elements of concern during ASR operations. Major-element trends in the cores often reflect lithologic changes in the Floridan Aquifer System. This includes decreases in Ca and Sr and increases in Mg associated with dolomitization in the Avon Park Formation. Trace-metal concentrations vary systematically within hydrostratigraphic units. Mercury commonly exhibits elevated concentrations near the base of the UFA, whereas Mo is often enriched near the top of the UFA. Elevated concentrations of Hg, As, Mo, Ni, and other trace metals frequently occur at hydrostratigraphic boundaries, formation contacts, clay-rich intervals, and especially within organic-rich layers. Organic layers contained metal concentrations several times greater than surrounding carbonate rocks and hosted the highest measured concentrations of Hg, As, and Mo in the cores. The paucity of organic layers and generally lower metal concentrations in the UFA suggest it may represent a favorable zone for ASR storage. In contrast, the APPZ and LFA contain numerous metal-enriched organic layers which may increase the potential for trace metal mobilization during ASR operations. These results suggest pXRF characterization provides an effective tool for geochemical characterization of storage zones and evaluating water-quality risks potentially associated with ASR development.

Water doi: 10.3390/w18202551

Authors: Ioana Pastor Alexandru Nedelea Laura Comănescu Dănuț Tanislav

Soil loss due to erosion is a form of land degradation, having significant effects on agricultural productivity, water resource quality, and food security. The morphometric analysis of the drainage network is based on mathematical relationships and geometric progressions. In previous studies, several morphometric parameters have been analyzed in relation to stream order. While numerous studies have assessed soil loss at the watershed level, its spatial variability at the sub-watershed level remains less understood, even though it can highlight sectors that disproportionately contribute to soil loss. Thus, this study aims to analyze whether the RUSLE-estimated soil loss values follow the same morphometric relationship and geometric progressions by examining the hierarchical distribution of soil loss in the 39 sub-watersheds of the Buzău River Basin. The methodology consisted of extracting the mean and summed values of soil loss from the RUSLE2015 raster for all 9369 sub-watersheds, which were hierarchized into seven orders of streams. We created two laws of summed and mean soil loss, and the law of the number of sub-watersheds corresponds to the law of the number of segments. The three data series exhibit geometric progression patterns for which ratios have been calculated. Internal variations in the estimated soil loss have been observed. The sub-Carpathian sector is the most susceptible to the estimated mean (66%) and total (73%) soil loss. Sub-watersheds whose area is smaller or comparable with that of other sub-watersheds in the Carpathian sector exhibited much higher soil loss values (SW 11- 0.16 t ha−1 yr−1 vs. SW 33- 3.36 t ha−1 yr−1). The Slănic sub-Watershed loses a total of 202,325.48 t yr−1, while Bâsca loses only 50,573.86 t yr−1, even though its area is much larger (78,300 ha). The highest values of mean soil loss are recorded in Oleșești, at 9.19 t ha−1 yr−1. These results can support authorities in identifying and prioritizing sub-watersheds that may require soil conservation measures and can be reproduced in watersheds with different characteristics.

Water doi: 10.3390/w18202550

Authors: Sujin Lee Sanggyun Kim Junghyeon Kim Imgyu Byun

This study compared time-dependent EPS and protein oxidation indicator responses during Fe(II)-activated peroxydisulfate (Fe(II)/PDS) and calcium hypochlorite/ferric chloride (Ca(OCl)2/FeCl3) conditioning of food waste digestate (FWD). Dewatering performance was evaluated across reagent dosages, while molecular indicators were followed over 0–60 min at the selected dosages. Protein (PN) and polysaccharide (PS) concentrations were measured in soluble, loosely bound, and tightly bound EPS (S-EPS, LB-EPS, and TB-EPS), together with thiol, protein carbonyl, and advanced oxidation protein product (AOPP) responses. Under the selected conditions, Fe(II)/PDS reduced capillary suction time (CST) from 1289.9 to 61.2 s and cake water content from 94.67% to 59.33%, whereas Ca(OCl)2/FeCl3 reduced them to 30.5 s and 69.17%, respectively. Ca(OCl)2/FeCl3 yielded the lower CST, while Fe(II)/PDS yielded the lower cake water content after filter-press compression. Fe(II)/PDS showed greater depletion of detectable S-EPS PN, persistent thiol loss, and a transient AOPP increase. Ca(OCl)2/FeCl3 showed a greater normalized protein carbonyl response without a corresponding AOPP increase. These findings show that the two conditioning treatments produced contrasting dewatering outcomes and distinct EPS and protein oxidation indicator responses.

Water doi: 10.3390/w18202549

Authors: Sunghwan Lee Byunghyun Kim Gwangseob Kim

A rapid and accurate urban inundation prediction system is important for reducing the impacts of urban flooding. This study comparatively evaluates three deep learning models—a Transformer, CNN-LSTM, and GNN—as surrogate models that link rainfall time series with the spatial distribution of inundation. A dataset of 1000 rainfall–inundation pairs was constructed using the physics-based EPA-SWMM/FLO-2D framework under a range of synthetic and observed rainfall events with durations of 1 h, 2 h, and 3 h. The three deep learning models were trained to approximate the inundation responses generated by the physics-based simulations, and their predictive performance was evaluated using RMSE, NSE, IoU, and F1 score, together with computational time, threshold sensitivity, and robustness to different train–test partitions. For the 30 common evaluation events, the Transformer achieved an RMSE of 0.034 ± 0.011 m, NSE of 0.908 ± 0.018, IoU of 0.903 ± 0.020, and F1 score of 0.949 ± 0.016, showing the highest overall predictive performance among the three models under the conditions considered in this study. The training times of the three models were relatively similar, ranging from 3268.1 to 3407.5 s, while inference times ranged from 0.031 to 0.044 s, substantially shorter than the mean EPA-SWMM/FLO-2D simulation time of 293.1 s. Threshold-sensitivity analysis and repeated random train–test splits showed a similar relative performance pattern among the models, while 50-run Monte Carlo cross-validation of the Transformer indicated relatively consistent performance across repeated data partitions. These results demonstrate the potential of deep learning surrogate models for rapid urban inundation prediction and provide a comparative assessment of the suitability of different architectures for approximating physics-based inundation responses.

Water doi: 10.3390/w18202547

Authors: Chuanlei Wen Lifeng Chen Hongbing Zhao Yalu Han Hengtian Li Yuan Xiu Yuangeng Cheng

The water–energy–food (WEF) nexus is central to regional sustainable development, particularly in resource-based regions (RBRs) facing resource depletion and ecological strain. While existing studies have examined internal WEF linkages and extended the framework to include external dimensions such as ecology and land, the stage-based succession of limiting factors across developmental stages has received limited attention, and resource-based cities in which energy and grain production functions coexist remain underexamined. Taking Daqing, a typical resource-based city in China, as a case study, this paper constructs a comprehensive evaluation index system covering water, energy, food, and regional development subsystems. The CRITIC method is adopted to calculate indicator weights, and the coupling coordination degree model is applied to analyze the evolutionary characteristics of the WEF system’s coordinated development over the period 2005–2023. The obstacle degree model is further employed to identify obstacle factors across different stages. The results indicate that the comprehensive evaluation index experienced three evolutionary stages: rapid growth, structural adjustment, and recovery and improvement. The coupling degree remained at a high level, increasing from 0.915 to 0.999, while the coupling coordination degree rose from 0.508 to 0.789, evolving from borderline coordination to moderate coordination. The dominant obstacle factors exhibit notable succession characteristics, shifting from energy and water constraints to food subsystem pressures, and finally to water supply–demand imbalances. The coordinated development of Daqing’s WEF system is driven by three core forces: the oil and gas industry cycle, water resource regulation policies, and grain planting structure adjustments. These findings provide theoretical references and practical implications for optimizing resource management and advancing sustainable development in RBRs.

Water doi: 10.3390/w18202548

Authors: Yared Gebregziabher Manoj K. Jha

Reliable simulation of hurricane-induced flooding is challenging because rainfall–runoff generation, river flow, and floodplain inundation interact across large basins. This study evaluated the cross-event transferability of a fully distributed, two-dimensional HEC-RAS Rain-on-Grid (RoG) model for the Tar–Pamlico River Basin in eastern North Carolina. The model integrates terrain, land cover, soil-infiltration properties, and gridded rainfall within a hydrodynamic framework. It was calibrated using Hurricane Matthew (2016) and was independently validated for Hurricane Florence (2018) using unchanged parameters. Performance was assessed against observed discharge, flood depth, and inundation extent. Across streamflow gages, calibration yielded Nash–Sutcliffe efficiency (NSE) values of 0.73–0.99, coefficients of determination (R2) of 0.78–0.99, and ratios of root mean square error to observation standard deviation (RSR) of 0.10–0.51. Independent validation produced NSE values of 0.63–0.98, R2 values of 0.81–0.99, and RSR values of 0.15–0.60, indicating consistent performance despite differing hurricane rainfall and flood responses. The validated model was subsequently applied to a 500-year design storm to generate basin-scale flood-hazard information. The findings demonstrate that a calibrated basin-scale RoG model can retain useful predictive capability across independent hurricane events and support flood-hazard assessment and emergency planning in hurricane-prone river basins.

Water doi: 10.3390/w18202545

Authors: Angelos Chasiotis Dimitrios Piromalis Panagiotis T. Nastos

Water lost from distribution networks has already consumed electricity, but the associated greenhouse gas burden is rarely quantified, because water balances and organizational emission inventories use different boundaries. This study links the two within the Greek managerial-adequacy framework for a purposive sample of eight utilities and 14 utility-year observations (2024–2025). Electricity supply points are classified by activity and the attribution is graded, which isolates water-supply electricity from organizational totals that other activities can dominate: in one island municipality, fugitive emissions from solid-waste disposal make up 94% of the declared total. Water-supply energy intensity ranges from 0.538 to 2.434 kWh/m3 and operational carbon intensity from 0.198 to 0.895 kg CO2eq/m3 of system input. Under proportional average-intensity allocation, reported real losses carry 22.0–67.5% of each utility’s water-supply electricity emissions, or 2708 t CO2eq in the 2025 cross-section. These are accounting allocations from top-down water balances, not measurements of leak-specific energy use. A conditional screening shows that leakage reduction overlaps European public-investment carbon values only under stated unit-cost assumptions, and that the carbon case weakens as the grid decarbonizes while the water and electricity savings do not. The results support activity-level electricity reporting and the joint consideration of leakage, energy intensity, and system scale when mitigation measures are prioritized.

Water doi: 10.3390/w18202543

Authors: Hao Chang Linlin Xie Han Chai Zhengkang Zhang Jie Mei Guangjie Peng

To address diaphragm stress concentration and poor delivery stability in conventional diaphragm pumps, this study investigates an opposed balance pump equipped with a radial balance device. A dynamic mesh technique based on user-defined function (UDF) was integrated with a fluid–structure interaction framework, a spring-based smoothing model, and a local remeshing criterion to synchronize computational-domain motion with diaphragm deformation under large-deformation conditions. Numerical simulations were combined with particle image velocimetry (PIV) measurements around the umbrella valve to experimentally characterize local velocity distributions and vortex evolution. Six operating conditions from 0.2Q to 1.2Q were examined to characterize the coupled evolution of diaphragm stress, total deformation, and internal flow. The results show that the maximum equivalent stress and total deformation vary nonlinearly with flow rate. The diaphragm exhibits the most favorable mechanical-to-fluid load ratio and the most stable response at 0.6Q–0.8Q. Symmetrical radial flow channels and the radial balance device regulate internal flow organization and facilitate fluid load redistribution by improving pressure uniformity and reducing asymmetric hydraulic loading, thereby decreasing both the maximum diaphragm stress and its fluctuation amplitude. Vortex evolution and pressure pulsation are identified as the primary hydrodynamic mechanisms causing alternating diaphragm loads. This study provides a theoretical basis for radial balance structure optimization, diaphragm load regulation, and the development of highly stable diaphragm pumping systems with improved hydraulic stability.

Water doi: 10.3390/w18202546

Authors: Zahra Taghavi Zinjenab Elmar C. Fuchs Jakob Woisetschläger Luewton L. F. Agostinho Herman L. Offerhaus

This study combines experimental characterization, computational fluid dynamics (CFD) and magnetostatic modelling to investigate a rotating vortex-based nanobubble generator incorporating six permanent magnets. The combined approach distinguishes the hydrodynamic generation pathway from the possible role of magnetic fields in interfacial stabilization. Experiments were performed at 600 rpm and 25 °C using geometrically matched impellers containing either demagnetized inserts or NdFeB N45 magnets arranged in an alternating south–north (S–N) configuration. In two independent experiments, the mean NTA-derived apparent hydrodynamic diameter decreased from 211.2 and 141.7 nm in the controls to 88.2 and 76.9 nm under magnetic treatment, respectively, while detected particle concentrations increased from 9.17 × 107 and 7.48 × 107 to 1.70 × 108 and 2.45 × 108 particles mL−1. Both magnetic size distributions were strongly right-skewed, with skewness coefficients of 4.06 and 3.76, indicating a dominant small-size population with a persistent larger-size tail. In a separate measurement series using freshly generated samples, the mean zeta potential shifted from −4.70 ± 3.29 mV for the control to −35.30 ± 1.54 mV for the S–N condition. CFD predicted local velocities up to 1.57 m s−1 and a minimum gauge pressure of −156 Pa. The corresponding absolute pressure remained well above the vapour pressure of water, supporting vortex-driven gas entrainment, a modest reduction in equilibrium gas solubility and shear-driven fragmentation rather than conventional vapour cavitation. Magnetostatic modelling predicted local flux densities up to approximately 0.45 T. Scaling estimates indicated that direct magnetostatic stabilization, bulk magnetohydrodynamic forcing and simple Faraday-induced polarization were insufficient to explain the observed magnetic response. The results support a two-level interpretation in which vortex hydrodynamics drives generation, while magnetic exposure may influence interfacial stabilization, reflected most clearly in the more negative zeta potential. These findings provide a basis for further development of magnetic-assisted nanobubble generators for potential aeration and water-treatment applications.

Water doi: 10.3390/w18202544

Authors: Marin Ordulj Helena Ukić Boljat Eli Marušić Merica Slišković Maja Krželj

Sanitary wastewater discharges from recreational vessels are a difficult-to-quantify source of pressure in coastal anchorages because discharge events are intermittent, mobile and strongly dependent on user behaviour. We developed an integrated screening framework that jointly interprets environmental state (faecal indicator bacteria; FIB), pressure proxies (instantaneous vessel abundance and size structure), and behavioural/infrastructure context (a survey of wastewater systems and disposal practices). Ninety-six seawater samples from three stations were analysed for Escherichia coli and intestinal enterococci during 32 morning/afternoon campaigns. All individual samples were below the Croatian single-sample thresholds for excellent sea-bathing quality (E. coli < 100 and intestinal enterococci < 60 CFU/100 mL), although intestinal enterococci and E. coli were detected in 32% and 15% of the samples, respectively. The microbiological signal was descriptively stronger in the morning even though vessel abundance was substantially higher in the afternoon (121 vs. 266 vessels), and the highest FIB concentrations occurred at the southern low-local-pressure reference station, which had the fewest observed vessels (44). These differences were not statistically significant. Survey data showed that 82% of the respondents used vessels equipped with black-water-holding tanks, while marina pump-out facilities were used infrequently and disposal during navigation was reported more often. The integration therefore lies in triangulating non-equivalent lines of evidence: microbiological signals, observed boating pressure, and user/infrastructure conditions. This approach is intended for first-line screening and targeted monitoring, not for direct source attribution.

Water doi: 10.3390/w18202542

Authors: Longyu Li Ziyi Zhao Dan Zi Yu Sha Haijun Yan

A three-dimensional droplet motion model considering the rotational effect of the sprinkler tray was established in a fixed reference frame for low-pressure rotary sprinklers to reveal the effects of tray rotation of a rotary sprinkler on the flight trajectories of water droplets and spray uniformity. Conventional ballistic models for fixed sprinklers only incorporate radial and vertical ejection velocities and neglect the circumferential velocity generated by tray rotation, which cannot describe the circumferential deflection behavior of water droplets. The circumferential velocity induced by tray rotation was introduced as the initial boundary condition of the droplets, and an initial velocity model of the droplets leaving the tray, including radial, circumferential and vertical components, was constructed. Meanwhile, influences of air drag, gravity, buoyancy, ambient wind speed and evaporation on the droplet flight process were comprehensively considered. The fitting performance of Rosin–Rammler, Upper-Limit Log-Normal and Gamma distributions for droplet size was evaluated based on laser disdrometer measured data, showing that the Gamma distribution performed best and can serve as the droplet size input for trajectory and spray uniformity calculations. With droplet sizes and initial velocities defined, the Runge–Kutta fourth-order (RK4) method was adopted to solve three-dimensional trajectories, obtaining droplet distributions and uniformity coefficient through landing-point interpolation and grid statistics. Model validation results show that the simulated ranges of single water droplets agree well with the measured values, with relative errors all controlled within 6%. Further comparison of the spray characteristics between fixed and rotary sprinklers reveals that the circumferential initial velocity imparted to droplets by the rotational effect can significantly alter their spatial flight trajectories and landing point distributions, enabling droplets to complement each other in the circumferential direction and thereby enhancing the continuity of spray coverage. The single-sprinkler application uniformity coefficient was increased from 54.6% in the fixed state to 76.9% in the rotating state under the identical operating conditions. The findings can provide a theoretical basis and computational tools for analyzing the spraying mechanism, structural optimization and application uniformity improvement of low-pressure rotary sprinklers. Experiments in this study had no external wind speed criteria, but model development includes wind speed if relevant.

Water doi: 10.3390/w18202540

Authors: Claudiu-Marian Cristia Vlad-Florin Pîrăianu Sanda Budea Andrei-Mugur Georgescu Sanda-Carmen Georgescu

This study focuses on increasing the energy efficiency and reducing the operating costs of the pressurized irrigation system in Sabangia village in the Dobrogea region of Romania. The recently modernized sprinkler-based and drip irrigation subsystems, covering 1205 ha, receive water from a canal-pumping station (PS) commissioned in the 1970s. That PS features obsolete pumps and inoperable or miscalibrated instrumentation. To select new pumps to refurbish the PS, firstly, a hydraulic analysis-based design was conducted in EPANET 2.2 to assess system needs. Secondly, a renewable energy supply solution was identified to cover the PS’s electrical energy consumption: a grid-connected Canal-Top Solar (CTS) PV power plant, where all PV panels are placed on a steel-truss structure above and along the irrigation canal, which feeds the PS. Thus, solar energy can be harvested without affecting the agricultural land. Two CTS PV power plant solutions were analyzed, with different installed capacities: one with an installed capacity of 922 kWp (PV Park A), and the other twice as large with an installed capacity of 1843 kWp (PV Park B, representing the maximum capacity that can be installed on the targeted canal). The maximum amount of energy produced by each CTS PV power plant was assessed in PVsyst V7.1.0. Each grid-connected power plant was conceptualized as a large-scale agricultural prosumer, in which electricity generation is coupled with the electricity demand of the pressurized irrigation system, while surplus electricity can be exchanged with the grid. The electrical energy balance analysis showed that the proposed refurbishment solutions are sustainable: the PS energy consumption can reach a maximum of 655.31 MWh per year, while the maximum annual energy produced can reach 1442 MWh with PV Park A, or 2891 MWh with PV Park B; the surplus green energy can be injected into the grid. The financial impact of both agricultural prosumer cases was evaluated through an analysis of Day-Ahead Market costs versus revenues.

Water doi: 10.3390/w18202541

Authors: Jin Hou Yongheng Wang Xi Zhu Yashan He Tijian Zeng Yu Chen Qiaofeng Tan

The increasing integration of variable renewable energy (VRE) into power grids has significantly widened the peak-to-valley difference in net load and intensified its volatility. To follow these rapid load changes, cascade hydropower plants must frequently adjust their output, operate within unstable oscillation zones, or undergo repeated start-stop cycles. This creates a growing conflict between the system’s demand for peak shaving and the actual operational capabilities of hydropower plants. To address this challenge, this paper proposes a method for reconstructing the load curve based on fuzzy recognition of peak-valley characteristics. By adaptively adjusting the number of identified features, the method transforms the highly fluctuating net load into a multi-segment linear form. This preserves essential peak and valley information while promoting output stability. Building on this reconstructed load curve, a short-term peak-shaving model for cascade hydropower is developed, aiming to minimize the standard deviation of the residual load. The model is solved using an improved progressive optimality algorithm (POA) that integrates feasible region reduction with a multi-segment, variable-step-size search strategy. The peak-shaving performance is evaluated under three VRE penetration scenarios: low (10%), medium (20%), and high (40%). A case study conducted on China’s Wujiang River demonstrates the effectiveness of the proposed method. The load curve reconstruction transforms hydropower output from hourly sawtooth-like fluctuations into a stepwise pattern, albeit with a slight reduction in the peak-to-valley difference optimization rate (PVOR). For example, in the 10% penetration scenario, the frequency of output adjustments decreases by 73.2%. As the VRE penetration rate increases, the net peak-to-valley load difference grows sharply, and the PVOR of the reconstruction scheme declines from 26.70% to 9.12%. Nevertheless, the frequency of output adjustments does not exceed 15 times, thereby maintaining stable operation. The proposed approach achieves a reasonable trade-off between peak-shaving effectiveness and operational stability, offering a practical solution for hydropower dispatch in grids with high VRE penetration rates.

Water doi: 10.3390/w18202539

Authors: Andrea Scipilliti Antonia Granata Roberta Minutoli Gualtiero Basilone Rosalia Ferreri Giovanni Giacalone Ignazio Fontana Marco Barra Ylenia Guglielmo Andrea Geraci Alice Leone Aurora Piscitelli Angelo Bonanno Salvatore Aronica Letterio Guglielmo Simona Genovese

This study presents the first recorded observation of the calanoid copepod Calanopia elliptica (Dana, 1849–1852) in the waters between the southern coast of Sicily (Italy) and Malta, and the Central Mediterranean Sea in general. This area is characterised by heavy traffic of cargo ships passing through the Suez Canal to enter and exit the Mediterranean Sea. Moreover, water masses from both eastern and western basin flow through the Strait of Sicily and highly influence the waters surrounding Malta. These two aspects make this area suitable for the arrival of a vast array of lessepsian and Atlantic invaders, brought by current or ballast waters, or a combination of both. For this reason, a total of 32 zooplankton samples collected during the summer of 2025 were analysed for species diversity and abundance. A total of 133 organism taxa were identified to the lowest taxonomical level possible. General community analyses revealed that the composition of the zooplanktonic community across the study area is tied mainly to water column stability. The consistent frequency (53.13%) but relatively low abundances of C. elliptica (maximum 1.747 ind/m3) across multiple samples may indicate the onset of a new colonisation, as its known invasion range had previously been confined to the eastern basin of the Mediterranean Sea. Analyses suggest that the abundance of this copepod in the study area is mainly tied with low dissolved oxygen levels and temperatures, while seemingly unrelated to the other environmental parameters and to the time of the day in which it was sampled. These findings are just at the start of the analysis of a time series of zooplankton samples in the area. Hence, future studies based on it are necessary to identify trends in the abundance of this species over the past and future years, as well as any potential impacts on the native community.

Water doi: 10.3390/w18202538

Authors: Geng Qu Yiming Chen Hualong Luan Chengwei Hu Chengtai Zheng Hao Lin Hamidreza Rahimi

Understanding the morphological evolution and sediment transport characteristics of meandering rivers is crucial for river regulation and management. This experimental study employs the natural river model method in a 50 m × 6 m laboratory flume, with four groups of experimental models designed to investigate morphodynamic evolution and sediment transport characteristics under controlled hydrodynamic conditions. The input parameters of the physical model cover discharge rates (10–40 L/s), suspended sediment concentrations (0.6–1.4 kg/m3), hydro-sediment cycle frequencies (2–6 cycles per test), bed sediment grain sizes (0.2 mm and 0.5 mm), and longitudinal channel slope (0.001). Using advanced measurement techniques including acoustic Doppler velocimetry and automated topographic mapping, we systematically examined channel response to these varying hydro-sediment conditions. Results demonstrate that sinuosity development is enhanced by shorter hydro-sediment cycles and elevated sediment concentrations (reaching φ=1.35 in high-concentration scenarios), while excessive discharge suppresses meandering through overbank erosion and backwater effects. High-resolution velocity and sediment concentration measurements reveal a decoupling between flow and sediment transport pathways: as discharge increases, the main flow path shifts laterally toward the convex bank upstream of the apex but returns toward the concave bank downstream, while suspended sediment transport consistently deflects toward the convex bank with increased vertical dispersion. These findings provide fundamental insights into the fluid mechanical processes governing meander evolution, with significant implications for river engineering and morphodynamic modeling.

Water doi: 10.3390/w18202537

Authors: Zhiying Zou Ling Wei Low Fatehah Mohd Omar

Saline attached-growth biofilters serving live crustacean cultures are seldom characterised with the quantitative tools of biological nitrogen-removal engineering. Two saline moving bed biofilm reactors (MBBRs) serving live mud crab (Scylla paramamosain) cultures ran for 65 days at nominal hydraulic retention times of 60 and 120 min, as independent case trajectories, not a replicated comparison. Through the 35 days of live-animal loading, both held total ammoniacal nitrogen removal above 85%, including across reduced-feeding, molting, and post-molt phases, with effluent near 0.07 mg L−1. Batch assays at ammonia saturation gave zero-order kinetics, apparent activation energies of 40.2 (95% CI 33.5–46.9) and 54.1 (46.6–61.6) kJ mol−1, and temperature coefficients θ = 1.055 and 1.075. Tracer testing confirmed near-completely-mixed hydraulics, so the biofilm experienced the effluent concentration: the reactor oxygen-to-nitrogen ratio exceeded 60 g O2 (g N)−1, the ammonia-limited regime, in which tertiary MBBRs show first-order, transport-controlled behaviour and a near-unity apparent temperature coefficient. The batch coefficients therefore describe the biofilm at saturation, not the operational rate-limiting step. Dual controls attributed essentially all nitrification to the carrier biofilm. Saline MBBRs and crustacean recirculating aquaculture systems have each been studied separately; their combination supplies design parameters for a regime absent from freshwater and synthetic-feed datasets.

Water doi: 10.3390/w18202536

Authors: Hanlin Wang Tianhu Chen Mengxue Li Chang Liu Guoqing Xu Zijun Xiao Ruoqing Fan Zhengwei Pan Lanbao Zhu

Fe(III) is widely present in non-stoichiometric pyrrhotite (Fe1−xS, 0 < x < 0.125); however, its role in determining the catalytic activity of Fe1−xS remains unclear. Herein, Fe1−xS with varying Fe(III) were prepared via the sulfidation of goethite and the pyrolysis of pyrite at different temperatures, respectively, and subsequently employed to activate peroxydisulfate (PDS) for tetracycline (TC) removal. A combination of characterization and chemical analysis revealed that the Fe(III) content in sulfurized Fe1−xS and pyrolytic Fe1−xS decreased linearly with increasing sulfidation temperature (R2 = 0.9875) and calcination temperature (R2 = 0.9665), respectively. Electrochemical and zeta potential measurements showed that both the electron-transfer capability and surface electronegativity of Fe1−xS increased with increasing Fe(III) content. Importantly, in the Fe1−xS/PDS system, the Fe(III) content in sulfurized Fe1−xS and pyrolytic Fe1−xS was positively correlated with the second-order reaction rate constant (k2, R2 = 0.9276) and first-order reaction rate constant (k1, R2 = 0.9741) for TC removal, respectively, suggesting a clear structure-activity relationship between Fe(III) content and catalytic activity. Meanwhile, Fe release, reactive oxygen species (ROSs) generation, and PDS consumption increased with increasing Fe(III) content in Fe1−xS. In addition, sulfurized Fe1−xS and pyrolytic Fe1−xS show a wide pH operating range and moderate reusability. These findings provide valuable insights into the rational design of Fe1−xS-based catalysts for advanced oxidation processes to remove refractory organic pollutants.

Water doi: 10.3390/w18202533

Authors: Nathan Figueredo Samuel J. Bentley Giancarlo Portocarrero Faith Walton Jeffrey Duxbury Emily Wei Melanie Damour Ioannis Y. Georgiou Navid Jafari Kehui Xu Z. George Xue Zhengchen Zang

We present the first integrated regional subaqueous Mississippi River sediment budget to better understand how declines in sediment load from the Mississippi River over the 20th and 21st centuries contributed to the development and retrogradation of the submarine Mississippi River Delta Front (MRDF). This retrogradation can be partly attributed to downslope mass transport, which may move sediment more rapidly than replenishment from proximal fluvial sources. 210Pb/137Cs geochronology from 67 sediment cores was utilized to calculate apparent sediment mass accumulation rates (MAR) during the 20th and early 21st centuries. 210Pb and 137Cs regional maps documenting MARs from 1953 to 2025 were created to document sediment accumulation across the MRDF, which identified up to 73.8 Mt/y. A regional mass-accumulation budget for the subaqueous delta of this river-dominated system, when compared to mean 1939–2010 sediment discharge rates, indicates an approximate time-averaged retention of 25% of fluvial sediment discharge from major historical outlets on the MRDF. Furthermore, patterns of accumulation record the effects of major anthropogenic reductions in fluvial sediment load, as well as the complex interactions between oceanic and gravity-driven processes.

Water doi: 10.3390/w18202535

Authors: Parul Tiwari Tanishqa Goyal Don Kulasiri

In the original publication [...]

Water doi: 10.3390/w18202534

Authors: Yurong Li Xinyue Yang Ming Zeng Yanfei Yang Yinshan Xu

To mitigate water supply security risks induced by saltwater intrusion in the Yangtze Estuary during dry seasons, this study investigates the characteristics of low-flow runoff variation at the Datong Station and develops a one-dimensional hydrodynamic model for the reach from Yichang to Jiangyin. The model is used to simulate the discharge response at Datong under various augmentation release schemes from the upstream reservoir group, dominated by the Three Gorges Dam (TGD). Using the extreme drought event of 2022 as a validation case, we propose optimized freshwater replenishment strategies for salinity suppression. Key findings include the following: (1) The seasonal water-storage operation (i.e., storing wet-season water for dry-season use) significantly increases dry-season discharge at Datong and substantially reduces the frequency of extreme low-flow events. (2) The response time of the maximum influenced discharge depends primarily on the duration of augmentation; as the TGD release duration increases from 1 to 30 days, the peak influenced discharge at Datong appears between 12 and 33.5 days after the start of replenishment. (3) The TGD augmentation release exhibits a linear positive correlation with the maximum influenced discharge at Datong; when augmentation lasts more than 30 days, the replenishment efficiency stabilizes at 80–82.5%. Considering the long-distance runoff propagation time along the mainstream, a steady-discharge mode is recommended for salinity suppression. In emergency conditions, replenishment should be initiated at least 4 days in advance; if augmentation is to be maintained for 10 days, then reservoir regulation should commence 18–20 days before the anticipated saltwater intrusion event. Practical application during the 2022 drought confirms that coordinated augmentation from the upstream reservoir group effectively elevates discharge at Datong and pushes the saltwater front downstream, substantially extending the water intake window for estuarine water sources. The derived runoff response characteristics and optimized dry-season regulation schemes can improve water supply reliability for key water sources in the Yangtze Estuary, ensure water security for Shanghai and surrounding areas, and provide theoretical and technical support for joint salinity-regulation control and estuarine water security management.

Water doi: 10.3390/w18202532

Authors: Jihyeon Yun Si-On Seo Jong-Hwan Lee Woo-Chun Lee Sang-Woo Lee Do Hwan Jeong Yu-Yeon Jeong MoonSu Kim Soon-Oh Kim

This study investigated the hydrogeochemical and mineralogical factors governing the occurrence of U and Rn in a fractured granitic aquifer. A 120-m-deep borehole was drilled, and depth-discrete groundwater samples were collected during wet and dry seasons for analyses of water quality and naturally occurring radioactive materials; petrographic and mineralogical analyses were conducted on the recovered drill core. U and Rn concentrations reached 488.1 μg L−1 and 1549.8 Bq L−1, respectively, exceeding Korean drinking-water criteria. Both generally increased with depth and were lower in the dry season than in the wet season. Oxic, mildly alkaline groundwater with elevated HCO3− favored U mobilization through uranyl–carbonate complexation, whereas Rn was primarily controlled by fracture connectivity and mixing between shallow and deep groundwater. Microfractures and pores in metamict U–Th-bearing minerals provided reactive surfaces and release pathways that promoted U leaching and Rn emanation. The occurrence of U and Rn therefore reflects the coupled effects of hydrogeochemical conditions, fracture development, groundwater mixing, and the susceptibility of radioactive minerals to alteration. These findings provide a mechanistic basis for interpreting and predicting naturally occurring radionuclide behavior in fractured granitic aquifers.

Water doi: 10.3390/w18202531

Authors: Catarina Silva Rui Viegas Gabriela Faria Margarida Campinas Raquel Araújo Cláudio Costa Maria Rosa

A practical model to forecast the removal of contaminants of emerging concern (CECs) in activated sludge (AS) wastewater treatment plants (WWTPs) was developed. Eight full-scale campaigns were conducted in three AS-WWTPs (seven reactor datasets); 57 CECs were analyzed, 22 quantified in influent, and 13 CECs used for model calibration. The previously observed sigmoidal correlation between CEC removal and biodegradation rate (kbio) was validated and a pseudo-first-order kinetic model was adapted to include a lumped correction factor ‘a’ in addition to Mixed Liquor Suspended Solids (MLSS), Hydraulic Retention Time, and a CEC biodegradation constant (kbio). Model transferability was assessed using two WWTPs from a previous study. A global ‘a’ value provided a first approximation, while site-specific calibration improved R2 from 0.71–0.83 to 0.90–0.95. ‘a’ ranged from 0.19 (oxidation ditch; nitrification rate 5.8 g N-NH4/(kgVSS·d)) to 0.61 (anaerobic/anoxic/oxic AS system; 27 g N-NH4/(kg VSS·d)). The model supports AS operational scenario analysis and integration with advanced treatments to meet the 80% CEC (micropollutant) removal target of the revised Urban Wastewater Treatment Directive. In an illustrative ForecastTool scenario, increasing MLSS from 3 to 5 g/L increased AS removal of six CECs (from the twelve listed in the directive) from 32% to 45%, reducing the modeled ozone dose from 16 to 12 g/m3. The model requires site-specific calibration of ‘a’.

Water doi: 10.3390/w18202530

Authors: Dhruvojyoti Srivastava Vivek Agarwal Sujata Goswami

The Tigris and Euphrates river basin is among the most water stressed transboundary systems on Earth, yet observationally grounded, basin-resolved assessments of its groundwater have not kept pace with the deepening crisis of the 2020s. Here, we combine mascon solutions of total water storage anomalies from GRACE and GRACE-FO (CSR RL06.3, 0.25° grid) with GLDAS Noah v2.1 land surface storage to isolate groundwater storage anomalies, computed separately for each basin over 2002 to 2026. Anomalies are referenced to a 2004 to 2009 baseline and composited into hydrologic-year seasons. Both basins show sustained and highly significant decline. Total water storage fell at 0.95 and 0.75 cm per year in the Tigris and Euphrates, and groundwater was reduced by 0.83 and 0.65 cm per year (Mann–Kendall p < 0.001, robust to serial correlation). The groundwater residual accounts for about 87% of the total loss. Because it also contains unmodelled surface water, this is an upper estimate, but groundwater remains about two-thirds of the loss under a surface-water sensitivity analysis. The record contains two depletion phases, the 2007 to 2009 drought and a deeper decline after 2021, separated by a transient recovery in 2019 to 2021, with the Tigris depleting faster throughout. Groundwater loss in the Tigris accelerated from 0.88 cm per year over 2002 to 2020 to 2.83 cm per year over 2021 to 2025. Net wet season groundwater storage gain in the Tigris fell from 11.7 cm in 2005 to zero in 2025; across all years from 2003 to 2025, however, the gain shows no significant trend and closely tracks wet season precipitation (r = 0.83), so the 2025 minimum reflects the driest winter of the record rather than a loss of recharge capacity. Spatially, the deficits expanded from near neutral in 2005 to region-wide and severe by 2025 and were deepest along the northeastern Zagros margin. These results extend the established GRACE record of Middle Eastern depletion by more than a decade and show that depletion proceeds through a lowering of the whole seasonal cycle, with dry season losses exceeding wet season gains, which has direct consequences for transboundary water governance.

Water doi: 10.3390/w18202529

Authors: Tao Li Tao Xia Shuai Wang Yan Zhang Zhengjun He Suifeng Wang

Concrete-face rockfill dams (CFRDs) constructed in narrow valleys and on spatially heterogeneous foundations may experience nonuniform seepage and deformation, while local defects in the seepage-control system can further affect their operational safety. This study establishes a three-dimensional finite element model of the 90 m-high Yecha CFRD to systematically evaluate seepage behavior, stress–deformation response, face slab performance, and slope stability under normal, extreme-water-level, and representative defect scenarios. The seepage analysis considers different reservoir levels as well as peripheral-joint failure, face slab cracking at different elevations, and grout-curtain degradation, while the nonlinear mechanical behavior of the rockfill is described using the Duncan–Chang E–B model with parameters obtained from large-scale triaxial tests. Under normal storage, the seepage-control system remains effective, with a total seepage discharge of 3240.18 m3/d. The maximum dam settlement is 25.15 cm, corresponding to 0.279% of the dam height, and the slope safety factor is 1.48. Low-elevation face slab cracking is identified as a critical local seepage scenario, increasing the hydraulic gradient in the cushion material to 3.39, above the allowable value of 0.45. In addition, a 20% reduction in the mechanical parameters of the main rockfill zones increases the maximum settlement and face slab deflection by 84% and 74%, respectively, indicating a pronounced sensitivity to rockfill mechanical properties. Under the check flood level, the minimum slope safety factor decreases to 1.39 but remains above the code requirement. These results highlight low-elevation face slab integrity and rockfill compaction quality as key factors governing the seepage and deformation safety of CFRDs and provide a practical basis for defect-oriented monitoring and safety assessment.

Water doi: 10.3390/w18202528

Authors: Ali Raeisi Isa-Abadi Iman Ahmadianfar Miklas Scholz

Flood routing is a critical component of hydrological modeling and flood risk management. An improved biogeography-based optimization (IBBO) algorithm is proposed for determining the optimal parameter values of a multi-partition nonlinear Muskingum flood routing model. The evaluation was conducted for two model structures, namely, the three-partition (3P) and five-partition (5P) configurations, using three benchmark datasets: Wilson, Wyre River, and Viessman–Lewis. IBBO was compared with six algorithms—artificial bee colony (ABC), differential evolution (DE), grey wolf optimizer (GWO), chaotic salp swarm algorithm (CSSA), hybridizing sum-local search optimizer (HSLSO), and standard biogeography-based optimization (BBO)—using 30 independent runs for each case. Across the six benchmark scenarios, IBBO achieved the lowest best and mean SSQ values, with best SSQ values of 0.93, 5.99, and 9673.51 for the Wilson, Wyre, and Viessman–Lewis events, respectively. Moreover, IBBO provided an excellent fit to the hydrographs, with VarexQ values (variance explained) ranging from 99.62% to 99.99%, and substantially reduced the total absolute deviation (SAD = 3.11 for Wilson 5P and 9.83 for Wyre 5P) and the peak discharge error (DPO = 0.01). Across all benchmarks, the 5P configuration improved routing accuracy relative to the 3P configuration, owing to its greater model flexibility. Finally, the robustness of the proposed 5P configuration against over-parameterization is rigorously verified using an extended dataset from the Dinavar River, which provides a higher data-to-parameter ratio and confirms the model’s superior predictive accuracy. Overall, the results demonstrate that IBBO provides superior calibration accuracy and convergence stability for multi-partition nonlinear Muskingum models across the benchmark events investigated in this study.

Water doi: 10.3390/w18202527

Authors: Ta-Jen Chu Wen-Shu Huang Tian-Sheng Chen

Global demand for aquaculture and fishery products, as well as ecological and environmental sustainability, is driving the adoption of new technologies and processes in aquaculture and fisheries [1–7] [...]

Water doi: 10.3390/w18202525

Authors: Xiaorong He Yufeng Gong Dejian Zhang Lei Yang Hulin Guo Xiaoxue Ding Liang Qi Zehong Huang

Riverine carbon transport is jointly controlled by vegetation dynamics, hydrological processes, and reservoir operation, but these interactions remain difficult to quantify in data-limited mountain basins. In this study, we adopted a previously developed dynamic phenology-constrained SWAT-C model (DPC-SWAT-C) and applied it to the middle Jinsha River Basin. Annually varying start-of-season and end-of-season data were used as external inputs to constrain vegetation growth. The original SWAT-C and DPC-SWAT-C models were evaluated using monthly discharge and leaf area index observations, while total organic carbon (TOC), inorganic carbon (IC), and total carbon (TC) observations from two field campaigns in 2024 were used to evaluate spatial model performance. DPC-SWAT-C increased NSE from 0.22 to 0.64 for leaf area index, from 0.58 to 0.80 for TOC, from 0.68 to 0.82 for IC, and from 0.41 to 0.75 for TC, whereas discharge NSE remained nearly unchanged (0.762–0.764). The 2003–2024 simulations showed higher TC concentrations during the dry season and lower concentrations during the wet season. Under the reservoir-development scenario, downstream TC concentration peaks and temporal variability were reduced. Mean annual TC load at the reservoir outlet decreased from 2.729 × 106 to 2.238 × 106 t C yr−1, a reduction of 17.9%. These results show that observation-based phenological constraints improved vegetation and spatial carbon simulations in the basin and suggest that the planned Longpan Reservoir may reduce downstream carbon export.

Water doi: 10.3390/w18202526

Authors: Fayera Gudu Tufa Fekadu Fufa Feyessa Adisu Befekadu Kebede Wagari Mosisa Kitessa Seifu Kebede Debela Alemu Yenehun Thomas Hermans Kristine Walraevens

Volcanic aquifers are globally important groundwater resources, but their pronounced heterogeneity arising from lava emplacement, volcanic facies, structural features, and differential weathering makes hydrogeological characterization challenging. In many developing regions, limited field data further constrain aquifer characterization, increasing uncertainty in groundwater development and management. This challenge is evident in the Gilgel Gibe Catchment, where increasing groundwater demand and limited hydrogeological information require improved understanding of aquifer properties and productivity. This study characterized the aquifer systems of the Gilgel Gibe catchment primarily through lithological log and pumping test interpretations, supported by spring discharge measurements. A total of 30 deep boreholes were analyzed using pumping test data, including 14 with suitable recovery test data. Lithostratigraphic logs were integrated with diagnostic plots to identify aquifer conditions and select appropriate analytical solutions. The aquifer system is predominantly confined, followed by leaky-confined and locally unconfined conditions, interpreted using the Theis, Hantush-Jacob, and Neuman methods, respectively. Estimated transmissivity ranges from 3.9 × 10−6 to 1.3 × 10−2 m2/s, while spring discharges varied from 0.002 to 5 L/s. The Setema, Upper, Middle, and Lower Basalt, and Trachyte flows form low to moderately productive, fracture-controlled aquifers. The Lower Pyroclastic deposits and stratified tuffs form low-productivity aquifers due to the predominance of tuffs, while rhyolite exhibits low productivity due to the predominance of massive lava layers. Alluvial deposits form shallow aquifers dominated by intergranular porosity, underlain mainly by low-permeability tuffaceous materials. These findings provide a hydrogeological basis for guiding groundwater exploration, supporting well-field development, and informing sustainable groundwater management in volcanic terrains.

Water doi: 10.3390/w18202524

Authors: Qiang Han Mosammat Mustari Khanaum Yang Ou Xiaoyu Zhang Xinru Cheng

Assessing the impact of ecological water conveyance (EWC) on riparian vegetation is crucial for the management of ecological hydrology in arid areas. This study proposed a random forest model that considers time lag and cumulative effects to simulate the spatiotemporal response of vegetation to EWC. By designing comparative models, the advantages of time lag and cumulative effects in elucidating the sustained impact of groundwater and meteorological factors on vegetation were demonstrated. The RF model was integrated with the MODFLOW model, resulting in an improved RF-MODFLOW model; this model outputs groundwater depth and vegetation spatiotemporal distribution data. The RF-MODFLOW model has the advantages of a clear physical mechanism and concise structural design. Applications downstream of the Tarim River Basin (DTRB) have shown that maintaining or increasing the existing EWC volume can ensure the stable recovery of vegetation coverage density and range. However, if the EWC volume were reduced by 30% due to water scarcity, the vegetation would experience significant degradation once again. This proves that the ecosystem in the DTRB is fragile and its sustainability highly depends on EWC. By calculating the coefficient of variation, it was demonstrated that the impact of EWC on riparian vegetation decreases with increasing distance from the river channel, with the maximum impact range between 2000 and 2500 m. The combination of the RF-MODFLOW model and scenario analysis could provide scientific support for managing EWC.

Water doi: 10.3390/w18202522

Authors: Yong Xiong Zhongfa Zhou Xiaoduo Wang Wei Zhang Huijing Wei Yang Bai Mingyang An

Differences in the dissolution kinetics between dolomite and limestone constrain both the understanding of regional carbon cycling and the precision of speleothem-based paleoclimate reconstructions. To elucidate the mechanisms by which hydrogeochemical processes in a dolomite cave regulate dissolved inorganic carbon isotopes (δ13C-DIC), this study analyzed hydrochemical parameters and δ13C-DIC of five hydrological flow types, coupled with soil and cave CO2 and their isotopic compositions, based on monitoring data from 2019 to 2025 at Mahuang Cave (dolomite) in southwestern China, and compared them with six limestone caves. The results show that the hydrochemistry of Mahuang Cave is of the Ca·Mg-HCO3 type, with major ions exhibiting higher concentrations in the warm season and lower in the cold season, while δ13C-DIC is lighter in the rainy season and heavier in the dry season. On the interannual scale, δ13C-DIC shows only a weak correlation with ENSO phase variability, suggesting that the direct modulation of ENSO signals on the cave system is relatively limited. Water–rock–gas interactions and hydrological flow paths regulate the spatial gradient of δ13C-DIC (approximately 2.7‰): rapid fracture flow transmits light carbon signals of soil CO2 in an open system, slow matrix flow enriches heavy isotopes through enhanced prior calcite precipitation (PCP) in a near-closed system, and the underground river exhibits decoupling between Sr/Ca and δ13C-DIC due to multi-source mixing. Compared with limestone caves, Mahuang Cave is characterized by high soil CO2, low cave CO2, and heavier δ13C-DIC, which is attributed to the slow dissolution of dolomite, inhibited CO2 transport through thick overlying strata, and limited degassing due to low cave temperature. This study provides empirical evidence for understanding carbon cycling mechanisms in dolomite regions and emphasizes the need to account for lithological constraints.

Water doi: 10.3390/w18202523

Authors: Angelica Zizzamia Ângela Almeida Érika Sousa Rosanna Ciriello Sabino Bufo Vânia Calisto Filomena Lelario

This study evaluated and compared two distinct adsorbent systems for removing the phosphodiesterase type-5 (PDE-5) inhibitors sildenafil (SILD) and tadalafil (TAD) from water, using biomass-derived activated carbon (AC) and montmorillonite (MMT) in either its raw or didodecyldimethylammonium bromide (DDAB)-modified form. Spent brewery grains (SBG) were used as a renewable precursor to produce AC via conventional and microwave-assisted pyrolysis, while raw MMT and DDAB-modified MMT were investigated as alternative surface-engineered adsorbents. Batch adsorption experiments showed that AC produced via microwave-assisted pyrolysis exhibited higher removal efficiency under the investigated conditions compared with AC produced via conventional pyrolysis. Microwave-derived AC reached equilibrium within 2 h, achieving removal efficiencies of 90.3 ± 0.1% for SILD and 95 ± 2% for TAD. Under the specific adsorption conditions studied, the Langmuir-estimated adsorption capacities were 207 ± 10 mg g−1 and 119 ± 6 mg g−1, respectively. The DDAB-modified MMT also significantly outperformed the raw MMT, reaching equilibrium within 1 h, with removal efficiencies of 84.9 ± 0.1% for SILD and 91 ± 3% for TAD, and Langmuir-estimated adsorption capacities of 39 ± 3 and 38 ± 1 mg g−1, respectively. These results demonstrate that microwave-derived AC and DDAB-modified MMT represent adsorbent systems exhibiting different adsorption profiles and provide comparative information on the adsorption behaviour of materially distinct adsorbents for removing pharmaceutical contaminants from water.

Water doi: 10.3390/w18202521

Authors: Peifeng Han Wenrui Gao Song Gu Haitao Xu Shasha Yi Songbo Ren

Scaled flume tests based on Froude similarity (λ = 1:50) were conducted to clarify the internal stress-field evolution and multi-level protection mechanisms during flood scour of riverside highway embankments. An 18-channel miniature earth-pressure system embedded along the slope, with dual-view cameras, provided synchronous acquisition. Six non-replicated tests covered three protection levels (unprotected; semi-protected with gabion and geotextile; fully protected with an additional spur dike) at three flow velocities, yielding approximately 288,000 time-series readings (about 16,000 synchronous time steps). Scour failure followed a unified four-stage evolution: flow establishment and seepage onset, scour expansion and toe instability, progressive collapse and failure surface extension, and scour-hole stabilization with residual transport. Increasing velocity accelerated failure and shifted the mode from progressive toe scour to rapid retrogressive erosion. Protection structures exerted a dual effect, delaying failure at low velocities through weight stabilization and energy dissipation but potentially intensifying local scour at high velocities through flow concentration. Using internal earth pressure and higher-order statistical moments, a preliminary criterion distinguishing surface scour from internal erosion was proposed. The weight-stabilizing effect of the gabion self-weight was quantitatively characterized. AI1-13 was identified as a candidate early-warning sensor, and a dual warning signal (rise-then-fall and skewness reversal) was observed. A tentative three-level early-warning framework is proposed. Owing to the non-replicated, reduced-scale nature of the tests, these quantitative indicators are presented as preliminary bounds rather than validated field thresholds. The findings clarify embankment protection failure mechanisms and highlight the influence of hydraulic intensity and protection configuration on scour resistance.

Water doi: 10.3390/w18202520

Authors: Jiabao Yang Jun Zhang Shaonan Zhu

Drought risk under climate change depends not only on atmospheric forcing but also on how precipitation, snowpack, evapotranspiration, streamflow, soil moisture, and groundwater respond together. Using the severe 1960s drought as a baseline event, we examine hydrological responses to climate analogues of the 1960s drought in a regional hydrological domain of the northeastern United States. The integrated ParFlow-CLM model was driven at hourly, 1 km resolution with WRF pseudo-warming forcings for four scenarios: the historical 1960s drought (1961–1967) and future 2020s, 2040s, and 2090s scenarios. Model performance was evaluated against daily streamflow from 321 USGS gauges. Most gauges had correlation over 0.5 and absolute relative bias below 1, indicating that the model captured the main historical drought response. Under the pseudo-warming scenario applied here, future simulations showed higher precipitation and generally higher streamflow, but they also showed greater variability, with the 2090s producing the largest fluctuations. Warming sharply reduces spring snowpack, so that spring streamflow falls below the 1960s baseline despite wetter future conditions. Subsurface storage increases as precipitation and infiltration rise, contributing more baseflow to river. These results show the hydrological risk in these pseudo-warming analogues over the northeastern United States depends on the coupled response of snow, streamflow, and subsurface storage, rather than on precipitation alone, improving regional drought assessment and planning.

Water doi: 10.3390/w18202519

Authors: Ahmad Jamrah Tharaa M. Al-Zghoul Warqaa Th. Aness Zakaria Al-Qodah Ghanim Q. Al-Jameel Bilal Khan

The growing complexity and variability of industrial wastewater (IWW) require treatment strategies that can support reliable prediction, monitoring, optimization, and operational decision-making. Artificial intelligence (AI) and machine learning (ML) have increasingly been applied to these functions; however, the literature remains fragmented across pollutants, treatment processes, and modeling approaches. This study presents a critical bibliometric review of 151 Scopus-indexed publications on AI/ML applications in IWW treatment published between 2016 and 2025. Publication output increased substantially, reaching 35 publications in 2024 and 67 in 2025, compared with 1–4 publications annually during 2016–2019. China was the leading contributor with 54 publications, followed by India with 26, while Saudi Arabia and the United States each contributed 15. The main research directions included prediction and soft sensing, process optimization and control, monitoring and digitalization, adsorption and material-based treatment, membrane processes, and advanced oxidation and degradation. Artificial neural networks, support vector machines, random forests, and hybrid models were among the most frequently applied techniques. Study-level assessment of 38 technically assessable original AI/ML applications showed that 34 studies (89.5%) relied on offline or retrospective model evaluation, whereas only four (10.5%) demonstrated online or real-time AI/ML evaluation or operation. Conventional internal validation predominated among studies for which validation design could be established, while independent temporal, cross-domain, cross-scale, or field-based validation remained comparatively uncommon. Laboratory- and bench-scale applications were common, although several studies used full-scale industrial data. Major barriers to practical deployment include limited transferability across wastewater matrices, insufficient field-scale validation, inconsistent sensor and data quality, limited interpretability, and weak integration with treatment-plant control systems. Chemical oxygen demand soft sensing, pH and chemical-dosing support, and real-time monitoring and anomaly detection represent promising pathways for near-term implementation, while closed-loop control requires stronger validation of reliability, safety, and long-term performance. Overall, the field is transitioning from isolated, model-centered research toward system-level deployment, where transferability, validation, interpretability, and control integration are as important.

Water doi: 10.3390/w18202517

Authors: Akhmetkal Medeu Vitaliy Zhdanov Viktor Blagovechshenskiy Nina Pimankina

In the Republic of Kazakhstan, runoff in lowland rivers is 90% determined by snowmelt. Therefore, assessing snow reserves in a changing climate is of great scientific and applied importance. This work aims to assess how global climate change affects snow cover characteristics in Western Kazakhstan in the Caspian Sea basin. For the first time, we conducted a comprehensive assessment of snow cover depth, water equivalent, and snow cover duration in the drainage basin. We used statistical analysis of data from 50 meteorological stations for the period 1950–2024. Only data from 14 meteorological stations in the Mugalzhar lowlands (north of the Aktobe region) and on the Podural plateau (north of the West Kazakhstan region), where errors did not exceed 2–4%, were suitable for climate studies. The results showed an increase in average snow height by 3 cm, a decrease in maximum height by 4 cm, and a 17-day reduction in the duration of stable snow cover. However, these trends are not statistically significant (the coefficient of determination is 0.02–0.24), and their values fall within the statistical error. The calculated Pearson and Spearman indicators confirm a statistical relationship between individual global and regional climate indicators (correlation coefficients of 0.23–0.40 at the significance level p = 0.03). However, most snow cover indicators show no statistical dependence: correlation coefficients range from −0.02 to 0.20, with p = 0.30–0.90. The results obtained indicate a random, stochastic nature of the long-term dynamics of depth, water equivalent, and duration of snow cover in the region under study.

Water doi: 10.3390/w18202518

Authors: Xue Yu Fuyun Sun Zhiyong Yan Lin Luo

Aged landfill leachate is difficult to treat biologically because of its low biodegradability and limited carbon availability. Carbon-rich transfer station wastewater is a potential co-substrate, but its use in staged biological co-treatment requires evaluation. This study examined coagulation pretreatment of transfer station wastewater followed by co-treatment with aged leachate in a two-stage anoxic/oxic system. Water-quality and optical analyses showed differences in biodegradable-carbon availability and dissolved organic matter composition: protein-like components were more prominent in transfer station wastewater, whereas humic- and fulvic-like components predominated in aged leachate. During 60 d of operation, average removal efficiencies for chemical oxygen demand, ammonium nitrogen, and total nitrogen were 93.4%, 91.12%, and 85.0%, respectively. Amphiplicatus was among the dominant bacterial taxa, and unclassified groups dominated the fungal community. Defluviicoccus was relatively more abundant in the first anoxic compartment, whereas Candida was more abundant in the final oxic compartment. The results support the use of transfer station wastewater as a carbon-rich co-substrate for biological treatment of aged leachate.

Water doi: 10.3390/w18202515

Authors: Holger Manuel Benavides-Muñoz Leirys María Benavides-Ortega

Flood-risk index classification asks whether a classifier can distinguish high- from low-risk locations from composite risk indicators, and whether that ability survives contact with real geography. Six classifiers—Logistic Regression, Decision Tree, Random Forest, Gradient Boosting, LightGBM, and CatBoost—were benchmarked on a 1,117,957-record synthetic dataset (Resurrectum Diluvium, Kaggle); Logistic Regression achieved the highest AUC-ROC (0.93) by a small but significant margin, hypothetically attributable to the additive construction of the synthetic indices. The same pipeline was applied to the Federal Emergency Management Agency (FEMA) National Risk Index at county resolution (n = 3140), using a loss-per-exposure target after raw dollar losses proved population-correlated (r = 0.63). The ranking inverted: Random Forest reached AUC = 0.79 against 0.67 for Logistic Regression, and leave-one-region-out cross-validation collapsed every model toward chance (mean AUC 0.52–0.55). A census-tract replication within the same NRI framework (n = 84,034) reproduced the pattern: Random Forest again led under random splitting (AUC = 0.85), tree ensembles lost the most under spatial cross-validation, and Logistic Regression, weakest under random splitting, generalized best across untrained regions (mean AUC = 0.64). Across three stages and 1.2 million observations, random-split validation overestimated spatial transferability, which becomes visible only when geography is excluded from at least one evaluation fold.

Water doi: 10.3390/w18202514

Authors: Shynar Gabdulina Oxana Miroshnichenko Evgeny Sotnikov Kanat Kanafin Daniel D. Snow

Open-pit mines extending below the water table require continuous dewatering, which creates large hydraulic depression cones, reverses or accelerates natural gradients, and progressively mobilizes hazardous elements in groundwater through sulfide oxidation—effects that persist long after mine closure. The cessation of dewatering operations at the Nikolaevsky polymetallic open-pit mine in the Shemonaikha District, East Kazakhstan Region, Kazakhstan, in August 2012 terminated approximately 52 years of active dewatering (December 1960–August 2012), during which groundwater levels in the fractured Paleozoic aquifer were drawn down from a pre-mining static head of about +340 m a.s.l. by approximately 400 m. During the dewatering period, sulfide oxidation generated acidic metalliferous drainage in seeps, fundamentally altering the hydrochemical regime of the area. This study examines groundwater table recovery and subsequent hydrogeological changes under two scenarios. The first scenario, caused by the termination of mine dewatering and subsequent natural pit lake formation, focused on the evolution of groundwater levels, development of a pit lake, influence on regional groundwater flow, and potential impacts on the Ust-Talovka municipal reservoir intake located 3 km from the pit. The second scenario evaluates the co-disposal of local process tailings into the flooding pit as an alternative to surface tailings impoundment, assessing its effect on refill rate, water chemistry, and hydrogeological risk. Field surveys, hydrochemical sampling (62 water samples collected in July and October 2019), laboratory physicochemical modeling of tailings pulp–pit water interactions, water balance calculations, and a three-dimensional numerical groundwater flow model were employed to predict the consequences for local groundwater availability and quality. Pit lake water quality has improved substantially since dewatering stopped (pH increased from below 4 during mining to 6.85–7.29 by 2019); however, although metal concentrations have begun to decrease, Zn, Cd, Mn, and Pb remain above drinking water standards. Under median climatic conditions, the analytical water balance forecast indicates that the pit lake level will approach equilibrium at approximately +335 m a.s.l. after ~375 years; sensitivity tests show that the equilibrium level (≈320–340 m a.s.l.) and the filling time are strongly controlled by the adopted evaporation and precipitation values. In-pit tailings disposal shortens the filling period by approximately 12–15 years. Advective transport modeling over 200 years, under the stated conservative assumptions, predicts that metal plumes do not reach the Ust-Talovka municipal water intake, whereas a proposed alternative surface tailings facility would lie within the intake’s 200-year capture zone, which favors in-pit disposal of the tailings. These findings provide a scientific basis for post-mining hydrogeological risk assessment and demonstrate the utility of combined analytical and numerical modeling for evaluating pit lake evolution and tailings disposal options at comparable deep pits in arid continental climates, subject to site-specific verification.

Water doi: 10.3390/w18202516

Authors: Qi Li Xiaoyu Zhang Tingyu Shi Qixin Qiu Yang Ni Yanhong Feng Zhewei Hu Tianning Li Lingya Kong Aijing Yin Wenbing Ji Caiyi Zhao

Groundwater contamination at active petrol stations is a global concern, yet distinguishing natural hydrogeochemical backgrounds from anthropogenic signals remains challenging. We conducted a comprehensive survey at 21 petrol stations in central China, analyzing 62 groundwater and 21 soil samples for 45 parameters, including metals, BTEX, MTBE, petroleum hydrocarbons, and conventional ions. Using Positive Matrix Factorization (PMF) coupled with spatial statistics and hydrogeological analysis, we resolved four robust sources. Factor 1 (geological background) contributed 60–70% of Mn/Al and 48–93% (mean 68%) of the individual soil heavy metals. Factor 2 (reductive pollution) contributed 75–85% of NH4+-N, oxygen consumption (CODMn), and elevated Fe, exceeding 90% in certain hotspots. Factor 3 (petroleum hydrocarbons) contributed 75–85% to MTBE (mean 83%) and 50–65% to groundwater petroleum hydrocarbons (C10–C40; mean 58%), confirming point-source releases. Factor 4 (industrial solvents) dominated VOCs at an isolated site (92%). Conventional exceedance assessment misclassified geogenic Mn (26.2-fold exceedance, 62% natural) as high priority while underestimating anthropogenic NH4+-N (moderate mean exceedance, 81% human-derived). The “coarse-over-fine” stratigraphy controls spatial patterns, with low-permeability clay inducing long natural-attenuation lags (8–>30 years). We propose a source-differentiated management framework, transitioning from compliance-based to risk-based regulation. This approach provides a transferable paradigm for source apportionment in urbanizing regions facing similar contamination challenges.

Water doi: 10.3390/w18202513

Authors: Feng Han Tao Lin Fujie Li Zhe Hao Bin Ma Jinjie Wang

Long-term ecological water conveyance has been implemented to reconnect hyper-arid inland-river corridors, but ecological effectiveness cannot be inferred from delivered water volume alone. We assessed ecohydrological changes in the lower Tarim River from 2000 to 2023 using annual water conveyance records, groundwater observations, growing season Carnegie–Ames–Stanford Approach (CASA) net primary productivity (NPP), Landsat-derived Normalized Difference Salinity Index (NDSI), climate data, and four operational NPP-NDSI states. Annual conveyance averaged 4.08 × 108 m3 and peaked in 2017 at 12.09 × 108 m3. Mean groundwater depth decreased from 7.49 m in 2010 to 4.25 m in 2023. Current-inclusive multi-year conveyance windows were more strongly negatively associated with groundwater depth than same-year conveyance (W3: rho = −0.743; W4: rho = −0.782); Newey–West tests remained significant at lags 1–3, and moving-block bootstrap intervals excluded zero for W3 and W4, whereas the strictly antecedent three-year metric was less robust. The high-NDSI area decreased from 1795.04 to 42.19 km2, whereas the higher-productivity area increased from 91.81 to 1127.81 km2. A paired Enhanced Thematic Mapper Plus/Operational Land Imager (ETM+/OLI) analysis showed high NDSI correspondence (r = 0.980) but a mean OLI-minus-ETM+ bias of −0.0122; the corresponding 2010 cross-sensor adjustment was 63.9% of the absolute raw 2010–2015 mean-NDSI shift. Cross-era NDSI class areas and sampled-state trajectories are therefore treated as sensor-sensitive descriptive quantities. Spatial support sensitivity was also important: the functionally limited low-salinity state (FLLS) was the largest 2023 state on the fine-alignment grid (53.93%), whereas the higher-productivity low/moderate-NDSI state (HPLN) became dominant after aggregation to 500 m (66.57%); so, no scale-invariant claim is made about the dominant 2023 state. A fixed-2000-land-cover CASA run produced no material change in NPP because the land-cover transitions represented in the common mask occurred among classes sharing the same NDVI endmembers and εmax. Overall, the results support asynchronous indicator change and a state-based monitoring framework, while temporal dependence, irregular groundwater sampling, residual spatial autocorrelation, cross-sensor discontinuity, and spatial support constrain causal and fine-scale inference.

Water doi: 10.3390/w18202512

Authors: Dariusz Wrzesiński Wiktoria Brzezińska Leszek Sobkowiak

Flood non-stationarity is usually assessed from annual maxima, which merge seasons and magnitudes and can conceal changes confined to one part of the extreme-value distribution. Here, the Mudelsee point-process framework—comprising peaks-over-threshold sampling, declustering, kernel estimation of the time-varying occurrence rate λ(t), bootstrap confidence bands, and the Cox–Lewis test—is combined with a fully seasonal design and three disjoint magnitude classes and applied to daily discharges during 1951–2024 from three contrasting Polish catchments: the lowland Mogilnica, the lake-district Rega, and the Carpathian Poprad. Seasonal thresholds Q80, Q90, and Q95, derived separately for the cold (November–April) and warm (May–October) half-years, yield 18 occurrence-rate panels. Two of these depart significantly from a constant rate in opposite directions: the occurrence rate of extreme (>Q95) warm-season floods declined in the Rega River (u = −3.171, p = 0.001; λ^ ≈ 1.20 → 0.45 yr−1) and increased in the Poprad River (u = 1.893, p = 0.029; ≈1.35 → 2.00 yr−1), whereas in the Mogilnica River, no panel reached significance. Only the decline in the Rega River survives within-river Benjamini–Hochberg correction (padj = 0.006); this is corroborated by classical trend tests, by the concordant sign of all six of its occurrence-rate panels (p = 0.031), and by a 33% loss of the warm-season quickflow volume. Both signals are robust to the declustering interval and to the bandwidth, but neither remains significant when the thresholds are allowed to track the shifting flow distribution, so they describe the frequency exceeding a fixed discharge rather than a change in the point-process intensity itself. A Monte Carlo power analysis shows that none of the sixteen non-significant panels contain an effect large enough to be detectable at its event count; these null results are uninformative rather than evidence of stationarity. Flood-regime change in Poland is thus season- and magnitude-specific, and largely invisible to annual-maximum analysis.

Water doi: 10.3390/w18202511

Authors: Changliang Ye Yuan Zheng Kan Kan Ran Tao Huixiang Chen

Hydraulic machinery has accompanied the development of human civilization from early waterwheels and Archimedean screws to modern pumps, hydraulic turbines, and reversible pump-turbines [...]

Water doi: 10.3390/w18202510

Authors: Wioletta Przystaś

As industrial wastewaters typically contain complex dye mixtures rather than individual compounds, their biological treatment is more challenging and environmentally relevant than the decolorization of single-dye solutions. This study evaluated, for the first time, the long-term performance of immobilized Polyporus picipes in the treatment of a mixture of azo, triphenylmethane, and anthraquinone dyes (1:1:1, w:w:w). The aim of this study was to investigate removal of that mixture by immobilized biomass of RWP17 strain under two aeration regimes. Process efficiency was assessed through decolorization performance, biomass growth evaluation, and ecotoxicological analyses using Daphnia magna and Lemna minor. Both aeration regimes achieved high and stable decolorization efficiencies over nine operational cycles. Periodic aeration provided treatment efficiency comparable to continuous aeration despite lower biomass concentrations, indicating more efficient biomass utilization and possible involvement of biotransformation in the process. In contrast to the persistent toxicity of dye mixture observed towards aquatic invertebrates, treated effluents exhibited low phytotoxicity despite repeated dye loading, suggesting that dye removal occurred predominantly through biotransformation rather than sorption alone. These findings highlight the potential of the relatively unexplored species Polyporus picipes for the treatment of complex dye mixtures and emphasize the importance of integrating ecotoxicological endpoints into process evaluation.

Water doi: 10.3390/w18202508

Authors: Wenhui Liu Lantian Guo Guizhang Zhao Chunyan Zhang Kui Suo Zhenzhen Qi Xiaochun Lv

Groundwater is one of the main water supplies for Zhengzhou City. Changes in groundwater depth negatively affect the water supply and geological stability of the city. Based on groundwater monitoring data from 1999 to 2024, this paper investigates the spatiotemporal changes in shallow groundwater depth in Zhengzhou and their driving factors. Trend analysis, ordinary Kriging interpolation, and Pearson correlation analysis were first employed to characterize the spatiotemporal evolution patterns of groundwater depth. A principal component regression (PCR) framework was then applied to reduce multicollinearity among hydro-climatic and water-use variables and to quantify their integrated relationships with groundwater depth at individual monitoring wells. The main findings are as follows: (1) Over the past 25 years, groundwater depth in Zhengzhou has gradually increased, with an average decline rate of 0.68 m per year. The most rapid increase occurred from 1999 to 2012. (2) Spatially, groundwater depth is greatest in the central urban area (average 35.2 m) and decreases with distance from the city center, forming a depression cone in the downtown area. (3) Anthropogenic factors dominate groundwater depth variation. Groundwater extraction shows a strong positive correlation with groundwater depth, and standardized regression coefficients indicate that domestic water consumption and groundwater supply are the key drivers of groundwater deepening and recovery, respectively. Rapid urbanization has led to water table decline, while changes in precipitation have had relatively minor effects. (4) Socioeconomic factors, such as expansion of construction land, population growth, and industrialization, have also contributed to the increase in groundwater depth by raising water demand and reducing infiltration recharge. The PCR-based analysis provides a parsimonious and spatially explicit basis for understanding groundwater-depth dynamics in a rapidly urbanizing plain city and offers practical guidance for targeted groundwater management, extraction control, and ecological water replenishment in Zhengzhou and similar regions.

Water doi: 10.3390/w18202503

Authors: Carlos J. A. Campos Sarah Purnell Kata Farkas

Sanitary surveys support the classification of shellfish harvesting areas and the design of microbiological monitoring programs under European shellfish hygiene legislation. These surveys identify sources of fecal contamination and assess the effect of environmental factors on shellfish water quality. This study presents a scoping review of 110 sanitary survey reports from seven European countries (Scotland, England, Wales, Ireland, France, Denmark and Portugal), covering the period 2007–2026. Reports were identified from websites of research organizations, regulatory agencies, and technical contractors responsible for sanitary survey preparation, and screened against inclusion criteria based on regulatory requirements and methodological detail. A structured data extraction framework based on the PRISMA-ScR extension for scoping reviews was used to harmonize survey components across reports. Extracted variables included catchment characterization, wastewater treatment and discharge reporting, meteorological and hydrodynamic assessment, shoreline survey implementation, justification of representative monitoring points, and design of monitoring plans. Substantial heterogeneity in report content and analytical approaches was observed. Rainfall was considered in all 110 reports, but formal statistical evaluation of relationships between rainfall and microbiological contamination was undertaken in 43/110 reports (39%). At least one statistically significant rainfall–microbiology relationship was explicitly reported in 36/110 reports (33%). Hydrodynamic modelling was used in 53/110 reports (48%), with substantial variation among jurisdictions. While all surveys identified potential sources of fecal contamination, the inclusion of quantitative indicators such as wastewater population equivalents, discharge characteristics and statistical rainfall analyses varied considerably. Hydrodynamic assessments ranged from descriptive tidal characterization to model-based dispersion analyses, and the justification of monitoring locations and harvesting area boundaries differed across reports. These results indicate that sanitary surveys are not methodologically standardized across the jurisdictions included in this review. Greater harmonization of reporting standards and environmental analysis could improve transparency and comparability in shellfish classification systems and overall shellfish hygiene.

Water doi: 10.3390/w18202509

Authors: Monika Liugė Jurate Kumpiene Ivan Carabante Elena Servienė Dainius Paliulis

This study systematically compared six electrode materials: BDD, MMO, graphite, aluminum, iron, and titanium for the electrochemical treatment of aqueous solutions containing CR, NGB, Rh B, and MB. The dye concentration (10 mg L−1), supporting electrolyte (0.25 M NaCl), and nominal current density (13.0 mA cm−2) were kept constant, while electrode geometry, total current, and operating voltage differed among systems. Maximum decolorization efficiencies of 31–99.5% were observed after 60 min. BDD, MMO, and graphite produced the highest decolorization of CR, Rh B, and MB, whereas NGB was the most resistant dye (31–42%). Estimated specific electrical energy consumption at 60 min was approximately 12–15 kWh m−3 for BDD, 2.22–2.96 kWh m−3 for MMO, 3.46–4.33 kWh m−3 for graphite, 4–6 kWh m−3 for aluminum and iron, and 28–30 kWh m−3 for titanium. Because UV–Vis absorbance primarily reflects loss of chromophoric structures, the results are interpreted as decolorization rather than proof of complete degradation or mineralization. Graphite therefore represents a promising low-cost candidate for further evaluation, particularly with respect to durability, mineralization, transformation products, and performance in real textile wastewater.

Water doi: 10.3390/w18202505

Authors: Mengxia Zhou Ang Gao Zhun Xu Miaomiao Wu Shenao Lang Jie Gao Jicun Huang Song Xue

To clarify airflow allocation and its driving mechanisms in a complex ventilation system during multi-tunnel flood discharge, a prototype-scale three-dimensional air–water two-phase flow model was developed for the three spillway tunnels and the complete ventilation system of the Baihetan Hydropower Station. The model included the upstream reservoir, three spillway tunnels, multi-level ventilation passages, and downstream channel, and was evaluated against prototype air-discharge measurements and outlet surface-velocity observations. At the normal pool level with all three spillway tunnels fully open, the Y-shaped ventilation tunnels, upper-section ventilation adit, and steep-slope-section ventilation tunnels accounted for 17.1%, 37.0%, and 45.9% of the total air inflow, respectively. Although individual ventilation components showed different inter-tunnel allocation patterns, their combined effects produced similar total air discharges among the three tunnels. Flow separation and vortices in the Y-shaped ventilation tunnels reduced the effective flow area, producing local peak air velocities approximately twice the cross-sectional mean. In the upper-section ventilation adit, axial momentum, branch-turning resistance, and the terminal boundary jointly produced sequential flow diversion that increased from Spillway Tunnel No. 3 to No. 1. Air discharge through each branch in the steep-slope section was jointly controlled by the effective pressure difference and passage resistance. Compared with external independent air supply, intake from the tunnel-roof airspace reduced aerator air discharge and shortened aeration cavities. Although the results are specific to the Baihetan configuration, they highlight the need to evaluate complex spillway-tunnel ventilation systems using their complete connected geometry rather than isolated ventilation branches.

Water doi: 10.3390/w18202506

Authors: Dong Yeol Lee Kyong Oh Baek Young Do Kim

River confluences are highly heterogeneous hydraulic environments where flows with different discharges and temperatures merge, generating complex three-dimensional flow structures and thermal mixing that directly influence downstream mass transport, water quality, and aquatic ecosystems. In this study, a three-dimensional numerical model was used to investigate flow structures and thermal mixing at a 90° open-channel confluence. The study was designed to systematically examine how changes in discharge ratio modify three-dimensional flow and thermal mixing under the same channel geometry and total discharge, and how these responses differ between isothermal and non-isothermal conditions. Four main-to-tributary discharge ratios were combined with two thermal conditions. In the isothermal condition, the main channel and tributary had equal inflow temperatures. In the non-isothermal condition, the main channel inflow was 10 °C warmer than the tributary inflow. Eight cases were analyzed quantitatively in terms of the spatial trajectories of the maximum-velocity and thermal cores, momentum ratio, densimetric Froude number, mixing index, and gradient Richardson number. The results showed that the initial position of the maximum-velocity core was governed primarily by the relative momentum of the two incoming flows, whereas density and buoyancy effects induced by the temperature difference developed progressively downstream, indicating distinct spatial ranges over which momentum and buoyancy influenced the flow. When tributary momentum was substantially dominant, rapid initial mixing occurred together with a spatially extensive density-inversion structure. In contrast, when main-channel momentum was dominant, stable density stratification developed and delayed thermal homogenization. These results suggest that thermal mixing at river confluences with temperature differences is governed not by buoyancy alone, but by the interaction between the relative momentum of the main-channel and tributary flows and buoyancy. In particular, even under the same temperature difference, variations in discharge ratio altered the relative importance of inertia-driven three-dimensional rearrangement of the incoming water masses and density stratification, thereby producing distinct thermal-mixing characteristics. This study provides a quantitative basis for interpreting thermal mixing at river confluences in terms of the coupled effects of flow structure, momentum, and density-driven processes.

Water doi: 10.3390/w18202507

Authors: Pengfei Hou Shuangming Wang Enke Hou Dong Feng Xiaoshen Xie Mingyi Cui

The development height of the water-conducting fractured zone (HWCFZ) serves as an important basis for the prevention of mine water disasters and assessment of water resource impacts. In recent years, with the increasing adoption of super-wide coal mining longwall panels with a width exceeding 300 m, studies on their HWCFZ have been limited and relevant field measurement data remain sparse. This study aimed to determine the development HWCFZ in super-wide longwall panels during the mining of medium-depth coal seams. The research area comprised the adjacent 01 and 02 fully mechanised longwall panels in Xiaobaodang No. 2 Coal Mine, China, with widths of 300 m and 450 m, respectively. The development HWCFZ was determined via drilling exploration and numerical simulation. The results revealed that compared with the conventional longwall panel with a 300 m width, the HWCFZ in the central area and near the boundary roadway area increased in the super-wide longwall panel with a 450 m width. The HWCFZ increased by 6.4 m and 5.9 m, corresponding to growth rates of 11.3% and 8.4%, respectively. The HWCFZ in the boundary areas of both longwall panels was greater than that in the central areas, exhibiting a saddle-shaped distribution characterised by lower values in the middle and higher values on both sides along the inclination direction. According to the numerical simulation results, the width of the coal mining face exhibited a nonlinear positive correlation with the maximum HWCFZ. A width of 300 m represented the threshold at which the rate of increase of the HWCFZ began to decline, whereas a width of ~450 m represented the critical threshold beyond which the HWCFZ tended to stabilise. These findings offer valuable insights for the accurate prediction of the HWCFZ in super-wide longwall panels, the prevention of mine water disasters and assessment of water resource impacts.

Water doi: 10.3390/w18202504

Authors: Zuping Zhang Pingheng Yang Wenjing Guo

Comparisons of Cambrian-hosted brines across sedimentary basins are complicated by differences in initial salinity, host lithology, hydrogeological setting, and later fluid circulation. We compiled TDS, major-ion concentrations, stable water isotope values (δ18O and δD), and available 87Sr/86Sr ratios for 164 published hydrochemical records from the Sichuan and Tarim basins, Siberian Platform, Illinois Basin, St. Lawrence Lowlands, and Baltic Basin. The records were assigned to nine basin or sub-basin comparison groups. Total dissolved solids (TDS), Cl− concentration, the ρ(Cl−)/ρ(Br−) mass ratio, and the n(Ca2+)/n(Mg2+) molar ratio differed significantly among the groups. Aggregation by well or identifiable hydrogeological unit retained significant differences in all four variables, while aggregation by source publication preserved the principal regional rankings (Spearman ρ = 0.85–0.98). Among records with complete major-ion data, Na–Cl facies characterized the plotted records from Sichuan, Tarim, Illinois, and the Baltic Basin, whereas Ca–Cl facies characterized most plotted records from the St. Lawrence Lowlands and the Siberian Platform. ρ(Cl−)/ρ(Br−) relationships in Tarim, central Sichuan, Illinois, and some Siberian records were compatible with an evaporated marine component. Elevated ρ(Cl−)/ρ(Br−) ratios in the St. Lawrence Lowlands and northeastern and eastern Sichuan were consistent with additional halite-derived chloride and later fluid modification, while the lower salinity of eastern Sichuan indicated additional dilution. Stable water isotope values indicated regional differences in meteoric-water influence and oxygen-isotope exchange, while available 87Sr/86Sr ratios distinguished basin-specific solute contributions. Together, the major-ion and isotope patterns organize regional brine chemistry along four interpretive dimensions: salinity acquisition, host–rock reactions, burial and hydrogeological confinement, and later fluid circulation. By integrating six Cambrian and Cambrian-connected aquifer systems within a comparative framework in which each record was traced to its original source, this study distinguishes shared hydrochemical characteristics from region-specific pathways of brine evolution.

Water doi: 10.3390/w18202501

Authors: Seong-Dae Moon Namhyun Kim Seong-Cho Jeon Su-Ok Hwang Byeong-Hun Han Dae-Sik Hwang Eun-Mi Kwon Jung-Suk Lee Young-Seok Han Baik-Ho Kim

Recurrent freshwater cyanobacterial harmful algal blooms (CyanoHABs) are often managed as isolated episodes. Rapid clearing can leave nutrient stores, sediment recycling, benthic recruitment, and food web instability largely unchanged. This critical narrative review summarizes intervention roles, failure modes, and monitoring needs using a structured inventory of 53 selected core sources, with contextual reviews and guidance. Searches covered PubMed, selected publisher interfaces, and citation tracing through 27 September 2026; the inventory is not an exhaustive or systematic evidence map. Of 30 empirical sources, only seven extend beyond six weeks, including one 56-day mesocosm, so evidence for sustained recurrence reduction is limited. We distinguish Tier 1 (prevention and ecological stabilization), Tier 2 (targeted response and localized exposure reduction), and Tier 3 (restricted emergency containment). The proposed Intervention Decision Audit adapts established adaptive management and impact assessment principles into a practical checklist linking the recurrence mechanism, study scale and follow-up, intervention choice, safeguards, responsible authority, exit conditions, and outcome evaluation. Its contribution is this explicit linkage for recurrent CyanoHAB decisions, rather than new principles of adaptive management. Success should be assessed through bloom recurrence and duration, toxin and exposure risk, ecological condition, and dependence on repeated emergency treatment. The checklist has not yet been prospectively validated in management practice.

Water doi: 10.3390/w18202502

Authors: Giulia Lussana Giulio Senes Natalia Fumagalli

This review examines how the hydrological performance of implemented, ground-based urban green and blue infrastructure (GBI) and nature-based solutions (NBSs) is monitored and assessed. It combines bibliometric mapping, a targeted systematic review, and an indicator crosswalk. The bibliometric dataset included 2426 publications, while the targeted review analyzed 12 empirical-monitoring articles and 7 assessment-framework publications. Empirical studies covered catchment and sewershed monitoring, practice-scale inlet–outlet monitoring, and local infiltration or media-hydraulic characterization. Frameworks instead interpreted hydrological evidence alongside broader planning, management, resilience, and governance objectives. The crosswalk compared thirteen water-related functions, of which six were shared between the two corpora. Infiltration was the only function for which the two corpora shared a closely related primary measurand, although even here they relied on different test designs and measurement resolutions. The other five shared functions corresponded functionally, but diverged in measurand, temporal basis, denominator, or comparator. The remaining seven functions were represented in one corpus only, accounting for 26 of the 66 empirical and 23 of the 42 framework indicator records.

Water doi: 10.3390/w18202500

Authors: Timothy Robson John Webb

Surface water level changes can alter nearby groundwater levels due to recharge or mechanical loading. It is important to distinguish these processes so that the groundwater recharge mechanisms are not misinterpreted. At Lake Tutchewop, a salt disposal basin in the Murray–Darling Basin of southeastern Australia, groundwater chemistry shows that recharge from the lake generally extends < 165 m laterally, but groundwater levels fluctuate synchronously with lake levels well beyond this distance. To determine whether this synchronicity is due to lake pressure loading, impulse response function (IRF) modelling was applied to groundwater level data from 41 monitoring bores that surround the lake. Models using three inputs (rainfall, evapotranspiration and lake levels) outperformed those using two inputs (rainfall and evapotranspiration) for bores up to ~5 km from the lake and up to ~75 m deep, far beyond the demonstrated extent of physical recharge from the lake. This confirmed that lake pressure loading has a significant influence on groundwater levels around Lake Tutchewop, raising the levels by up to 0.3 m close to the lake. The model results also showed that lake loading has a more substantial impact on groundwater in the confined aquifer beneath the lake, and on clay-dominated lithologies. The results have significant management implications, confirming that lake leakage affects a relatively small area and has little impact on nearby agricultural land.

Water doi: 10.3390/w18202499

Authors: Osama Harbi Omran Abdelhaleem Khader Issam A. Al-Khatib Yung-Tse Hung

The Jenin Industrial Free Zone Wastewater Treatment Plant (JIFZ-WWTP), an extended-aeration activated-sludge facility designed for domestic sewage, is required to serve an industrial catchment where unregulated effluents may enter without pretreatment. Because the plant was not yet operational, this study assessed its likely performance and shock-load vulnerability through dynamic simulation in GPS-X (v8.5, ASM1-based MANTIS), using a model calibrated on 728 laboratory measurements from a comparable operating plant (Jericho WWTP) and adapted to Jenin-specific conditions—an explicit methodological limitation. Under optimized steady state (RAS 460 m3/day, WAS 60 m3/day, capacity 1000 m3/day), the model indicated high simulated removals of TSS (95%), COD (90%) and cBOD5 (94%) but limited total-nitrogen removal (34%); simulated effluent COD (109 mg/L) marginally exceeded the Class C reuse target. A 1000 m3/day untreated industrial shock load over ten days drove near-complete nitrification failure, secondary-clarifier sludge washout and severe effluent exceedances (COD ≈ 8000 mg/L). Monte Carlo analysis showed that only 33% of influent scenarios meet the COD and cBOD5 limits simultaneously. Increasing the waste-activated-sludge rate was the most effective simulated recovery measure. These results, which require field validation once the plant is commissioned, indicate insufficient buffering against high-strength industrial inputs and support mandatory source pretreatment, continuous influent monitoring with early warning, and an anoxic stage with external carbon dosing.

Water doi: 10.3390/w18202498

Authors: Dong-Woo Jang Ki-Young Kim Kwon-Seok Kim

Water utilities increasingly manage residual chlorine, conductivity, turbidity and water temperature in district metered areas (DMAs) from continuous on-line analyzers rather than from grab samples. Every decision that follows, from adjusting booster chlorination to ordering a flush or sending a crew, assumes that the analyzers are reporting the truth. In the Incheon network studied here, one year of hourly data from five DMAs contained a network-wide telemetry outage, water-temperature readings of up to 4913 °C, negative chlorine values and a turbidity channel frozen for 46 h, none of which the supervisory system had flagged. This paper asks whether such sensor and telemetry faults can be detected automatically, within the hour, at an alarm rate a control room will accept, using only the hourly data the utility already archives. Eleven unsupervised detectors from three families, statistical charts on the current reading or on time-series residuals (Hotelling T2, MEWMA, seasonal profile, VAR residual, dynamic PCA), general-purpose outlier detectors (Isolation Forest, one-class SVM, local outlier factor) and small neural networks (LSTM autoencoder, prediction-residual LSTM, a compact Transformer autoencoder), were run under one protocol and judged against the real faults and 900 injected faults of four types, with performance expressed as the operator sees it: events caught, hours to detection, and false alarms per week, counted both as alarm hours and as separate alarm episodes, with bootstrap intervals. Every family caught the real faults (seven events from three independent incidents) within the hour. They differed on the injected faults (recall 0.28–0.63) and above all on false alarms: the two LSTM models raised 0.5–0.8 alarm hours per DMA-week, and the current-reading control charts raised 9–10; counted as separate episodes, the spread was only 0.4–1.5. The prediction-residual LSTM, the Transformer autoencoder and the VAR residual chart were on the recall–false-alarm frontier in 100%, 91% and 60% of bootstrap resamples, which places the advantage in the use of the signal’s recent history rather than in any model family, and the ordering held under tuning of the baselines, other thresholds and other window lengths. Frozen-sensor faults escaped every model and were recovered by a one-parameter constancy rule. Models trained on four DMAs transferred to the fifth with a recall loss of 0.02 provided the alarm threshold was set from at least one month of local data, and the autoencoder’s error decomposition named the faulted sensor in 84% of detected injected faults. The result is a monitoring layer that flags a failed analyzer or telemetry link within the hour, names the sensor, and separates a data problem from a genuine water-quality change before dosing, flushing or field visits are decided on; it does not see flow or pressure and cannot detect leaks or shutdowns.

Water doi: 10.3390/w18202497

Authors: Zhijun Zhou Wensheng Xiao Jia He Jinbao Chen Yandong Lang Zhonggai Zhao

The nonlinear dynamics and varying operating conditions of hydroturbine regulation systems pose significant challenges to accurate modeling and effective control. Controllers based on simplified models or local linearizations may deteriorate beyond their calibration regions, while conventional reinforcement learning methods often suffer from high exploration complexity and unstable training. This paper proposes a Deep-Koopman-based implicit structured Q-learning strategy (DK-ISQL) for nonlinear hydroturbine regulation systems. A bilinear Deep-Koopman model is developed to represent the effects of control inputs and operating conditions through explicit state transitions in a lifted space. Based on this structure, the action-value function is formulated as a quadratic function of the control input, enabling analytical action optimization without an additional actor network. DK-ISQL was compared with PID, LQI, Koopman-MPC, DDPG, TD3, and PPO on a nonlinear physics-based hydroturbine object under varying static heads and power reference steps, with reinforcement learning convergence evaluated over five random seeds. DK-ISQL achieved average active power MAEs of 0.1674 MW and 0.1369 MW in the multi-head and reference-step tests, respectively, representing reductions of 16.8% and 26.7% compared with PID, the best-performing baseline in both tests. Across five random seeds, all DK-ISQL runs reached and remained below the 0.40 MW active power MAE threshold, converging faster and more consistently than DDPG, TD3, and PPO.

Water doi: 10.3390/w18202496

Authors: Yu Zheng Jianyong Hu Gaohui Li Jinke Mao Jinfeng Hu Yubing He

Under large water level fluctuations, emergency pump shutdown in floating pump stations tends to induce severe water hammer oscillations, with consequences including excessive negative pressure, potential cavitation and water-column-separation risk, and uncontrolled pump reverse rotation; this seriously threatens the operational safety of water intake systems. We seek to develop an economical and effective water hammer protection strategy. Therefore, we study a long-distance water conveyance project with a floating pump station, establish a numerical model of hydraulic transient processes, and carry out a numerical simulation of a pump-trip water hammer, enacting a combined protection strategy that integrates rules on pump outlet valve closure and air vessels. Meanwhile, we analyze the regulation effects of key parameters, including air vessel volume, connecting pipe diameter, and water–air ratio (the ratio of initial water volume to initial air volume inside the air vessel), on the pipeline pressure and pump rotational speed. Overall, with the simultaneous shutdown of three pumps at the minimum operating water level, negative pressure seriously exceeds its limits in the absence of protective measures. In optimizing the valve closure rule alone, we can effectively suppress reverse pump rotation, but this fails to effectively address the issue of negative pipeline pressure. After introducing air vessels to form a combined protection system, the indicative negative-pressure severity in the pipeline significantly improves due to the synergistic effect of valve closure (suppressing reverse rotation) and air vessels (regulating the pressure). On this basis, we identify the best-performing option among the investigated cases, on the premise that a larger volume is economically unjustified, via multi-parameter comparative analysis. This consists of a two-stage valve closure rule (a 5 s fast closure duration + 80% fast closure angle + 35 s slow closure duration) alongside an air vessel with a 15 m3 volume, a 0.3 m connecting pipe diameter, and a 1:1 water–air ratio, and a terminal air valve with a 300 mm air intake diameter. This scheme balances hydraulic safety and engineering economy; the maximum pipeline pressure, minimum pipeline pressure, and maximum pump reverse speed all meet specification requirements, enabling risk control for the investigated pump-trip water-hammer conditions. These research findings provide a theoretical basis and technical support for the design of water hammer protection schemes in similar water conveyance projects at floating pump stations.

Water doi: 10.3390/w18202495

Authors: Zijun Xiao Jian Sun Binliang Lin Jiamei Wang

River water temperature (RWT) in the upper Yangtze River has been substantially altered by intensive reservoir regulation and climate change, yet the respective contributions of these drivers and their interactions are not fully understood. Here, we developed an attribution framework that integrates a watershed hydrological model, a hydrothermal dynamics model and multiple linear regression models to reconstruct RWT under a range of counterfactual scenarios. This framework provided estimates of driver contributions and elucidated the discharge- and temperature-mediated pathways through which RWT was modified. Results showed that climate change made the largest contribution to annual mean warming, accounting for approximately 49–56% of the observed increases. In contrast, dams dominated seasonal RWT changes. At the Three Gorges Reservoir (TGR) inlet, upstream cascade dams (CDs) cooled RWT by 0.77 °C in spring and warmed it by 0.74–1.02 °C in autumn and winter. At the TGR outlet, the TGR cooled RWT by 3.00 °C in spring and warmed it by 1.58–2.64 °C in autumn and winter. Pathway analysis further revealed two contrasting mechanisms through which upstream CDs regulate the TGR thermal effect: CD-induced discharge alterations generally attenuated the TGR’s thermal effect, whereas CD-induced changes in TGR inflow temperature generally amplified it.

Water doi: 10.3390/w18202494

Authors: Guillaume Deruy Mathias Monnot Marc Henry Sylvain Durécu Philippe Moulin

PFASs have emerged as contaminants of significant concern, drawing increasing attention from scientists, regulators, and industries worldwide. The presence of PFASs in effluents is described in terms of the following: (i) the quantity of PFASs in PFAS synthesis plants and in the pharmaceutical and agrochemical industries, assessed by considering their production volumes and their presence and distribution in effluents, as well as their purification or recovery using dedicated systems within the plants, and (ii) the types of industries using PFASs, such as the semiconductor manufacturing by photolithography, electroplating baths for chromium plating of metals, water-repellent treatments for paper, leather, and textiles, and the formulation of numerous products. This review provides a structured overview of operational and mature treatment processes of waters or effluents containing PFASs. Indeed, conventional water treatment technologies capable of removing PFASs are already commercially available. These include adsorption using granular activated carbon, Anion Exchange Resins, and high-pressure membrane filtration. However, these are separation-based processes that are primarily effective for long-chain PFASs and generate waste streams highly concentrated in PFASs. Currently, the only large-scale option for destructive treatment of PFASs in liquid, solid and possibly gaseous matrices is thermal decomposition in hazardous waste incinerators dedicated to the incineration of halogenated hazardous waste. The review will describe and provide an overview of the performances and operating conditions of all of these processes. It will finally technically, economically, and environmentally compare all the processes (alone and in combination) and open research perspectives in the field.

Water doi: 10.3390/w18202493

Authors: Sayat Alimkulov Lyazzat Makhmudova Elmira Talipova Lyazzat Birimbayeva Aliya Nurbatsina Oirat Alzhanov

Changes in climatic conditions are accompanied by a transformation of river runoff formation processes, while the direction and intensity of the hydrological response can differ significantly even between geographically adjacent river basins. The study aimed to conduct a comparative evaluation of the climate sensitivity of river runoff for six main rivers in the Shu–Talas water management basin to changes in air temperature and atmospheric precipitation. The study was based on long-term time series of monthly mean water discharge, air temperature, and atmospheric precipitation using correlation, lag, regression, and scenario analyses. Scenario modeling was performed for air temperature changes ranging from +0.5 °C to +3.0 °C and atmospheric precipitation changes from −30% to +30%. A pronounced spatial and seasonal heterogeneity of the climate response of the studied rivers was identified. Under the combination of ΔT = 3 °C and ΔP = +30%, the average relative change in calculated river runoff ranges from +2% for the Teris River to +49% for the Merke River. Under the combination of ΔT = 3 °C and ΔP = −30%, the most substantial decrease in average calculated river runoff was obtained for the Merke River (−43%), the Teris River (−40%), and the Koragaty River (−34%). Seasonal analysis revealed a significantly larger response amplitude in individual months. The maximum positive change reaches +93% for the Merke River in November and +52% for the Yrgayty River in October. For quantitative inter-basin comparison, integral climate sensitivity coefficients εT and εP were proposed. The highest absolute temperature sensitivity was established for the Teris River (εT = −6.31%Q/°C) and the Talas River (εT = +4.54%Q/°C). The maximum sensitivity to changes in atmospheric precipitation is characteristic of the Merke River (εP = 1.54% Q/1% P). These scenarios constitute a standardized climate sensitivity experiment designed for inter-basin comparison and should not be interpreted as projections of specific future changes in river discharge. The results reveal substantial inter-basin and intra-annual differences in the statistical sensitivity of river discharge to air temperature and precipitation, providing a comparative basis for identifying priority basins and seasons for further hydrological modeling and for informing the development of water management adaptation measures in the Shu–Talas basin.

Water doi: 10.3390/w18202492

Authors: Chundong Wu Jinku Liu Sijian Wang Zhanbin Guo Chenxi Li

Anaerobic digestion of high-lipid waste possesses substantial biomethanation potential. However, its stability is readily inhibited by the accumulation of long-chain fatty acids (LCFAs). In this study, pure stearic acid and oleic acid were employed as model LCFA substrates to simulate LCFA inhibition conditions, and the mitigation effects of Ruminococcus flavefaciens (R. flavefaciens) bioaugmentation on LCFA inhibition were systematically evaluated; metagenomic analysis was conducted to analyse metabolic processes. The results demonstrated that a 1% (v/v) R. flavefaciens addition increased cumulative methane yield by up to 270.9% compared to the LCFAs-only reaction. R. flavefaciens addition was associated with enhanced LCFA conversion and promoted acetate formation. Metagenomic analysis suggested shifts in microbial community abundance, with modest increases in β-oxidation-associated Syntrophomonas and the acetotrophic methanogenic archaeon Methanosarcina. Analysis of metabolic pathway-related enzyme genes revealed that R. flavefaciens addition was associated with higher abundance of key genes involved in LCFA activation, β-oxidation, and acetate-utilising methanogenesis, potentially contributing to putative LCFA conversion, alleviating LCFA inhibition. Concurrently, carbohydrate-active enzyme analysis revealed that R. flavefaciens addition elevated glycosyltransferase and carbohydrate esterase potentials associated with extracellular polysaccharide synthesis and substrate deacetylation, which may enhance substrate accessibility and biofilm formation, thereby sustaining metabolic continuity.

Water doi: 10.3390/w18202491

Authors: Shan Wang Jianxun Zhang Lizhen Wang Haifa Jia

Carbon and water systems exhibit complex synergies and trade-offs and are closely interconnected through the social water cycle. This study examines eight prefecture-level regions in Qinghai Province from 2010 to 2024. A comprehensive carbon–water evaluation system and coupling coordination degree (CCD) model were used to characterize the spatiotemporal evolution of carbon–water coupling coordination, while CatBoost-SHAP was applied to identify the main factors associated with coordination across water withdrawal, use, and discharge processes. The results show that: (1) the carbon–water CCD exhibited an overall fluctuating upward trend, with the comprehensive evaluation index of the carbon subsystem generally higher than that of the water resources subsystem; (2) coordination showed pronounced spatial heterogeneity, characterized by relative stability in high-level regions and gradual improvement in low-level regions; and (3) water resource use within the social water cycle was closely associated with carbon–water coupling coordination, with indicators related to agriculture, the forestry–animal husbandry–fishery sector, and water supply showing relatively high model importance. Accordingly, carbon–water synergistic management should improve water use efficiency in production sectors, strengthen matching between water supply and end-use demand, and implement differentiated management according to regional resource endowments, ecological functions, and socioeconomic development levels.

Water doi: 10.3390/w18202490

Authors: Hongzihui Deng Pingheng Yang Wenxian Du Dan Luo

The research objective is to constrain the genesis and evolution of medium–low temperature geothermal waters hosted in carbonate rocks within complex fault-controlled settings, which represent cost-effective geothermal resources yet remain poorly understood in terms of their hydrochemical behavior and recharge mechanisms. The methodology involves a comprehensive multi-isotopic and hydrogeochemical investigation of 17 geothermal water samples (13 hot springs and 4 wells) collected from southeastern Chongqing, southwestern China. Analytical techniques include ion chemistry, stable water isotopes (δDH2O, δ18OH2O), sulfate isotopes (δ34SSO4, δ18OSO4), and 87Sr/86Sr ratios, complemented by chemical geothermometry and principal component analysis. Field investigations and laboratory measurements were systematically conducted to ensure data robustness. The results, along with their implications, reveal several key trends. Isotopic altitude effects indicate that recharge occurs in mid-altitude mountains (elevations of 767–1267 m). Water–rock interactions are predominantly governed by halite and gypsum dissolution, with sulfate isotopes and 87Sr/86Sr ratios (ranging from 0.7090 to 0.7098) consistently confirming that Sr2+ and sulfate are largely derived from evaporite dissolution. Geothermometer calculations yield average reservoir temperatures of approximately 79.3 °C across the study area. Notably, during upwelling, mixing with shallow karst water results in an average cold-water fraction of 35% (up to 95% in the most diluted sample), substantially lowering its surface temperature. Based on these trends, a conceptual model is proposed wherein meteoric water infiltrates, is heated at depth, rises along fault systems, and undergoes continuous cold-water mixing during ascent. The significance of these findings lies in providing a refined understanding of geothermal water evolution in fold-thrust belts, thereby supporting the sustainable exploration and utilization of low-enthalpy geothermal resources in carbonate aquifers.

Water doi: 10.3390/w18202489

Authors: Sérgio Ricardo Toledo Salgado Teresa Viseu Elsa Carvalho

Consequence-based dam classification is central to dam safety management, yet screening and regulatory approaches often rely on proxy measures of downstream exposure without explicitly considering hydraulic severity or wave arrival time. This limits discriminatory capacity, particularly where detailed exposure, demographic, evacuation, and asset-level consequence data are unavailable. This study introduces the Assessment of Technical Simplified Consequences (AT-SAC), a screening-oriented framework using widely available geospatial data. AT-SAC integrates five dimensions—Population at Risk (PAR), Wave Arrival Time at Residences (WTR), critical infrastructure (INF), environmentally sensitive areas (ESA), and socioeconomic disruption (SD)—within hydraulically conditioned consequence zones. The internal behavior of the classification structure was evaluated across 592 logically admissible consequence combinations under the baseline and two alternative weighting schemes, showing limited sensitivity to the relative weighting of the two life-safety criteria. Applied to four dams in northeastern Brazil with contrasting structural and downstream exposure conditions, AT-SAC differentiated the cases across four consequence tiers, from Significant to Extreme. Compared with two Brazilian regulatory classification systems, AT-SAC provided greater differentiation by separating exposure magnitude from response-related constraints, supporting transparent consequence-based prioritization under limited-data conditions.

Water doi: 10.3390/w18202488

Authors: Qian Zheng Ningge Zhang Peize Yu

Under the dual stress of climate change and intensive human activities, vegetation dynamics in the Huaihe River Basin, a typical north–south climatic transition zone in China, merit close attention. Net Primary Productivity (NPP) serves as a core metric for characterizing ecosystem carbon-sink capacity and vegetation growth status. Elucidating its spatiotemporal patterns and driving factors is of great significance for regional ecological conservation and adaptive management. Taking the Huaihe River Basin as the study area, this study utilizes MOD17A3HGF NPP datasets and multi-source geospatial data spanning 2000–2024. Integrating trend analysis, the Hurst exponent, residual analysis, and the Geodetector model, this work aims to reveal the spatiotemporal evolution and prospective change trends of vegetation NPP, and to quantitatively identify the independent and interactive effects of climate, topography, and human activities on NPP spatial differentiation. The results show that: (1) Temporally, vegetation NPP exhibits an overall fluctuating upward trend, increasing from 370 gC·m−2·yr−1 to 475 gC·m−2·yr−1, with a multi-year average of 422.9 gC·m−2·yr−1. The period 2013–2014 marks a prominent inflection point for NPP growth. Spatially, NPP follows a distribution pattern of high values in the southeast and low values in the northwest. (2) NPP shows an increasing trend across 94.09% of the basin. Meanwhile, 86.27% of the study area is characterised by anti-persistence, i.e., historical vegetation improvement accompanied by prospective degradation risks, which poses substantial challenges to ecosystem resilience. (3) Climatically, precipitation exhibits strong positive correlations with NPP, followed by temperature. Topographically, the maximum NPP occurs within the elevation band of 500–1000 m and the slope gradient range of 25–35°. Human activities exert positive promotional effects over most parts of the basin, presenting a spatial gradient with high contributions in western mountainous regions, moderate contributions in eastern plains, and low contributions around urban peripheries. (4) Precipitation, elevation, and geomorphic type are the dominant driving factors. Most pairwise factor interactions produce enhanced explanatory power, among which the interaction between elevation and precipitation yields the highest explanatory capacity. This coupling reflects topographic modulation of hydrothermal conditions and the spatial redistribution of precipitation, which creates divergent water availability and vegetation habitats across terrain units. Population density exhibits weak explanatory power when acting independently; nevertheless, its explanatory capacity rises substantially after interacting with precipitation and elevation. This finding indicates that anthropogenic impacts on vegetation are embedded within specific natural environmental contexts.

Water doi: 10.3390/w18202487

Authors: Shu Gao Kejun Dong Liangwan Rong Ming Zhao

Granular porous media are widely used in groundwater, filtration, drainage, and packed-treatment systems, where pressure loss is commonly represented by macroscopic correlations or reduced pore-network conductance models. These approaches provide useful descriptions of hydraulic response, but the development of nonlinear behaviour across individual pore connections remains incompletely characterised. This study combines pore-resolved computational fluid dynamics (CFD), a Delaunay-based pore–throat–pore representation, and Gaussian Process Regression (GPR) to examine local pressure–velocity responses in four monodisperse sphere-packing realisations. The CFD-derived throat-centre velocity is used together with throat geometry, particle arrangement, and adjacent pore-body geometry to construct a common response mapping across the sampled flow conditions. The analysis reveals a broad distribution of pair-specific nonlinear transition susceptibilities and progressive, network-dependent activation as the inlet velocity increases. Particle arrangement shows the most persistent association with transition susceptibility, while the broader pore–throat–pore geometry contributes to the representation of local hydraulic response. Comparison with the bed-scale CFD pressure loss provides a descriptive, non-mechanistic quantitative cross-scale comparison: the extent of local activation and the relative quadratic contribution to the bed-scale response follow different packing-level orderings and are not directly proportional. The framework therefore provides a pore-pair perspective on heterogeneous nonlinear flow while remaining limited to the investigated packing realisations and the CFD-sampled response domain.

Water doi: 10.3390/w18202486

Authors: Markus Pichler Dirk Muschalla

In-sewer measurements provide valuable insights into urban catchment behaviour, but their interpretation requires distinguishing dry- and wet-weather contributions. This study presents a novel, parameter-light method for decomposing long-term flow and load-rate measurements into continuous dry-weather (DW) and wet-weather (WW) components. The approach combines characteristic diurnal patterns for different day categories with a time-varying DW level and a DW/WW indicator to estimate the DW contribution. This enables identification of WW event start and end and consistent separation of DW and WW contributions. The method was evaluated using three years of high-resolution in-sewer flow data; the corresponding COD load-rate series and a 12-year WWTP inflow series were also analysed. For the in-sewer flow data, the method achieved a root-mean-square error of 4.2 L/s at a mean DW flow of 38 L/s and reduced estimation uncertainty compared with a reference method. Multi-year observations improve long-term DW volume estimation, whereas shorter periods are suitable for estimating DW contributions to individual WW events. The method supports WW-event detection without rainfall measurements, separation of event-specific DW and WW loads and volumes, and reconstruction of continuous DW time series for subsequent modelling and analysis.

Water doi: 10.3390/w18202485

Authors: Minghua Luo Rui Ma Canming Yuan Zhiwei Ni Bibo Dai Jinxin Huang Xin Pan

Landslides pose severe threats to life and property, necessitating rapid and accurate identification for effective hazard assessment and emergency response. This study proposes an improved SegFormer model for precise landslide extraction from high-resolution remote sensing imagery. To address the limitations of existing segmentation methods in handling complex backgrounds and irregular boundaries, the proposed framework integrates several structural enhancements. These include a squeeze-and-excitation module to suppress background noise, an auxiliary edge-fusion branch to capture explicit boundary details, and an adaptive feature gating mechanism to refine feature representation. The model is trained using focal loss to mitigate class imbalance and employs a three-stage recognition process, culminating in post-processing with dense conditional random fields for boundary refinement. Herein, the experimental results on a dataset of 100 high-resolution satellite images demonstrate that this approach outperforms the classical U-Net architecture and traditional thresholding techniques. The model achieved an accuracy of 0.976, a precision of 0.918, a recall of 0.947, and an F1-score of 0.932. These findings confirm that the proposed method offers exceptional accuracy and robustness, providing an effective automated tool for large-scale landslide detection in complex terrain.

Water doi: 10.3390/w18202484

Authors: Naeman Tuyoleni Kapofi Manny Mathuthu

Primordial radionuclides (226Ra, 232Th, and 40K) occur naturally in varying concentrations within environmental media. Anthropogenic activities that disturb the Earth’s crust, such as drilling and mining, have the potential to alter the concentrations of these radionuclides in environmental compartments, including water and soil. Through various exposure pathways, naturally occurring radionuclides contribute to the radiation dose received by humans on a daily basis. The Groot-Aub settlement, located in central Namibia, relies heavily on groundwater as its primary water source. To meet increasing water demand, several boreholes have been drilled in the area over recent years. This situation necessitated the present study, which aimed to evaluate the concentrations of naturally occurring radionuclides (226Ra, 232Th, and 40K) and assess the associated radiological health risks in groundwater from the study area. A total of ten boreholes were sampled and analyzed for radionuclide activity concentrations using a high-purity germanium (HPGe) gamma-ray detector. The results reveal mean activity concentrations of 11.77 ± 0.86 Bq L−1, 6.24 ± 1.97 Bq L−1, and 780.30 ± 12.17 Bq L−1 for 226Ra, 232Th, and 40K, respectively. These mean values exceed the guidance levels established under the International Drinking Water Guidelines. The mean total annual effective ingestion dose (AEID) values for the four age groups are observed in the following order: children < teenagers < infants < adults (≤1 year, 1–12 years, 12–17 years, and >17 years, respectively). The mean total AEID for the adult age group is slightly higher than the worldwide Individual Dose Criterion (IDC) of 0.1 mSv y−1, whereas the corresponding values for the other three age groups remain within the recommended limit. Furthermore, the mean values of the hazard indices (Hex, Hin, Iα, and Iγ), as well as the mean absorbed dose rate (D), are all within their respective permissible limits. In addition, the mean annual gonadal equivalent dose (AGED) is 307.45 ± 11.26 μSv y−1, exceeding the globally recommended permissible limit. The mean excess lifetime cancer risk (ELCR) values range from 5.73 × 10−5 for the child age group to 1.26 × 10−3 for the adult age group. Only the mean ELCR value for adults exceeds the worldwide permissible limit, while the values for the remaining age groups are within acceptable levels. With the exception of the adult age group, the findings indicate that groundwater consumption in Groot-Aub is, on average, radiologically safe. However, the elevated AEID, AGED, and ELCR values observed for the adult age group suggest a potential risk of adverse radiological health effects, arising from the lifelong ingestion of radionuclides in groundwater and the cumulative effects of long-term radiation exposure. Consequently, periodic radiological monitoring of groundwater quality in the study area is recommended, together with appropriate mitigation and regulatory measures where necessary, to ensure the continued protection of public health.

Water doi: 10.3390/w18192483

Authors: Mantas Brazauskas Arvydas Povilaitis

Closed, low-exchange systems are promoted for sustainable intensification, yet recirculating aquaculture systems (RASs) and biofloc technology (BFT) are rarely compared on a common evidence base. This review compares them across water quality, growth, feed conversion, stocking density, biosecurity and sustainability, using African catfish (Clarias gariepinus) as a reference and appraising each claim against predefined criteria. Bibliometric analysis in two databases shows that the fields barely intersect (2.1% and 3.3% of corpora); tilapia and shrimp account for 85% of biofloc records against 1.9% for C. gariepinus, for which one indexed comparison exists. Of twelve claims appraised, three rest on no paired evidence and four on a single trial; only one carries high confidence, so condition-specific indications replace a general ranking. The best-supported difference is structural: BFT operates at roughly three to five times the suspended-solids load of RAS. BFT improved feed conversion in eight of ten trials, but this benefit is feeding-mode dependent: significant for the omnivorous species tested alongside African catfish but not for the catfish itself, whose case for BFT rests on expected capital and water savings, each reported in one trial, and robustness. Short trials largely capture establishment, not operation; whole-cycle trials on commercial species remain the priority.

Water doi: 10.3390/w18192482

Authors: Hardianti Alimuddin Kuriko Yokota Keita Nishi Widyastuti Kusuma Wardhani Minh Ngoc Nguyen Takanobu Inoue

This study quantified the linkage between the watershed abundance of agricultural mulch film and its accumulation along riverbanks in Hamada River catchment, Japan, by integrating riverbank monitoring, catchment-wide surveys, hydrological connectivity assessment, and delivery ratio estimation. Black film was predominantly associated with red perilla, while silver film was almost exclusively used for tobacco. Riverbank monitoring from 2023 to 2025 showed that mulch film contributed disproportionately more to surface area coverage than to weight density, reflecting its thin, sheet-form geometry. Its accumulation was significantly associated with episodic hydrological connectivity, whereas other macroplastics showed few significant hydrological associations. This study provides quantitative estimate of the delivery ratio of agricultural mulch films from agricultural land to river systems, a linkage rarely quantified in prior studies. Annual delivery ratio of silver film ranged from 0.17% to 0.31%, with the highest value in the year for the lowest watershed abundance, indicating that delivery was not determined solely by abundance. In 2025, the delivery ratios were 0.18% for silver and 0.06% for black film, both below 1% but differing by a factor of three despite black film’s greater watershed abundance. These findings highlight the need for an abundance-based plastic mulch management strategy at the catchment scale.

Water doi: 10.3390/w18192481

Authors: Wen Zhang Jianglong Cui Boxiong Cao Hui Li

Reservoir regulation changes downstream flow regimes, which affects pollutant dilution, residence time, transport, and ecological exposure in aquatic ecosystems. This study developed a Bayesian-network-assisted ecological reservoir operation framework to support monthly decisions under inflow uncertainty while balancing water-supply reliability and flow-regime protection. A genetic-algorithm optimization model was used to minimize a weighted objective combining the water-supply shortage index and the hydrological alteration degree. Optimized monthly release, water supply, and storage samples were then used to train a Bayesian network, with inflow and initial storage as input variables and release and water supply as output variables. The framework was applied to the Tanghe Reservoir, China, using the monthly inflow records from 1950 to 1969; the records from 1950–1964 were used for training and those from 1965–1969 for validation. Under the equal-weight baseline scenario, the optimization produced a shortage index of 0.060 and a hydrological alteration degree of 0.276. The Bayesian network reproduced the main optimized operating patterns and gave clear release probabilities under different inflow–storage combinations. These results show that the method can support reservoir operation decisions that balance the water supply and flow-regime protection. The method is most suitable for reservoirs where ecological risk is strongly affected by flow alteration and direct pollutant observations are limited.

Water doi: 10.3390/w18192480

Authors: Sandeepa Samarasinghe Anuradha Hewaarachchi Pansujee Dissanayake Shameen Jinadasa Upaka Rathnayake Rohan Weerasooriya

The Kelani River is one of the most important freshwater resources in Sri Lanka, supplying drinking water, supporting aquatic ecosystems, and sustaining industrial and agricultural activities. However, increasing anthropogenic pressures have intensified the need for comprehensive long-term assessments of river water quality. This study evaluated the spatio-temporal variability of six physicochemical water-quality parameters (pH, temperature, turbidity, chemical oxygen demand, dissolved oxygen, and chloride) using monthly observations from twelve monitoring locations covering January 2007 to May 2022, representing the most up-to-date long-term CEA monitoring record available to the authors at the time of data acquisition. An integrated statistical framework comprising correlation analysis, Granger causality testing, vector autoregressive (VAR) modelling, ARIMA and seasonal ARIMA (SARIMA) forecasting, K-means time-series clustering, Pettitt temporal homogeneity testing, changepoint detection, and regression kriging was applied to investigate temporal dynamics, predictive relationships, temporal stability, and spatial variability. VAR, ARIMA, and SARIMA were selected as interpretable baseline models for assessing lagged dependence and seasonal temporal structure in the monthly water-quality series; comparison with machine-learning and hybrid models was beyond the scope of this study. The best-performing imputation method varied among parameter–location series; for pH, the minimum RMSE values of the selected methods ranged from 0.07 to 0.27. Temporal forecasting performance was also strongly parameter- and location-dependent. For DO, test-set RMSE ranged from 0.69 to 1.33 mgL−1, whereas chloride forecast RMSE ranged from 5.60 to 838.56 mgL−1, with the largest error observed at Victoria Bridge, reflecting the pronounced variability of the downstream chloride series. After Bonferroni correction across the 360 directional parameter–site comparisons, only two Granger-predictive relationships remained statistically significant: COD → chloride at Maha Oya and temperature → pH at Kaduwela Bridge. The corresponding VAR models had R2 values of 0.20 and 0.25, respectively, indicating modest explanatory power, while ARIMA and SARIMA models provided satisfactory forecasting performance for several parameters. The Pettitt homogeneity assessment identified nine candidate shifts at the unadjusted 5% significance level, but none remained statistically significant after Bonferroni correction across the 72 parameter–location tests. Regression kriging provided an exploratory representation of spatial variability in water-quality characteristics along the river. Overall, the proposed framework provides a robust statistical approach for long-term river water-quality assessment and supports evidence-based monitoring, pollution management, and sustainable river basin management, contributing to Sustainable Development Goal 6.

Water doi: 10.3390/w18192479

Authors: Xinlin Zhang Jinbao Liu

In mountainous regions with uneven gauge coverage, satellite precipitation errors are amplified by nonlinear rainfall–runoff processes, while conventional hourly merging often relies on a single continuous regression that inadequately handles zero inflation and intensity heterogeneity. We propose a hierarchical intensity-aware framework comprising a wet/dry gate, a frequency-matched four-class intensity router, and a shared long short-term memory (LSTM) network with class-conditional outputs. In the upper Fujiang River basin, GPM, CMORPH, ERA5-Land and topographic variables were used as predictors; models were trained on 2010–2013, with 2014 retained for temporally held-out validation across point and areal scales, spatial cross-validation and streamflow simulation. Progressive ablation shows that intensity stratification drives the main point-scale gain (Kling–Gupta efficiency (KGE), 0.22 → 0.43), while temporal modeling improves held-out catchment-event performance (KGE 0.75). Oracle diagnosis identifies intensity routing as the main remaining bottleneck, and attribution and source-ablation analyses show that data-source value varies with prediction stage and evaluation scale. Hydrologically, merged precipitation raises the overall Nash–Sutcliffe efficiency (NSE) from −0.13 (GPM) and −0.21 (CMORPH) to 0.40 and reduces absolute peak bias from 52–55% to 32%. Routing discrimination remains the principal residual limitation under the present architecture.

Water doi: 10.3390/w18192478

Authors: Duygu Keskin Nilüfer Ülgüdür

The coexistence of dyes and phosphate in industrial effluents creates a treatment challenge because both contaminants can occur as negatively charged species while interacting differently with adsorbent surfaces. To explore a potential solution, this study evaluated magnesium oxysulfite/sulfate (MgOS) for methyl orange (MO) and phosphate adsorption under single- and binary-solute conditions. MgOS was characterized by complementary physicochemical and surface analyses, and adsorption equilibrium, kinetics, thermodynamics, pH effects, and competitive behavior were examined. MgOS exhibited a mesoporous, chemically heterogeneous structure and maintained effective adsorption over a broad pH range with an apparent pH-regulating effect. Adsorption capacities reached 50.6 mg g−1 for MO and 16.3 mg g−1 for phosphate in single-solute systems. MO reached equilibrium within 7–45 min and was generally described by pseudo-first-order kinetics. Phosphate required 150–360 min and showed concentration-dependent kinetic behavior, with PSO and Elovich models providing the best fits depending on the fitting approach and initial concentration. MO adsorption was spontaneous and exothermic, while phosphate adsorption was spontaneous and endothermic. Surface characterization supported electrostatic interactions, hydrogen bonding, and Mg-site coordination for MO, whereas phosphate removal involved ligand exchange, inner-sphere coordination, and Mg-O-P/Mg-phosphate-like species. Phosphate reduced MO adsorption by 11.9–30.7% in binary systems, while phosphate adsorption remained comparatively stable. MgOS therefore showed potential for simultaneous MO and phosphate removal under competitive conditions.

Water doi: 10.3390/w18192477

Authors: Jia Li Longhu Yuan Shiyu Mou Yanfei Yang Yuni Xu Zaini Chen Jun Zhang Yanjun Zhu

Joint refill of cascade reservoirs must balance flood control safety against water conservation and hydropower generation, yet conventional operation applies fixed flood-limiting water levels that ignore the time-varying nature of flood risk within a flood season. Existing refill optimization models rarely embed flood season staging as time-varying operational constraints, which limits their ability to capture stage-dependent flood risk and refill opportunity, particularly in cascades headed by a large regulating reservoir. This study develops a framework that identifies flood season stages via the mean change-point method across multiple hydrological stations, transforms the stage boundaries into time-varying water-level constraints, and embeds them in a genetic algorithm-based joint refill optimization model for the Dadu River cascade in southwestern China. Applied to a 65-year inflow record, the framework consistently identifies early August as the main-to-post-flood transition and a secondary autumn flood rebound from mid-September to early October. Relative to the design scheme based on approved conventional operating rules and fixed flood-limiting water level controls, the optimized operation increases the multi-year average total generation of the five-station cascade by 10.08%, from 507.98 × 108 kWh to 559.16 × 108 kWh, while achieving a 100% filling rate at the leading Shuangjiangkou reservoir and maintaining acceptable flood storage during the post-flood period. By demonstrating that within-year inflow trend substantially modulates refill outcomes, especially when annual inflow volumes are comparable, the framework offers differentiated refill strategies and a transferable approach for cascade systems with newly commissioned leading reservoirs in monsoon-driven basins.

Water doi: 10.3390/w18192476

Authors: Abin Raj Chapagain Iman Maghami Daniel P. Ames Sujan Chandra Mondol Nathan Swain Gustavious P. Williams

Evapotranspiration (ET) forecasts from the U.S. National Water Model (NWM) carry systematic biases that are most apparent in water-stressed, intensively managed regions. This study develops a machine learning (ML) post-processing framework that bias-corrects 1–7 day accumulated ET (ACCET) forecasts from the NWM medium-range configuration using NWM meteorological forcings, the raw NWM-ACCET forecast, and auxiliary spatial and temporal predictors. Three tree-based models—Random Forest (RF), XGBoost, and LightGBM—were trained on AmeriFlux eddy-covariance observations at four California model-development sites and evaluated using nested five-fold temporally blocked cross-validation with a ±7-day purge window; two additional sites were withheld for independent off-site validation. All three models substantially outperformed the raw NWM forecasts. Pooled out-of-fold performance across the four model-development sites yielded R2 values of 0.832–0.854 and mean-normalized root mean squared error (NRMSE) values of 0.427–0.460, compared with R2 = 0.086 and NRMSE = 1.206 for the raw NWM forecasts. LightGBM and XGBoost were favored over RF in this four-site out-of-fold evaluation. Independent off-site validation yielded R2 values of 0.796–0.874 and NRMSE values of 0.380–0.459, with RF showing the most robust overall performance. Converting ACCET to lead-time-specific increments revealed substantially stronger lead-time degradation than was apparent from the accumulated metrics. Feature-importance and SHapley Additive exPlanations (SHAP) analyses identified wind, lead time, seasonality, and radiation as dominant predictors. The framework offers a practical route to more reliable operational ET forecasts for water management, agriculture, and drought monitoring, with potential for extension to climatically similar regions.

Water doi: 10.3390/w18192475

Authors: Karol Plesiński Kacper Cedro

The aim of the study was to assess hydrodynamic conditions in the low-flow channels of the block ramps with regard to the migration potential of brown trout (Salmo trutta). The research was conducted on the Porębianka Stream, where a cascade of 25 block ramps had been constructed in the outlet reach to stabilise the watercourse’s longitudinal profile. The analysis was performed for all 25 block ramps, but the detailed presentation of the results was only shown for four of them (7, 13, 18 and 19). Field measurements were performed under four flow conditions, defined as low, medium–low, medium and high. The analysis included three parameters that determine the potential passability of migration: water depth, flow velocity, and the water-level drop between the stilling basin and the downstream reach. Flow velocities were assessed against threshold values that depend on the length of the section the fish must negotiate. The results showed that the mere presence of a low-flow channel concentrating the discharge does not guarantee the maintenance of ecological continuity in the watercourse. Under low-flow conditions, the main limiting factor was insufficient water depth. In contrast, at higher discharges, the dominant constraints were exceedances of permissible flow velocities and the absence of a continuous corridor of reduced velocity. The most favourable migration conditions were identified in the low-flow channel of block ramp nos. 7 and 19, from medium–low to medium flow and from low to medium–low flow conditions, respectively. Block ramps nos. 13 and 18 acted as complete barriers under all of the analysed water discharges. The assessment of the entire cascade demonstrated that when flow velocity, water depth and water level drop were considered simultaneously, only four of the low-flow channels (nos. 6, 7, 17 and 19) could be classified as passable or conditionally passable. The obtained results indicate the need for a comprehensive assessment of block ramps, including several flow conditions and the continuity of a potential migration trajectory. The modernisation of the most problematic channels should aim to increase water depth, reduce excessive flow velocities, reduce local water-level drops, and introduce a more diverse flow structure that resembles natural hydraulic conditions.

Water doi: 10.3390/w18192474

Authors: Yike Chen Yanbing Chi Penghong Li

Continuous river water-quality monitoring increasingly captures short-term fluctuations that are poorly represented by conventional static assessments, yet frameworks for translating high-frequency observations into interpretable dynamic water-quality states remain limited. In this study, we developed a state-based framework for dynamic water-quality characterization using continuous river monitoring data. Ecological water quality departure (EWQD) was first used to quantify deviations from background conditions, after which two complementary descriptors, exposure level (EWQDL) and exposure variability (EWQDV), were introduced to characterize the magnitude and temporal instability of water-quality departures. Their joint distribution was then used to construct a two-dimensional dynamic state space, from which four representative departure states were identified to describe distinct combinations of departure intensity and temporal variability. Machine-learning models were further employed to identify the environmental controls associated with transitions among these dynamic states. The results showed that 34.7% of monitoring days exhibited within-day transitions in water-quality states, demonstrating substantial short-term variability. Simulated conventional grab sampling failed to identify 18.8% of unfavorable water-quality states revealed by continuous monitoring, illustrating the information loss that can arise from discrete observations. The EWQDL–EWQDV state space distinguished persistent, transient, stable, and highly unstable departure regimes that could not be differentiated from departure magnitude alone. Hydrometeorological conditions, particularly antecedent rainfall and temperature, were the dominant controls on dynamic state transitions, whereas land use primarily regulated the background susceptibility of river systems to water-quality departures. These findings demonstrate that river water quality is better represented as a time-varying state process than as a static condition. The proposed framework provides a systematic approach for translating continuous monitoring records into interpretable dynamic states and offers a basis for more representative water-quality characterization and adaptive monitoring strategies.

Water doi: 10.3390/w18192473

Authors: Ruer Sun Zhun Xu Shiqiang Wu

Semi-enclosed bays subject to intensive thermal discharges present significant challenges in quantifying cumulative thermal effects and assessing thermal environmental carrying capacity. Taking Daya Bay as the study site, this paper develops a two-dimensional hydrodynamic–thermal coupling model using MIKE 21 FM to simulate the spatially integrated temperature rise field induced by four thermal discharge sources under a worst-case hydro-meteorological scenario—characterized by neap tide conditions and a low wind speed of 1.5 m/s. Model performance is rigorously validated against in situ monitoring data and Landsat-derived sea surface temperature observations. Building upon this validated simulation framework, the thermal environmental carrying capacity is quantified via the contour-constraint method, and the spatial compatibility between the simulated temperature-rise contours and designated marine functional zones is systematically evaluated. Results show the following: (1) Intake recirculation significantly reduces the effective thermal load discharged into the bay, and the 1 °C temperature-rise envelope is reduced by 49.2% after intake flow correction. (2) Under the benchmark parameter, the bay-scale thermal environmental capacity utilization rate is 90.7% with approximately 2000 MW residual capacity, and the comprehensive uncertainty range is ±13% to ±17% considering parameter sensitivity. (3) The 1 °C temperature-rise contour overlaps with the core protected area by about 8.7 km2, showing potential spatial conflict with ecological zoning. This study offers technical support for optimizing the spatial layout of thermal discharges and implementing total load control in semi-enclosed bays.

Water doi: 10.3390/w18192472

Authors: Feng Liu Lu Chang Huiyu Zhao Ruidong Jian Danjun Wang Zhigang Han

Semi-arid loess basins in the middle Yellow River have rapid runoff responses, short hydrological memory, and sparse gauging networks, so pooled metrics across all stations can conceal forecast failures in low-flow tributaries and during dry periods. This study proposes DaSTGODE, a data-augmented spatiotemporal graph ordinary differential equation model with a structural water balance constraint. DaSTGODE integrates directed advection–diffusion propagation, soil-moisture-limited evapotranspiration, and a recursive water balance within a unified framework, thereby closing the water budget at every forecast step through the model structure. A reference scenario with perfect meteorological forcing, DaSTGODE_pre, is also established. It supplies the decoder with meteorological conditions over the forecast window as future meteorological forcing and quantifies the potential contributions of future precipitation, air temperature, and potential evapotranspiration by channel. Using daily records from 10 stations in the Wuding River basin from 2006 to 2020, DaSTGODE is compared with long short-term memory (LSTM) and graph long short-term memory (GraphLSTM) models for 1-, 3-, 6-, and 12-day forecast windows. DaSTGODE increases pooled Nash–Sutcliffe efficiency (NSE) from 0.532 and 0.473 for the best baseline to 0.599 and 0.567 for the 6- and 12-day windows, respectively. Relative to the best baseline, DaSTGODE increases the 1-day station-macro logarithmic NSE (logNSE) from 0.266 to 0.612 and reduces the mean number of stations with a negative NSE in the 6-day window from 4.6 to 2.0. Under the reference scenario in which future meteorological conditions are known, DaSTGODE_pre increases the 6-day outlet NSE from 0.141 for DaSTGODE to 0.331, and future precipitation alone provides 94% of the gain obtained from all three meteorological channels. HBV virtual nodes yield only small improvements in metrics at gauged stations, but provide daily streamflow forecasts at the outlets of 16 ungauged subbasins. Taken together, these results show that, under the semi-arid and sparsely gauged conditions examined here, the complete physical graph ODE kernel mainly improves cross-station reliability and relative low-flow dynamics, while the perfect meteorological forcing experiment quantifies the contribution of meteorological information over the forecast period to accuracy at medium and long forecast windows and identifies the channels responsible for that contribution.

Water doi: 10.3390/w18192471

Authors: Suiju Lv Yingying Gao Wenguang Chen Dandan Liu

To mitigate the severe recirculation and sediment deposition induced by highly sediment-laden flow in the lateral-inflow forebay of the No. 3 Pumping Station in Hong sipu, Ningxia, within the Yellow River Basin, this study investigates the effects of different corner configurations of the left and right sidewalls on the hydraulic characteristics of the forebay flow. A three-dimensional numerical model was established using ANSYS Fluent, with the Realizable κ−ε turbulence model and the Mixture multiphase model for water–sediment two-phase flow. The numerical model was validated against field measurements, and the variations in the flow-field structure and flow velocity in the lateral-inflow forebay with different sidewall contraction angles were obtained. The results indicate that after the flow enters the forebay from the channel, it rapidly changes direction under the influence of suction from the pump units, resulting in clearly differentiated flow regions within the lateral-inflow forebay. A high-velocity flow region forms in the central part of the forebay, while two irregular vortices of different sizes develop on both sides. As the angle α at the left sidewall corner gradually decreases, both the area of the recirculation zone and the vortex scale are significantly reduced. When the sidewall contraction angle α is 0.12 °, the reverse-flow area in the forebay decreases by 36.04%, while the sediment accumulation area decreases by 17.81%, effectively alleviating sedimentation in the forebay of water-diversion pumping stations located on sediment-laden rivers. Furthermore, under the α = 0.12° condition, which exhibited the best hydrodynamic performance among the investigated cases, variations in the angle β of the right sidewall within the range of 50–84° produce no significant changes. The findings can provide guidance and reference for the design, renovation, and upgrading of similar pumping stations.

Water doi: 10.3390/w18192470

Authors: Holger Manuel Benavides-Muñoz

Daily precipitation projections for tropical high-altitude stations are critical for water resource management and flood risk assessment yet remain limited in data-scarce mountain environments. This study applies a chronology-preserving quantile delta mapping framework to the same four CMIP6 general circulation models under three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5), comparing a historical baseline (1981–2010) with a future period (2051–2080) at a high-altitude tropical station (2160 m a.s.l.) in southern Ecuador. Observations derive from the SC-PREC4SA homogenized daily precipitation product. Pre-correction evaluation across nine performance metrics shows that all raw CMIP6 outputs yield negative Nash-Sutcliffe Efficiency when compared against point-scale observations over complex terrain, consistent with the systematic wet biases intrinsic to coarse-resolution GCM grids. Composite ranking by KGE, NSE, and Pearson r identified MPI-ESM1-2-LR as the best-performing model (r = 0.830). Independent split-sample validation (calibration 1981–2000, evaluation on the withheld 2001–2010 period) confirms out-of-sample skill, with Kling–Gupta efficiency improving from negative values for every raw model to 0.60–0.76 after correction. Ensemble mean annual precipitation changes are modest and directionally mixed (−1.3% to +2.2%), while extreme-event indices show consistent tail intensification: 50-year daily return levels rise from 67.6 mm/day to 71.5–115.2 mm/day across models and scenarios. A two-way variance decomposition shows that inter-model structural uncertainty exceeds scenario uncertainty in every calendar month, averaging 71% of total variance against 5% for scenario choice and 24% for their interaction. A Mann–Whitney comparison pooling bootstrap replicates across models detects a statistically significant difference in return levels between SSP2-4.5 and SSP5-8.5, in contrast with the inconclusive result obtained from the four-model point estimates alone, illustrating the sensitivity of such tests to sample construction in small multi-model ensembles. The fully documented computational pipeline constitutes a transferable methodological framework for probabilistic precipitation projection in data-scarce tropical highland stations across the Andes, directly supporting local water-resource planning, agricultural scheduling, and flood-risk infrastructure design.