Water

20 pages, 27082 KB

Open AccessArticle

Optimization of the Symbiotic System Between Sulfate-Reducing Bacteria and Sulfide-Oxidizing Bacteria and Study on the Mechanism of Repairing Acidic Mine Drainage

by Yangyang Jiang, Junzhen Di, Yicheng Sun and Shengxia Huang

Water 2026, 18(16), 1985; https://doi.org/10.3390/w18161985 - 13 Aug 2026

Abstract

Acidic mine drainage (AMD) rich in heavy metals and sulfates causes severe environmental hazards. SRB and SOB are ideal remediation strains, yet their microaerophilic symbiotic metabolism and metabolite characteristics remain ambiguous. This study explores their symbiotic metabolic mechanisms, optimizing culture parameters via response [...] Read more.

Acidic mine drainage (AMD) rich in heavy metals and sulfates causes severe environmental hazards. SRB and SOB are ideal remediation strains, yet their microaerophilic symbiotic metabolism and metabolite characteristics remain ambiguous. This study explores their symbiotic metabolic mechanisms, optimizing culture parameters via response surface methodology and multi-objective genetic neural network algorithms. The optimal conditions are 32.60 °C, pH = 7.20, strain ratio at 1:1 and DO = 0.3–0.5 mg/L, achieving 80.27% sulfate removal and 60.60% elemental sulfur production. Under optimized microaerobic symbiosis, Cu²⁺, Zn²⁺ and sulfate removal rates reach 90.16%, 80.59% and 63.97%, with a S⁰ yield of 64.67%. SEM-EDS, XRD, XPS, and microbial diversity analysis verify that heavy metals are eliminated as metal sulfide precipitates, and most of the sulfate transforms into recyclable elemental sulfur. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

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Graphical abstract

23 pages, 45379 KB

Open AccessArticle

Rooftop Rainwater Retention Potential in Former Agricultural Areas Under a Changing Climate: A True Orthophoto-Based Assessment of a Suburbanizing Polish Village

by Tomasz Oberski, Renata Ďuračiová and Mohammad M. Jaber

Water 2026, 18(16), 1984; https://doi.org/10.3390/w18161984 - 13 Aug 2026

Abstract

Rapid conversion of agricultural land into low-density housing reshapes local water balances at a time when climate change is intensifying hydrological extremes in Central Europe. This study evaluates the rooftop rainwater harvesting (RWH) potential of a newly urbanized housing estate in Rokietnica (Greater [...] Read more.

Rapid conversion of agricultural land into low-density housing reshapes local water balances at a time when climate change is intensifying hydrological extremes in Central Europe. This study evaluates the rooftop rainwater harvesting (RWH) potential of a newly urbanized housing estate in Rokietnica (Greater Poland Voivodeship, Poland) using a publicly available true orthophoto (5 cm ground sampling distance) as a reliable geometric data source. Roof footprints of 41 single-family buildings (5305 m² in total) were manually vectorized in QGIS and combined with monthly precipitation recorded at the nearest meteorological station (Złotniki) in a simplified volumetric model (V = A × R × C, with C = 0.95). To place the single reference year (2021) in its climatic context, the full 72-year precipitation record (1952–2023) was analyzed using the Mann–Kendall test and Sen’s slope estimator. The results indicate a harvestable volume of approximately 2642 m³ in 2021 (53–73 m³ per building; mean 64 m³), with May and August jointly accounting for almost one-third of the annual total. Annual precipitation at Złotniki exhibits a statistically significant increasing trend (+1.29 mm yr⁻¹; p = 0.028) concentrated in winter and early spring, while summer totals remain trendless but highly variable. A monthly storage simulation driven by the recent 30-year record (1994–2023) shows that summer garden irrigation, the dominant practical application of harvested rainwater in Polish households, is considerably harder to meet from the roof alone than year-round indoor non-potable uses: a 5 m³ tank covers approximately 73% of the seasonal demand of a 100 m² garden plot, while a 3–5 m³ tank would theoretically secure 91–98% of toilet-flushing demand for a four-person household. Under Poland’s national rainwater co-financing scheme (formerly “Moja Woda,” active 2020–2024, succeeded by “Mikroretencja” from June 2026), simple payback periods of roughly 3–7 years make household installations financially defensible. The findings suggest that true orthophotos enable rapid, low-cost RWH assessments in dynamically developing suburbs, and that storage sizing should anticipate the ongoing seasonal redistribution of precipitation under climate change. To our knowledge, this is the first study to combine free national true-orthophoto imagery, a 72-year Mann–Kendall trend analysis, and a subsidy-linked storage-reliability simulation within a single suburban rainwater-harvesting assessment. Full article

(This article belongs to the Section Urban Water Management)

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26 pages, 13092 KB

Open AccessArticle

Analysis and Characterization of Sludge Produced by Natural Extract-Facilitated Electrocoagulation for Hardness Removal

by Neali Valencia-Espinoza, Brenda S. Morales-Verdin, Daniel M. Paredes-Molina, Fabricio G. Mendez-Landin, James McGree, Alain R. Picos-Benítez, Patricio J. Espinoza-Montero, Alejandro Vega-Rios, Ashantha Goonetilleke, Locksley F. Castañeda, Erick R. Bandala and Oscar M. Rodriguez-Narvaez

Water 2026, 18(16), 1983; https://doi.org/10.3390/w18161983 - 13 Aug 2026

Abstract

This study focused on the generation and characterization of sludge produced by electrocoagulation (EC) combined with Moringa oleifera seed extract (MOSE) to remove water hardness. First, an experimental data set was generated and used as the baseline data for mathematical modeling to identify [...] Read more.

This study focused on the generation and characterization of sludge produced by electrocoagulation (EC) combined with Moringa oleifera seed extract (MOSE) to remove water hardness. First, an experimental data set was generated and used as the baseline data for mathematical modeling to identify the effects of different parameters on Ca²⁺ and Mg²⁺ ion hardness removal. Then, using the generated data set, operational conditions were optimized using neural networks integrated with a genetic algorithm, resulting in the selection of Fe electrodes, 12.5 mL of MOSE per 100 mL of water, a current density (j) of 49.16 mA cm⁻², and a reaction time of 5.3 min, considering Ca²⁺ ions as the sample contaminant. Additionally, machine learning analysis identified contaminant type, reaction time, and cathode material as the most influential variables affecting sludge formation, with optimal conditions identified for both Ca²⁺ and Mg²⁺ ion systems. For all the mathematical models, experimental validation was performed. The MOSE extract was characterized for the presence of proteins, polyphenols, flavonoids, and polysaccharides, which provide functional groups that promote aggregation and floc development. Sludge characterization by FT-IR, TGA, and TEM revealed the formation of organic–inorganic hybrid matrices composed of biomolecules interacting with electrochemically generated Fe³⁺ and Al³⁺ species, as well as Ca²⁺ and Mg²⁺ ions. These results highlight the role of plant-derived biomolecules in modulating the sludge structure and composition, providing insight into the mechanisms of sludge formation and the implications for handling and valorization of EC-based water treatment systems. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

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21 pages, 13635 KB

Open AccessArticle

Multi-Year Variation Characteristics and Driving Forces of Groundwater Levels in the Yibin Area, Southern Sichuan, China

by Xiaobo Lv, Bin Liu, Jibin Chen, Kailong Wang and Jingwen Kang

Water 2026, 18(16), 1982; https://doi.org/10.3390/w18161982 - 13 Aug 2026

Abstract

To support groundwater protection and sustainable utilization in southern Sichuan, this study aims to clarify the multi-year variation characteristics of groundwater levels (GWLs) and identify their main driving factors in the Yibin region. In this paper, 2019–2024 GWL monitoring records, hydrometeorological data, and [...] Read more.

To support groundwater protection and sustainable utilization in southern Sichuan, this study aims to clarify the multi-year variation characteristics of groundwater levels (GWLs) and identify their main driving factors in the Yibin region. In this paper, 2019–2024 GWL monitoring records, hydrometeorological data, and multi-source geospatial datasets were integrated. Trend analysis, centroid migration modeling, continuous wavelet transform, Geodetector, and Fast Fourier Transform-based cross-correlation analysis were used to examine GWL dynamics and their controlling factors. The results show that GWL depth exhibits a distinct “shallow-northwest to deep-southeast” pattern, which is closely associated with regional aquifer lithology and hydrogeological conditions, with the most pronounced fluctuations occurring in the northwest. From 2019 to 2024, GWLs showed multi-scale periodic oscillations, with dominant periods of 50–64 months. GWLs in the red-bed region showed a continuous and slow decline, whereas those in the carbonate rock region remained relatively stable with a slight decreasing trend. Among the 13 hydrometeorological, geographic, and human activity factors, cropland area and precipitation had the strongest individual explanatory power. Their interactions with other factors produced nonlinear or bi-factor enhancement effects. The sustained expansion of cropland, together with declining precipitation, suggests that the observed phased and gradual decline in GWLs during 2019–2024 may be associated with a combined climate–human activity forcing mechanism. Annual GWL peaks were weakly and positively correlated with rainfall and temperature, while the lag between rainfall infiltration and GWL response varied with lithology. Full article

(This article belongs to the Section Hydrogeology)

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33 pages, 6924 KB

Open AccessArticle

Geochemistry of Methane and Sulfide Sulfur in the Bottom Sediments of Small Lakes in Southern Russia

by Dmitry Gar’kusha, Yury Fedorov, Yury Andreev, Asya Ovsepyan, Natalya Tambieva, Konstantin Dergachev and Boris Talpa

Water 2026, 18(16), 1981; https://doi.org/10.3390/w18161981 - 13 Aug 2026

Abstract

Small lakes are widespread, yet their biogeochemistry, particularly regarding greenhouse gases, remains insufficiently studied. This article presents the findings from an investigation of six small lakes in the Southern European part of Russia, conducted from September to October 2024. The primary aim was [...] Read more.

Small lakes are widespread, yet their biogeochemistry, particularly regarding greenhouse gases, remains insufficiently studied. This article presents the findings from an investigation of six small lakes in the Southern European part of Russia, conducted from September to October 2024. The primary aim was to examine the coupled distribution of methane (CH₄) and sulfide sulfur (a key metabolite of H₂S) in the lake sediments, in relation to geochemical parameters such as pH, Eh, sediment density, moisture, and the contents of sulfate ions (SO₄²⁻), organic matter, and granulometric composition. The studied sediment layers, reaching depths of up to 110 cm, consist primarily of silty clay. The lakes studied represent both freshwater (0.2–0.7 g/L) and brackish (1.3–24.2 g/L) systems. During the study period, the water column exhibited temperatures of 10.4–22.1 °C, pH values of 7.36–8.53, and dissolved O₂ concentrations ranging from 3.16 mg/L (34% saturation) to 11.79 mg/L (125% saturation). Methane concentrations in the water varied widely, from 1.6 µL/L to 37,380 µL/L. The lowest values were found in the highly mineralized Lake Bolshoy Tambukan (1.6–2.0 µL/L), while exceptionally high concentrations were detected in the bottom waters of the thermally stratified freshwater Lake Staroe. In the shallow, productive freshwater lakes, a significant portion of the organic matter undergoes limited mineralization in the water column and settles to the sediments as partially decomposed remains of sand- and coarse-silt-sized organisms. The subsequent degradation of this labile organic matter reduces bottom-water oxygen, triggering intense anaerobic processes in the upper sediment layer. In these freshwater sediments, where sulfate concentrations are relatively low, sulfate reduction is typically suppressed. Combined with an abundance of labile substrates, this condition fosters intensive methanogenesis, resulting in maximum CH₄ concentrations (33–179 µg/g). Under stable thermal stratification, such high CH₄ concentrations can also accumulate in the bottom water (e.g., up to 37. 4 mL/L in Lake Staroe), posing a risk of significant pulse emissions during autumn mixing. Conversely, the brackish Lake Bolshoy Tambukan exemplifies the crucial role of sulfate reduction, which is stimulated by sulfate-dependent anaerobic oxidation of CH₄. This process acts as a powerful natural biogeochemical barrier that curtails the emission of a major greenhouse gas. The sediments of this lake exhibited minimal CH₄ content (0.14–0.57 µg/g) alongside maximal sulfide sulfur concentrations (1.06–8.57 mg/g). Overall, this theoretical and experimental analysis demonstrates that sulfate reduction is a key determinant of redox potential, acid–base conditions, and the vertical distribution of CH₄ in the anaerobic sediments of small lakes in Southern Russia. Given the projected salinization of lakes in steppe and arid landscapes under climate change, a reduction in CH₄ emissions to the atmosphere is likely due to the enhanced sulfate-dependent anaerobic CH₄ oxidation associated with sulfate reduction in the sediments. Full article

(This article belongs to the Section Water Quality and Contamination)

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26 pages, 957 KB

Open AccessArticle

Study on the Measurement and Enhancement Pathways of Ecological Efficiency of Marine Fisheries in China’s Coastal Areas

by Xueqi Zhang and Siyan Zhu

Water 2026, 18(16), 1980; https://doi.org/10.3390/w18161980 - 13 Aug 2026

Abstract

Marine fisheries play a vital role in ensuring food supply and sustaining livelihoods in coastal regions of China. However, the expansion of aquaculture has led to increasing carbon emissions and mounting pressure on resources and the environment, making the improvement of ecological efficiency [...] Read more.

Marine fisheries play a vital role in ensuring food supply and sustaining livelihoods in coastal regions of China. However, the expansion of aquaculture has led to increasing carbon emissions and mounting pressure on resources and the environment, making the improvement of ecological efficiency a critical issue for the sustainable development of the industry. From the perspective of carbon emissions as undesirable output, this paper employs the DEA-SBM model and the GML index to measure the ecological efficiency of marine fisheries across nine coastal provinces in China from 2006 to 2023. Furthermore, using fixed-effects models, mediation-effect models, and grouped regression models, this study empirically examines the impacts of fishermen’s income and environmental regulations on the ecological efficiency of marine fisheries and their transmission mechanisms. The results indicate that ecological efficiency exhibits fluctuating trends across provinces, with significant inter-provincial disparities. Fishermen’s income has a significant positive effect on ecological efficiency, while environmental regulations show a significant negative effect. Digitalization level significantly promotes ecological efficiency, whereas fishery disaster losses significantly inhibit it. Technological adoption intention plays a partial mediating role in the pathways through which both fishermen’s income and environmental regulations affect ecological efficiency. Significant regional heterogeneity is observed, with the eastern coastal region exhibiting the strongest effects of various factors and the northern coastal region showing the weakest. Accordingly, this paper proposes differentiated enhancement pathways for ecological efficiency from four dimensions, including technological innovation-driven development, industrial structure optimization, environmental policy regulation, and regional coordinated governance, with the aim of providing theoretical foundations and policy references for the low-carbon transformation and sustainable development of marine fisheries in China’s coastal areas. Full article

(This article belongs to the Special Issue Governance of the Marine Ecological Environment and High-Quality Blue Development)

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16 pages, 3650 KB

Open AccessArticle

TiO₂ or ZnO Nanoparticles Assembled into Zn/Al-Layered Double Hydroxides for Removal of Phosphate Species from Water

by Andres Sanchez Garcia, Adalberto Zamudio-Ojeda, Gregorio Carbajal-Arízaga, Daniel Ramírez-González, Danny Reible, Santiago José Guevara-Martínez and Cesar Gómez-Hermosillo

Water 2026, 18(16), 1979; https://doi.org/10.3390/w18161979 - 13 Aug 2026

Abstract

Phosphorus is recognized as one of the primary contributors to eutrophication in freshwater ecosystems. Among the various strategies proposed to mitigate its impact, adsorption-based removal has emerged as one of the most widely adopted and effective approaches globally. In this study, Zn/Al-layered double [...] Read more.

Phosphorus is recognized as one of the primary contributors to eutrophication in freshwater ecosystems. Among the various strategies proposed to mitigate its impact, adsorption-based removal has emerged as one of the most widely adopted and effective approaches globally. In this study, Zn/Al-layered double hydroxides (LDHs) were synthesized by varying the molar ratio of cations to obtain materials with different cationic densities. The materials were additionally modified via a co-precipitation method to incorporate titanium dioxide (TiO₂) or zinc oxide (ZnO) nanoparticles to synthesize novel composite nanomaterials aimed at phosphate species removal from aqueous solutions. The resulting materials demonstrated orthophosphate adsorption capacities exceeding 45 mg/g in most cases. Adsorption kinetics were evaluated using pseudo-first order and pseudo-second order models, while equilibrium data were fit to the Langmuir and Freundlich isotherms. The results indicated that the pseudo-second order model and the Langmuir isotherm provided the best fit, suggesting that the adsorption process is predominantly chemisorption occurring on a homogeneous monolayer. These findings highlight the potential of TiO₂/ZnO–LDH composites as efficient adsorbents for phosphorus remediation in aquatic environments. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Pollution-Driven, Persistent, and Emerging Threats to Urban Surface Water Quality)

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24 pages, 26408 KB

Open AccessArticle

Historical and Contemporary Impacts of Land Use on the Functioning of the Fraxino-Alnetum Community in the Biała Przemsza River Valley (Case Study, Southern Poland)

by Oimahmad Rahmonov and Agnieszka Czajka

Water 2026, 18(16), 1978; https://doi.org/10.3390/w18161978 - 13 Aug 2026

Abstract

River ecosystems play a key role in both natural and urbanized environments, acting as essential links in ecological systems. However, they are increasingly exposed to the synergistic effects of anthropogenic pressure and hydrological instability. This study aims to identify and assess changes in [...] Read more.

River ecosystems play a key role in both natural and urbanized environments, acting as essential links in ecological systems. However, they are increasingly exposed to the synergistic effects of anthropogenic pressure and hydrological instability. This study aims to identify and assess changes in land use and their impact on the phytosociological structure and functioning of ash-alder (Fraxino-Alnetum) patches in floodplains. Based on cartographic analyses (1941, 1961, 2025) and detailed geobotanical surveys (2024–2025) conducted at six representative sites, the spatio-temporal dynamics of land use and vegetation habitat conditions were evaluated using ecological indicator values. The results indicate a substantial landscape transformation: a transition from areas dominated by agricultural and forest ecosystems to zones heavily altered by urban expansion, transport infrastructure, and industrialization. Phytosociological analyses show that while species richness remains relatively stable, floristic composition is changing due to hornbeam succession and the emergence of mesophilous species. The presence of non-native species indicates ongoing anthropization in plant patches. Furthermore, hydromorphological modifications, including bank reinforcement and channel deepening in the vicinity of sports and railway infrastructure, have hindered natural river dynamics and accelerated floodplain drainage. The observed changes indicate that ash-alder forests in the Biała Przemsza valley are in a transitional phase between riparian and oak-hornbeam communities, with a clear oak-hornbeam transformation evident in many areas, driven by changes in water relations. This study highlights the urgent need to implement integrated restoration strategies that account for both hydrological catchment recovery and the mitigation of urban pressure to ensure the long-term resilience of riparian ecosystems. Full article

(This article belongs to the Section Ecohydrology)

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28 pages, 12170 KB

Open AccessArticle

Layer-Scale Spectral–Sediment Relationships and Calibrated Uncertainty from Underwater Hyperspectral Observations During an Upper-Yangtze Flood Event

by Lele Deng, Yangliu Yang, Yihang Su, Rihui An, Lei Yang and Xinbo Liu

Water 2026, 18(16), 1977; https://doi.org/10.3390/w18161977 - 13 Aug 2026

Abstract

Within a single flood event, this study evaluated the empirical relationship between underwater hyperspectral observations and layer-scale suspended sediment concentration (SSC) and calibrated its predictive uncertainty. The dataset comprised 101 paired observations from 25 complete four-position verticals (n = 100) plus one [...] Read more.

Within a single flood event, this study evaluated the empirical relationship between underwater hyperspectral observations and layer-scale suspended sediment concentration (SSC) and calibrated its predictive uncertainty. The dataset comprised 101 paired observations from 25 complete four-position verticals (n = 100) plus one isolated record. Sample-level leave-one-out cross-validation (LOOCV) provided the primary estimate of event-internal layer-level interpolation, while leave-one-vertical-out validation (LOVO) assessed sensitivity to an unseen vertical. Under LOOCV, random-forest models reached R² ≈ 0.78–0.79 and RMSE ≈ 0.087 kg/m³; on the complete-vertical subset, spectra-only RF_log1p decreased to R² = 0.595 and RMSE = 0.120 kg/m³ under LOVO. Discharge and interpolated stage added event-specific context (Q/stage-only LOVO R² = 0.699), but cross-date transfer remained poor. Raw quantile-regression-forest intervals under-covered the nominal 90% level; conformal calibration restored coverage at the cost of wider intervals (grouped PICP90 0.721 → 0.927; MPIW90 0.234 → 0.617 kg/m³). The four positions showed a weak within-vertical effect (Friedman χ² = 11.93, p = 0.0076; Kendall’s W = 0.159), with no pairwise contrast significant after Holm correction. The results support calibrated event-internal interpolation at sampled layers, but do not resolve a monotonic vertical profile or support transfer across dates, stages, stations, or events without recalibration. Full article

(This article belongs to the Special Issue Machine Learning Models for Hydrological Inference: A Case Study for Flood Events)

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6 pages, 500 KB

Open AccessArticle

Beyond the Constant Stress Assumption: A Mechanistic Derivation of the Log-Law for Open Channel Flow

by Keqi Zheng, Ranran Mao, Qijun Li and Nian-Sheng Cheng

Water 2026, 18(16), 1976; https://doi.org/10.3390/w18161976 - 13 Aug 2026

Abstract

The logarithmic law of the wall is a foundational element in turbulence modeling. Its classical derivation, rooted in Prandtl’s mixing-length theory, is predicated on the existence of a constant shear stress layer. This paper demonstrates that this foundational assumption is not strictly satisfied [...] Read more.

The logarithmic law of the wall is a foundational element in turbulence modeling. Its classical derivation, rooted in Prandtl’s mixing-length theory, is predicated on the existence of a constant shear stress layer. This paper demonstrates that this foundational assumption is not strictly satisfied for two-dimensional, uniform open-channel flows, where the Reynolds shear stress profile exhibits a distinct peak near the bed and never forms a true constant stress zone. We present a novel mechanistic derivation that circumvents this inconsistency. By reframing the bed shear stress as the time-averaged momentum flux from discrete, wall-coherent eddy impacts, we recover the log law through a mechanistic framework. Our model starts from the physical definition of the Reynolds stress at the bed, employs kinematic scaling for the velocity fluctuations, and incorporates the geometric constraint of eddy size. This approach does not require a constant stress layer and provides a more physically defensible explanation for the emergence and robustness of the log-law, directly linking it to the underlying structure of wall turbulence. The derivation resolves the long-standing paradox between the theory’s assumption and the empirical reality in open channel flows. Full article

(This article belongs to the Section Hydraulics and Hydrodynamics)

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17 pages, 1134 KB

Open AccessArticle

Precipitation of F^– Ions on the Mineral Surfaces in Water Purification Processes

by Mariya A. Pashkevich, Vladimir G. Povarov and Daria D. Borisova

Water 2026, 18(16), 1975; https://doi.org/10.3390/w18161975 - 12 Aug 2026

Abstract

This study investigates the kinetic parameters required for the engineering design of treatment plants employing fluorite precipitation technology. Particular emphasis is placed on the selection of a substrate for fluorite precipitation at the minimum acceptable calcium ion concentration, as well as on determining [...] Read more.

This study investigates the kinetic parameters required for the engineering design of treatment plants employing fluorite precipitation technology. Particular emphasis is placed on the selection of a substrate for fluorite precipitation at the minimum acceptable calcium ion concentration, as well as on determining the precipitation rate of fluoride ions onto a substrate of given composition. In addition, the particle size of the substrate materials was examined. The degree of substrate dispersion was constrained by technological requirements: finely dispersed materials impede separation from the solution and reduce the filtration rate, whereas coarse-grained substrates provide insufficient contact area between the solution and the substrate. Full article

(This article belongs to the Section Wastewater Treatment and Reuse)

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22 pages, 5427 KB

Open AccessArticle

Assessing Water Security in Dhaka City Slums

by Shamsunnahar Runu and M. Shahjahan Mondal

Water 2026, 18(16), 1974; https://doi.org/10.3390/w18161974 - 12 Aug 2026

Abstract

Water security is a prerequisite for achieving the Sustainable Development Goals, yet water insecurity remains a critical challenge in urban slums. This study assesses the water security in the slums of Dhaka City, Bangladesh by integrating multiple dimensions of water security, such as [...] Read more.

Water security is a prerequisite for achieving the Sustainable Development Goals, yet water insecurity remains a critical challenge in urban slums. This study assesses the water security in the slums of Dhaka City, Bangladesh by integrating multiple dimensions of water security, such as water supply, sanitation and hygiene, water environment, water and climatic risks, and water governance. Suitable indicators and variables are used to capture the key dimensions of water security. A mixed-method approach, incorporating quantitative water quality assessment, waterlogging assessment and household survey, and qualitative focus group discussions, in-depth interviews and key informant interviews, is followed for data collection. The results reveal that the water security index (WSI), on a scale of 5.00, varies from 1.72 for Rajur slum to 3.34 for Nabinagar Housing slum. Among the dimensions, the score varies from 1.86 for water environment to 3.05 for water supply. Thus, there is a wide variation in WSI from slum to slum and in score from dimension to dimension. The study suggests improving drainage, sewerage and household solid waste collection systems, cleaning water bodies, improving drinking water quality, and raising awareness on menstrual hygiene management for enhancing water security in Dhaka’s slums. Full article

(This article belongs to the Section Water Use and Scarcity)

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35 pages, 28590 KB

Open AccessArticle

Transient Internal Flow and Energy Conversion Characteristics of a Siphon Vertical Axial-Flow Pump Hydraulic System During Startup

by Yadong Zhu, Hui Wang, Zhuangzhuang Sun, Zhonsheng Zhou, Cheng Yuan, Weixuan Jiao and Yang Yang

Water 2026, 18(16), 1973; https://doi.org/10.3390/w18161973 - 12 Aug 2026

Abstract

Siphon vertical axial-flow pump systems are widely used in large-scale low-head pumping stations, irrigation and drainage projects, urban flood control, and water diversion engineering, where safe and stable operation is essential for hydraulic system reliability. Compared with steady operating conditions, the startup process [...] Read more.

Siphon vertical axial-flow pump systems are widely used in large-scale low-head pumping stations, irrigation and drainage projects, urban flood control, and water diversion engineering, where safe and stable operation is essential for hydraulic system reliability. Compared with steady operating conditions, the startup process involves rapid variations in impeller speed, flow rate, pressure distribution and hydraulic energy transfer, resulting in highly transient hydraulic behavior and obvious instability in the internal flow field. To clarify the transient hydraulic response of a siphon vertical axial-flow pump system during startup, an unsteady numerical model was established by coupling the impeller speed control equation with a dynamic boundary condition implemented through a user-defined function. The time-dependent evolution of flow rate, head, blade loading, pressure distribution, internal flow pattern and energy conversion characteristics was then investigated during the whole startup process. The results show that the pump system undergoes a distinct transition from an initially unstable flow state to a quasi-steady operating condition. At the early startup stage, the flow passage is not fully established, and the pump operates under a low-flow transient condition, leading to strong flow disorder, uneven blade loading and a sharp fluctuation in head. With the increase in rotational speed and flow rate, the internal flow gradually becomes organized, the pressure distribution on the blade surface tends to be more uniform, and the hydraulic energy transfer process becomes progressively stable. The pump head first exhibits an abnormal transient peak, then decreases rapidly, and finally recovers to a stable value as the flow field is fully established. The study reveals the transient evolution mechanism of hydraulic performance and energy conversion during startup, providing a theoretical basis for improving startup control strategy and operational stability of siphon vertical axial-flow pump systems. Full article

(This article belongs to the Section Hydraulics and Hydrodynamics)

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15 pages, 964 KB

Open AccessArticle

Investigating Cladocera Community Composition in Wetlands with Different Hydrological Types

by István Gyulai, Andrea Böjthe Clara, Umar Abba Kawu, Andor G. Soltész, Tamás Karches, János Korponai and Sheila Mumbi A. Wamugi

Water 2026, 18(16), 1972; https://doi.org/10.3390/w18161972 - 12 Aug 2026

Abstract

Climate change and global warming are increasingly affecting freshwater bodies both locally and globally, resulting in fluctuating water levels. Understanding how Cladocera communities are organized across different water body types is important for ecological assessment and conservation. In this study, we compared Cladocera [...] Read more.

Climate change and global warming are increasingly affecting freshwater bodies both locally and globally, resulting in fluctuating water levels. Understanding how Cladocera communities are organized across different water body types is important for ecological assessment and conservation. In this study, we compared Cladocera assemblages between different wetland types with different water body types and evaluated the role of physicochemical characteristics and spatial structuring in shaping the community distribution patterns. Six water bodies were selected for our study; each contained three sampling points spaced at least 75–100 m apart. Cladocera specimens in the filtrate samples were identified at the species level. Homogeneity of multivariate dispersions (PERMDISP) and PCA analysis of site-related spatial effects were used to test differences in community composition. Based on previous studies and results, we concluded that the water body type significantly influenced the composition of Cladocera communities among the wetlands investigated. Full article

(This article belongs to the Special Issue Aquatic Ecosystem Assessment: Zooplankton)

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28 pages, 18814 KB

Open AccessArticle

Using Chemical Monitoring Data to Distinguish Natural Background Concentrations and Anthropogenic Impacts in Lake Sevan Tributaries, Armenia

by Vahe Movsisyan, Habet Madoyan, Gayane Shahnazaryan, Anna Zatikyan, Alexander Arakelyan, Wolf von Tümpling and Martin Schultze

Water 2026, 18(16), 1971; https://doi.org/10.3390/w18161971 - 12 Aug 2026

Abstract

This study evaluates whether existing long-term monitoring data are sufficient to distinguish natural background concentrations from anthropogenic influences on chemical river water quality in Lake Sevan basin. A comprehensive dataset covering physicochemical parameters, nutrients, and trace metals was analyzed for nine major tributaries [...] Read more.

This study evaluates whether existing long-term monitoring data are sufficient to distinguish natural background concentrations from anthropogenic influences on chemical river water quality in Lake Sevan basin. A comprehensive dataset covering physicochemical parameters, nutrients, and trace metals was analyzed for nine major tributaries with different geological settings and land-use characteristics. Multivariate statistical analysis was applied to identify baseline conditions and deviations attributable to human activities. The results indicate that water chemistry is primarily controlled by lithology and hydrological regime, particularly in minimally impacted headwater regions. In contrast, elevated concentrations of nutrients (e.g., nitrate and phosphate) and selected trace elements were associated with agricultural runoff, urban discharge, and localized industrial inputs. Spatial patterns reveal clear gradients of increasing anthropogenic impact downstream and in densely populated sub-basins. The study also demonstrates that, while the current monitoring network is suitable for assessing the overall chemical status of rivers, it is less effective in defining natural background levels and quantifying individual pollution sources due to limited upstream reference conditions. Overall, this approach provides a scientific basis for improved water quality management and policy implementation in the Lake Sevan basin. The findings highlight the importance of integrating long-term monitoring data with statistical tools to support sustainable watershed management in vulnerable catchments. Full article

(This article belongs to the Section Water Quality and Contamination)

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28 pages, 9083 KB

Open AccessArticle

Two Centuries of Lekhziri Glacier Evolution in the Georgian Caucasus and Recent Proglacial Lake Development

by Levan G. Tielidze, Sophio Gorgijanidze, Akaki Nadaraia and Roman M. Kumladze

Water 2026, 18(16), 1970; https://doi.org/10.3390/w18161970 - 12 Aug 2026

Abstract

Mountain glaciers constitute sensitive indicators of climate variability and represent essential freshwater reservoirs for downstream ecosystems and societies. Although glacier change in the Greater Caucasus has been extensively investigated at regional scales, detailed long-term reconstructions of individual glacier systems remain comparatively scarce. In [...] Read more.

Mountain glaciers constitute sensitive indicators of climate variability and represent essential freshwater reservoirs for downstream ecosystems and societies. Although glacier change in the Greater Caucasus has been extensively investigated at regional scales, detailed long-term reconstructions of individual glacier systems remain comparatively scarce. In this study, we reconstruct two centuries of evolution of Georgia’s largest Lekhziri Glacier and document the recent formation of its proglacial lake. The Little Ice Age glacier extent (AD ~1820) was reconstructed from moraine complexes, whereas later glacier outlines were derived from historical topographic maps, Landsat, SPOT, PlanetScope, and unmanned aerial vehicle (UAV) data spanning 1890–2025. Glacier terminus elevation was analysed using the Copernicus Digital Elevation Model, whereas long-term climatic variability was evaluated from summer air temperature and winter precipitation records obtained from the local meteorological station. The results demonstrate that Lekhziri Glacier experienced substantial and accelerating retreat during the past two centuries. Glacier area decreased from 46.67 ± 2.53 km² in ~1820 to 28.31 ± 0.62 km² in 2025, representing a net reduction of −18.36 km² (−39.34%) with an average annual decrease of −0.19% yr⁻¹. Area loss accelerated markedly after 2000, reaching −0.66% yr⁻¹ during 2000–2014 and −0.87% yr⁻¹ during 2014–2025. Over the last two centuries, the glacier terminus retreated by approximately −4.78 km, equivalent to an average retreat rate of −32.4 m yr⁻¹, while the terminus elevation migrated upward by nearly 600 m, from ~1718 to ~2317 m a.s.l. The glacier also underwent pronounced structural fragmentation after 2014, fundamentally altering its geometry and flow configuration. Concurrently, a proglacial lake first identified in 2019 with an area of 10,805 m² expanded rapidly to 28,947 m² in 2022 and 38,260 m² in 2025, with its continued existence confirmed by UAV observations in 2026. Meteorological records indicate a persistent increase in summer air temperature since the mid-twentieth century, accompanied by a decline in winter precipitation, consistent with the observed acceleration of glacier recession. This study provides one of the most comprehensive reconstructions of glacier evolution to date for an individual glacier in the Greater Caucasus and contributes new insights into the changing dynamics of glacierized mountain landscapes under continued climate warming. Full article

(This article belongs to the Section Water and Climate Change)

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18 pages, 5428 KB

Open AccessArticle

Experimental Study of Francis Turbine with Variable Speed Operation

by Thiago Soares Corrêa, Zulcy de Souza and Luiz Antonio Alcântara Pereira

Water 2026, 18(16), 1969; https://doi.org/10.3390/w18161969 - 12 Aug 2026

Abstract

This study specifically investigates the operating range of a normal Francis turbine through the production of experimental data and characteristic performance curves under both constant and variable rotational speed operating conditions. For the constant speed condition, a specific speed of 204.6 was found [...] Read more.

This study specifically investigates the operating range of a normal Francis turbine through the production of experimental data and characteristic performance curves under both constant and variable rotational speed operating conditions. For the constant speed condition, a specific speed of 204.6 was found for turbine maximum efficiency attained with a guide vane aperture at 60%. The variable speed tests were conducted by keeping the specific speed around 204.6 with the guide vane aperture fixed at 60%. These tests have successfully produced results of turbine maximum efficiency very close to the maximum efficiency for the constant speed condition. The most important contribution of this paper is to report an increase in the operational range of the hydraulic turbine with variable speed operation, particularly when working at a lower flow rate and water head. The results obtained have demonstrated incomplete dynamic similarity between homologous Francis turbines. In other words, the concept of identical hydraulic turbines working with variable speed and producing the same maximum efficiency has been verified. The work also demonstrates an approach to the operation of hydroelectric generating units, aiming at improved compatibility between water availability and the electrical energy supplied to consumers. Full article

(This article belongs to the Special Issue Hydrodynamics in Pumping and Hydropower Systems, 2nd Edition)

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37 pages, 48144 KB

Open AccessArticle

Groundwater Aquifer Characterization and Potential Assessment of the Shallow Aquifers in the Volcanic Highlands of Northwestern Ethiopia

by Alemu Yenehun, Fenta Nigate, Ashebir Sewale Belay, Mekete Dessie, Adugnaw Birhanu, Mulugeta Azeze, Enyew Adgo, Jan Nyssen and Kristine Walraevens

Water 2026, 18(16), 1968; https://doi.org/10.3390/w18161968 - 11 Aug 2026

Abstract

Estimating transmissivity and hydraulic conductivity is crucial for groundwater resource assessment, flow modeling, pollution remediation, and sustainability studies. In the volcanic highlands of Ethiopia, millions rely on hand-dug wells and springs for drinking and irrigation, yet the hydraulic properties of these shallow aquifers [...] Read more.

Estimating transmissivity and hydraulic conductivity is crucial for groundwater resource assessment, flow modeling, pollution remediation, and sustainability studies. In the volcanic highlands of Ethiopia, millions rely on hand-dug wells and springs for drinking and irrigation, yet the hydraulic properties of these shallow aquifers remain largely uncharacterized. This study provides the first comprehensive estimation of transmissivity and hydraulic conductivity for the shallow groundwater aquifers in the Lake Tana Basin through integrated analyses of pumping and slug tests. The effective dataset comprised 31 tests, unevenly distributed among four aquifer types: eight in Quaternary basalt, 13 in weathered basalt regolith, seven in pyroclastic deposits, and three in alluvio-lacustrine sediments. Time-series groundwater level data were additionally used to characterize seasonal recharge responses and recession behaviors. Quaternary basalt aquifers showed high transmissivity values of 117–1064 m²/d, with a geometric mean of 235 m²/d, reflecting the influence of open and hydraulically connected fractures. Weathered basalt regolith aquifers had transmissivity values of 0.27–71 m²/d, with a geometric mean of 3.09 m²/d, whereas pyroclastic aquifers ranged from 0.17 to 11 m²/d, with a geometric mean of 0.96 m²/d. The alluvio-lacustrine aquifers ranged from 1.68 to 173 m/d, with a geometric mean of 8.56 m²/d; however, this estimate should be interpreted cautiously because it is based on only three tests. This study reveals strong heterogeneity within and across aquifers. Pumping tests were generally more applicable to the relatively transmissive Quaternary basalt aquifers, whereas slug tests provided a practical approach for characterizing shallow weathered regolith, pyroclastic, and alluvio-lacustrine aquifers. Seasonal groundwater level patterns varied with geology and topographic position: aquifers on slopes and plateaus generally showed rapid recharge and recession responses, whereas those at foothills and floodplains exhibited more sustained groundwater levels, probably because of lateral inflow and interactions with river water. The findings provide preliminary hydraulic-property ranges for groundwater assessment and indicate that fractured Quaternary basalt aquifers may represent promising targets for water-supply development. Full article

(This article belongs to the Section Hydrogeology)

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22 pages, 18440 KB

Open AccessArticle

Groundwater Circulation Well Test for Synergistic Remediation of a Heterogeneous Site: Extraction, Tracing and Oxidation

by Han Ke, Xiaowen Wu, Minliang Fei, Shuning Zheng, Ling Li, Tingjun Wang, Jie Hu, Chensheng Zhang and Chaofeng Shen

Water 2026, 18(16), 1967; https://doi.org/10.3390/w18161967 - 11 Aug 2026

Abstract

Field tests were conducted at a heterogeneous industrial site using one circulation well and six monitoring wells. Groundwater circulation well (GCW) extraction–injection (30 d), multi-component tracing (6 h), and circulation–oxidation (20 h) tests were performed to investigate the flow-field characteristics and their influence [...] Read more.

Field tests were conducted at a heterogeneous industrial site using one circulation well and six monitoring wells. Groundwater circulation well (GCW) extraction–injection (30 d), multi-component tracing (6 h), and circulation–oxidation (20 h) tests were performed to investigate the flow-field characteristics and their influence on multi-component solute transport. The results suggested that the extraction–injection circulation mode increased the flow rate of the single well from 0.5 m³/h to 3.5 m³/h, establishing a composite flow field with near-field circulation and far-field outward expansion. Short-term circulation achieved limited concentration attenuation primarily near the well with rebound. Long-term circulation elevated the average concentration attenuation rates of benzene from 13% in the short-term test to 61%, and chemical oxygen demand (COD) from 16% to 47%, expanding the remediation scope of the circulation well. Bromide tracer tests and an advection–dispersion equation characterized the heterogeneous flow field with preferential flow channels and slow migration zones. Furthermore, sulfate tracer transport was governed by adsorptive retardation and advective delivery. Circulation–oxidation tests showed that benzene and COD showed higher concentration attenuation than naphthalene. After cessation, benzene and COD concentration attenuation rates increased by 39% and 29% compared to the short-term test without oxidation. Electrical resistivity tomography (ERT) revealed the downward diffusion of the oxidant, suggesting that the circulation well system enhances oxidant transport and expands the oxidant-affected zone. This research provides field-scale diagnostic evidence and in situ diagnostic methodologies for GCW remediation at complex contaminated sites. Full article

(This article belongs to the Section Hydrogeology)

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