Water doi: 10.3390/w18101170

Authors: Zhijia Yu Yu Ping Wenqing Ji Qi Wang Jianggen He Yufeng Qi Xiaoying Deng Xinyi Wang

To overcome the rapid expansion of the drawdown cone, severe inter-well interference, and high operating costs caused by independent geothermal well operation, this study investigated the coordinated optimal scheduling of geothermal water extraction. Fifteen geothermal production wells in the main urban area of Kaifeng City were selected as the study case. The intake intervals of these wells are located at depths of 1020 to 1330 m. Based on the exploitable yield of the geothermal reservoir, user water demand, and well layout, a management model for coordinated scheduling was developed. Design drawdown, water demand, and heating capacity were used as constraints. The objectives were to minimize operating cost, nodal drawdown, and drawdown interference between wells. The results from several optimization algorithms show that the improved Cheetah Optimization Algorithm converged faster and produced more consistent solutions. Compared with the preoptimization scheme, the optimized scheme reduced total operating cost by 31.64%, total drawdown in the study area by 69.5%, and the sum of inter-well drawdown interference by 34.7%. This study provides useful support for selecting efficient optimization algorithms and offers a basis for the scientific development, utilization, and protection of geothermal water resources.

Water doi: 10.3390/w18101169

Authors: Yanyu Lin Tangzhe Nie Shaodong Liu Hao Yan Yuxuan Wang

To investigate the effects of water-saving irrigation and different straw retention methods on soil CH4 and N2O emissions from paddy fields in cold regions and their potential underlying mechanisms, a field experiment was conducted in Qing’an City, Heilongjiang Province. Two water management regimes were set, combined with four straw retention treatments. The static chamber-gas chromatography method was used to monitor CH4 and N2O emission fluxes during the entire rice growth period. Meanwhile, soil pH, oxidation–reduction potential (Eh), dissolved oxygen (DO), and dynamic changes in carbon and nitrogen substrates were measured, and the global warming potential (GWP) and greenhouse gas emission intensity (GHGI) were comprehensively evaluated. The results showed that controlled irrigation significantly increased soil dissolved oxygen content and oxidation–reduction potential. Compared with conventional flooding irrigation, total CH4 emission decreased by more than 50%, while N2O emission increased by 1.5–2.5 times, exhibiting an obvious divergent correlation with the two gas emission fluxes. Among different straw retention methods, organic fertilizer returning and direct straw returning significantly promoted CH4 emission by supplying easily decomposable organic carbon. In contrast, biochar, due to its stable carbon structure and favorable pore properties, inhibited CH4 emission without significantly stimulating N2O emission. The treatment of controlled irrigation combined with biochar returning (CB) achieved the lowest global warming potential and greenhouse gas emission intensity at 7230.82 kg CO2-eq/hm2 and 0.8054 kg CO2-eq/kg, respectively, while maintaining high rice yield. Path analysis based on soil physicochemical properties and emission fluxes further revealed that Eh and DO were significantly negatively correlated with CH4 emission but positively correlated with N2O emission. Path inference from flux and substrate data indicated that carbon and nitrogen availability were the key factors limiting the denitrification process. In conclusion, the combined application of controlled irrigation and biochar returning can realize the synergistic effect of stable yield and emission reduction in cold-region paddy fields by improving soil aeration and regulating the transformation of carbon and nitrogen substrates, providing a scientific basis for establishing a green and low-carbon rice production technology system for black soil in cold regions.

Water doi: 10.3390/w18101168

Authors: Zinette Bergman Manfred Max Bergman Srikantaiah Vishwanath Varsha Shridhar Avinash Krishnamurthy Ashwin Gupta Jan Obernosterer

Urban lake ecosystems in rapidly growing cities face multiple, interlinked pressures. This article examines how these pressures are understood and addressed in research and practice by synthesising 413 academic, policy, and practitioner studies on lake degradation and restoration in the Bengaluru region, India. Using Content Configuration Analysis, we pursue four lines of inquiry: typifying dominant research approaches; mapping how major drivers—climate change, urbanisation, expanding consumption, and governance fragmentation—generate pressures; analysing sewage treatment plants (STPs) as responses that can themselves become new stressors; and comparing national restoration guidelines with locally developed strategies. Our analysis shows that lake problems are frequently framed as discrete technical issues, whereas degradation operates through recursive driver–pressure–response dynamics that cut across ecological, institutional, and social domains. The STP cases illustrate this mismatch, where mandated solutions can generate unintended pressures when institutional capability or ecological integration is weak. Comparisons between national guidelines and locally grounded practices reveal broad alignment in restoration principles but persistent gaps remain in implementation capacity, coordination, financing, and integration with land-use and urban resilience planning. Based on our analyses, we argue for reconceptualising urban lakes as complex socioecological systems rather than bounded technical units. Such a perspective supports restoration strategies that are nationally coherent yet locally attuned, strengthening ecological function, social equity, and urban resilience. More broadly, the findings contribute to debates on the restoration and governance of urban water bodies by demonstrating how national policy frameworks can be reinforced through locally grounded socioecological knowledge.

Water doi: 10.3390/w18101167

Authors: Xi Qiang Menglin Guo Yuling Song Songcui Wu Shan Gao Xiujun Xie Xuehua Liu Xulei Wang Quancheng Fan Jing Zhang Lijun Wang Guangce Wang

Actual printing and dyeing wastewater (APDW), as one of the most difficult types of wastewater to treat, has become a significant environmental risk due to its toxicity and the challenges associated with its degradation. Microalgae-based treatment of APDW is a promising, eco-friendly, and cost-effective strategy. In this study, a cyanobacterium, Synechocystis aquatilis, was isolated from APDW. The strain demonstrated good environmental tolerance and the capacity to remove pollutants and valorize biomass simultaneously. Under optimized conditions, it removed COD (120.27 mg·L−1·d−1), NH4-N (0.89 mg·L−1·d−1), and total phosphorus (9.52 mg·L−1·d−1), while achieving substantial decolorization. The strain concurrently accumulated lipids (373.08 mg/g), polysaccharides (167.85 mg/g), and proteins (72.05 mg/g). Mechanistic analyses revealed that S. aquatilis microalgae adsorb dyes and impurities via bioadsorption and then biodegrade dyes and nitrogen and phosphorus compounds via NADPH generation, glutamate and butyrate metabolism, and oxidoreductase activity. This study presents a promising application of S. aquatilis as a novel and environmentally friendly treatment method for APDW, enabling simultaneous wastewater treatment and resource recovery.

Water doi: 10.3390/w18101164

Authors: Wenhao Li Hao Chen Jialiang Huang Weiqi Zhou Ning Fang Yali Guo Xiankai Wang

With the increasing frequency of desilting in urban drainage systems, the safe disposal and resource reuse of sewer sediments have become a prominent practical challenge. Screened sand, the most promising component for resource recovery from sewer sediments, still lacks systematic insight into its pollution risks and the necessity of pretreatment. In this study, 120 raw sewer sediment samples were collected from sanitary, storm, and illicitly connected (IC) storm sewers in Shanghai, alongside seasonal screened sand samples. We systematically characterized their physicochemical properties and heavy metal and antibiotic pollution profiles, and evaluated the purification performance of ultrasonic treatment, sodium hexametaphosphate (SHMP) washing, and their coupled processes. Results revealed significant differences in sediment properties across pipeline types. Screened sand, dominated by SiO2 and CaO, shows preliminary potential for reuse as a low-grade bulk building material, but its organic loss on ignition (LOI) of 5.29–13.42% exceeded the reuse limit. Concentrations of heavy metals and antibiotics were generally higher in screened sand than in raw sediments, with further enrichment in the fine sand fractions, indicating that screening only redistributed contaminants rather than eliminated them. The coupled ultrasonic–SHMP process, applied for the first time to screened sand from sewer sediments, achieved optimal performance, with a maximum LOI reduction and over 85% removal of certain antibiotics, without damaging the sand’s mineral skeleton. This study provides a scientific basis for the safe resource reuse of screened sand.

Water doi: 10.3390/w18101166

Authors: Pinit Tanachaichoksirikun

Small islands often face chronic water shortages due to limited storage capacity, seasonal variability, and growing demand from tourism and urbanization. Si Chang Island, Thailand, experiences severe dry-season water scarcity, requiring improved water supply planning. This study applies the EPANET hydraulic modelling tool to design and evaluate water distribution networks under two scenarios: (1) a surface water supply system from the Si Chang Reservoir, and (2) a groundwater-based system near the island’s football field. Using Darcy–Weisbach head loss calculations and demand estimates, we assessed flow velocity, pressure, and construction costs. Both systems met design criteria, but the reservoir-based option achieved better cost efficiency (2.81%) and reliable pressure (minimum 15.05 m) with an average velocity of 1.20 m/s. The system can supply approximately 130% of the estimated demand, corresponding to a surplus capacity of about 30%. The findings demonstrate how hydraulic modelling can guide infrastructure planning for small, data-limited islands. Integrating technical design with policy considerations enhances the reliability, cost-effectiveness, and resilience of water supply systems. The approach presented herein offers a practical framework for decision-makers addressing water scarcity challenges on small islands worldwide.

Water doi: 10.3390/w18101165

Authors: Garza-Pimentel Yunue González-Olvera Marcos Angel Santos-Reyes Jaime Reynaldo

Mexico City experiences severe water stress driven by aquifer overexploitation and recurrent droughts. Effective water management requires operational spatial monitoring systems capable of spatially reconstructing meteorological anomalies across multiple temporal scales. In this work we developed an explainable deep learning framework using Long Short-Term Memory (LSTM) networks to spatially reconstruct three drought indices—the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and Reconnaissance Drought Index (RDI)—across five accumulation scales (3, 6, 12, 18, and 24 months). To strictly isolate genuine meteorological deviations, we adopted a hybrid statistical approach: SPI was computed following the standard WMO methodology using Gamma distribution fitting, while SPEI and RDI were computed using empirical monthly standardized anomalies to ensure robustness in non-stationary urban climates without forcing distributional assumptions. Model generalization was evaluated using a leave-one-microsite-out validation strategy, training on two stations and testing on a spatially isolated third station, with inter-station distances ranging from 1.8 to 6.7 km, sufficient to capture urban microclimatic heterogeneity while remaining within the same regional climate zone. We quantified feature importance using SHapley Additive exPlanations (SHAP) to provide mathematical transparency. The LSTM achieved predictive performance at long-term scales by effectively capturing deep sequential memory, while short-term reconstructions reflected the inherent noise of urban convective precipitation. The framework demonstrates reliable intra-urban spatial generalization capacity, supporting the development of diagnostic tools for metropolitan water stress assessment.

Water doi: 10.3390/w18101163

Authors: Dunia Virto González Lidia Ruiz Pérez Isabel González-Barragán María Jesús González Morales

Sustainable groundwater management in regions subjected to intensive agricultural pressure requires reliable simulation tools capable of anticipating the impacts of climate change. However, in overexploited multilayer aquifers such as Tierra del Vino, locally calibrated predictive tools capable of quantifying climate-driven piezometric decline remain scarce. This study develops a numerical groundwater flow model using MODFLOW for the Tierra del Vino aquifer (Spain), a multilayer detrital system currently characterized by a critical quantitative status. Agricultural irrigation accounts for approximately 94% of total groundwater withdrawals, making it the dominant anthropogenic pressure on the system. The model was manually calibrated through more than 500 iterations, achieving a consistent representation of groundwater dynamics. Statistical evaluation based on groundwater level data from 34 piezometric monitoring points distributed across the aquifer yielded a good fit (NSE = 0.816; R = 0.928), supporting the suitability of the model for scenario analysis. Under the RCP 8.5 climate scenario, aquifer recharge could decrease by 31.75%, resulting in a significant piezometric decline within the system. At the representative well selected for the farm-scale agricultural impact analysis, this decline reaches 3.33 m and is used to evaluate its effect on pumping energy costs. The implementation of management measures proposed by the water authority reduces this decline to 1.84 m, although overexploitation conditions persist. These results indicate that current administrative restrictions are insufficient on their own and that future management should adjust abstraction rights to projected recharge conditions, maintaining the exploitation index below 0.8 to reduce the risk of long-term overexploitation. In this context, aquifer resilience is interpreted as the capacity of the groundwater system to respond to the combined pressures of climate change and agricultural abstraction while maintaining its hydrological functioning.

Water doi: 10.3390/w18101162

Authors: Bettina Neunteufel Günter Gruber Dirk Muschalla

Industrial and municipal wastewater may contain substances that inhibit biological processes in wastewater treatment plants (WWTPs), posing risks to operational stability and environmental protection. The aim of this study is to evaluate the practical suitability of the ISO 8192:2007 respiration inhibition test for assessing the toxicity of wastewater. Nitrified activated sludge from a municipal WWTP was used to analyze wastewater from three industrial companies, wastewater from several discharge locations at a hospital, and WWTP influent. Oxygen consumption and inhibition were determined at sample-specific dilution levels and the reference substance 3,5-dichlorophenol. Two samples from the dental department of the hospital showed toxic effects on activated sludge respiration (inhibition > 50%), while no toxic effects were observed in the remaining samples. Several samples exhibited stimulatory effects (inhibition < 0%), indicating the presence of readily biodegradable organic matter. However, inhibitory effects (0–50% inhibition) were detected in individual wastewater samples at higher concentrations. This demonstrates that the method can detect toxicological changes in wastewater and is suitable for routine monitoring and early warning in WWTPs.

Water doi: 10.3390/w18101161

Authors: David Amouroux Emmanuel Tessier Andrea Romero-Rama Sandrine Veloso Jonathan Deborde Laurent Lanceleur Mathieu Sebilo Maïté Bueno

Selenium plays a crucial role in estuarine biogeochemistry, balancing essential nutrient functions with potential environmental toxicity. This study examines the seasonal distribution of dissolved Se species, including volatiles, in the Adour estuary in relation to anthropogenic influences. To characterize major Se inputs from upstream watersheds to downstream tributaries, water samples were collected at low tide during three different seasons in upstream freshwaters, industrial/urban effluents and downstream estuarine waters. A tidal-cycle sampling campaign was conducted under low discharge conditions to assess Se dynamics during downstream estuarine mixing. Total dissolved Se (TDSe) concentrations ranged from 71 (pristine river) to 656 ng L−1 (industrial/urban-impacted tributaries). TDSe correlated strongly with nitrate (r = 0.84) in upstream waters, indicating significant agricultural and livestock contributions at the watershed scale. Selenate was the dominant species, followed by Se(-II+0) fraction and selenite. Volatile Se compound concentrations varied from 51 to 2757 pg L−1. Seasonal changes suggest that Se speciation is mainly controlled by watershed inputs derived from land use (agricultural and livestock practices) rather than downstream estuarine inputs. This speciation study further indicates that Se reactivity/bio-availability in estuarine systems can be largely influenced by anthropogenic activities, although further characterization of the aqueous reduced Se fraction is still needed.

Water doi: 10.3390/w18101160

Authors: Zitong Huang Haiqing Liao Meichen Ji Yule Luo Fang Yang Danni Liu Yiling Zhong Dongxia Feng Weilong Jiang Yuying Shi Matti Leppäranta

Dissolved organic matter (DOM) plays a central role in estuarine carbon cycling and exhibits dynamically coupled interactions with chlorophyll-a (Chl-a). Under increasing nutrient loads, elevated Chl-a concentrations and shifts in DOM composition serve as key indicators of eutrophication in estuarine aquatic ecosystems. Previous studies have mainly focused on the composition and fluorescence properties of DOM in rivers and lakes. Here, 84 water samples were collected from the Ganjiang River Estuary of Lake Poyang during wet, normal, and dry seasons across the mainstream, middle, and south branches. The average Chl-a concentration showed wet season (6.61 μg·L−1) > normal season (4.54 μg·L−1) > dry season (2.01 μg·L−1). By employing EEM-PARAFAC, five fluorescent components were identified, including C1, C2, C3, C4, and C5. Notably, microbial humic-like substances remained consistently high during the wet season. Two-dimensional correlation spectroscopy was further employed to evaluate sequential changes in DOM components, while a moving window was used to identify temporal variation characteristics. Based on Noda’s rules, the DOM response sequence was identified as C3→C2→C1→C4→C5. Kernel PCA showed that the variable cluster represented by PC1, which consisted of organic pollutants and nutrients, co-varied negatively with Chl-a, whereas the PC2 cluster, representing biogenic organic matter, co-varied positively with Chl-a. Moreover, partial least squares path modeling showed that humic-like and tryptophan-like substances were positively correlated with Chl-a, with the path coefficients of 0.47 and 0.19, respectively. These findings revealed the interaction patterns between DOM components and Chl-a at the river-lake confluence zone, thereby enhancing our understanding of the factors influencing the spatio-temporal variations in Chl-a concentration, and further providing a guide for the control of algal blooms.

Water doi: 10.3390/w18101159

Authors: Wen-Lin Wang Rey-May Liou Chuan-Chi Chien Zong-Yu Wu Yung-Chi Kuo Shih-Chi Lee

Livestock wastewater is an important source of nitrogen pollution, but it also represents a potential feedstock for nitrogen recovery. In this study, longan wood-derived biochar was used as an immobilization carrier in a bio-ammonification system developed with aerobic and facultative ammonifying bacteria isolated from swine wastewater. The system was designed to enhance microbial retention and promote the conversion of organic nitrogen into ammonium concentration (NH4+-N) under oxygenated conditions. Among the tested strains, Lysinibacillus sp. (strain 4-1) showed the highest ammonification activity, reaching an NH4+-N concentration of 340 mg/L in NB medium within 5 days. In sterilized swine wastewater, the biochar-immobilized strain 4-1 achieved 47.17% organic nitrogen removal. The results suggest that coupling microbial ammonification with biochar immobilization may provide a low-carbon approach for nitrogen recovery from livestock wastewater and facilitate decentralized bio-ammonia production.

Water doi: 10.3390/w18101158

Authors: Edward A. Delgado Suero Christine E. Stauber Karen E. Nielsen José O. Payero César E. Cruz Mena

Santiago, Dominican Republic, faces a growing deficit in the supply of drinking water. Rainwater harvesting systems have the potential to provide a reliable and sustainable source of drinking water. This research examines water quality from the pilot testing of a rainwater harvesting system designed to directly capture rainwater in planter boxes, pre-filter it and store it. The pilot testing consisted of a field experiment comparing rainwater harvested with four filter media compositions with varying levels of sand (34, 62, 66 and 76%). From May 2024 to May 2025, bi-weekly water samples were tested for physicochemical and microbiological parameters including pH, electrical conductivity, total dissolved solids, turbidity, biochemical oxygen demand, heterotrophic bacteria, total and fecal coliforms, E. coli, and Enterobacteriaceae. Statistical models were fitted for each water quality parameter, using linear mixed-effects models or generalized linear mixed-effects models with a logit link, to evaluate the association between filter unit design and water quality outcomes. Results showed that physicochemical quality met Dominican drinking water standards but infrequently met bacteriological standards. However, filters with higher sand composition produced higher quality water for both physicochemical and microbiological parameters. Additional treatment such as chlorination would reduce bacteria and protect the water during storage.

Water doi: 10.3390/w18101157

Authors: Qianqian Zhang

As a critical component of the Earth’s ecosystem, aquatic environments are under sustained pressure from multiple pollution sources, including industrial and agricultural activities, urban runoff, wastewater treatment plant effluent, and atmospheric deposition [...]

Water doi: 10.3390/w18101156

Authors: Germania Tulcán Leandro Morillo David Naranjo Isabel Espinoza-Pavón Christian Sandoval-Pauker William Villacis Oñate Paul Vargas Jentzsch Florinella Muñoz Bisesti

Thiabendazole (TBZ) is a fungicide widely used in agriculture and frequently detected in water bodies and effluents from greenhouse and food processing activities. In this study, the removal and mineralization of TBZ from water by electron beam irradiation, in the absence and presence of hydrogen peroxide (H2O2), were investigated. Synthetic aqueous solutions containing TBZ (10 mg L−1) were treated at absorbed doses of 2, 3, and 4 kGy, using different H2O2 concentrations (0, 5, 10, and 15 mM). The effectiveness of TBZ removal was evaluated by determining residual TBZ concentrations, while mineralization was assessed through changes in total organic carbon (TOC), sulfate, and nitrate concentrations, together with pH and electrical conductivity measurements. Under all investigated conditions, complete TBZ degradation was achieved, with final concentrations below the detection limit of the chromatographic method. However, mineralization was partial and strongly dependent on treatment conditions. The highest mineralization degree was obtained at 4 kGy and 15 mM H2O2, resulting in a TOC removal of 52.4% and sulfur and nitrogen mineralization ratios of 50.2% and 13.7%, respectively. These results demonstrate that electron beam irradiation is highly effective for TBZ degradation. At the same time, while oxidant-assisted conditions are required to enhance mineralization, this highlights the need to distinguish between pollutant removal and complete mineralization in water treatment processes.

Water doi: 10.3390/w18101155

Authors: Angie Tatiana Ortega-Ramírez Isaías Daniel Hinojosa-Flores Elías Luis Ángel Martínez González Emilio Ramírez Cid Andrea Sánchez Chávez

The city of Bogotá is currently facing a water crisis marked by a worrying drop in the levels of the watershed subsystems that supply more than eight million people. This situation is exacerbated by population growth, climate change, deforestation, and poor water resource management. This research analyzes the current situation of water management in Bogotá based on hydrometeorological data, demographic forecasts, and surveys of citizen perception and adaptation to different measures, such as rationing. It highlights the high dependence on the spatial analysis highlights the high dependence on the areas primarily supplied by the Chingaza system presented higher vulnerability due to their dependence on a single supply source, as well as the evident impact of the El Niño phenomenon and the limited implementation of structural measures by the population. The results show that most people resort to immediate and cost-effective solutions, postponing the implementation of long-term sustainable strategies. Similarly, rationing affected different aspects of the daily routine of a large part of Bogotá’s population. Thus, this study highlights the need to strengthen water infrastructure, improve environmental education, and promote comprehensive public policies that ensure the sustainability of a resource as indispensable as water.

Water doi: 10.3390/w18101154

Authors: Mengfei Liu Jianwei Zhang Yiwen Chen Meng Zhou Yunxiao Pan Ye Hong Yaohua Hu

Under complex disturbances and backwater time-delay conditions, traditional open-channel gate water level control suffers from insufficient accuracy and slow response, readily causing water level overruns, control instability, and engineering safety risks. To overcome the limitations of conventional controllers in responding to rainfall disturbances, this study proposes a Model Predictive Control (MPC) algorithm based on the Integrator Delay (ID) model. The approach first integrates an LSTM-KAN (Kolmogorov–Arnold Network) model for accurate rainfall prediction, providing reliable inputs for disturbance feedforward. Subsequently, leveraging the SWMM simulation model and the PySWMM library, ID model parameters (backwater area and lag time) are identified in real time through impulse response testing. A state-space representation is then formulated and incorporated into the MPC rolling optimization framework, enabling precise water level forecasting over the prediction horizon. Simulation results demonstrate that the average computation time for 24-hour tests is only 240 seconds, with markedly reduced water level deviations. Experimental validation confirms superior performance under steady flow conditions (flow fluctuations < 0.007 m3/s; settling time ≈ 210 seconds) and constant water level control, achieving water level deviations < 0.05 m in known disturbance scenarios. Compared with the conventional Linear Quadratic Regulator (LQR), the proposed MPC algorithm reduces gate response time by 6.38–19.80% under the tested rainfall conditions. The proposed method establishes a complete closed-loop framework integrating rainfall prediction, water level forecasting, and combined feedforward-feedback control, offering an efficient and practical solution for open-channel gate water level management in smart water conservancy systems. It holds considerable theoretical significance and application value.

Water doi: 10.3390/w18101153

Authors: Sevgi Cavdar Muhammad Ashraf Muhammad Ben R. Hodges

Rapidly removing rainfall from roadways is necessary to avoid vehicle accidents caused by hydroplaning or suddenly unbalanced forces on the front wheels. Ensuring adequate water removal and minimal bypass requires correct sizing of drainage structures. Undepressed curb opening inlets (UCOIs) are often preferred along high-speed roads where curb depressions can cause a loss of vehicle control. Recent work has shown that classic curb inlet design equations can be in error for long curb opening inlets (>2 m). This study provides results of laboratory experiments that build on recent work to evaluate the performance of different curb inlet equations. A new approach using neuro-fuzzy modeling that applies the proven adaptive neuro-fuzzy inference systems (ANFIS) was evaluated for use in sizing UCOI. This study aims to find the method that has the best hydraulic performance. Results show that some earlier models actually estimate inlet lengths better than more recent design equations under some roadway configurations. The use of the ANFIS approach provides the lowest root mean square errors and mean absolute percentage errors when compared to available models and may be adopted in the practice of UCOI inlet design safely.

Water doi: 10.3390/w18101149

Authors: Zvesdimira Tsvetanova Rosen Boshnakov Tanya Chan Kim Hristo Najdenski

Antibiotic resistance (ABR) is a significant threat to human and animal health, as well as to the environment. Antibiotic residues, antibiotic-resistant bacteria and antibiotic resistance genes are emerging contaminants of water resources. The present study aimed to assess the prevalence of ABR among waterborne enterococci in an anthropogenic-affected section of the Yantra River (Bulgaria). The susceptibility of 426 strains to 13 antibiotics (ABs) was tested by the disk diffusion method, and the genes encoding resistance by PCR analyses. A total of 39% of isolates were found to be antibiotic-resistant, with 9% mainly being multidrug-resistant to three AB classes. The most common resistance was to erythromycin (19%), tetracycline (18%) and ampicillin (14%), encoded by the ermB, tetM and blaTEM genes. A total of 3% of isolates were ciprofloxacin-resistant and only 1% was resistant to vancomycin or high-level gentamicin. All isolates were susceptible to teicoplanin and linezolid. Spatial variations in ABR levels were found, with the lowest abundance of antibiotic-resistant enterococci occurring in upstream river waters, away from urban areas, and the highest in urban areas. The spread of waterborne antibiotic-resistant enterococci highlights the need for water pollution management, monitoring and control to limit anthropogenic pressures through wastewater discharges and diffuse fecal pollution, and to ensure the ecological well-being of receiving waters.

Water doi: 10.3390/w18101152

Authors: Monin Nong Toru Konishi Takuto Kumagae Hideo Amaguchi Yoshiyuki Imamura

Rapid peri-urban expansion has intensified flood risk in Southeast Asian cities through wetland loss, rural–urban migration, and delayed infrastructure development. This study examines the spatial and temporal dimensions of flood risk in Phnom Penh, Cambodia using a multi-factor framework based on hazard, exposure, vulnerability, and coping capacity. Vulnerability and coping capacity are analysed at both community and household levels. Migrant settlement duration captures differences in exposure and adaptive capacity over time. A composite flood risk index is constructed from survey data using the Rank Order Centroid weighting method. Results show that exposure is the dominant driver of flood risk, exceeding the influence of hazard intensity and largely shaping spatial patterns. Community-level vulnerability and coping capacity exert stronger effects than household-level characteristics, highlighting the importance of infrastructure and local settings. Flood risk varies across migrant groups: new migrants face the highest risk due to elevated exposure and vulnerability, while long-term migrants experience lower risk as adaptive capacity improves over time. However, risk reduction varies across groups, with persistent challenges linked to infrastructure and disaster preparedness systems. These findings highlight the importance of community-scale resilience strategies and targeted infrastructure investment to reduce flood risk in rapidly urbanising cities.

Water doi: 10.3390/w18101151

Authors: Lele Xiao Donghou Cao Chao Niu Songsong Cheng Chuanwei Jia Menghan Ma Yanchao Wang

Understanding how the development of large-scale coal mining bases affects river hydrochemistry is a key scientific issue in the field of water environment research. In this study, the Qingyang–Binzhou section of the Jinghe River Basin was selected as the study area, and a total of 29 water samples were collected in April 2025 from the upper to lower reaches of the coal mining base. Hydrochemical analysis, ion ratio methods, and the positive matrix factorization (PMF) model were comprehensively applied to systematically characterize the hydrochemical features and identify the pollution sources in the river under the influence of large-scale coal mining activities. The results showed that the mean concentrations of Na+, SO42−, Cl−, and total dissolved solids (TDS) in the mainstream were as high as 414 mg/L, 728 mg/L, 226 mg/L, and 1636 mg/L, respectively, reflecting a significant impact of coal mining activities on river hydrochemistry. Four spatial variation patterns were observed along the river: the first pattern was characterized by “stable in the upper reaches, sharp increase in the middle reaches, and fluctuating increase in the lower reaches,” represented by Na+ and SO42−; the second pattern showed “stable in the upper reaches, slight decrease in the middle reaches, and fluctuating decrease in the lower reaches,” represented by pH; the third pattern exhibited “fluctuating in the upper reaches, sharp decrease in the middle reaches, and extremely low levels in the lower reaches,” represented by NO3−; and the fourth pattern was dominated by irregular variations controlled by nitrogen transformation processes, represented by NH4+ and NO2−.Gibbs plots and ion ratio diagrams indicated that the hydrochemistry of sites unaffected by coal mine drainage was primarily controlled by rock weathering, whereas contaminated samples shifted toward the evaporation-concentration zone and extended beyond its typical range, reflecting an “anthropogenic salinization effect” induced by the input of mine water superimposed on the arid to semi-arid climatic background. The PMF model identified three main pollution sources: coal mining and mine water discharge (48.3%), domestic sewage (30.2%), and carbonate weathering (21.5%). This study reveals the significant modification mechanism of river hydrochemistry by large-scale coal mining base development, providing a scientific basis for targeted water pollution control in the Jinghe River Basin and for water environment management in similar mining areas.

Water doi: 10.3390/w18101150

Authors: Aanchal Kumari Chomphunut Poopipattana Hiroaki Furumai Manish Kumar

Pharmaceuticals and personal care products (PPCPs) are widely recognized as persistent contaminants in urban aquatic systems, yet their behavior is typically interpreted under steady-state assumptions driven by continuous discharge of treated wastewater. This paradigm overlooks the dominant role of episodic pollution pulses associated with combined sewer overflow (CSO) events. This review advances a new conceptual framework in which PPCP contamination is understood as a manifestation of complex phenomenon, arising from the interaction of intense precipitation, hydraulic exceedance of sewer systems, and mobilization of accumulated contaminants. We critically synthesize current knowledge on the occurrence, transport, transformation, and removal of PPCPs across wastewater effluents and CSO discharges, integrating insights from degradation kinetics, environmental monitoring, and treatment technologies. Comparative analysis reveals strong matrix-dependent variability in PPCP attenuation, with enhanced degradation in estuarine and marine systems driven by complex photochemical and biogeochemical interactions. However, under CSO-driven pulse conditions, these processes become transient and non-linear, challenging conventional assumptions of steady-state degradation and risk assessment. The findings highlight that CSO events can generate short-duration but high-intensity contamination peaks, often exceeding baseline concentrations and potentially amplifying ecological risks and antimicrobial resistance selection. We propose a matrix-reactivity and pulse-driven framework to better capture the dynamic fate of PPCPs under real-world conditions. Future research should prioritize event-based monitoring, real-time sensing, and time-resolved risk assessment models to address the limitations of current approaches. This work redefines PPCP pollution as a dynamic, episodic, extreme-event-driven process, with important implications for urban water management under increasing climatic variability.

Water doi: 10.3390/w18101148

Authors: David Patiño-Ruiz Oscar E. Coronado-Hernández Manuel Saba

Draining operations using pressurised air can produce sub-atmospheric pressures that pose a significant risk to structural integrity, given the pipe stiffness class. This research presents a modelling strategy for predicting water velocities during the occurrence of this phenomenon. The proposed approach combines a physically based hydraulic formulation with machine learning techniques for making this prediction. A calibrated rigid water column model is first employed to reproduce the transient interaction between the expanding air phase and the draining water column. Input parameters include pipe bridge height varying from 0.5 to 3.0 m, a valve loss dimensionless coefficient ranging from 2.0 to 14.0, and an initial water column length between 163.0 and 286.3 m. Subsequently, a Monte Carlo scheme is used to generate a representative dataset. A total of 28 models were assessed, among which a wide neural network demonstrated superior predictive capability, achieving root-mean-square error values between 0.043 and 0.056 m/s and coefficients of determination ranging from 0.996 to 0.997 for the validation and testing stages, respectively. Sensitivity analyses indicate that the minor loss coefficient governs the water velocity response, whereas geometric features such as the pipe bridge height exert a comparatively minor influence.

Water doi: 10.3390/w18101147

Authors: Wenjie Zhang

The rapid advancement of industrialization and urbanization has brought about significant challenges to water quality and environmental health [...]

Water doi: 10.3390/w18101146

Authors: Yuxin Fang Jingrui Mo Wenxiang Ding Rui Zeng Yurun Li

Marine heatwaves (MHWs) in the Eastern China Seas exert profound ecological and economic impacts, highlighting the need for reliable indicators to support early prediction. Based on observations from 1982 to 2022, this study identifies three characteristic patterns linking annual maximum sea surface temperature (Tmax) with summer MHWs: in July, the northern region follows a pattern where earlier Tmax favors more frequent MHWs; in August, the whole study area is dominated by a mode where Tmax coincides with the seasonal threshold peak, driving widespread MHWs; and in September, the southern region exhibits a pattern where later Tmax favors more frequent MHWs. A threshold-based method integrating both Tmax and its timing demonstrates strong skill in assessing MHW occurrence and exhibits practical utility when validated with independent observations from 2023 to 2024. Long-term warming of Tmax, together with regionally divergent trends in its seasonal timing, closely aligns with observed increases in MHW days. Significant correlations between Tmax and preceding monthly mean SST suggest that Tmax integrates accumulated thermal conditions and carries seasonal memory, offering a potential pathway from seasonal SST prediction to early MHW risk assessment. These findings clarify the structured and regionally differentiated Tmax–MHW relationship, demonstrate the feasibility of a Tmax-based assessment framework, and provide a scientific basis for improving seasonal monitoring and early warning of MHWs under sustained climate warming.

Water doi: 10.3390/w18101145

Authors: Dana Claudia Filipoiu Daniela Gitea Raul Ștefan-Pantiș Alin Mogos Ștefan Știer Gabriela S. Bungau Delia Mirela Tit

This study evaluated the occurrence, spatial distribution, and associated human health risks of trace metals in water intended for human consumption from urban and rural areas of Satu Mare County (northwestern Romania) based on monitoring data collected between 2022 and 2024. A total of 271 samples from 122 localities were analyzed for As, Cd, Cr, Mn, Ni, Pb, and Se using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). Spatial analysis, non-parametric statistics, Spearman correlation, and principal component analysis (PCA) were applied to identify distribution patterns and differences between supply systems. Arsenic was identified as the main contaminant of concern, with concentrations reaching 320.5 µg/L, primarily in rural groundwater sources. Most other metals remained below regulatory limits, and elevated concentrations were spatially localized rather than widespread. Non-carcinogenic risk (HRI > 1) was observed in 5.74% of samples, while arsenic-related carcinogenic risk (ILCR > 10−6) occurred in a limited number of locations in 2024, with no values exceeding 10−4. Risk estimates were based on total arsenic concentrations and should be interpreted conservatively due to the lack of speciation. No statistically significant differences between urban and rural areas were observed for most metals, except for manganese. Multivariate analysis revealed distinct geochemical behaviors, with a Pb–Ni–Se–Cd cluster in rural samples, while arsenic and manganese showed more independent patterns consistent with redox-controlled processes. Urban samples showed more coherent patterns and higher variance explained by PCA (78.9%) compared to rural datasets (60.1%). Risk estimates were based on total arsenic concentrations and should be interpreted conservatively. The findings highlight the vulnerability of decentralized groundwater systems and support targeted monitoring strategies in line with Directive (EU) 2020/2184.

Water doi: 10.3390/w18101144

Authors: Katarzyna Pietrucha-Urbanik Janusz Rak

The third edition of this Special Issue appears at a time when water utilities are being reshaped by digitalisation, climate variability, ageing infrastructure and rising expectations regarding service continuity [...]

Water doi: 10.3390/w18101143

Authors: Cem B. Avcı

Classical pumping-test interpretation relies on instantaneous drawdown and its time derivative, both of which amplify measurement noise. This study introduces cumulative drawdown, or absement, as the primary state variable for confined aquifer pumping-test analysis. Time integration of the transient flow equation yields a governing relationship connecting instantaneous drawdown to the spatial curvature of cumulative drawdown. A closed-form absement kernel is derived from the Theis solution and cast in dimensionless form, yielding four diagnostic operators: absement A(t), time-averaged absement A(t)/t, windowed ΔA/Δt, and the normalized absement derivative (NAD). The four operators read different features of the same drawdown record and together cover parameter estimation, scale-resolved diagnostics, and flow-regime identification. Monte Carlo testing (N = 50) under combined Gaussian, log-time jitter, and quantization noise recovers transmissivity to within 0.1% of the true value (p > 0.5). Field tests on homogeneous and heterogeneous confined aquifers reproduce classical Theis and Cooper–Jacob estimates and identify two scale-dependent regimes in the Oude Korendijk dataset.

Water doi: 10.3390/w18101142

Authors: Miao Feng Zhu Liu Tao Su

Rain-on-snow (ROS) is a hydrometeorological phenomenon in which liquid precipitation falls onto an existing snowpack, augmenting runoff through the combined effects of rainfall and accelerated snowmelt. Anthropogenic climate change is progressively shifting the rain-to-snow partitioning of precipitation and altering land-surface conditions across mid- to high-latitude mountainous regions, thereby heightening flood potential. Most previous work, however, has addressed ROS at regional scales and over historical periods; hemispheric-scale assessments of future ROS dynamics and their implications for flood hazard and societal exposure remain scarce. Here we apply 10 bias-corrected CMIP6 models together with ERA5-Land reanalysis data to project changes in ROS days across the Northern Hemisphere under four Shared Socioeconomic Pathway (SSP) scenarios. ROS days are coupled with flood frequency analysis to quantify changes in ROS flood occurrence, and gridded population and Gross Domestic Product (GDP) data are integrated to evaluate future population-socioeconomic exposure. Under low-to-medium emission scenarios, ROS days increase substantially over historical hotspots, whereas under high-emission scenarios they decline at mid- to high latitudes yet expand into previously unaffected high-latitude and inland cold regions. ROS flood days respond nonlinearly to ROS frequency because progressive snow water equivalent loss limits runoff generation, causing ROS floods to decrease in some mountainous areas even as ROS events become more frequent. Population-socioeconomic exposure exhibits a corresponding polarization: it declines in mid-latitude regions where snow cover is disappearing but rises sharply at high latitudes, with high-emission pathways accelerating the northward migration of disaster risk. These findings bridge critical gaps in large-scale ROS climatology and shed light on future changes in ROS-induced hydrological extremes. Besides, the findings facilitate the creation of regionally focused adaptation strategies and provide useful references for integrating climate model projections with remote sensing observations to improve future monitoring and risk assessment of ROS-related floods.

Water doi: 10.3390/w18101141

Authors: Yasmeen Saleem Davie M. Kadyampakeni

Sustainable southern highbush blueberry production in Florida is increasingly constrained by freshwater competition, variable rainfall, and the chemical vulnerability of coarse-textured and organic-based production media. Reclaimed water irrigation and biochar amendment are promising strategies for improving water use efficiency and root zone function, but their combined implications for blueberry systems remain insufficiently understood. This review synthesizes the current knowledge on blueberry production requirements, the regulatory and operational context of reclaimed water use, and the physical and chemical roles of biochar in sandy and pine bark-based substrates relevant to horticulture in Florida. Particular emphasis is placed on mechanistic links among reclaimed water chemistry, substrate properties, and root zone processes that govern salinity, pH drift, nutrient retention, and solute leaching. The literature indicates that reclaimed water can improve irrigation reliability and provide supplemental nutrients, but may also introduce sodium, chloride, boron, and other constituents, as well as alkalinity, which alter substrate chemistry and increase the risk of salinity stress and nutrient imbalance. Biochar may enhance water retention, cation exchange, and sorption capacity, but its effects are strongly dependent on feedstock, production conditions, aging, application rate, and substrate context. Overall, successfully integrating reclaimed water and biochar into blueberry systems requires substrate-specific and constituent-resolved evaluation under production conditions relevant in Florida.

Water doi: 10.3390/w18101140

Authors: Xiaodong Cheng Jian Tong Maomei Wang Yi Xu Sicheng Wan Kaiyong Rao

With the increasing development of underground spaces adjacent to urban levees, contact seepage frequently occurs at the interface between the soil and underground structures. However, traditional geophysical detection methods are often rendered ineffective in such environments due to spatial restrictions and detection blind spots. To address these challenges, this paper proposes a vertical-array lateral scanning detection method. This approach utilizes electrical resistivity tomography (ERT) with flat-base electrodes and ground-penetrating radar (GPR) to acquire data directly from vertical wall surfaces. The feasibility of this method is validated through numerical simulations and field data. The results indicate that the proposed method effectively overcomes the high-resistance shielding effect of hardened walls and clearly reveals the electrical structure of the soil behind the wall. Specifically, the contact seepage zone manifests as a layered low-resistivity feature immediately adjacent to the wall, while the penetrating leakage channel presents as a continuous low-resistivity anomaly extending from the contact interface deep into the levee body. These findings confirm the applicability of this technology for the qualitative identification and effective detection of hazards in complex, space-restricted urban environments.

Water doi: 10.3390/w18101139

Authors: Shengjie Yang Jianlong Li He Yang Liang Zhong Tao Liu Zhengguo Sun

Water scarcity is an increasingly pressing global concern, making the sustainable development of water resources a critical priority. Revered as the “Sacred Sea,” Lake Baikal holds the largest volume of freshwater in any single lake in the world, with exceptional water quality, conferring it with considerable global strategic importance. This study reviews the hydrological dynamics of Lake Baikal, including water level fluctuations and runoff patterns, and examines water resource utilization (including virtual water and long-distance diversion), along with its potential, challenges, and associated ecological risks, in an integrated manner. Previous studies reveal an interannual cycle of fluctuating water levels, with annual peaks typically occurring between September and October. Outflow runoff closely depends on lake water levels, while inflow runoff exhibits considerable variability. The Selenga River, the largest tributary originating from the Mongolian Plateau, significantly influences the lake’s hydrology and ecological integrity. Current water uses primarily include domestic supply, regional industry, and fisheries, while agricultural water use is relatively limited and mainly occurs within tributary catchments. Emerging options, such as virtual water trade, may offer relatively more manageable alternatives to large-scale transboundary water transfers in certain contexts. Given the multiple disturbances and potential impacts on the Lake Baikal ecosystem, this study advocates prioritizing ecological protection in water resource utilization and underscores the necessity of comprehensive, system-level assessments prior to any water extraction or diversion activities.

Water doi: 10.3390/w18101138

Authors: Alaa Aldein M. S. Ibrahim Mfanasibili Nkonyane Mlondi Ngcobo Tom Walingo Jules-Raymond Tapamo

Predicting algal proliferation in freshwater systems is crucial for effective water quality management and ecological sustainability. This study proposes a novel data-driven framework that integrates correlation-based feature ranking with a concatenation-enhanced artificial neural network (ANN) architecture to improve algae prediction accuracy. The analysis was conducted through a systematic evaluation of parameter relationships, employing Pearson’s correlation coefficient and standardized coefficients (Beta) to determine feature importance. Based on the magnitude of these coefficients, the input variables were progressively grouped into six feature sets, enabling a comparative assessment of predictive performance. The ANN models were trained and validated using root mean squared error (RMSE), mean absolute error (MAE) and Normalized Nash–Sutcliffe Efficiency (NNSE) as evaluation metrics. The results demonstrate that the fourth feature set, including chlorophyll-a, temperature, dissolved oxygen, total dissolved solids, and ammonia (NH3), identified through combined Pearson and Beta analysis, achieved the lowest prediction errors and superior generalization performance. These findings highlight the effectiveness of feature selection guided by correlation and standardized coefficients in enhancing ANN performance for algae prediction. The proposed framework offers valuable insights for improving the predictive modeling of algal dynamics, thereby supporting proactive water quality monitoring and the sustainable management of aquatic ecosystems.

Water doi: 10.3390/w18101137

Authors: Teresa Guarda Oscar E. Coronado-Hernández Jairo R. Coronado-Hernández

Water utilities frequently perform pipeline-emptying operations for maintenance, repair, and operational management. This process involves transient flow conditions with entrapped air. It must be carefully controlled, as the expansion of air pockets can generate sub-atmospheric pressures that may lead to pipeline collapse. The mathematical modelling of emptying processes with air valves has been extensively studied in recent years; however, such approaches typically rely on complex algebraic–differential equation systems. This study advances understanding of this phenomenon by proposing a novel procedure that uses a machine learning model to approximate system behaviour while avoiding fully coupled hydraulic formulations. An experimental facility consisting of a pipeline with an internal diameter of 0.042 m and a total length of 4.6 m was used, in conjunction with a complete regulation valve manoeuvre. The system was first calibrated using experimental data and subsequently employed in Monte Carlo simulations to generate a dataset for training the machine learning model. The results demonstrate that a Rational Quadratic Gaussian Process Regression model can accurately predict the minimum sub-atmospheric pressure, achieving a coefficient of determination greater than 0.999 during validation and testing. The proposed framework is presented as a proof-of-concept and has been validated only for the specific case study analysed. While the results highlight its potential to support planning for emptying operations under varying air-admission conditions and air-pocket sizes, further validation is required before generalising to real-world water distribution systems. For practical implementation, the model must be appropriately trained for each specific installation.

Water doi: 10.3390/w18101134

Authors: David Choque-Quispe Mabel Yésica Maucaylle Aroni Frida E. Fuentes Bernedo John Peter Aguirre-Landa Katia Choque-Quispe Delma D. Reynoso-Canicani Henrry W. Agreda Cerna Bryan Jefferson Abollaneda Altamirano Arturo Rojas Benites Alfredo Prado Canchari Edwin Mescco Cáceres Medalit Villegas Casaverde

The quality of water for human consumption depends on the supply method and source type. Water may contain pathogens and excessive constituents that pose health risks, and timely monitoring and planned service provision help ensure its quality. This study assessed the supply system, quality, and health risks associated with the consumption of water from three sources in the high-elevation Andean city of Andahuaylas, Peru, managed by the Municipal Sanitation Service Provider Chanka (EMSAP). The sources were found to provide between 0.8 and 32 L/s, with consumption of about 17 m3 per connection per month, at a cost of 0.20 USD/m3. The system shows a current deficit and a projected deficit for 2027 due to increasing user debts and the absence of mechanisms for payment for ecosystem services (PESs), despite the existence of cross-subsidies. Water quality, assessed using the WQI-Pe, ranged from regular to excellent, although with high levels of heavy metals according to the Environmental Quality Standards for Water (EQS–Peru), which increases the non-carcinogenic health risk. Chronic non-carcinogenic exposure (HQ) from consumption and dermal contact exceeded one, mainly for arsenic (As), while the deterministically and probabilistically evaluated incremental lifetime cancer risk (ILCR) was linked to high levels of As, Cr, and Cd across all age groups (infants, children, adolescents, and adults). Overall, this study provides insight into the state of water in areas without conventional treatment, so the implementation of buffer zones in the basin’s headwaters in localities with similar characteristics is vital.

Water doi: 10.3390/w18101135

Authors: James N. McNair Daniel Frobish Isabelle Ciarrocchi Richard R. Rediske

Quantitative analytical methods for measuring concentrations of chemical substances in aquatic systems typically have acceptable accuracy and precision only for an intermediate range of analyte concentrations. Outside this range, the uncertainty of concentration estimates is too high to justify reporting them as valid measurements for use in statistical analyses. Therefore, concentration estimates falling below the lower reporting limit (LRL) are typically reported as the LRL, along with a code indicating that the measured values fell below the LRL. Such data are called left-censored data. Similarly, concentration estimates falling above the upper reporting limit (URL) are typically reported as the URL, along with a code indicating that the measured values exceeded the URL. Such data are known as right-censored data. Censored data violate assumptions underlying most traditional statistical methods, such as t-tests, regression analysis, and analysis of variance. We briefly review various statistical methods that have been employed for the analysis of censored concentration data, then review in greater detail some modern statistical survival-analysis methods that have become available in standard software within the last 10 years and can be applied to concentration data with both left- and right-censored values. Methods are illustrated with real data.

Water doi: 10.3390/w18101136

Authors: Guang Yang Chao Zhang Sichu Bai Bo Wang Jing Sun Jing Li Quanbao Su Chao Ma Gang Wang

Located in eastern China, the Nanshu area is abundant in groundwater resources with favorable water quality, acting as a critical water supply source for the region. In recent years, the regional groundwater environment has been significantly disturbed by continuous anthropogenic activities, which has aroused widespread concern. In this study, correlation analysis, principal component analysis, hydrochemical methods, the Entropy Weight Water Quality Index, and the Human Health Risk Assessment model were comprehensively applied to systematically investigate groundwater in the Nanshu area. The research objectives are to determine the health risk levels of regional groundwater and provide a scientific basis for the protection and rational utilization of groundwater resources. The results indicate that groundwater in the study area is weakly alkaline freshwater, dominated by the HCO3-Ca hydrochemical type. With favorable groundwater circulation conditions and weak evaporative concentration effects, it generally exhibits the typical natural hydrogeochemical characteristics of shallow groundwater in the piedmont regions of northern China. The chemical composition of groundwater is mainly controlled by water–rock interactions. The dissolution of silicate minerals, gypsum, halite and sepiolite, together with significant reverse cation exchange, collectively shape the hydrochemical composition, and natural hydrogeological conditions form the basic pattern of regional water quality. The overall potability of groundwater in the study area is moderate. Approximately 30% of the groundwater is unsuitable for direct drinking due to anthropogenic pollution, and agricultural activities and domestic sewage discharge have become key factors causing local water quality degradation. Non-carcinogenic health risks posed by groundwater nitrate vary significantly among different populations. The risk level for infants and young children is much higher than that for adults, posing a substantial health threat to sensitive populations. According to the findings, it is recommended to focus on controlling the groundwater risk sources in the central area, strengthen the dynamic monitoring of water quality in water source zones, and strictly regulate regional development activities, so as to achieve the sustainable utilization of groundwater resources.

Water doi: 10.3390/w18101133

Authors: Andrei-Mirel Florea Riana Iren Radu Alina Petronela Comăniță Bercu Sevastel Mircea

In order to ensure agricultural productivity and, implicitly, food security, irrigation is indispensable in regions with extensive agricultural areas subject to water stress. In such areas, approaches are needed to optimize water resources and better understand irrigation needs, aspects that cannot be captured exclusively through administrative reporting. This study analyzed the annual dynamics of irrigation in Galați County, Romania, during 2017–2025 using satellite data, spatial analysis techniques, and public administrative records. Using a Random Forest classifier applied to multitemporal Sentinel-2 and Landsat data, annual maps of irrigated areas were generated and their distribution inside and outside official irrigation systems was analyzed. Satellite-detected irrigated area varied from 19.1 thousand ha in 2017 to 41.8 thousand ha in 2023, broadly consistent with hydroclimatic variability. Agreement between satellite data and official reports was moderate at the aggregate level (r = 0.782, R2 = 0.612), but strong at the irrigation-scheme level (r = 0.907, R2 = 0.822). Spatial analysis further showed that 60.1% of the cropland-filtered outside-system irrigated area was located within 500 m of the nearest potential surface water source. The results indicate that satellite-based analysis can serve as a useful complementary tool for irrigation monitoring, spatial assessment, and county-scale irrigation auditing.

Water doi: 10.3390/w18101132

Authors: Xiujuan Li Yisu Zhou Chunhui Wang Jingqing Liu

Precise coagulant dosage control is essential for stable drinking-water treatment, yet conventional machine learning (ML) methods can be sensitive to data conditions. This study evaluates a large language model (LLM)-based in-context workflow for this tabular prediction task using the DeepSeek family, benchmarked against XGBoost, ANN, SVM, and k-NN under a shared chronological protocol. We examined performance across feature configurations, training-pool conditions, and outlier subsets. On the HQ-WTP case dataset, full-feature input outperformed temperature-only input, indicating the value of multivariate information. Performance responses to training-pool condition were model-dependent, with no universal optimum. Under the fixed protocol, in the full-feature test setting, the strongest tabular baseline showed the strongest test performance, while DeepSeek-Reasoner and DeepSeek-Chat showed intermediate performance, and DeepSeek-R1-Distill-Qwen-32B showed relatively lower stability. DeepSeek-Reasoner reached its best test performance at the 1/2 condition. We also coded narrative rationale patterns in generated responses and performed a protocol-based hallucination audit. DeepSeek-Reasoner showed comparatively lower hallucination incidence and more stable error behavior in this benchmark. These analyses are interpreted as response-level reliability evidence rather than verification of internal computational mechanisms. Overall, the study provides transparent, case-specific benchmark evidence for LLM-assisted decision support, while broader deployment claims require strict hallucination control, human-in-the-loop safeguards, and independent multi-site validation.

Water doi: 10.3390/w18101131

Authors: Yonggang Lu Mengjiao Min Yanzhi Li Zhiwang Liu Wenxuan Liu Bo Gao Weiqiang Zhao

With the rapid depletion of terrestrial mineral resources, the global demand for deep-sea mineral resource exploitation has become increasingly urgent. The hydraulic lifting system centered on deep-sea mining pumps is internationally recognized as the most commercially viable deep-sea mining system. In this paper, a deep-sea mining pump is taken as the research object, and the flow and wear characteristics of solid–liquid multiphase transport within the pump are investigated. Results show that as particle concentration increases, the non-uniformity of pressure and velocity distributions in the impeller flow channel also increases, indicating that particle-induced disturbances significantly compromise flow field uniformity. As the particle diameter increases, the wear dead angle area continues to expand, and the wear patterns and extents on each surface of the impeller and guide vane differ significantly. The particle collision frequency, particle kinetic energy, flow field structure, and shielding effects collectively influence the variation in wear amount.

Water doi: 10.3390/w18101130

Authors: Biyou Li Jingyun Huang Qifen Luo Yuan Zeng Zuoxiang Zhang Jianshu Zhou Yizhen Cheng

This study prepared alkali-modified porous biochar (KABC-1h) from straw via KOH impregnation and pyrolysis and systematically investigated its adsorption performance toward tetracycline (TC) in water. The optimal modification condition was determined as 2 mol/L KOH impregnation for 1 h followed by pyrolysis at 600 °C. Characterization results showed that alkali modification significantly increased the BET-specific surface area to 132.56 m2/g, enriched hierarchical micro-mesoporous structure, and introduced abundant oxygen-containing functional groups. The maximum adsorption capacity of KABC-1h for TC reached 21.60 mg/g, much higher than 14.11 mg/g of unmodified biochar (BC). Adsorption kinetics followed the pseudo-second-order model well, revealing that chemisorption dominated the rate-controlling step. Adsorption isotherms fitted the Freundlich model better, indicating multilayer heterogeneous adsorption on the biochar surface. Mechanism studies confirmed that TC adsorption was realized mainly through hydrogen bonding, π-π interaction, and surface complexation, whereas electrostatic interaction played a minor role. Moreover, KABC-1h exhibited stable adsorption efficiency over a wide pH range (4.5–11.5) and strong anti-interference ability against coexisting ions, with 59.0% removal efficiency retained after three regeneration cycles. This work demonstrates that KOH-modified porous biochar is a promising adsorbent for efficient TC removal from aqueous solution, providing a feasible strategy for agricultural waste valorization and antibiotic wastewater treatment.

Water doi: 10.3390/w18101129

Authors: Oscar Pérez-Sandoval Cristian Boyain y Goytia-Luna Cruz Robles Rovelo Erick Mattos-Villarroel Jose Gómez-Rodríguez Pedro Alvarado-Medellin

Leak localization and maintenance in water distribution networks (WDNs) are essential for reducing water losses and operating costs; however, they usually require extensive monitoring and large datasets. This work proposes a methodology that combines topological sectorization of a hydraulic node network and deep learning techniques to improve leak location by selecting representative nodes to reduce the spatial dimensionality of the WDNs. The network is partitioned using a Spectral Clustering algorithm to identify key nodes based on a weighted criterion that considers pressure variability, flow rate, and proximity to the centroid. Subsequently, a Bidirectional Long Short-Term Memory (Bi-LSTM) neural network classifies the cluster and sub-cluster where a leak occurs, using pressure and flow time series simulated in EPANET. This methodology was validated on the L-Town network, achieving an accuracy of 99.94% for cluster classification and 99.82% for sub-clusters, with a validation loss of 0.024%. During validation with 117 unseen leakage scenarios, the model reached an overall effectiveness of 85%. Moreover, Spectral Clustering outperformed K-Means in preserving physical connectivity. These results confirm the efficiency of the proposed methodology and highlight its potential for application in other hydraulic networks.

Water doi: 10.3390/w18101128

Authors: Chang Liu Hanbin Gu Jie Song Hui Li Ankai Ren Dongxu Wang

Fishing buoys are confronted with the problems of insufficient power supply and loss. To address these challenges, a small innovative fishing buoy equipped with an internal pendulum and powered by wave energy is designed. Its structural shape enables it to maintain a stable surfing state, thereby facilitating more efficient wave energy capture. Free decay tests and wave energy capture tests were conducted via numerical and experimental simulations. A mathematical model was proposed and validated using experimental data. Through free decay tests, the natural periods of the device in heave and pitch motions were obtained, which ranged from 1.0 to 1.42 s. The results of the wave energy capture tests indicate that the device can capture approximately 300 mW of electrical power under small-wave conditions. Additionally, the mechanical damping coefficient of the buoy-pendulum system was estimated to be 0.15 Nms/rad, and the mechanical efficiency of the wave energy converter was 15%. Preliminary optimization was carried out through numerical model simulation, which is conducive to the refined design of the device. This study provides a reference for the development and design of similar wave energy conversion devices.

Water doi: 10.3390/w18101127

Authors: Kensuke Sakurai Chika Abe

The high-rate contact stabilization (HiCS) process is a potential technology for recovering energy from organic matter in wastewater; however, further performance improvement is required. This study proposes a biologically enhanced HiCS (BE-HiCS) process that introduces waste-activated sludge (WAS) from a separate conventional activated sludge (CAS) train within a wastewater treatment plant (WWTP) into the HiCS stabilization tank. The performance of the proposed process was verified using a pilot-scale plant. In a scenario combining the CAS and BE-HiCS processes, which is considered feasible for practical WWTP implementation due to the ready availability of WAS, a recovery of 0.24 ± 0.03 g-COD/g-COD of the influent COD mass was projected. This value was statistically significantly higher than that achieved by either the CAS process alone or the HiCS process alone. In this scenario, WAS was added to the BE-HiCS process at a ratio of 0.15 ± 0.03 g-COD/g-COD, resulting in a net recovery rate of 0.33 ± 0.04 g-COD/g-COD, after subtracting the COD contribution of the added WAS. The superior organic matter recovery of the BE-HiCS process was attributed to its enhanced ability to convert non-particulate organic matter into sludge through absorption and adsorption, while maintaining adequate sludge settleability for effective solid–liquid separation.

Water doi: 10.3390/w18101126

Authors: Marta Kiraga Julia Górka Barbara Żarska Anna Markiewicz Beata Fornal-Pieniak

The structural integrity of hydraulic structures is frequently weakened by local scour processes downstream of weirs. This study investigates the relationship between hydraulic parameters and erosion patterns to improve the predictability of bed deformation. The research methodology integrates detailed field measurements from the Radomka River in Piaseczno with laboratory experiments using a 1:30 physical scale model of the existing weir. Bed shear stress demonstrated the strongest correlation with maximum scour depth (r ≈ 0.93; RMSE ≈ 0.0032), as it directly represents the tangential force acting on sediment particles at the bed surface, which controls their entrainment, transport capacity, and ultimately the intensity of local scour development, whereas near-bed velocity showed weak and non-significant dependence (r ≈ 0.26; ρs ≈ −0.11). This weak dependence reflects the dominance of turbulence-induced velocity fluctuations and localized vortical structures in the near-bed region, which obscure the relationship between mean velocity and sediment mobilization. The relationships between mean velocity, Froude number, and scour depth were moderate (r ≈ 0.63–0.73) and showed nonlinear characteristics, confirmed by HSIC values up to 9.1 × 10−3, due to the complex interaction between flow structures and evolving bed morphology. This nonlinearity results from the interaction between turbulent flow structures, jet-induced vortices, and the dynamically evolving bed morphology, combined with the threshold-controlled and nonlinear response of sediment transport to hydraulic forcing. Among all tested parameters, bed shear stress ranked as the dominant predictor of scour depth, outperforming velocity-based indicators. These findings imply that including bed shear stress parameters significantly improves hydraulic structure safety assessments. This study based on 11 experimental runs concludes that a combined field and laboratory approach provides a robust framework for river engineering. Finally, an improved understanding of erosion mechanisms, as presented in this work, enhances the prediction of local scour development and supports the design of more resilient hydraulic infrastructure.

Water doi: 10.3390/w18101125

Authors: Tianyun Zhang Wei Jiang Nian Wei Jiafeng Fang Nannan Li Minghua Min Ruiliang Fan Longling Ouyang Tao Zhang Weimin Quan

The current approach to coastal oyster reef restoration currently relies on conventional plastics, raising concerns about plastic pollution. Therefore, developing biodegradable alternatives, such as nano-montmorillonite-modified polylactic acid materials (PLA), has become a priority. This study compared oyster recruitment on PLA substrates with that on four conventional plastic substrates (polyethylene (PE), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polyvinylidene chloride (PVDC)) through field experiments, examining how PLA substrate thickness and surface roughness influence oyster recruitment. Additionally, we evaluated the responses of oyster populations and associated macroinvertebrate communities after ten months of restoration using PLA-based versus polyethylene (PE) shell-bag reefs. The results showed no significant difference in oyster recruitment between PLA and conventional plastic substrates (p > 0.05). However, increasing the thickness and surface roughness of the PLA substrates significantly enhanced the recruitment of juvenile oysters (p < 0.05). After ten months, there was no significant difference in oyster abundance between PLA and PE shell bag reefs; however, there was a significant difference in resident macroinvertebrate abundance, with abundances markedly higher on PLA reefs (1372 ± 220 ind./m2 vs. 545 ± 90 ind./m2; p < 0.05). This study highlights the potential of PLA as a promising alternative to conventional plastics. However, its rapid degradation limits its applicability in high-energy environments. Furthermore, given that a comprehensive assessment of the microplastic risks associated with its degradation has not yet been conducted, large-scale application is not currently recommended.

Water doi: 10.3390/w18101124

Authors: Nickolas D. Polychronopoulos Lefteris Benos Elif Hasret Kumcu Ioannis Sarris Evangelos Keramaris

Gravity currents in open channels are important transport mechanisms that influence the propagation of saline plumes in rivers, reservoirs and waterways. Predicting the evolution of the current front in channels with varying geometry and bed roughness conditions remains a challenge due to the non-linear interactions between geometric confinement, buoyancy and hydraulic resistance. In the present study, an explainable machine learning (ML) framework is developed to predict the front propagation of saline gravity currents in a composite trapezoidal open-channel configuration. Eight ML algorithms were employed, combined with a group-aware validation procedure to ensure generalization. Model performance was assessed utilizing standard regression metrics. Among the tested ML models, the CatBoost algorithm achieved the highest predictive accuracy. Interpretation of the model was carried out with the Shapley Additive Explanation (SHAP) approach to quantify the contribution of governing variables including time, initial water depth, density difference and bed condition. The SHAP analysis reveals that the initial depth in the channel has a stronger impact on the front propagation than the density difference, reflecting the combined effects of buoyancy, geometric confinement and bed roughness. Bed roughness is also a contributing factor to propagation dynamics by modifying hydraulic resistance. The proposed ML-SHAP framework provides a robust and interpretable tool for gravity current evolution prediction in channels with complex geometry and varying bed roughness. It may further aid in rapid assessment of transport processes in hydraulic and environmental settings.

Water doi: 10.3390/w18101123

Authors: Junhyeong Lee Jung-Hwan Yun Yujin Kang Seonuk Baek Hung Soo Kim

Smart water grid technologies have been widely adopted as a key component of digital transformation in water resource management, where real-time household water consumption data collected from smart water meters serve as fundamental inputs. However, these datasets often contain numerous outliers and missing values due to communication errors, which degrade data reliability and hinder accurate analysis. This study proposes an improved framework for outlier detection and missing data imputation tailored to the characteristics of cumulative household water consumption data. The proposed imputation methods were evaluated against conventional approaches using error metrics, and the results demonstrated significant improvements in accuracy, with RMSE values substantially lower than those of the reference method. In addition, prediction models with varying levels of complexity were explored to examine how improved data quality influences forecasting performance. The results indicate that, although data preprocessing enhances data reliability, prediction performance remains limited due to the inherent variability and stochastic nature of household water consumption data. Prediction models with varying levels of complexity were constructed and evaluated using the corrected datasets. The performance of the models varied depending on dataset characteristics, and no single model consistently outperformed others. Overall, this study highlights the critical role of data quality improvement in smart water management systems and provides practical insights into missing data imputation, while suggesting that further advancements in prediction require additional explanatory variables and more sophisticated modeling approaches.

Water doi: 10.3390/w18101122

Authors: Xiang He Xun Zhou Zheming Shi Fengji Yang Boqiang Xue Tong Zhang Xuelan Dong Chao Yang

To address the challenges of identifying mine water inrush sources and the low efficiency of risk control under complex karst hydrogeological conditions in the Beiya Gold Mine, Yunnan, this study proposes an intelligent identification model integrating nonlinear feature extraction and intelligent parameter optimization. Utilizing 42 sets of measured water samples (comprising karst springs, surface water, and solution caves), a coupling identification model was constructed based on 11-dimensional features including hydrochemical indices and hydrogen–oxygen isotopes. The model employs Kernel Principal Component Analysis (KPCA) to extract discriminative low-dimensional features from nonlinear data, while the critical parameters of the Support Vector Machine (SVM) are optimized via an Improved Sparrow Search Algorithm (ISSA) to enhance generalization performance. The results demonstrate that the following: (1) the proposed model achieves an identification accuracy of 91.7% on the independent test set, significantly outperforming benchmark models such as RF and standard SVM; (2) three sets of comparative experiments indicate that the fusion of multi-source features yields superior identification performance compared to single-source inputs; and (3) SHAP (shapley additive explanation) interpretability analysis reveals that HCO3−, Mg2+, Ca2+, and F− are the core discriminative factors, with their contribution patterns aligning closely with the hydrogeochemical evolution mechanisms of the mining area. This model achieves a synergy between high-precision identification and mechanical interpretability, providing reliable technical support for water disaster prevention in karst mining areas.

Water doi: 10.3390/w18101121

Authors: Jiaojiao Lv Yu Zhang Yifan Wang Zhihui Wang Dongyong Sun Huan Ma Xuedi Zhang

During severe drought conditions, water supply risks tend to be concentrated at critical water intake nodes and vulnerable river segments, while the conventional total balance method is inadequate for depicting the spatial evolution of these risks. This study developed a node-based water supply security assessment framework for the Feng River Basin, a representative watershed in the piedmont transition zone. The framework coupled SWAT-simulated runoff with a supply–demand balance model and evaluated water supply reliability at both the node and basin scales. Two scenarios were compared: an artificial water system scenario and an artificial water system with an engineering-based water resource allocation scenario. Dry (P = 75%) and extremely dry (P = 95%) conditions were considered to examine the performance of artificial regulation under drought stress. The results showed that basin-scale water supply reliability remained relatively stable, ranging from 0.833 to 0.853 under different scenarios. However, the node-scale results revealed strong spatial heterogeneity. Nodes 1 and 3 maintained full or nearly full reliability, whereas Nodes 4, 6, and 7 showed relatively low reliability and higher water shortage risk. Under the P = 75% scenario, engineering-based water resource allocation increased basin-scale reliability from 0.848 to 0.853, indicating a slight improvement in supply–demand balance. In contrast, under the P = 95% scenario, reliability decreased from 0.839 to 0.833 after introducing water resource allocation, suggesting that transfer-based interventions may have limited effectiveness when natural inflow is severely reduced. In particular, Node 7 showed a marked decline in reliability under the allocation scenario, indicating that water supply risks may be redistributed and concentrated at specific intake nodes under extreme drought conditions. The scenario comparison further indicates that water diversion strategies may produce a dual effect of local improvement and global reconfiguration. Insufficient supply intensity may result in engineering interventions that cause downstream water reduction impacts, leading to a spatial redistribution and shifting of risks rather than their systemic eradication. This study seeks to transition the evaluation paradigm from “total safety” to “node safety,” establishing a scientific foundation for enhancing the emergency response system in critical areas of the basin.

Water doi: 10.3390/w18101120

Authors: Nan Zhang Xiaoling Lv Yongjie Zhang Qingling Liu Xuezhi Zhang

Accurate and rapid identification of microalgae in ship ballast water is critical for preventing the spread of invasive aquatic species and ensuring ecological security. However, traditional manual microscopic examination is labor-intensive and limited by challenges such as high intra-class morphological variability, frequent cell aggregation, and inter-class similarity among microalgae. This study proposes YOLO11-DBalgae, a specialized end-to-end object detection framework designed for fine-grained microalgae recognition in complex aquatic environments. Two key architectural innovations are introduced into the YOLO11n baseline—a Detail-enhanced Vanishing-prevention Block (DVB), which processes input features through a VoVGSCSP cross-stage aggregation module followed by parallel Conv and DSConv paths, preserving fine-grained boundary signals of morphologically diverse algal cells during repeated downsampling, and a Bidirectional Feature Pyramid Network (BiFPN), which employs learnable cross-scale weighting to optimize multi-scale feature fusion across the extreme size range of co-occurring microalgal targets. Experimental results demonstrate that YOLO11-DBalgae achieves an mAP@0.5 of 97.3%, representing an improvement of 7.0 percentage points over the baseline YOLO11n model. The model sustains an inference speed of 240 FPS with 2.83 M parameters, maintaining a lightweight and deployment-viable profile. Qualitative analysis via per-class precision–recall curves, detection visualization, and Grad-CAM attention maps confirms the model’s robustness in recovering near-invisible weak-feature targets, minimizing false detections within dense cell clusters, and accurately distinguishing morphologically convergent species. The proposed framework provides a practical and deployable solution for automated microalgae monitoring, offering maritime regulatory bodies an efficient and reliable tool for ballast water management.

Water doi: 10.3390/w18101119

Authors: Seon-Jae Baek Seung-Hyo Lee

A C/Zn-ZnO/TiO2/Fe-FexOy (C/ZTF) nanocomposite photocatalyst with magnetic recoverability was synthesized by liquid-phase plasma (LPP) processing. Structural and surface analyses revealed that the photocatalyst consisted of TiO2, Zn-ZnO, and Fe-FexOy domains integrated with a turbostratic-like carbon matrix and accompanied by defect-rich surface features. These structural characteristics are considered to support broader light absorption and more efficient interfacial charge migration. Under LED irradiation, C/ZTF achieved 95.8% degradation of methylene blue (MB) within 60 min at pH 7, while 92.5% degradation of tetracycline (TC) was achieved within 100 min at pH 9. Photoelectrochemical and photophysical analyses indicated that C/ZTF promoted charge separation and reduced carrier recombination more effectively than the individual component photocatalysts. Scavenger experiments suggested that •OH was the dominant reactive species in MB degradation, while •O2−, h+, and e− also contributed to the reaction. The enhanced photocatalytic performance of C/ZTF is associated with improved charge separation and interfacial charge-transfer behavior in the multicomponent heterostructure. The carbonaceous phase is considered to contribute to this process, and the overall photocatalytic behavior is discussed in relation to a dual Z-scheme-like pathway. These results provide design insight for recyclable multicomponent photocatalysts for environmental remediation.

Water doi: 10.3390/w18101118

Authors: Zhi Zhang Kailin Duan Youping Li Bo Xu Ke Liu Shenming Ren Lei Zheng Yuquan Zhang

The rapid increase in the penetration of renewable energy has imposed more stringent requirements on the regulation capacity and response speed of Francis turbines in modern power grids. Vortex-induced energy loss significantly constrains the energy performance and hydraulic stability of giant Francis turbines. However, the formation mechanisms of vortex-induced hydraulic loss near the operating boundary remain insufficiently understood. Based on numerical simulations and parameter validation under 30 representative operating conditions, three 50% rated load conditions located near the operating boundary were strategically selected for detailed investigation. By integrating rigid vorticity analysis with entropy production theory, the vortex dynamics and hydraulic loss characteristics were systematically quantified and visualized. The results indicate that entropy production rates caused by turbulent dissipation and wall shear constitute the primary components of hydraulic loss, among which entropy production rate caused by turbulent dissipation (EPRT) is more sensitive to variations in external operating conditions and dominates both the magnitude and spatial distribution of energy dissipation. Distinct loss evolution patterns are observed in the runner and the draft tube. Recirculation and separation flows along the blade surfaces alter the normal blade loading distribution in the runner. In the draft tube, hydraulic loss is mainly governed by the energy dissipation associated with the interaction between the main flow region and the reverse flow region, while the intensity of hydraulic loss is not directly related to the specific vortex morphology. Overall, shear vorticity remains the key mechanism responsible for the increase in EPRT. This study provides theoretical insights and practical evidence for understanding the mechanisms of vortex-induced energy loss in giant Francis turbines and for quantitatively evaluating the distribution and evolution of hydraulic loss.

Water doi: 10.3390/w18101116

Authors: Yunwei Li Yanxia Liu Yafei Luo Haijun Huang

The estimated spatiotemporal characteristics of particulate matter in the ocean vary with the measurement method used. This variation introduces considerable uncertainty in our understanding of how particle scattering cross-section, particle size, and carbon content relate to one another at local, regional, and global scales. A more accurate and detailed characterization of the spatiotemporal variations of particles in the water column and of the contribution of different types of particles to the optical parameters of water are crucial for improving our understanding of the marine biogeochemical cycle. In this study, we investigated how composition, size, and particulate organic carbon (POC) content of particulate matter, along with their corresponding optical proxies, change in the upper 200 m of an oligotrophic region in the tropical Western Pacific Ocean. We estimated the contributions of various water components to the particle backscattering coefficient and to POC. Using newly collected, vertically resolved data, we derived depth-resolved net primary productivity (NPP) with the absorption-based production model (AbPM) and the carbon-based production model (CbPM); both models account for vertical variations in water column properties. Our results indicated that particles larger than 8 µm (especially minerals and aggregates) accounted for an increasing amount of POC at depths greater than 100 m, with a maximum at 500 m. In contrast, chlorophyll content decreased steadily with depth. Our comparison of the backscatter and absorption coefficients (optical proxies of POC) had the same trend, although the specific components that contributed to POC were different. Changes in parameters such as particle composition, size, POC content, and their optical proxies all corresponded to changes in the deep chlorophyll maximum (DCM) along the latitudinal gradient. When we compared the NPP estimates from the two approaches, the CbPM yielded higher values than the AbPM in surface waters, likely because of the way particles are distributed vertically. In areas where the DCM was deeper, the AbPM provided a better accounting of how individual components contributed to the NPP. Together, these findings clarify how particle composition and its vertical variability influence POC and inherent optical properties (IOPs) in this oligotrophic region. They also offer a basis for interpreting water column characteristics and assessing how changes in NPP may affect biogeochemical processes.

Water doi: 10.3390/w18101117

Authors: Mohammadnabi Jalali Ali Reza Massah Bavani Mohammadreza Shahbabegian

This study investigates how land use changes upstream and the Kamal Khan Dam have reshaped patterns of water allocation and intensified hydropolitical tensions in the Helmand/Hirmand Transboundary River Basin (HTRB). Remote sensing and deep learning techniques were employed to analyze land use changes from 2012 to 2024. After radiometric and atmospheric corrections were applied to Landsat imagery, pixel-based classification was performed using a Deep Belief Network model. Additionally, hydrological changes were analyzed using Sentinel-2 data, with attention paid to the diversion of water flows toward the Godzareh Depression. The classification results revealed considerable expansion of agricultural land downstream of the Kajaki Dam, primarily at the expense of rangeland, forest, and barren land. Moreover, sentinel imagery confirmed that, following the commissioning of the Kamal Khan Dam in 2021, systematically diverted Helmand/Hirmand hydrosystem flows toward the Godzareh Depression. Also, this study applied the painted water framework to analyze the evolution of hydropolitical dynamics in the HTRB across two critical periods, 1954–1980 and 2010–2025. The analysis revealed a fundamental transformation from green water-dominated natural flow regimes to infrastructure-controlled systems characterized by concurrent increases in both yellow water (controlled but not immediately consumed) and red water (controlled and consumed). The Kamal Khan Dam’s operationalization represents a pivotal inflection point, dramatically expanding Afghanistan’s yellow water reserves. This dual expansion of controlled water categories, empirically documented through satellite imagery, confirms the emergence of negative hydrohegemony in the basin. Consequently, Iran’s position has transitioned from a historically stable painted water class to one characterized by critical dependency.

Water doi: 10.3390/w18101115

Authors: Hao Hu Yizi Shang Dongfang Liang

Computer modelling has become indispensable to environmental hydraulics and water resource engineering, where researchers and practitioners are increasingly required to analyse complex and dynamic water systems across a wide range of spatial and temporal scales [...]

Water doi: 10.3390/w18101114

Authors: Eunkyung Lee Jungwon Ji Sooyeon Yi Jeongin Yoon Jaeeung Yi

Hydropower is a major renewable energy source, and improving the operational efficiency of existing hydropower systems has become essential. The objectives of this study are to (a) develop a specific energy-based hydropower efficiency method at a daily scale; (b) establish a comparable and general indicator for hydropower reservoir operation planning; (c) propose an operational strategy and practical decision support tool that maximizes generation performance under identical generation discharge constraints. We develop a method to estimate specific energy for different power output levels using the power output and discharge relationship and construct operating combinations based on the output range with the highest specific energy. We applied it to a single day and extended it to an entire month, using Hwacheon hydropower dam in South Korea. The results show that the daily increase ranged from 2.73 to 18.4 MWh, and the total monthly cumulative increase was 177.39 MWh. This corresponds to a potential increase of about 2.1 GWh in electricity generation. This approach achieves higher energy generation than observed operational performance. A specific energy-based operational strategy can consistently improve generation performance across varying hydrologic conditions. Specific energy provides a practical decision support tool for improving generation performance under water resource constraints.

Water doi: 10.3390/w18101113

Authors: Fu Wang Fengling Yu Yan Li Xiaohe Lai

Coastal regions are characterized by their flourishing economies and dense human settlements [...]

Water doi: 10.3390/w18091112

Authors: M. Hassan M. B. Rasheed Inam Ullah Khan K. A. A. Gamage

In recent years, the industrial decarbonization in the cement sector has introduced secondary environmental impact due to an increase in power and water demand. Deploying carbon capture, utilization, and distributed storage requires an uninterrupted supply of power and water to achieve net-zero targets. However, the traditional static optimization algorithms seem insufficient in addressing the high-frequency and dynamic renewable networks. To overcome these issues, this work develops a dynamic water-energy-carbon trade-off optimization model for industrial decarbonization, with the deployment of Carbon Capture, Utilization, and Storage system in the cement sector within a United Kingdom industrial cluster. The key objective is to quantify and control the secondary burden that low-carbon interventions can impose on electricity systems and local water resources. Firstly, the Water-Energy-Carbon problem is treated as a tri-lemma, which is formulated as a continuous Markov Decision Process. Then the optimization problem is solved via a Soft Actor-Critic Deep Reinforcement Learning algorithm under coupled and resource-constrained abstraction inputs. This work further introduces the Water-Carbon Mitigation Penalty Index as a diagnostic metric for measuring the marginal increase in water burden associated with carbon mitigation. The results show that unmanaged distributed carbon-mitigation pathways increase local hydrological stress by 2.15–5.17% relative to baseline operating conditions. Although the proposed algorithm successfully reduces the nexus cost by up to 70.5% and achieves 13.83% carbon reduction by shifting from freshwater abstraction to reclaimed municipal wastewater and by coordinating operation with low-carbon hydropower availability. These results show that dynamic AI-based scheduling can support net-zero transitions while reducing pressure on regional hydro-ecological systems.

Water doi: 10.3390/w18091110

Authors: Kai Wang Guangsen Xia Yonggang Jia Yibao Wang Lili Zhang Shaoyan Wang Xu Chai Yang Zhou Lin Cao Zhibo Cheng Haiyuan Liu Maoqiu Ran Haibo Xu Yonghong Lu Zhigang Gai

Electrochemical oxidation (EO) possesses numerous advantages and great potential for organic pollutant degradation. However, traditional plate anodes for EO are limited by pollutant mass transfer, leading to low oxidation efficiency and high energy consumption. Herein, a three-dimensional (3D) polyacrylonitrile-based carbon fiber brush (PAN-CFB) anode was employed to enhance mass transfer and improve oxidation efficiency. The oxidation capacity of the PAN-CFB anode was compared with those of boron-doped diamond (BDD) and Ti/IrO2-Ta2O5 plate anodes using oxalic acid (OA), phenol, and perfluorooctanoic acid (PFOA) as target pollutants, respectively. Experimental results demonstrated that the 3D PAN-CFB anode exhibits superior direct oxidation capacity compared to BDD and the Ti/IrO2-Ta2O5 plate anode in degrading OA, which is attributed to the significantly enhanced mass transfer of OA toward the brush anode surface. Under a constant current of 400 mA for 240 min, the total organic carbon (TOC) removal from 50 mmol/L OA reached 90.5%, 57.5% and 6.6% for PAN-CFB, BDD and the Ti/IrO2-Ta2O5 anode, respectively, and the energy consumption followed the order of PAN-CFB (5.5~8.9 kWh/kgTOC) < BDD (11.2~19.3 kWh/kgTOC) < Ti/IrO2-Ta2O5 (76.1~120.7 kWh/kgTOC). However, the 3D PAN-CFB anode exhibited poor stability at high potential and failed to promote phenol and PFOA degradation due to the weak direct oxidation capacity toward the two pollutants and the poor generation capacity of reactive oxygen species, associated with its low oxygen evolution potential. Therefore, future efforts should focus on developing stable 3D brush electrodes with a higher oxygen evolution potential to enable non-selective oxidation of a broader range of pollutants.

Water doi: 10.3390/w18091111

Authors: Johanna Beltrán Pablo Pedreros Guido Carrasco Silvia Basualto Oscar Parra Roberto Urrutia

Cyanotoxins were evaluated in seven water bodies in central Chile (Avendaño, Lo Galindo, Grande de San Pedro, Lanalhue, Vichuquén, Torca, and Llico) from October 2022 to May 2023. Microcystins (MC-RR, MC-YR, MC-LR, MC-LA) and nodularin were quantified by HPLC-DAD, and their relationships with environmental variables and cyanobacterial abundance were assessed using Spearman correlation and principal component analysis (PCA). Cyanotoxins were detected in six systems, with MC-LR as the dominant congener. The highest concentration (407.5 µg/L) occurred in the mesotrophic Laguna Grande de San Pedro. Correlation analysis showed nodularin positively associated with conductivity (ρ = 0.40, p < 0.05), while microcystins were negatively correlated with temperature (ρ to −0.60, p < 0.05). PCA explained 57.7% of variance, distinguishing toxin patterns along gradients of temperature, pH, conductivity, and N:P ratio. Cyanotoxin occurrence was weakly related to cyanobacterial abundance but consistently associated with low N:P ratios. These findings confirm the presence of cyanotoxin-producing strains in the studied water bodies and highlight the need to integrate nutrient dynamics, cyanobacterial community structure, and multi-congener toxin analysis into monitoring programs. Furthermore, the results demonstrate that mesotrophic systems could represent emerging sources of cyanotoxin production, underscoring the need to improve risk assessment and management strategies.

Water doi: 10.3390/w18091109

Authors: Catarina Jorge Rita Salgado Brito Maria do Céu Almeida

The revised EU Urban Wastewater Treatment Directive (UWWTD, EU 2024/3019) expands the scope of the previous directive (Council Directive 91/271/EEC, 1991) by explicitly including combined sewer systems, stormwater discharges, and overflow events while promoting energy neutrality and reducing greenhouse gas (GHG) emissions across urban wastewater systems. Although the Directive establishes energy accountability at the system level, it does not define how energy performance in wastewater collection networks should be structured, assessed, or benchmarked, resulting in a significant implementation gap. This paper presents a novel, regulatory-aligned, data-driven framework to organise, analyse, and interpret energy-relevant information in support of UWWTD requirements, with specific focus on wastewater collection networks. Using Portuguese regulator datasets, supplemented with published sources, existing metrics are reorganised into energy-significant dimensions that differentiate structural, excess-driven, operational, and renewable-related components of energy use. The preliminary findings show that available datasets already support a screening-level diagnosis of specific energy intensity, pumping-related energy shares, inflow-driven excess volumes, and associated GHG emissions. However, important gaps remain regarding subsystem disaggregation, hydraulic normalisation, and measurement granularity. The study restructures existing information into a novel audit-compatible framework, proposes additional metrics and measurement requirements, and identifies measures to facilitate UWWTD implementation. Although developed for the Portuguese context, the framework offers a scalable pathway for integrating wastewater collection networks into energy neutrality governance across European Member States.

Water doi: 10.3390/w18091108

Authors: Xiaolan Ji De Wang Xinpeng Tian Xiaoli Bi Xiaoli Wang

Driven by global warming, increasing extreme precipitation events (EPEs) threaten low-lying coastal ecosystems. This study focused on the contemporary Yellow River Delta and established a continuous framework linking extreme precipitation, groundwater, and vegetation, based on long-term extreme precipitation changes during 1960–2022 and vegetation dynamics during 2001–2022. Using regional precipitation records, groundwater observations from 16 monitoring wells, and five-day kernel normalized difference vegetation index (kNDVI) data, we compared two EPEs that exceeded the 99th-percentile wet-day precipitation threshold and had complete precipitation–groundwater–vegetation observations. Our findings reveal that: (1) extreme precipitation was intensified in the study area, with an R99p trend of 19.1 mm/10 a; (2) vegetation disturbance was stronger and more persistent after the 2019 Lekima event, with a mean post-event kNDVI anomaly of −12.8%, whereas the 2022 Chaba event produced a weaker, later, and more spatially limited negative response; (3) groundwater response was also stronger in 2019, as the proportion of wells with above-surface water levels reached 43.8%, compared with 12.5% in 2022, indicating more extensive and longer-lasting inundation; (4) the shallowest post-event groundwater depth was significantly negatively correlated with kNDVI anomalies (r = 0.579, p < 0.001), and during the 2019 event, the kNDVI fell below about −17% when surface inundation lasted for 6 days. These results indicate that groundwater is a key hydrological link connecting extreme precipitation and vegetation response. This study provides new evidence for the identification and adaptive management of ecological risks in low-lying coastal deltas.

Water doi: 10.3390/w18091107

Authors: Tae-Sung Cheong Seojun Kim Kang-Min Koo

Small streams exhibit rapid and nonlinear flood responses due to steep slopes, short flow paths, and limited storage capacity, making real-time flood prediction difficult under both computational and data constraints. This study presents a measurement-based flood prediction framework for real-time estimation of flood discharge and depth in small-stream basins. Conventional approaches, such as physically based hydrodynamic models, require detailed boundary conditions and high computational cost, while data-driven models often lack physical interpretability. The proposed framework integrates high-frequency monitoring data from the Small-Stream Smart Monitoring System, short-term rainfall nowcasting from the MAPLE system, and nonlinear regression-based hydraulic relationships within a unified operational structure. Rainfall–discharge nomographs and depth–discharge rating curves were developed using a four-parameter logistic regression model based on long-term observations from 12 small streams in Korea. Additional comparisons with alternative regression forms confirmed the suitability of the 4PL model for representing nonlinear hydrological responses. Forecast rainfall was used to estimate discharge, which was subsequently converted to flood depth through calibrated rating curves. For ungauged reaches, depth–discharge relationships were derived using HEC–RAS-based scenario simulations and the Manning equation to enable spatially continuous prediction along stream networks. Model performance was evaluated using independent validation events, showing mean prediction accuracies of approximately 89% for discharge and 90% for flood depth. The framework reduces computational demand by relying on pre-established relationships while maintaining physically interpretable structures. The results indicate that the proposed approach can support real-time flood prediction in small streams under conditions like those examined in this study, although its applicability to other regions requires site-specific calibration and further validation.

Water doi: 10.3390/w18091106

Authors: Daniela Alvear-Sayavedra Daning Montaño-Ocampo Mariana Capparelli Jorge Celi Marcela Cabrera Rodrigo Espinosa

The Western Amazon is a global biodiversity hotspot, yet the Upper Napo River Basin (UNRB) remains understudied regarding aquatic ecosystem health along anthropogenic gradients. We integrated benthic macroinvertebrate assemblages with physicochemical and microbiological indicators across 45 sites to assess ecological quality under four impact scenarios: Few Threats (FT, reference sites; n = 6), Crop/Aquaculture (CA; n = 22), Gold Mining (GM; n = 10), and Wastewater Discharge (WD; n = 7). Analysis of 2285 individuals (62 families) revealed clear degradation across the anthropogenic gradient. Reference sites (FT) exhibited high integrity (q0 = 24.3 families), establishing the regional baseline for Andean–Amazonian freshwater ecosystems. In stark contrast, GM sites showed catastrophic defaunation (q0 = 9.9 families) coupled with extreme turbidity (1320 ± 1589 NTU) and heavy metal mobilization (Fe: 430 ± 229 µg/L; Cu: 338 ± 128 µg/L), placing these reaches in “Bad” ecological status (Ecological Quality Ratio, EQR ≤ 0.16). Wastewater sites reached critical fecal coliform levels (33,708 ± 58,047 CFU/100 mL)—165-fold higher than FT sites—indicating severe sanitary impairment and community collapse (EQR = 0.28, dominated by Chironomidae at 80%). The application of ASPT (Average Score Per Taxon) and EQR proved essential for detecting functional shifts toward tolerant assemblages even when raw biotic scores appeared moderate. Crop/Aquaculture sites showed intermediate degradation (EQR = 0.37–0.38), reflecting chronic pesticide exposure and habitat loss. We conclude that gold mining and wastewater discharge are the primary drivers pushing the UNRB toward ecological collapse, with GM exerting the most severe impact on aquatic biodiversity. Safeguarding this global freshwater stronghold requires immediate implementation of multimetric biomonitoring, enhanced mining regulation, wastewater treatment infrastructure, and establishment of Indigenous-led fluvial reserves to maintain long-term connectivity.

Water doi: 10.3390/w18091105

Authors: Uğur Boyraz Emin Ayvaz

This study investigates the role of longitudinal aquifer slope in controlling stream–aquifer interaction within bounded floodplain aquifer systems. A series of numerical simulations were conducted to analyze groundwater flow patterns, hyporheic exchange fluxes, and contaminant transport behavior under varying slope conditions. The results showed that increasing slope does not simply enhance hydraulic gradients but fundamentally reorganizes subsurface flow structure. As the slope increases, groundwater flow becomes progressively aligned with the stream, reducing lateral connectivity and confining exchange to a narrow corridor adjacent to the stream. This reorganization leads to the expansion of hydraulically inactive zones and a non-linear response in hyporheic exchange. Exchange flow rates initially increase at low to moderate slopes but decline beyond a threshold at higher slopes, despite higher local gradients. The transition begins at around a 2% slope and becomes pronounced within the range of approximately 3–7%, indicating a shift in flow regime rather than a continuous scaling of interaction intensity. Particle tracking analyses further reveal that slope controls the spatial distribution of contaminant vulnerability. While the overall extent of active transport zones decreases with increasing slope, localized transport potential intensifies near the stream boundary due to higher velocities and reduced residence times. These findings demonstrate that hydraulic gradient magnitude alone is insufficient to characterize stream–aquifer interaction and highlight the importance of flow geometry and connectivity. The results provide a process-based framework for understanding slope-controlled hyporheic exchange and offer insights for improving groundwater vulnerability assessment and management in alluvial systems.

Water doi: 10.3390/w18091104

Authors: Gulfairus Bizhanova Maral Abdibattayeva Wang Ping Umut Mussina Laura Kurbanova Arman Zhumazhanov Dana Akhmetzhanova Ospan Doszhanov Bekzat Ismukhanbetov Didar Bolatova Yerlan Doszhanov

Ammonium nitrogen (NH4+-N) is a key biogenic pollutant in aquatic systems. This study evaluated natural diatomite (Aktobe region) and zeolite (Shankhanai, Zhetysu region) as low-cost, environmentally benign sorbents for NH4+-N removal, and examined the effects of thermal (200–750 °C; 450 °C selected) and alkaline (0.5 M NaOH) treatments on their structural, textural and adsorption properties. Materials were characterized by XRD, XRF, FTIR, SEM-EDX and adsorption performance was assessed by kinetic and equilibrium experiments. Specific surface area and pore characteristics were determined from low-temperature nitrogen adsorption–desorption measurements, and the specific surface area was calculated using the Brunauer–Emmett–Teller (BET) method. Thermal treatment at 450 °C increased the specific surface area of diatomite (46.3 m2/g) and pore volume, and subsequent alkaline activation further enhanced adsorption activity. The modified diatomite achieved up to 84.6% removal of NH4+-N with an equilibrium capacity qmax = 1.758 mg/g. Adsorption kinetics were best described by the pseudo-second-order (PSO) model, which may indicate a substantive role of surface chemical interactions. Equilibrium data were fitted with Langmuir and Freundlich models: the modified diatomite fitted Langmuir best (R2 = 0.999), which may suggest predominance of a monolayer adsorption mechanism under the studied conditions, whereas natural samples and the zeolite were better described by the Freundlich model, reflecting likely surface energetic heterogeneity. Separation factor values (RL = 0.068–0.643) indicate favorable adsorption within the investigated concentration range. The point of zero charge (pHpzc) was determined for all sorbents (5.3–6.3), confirming that at pH 7 the surface carries a negative charge favorable for electrostatic attraction of NH4+ cations. Reusability tests over five consecutive adsorption–desorption cycles showed that modified diatomite and modified zeolite retained 93.4% and 92.3% of their initial removal efficiency, respectively, indicating acceptable stability under the applied regeneration conditions. These results demonstrate the potential of alkaline-modified diatomite and zeolite as effective sorbents for ammonium removal from wastewaters, contributing to the mitigation of eutrophication risks.

Water doi: 10.3390/w18091103

Authors: Barry Hibbs Alfredo Granados-Olivas

A widely reproduced error in hydrogeologic maps originated from a provisional delineation drawn in the mid-1990s to depict the southern extent of the Mesilla Bolson aquifer along the western margin of the El Paso–Juárez metropolitan area. The delineation was created solely to satisfy a U.S. Environmental Protection Agency contractual milestone during early binational groundwater inventory efforts and was never intended to represent a final hydrogeologic basin limit. Nevertheless, the outline persisted, became institutionalized in reports, models, management documents, and public imagery, and was ultimately labeled the “Mesilla/Conejos–Médanos Basin Transboundary Aquifer,” where it continues to be treated as a valid transboundary aquifer delineation. This paper documents the origin of the provisional delineation and proposes a revised delineation for the Mesilla/Conejos–Médanos Basin Transboundary Aquifer, based on internationally recognized definitions of transboundary aquifers and groundwater basins, including United Nations frameworks, and established scientific criteria. These criteria include basin-scale geologic and structural controls, hydrostratigraphic continuity, groundwater divides, and permeability contrasts at basin interfaces. Results indicate that the newly defined aquifer delineation falls within Mexico’s much larger administrative Acuífero Conejos–Médanos (0823), a unit that represents groundwater management jurisdiction in Mexico rather than solely a hydrogeologic basin. The proposed transboundary aquifer is defined on hydrogeological principles and does not coincide with either the administrative unit of Mexico or the historic provisional outline that has become widely used by multiple binational entities and by different experts in groundwater science.

Water doi: 10.3390/w18091102

Authors: Mingyue Li Yongchao Wang Shuling Chen Wenhui Liu Guodong Chai Zhongfeng Jiang Fang Yang

This work focused on the Xinghua River, a typical urbanizing river, to investigate how different anthropogenic activities affect the composition, sources, and environmental impact of dissolved organic matter (DOM) during urbanization. Using fluorescence spectroscopy combined with multivariate statistics, we systematically explored DOM characteristics and their response to urbanization. A total of four fluorescent components were identified, including protein-like components C1 and C3, and humic-like components C2 and C4, with protein-like substances constituting the major fraction of DOM. Fluorescence indices indicated that DOM in the Xinghua River was primarily derived from autochthonous sources (FI > 1.9), with a low degree of humification reflecting the dominance of fresh organic matter input during urbanization. Spatial analysis revealed that from upstream to downstream, the source of DOM gradually shifted from autochthonous dominance to increased allochthonous input, accompanied by increasing trends in both protein-like and humic-like components, indicating an accumulative effect of anthropogenic activities along the river. 2D-COS further revealed that the transformation sequence of DOM components along the flow direction was C3 → C1 → C4 → C2, suggesting that tyrosine/tryptophan-like substances were the most sensitive to anthropogenic disturbance. Redundancy analysis identified total phosphorus (TP), total dissolved solids (TDS), and permanganate index (CODMn) as the key environmental factors influencing DOM distribution, highlighting the synergistic regulatory roles of nitrogen and phosphorus nutrients and organic pollution loads on DOM composition. This study not only elucidates the gradient effects of human activities on DOM in the Xinghua River but also provides a scientific basis for water management in urban rivers worldwide, particularly for zone-based control and source-oriented management.

Water doi: 10.3390/w18091101

Authors: Yu Chang Menghao Fang Qing Lu Dawei Zhang Weiying Li

To clarify the control mechanism of water quality parameters on metal particle release from pipe scales in aging ductile iron water supply pipelines (service life > 20 years), this study conducted single-factor experiments to explore the effects of pH, temperature, concentration of humic acid (HA) and Mn2+ on Fe, Mn, and Al particle release. Combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for quantitative detection, first-order/second-order kinetic fitting, and X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) characterization, the results showed that an increase in temperature generally promoted the aggregation and sedimentation of metal particles, among which Fe and Mn particles were more sensitive to temperature changes. pH affected the sedimentation process by controlling metal ion speciation and particle surface charge: low pH significantly accelerated pipe scale dissolution, while weakly alkaline conditions prolonged particle suspension time. Low-concentration HA (0.5 mg/L) promoted particle dissolution, whereas high-concentration HA (1.0–2.0 mg/L) extended particle retention time through surface coating. Mn2+ concentration exhibited an obvious concentration-dependent effect: the range of 20–50 μg/L enhanced particle suspension stability, while 80–100 μg/L accelerated particle aggregation and sedimentation. The pipe scales mainly consisted of Fe3O4, Fe2O3, Mn3O4, and Al2O3, with metal release regulated by the “element complexation–particle aggregation–crystal growth” pathway. Particle sedimentation followed first-order kinetics. Controlling pH at 7.0, temperature < 30 °C, and reducing HA/Mn2+ concentrations effectively weakened metal particle migration. This study reveals the coupled effect mechanism of water quality parameters, providing theoretical and technical support for optimizing water quality control and solving the “yellow water” problem.

Water doi: 10.3390/w18091100

Authors: Tamadhor Almahmoud Litty Mary Abraham Mohammad Abdullah Alolayan Bader Shafaqa Al-Anzi

The performance of a tubular solar still in an arid region was evaluated for producing freshwater from various water sources. The water sources fed to the tubular solar still were blowdown from a seawater desalination plant, recovered water from an oil production facility, rejected seawater from a reverse osmosis treatment plant, seawater, and rejected groundwater from a reverse osmosis treatment plant. The TDS for these water sources ranged from 17,210 mg/L for groundwater to 221,710 mg/L for produced water. Compared with other water types, produced water had distinct characteristics: low pH, a petroleum-like odor, and a reddish-brown color. The estimated average production rates were 5.1, 5.9, 6.1, 6.6, and 6.8 L/m2·day for produced water, reverse osmosis-rejected water, desalination plant blowdown, seawater, and reverse osmosis-rejected groundwater. Different TSS designs were examined to determine whether production rates could be improved using tap water. Production increased slightly when a blackened basin, steel mesh, or both were applied as heat-absorption enhancements. Therefore, the tubular solar still without any enhancements was found to be a better option due to its lower cost and simpler design. The composition of the residual salts (65–73%) did not meet the 97% standard set by the FAO. The results of the study are promising for future upscaling projects aimed at enhancing water security in rural areas and arid regions.

Water doi: 10.3390/w18091099

Authors: Qingguo Wang Yabing Ma Mingyang Ren Heng Liu

Given the escalating impacts of global climate change and extreme weather events, the accurate stability assessment of rainfall-induced landslides necessitates a comprehensive consideration of both seepage processes and the inherent spatial variability of soils. Traditional deterministic and two-dimensional (2D) analyses often fail to capture the multi-dimensional kinematic features of slope failures and the stochastic nature of soil heterogeneity, thereby leading to inaccurate risk assessments. This study proposes a three-dimensional (3D) slope reliability analysis framework. Within this framework, a 3D slope geometric model is constructed using GeoStudio 2025.1.0 software, and seepage analysis is conducted by the SEEP3D module. To account for soil spatial variability, the Karhunen–Loève (K-L) expansion method is employed to discretize key shear strength parameters (effective cohesion and effective angle of internal friction). The factor of safety (Fs) is evaluated using the 3D simplified Bishop method, which is then coupled with Monte Carlo simulations to determine the probability of failure (Pf). The results show that rainfall infiltration causes progressive dissipation of shallow matric suction and a significant rise in the groundwater table near the slope toe, resulting in reduced effective stress in the critical resistance zone. As rainfall intensity increases, the Fs decreases approximately linearly from 1.14 to 0.90, whereas the Pf increases nonlinearly from nearly 0 to 98.36%. Under the rainstorm condition, although the Fs remains above unity at 1.063, the corresponding Pf reaches 23%, indicating that deterministic evaluation based only on the Fs may underestimate the actual failure risk. The proposed framework provides a quantitative tool for evaluating rainfall-induced slope instability by integrating transient hydraulic response, three-dimensional spatial variability, and probabilistic reliability assessment.

Water doi: 10.3390/w18091098

Authors: Boyan Sun Xiaomin Liu Guoqing Wang Ping Miao Kang Xie Hongli Ma

Flood risk assessment is essential for flood control and disaster mitigation in arid and semi-arid river basins, where conventional univariate and bivariate frequency analyses struggle to capture nonlinear dependence among flood variables and often underestimate extreme synergistic risks. This study focuses on the Wulanmulun River Basin in Inner Mongolia and employs long-term observations from the Zuanlongwan and Wangdaohengta hydrological stations. A trivariate D-vine Copula model was constructed to jointly characterize peak discharge, total flood volume, and water level. Optimal vine structures differ between the stations (Qp–H–W and W–Qp–H) and outperform traditional Copula models in representing extreme joint risks. The ternary joint return periods reveal two distinct flood risk transmission modes, “jump” and “accumulation”, and joint exceedance probabilities under low, medium, high, and ultra-high-risk scenarios are 6.4%, 31.95%, 37.64%, and 5.75% at Zuanlongwan, and 4.7%, 35.24%, 45.78%, and 0.53% at Wangdaohengta, indicating concentration in medium-to-high risk ranges. The validation at Longtouguai Station showed an error RSME of 0.0630 and an R2 of 0.905, confirming the reliability of the model framework. These results indicate that the proposed framework can effectively capture multivariate flood dependencies and provide a scientific basis for flood control design, risk zoning, and emergency management of small and medium rivers in arid and semi-arid regions.

Water doi: 10.3390/w18091097

Authors: Zhonglin Wu Rajesh Kumar Soothar Habibullah Memon Farman Ali Chandio Sher Ali Shaikh

Plastic film mulching combined with raised bed–furrow irrigation is an effective technique for enhancing the seed yield, oil contents, and plant-level water use efficiency of sunflower cultivation, while also optimizing water footprint. In this study, a field experiment was carried out at the experimental station of the Department of Irrigation and Drainage during 2023–2024. The trial involved three types of raised bed–furrow irrigation (raised beds with 60, 45, and 30 cm ridges and 30 cm furrows) with and without mulching practices. The results revealed that the treatments combining mulching with raised beds showed higher soil temperature and moisture contents compared to non-mulching treatments. The highest seed yield and oil content were recorded in furrow irrigation with mulching, representing a 35% increase in yield and a 28% increase in oil content compared to the control treatment. Seed yield was positively correlated with oil content. Additionally, the highest plant-level water use efficiency was observed in a raised bed 45 cm in size with mulching, while the highest total water footprints were recorded in a raised bed with a 60 cm ridge and non-mulch treatment, both exceeding the control treatment. It is concluded that sunflower cultivation under mulching combined with raised bed–furrow irrigation significantly enhances crop and water productivity.

Water doi: 10.3390/w18091096

Authors: Ewa Dacewicz Karol Plesiński Ewa Łobos-Moysa

This study assessed the impact of pandemic-related changes in treated wastewater on surface water quality and ecological status of the Raba River within the Natura 2000 site. Particular attention to the reliability of the Kasinka Mała wastewater treatment plant operating in this protected area during the two study periods—pre-pandemic (PP) and COVID-19 (CP)—was given. For this purpose, current standard monitoring methods (ecological status of a small flysch stream, existing and potential threats to the Natura 2000 site) and extended monitoring methods (river’s utility values, technological reliability of the treatment plant operating with SBR technology, reliability rating of the river as a sewage receiver) were used. The results indicated that biodegradable carbon compounds (as dissolved and suspended forms) and ammonium nitrogen were the dominant factors determining water quality. Their presence reduced the Raba River’s utility value—determined by what is required of surface water treatment—by at least one class. During the CP, the reliability analysis showed that the river remained in a reduced class for 145 days due to elevated BOD5 and nearly one-third of the year due to elevated TSS levels. For approximately half of the year, ammonium nitrogen concentrations exceeded the threshold of 1.8 mg·dm−3, thereby further reducing the class of water quality. Technological reliability of the WWTP during PP for BOD5, COD, TSS, NH4+–N, and PO4−3–P was 43%, 100%, 30%, 86%, and 100%, respectively. This means that permitted values of COD and PO4−3–P were maintained. The exceedances of limits concerned BOD5 (25 mg O2·dm−3 for 208 days), TSS (35 mg·dm−3 for 256 days), and NH4+–N (15 mg·dm−3 for 51 days). During CP, the technological reliability of the WWTP decreased rapidly for the following pollutants to 5%, 18%, 18%, 30%, and 89%, respectively. This means that permissible concentrations of BOD5 (25 mg O2·dm−3 for 347 days), COD (125 mg O2·dm−3 for 241 days), TSS (35 mg·dm−3 for 299 days), NH4+–N (15 mg·dm−3 for 256 days), and PO4−3–P (2 mg·dm−3 for 40 days) were exceeded. A two-year monitoring campaign has shown that small flysch rivers receiving treated wastewater may experience prolonged changes in water quality under conditions of increased anthropopressure. Effective ecosystem protection should, therefore, include extended monitoring and stricter management of BOD5, TSS, and NH4+–N in SBR systems in protected areas.

Water doi: 10.3390/w18091095

Authors: Yacheng Sun Yasong Chen Yuzhen Li Tingting Li Wenlong Zhang

Accurate forecasting of urban rainfall-runoff pollution across large river basins is essential for urban water management. However, this task faces formidable challenges due to the scarcity of locally monitored data and the heterogeneity in hydrological and pollution processes. To address these challenges, we proposed a novel three-tiered framework comprising (1) functional area clustering using 16-dimensional features to identify zones with shared pollution mechanisms and establish a physical parameter library; (2) a hybrid physics-informed data-driven model integrating SWMM with a Residual-BiLSTM-Multi-Head Attention (RLA) model; and (3) cluster-based transfer learning enabling predictions in data-scarce zones. The framework’s efficacy was demonstrated through a multi-tiered dataset for the Yangtze River Basin. First, a knowledge base comprising 2390 reported rainfall events across 57 functional areas was synthesized to inform the functional clustering and establish a shared physical parameter library. Subsequently, intensive field monitoring from two representative residential areas was used to train and validate the hybrid model. In data-rich zones within a cluster, the model achieved high accuracy (R2 > 0.82). For data-scarce zones within the same functional cluster, the model maintained a promising performance (R2 > 0.5). This study presents a novel basin-scale framework, with its initial application and preliminary validation in the Yangtze River Basin.

Water doi: 10.3390/w18091094

Authors: Lamfaddal El Hani Nir Y. Krakauer Ridouane Kessabi Mohamed Belmahi Jawad Khachab Abdelouahed Bouberria

This article analyzes the state of water resources in the Guercif Plain (Morocco) under the combined effects of drought and increasing consumption pressures. The study adopts a quantitative and analytical approach based on climatic and hydrological data, demographic information, and Landsat satellite imagery. The main findings reveal pronounced rainfall variability with an overall declining tendency, with drought years accounting for approximately 58% of the observation period. This climatic context has been accompanied by strong interannual fluctuations in the discharge of Oued Melloulou, with a slight long-term declining trend, along with a continuous and accelerating groundwater decline in the Tafrata aquifer at an average rate of 0.98 m per year. The analysis also indicates an estimated urban water deficit approaching 77% under peak demand conditions in 2025. Furthermore, NDVI-based analysis of satellite imagery highlights a marked expansion of irrigated areas in the Guercif Plain, increasing from about 2% of the total plain area in 1985 to approximately 9% in 2020. This vegetation expansion is largely associated with irrigation development, suggesting increasing pressure on groundwater resources rather than recovery linked to rainfall conditions. Overall, the findings raise critical concerns regarding the long-term sustainability of water resources and underscore the need for integrated and adaptive water-management strategies under persistent drought conditions.

Water doi: 10.3390/w18091093

Authors: Ayesha Kabir Abubakar Shitu Zhangying Ye Xian Li He Ma Gang Liu Songming Zhu Jing Zou Ying Liu Dezhao Liu

The recirculating aquaculture system (RAS) marks a significant shift in global aquaculture, transitioning to controlled, land-based production. This review highlights technological advancements that enable the treatment and reuse of over 90% of water, thereby enhancing water quality and production efficiency. These features position RAS as a cornerstone of sustainable seafood production. This review introduces the RAS Readiness Level (RRL) framework which is a novel, structured approach to assess the commercial maturity of emerging RAS technologies. Applying the RRL to six key technological domains (from digital AI systems to biological PHB recovery) reveals a pervasive pilot-scale purgatory where most innovations stagnate at RRL 4–6. It further addresses advanced processes such as membrane bioreactors, denitrification reactors, and the conversion of waste into valuable products. Furthermore, this review addresses persistent challenges, including high energy demand, economic viability, and the accumulation of pathogens. Finally, it focuses on the emergent integration of the Internet of Things (IoT) and artificial intelligence (AI), which are revolutionizing RAS management through data-driven optimization. By synthesizing current innovations, this review envisions a future of intelligent, closed-loop RAS where advanced IoT- and AI-driven technologies optimize water quality and feeding strategies to minimize ecological impact while enhancing sustainability and productivity.

Water doi: 10.3390/w18091092

Authors: Zhuang Zhao Xi Yang Canping Jiang Feng Yi Haimin Wu

Geomembranes are extensively used for seepage control in the reservoir of pumped-storage power stations due to their superior deformability, ease of construction, and low cost. The deformation behavior of geomembranes under high hydraulic pressure is of great importance for seepage-control design and operational safety evaluation. Nevertheless, existing hydrostatic pressure resistance tests cannot effectively measure the hydraulic bulging deformation of geomembranes subjected to water pressure. This study proposes a non-contact binocular vision method to quantify the hydraulic bulging deformation of geomembranes. The method combines underwater camera calibration, image enhancement, stereo matching, triangulation, and three-dimensional reconstruction to achieve both visualization and accurate measurement of geomembrane deformation. After experimental validation and accuracy calibration, the proposed method was preliminary applied to four geomembrane materials, including HDPE, LLDPE, PVC, and TPO, under hydraulic loading. The results show that the measurement error is less than 5% in the large-deformation range under medium and high water pressures. The method can effectively capture the hydraulic bulging behavior of geomembranes and accurately characterize the deformation features of different materials under high hydraulic pressure. This study provides a practical technical approach for underwater deformation measurement of geomembranes and supports seepage-control design and operational safety monitoring.

Water doi: 10.3390/w18091091

Authors: Izmail Kantarzhi Maksim Afonyushkin

A study was conducted on the interaction of surface gravity waves with a relatively thin, free-floating ice floe compared to the height of the waves. Physical and numerical modeling, as well as analytical research, were used. An overview of scientific works on the research topic is presented. The physical model consisted of an experimental setup (wave flume) with a wooden plate exposed to gravitational harmonic waves of different lengths and periods. The numerical model is based on calculations performed in the LS-DYNA program, where the fluid was simulated using the Euler–Lagrange method, and solid bodies were considered rigid. Analytical studies use the theory of interaction of small-amplitude waves with floating breakwaters. It is shown that as the wave height increases for conditions of interaction between waves and ice floes of almost identical horizontal dimensions, one end of the floating body sinks into the water, which leads to a significant reduction in the drift speed of the ice floe. Formulas have been obtained that express the ratio of the ice floe’s speed to the wave velocity, as well as the ratio of the height of the incident waves to the height of the transmitted waves, depending on the ratio of the wavelength to the horizontal dimensions of the floating ice floe.

Water doi: 10.3390/w18091090

Authors: Dan Liu Jianyong Hu Yongye Li Shiang Mei Haitao Zhao Zhenzhu Meng Cundong Xu Jinxin Zhang Jie Jin Miaoyan Liu Yuqiang Wang Wanling Wu

Addressing the challenges of vague ability assessment, delayed teaching adjustment, and fixed cognitive challenge levels in sustainable engineering practice courses, this study proposes a “goal elevation-matrix evaluation-dynamic regulation” tripartite coupled sustainable teaching model. The model employs a value-oriented assessment matrix as the core diagnostic tool, integrating a dual-threshold regulation mechanism and standard iteration strategy within a four-year “design-implementation-diagnosis-iteration” closed loop. Empirical evidence demonstrates that ① a three-tier diagnostic model (overall-module-indicator attainment levels) identifies structural problems of the teaching content and pinpoints the key bottleneck; ② replacing redundant high-scoring modules with basic skill modules eliminates extreme values, improves distribution gradients, and trends to class performance at 75~85%; ③ iterative standard calibration supports progressive student competence development along a “familiar problems → new challenges” pathway. This study provides an empirically validated methodological framework for systematically implementing “scientific rigor, practicality, and appropriate challenge” in engineering practice courses while fostering sustainable engineering literacy.

Water doi: 10.3390/w18091087

Authors: Anıl Çelik Abdüsselam Altunkaynak Mehmet Özger

Accurate forecasting of sediment accumulation under extreme hydrodynamic forcing is essential for coastal engineering design and harbor management. This study evaluates the performance of Dynamic Mode Decomposition (DMD), optimized DMD (optDMD), and optimized DMD with stability constraints (optDMDs) for reconstructing and forecasting sediment accumulation height fields at the Dilderesi River mouth under a 50-year return period flood scenario. Sediment height fields generated using Delft3D are represented through reduced-order modal decompositions and the truncation rank is determined based on reconstruction-error analysis. Although all formulations reproduce the training data with negligible error, their predictive behavior differs during temporal extrapolation. Standard DMD exhibits rapid error growth at longer lead times. The optDMD formulation improves short- and intermediate-horizon performance but shows gradual degradation at extended lead times. Optimized DMD with stability constraints provides the most consistent long-horizon forecasts, maintaining high Nash–Sutcliffe efficiency and low RMSE across the full 9 h prediction interval. Examination of the continuous-time eigenvalue distributions and modal dynamics indicates that spectral characteristics of the reduced-order representation govern forecast robustness. The results demonstrate that enforcing spectral stability within reduced-order frameworks substantially enhances morphodynamic forecasting reliability under extreme flood conditions. The proposed approach provides a computationally efficient and physically consistent tool for sediment dynamics prediction in coastal engineering applications.

Water doi: 10.3390/w18091088

Authors: Marta Bartosik Renata Matuszewska Łukasz Mąka Jolanta Solecka

The objective of this study was to evaluate selected analytical procedures based on EN ISO 10705-2:2001 and EN ISO 10705-3:2024 for the determination of somatic coliphages in 100 mL water samples, taking into account the requirements of Directive (EU) 2020/2184, and to identify a procedure that can be adapted for routine analyses, as well as points at which laboratories may encounter difficulties. The study was conducted on two types of water samples: Type 1, comprising groundwater and treated water, and Type 2, comprising surface water. Samples were collected from water treatment plants at the point of distribution network supply (treated water), deep well intakes, and surface intakes (raw water). The study demonstrated the limited reliability of the procedure when applied to routine analyses. The recovery obtained for the method incorporating the selected modifications under the tested conditions was 72% for Type 1 water samples and 73% for Type 2 water samples. The introduction of legal regulations on the quality of water intended for human consumption, along with the requirement to test a new parameter for operational purposes, can pose a significant challenge for laboratories performing water analyses.

Water doi: 10.3390/w18091089

Authors: Cris Edward F. Monjardin Jerime Chris F. Mendez Rose Danielle G. Hilahan Maria Gemma Lou Hermosa Elmo Jr Z. Almazan Kevin Paolo V. Robles

Coastal aquifers are essential freshwater sources for domestic, agricultural, and industrial use, particularly in regions where surface water is limited. However, these systems face growing stress from saltwater intrusion, climate-driven reductions in recharge, sea level rise, and intensified groundwater extraction. This review synthesizes recent research on coastal aquifer responses to these pressures, highlighting the interplay between natural hydrogeologic conditions and human-induced demand. Across deltaic and sedimentary systems, studies consistently show declining groundwater levels, the landward migration of saline interfaces, and reduced aquifer buffering capacity, especially in areas with high evaporation and limited recharge. The review also evaluates emerging strategies to preserve coastal groundwater security. Integrated hydrological models, managed aquifer recharge (MAR), optimized abstraction schemes, and remote sensing-based monitoring are advancing adaptive management capabilities. In parallel, policy and nature-based interventions—such as aquifer protection zoning, wetland rehabilitation, and dune system restoration—support long-term resilience by enhancing natural recharge and reducing vulnerability. The overall findings reveal the need for climate-informed and locally tailored groundwater management. Future efforts should prioritize coupling high-resolution climate projections with aquifer system models, evaluating MAR viability in saline-prone environments, and strengthening collaborative governance frameworks to ensure sustainable and equitable use of coastal aquifers.

Water doi: 10.3390/w18091086

Authors: Guang Li Jie Guo Yewei Song Fengshan Ma

Natural mineral waters hosted in volcanic terrains are globally significant, but the co-enrichment mechanisms of metasilicate and strontium remain poorly understood. Here we investigate a Jurassic volcanic-hosted mineral water source in eastern China using hydrochemical analysis, 14C dating, stable isotopes, and structural analysis. The groundwater is of Ca–Mg–HCO3 type with slightly alkaline pH (7.44–7.63). Metasilicate (26.4–32.9 mg/L) and strontium (0.40–0.83 mg/L) co-enrichment is governed by plagioclase weathering in a bicarbonate-dominated, weakly alkaline environment where SrHCO3+ ion pairs enhance strontium mobility. Pearson-corrected 14C ages of 3900–4900 years reveal that millennial-scale residence time is critical for sufficient water-rock interaction and attainment of regulatory thresholds. A conduit-barrier system formed by NW-trending extensional-shear and NNE-trending compressional-shear faults controls groundwater flow paths and residence times, leading to systematic inter-well hydrochemical differentiation. These findings provide a theoretical basis for the genetic identification, potential evaluation, and sustainable management of high-quality mineral water resources in volcanic terrains.

Water doi: 10.3390/w18091085

Authors: Rumman Mowla Chowdhury Cheng Zhang Kauser Jahan Julia Renee Thornton

Southern New Jersey faces increasing flood risk due to several factors including rapid development, climate change, and aging infrastructure. This study evaluated the flood vulnerability of two municipal solid waste landfills located in Gloucester and Cumberland Counties. These sites are located near rural communities that rely on shallow groundwater for drinking water, which may be contaminated by floods. To assess these challenges, this research applies a hydrologic–hydraulic model to evaluate future flood vulnerability at the Cumberland County Improvement Authority (CCIA) landfill and the Gloucester County Solid Waste Complex (GCSWC) landfill. The method uses HEC-HMS and HEC-RAS 2D model simulations with climate-adjusted precipitation data derived from global climate models. Model performance was evaluated using Hurricane Ida (31 August–2 September 2021) by comparing HEC-RAS-simulated inundation extents with independently derived Sentinel-1 SAR flood maps generated in Google Earth Engine. Climate forcing was developed by deriving climate-adjusted 24 h precipitation–frequency (PF) design depths for 50-year and 100-year design storms under the Shared Socioeconomic Pathway (SSP) emissions pathways SSP2-4.5 (moderate) and SSP5-8.5 (high) for mid-century (2025–2050) and late-century (2070–2100) periods. These PF storm totals were converted to rainfall hyetographs using a fixed alternating variability method (AVM) temporal pattern within the coupled HEC-HMS/HEC-RAS modeling chain. Hazard amplification was primarily expressed through lateral inundation expansion and longer persistence of shallow flooding in low-relief operational zones, rather than uniform increases in peak depth across landfill interiors. Across both facilities, the landfill toe and adjacent access corridors were consistently identified as the most sensitive operational areas.

Water doi: 10.3390/w18091084

Authors: Lucky Baloyi Sikelela Mqhayi Harrison Pienaar Mxolisi B. Mukhawana Mike Butler Thokozani Kanyerere

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

Water doi: 10.3390/w18091083

Authors: Iryanti Fatyasari Nata Chairul Irawan Abubakar Tuhuloula Rinna Juwita Meilana Dharma Putra Yu-Lin Kuo Sri Novi Anggraini Norma Yunita

Agricultural byproducts cellulose-rich (~40%) sugarcane bagasse (SCB) and rice husk (RH) wastes may be used as fiber sources in biomaterials manufacturing. The hybrid biomass fibers are two kinds of fibers that should generate a biocomposite according to the functions and physical, chemical, and mechanical properties of materials. The biocomposite was synthesized using the solvothermal method. The FeCl3.6H2O was dissolved in C2H3NaO2 and C6H6O2 and later heated at 60 °C. The SCB and RH fiber (1:1) are added with HDMA into the mixture, then placed in a Teflon stainless steel autoclave at 200 °C for 6 h. The biocomposite was employed as a green adsorbent to treat wastewater through simultaneous adsorption. The biocomposite had 2.637 mmol g−1 of amine groups, which makes smaller magnetic particles and a high surface area of up to 79%. The pseudo-second-order kinetic model followed the Cu(II) and Pb(II) ions adsorption for 4 h (240 min), and the maximum adsorption capacities were 35.042 mg g−1 and 67.127 mg g−1, respectively, at the pH of 5. The biocomposite not only got rid of metal ions, but it also worked well to get rid of dye, total suspended solids (TSSs), and chemical oxygen demand (COD) as pollutants in wastewater. The biocomposite still worked well after being used four times.

Water doi: 10.3390/w18091082

Authors: Shun Kudo Atsuhiro Yorozuya Koji Yamada

Flood discharge observations in Japan are shifting from the conventional float-based methods to unmanned techniques such as radio-wave current meters. These approaches differ fundamentally in their measurement principles: the former is based on a Lagrangian framework, whereas the latter relies on a Eulerian framework. In this study, surface velocity fields obtained using particle image velocimetry (PIV) were used to track virtual tracers and derive Lagrangian surface velocities, providing a basis for examining the characteristics of Lagrangian and Eulerian measurements in an actual river under flood conditions. The uncertainties associated with the two frameworks were quantitatively compared, and the principal sources of uncertainty in Lagrangian measurements were identified. To achieve accurate discharge observation based on Eulerian measurements, the influences of measurement duration, subsection configuration, and vertical velocity distribution were investigated. The results suggest that measuring many points over a short duration is more effective than measuring a few points over a long duration. In a fixed-point measurement of subsurface velocity, a velocity dip was observed. Furthermore, the results quantitatively demonstrate the effects of bridge-pier wakes on the required averaging time and subsection configuration, highlighting the practical advantage of conducting observations on the upstream side of bridges.

Water doi: 10.3390/w18091081

Authors: Xiaofeng Liu Shanshan Xi Fazhi Xie Jingjing Yu Tianzhao Geng

The Yangtze River, the largest river system in Asia, continues to receive substantial nitrogen loads despite the implementation of management measures. Within this vast and complex system, the spatial patterns and drivers of key nitrogen transformation processes, such as nitrification and denitrification, remain poorly constrained. In particular, systematic isotopic evidence from studies spanning the entire upstream–midstream–downstream continuum remains scarce. This study integrates multiple isotopes (δ15N-NO3−, δ18O-NO3−, δ15N-NH4+) with hydrochemical techniques to elucidate the dominant controls on nitrogen transport and transformation and their spatial heterogeneity across the Yangtze River Basin. Results indicate that dissolved inorganic nitrogen (DIN) is the dominant form of nitrogen pollution in the basin. NO3− concentrations exhibited significant spatial variability, following the pattern downstream (2.86 mg/L) > upstream (1.83 mg/L) > midstream (1.75 mg/L). Isotopic signatures revealed that nitrification is the dominant process controlling the formation and transformation of NO3− throughout the basin. Most δ18O-NO3− values (−5.20‰ to +12.78‰) fell within or close to the theoretical range for nitrification, and a strong positive correlation was observed between δ15N-NO3− and δ15N-NH4+ (R2 = 0.72, p < 0.01), collectively confirming that the conversion of NH4+ to NO3− is the primary pathway. Conversely, denitrification was significantly suppressed under the prevailing high dissolved oxygen conditions (mean 9.78 ± 2.46 mg/L), as further evidenced by the lack of a significant correlation between δ15N-NO3− and ln(NO3−). Furthermore, preferential assimilation of NH4+ by phytoplankton reduced the efficiency of nitrate removal via biological assimilation and influenced isotopic composition. These findings provide a scientific basis for identifying priority nitrogen sources and optimizing targeted nitrogen management strategies in the Yangtze River Basin.

Water doi: 10.3390/w18091080

Authors: Hongyi Zhang Yanwei Zhai Zhiyuan Gu Chunyao Hou Chuke Meng Dawen Tan Weiyang Zhao

Cascading failures of clustered landslide dams can intensify downstream hazards not only by increasing peak flood magnitude but also by accelerating the rise of water level immediately upstream of successive dams, thereby shortening the available response time before overtopping. This study reports large-scale flume experiments on a three-dam cascade built with identical geometry and similar soil gradation, while systematically varying longitudinal spacing and inflow discharge. The principal measured variable, Cw(t), is defined here as the local forebay run-up/water-level record measured at a fixed gauge position immediately upstream of each dam. The run-up hydrographs were summarized using peak run-up Cwmax, threshold-arrival time ta defined at 0.1 Cwmax, time to peak tp, maximum rising-stage rate Smax, and above-threshold duration T. Across ten tests (five spacing configurations under low/high discharge), peak run-up at both downstream dams consistently exceeded that at Dam1, with amplification factors relative to Dam1 of 1.11–1.45 at Dam2 and 1.13–1.42 at Dam3; Dam3 was not always higher than Dam2. Amplification was much stronger in the rising-stage dynamics: Smax increased relative to Dam1 by factors of 1.56–11.0 at Dam2 and 2.27–14.0 at Dam3, demonstrating pronounced downstream wavefront steepening. Higher discharge produced earlier threshold arrivals and peaks throughout the cascade, whereas shorter spacing generally produced more impulsive downstream responses with sharper peaks and larger rate amplification. Overall, the dataset provides stage/run-up-based constraints on cascade amplification and indicates that, within the present experimental matrix, dam spacing is the dominant geometric control on flood propagation and downstream hazard escalation.

Water doi: 10.3390/w18091079

Authors: Jose Luis Chavez-Torres Kunyong Zhang Camila Nickole Fernandez-Morocho

Expansive clay slopes are vulnerable to progressive strength loss induced by repeated wetting and drying, a mechanism that drives shallow failure in active moisture zones. Reproducing this degradation experimentally is time-consuming and resource-intensive. This study evaluates whether Fully Softened Strength (FSS) can serve as a practical substitute for five wet–dry cycles in expansive clay slope stability assessment. Direct shear tests were conducted on wet–dry-cycled and reconstituted FSS specimens across fourteen experimental water contents. Strength parameters were incorporated into homogeneous and heterogeneous limit equilibrium slope models, considering degraded layer thicknesses of 1–5 m and suspended water table conditions. Equivalence was assessed using root mean square error (RMSE), prediction bias, and physical representativeness. Five wet–dry cycles produced a dominant cohesion reduction of 70.4% with minor changes in friction angle, reaching a quasi-stationary degraded state. FSS reproduced an equivalent system response through mechanical compensation between cohesion and friction—not through equality of strength parameters—under shallow failure conditions. The best statistical fit was obtained at w = 43.5% (RMSE = 0.314); however, w = 42.0%, coinciding with the liquid limit, provided a physically more robust interpretation with near-zero bias. Equivalence was found to be valid only for normal stresses ≤ 50 kPa, representative of shallow failure depths of 1–4 m.

Water doi: 10.3390/w18091078

Authors: Wei Li Sidan Lyu Xuefa Wen

Air–sea CO2 flux (FCO2) in the estuary–coastal continuum plays a vital role in global carbon sequestration; however, the mechanisms governing FCO2 spatial heterogeneity during early spring remain poorly understood, particularly the roles of distinct dissolved inorganic carbon (DIC) sources. In March 2025, we investigated the FCO2 spatial variability and DIC sources across the Yangtze River estuary and adjacent coastal areas using DIC concentration, pH, and δ13CDIC analyses. The study area was a net CO2 source (7.3 ± 8.7 mmol m−2 d−1), with the intensity declining progressively from the inner estuary to offshore areas. Physical mixing of three principal water masses established the following pattern: high-pCO2 Changjiang Diluted Water and Yellow Sea Coastal Current drove CO2 outgassing, while low-pCO2 East China Sea Shelf Water weakened it. Quantitative apportionment revealed atmospheric CO2 invasion as the dominant DIC source, followed by carbonate dissolution and organic matter degradation, with the latter declining from the inner estuary to offshore areas. The spatial variation in DIC source contributions further confirms that, superimposed on the physical mixing, biogeochemical processes—particularly biological activity—modulated reginal source intensities. This early-spring case captures a critical transitional window and highlights the necessity of integrating multi-factor regulation with DIC source partitioning to resolve carbon dynamics in the estuarine–coastal continuum.

Water doi: 10.3390/w18091076

Authors: Xiangyang Liu Hangbing Zhao Kang Yang Bin Sun

In sediment-laden irrigation channels, sediment deposition upstream of hydraulic measuring structures can degrade hydraulic performance, reduce measurement reliability, and increase maintenance demand. To clarify the effects of structural optimization on sediment transport and siltation resistance, physical model experiments were conducted on an airfoil weir-orifice facility under different discharges, structural angles, and sediment concentrations. The analysis focused on sediment deposition patterns, longitudinal water surface profiles, sediment concentration, suspended sediment transport rate, cross-sectional velocity distribution, vertical velocity gradient, and Froude number. The results showed that the optimized configuration produced a flatter and more uniform upstream bed morphology, and the average deposition thickness decreased from 4.83 cm to 4.31 cm, corresponding to a reduction of 10.58%. Under all tested conditions, the optimized configuration reduced upstream backwater, increased local flow velocity, and shifted the hydraulic jump closer to the facility outlet. Sediment concentration and suspended sediment transport rate were consistently higher after optimization, indicating enhanced sediment carrying capacity. In addition, the optimized configuration increased the vertical velocity gradient and Froude number, while all cases remained within the subcritical-flow regime. These findings demonstrate that structural optimization can simultaneously improve hydraulic regulation and siltation resistance, and provide an experimental basis for the application of streamlined hydraulic measuring structures in sediment-laden irrigation channels.

Water doi: 10.3390/w18091077

Authors: Pengyang Wang Ling Zhang Donglin Li Fengzhen Tang Xin Wang Yuanjian Wang

The traditional Muskingum model has difficulty representing complex hydraulic behaviors under high-flow conditions because it relies on simplified assumptions and fixed parameters. To address the pronounced nonlinearity and non-stationarity of flood routing in the arid Tarim River Basin, a hybrid forecasting framework was developed by coupling the Muskingum method with multiple machine learning algorithms (Ridge, LASSO, RF, and LSTM) to predict and correct Muskingum residuals. Global Muskingum parameters were identified using the L-BFGS-B algorithm to represent basin-scale routing characteristics. For rolling forecast, a multidimensional feature space was constructed by integrating routing gradients and hydraulic interaction terms. The results indicated that all hybrid models outperformed the traditional Muskingum method across lead times. The Ridge-based hybrid model achieved the best performance at short lead times, with the Nash–Sutcliffe efficiency (NSE) at a 4 h lead time increasing from 0.56 for the physical baseline to 0.977. For longer lead times (12–24 h), the LASSO-based hybrid model demonstrated higher robustness, which was attributed to L1-regularization-based feature selection. The key scientific contribution of this work lies in proposing a lead-time-dependent adaptive modeling strategy, revealing the structural characteristics of the residuals of the Muskingum model, and demonstrating that, in the study basin, simple linear models outperform complex models in multi-step correction. Overall, the proposed framework alleviates systematic underestimation during high-flow periods and provides a predictive scheme for arid-region rivers that preserves physical interpretability while improving forecasting accuracy.

Water doi: 10.3390/w18091075

Authors: Fatma Nihan Dogan Goksen Capar

This study evaluates nitrogen (N) and phosphorus (P) pollution in the Ankara River Sub-basin, Türkiye, using the grey water footprint (GWF) approach. A Tier-1 GWF approach was applied, complemented by a sensitivity analysis to assess the influence of key parameters, including leaching–runoff fractions and water quality thresholds. The results should be interpreted as indicative rather than absolute values, as they depend on assumptions related to leaching fractions and background concentrations. By integrating data from agricultural diffuse sources and municipal wastewater treatment plants (WWTPs), the research identifies critical pollution hotspots and sectoral pressures on water resources, causing water quality degradation. The results reveal that P is the primary limiting pollutant governing GWF magnitudes across the sub-basin. The total GWF was estimated at 8294 million m3 yr−1 in the sub-basin outlet. Approximately 10% and 31% of the basin-wide GWF were associated with fertilizer-based diffuse sources and WWTP1, respectively. The study demonstrates that regulatory compliance alone does not guarantee the protection of a river’s assimilative capacity. These results provide a basis for policy development, emphasizing the need to move beyond concentration-based regulations toward management frameworks that explicitly consider assimilative capacity and cumulative basin-scale impacts.

Water doi: 10.3390/w18091074

Authors: Sofía Sanipatín Diego Barzallo Paúl Palmay Carlos Medina

This study investigates the synthesis and kinetic behavior of a magnetic biochar derived from avocado seed biomass for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Magnetite (Fe3O4) was synthesized through different routes, including nitrogen-assisted coprecipitation, redox-controlled coprecipitation, polyol, sol–gel, and sonochemical methods, to evaluate their structural properties and iron incorporation efficiency. Based on compositional and crystallographic analyses, the coprecipitation under an inert atmosphere exhibited improved phase purity and higher Fe3O4 content, which was selected for in situ incorporation onto biochar produced by pyrolysis at 450 °C. The resulting magnetic material and composite were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), confirming the suitability of the synthesis method and the successful deposition of magnetite onto the porous carbon matrix while preserving its structural integrity. Batch adsorption experiments were conducted at pH 2.0 to evaluate the effect of adsorbent dose and initial Cr(VI) concentration. The adsorption process reached equilibrium within 120 min and was better described by the pseudo-second-order kinetic model (R2 ≥ 0.98), suggesting that chemisorption governs the rate-controlling step, with diffusion phenomena contributing but not dominating the overall mechanism. The maximum adsorption capacity predicted by the kinetic model reached 42.49 mg g−1 at an initial concentration of 100 mg L−1. The results demonstrate that avocado-seed-derived magnetic biochar represents a sustainable and effective material for chromium-contaminated water treatment, integrating agro-industrial waste valorization with enhanced adsorption performance and magnetic separability.

Water doi: 10.3390/w18091073

Authors: Yali Zhao Xuecheng Wang Fansen Meng Xiaoyan Chen

Water quality classification is essential for freshwater ecosystem protection but faces challenges posed by spatiotemporal dependencies and class imbalance. To address these issues, this paper proposes the Adaptive Graph Convolutional Long Short-Term Memory Network (AGConvLSTM), which integrates adaptive graph convolution into the LSTM gating mechanism to explicitly capture spatiotemporal dependencies. As complementary components, station-wise Principal Component Analysis (PCA) preserves spatial heterogeneity in feature structures, while DTW-SMOTE with adaptive sampling and dynamic denoising mitigates class imbalance. Evaluated on five-year water quality data from 13 stations in the Taihu Basin, China, AGConvLSTM achieves a test accuracy of 69.34% and an F1 score of 69.68%, outperforming baseline models. Station-wise accuracy ranges from 49.12% to 88.48%, reflecting spatial heterogeneity. These results suggest that spatiotemporal fusion within recurrent units provides an effective pathway for multi-station water quality classification and offers practical value for watershed early warning systems.

Water doi: 10.3390/w18091072

Authors: Konstantinos V. Arsenopoulos Dionie Smith Diakidi Eleni I. Katsarou Eleni Michalopoulou Elias Papadopoulos John O’Doherty Manos Vlasiou George C. Fthenakis

This review paper provides a comprehensive overview of the use of water in livestock and poultry nutrition, focusing on both quantitative requirements and quality standards. The review is based on the evaluation and synthesis of the published scientific literature addressing water intake, physiological functions, and quality parameters in farm animals. It summarizes the physiological roles of water in key metabolic processes and examines the primary factors influencing water requirements, including animal species, stage of production, and environmental conditions. Furthermore, the article compiles available data on water intake across major livestock systems and outlines the physicochemical and microbiological characteristics required to ensure animal health and food safety. Water constitutes a large proportion of body weight, ranging from 50% to 95% depending on species, and is essential for nutrient transport, thermoregulation, and waste elimination. Water requirements are highly variable and influenced by multiple interacting factors, such as ambient temperature, humidity, and dietary composition. Ensuring continuous access to adequate quantities of safe, high-quality water is essential for optimizing animal health, productivity, and welfare and should be integrated into routine farm management and regulatory frameworks.

Water doi: 10.3390/w18091071

Authors: Tao Tian Lingyun Mo Litang Qin Junfeng Dai Dunqiu Wang Qiutong Lu

Water pollution control for wetland lakes has undergone a fluctuating development process. Effective pollution management requires not only scientific water quality monitoring data but also clear identification of pollution sources within the study area. Accordingly, this study investigated Mudong Lake, the core area of the Huixian Wetland, and conducted water quality monitoring in January 2023 (dry season) and June 2023 (wet season). Based on the Water Quality Index (WQI) assessment results, water quality was better in the wet season than in the dry season. To identify pollution sources, the Absolute Principal Component Score-Multiple Linear Regression (APCS-MLR) model was applied. The results showed that pollution in the dry season was mainly derived from aquaculture and agricultural non-point source pollution, anthropogenic point source pollution, and internal release from sediments, while pollution in the wet season exhibited mixed characteristics, driven by agricultural non-point sources, domestic sewage discharge, and natural factors. Source apportionment analysis indicated that composite pollution sources (domestic sewage and aquaculture wastewater), agricultural non-point source pollution, and other unidentified sources contributed 43.71%, 34.11%, and 22.18% of the total pollution load, respectively. The findings of this study can provide a scientific basis for pollution control, emission reduction, and the targeted management of Mudong Lake.