Water

25 pages, 4518 KB

Open AccessArticle

Time Series Analysis and Periodicity Analysis and Forecasting of the Dniester River Flow Using Spectral, SSA, and Hybrid Models

by Serhii Melnyk, Kateryna Vasiutynska, Oleksandr Butenko, Iryna Korduba, Roman Trach, Alla Pryshchepa, Yuliia Trach and Vitalii Protsiuk

Water 2026, 18(2), 291; https://doi.org/10.3390/w18020291 - 22 Jan 2026

Viewed by 593

Abstract

This study applies spectral analysis and singular spectrum analysis (SSA) to mean annual runoff of the Dniester River for 1950–2024 to identify dominant periodic components governing the hydrological regime of this transboundary basin shared by Ukraine and Moldova. The novelty lies in a [...] Read more.

This study applies spectral analysis and singular spectrum analysis (SSA) to mean annual runoff of the Dniester River for 1950–2024 to identify dominant periodic components governing the hydrological regime of this transboundary basin shared by Ukraine and Moldova. The novelty lies in a basin-specific integration in the first systematic application of a combined spectral–SSA framework to the Dniester River, enabling consistent characterization of runoff variability and assessment of large-scale natural drivers. Time series from three gauging stations are analysed to develop data-driven runoff models and medium-term forecasts. Four stable groups of periodic variability are identified, with characteristic timescales of approximately 30, 11, 3–5.8, and 2 years, corresponding to major atmospheric–oceanic oscillations (AMO, NAO, PDO, ENSO, QBO) and the 11-year solar cycle. Cross-spectral and coherence analyses reveal a statistically significant relationship between solar activity and river discharge, with an estimated lag of about 2 years. SSA reconstructions explain more than 80% of discharge variance, indicating high model reliability. Forecast comparisons show that spectral methods tend to amplify long-term trends, CNN–LSTM models produce conservative trajectories, while a hybrid ensemble approach provides the most balanced and physically interpretable projections. Ensemble forecasts indicate reduced runoff during 2025–2028, followed by recovery in 2029–2034, supporting long-term water-resources planning and climate adaptation. Full article

(This article belongs to the Section Hydrology)

► Show Figures

Figure 1

30 pages, 1669 KB

Open AccessReview

Physicochemical Properties and Adsorption Mechanisms of Bentonite–Sawdust-Derived Carbon Composites

by Rabiga M. Kudaibergenova, Olzhas N. Nurlybayev, Ivan Kazarinov, Aisha N. Nurlybayeva, Seitzhan A. Orynbayev, Nazgul S. Murzakasymova, Elvira A. Baibazarova and Arman A. Kabdushev

Water 2026, 18(2), 290; https://doi.org/10.3390/w18020290 - 22 Jan 2026

Cited by 2 | Viewed by 827

Abstract

The escalating global water crisis necessitates the development of efficient, sustainable, and cost-effective remediation technologies. This review highlights bentonite–sawdust-derived carbon composites as a promising class of adsorbents for the removal of diverse water pollutants. The synthesis strategies, physicochemical properties, key interfacial adsorption mechanisms, [...] Read more.

The escalating global water crisis necessitates the development of efficient, sustainable, and cost-effective remediation technologies. This review highlights bentonite–sawdust-derived carbon composites as a promising class of adsorbents for the removal of diverse water pollutants. The synthesis strategies, physicochemical properties, key interfacial adsorption mechanisms, and adsorption performance toward different pollutant categories are systematically discussed. These hybrid materials exhibit synergistically enhanced properties, including increased surface area, optimized porosity, abundant functional groups, tunable surface charge, and improved structural stability, often outperforming the individual components. Their effectiveness has been demonstrated for both heavy metals (e.g., Cd and Pb) and organic contaminants (e.g., dyes and pharmaceuticals), governed by a combination of ion exchange, electrostatic attraction, π–π interactions, and pore-filling mechanisms. Current challenges related to large-scale production, long-term stability, and regeneration are critically evaluated, and future research directions for the sustainable application of these composites in advanced water treatment systems are outlined. Full article

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

► Show Figures

Figure 1

19 pages, 3834 KB

Open AccessArticle

Utilization of Coal-Based Activated Carbon (JA) for the Adsorption of Methyl Orange Azo Dye in Wastewater

by Lihua Dong, Qianwen Xu, Yang Yao, Yingjie Han and Guanghui Zhang

Water 2026, 18(2), 289; https://doi.org/10.3390/w18020289 - 22 Jan 2026

Viewed by 461

Abstract

Currently, the mainstream methods for dye removal internationally include advanced oxidation, catalytic degradation, and adsorption. Catalytic and oxidation methods are costly and unsuitable for large-scale application. While adsorption is straightforward, selecting and modifying raw materials poses significant challenges. Therefore, identifying readily available and [...] Read more.

Currently, the mainstream methods for dye removal internationally include advanced oxidation, catalytic degradation, and adsorption. Catalytic and oxidation methods are costly and unsuitable for large-scale application. While adsorption is straightforward, selecting and modifying raw materials poses significant challenges. Therefore, identifying readily available and inexpensive adsorbents is crucial for dye removal. This study utilized Type A coal as raw material to prepare a series of specialized activated carbon (JA) for adsorbing methyl orange from wastewater, followed by optimization. The optimized screening results indicated that JA-12 exhibited the highest methyl orange removal rate (90.54%). This performance is attributed to its larger micropore structure and increased pore volume. Further analysis revealed that the adsorption process follows pseudo-second-order kinetics and the Langmuir adsorption isotherm model (R² ≈ 0.999). Compared to the theoretical adsorption capacity calculated based on specific surface area, the adsorption capacity calculated based on pore volume (270.66 mg/g) was closer to the actual adsorption capacity, indicating that the pore structure of JA-12 plays a dominant role in the adsorption process. Combined with the Langmuir adsorption model, it can be inferred that dye molecules in solution adsorb onto the inner surface of JA-12 in a monolayer form. Surface functional group analysis revealed that protonation enhances JA-12’s adsorption capacity for the azo dye methyl orange. Collectively, our findings elucidate the removal mechanism of methyl orange using readily available coal as raw material to prepare low-cost specialty activated carbon, providing a framework for cost-effective, large-scale dye removal. Full article

(This article belongs to the Topic Advanced Processes and Technologies for Wastewater: Collection, Treatment, and Resource)

► Show Figures

Graphical abstract

20 pages, 1794 KB

Open AccessArticle

Origin, Composition and Spectroscopic Characteristics of Dissolved Organic Matter in Brine from Yuncheng Salt Lake

by Panyun Jiang, Hailan Chen, Meng Wang, Jinhua Li, Yuhua Cao, Jing Wang and Ming Li

Water 2026, 18(2), 288; https://doi.org/10.3390/w18020288 - 22 Jan 2026

Viewed by 631

Abstract

Dissolved organic matter (DOM) in salt lake brines comprises organic compounds dissolved in high-salinity aquatic systems. With complex composition and diverse sources, DOM significantly influences biogeochemical cycles, mineral formation, and resource development in salt lakes. However, few studies have investigated the characteristics and [...] Read more.

Dissolved organic matter (DOM) in salt lake brines comprises organic compounds dissolved in high-salinity aquatic systems. With complex composition and diverse sources, DOM significantly influences biogeochemical cycles, mineral formation, and resource development in salt lakes. However, few studies have investigated the characteristics and sources of DOM in salt lake brines. In this study, a DOM sample (YC-4) from brine of Shanxi Yuncheng Salt Lake was isolated and characterized using FT-ICR-MS, nuclear magnetic resonance spectroscopy, three-dimensional fluorescence spectroscopy, and parallel factor analysis. The results demonstrate that YC-4 DOM exhibits rich chemical diversity, primarily composed of lignin/CRAM-like compounds (54.26%), tannins (16.75%) and proteins (13.43%). The predominant carbon forms in YC-4 DOM were aliphatic C-O bonded compounds (33.74%), aliphatic compounds (24.31%), and carboxylic acid compounds (23.95%). YC-4 DOM consists of five fluorescent components: marine-like humic substances, two types of humic-like substances, fulvic-like substances, and one protein-like substance. The fluorescence signature, characterized by high fluorescence index (FI 1.99), low humification index (HIX 0.66), and high biological index (BIX 1.27), collectively indicates that the DOM in Yuncheng Salt Lake brine is predominantly autochthonous, weakly humified, and highly bioavailable. This study reveals the DOM feature within the “human–environment coupled system” of Yuncheng Salt Lake. The findings provide a scientific basis for the sustainable utilization of its brine DOM resources and further enrich the theoretical system of DOM biogeochemical cycle in high-salinity lake system. Full article

(This article belongs to the Section Hydrology)

► Show Figures

Figure 1

35 pages, 8072 KB

Open AccessArticle

Bioretention as an Effective Strategy to Mitigate Urban Catchment Loss of Retention Capacity Attributed to Land Use and Precipitation Patterns

by Krzysztof Muszyński

Water 2026, 18(2), 287; https://doi.org/10.3390/w18020287 - 22 Jan 2026

Viewed by 748

Abstract

This study provides a quantitative assessment of the combined effects of progressive urbanization and changes in precipitation patterns (PPs) on the urban water cycle. The primary objective was to evaluate historical (1940–2024) and projected (to 2060) changes in total annual surface runoff (TSR) [...] Read more.

This study provides a quantitative assessment of the combined effects of progressive urbanization and changes in precipitation patterns (PPs) on the urban water cycle. The primary objective was to evaluate historical (1940–2024) and projected (to 2060) changes in total annual surface runoff (TSR) and retention capacity (RC) in the highly urbanized catchment of the Dłubnia River in Cracow, Poland. Simulations were performed using the EPA SWMM hydrodynamic model, supported by digitized historical land-use maps and long-term meteorological records. The results demonstrate that the dominant driver of the observed 6.4-fold increase in TSR and 6.8-fold loss of retention capacity (LRC) over the study period was the progressive increase in impervious surfaces. Although inter-annual variability in the amount and structure of annual precipitation (AP) strongly correlates with annual TSR (r = 0.97), its contribution to the long-term upward trend in TSR is marginal (r = 0.19). Land use and land cover change (LULC) exhibits an extremely strong correlation with the long-term TSR trend (r = 0.998). The study also highlights the high effectiveness of nature-based solutions (NbSs), particularly bioretention cells (BCs)/rain gardens, in mitigating the adverse hydrological effects of excessive surface sealing. Implementation of BCs covering just 3–4% of the total drained roof and road area is sufficient to fully offset the projected combined negative impacts of further urbanization and climate change (CC) in scope Representative Concentration Pathways (RCP4.5 and RCP8.5) projections on catchment retention capacity by 2060. These findings position strategically targeted, relatively small-scale bioretention as one of the most effective and feasible urban adaptation measures in mature, densely developed cities. Full article

(This article belongs to the Special Issue Urban Water Management: Challenges and Prospects, 2nd Edition)

► Show Figures

Figure 1

23 pages, 745 KB

Open AccessReview

Beyond ‘Business as Usual’: A Research Agenda for the Operationalisation of Nature-Based Solutions in Flood Risk Management in The Netherlands

by Nicola Ann Harvey, Herman Kasper Gilissen and Marleen van Rijswick

Water 2026, 18(2), 286; https://doi.org/10.3390/w18020286 - 22 Jan 2026

Viewed by 904

Abstract

The Netherlands is widely recognised as the global leader in water management, with its flood risk management (FRM) infrastructure lauded as being of the best in the world. This status notwithstanding, Dutch FRM primarily maintains established infrastructural practices and experimental applications of NBSs [...] Read more.

The Netherlands is widely recognised as the global leader in water management, with its flood risk management (FRM) infrastructure lauded as being of the best in the world. This status notwithstanding, Dutch FRM primarily maintains established infrastructural practices and experimental applications of NBSs remain less frequent than established structural projects. This paper details and examines the challenges associated with the prevailing ‘business-as-usual’ approach to FRM in The Netherlands, in which traditional ‘grey’ infrastructural techniques are prioritised over innovative ‘green’ nature-based solutions (NBSs). In line with emerging international trends, such as the EU Water Resilience Strategy, NBSs are increasingly advocated as a strategic, complementary layer to enhance the resilience of existing safety frameworks rather than a self-evident replacement for them. Contrary to grey infrastructure, NBSs provide a number of environmental and social co-benefits extending beyond their flood and drought protection utility. The literature on NBSs details the design, effectiveness, and positive socio-economic impact of the operationalisation of such projects for FRM. This notwithstanding, the uptake and practical implementation of NBSs have been slow in The Netherlands. From a legal and policy perspective, this has been attributed to a lack of political will and the corresponding failure to include NBSs in long term FRM planning. Given the long planning horizons associated with FRM (50–100 years), the failure to incorporate NBSs can lead to policy lock-in that blocks future adaptations. Against this backdrop, this paper employs a semi-systematic literature review to clarify the obstacles to implementing NBSs in Dutch FRM and sets a research agenda that charts a course to mainstreaming NBSs in Dutch FRM. Seven core focus areas for future research are identified. The paper concludes by drawing on these identified focus areas to construct a research agenda aimed at systematically addressing each barrier to the practical operationalisation of NBSs in Dutch FRM, emphasising a hybrid green–grey approach which may serve to inspire similar research in other jurisdictions. Full article

(This article belongs to the Section Water Resources Management, Policy and Governance)

► Show Figures

Figure 1

46 pages, 9891 KB

Open AccessArticle

An Operational Streamflow Forecasting System for a Data-Scarce Catchment in Tanzania

by Preksedis Marco Ndomba and Ånund Killingtveit

Water 2026, 18(2), 285; https://doi.org/10.3390/w18020285 - 22 Jan 2026

Viewed by 795

Abstract

This paper reports the findings of the first initiative of developing a year-round streamflow forecasting system using the HBV hydrologic model in a data-scarce Ruvu catchment in Tanzania. Considering the importance of the Ruvu catchment as the main source of water to the [...] Read more.

This paper reports the findings of the first initiative of developing a year-round streamflow forecasting system using the HBV hydrologic model in a data-scarce Ruvu catchment in Tanzania. Considering the importance of the Ruvu catchment as the main source of water to the fast-growing mega city of Dar es Salaam, the researchers in this study made the most of the available data and their joint previous application experience of the modelling framework for the purpose of setting up a reliable operational model. In addition, the researchers adopted a phased approach of developing the streamflow forecasting system, using HBV as a hydrological model, which resulted in a simplified model structure with minimized complexity. For instance, the snow routine was removed as it is not relevant to the study area, and a few parameters were reduced to improve model efficiency. As a measure to demonstrate model performance, in addition to the Nash–Sutcliffe Efficiency (NSE) parameter used for model calibration and verification, several other error functions and graphical displays were used. The model performance values, as measured by NSE for calibration and verification periods, are 0.85 and 0.82 for Ruvu Roadbridge (1H8A), and 0.80 and 0.82 for Kidunda (1H3), respectively, and all are classified as “Very Good”. In addition, the PBIAS of less than ±5% in calibration indicates excellent water balance simulation. Furthermore, the forecast’s performance in this study is evidenced by an annual forecast R² of 0.933, with operational meteorological forecasts improving to 0.962 with “perfect” precipitation; dry season performance with R² of 0.964, demonstrating high skill in baseflow-dominated periods; and the PBIAS for forecasts of 0.866, indicating a slight systematic under-forecasting correctable by a ~15% precipitation adjustment. Although the Ruvu catchment has been characterized by this study as a data-scarce catchment, the results of the operational hydrological forecasting system vary with season and quality of forecast meteorological data, and the model is already launched for operational use. As evidenced by these study findings, the journey from data scarcity to operational forecast provision in the Ruvu catchment demonstrates that the principal barriers are fundamentally institutional and capacity-related. The authors suggest that any future forecasting initiative should put much emphasis on both the understanding of the modelling framework to be used and adequate data collection and analysis, in a synergetic manner with all relevant agencies. And it is also recommended to be vigilant regarding changes in the catchment characteristics and model performance during its life cycle, as the performance of the developed model is only valid under the condition that it was calibrated and validated. Full article

(This article belongs to the Section Hydrology)

► Show Figures

Figure 1

30 pages, 3470 KB

Open AccessArticle

Integrated Coastal Zone Management in the Face of Climate Change: A Geospatial Framework for Erosion and Flood Risk Assessment

by Theodoros Chalazas, Dimitrios Chatzistratis, Valentini Stamatiadou, Isavela N. Monioudi, Stelios Katsanevakis and Adonis F. Velegrakis

Water 2026, 18(2), 284; https://doi.org/10.3390/w18020284 - 22 Jan 2026

Cited by 1 | Viewed by 925

Abstract

This study presents a comprehensive geospatial framework for assessing coastal vulnerability and ecosystem service distribution along the Greek coastline, one of the longest and most diverse in Europe. The framework integrates two complementary components: a Coastal Erosion Vulnerability Index applied to all identified [...] Read more.

This study presents a comprehensive geospatial framework for assessing coastal vulnerability and ecosystem service distribution along the Greek coastline, one of the longest and most diverse in Europe. The framework integrates two complementary components: a Coastal Erosion Vulnerability Index applied to all identified beach units, and Coastal Flood Risk Indexes focused on low-lying and urbanized coastal segments. Both indices draw on harmonized, open-access European datasets to represent environmental, geomorphological, and socio-economic dimensions of risk. The Coastal Erosion Vulnerability Index is developed through a multi-criteria approach that combines indicators of physical erodibility, such as historical shoreline retreat, projected erosion under climate change, offshore wave power, and the cover of seagrass meadows, with socio-economic exposure metrics, including land use composition, population density, and beach-based recreational values. Inclusive accessibility for wheelchair users is also integrated to highlight equity-relevant aspects of coastal services. The Coastal Flood Risk Indexes identify flood-prone areas by simulating inundation through a novel point-based, computationally efficient geospatial method, which propagates water inland from coastal entry points using Extreme Sea Level (ESL) projections for future scenarios, overcoming the limitations of static ‘bathtub’ approaches. Together, the indices offer a spatially explicit, scalable framework to inform coastal zone management, climate adaptation planning, and the prioritization of nature-based solutions. By integrating vulnerability mapping with ecosystem service valuation, the framework supports evidence-based decision-making while aligning with key European policy goals for resilience and sustainable coastal development. Full article

(This article belongs to the Section Oceans and Coastal Zones)

► Show Figures

Figure 1

19 pages, 1863 KB

Open AccessArticle

Divergent Pathways and Converging Trends: A Century of Beach Nourishment in the United States Versus Three Decades in China

by Min Jiang, Jun Zhu, Fengjuan Sun, Miaohua Mao, Ping Dong, Chao Zhan, Guoqing Li, Xingjie Zhang, Xinlan Dong, Xing Jiang and Xuejie Wang

Water 2026, 18(2), 283; https://doi.org/10.3390/w18020283 - 22 Jan 2026

Viewed by 621

Abstract

Beach nourishment has become a globally adopted “soft” engineering measure to mitigate coastal erosion and sustain beach functions. This study conducts a systematic comparative analysis of beach nourishment practices between China and the United States, focusing on extensive project data and historical records. [...] Read more.

Beach nourishment has become a globally adopted “soft” engineering measure to mitigate coastal erosion and sustain beach functions. This study conducts a systematic comparative analysis of beach nourishment practices between China and the United States, focusing on extensive project data and historical records. The research examines differences in historical development trajectories, spatial distribution patterns, restoration philosophies, funding mechanisms, and key technologies. The results reveal that the U.S., with over a century of experience, exhibits large-scale, high-frequency nourishment projects supported by diversified funding and long-term maintenance strategies. In contrast, China, despite a later start (circa 1992), has achieved rapid progress in both project scale and technical innovation, though its approach remains more government-led and structurally oriented. This study also identifies converging trends in resource concentration between the two countries, as measured by a proposed “beach nourishment primacy” index. Based on these findings, the work offers strategic recommendations for the coastal management of China, including the establishment of a national nourishment database, adoption of Regional Sediment Management, and greater integration of ecological engineering principles. This comparative analysis provides valuable insights for coastal nations seeking to optimize beach nourishment strategies in the face of growing climatic and anthropogenic pressures; to further advance these efforts, future research could explore the integration of interdisciplinary approaches and intelligent technologies, aiming to deepen our understanding of coastal system complexity and support the development of dynamic adaptive management. Full article

(This article belongs to the Special Issue Coastal Engineering and Fluid–Structure Interactions, 2nd Edition)

► Show Figures

Figure 1

29 pages, 6210 KB

Open AccessArticle

Assessing Economic Vulnerability from Urban Flooding: A Case Study of Catu, a Commerce-Based City in Brazil

by Lais Das Neves Santana, Alarcon Matos de Oliveira, Lusanira Nogueira Aragão de Oliveira and Fabricio Ribeiro Garcia

Water 2026, 18(2), 282; https://doi.org/10.3390/w18020282 - 22 Jan 2026

Viewed by 797

Abstract

Flooding is a recurrent problem in many Brazilian cities, resulting in significant losses that affect health, assets, finance, and the environment. The uncertainty regarding extreme rainfall events due to climate change makes this challenge even more severe, compounded by inadequate urban planning and [...] Read more.

Flooding is a recurrent problem in many Brazilian cities, resulting in significant losses that affect health, assets, finance, and the environment. The uncertainty regarding extreme rainfall events due to climate change makes this challenge even more severe, compounded by inadequate urban planning and the occupation of risk areas, particularly for the municipality of Catu, in the state of Bahia, which also suffers from recurrent floods. Critical hotspots include the Santa Rita neighborhood and its surroundings, the main supply center, and the city center—the municipality’s commercial hub. The focus of this research is the unprecedented quantification of the socioeconomic impact of these floods on the low-income population and the region’s informal sector (street vendors). This research focused on analyzing and modeling the destructive potential of intense rainfall in the Santa Rita region (Supply Center) of Catu, Bahia, and its effects on the local economy across different recurrence intervals. A hydrological simulation software suite based on computational and geoprocessing technologies—specifically HEC-RAS 6.4, HEC-HMS 4.11, and QGIS— 3.16 was utilized. Two-dimensional (2D) modeling was applied to assess the flood-prone areas. For the socioeconomic impact assessment, a loss procedure based on linear regression was developed, which correlated the different return periods of extreme events with the potential losses. This methodology, which utilizes validated, indirect data, establishes a replicable framework adaptable to other regions facing similar socioeconomic and drainage challenges. The results revealed that the area becomes impassable during flood events, preventing commercial activities and causing significant economic losses, particularly for local market vendors. The total financial damage for the 100-year extreme event is approximately US $30,000, with the loss model achieving an R² of 0.98. The research concludes that urgent measures are necessary to mitigate flood impacts, particularly as climate change reduces the return period of extreme events. The implementation of adequate infrastructure, informed by the presented risk modeling, and public awareness are essential for reducing vulnerability. Full article

(This article belongs to the Special Issue Water-Soil-Vegetation Interactions in Changing Climate)

► Show Figures

Figure 1

16 pages, 2709 KB

Open AccessArticle

Occurrence, Seasonal Variation, and Microbial Drivers of Antibiotic Resistance Genes in a Residential Secondary Water Supply System

by Huaiyu Tian, Yu Zhou, Dawei Zhang and Weiying Li

Water 2026, 18(2), 281; https://doi.org/10.3390/w18020281 - 22 Jan 2026

Viewed by 552

Abstract

The widespread use of antibiotics has led to the persistence of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in drinking water systems, posing potential public health risks at the point of use. In this study, a residential secondary water supply system (SWSS) [...] Read more.

The widespread use of antibiotics has led to the persistence of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in drinking water systems, posing potential public health risks at the point of use. In this study, a residential secondary water supply system (SWSS) in eastern China was investigated over one year to characterize microbial communities, ARB and ARG occurrence, and their associations with water quality in bulk water and biofilms. Culture-based methods, flow cytometry, quantitative PCR, and high-throughput 16S rRNA and ITS sequencing were applied. Although conventional treatment removed 94.8% of total bacteria, significant microbial regrowth occurred during secondary distribution, with the highest heterotrophic plate counts observed in rooftop storage tanks (up to 4718 CFU/mL). ARG concentrations increased along the distribution line, and the class 1 integron intI1 was enriched in downstream locations, indicating enhanced horizontal gene transfer potential. Sulfonamide resistance genes dominated the resistome, accounting for more than 60% of total ARG abundance in water samples. Seasonally, ARG levels were higher in autumn and winter, coinciding with elevated disinfectant residuals and lower temperatures. Chlorine was negatively associated with total bacterial abundance, while positive correlations were observed with the relative abundance of several ARGs when normalized to bacterial biomass, suggesting selective pressure under oxidative stress. Turbidity and bacterial abundance were positively correlated with ARB, particularly sulfonamide-resistant bacteria. Biofilms exhibited more stable microbial communities and provided microhabitats that facilitated microbial persistence. Notably, fungal abundance showed strong positive correlations with multiple ARGs, implying that microbial interactions may indirectly contribute to ARG persistence in SWSSs. These findings highlight the role of secondary distribution conditions, disinfectant pressure, and microbial interactions in shaping resistance risks in residential water supply systems, and provide insights for improving microbial risk management at the point of consumption. Full article

(This article belongs to the Special Issue Advances in Control Technologies for Emerging Contaminants in Water)

► Show Figures

Figure 1

18 pages, 11982 KB

Open AccessArticle

A Baseflow Equation: Example of the Middle Yellow River Basins

by Haoxu Tong and Li Wan

Water 2026, 18(2), 280; https://doi.org/10.3390/w18020280 - 21 Jan 2026

Viewed by 462

Abstract

Existing baseflow estimation methods—such as exponential recession models, linear reservoir approaches, and digital filtering techniques—seldom account for anthropogenic disturbances or evapotranspiration-induced streamflow alterations. To address this limitation, a physically based baseflow equation that explicitly integrates human water withdrawals and evapotranspiration losses has been [...] Read more.

Existing baseflow estimation methods—such as exponential recession models, linear reservoir approaches, and digital filtering techniques—seldom account for anthropogenic disturbances or evapotranspiration-induced streamflow alterations. To address this limitation, a physically based baseflow equation that explicitly integrates human water withdrawals and evapotranspiration losses has been introduced. The governing equation was reformulated from a nonlinear storage–discharge relationship and validated against multi-decadal streamflow records in the Middle Yellow River Basin (MYRB). Results demonstrate that the proposed model accurately reproduces observed recession behavior across diverse sub-basins (NSE ≥ 0.94; RMSE ≤ 152 m³ s⁻¹). By providing reliable baseflow estimates, the equation enables quantitative assessment of eco-hydrological benefits and informs cost-effective water-resource investments. Furthermore, long-term baseflow simulations driven by climate projections offer a scientific basis for evaluating climate-change impacts on regional water security. Full article

(This article belongs to the Special Issue Application of Hydrological Modelling to Water Resources Management)

► Show Figures

Figure 1

17 pages, 247 KB

Open AccessArticle

Effect of Environmental Regulation on Performance of Water Environmental Governance: From the Perspective of Formal and Informal Environmental Regulation

by Yiwei Wang, Wenke Zhang, Yijing Weng, Debao Wang and Liheng Chen

Water 2026, 18(2), 279; https://doi.org/10.3390/w18020279 - 21 Jan 2026

Cited by 1 | Viewed by 418

Abstract

Developing high-quality regional integration requires a good-quality water environment. In this study, the impact of formal and informal environmental regulation (FIER) on water environment governance performance (WEP) is examined using a fixed-effects model and spatial Durbin model with a panel data sample of [...] Read more.

Developing high-quality regional integration requires a good-quality water environment. In this study, the impact of formal and informal environmental regulation (FIER) on water environment governance performance (WEP) is examined using a fixed-effects model and spatial Durbin model with a panel data sample of 281 cities from 2011 to 2022. It is found that (i) there is an inverted U-shaped relationship between FIER and WEP, which is first promoted and then inhibited and remains significant after endogeneity exploration and multiple robustness tests; (ii) the pressure of economic growth has weakened this elationship, while the digital economy has strengthened it; and (iii) further analysis reveals that there is an inverted U-shaped relationship between the local and spillover effects of FIER on WEP. Therefore, WEP can be improved by dynamically adjusting the intensity of FIER, optimizing the appraisal orientation of local governments, and accelerating the integration of digital economy and environmental governance Full article

(This article belongs to the Section Water Resources Management, Policy and Governance)

23 pages, 1715 KB

Open AccessArticle

From Identification to Guiding Action: A Systematic Heuristic to Prioritise Drivers of Change for Water Management

by Jo Mummery and Leonie J. Pearson

Water 2026, 18(2), 278; https://doi.org/10.3390/w18020278 - 21 Jan 2026

Viewed by 470

Abstract

Global water management faces a critical challenge: whilst scholarly consensus recognises that multiple, interacting drivers fundamentally shape water availability and management capacity, operational governance frameworks fail to systematically incorporate this understanding. This disconnect is particularly acute in public good contexts where incomplete knowledge, [...] Read more.

Global water management faces a critical challenge: whilst scholarly consensus recognises that multiple, interacting drivers fundamentally shape water availability and management capacity, operational governance frameworks fail to systematically incorporate this understanding. This disconnect is particularly acute in public good contexts where incomplete knowledge, diverse stakeholder values, and statutory planning mandates create distinct challenges. Using Australia’s Murray–Darling Basin as a pilot case, this research develops and demonstrates a rapid, policy-relevant heuristic for identifying, prioritising, and incorporating drivers of change in complex socio-ecological water systems. Through structured participatory deliberation with 70 experts spanning research, policy, industry, and community sectors across three sequential workshops and 15 semi-structured interviews, we systematically identified key drivers across environmental, governance, economic, social, and legacy dimensions. A risk and sensitivity assessment framework enabled prioritisation based on impact, vulnerability, and urgency. Climate change, drought, water quality events, and cumulative impacts emerged as the highest-priority future drivers, with climate change acting as a threat multiplier, whilst governance drivers show declining relative significance. Using these methodological innovations, we synthesise the I-PLAN heuristic: five interdependent dimensions (Integrative Knowledge, Prioritisation for Management, Linkages between Drivers, Adaptive Agendas, and Normative Collaboration) that provide water planners with a transferable, operational tool for driver identification and bridging to planning and management in data-sparse contexts. Full article

(This article belongs to the Special Issue From Theory to Practice: Implementing Resilience, Adaptation and Drivers of Change Frameworks in Water Basin Management)

► Show Figures

Figure 1

31 pages, 3779 KB

Open AccessArticle

Assessing Climate Change Impacts on Future Precipitation Using Random Forest Statistical Downscaling of CMIP6 HadGEM3 Projections in the Büyük Menderes Basin

by Ismail Ara, Mutlu Yasar and Gurhan Gurarslan

Water 2026, 18(2), 277; https://doi.org/10.3390/w18020277 - 21 Jan 2026

Viewed by 1025

Abstract

Climate change increasingly threatens the sustainability of regional water resources; therefore, robust station-scale precipitation projections are essential for basin-level planning. This study aims to develop and evaluate a hybrid, machine-learning-based statistical downscaling framework to generate monthly precipitation projections for the 21st century in [...] Read more.

Climate change increasingly threatens the sustainability of regional water resources; therefore, robust station-scale precipitation projections are essential for basin-level planning. This study aims to develop and evaluate a hybrid, machine-learning-based statistical downscaling framework to generate monthly precipitation projections for the 21st century in the Büyük Menderes Basin, western Türkiye, using the HadGEM3-GC31-LL global climate model from the CMIP6. Monthly observations from 23 rainfall observation stations and ERA5 reanalysis predictors were employed to train station-specific Random Forest (RF) models, with optimal predictor sets identified through a multistage selection procedure (MPSP). Coarse-resolution general circulation model (GCM) fields were harmonized with ERA5 data using a three-stage inverse distance weighting (IDW), Delta, and Variance rescaling approach. The downscaled projections were bias-corrected using Quantile Delta Mapping (QDM) to maintain the climate-change signal. The RF models exhibited strong predictive skill across most stations, with test Nash–Sutcliffe Efficiency (NSE) values ranging from 0.45 to 0.81, RSR values from 0.43 to 0.74, and PBIAS values from −21.99% to +5.29%. Future projections indicate a basin-wide drying trend under both scenarios. Relative to the baseline, mean annual precipitation is projected to decrease by approximately 12.2, 19.6, and 33.7 mm in the near (2025–2050), mid (2051–2075), and late (2076–2099) periods under SSP2-4.5 (Shared Socioeconomic Pathway 2-4.5, a moderate greenhouse gas scenario). Under the high-emission SSP5-8.5 scenario, projected decreases are 25.2, 53.2, and 86.9 mm, respectively. Late-century reductions reach approximately 15–22% in several sub-basins. These findings indicate a substantial decline in future water availability and underscore the value of RF-based hybrid downscaling and trend-preserving bias correction for water resources planning in semi-arid Mediterranean basins. Full article

(This article belongs to the Special Issue Climate Change Adaptation in Water Resource Management)

► Show Figures

Figure 1

22 pages, 7599 KB

Open AccessArticle

Spatiotemporal Evolution of Compound Dry–Hot Events and Their Impacts on Vegetation Net Primary Productivity in the Yangtze River Basin

by Hongqi Xi, Gengxi Zhang and Hongkai Wang

Water 2026, 18(2), 276; https://doi.org/10.3390/w18020276 - 21 Jan 2026

Cited by 1 | Viewed by 1041

Abstract

Compound dry–hot events increasingly threaten ecosystem productivity under global warming. Using ERA5-Land and MODIS NPP (2002–2024) for the Yangtze River Basin, we built climate indices and developed a Copula-based standardized compound dry–hot index (SCDHI) to detect events and examine spatiotemporal patterns. Trend and [...] Read more.

Compound dry–hot events increasingly threaten ecosystem productivity under global warming. Using ERA5-Land and MODIS NPP (2002–2024) for the Yangtze River Basin, we built climate indices and developed a Copula-based standardized compound dry–hot index (SCDHI) to detect events and examine spatiotemporal patterns. Trend and correlation analyses quantified NPP sensitivity and lag, and an NPP–SCDHI coupling framework assessed resistance and resilience across major vegetation types. Basin-wide monthly NPP increased slightly, while SCDHI decreased, indicating a warmer and drier tendency. Under dry–hot conditions, NPP was mainly negatively related to event intensity in the upper basin but positively related across much of the middle–lower plains. The mean NPP response time was approximately 2 months, with forests and croplands typically lagging 2–3 months. Under extreme stress, forests showed high resistance but limited recovery, whereas shrublands showed moderate resistance and low resilience. Cultivated vegetation exhibited the lowest resistance and weak resilience, grasslands had low resistance but relatively rapid recovery, and alpine vegetation showed moderate resistance and the highest resilience. Cultivated vegetation and grasslands may therefore represent high-risk types for ecological management. Full article

(This article belongs to the Special Issue Ecohydrology in the Context of Climate Change: Strategies for Management, Monitoring, and Modeling)

► Show Figures

Figure 1

15 pages, 1735 KB

Open AccessArticle

Small Kaplan Turbines Cause Lethal Injuries to Fish Populations During Downstream Passage

by Francisco Javier Sanz-Ronda, Juan Francisco Fuentes-Pérez, Ana García-Vega, Jorge Valbuena-Castro, Juan de María-Arnaiz and Francisco Javier Bravo-Córdoba

Water 2026, 18(2), 275; https://doi.org/10.3390/w18020275 - 21 Jan 2026

Viewed by 771

Abstract

Fish passage through turbines is one of the main environmental impacts of hydropower. Turbine type is a key factor influencing fish survival, and widespread Kaplan turbines are generally considered less dangerous than other turbine types. Nevertheless, while large Kaplan turbines have been extensively [...] Read more.

Fish passage through turbines is one of the main environmental impacts of hydropower. Turbine type is a key factor influencing fish survival, and widespread Kaplan turbines are generally considered less dangerous than other turbine types. Nevertheless, while large Kaplan turbines have been extensively studied, there is limited empirical evidence about the biological impact of small, high-speed Kaplan turbines on fish survival. In this study, we conducted controlled in situ fish experiments at a small and low-head hydropower plant (1 MW; head 8 m) using balloon tags and pressure sensors to quantify real mortality in two horizontal Kaplan turbines operating at full capacity: one small turbine (1.2 m Ø, 500 rpm, and 5 m³/s) and one larger unit (1.55 m Ø, 300 rpm, and 8 m³/s). Fish (95–190 mm) were released into the intake flow and monitored post-passage. Results showed higher mortality in the small turbine, with ~80% in 24 h, many exhibiting severe mechanical injuries such as complete sectioning of the head or spinal cord, with significantly higher mortality in larger fish. In contrast, the larger turbine showed a ~60% mortality rate and fewer traumatic injuries. Our findings highlight the underestimated impact of small, high-rpm Kaplan turbines on fish survival and underscore the need for adaptive turbine operation or structural modifications to minimize ecological damage during critical migration periods. Full article

(This article belongs to the Special Issue Research Status of Operation and Management of Hydropower Station, 2nd Edition)

► Show Figures

Figure 1

13 pages, 1436 KB

Open AccessArticle

Lipid Metabolism and Oxidative Stress Altered in Crucian Carp (Carassius auratus) Following Exposure to Microplastics Under Laboratory and Field Conditions

by Yuxuan Wu, Zeda Song, Yuguang Lu, Xi Wang, Lihui An and Hongwei Wang

Water 2026, 18(2), 274; https://doi.org/10.3390/w18020274 - 21 Jan 2026

Viewed by 495

Abstract

Microplastics are pervasive in aquatic environments; however, their impacts on aquatic organisms at environmentally relevant concentrations remain poorly understood, particularly under field conditions. To address this gap, we employed high-throughput sequencing to assess these impacts under both field and laboratory conditions using crucian [...] Read more.

Microplastics are pervasive in aquatic environments; however, their impacts on aquatic organisms at environmentally relevant concentrations remain poorly understood, particularly under field conditions. To address this gap, we employed high-throughput sequencing to assess these impacts under both field and laboratory conditions using crucian carp (Carassius auratus) as a model organism. Following a 4-week exposure in situ, the abundance of intestinal microplastics slightly increased from an initial level of 55.00 ± 59.73 items/fish to 72.67 ± 27.50 items/fish (p > 0.05). Accordingly, a total of 3036 differentially expressed genes (DEGs) were identified in the hepatic transcriptome, with notable enrichment in pathways related to lipid metabolism and oxidative stress. Furthermore, a positive correlation between intestinal microplastic abundance and exposure concentration was observed in fish following a 2-week laboratory exposure to polyamide (PA), with intestinal burdens ranging from 7.50 ± 3.54 to 367.50 ± 17.68 items/fish. The number of DEGs in the hepatic transcriptome, ranging from 41 to 380 items, demonstrated a nonlinear relationship with microplastic levels. Furthermore, these DEGs were primarily enriched in pathways associated with lipid metabolism and oxidative stress, including the PPAR signaling pathway (ko03320) and fatty acid degradation (ko00071). This suggests that microplastics at environmental levels may have detrimental effects on organisms through perturbations in lipid metabolism and oxidative stress. As expected, these findings provide essential insights for evaluating the ecological risks linked to microplastic pollution at environmental levels. Full article

(This article belongs to the Special Issue Studies on Toxic Effects in Aquatic Organisms and Ecosystems)

► Show Figures

Figure 1

25 pages, 9491 KB

Open AccessArticle

Determination of the Surface Watercourse Velocities by Using the Propeller Current Meter, Unmanned Aerial Vehicle, and Mobile Phone

by Sanja Šamanović, Bojan Đurin, Vlado Cetl and Farhad Bahmanpouri

Water 2026, 18(2), 273; https://doi.org/10.3390/w18020273 - 21 Jan 2026

Viewed by 604

Abstract

According to existing procedures for defining the velocity distribution across cross profile sections of watercourses (e.g., Entropy theory and Power Law theory), surface velocity is a key input parameter, together with cross-sectional bathymetry. Field measurements to obtain velocity values and their distributions are [...] Read more.

According to existing procedures for defining the velocity distribution across cross profile sections of watercourses (e.g., Entropy theory and Power Law theory), surface velocity is a key input parameter, together with cross-sectional bathymetry. Field measurements to obtain velocity values and their distributions are often difficult due to limited equipment, unreliable data, missing data, or hazardous conditions such as flooding and inaccessible locations. This creates a strong need for alternative approaches to measuring surface velocities in rivers. The application of unmanned aerial vehicles (UAVs), mobile phones, and traditional field instruments such as the Propeller Current Meter (PCM) can significantly improve measurement efficiency, especially in situations where conventional methods are not feasible. This paper presents an algorithm for comparing these measurement approaches and quantifying their differences. The methodology is demonstrated using a real case study on the Bednja River in Croatia, which flows through alluvial deposits. The results show that video-based surface velocity estimation using UAV and mobile phone imagery is feasible under real river conditions. Still, its accuracy depends strongly on flow conditions and surface characteristics. While UAV recordings provide reliable results in fast and turbulent flows, mobile phone videos yield more stable performance in smoother flow conditions, where additional surface texture is available from natural tracers. Full article

(This article belongs to the Special Issue Database Integration and Conceptual Frameworks in Hydrological Research)

► Show Figures

Figure 1

22 pages, 5142 KB

Open AccessArticle

The Impact of Plant Debris on Hydraulic Conditions in a Semi-Natural Fish Pass

by Natalia Walczak, Zbigniew Walczak and Mateusz Hammerling

Water 2026, 18(2), 272; https://doi.org/10.3390/w18020272 - 21 Jan 2026

Viewed by 495

Abstract

Fish passes are essential hydraulic structures that maintain longitudinal connectivity in regulated rivers, but their hydraulic performance may be affected by debris accumulation at chamber openings. This study investigates the influence of partial and total inlet blockage by plant debris on flow conditions [...] Read more.

Fish passes are essential hydraulic structures that maintain longitudinal connectivity in regulated rivers, but their hydraulic performance may be affected by debris accumulation at chamber openings. This study investigates the influence of partial and total inlet blockage by plant debris on flow conditions within a semi-natural fish pass under field conditions. Hydraulic measurements were conducted at multiple locations along the fish pass, and the effects of debris covering were evaluated using statistical and mixed-effects modeling approaches. Field measurements demonstrated that the Froude number decreases systematically with increasing distance from the inlet, indicating progressive longitudinal dissipation of flow energy along the chamber sequence. Partial debris accumulation caused only marginal changes in the Froude number, remaining close to the threshold of statistical significance. In contrast, mean flow velocity decreased markedly with increasing inlet blockage, by approximately 17% at 50% covering and by about 36% under full blockage, indicating that debris primarily acts as a hydraulic damper rather than inducing a change in flow regime. The highest variability in hydraulic conditions was observed in chambers associated with changes in flow direction and local geometry. These results highlight the dominant role of longitudinal layout and chamber geometry in shaping hydraulic conditions in semi-natural fish passes, while moderate debris accumulation affects local velocities without fundamentally compromising hydraulic functionality. From an ecological perspective, transition zones with elevated hydraulic variability may represent critical locations influencing the swimming effort and passage efficiency of migrating fish. Full article

(This article belongs to the Section Hydraulics and Hydrodynamics)

► Show Figures

Figure 1

76 pages, 15486 KB

Open AccessReview

Machine Learning in Climate Downscaling: A Critical Review of Methodologies, Physical Consistency, and Operational Applications

by Hamed Najafi, Gareth Lynton Lagerwall, Jayantha Obeysekera and Jason Liu

Water 2026, 18(2), 271; https://doi.org/10.3390/w18020271 - 21 Jan 2026

Cited by 2 | Viewed by 3010

Abstract

High-resolution climate projections are essential for regional risk assessment; however, Earth System Models (ESMs) operate at scales far too coarse for local impacts. This review examines how machine learning (ML) downscaling can bridge this divide and addresses a key knowledge gap: how to [...] Read more.

High-resolution climate projections are essential for regional risk assessment; however, Earth System Models (ESMs) operate at scales far too coarse for local impacts. This review examines how machine learning (ML) downscaling can bridge this divide and addresses a key knowledge gap: how to achieve reliable, physically consistent downscaling under future climate change. This article synthesizes ML downscaling developments from 2010 to 2025, spanning early statistical methods to modern deep learning (e.g., convolutional neural networks (CNNs), generative adversarial networks (GANs), diffusion models, and transformers). The analysis introduces a new taxonomy of model families and frames the discussion around the “performance paradox”—the tendency for models with excellent historical skill to falter under non-stationary climate shifts. Our analysis finds that convolutional approaches efficiently capture spatial structure but tend to smooth out extremes, whereas generative models better reproduce high-intensity events at the cost of greater complexity. The study also highlights emerging solutions like physics-informed models and improved uncertainty quantification to tackle persistent issues of physical consistency and trust. Finally, the synthesis outlines a practical roadmap for operational ML downscaling, emphasizing standardized evaluation, out-of-distribution stress tests, and hybrid physics–ML approaches to bolster confidence in future projections. Full article

(This article belongs to the Section New Sensors, New Technologies and Machine Learning in Water Sciences)

► Show Figures

Figure 1

21 pages, 2141 KB

Open AccessArticle

Biochar–Sponge Iron Modified Bioretention System Improved Nitrogen Removal Efficiency for Aquaculture Wastewater Treatment

by Jiang Wang, Wenqiang Jiang, Luting Wen, Chengcai Zhang, Junneng Liang, Linyuan Jiang, Xueming Yang and Shumin Wang

Water 2026, 18(2), 270; https://doi.org/10.3390/w18020270 - 21 Jan 2026

Viewed by 762

Abstract

To address the challenge of low nitrogen removal efficiency, particularly the difficulty in meeting total nitrogen (TN) discharge standards during low-temperature seasons and intermittent emission modes in conventional aquaculture wastewater treatment, this study proposed the novel application of bioretention systems. Biochar and sponge [...] Read more.

To address the challenge of low nitrogen removal efficiency, particularly the difficulty in meeting total nitrogen (TN) discharge standards during low-temperature seasons and intermittent emission modes in conventional aquaculture wastewater treatment, this study proposed the novel application of bioretention systems. Biochar and sponge iron were used as fillers to construct three bioretention systems: biochar-based (B-BS), sponge iron-based (SI-BS), and a composite system (SIB-BS), for evaluating their nitrogen removal performance for aquaculture wastewater treatment. Experimental results demonstrated that under intermittent flooding conditions at 8.0–13.0 °C and increasing TN loading (9.48 mg/L–31.13 mg/L), SIB-BS maintained stable TN removal (79.7–86.7%), outperforming B-BS and SI-BS (p < 0.05). Under continuous inflow (influent TN = 8.4 ± 0.5 mg/L) at 8.0–13.0 °C, SIB-BS achieved significantly lower effluent TN (2.57 ± 1.5 mg/L) than B-BS (5.6 ± 1.6 mg/L) and SI-BS (5.0 ± 1.5 mg/L) (p < 0.05). Meanwhile, when the temperature ranged from 8.0 to 26.3 °C, SIB-BS exhibited a more stable and efficient denitrification ability. Mechanistic investigations revealed that coupling biochar with sponge iron promoted denitrifying microbial activity and enhanced the functional potential for nitrogen transformation (p < 0.05). Specifically, biochar provided porous attachment sites and improved mass transfer, while sponge iron supplied readily available Fe²⁺ as an electron donor; their combination buffered iron oxidation and facilitated Fe²⁺-mediated electron transfer. At low temperature, SIB-BS further stimulated extracellular polymeric substances (EPS) secretion, strengthened biofilm stability without causing blockage, and improved the protective interactions between fillers, thereby increasing metabolic efficiency and sustaining TN removal under variable loading. This study provided a technical reference for the efficient denitrification of aquaculture wastewater. Full article

(This article belongs to the Section Water, Agriculture and Aquaculture)

► Show Figures

Figure 1

15 pages, 1411 KB

Open AccessArticle

Utilizing MALDI-TOF MS for Legionella pneumophila Subspecies Typing and Classification

by Lana Madagi, Shimon Edelstein, Hila Ben-Amram and Yehonatan Sharaby

Water 2026, 18(2), 269; https://doi.org/10.3390/w18020269 - 21 Jan 2026

Viewed by 628

Abstract

Legionella pneumophila (L. pneumophila), the primary causative agent of Legionnaires’ disease, is a waterborne bacterial pathogen that poses significant public health concern. This opportunistic pathogen commonly inhabits both natural and man-made water systems, particularly drinking water distribution systems (DWDSs), where it [...] Read more.

Legionella pneumophila (L. pneumophila), the primary causative agent of Legionnaires’ disease, is a waterborne bacterial pathogen that poses significant public health concern. This opportunistic pathogen commonly inhabits both natural and man-made water systems, particularly drinking water distribution systems (DWDSs), where it can proliferate and pose a risk to human health. In this study, we evaluated the potential of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for rapid and accurate subtyping of L. pneumophila. Our analysis included 70 L. pneumophila strains collected from the Middle East, representing one of the largest and most comprehensive MALDI-TOF MS-based subtyping of strains from this geographically underrepresented region. These strains, representing three Multi-Locus Variable Number Tandem Repeat Analysis (MLVA-8) genotypic groups (GT4, GT6, and GT15), have been extensively characterized in previous studies for their virulence traits, cytotoxicity patterns, and antimicrobial susceptibility profiles. Our findings revealed distinct genotype-associated spectral signatures with 30 discriminatory m/z peaks (p ≤ 0.005). These markers enabled accurate genotype-level classification, achieving over 85% classification accuracy with a Random Forest model and over 71% accuracy using a Decision Tree algorithm. Importantly, the m/z peak at 5358 was uniquely present in the GT15 strains, whereas m/z 5353 was consistently detected in both GT4 and GT6 isolates, demonstrating the potential of specific mass peaks to serve as reliable genotype markers. Furthermore, GT15 strains consistently formed a separate cluster in both Principal Component Analysis (PCA) and hierarchical analyses, whereas GT4 and GT6 exhibited partial overlap, reflecting their exceptionally high genomic similarity. Full article

(This article belongs to the Section Water and One Health)

► Show Figures

Graphical abstract

13 pages, 59409 KB

Open AccessArticle

Water Quality and Sediment Microbial Community Differences Between Sea Urchin Monoculture and Sea Urchin–Shrimp IMTA Systems

by Cuicui Wang, Yongyao Guo, Xinli Gu, Nshimiyimana Elisee, Bingbing Jiang and Bo Zhao

Water 2026, 18(2), 268; https://doi.org/10.3390/w18020268 - 21 Jan 2026

Cited by 1 | Viewed by 798

Abstract

Integrated multi-trophic aquaculture (IMTA) has emerged as an ecological intensification strategy capable of enhancing nutrient utilization and improving environmental stability in mariculture systems, yet the microbial mechanisms driving nutrient transformations remain insufficiently understood. This study investigated how culture mode (IMTA vs. monoculture) shape [...] Read more.

Integrated multi-trophic aquaculture (IMTA) has emerged as an ecological intensification strategy capable of enhancing nutrient utilization and improving environmental stability in mariculture systems, yet the microbial mechanisms driving nutrient transformations remain insufficiently understood. This study investigated how culture mode (IMTA vs. monoculture) shape water quality, sediment microbial communities, and nutrient cycling processes in a shrimp–sea urchin system by combining water-quality monitoring, nutrient analysis, 16S rRNA high-throughput sequencing, and redundancy analysis. IMTA significantly increased turbidity, chlorophyll-a, phosphate, ammonium, and nitrite compared with monoculture, while physico-chemical parameters remained stable. Sediment microbiota in IMTA exhibited substantially higher alpha diversity and showed a clear compositional separation from monoculture communities. At the genus level, IMTA sediments were enriched in Vibrio, Motilimonas, and Ruegeria, distinguishing them from monoculture systems. At the phylum level, IMTA was characterized by increased abundances of Proteobacteria and Bacteroidota, accompanied by a marked decline in Spirochaetota. Functional predictions indicated that microbial communities were predominantly characterized by pathways related to amino acid and carbohydrate metabolism, as well as nutrient remineralization. RDA and correlation analyses further identified turbidity, chlorophyll-a, phosphate, ammonium, and nitrite as the principal drivers of microbial divergence. Overall, the findings demonstrate that IMTA reshapes sediment microbial communities toward more efficient nutrient-processing assemblages, thereby promoting active nitrogen and phosphorus transformations and improving biogeochemical functioning relative to monoculture. These results provide mechanistic insight into how IMTA supports nutrient recycling and environmental sustainability in modern mariculture systems. Full article

(This article belongs to the Section Water, Agriculture and Aquaculture)

► Show Figures

Figure 1

20 pages, 6106 KB

Open AccessArticle

Global Changes in Agricultural Water Demand Driven by Climate and Crop Area Change

by Lingli Ye, Ying Guo, Yafang Zhang, Chao Zhao, Min Liu, Jing Wang and Yanjun Shen

Water 2026, 18(2), 267; https://doi.org/10.3390/w18020267 - 20 Jan 2026

Viewed by 533

Abstract

Growing agricultural water demand, driven by climate change and land-use intensification, is accelerating global water scarcity and threatening food and environmental security. This study quantifies spatiotemporal changes in crop water requirements (CWR) and irrigation water requirement (IWR) from 1980 to 2017 for wheat, [...] Read more.

Growing agricultural water demand, driven by climate change and land-use intensification, is accelerating global water scarcity and threatening food and environmental security. This study quantifies spatiotemporal changes in crop water requirements (CWR) and irrigation water requirement (IWR) from 1980 to 2017 for wheat, maize, and soybean. A corrected FAO crop coefficient method was used to estimate global CWR, while the logarithmic mean Divisia index (LMDI) was applied to decompose its drivers into climate and crop area changes. IWR was calculated to evaluate the increasing water stress in four representative river basins: the Haihe (HRB), Yellow (YRB), Mississippi (MRB), and Ganges (GRB) river basins. Multiple linear regression models were used to identify dominant drivers of water stress. Results show that from 1980 to 2017, CWR increased significantly for maize (+210 × 10⁸ m³) and soybean (+523 × 10⁸ m³) primarily due to crop area expansion, while wheat CWR declined (−109 × 10⁸ m³). Area growth contributed over +850 × 10⁸ m³ to global CWR increases. At the basin scale, IWR rose notably in HRB, YRB, and GRB, but declined in MRB. Regression analysis confirms that crop area change was the dominant driver of variations in IWR, particularly for soybean in HRB and maize in YRB, while precipitation exerted strong negative effects in some regions. This study provides a scalable framework for diagnosing agricultural water stress and its key drivers, supporting climate adaptation and irrigation planning under global change. Full article

(This article belongs to the Section Ecohydrology)

► Show Figures

Figure 1

29 pages, 742 KB

Open AccessReview

A Review of Modeling Approaches and Key Parameters in the Simulation of Wastewater Treatment Plants

by Marija Lazarevikj, Radmila Koleva, Emil Zaev, Darko Babunski and Zoran Markov

Water 2026, 18(2), 266; https://doi.org/10.3390/w18020266 - 20 Jan 2026

Cited by 1 | Viewed by 1351

Abstract

Besides the purification process in the wastewater treatment plant that includes mechanical, biological, and chemical approaches, analysis of hydraulic behavior is also fundamental. This means developing a digital replica of the physical process by simulating the hydraulic parameters. Studying fluid behavior in the [...] Read more.

Besides the purification process in the wastewater treatment plant that includes mechanical, biological, and chemical approaches, analysis of hydraulic behavior is also fundamental. This means developing a digital replica of the physical process by simulating the hydraulic parameters. Studying fluid behavior in the plant enables process optimization, improves plant behavior, prevents equipment malfunctions, and more. This paper focuses on defining the concept of a wastewater treatment plant prototype, simulating it, and identifying the available and most suitable software that enables efficient process simulation and validation. The hydraulic parameters, as per the literature review and the proposed concept, that will be simulated are pressure, flow, pressure drop, and water level. MATLAB/Simulink and Python programming languages are considered the most suitable software/programming languages for hydraulic parameters simulation. Full article

(This article belongs to the Special Issue Water Quality, Wastewater Treatment and Water Recycling, 2nd Edition)

► Show Figures

Figure 1

14 pages, 995 KB

Open AccessArticle

Antibiotics Induce Metabolic and Physiological Responses in Daphnia magna

by Katie O’Rourke, Izabela Antepowicz, Beatrice Engelmann, Ulrike Rolle-Kampczyk, Martin von Bergen and Konstantinos Grintzalis

Water 2026, 18(2), 265; https://doi.org/10.3390/w18020265 - 20 Jan 2026

Viewed by 992

Abstract

Antibiotics represent a unique and diverse group of drugs, which are known to exert deleterious effects on non-target species and contribute to the phenomenon of antimicrobial resistance. With central inclusion on the EU Surface Water Watch List, and reported known affects in multiple [...] Read more.

Antibiotics represent a unique and diverse group of drugs, which are known to exert deleterious effects on non-target species and contribute to the phenomenon of antimicrobial resistance. With central inclusion on the EU Surface Water Watch List, and reported known affects in multiple model organisms, the importance of the sufficient monitoring of antibiotics in the aquatic environment has been highlighted. Most studies report the impact of individual antibiotics following exposure for a single generation in animals. In this study, we assessed the impact of four antibiotics with different modes of action (amoxicillin, trimethoprim, erythromycin, and sulfamethoxazole) and their mixture on the sentinel species Daphnia magna over three generations, via biochemical markers and a targeted metabolomic analysis of central metabolic pathways. No mortality was observed at 50 mg/L of each selected antibiotic and their composite mixture. Thus, a working concentration of 1 mg/L was chosen to progress this study. Results indicated that enzyme activity was particularly sensitive to exposure to amoxicillin and the mixture, whereas trimethoprim and the mixture induced the most metabolic changes in glycolysis and the TCA cycle. Additionally, the quaternary mixture had a stronger impact on the first generation of daphnids, altering the activity of β-galactosidase, glutathione S-transferase, and acid and alkaline phosphatase, suggesting that Daphnia can adapt to stress caused by antibiotics. Full article

(This article belongs to the Special Issue Emerging Contaminants in Water Environments: Occurrence, Analysis and Ecotoxicity)

► Show Figures

Figure 1

12 pages, 2684 KB

Open AccessArticle

Enhanced Water–Root Coupling in Mongolian Pine Plantations Induced by Coal Mining Subsidence: A Comparative Study of Sand-Capped Loess and Sandy Soil

by Yongjin Guo, Haoyan Wei, Jie Fang, Min Li, Zhenguo Xing and Da Lei

Water 2026, 18(2), 264; https://doi.org/10.3390/w18020264 - 19 Jan 2026

Viewed by 601

Abstract

Understanding the dynamics of soil water and root systems is essential for managing and restoring ecosystems impacted by coal mining subsidence. However, existing research treats soil and plant responses separately, also with limited comparisons across different soil types, which hampers our understanding of [...] Read more.

Understanding the dynamics of soil water and root systems is essential for managing and restoring ecosystems impacted by coal mining subsidence. However, existing research treats soil and plant responses separately, also with limited comparisons across different soil types, which hampers our understanding of their coupled effects. We examined the distribution of plant roots, soil water content and stable isotopes within the root zone in the subsidence and non-subsidence plots located in mining areas with sand-capped loess and sandy soil. Our results show that coal mining subsidence induces cracks and fissures in both sand-capped loess and sandy soil, enhancing soil infiltration and increasing deep soil water (>1 m). The increase in deep soil water was more pronounced in sand-capped loess, where subsidence exhibited near-precipitation lc-excess values (−5.9‰ to −0.2‰) and also shifted the soil water infiltration mechanism from piston flow to preferential flow. Moreover, land subsidence provides a more suitable soil physical environment that supports the growth of deeper and more extensive plant roots. The coupling degree (D) between the soil water system and root system was significantly higher in subsidence areas (D > 0.4), indicating enhanced root water absorption. These changes benefit plant physiological activities and stress response, providing an adaptive mechanism for plants in subsidence regions. This study provides new insights into the effects of coal mining subsidence on the root-soil interface in Earth’s Critical Zones and serves as a foundation for ecological restoration and management in subsidence-impacted areas. Full article

(This article belongs to the Section Ecohydrology)

► Show Figures

Figure 1

20 pages, 5587 KB

Open AccessArticle

Pollution Characteristics and Ecological Risk Assessment of Organochlorine Pesticides and Polychlorinated Biphenyls in the Maoming Coastal Zone, China

by Qiqi Chen, Xuewan Wu, Tongzhi Lu, Lifeng Xu, Yan Li and Zhifeng Wan

Water 2026, 18(2), 263; https://doi.org/10.3390/w18020263 - 19 Jan 2026

Viewed by 723

Abstract

Coastal zones, as critical ocean–land–atmosphere ecotones, face significant ecological threats from persistent organic pollutants like organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). However, there are still obvious deficiencies in the understanding of the pollution characteristics and ecological risks of OCPs and PCBs in [...] Read more.

Coastal zones, as critical ocean–land–atmosphere ecotones, face significant ecological threats from persistent organic pollutants like organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). However, there are still obvious deficiencies in the understanding of the pollution characteristics and ecological risks of OCPs and PCBs in the coastal environment of South China, especially in western Guangdong. Due to the absence of prior research on these pollutants in the Maoming area, we measured the grain sizes from 157 sediment samples and the concentrations of PCBs and OCPs from 11 key locations to assess their environmental occurrence and risks. As analyzed by the GC-MS system, OCP levels range from 0.39 to 50.20 ng/g (mean 10.25 ng/g), while PCB concentrations range from 1.6 to 92.59 ng/g. Through the analysis of pollutant data and analysis of similar areas, we found that OCPs and PCBs in the Maoming coastal zone primarily originate from fishing port operations, ship antifouling paints, and historical legacy pollutants. In addition, the distribution of pollution is significantly controlled by hydrodynamic conditions and the semi-enclosed geomorphological characteristics of the bay. As grain size increases, the correlation with pollutant concentrations shifts from positive to negative. This trend reveals that finer-grained sediments in low-energy environments accumulate significantly higher levels of pollution compared to their coarser counterparts in more dynamic settings. Compared to other coastal regions globally, the study area demonstrates relatively lower pollution intensity. Dual assessments using Sediment Quality Guidelines (SQGs) and Sediment Quality Standards (SQSs) indicate a generally low probability of adverse biological effects, with elevated risk localized to sites near port activities. This study provides a scientific basis for the prevention and control of OCP and PCB pollution in the Maoming coastal zone and also provides a reference for pollution assessment in similar areas. Full article

(This article belongs to the Special Issue Sediment Pollution: Methods, Processes and Remediation Technologies)

► Show Figures

Figure 1

21 pages, 10379 KB

Open AccessArticle

Spatial Optimization of Urban-Scale Sponge Structures and Functional Areas Using an Integrated Framework Based on a Hydrodynamic Model and GIS Technique

by Mengxiao Jin, Quanyi Zheng, Yu Shao, Yong Tian, Jiang Yu and Ying Zhang

Water 2026, 18(2), 262; https://doi.org/10.3390/w18020262 - 19 Jan 2026

Cited by 2 | Viewed by 652

Abstract

Rapid urbanization has exacerbated urban-stormwater challenges, highlighting the critical need for coordinated surface-water and groundwater management through rainfall recharge. However, current sponge city construction methods often overlook the crucial role of underground aquifers in regulating the water cycle and mostly rely on simplified [...] Read more.

Rapid urbanization has exacerbated urban-stormwater challenges, highlighting the critical need for coordinated surface-water and groundwater management through rainfall recharge. However, current sponge city construction methods often overlook the crucial role of underground aquifers in regulating the water cycle and mostly rely on simplified engineering approaches. To address these limitations, this study proposes a spatial optimization framework for urban-scale sponge systems that integrates a hydrodynamic model (FVCOM), geographic information systems (GIS), and Monte Carlo simulations. This framework establishes a comprehensive evaluation system that synergistically integrates surface water inundation depth, geological lithology, and groundwater depth to quantitatively assess sponge city suitability. The FVCOM was employed to simulate surface water inundation processes under extreme rainfall scenarios, while GIS facilitated spatial analysis and data integration. The Monte Carlo simulation was utilized to optimize the spatial layout by objectively determining factor weights and evaluate result uncertainty. Using Shenzhen City in China as a case study, this research combined the “matrix-corridor-patch” theory from landscape ecology to optimize the spatial structure of the sponge system. Furthermore, differentiated planning and management strategies were proposed based on regional characteristics and uncertainty analysis. The research findings provide a replicable and verifiable methodology for developing sponge city systems in high-density urban areas. The core value of this methodology lies in its creation of a scientific decision-making tool for direct application in urban planning. This tool can significantly enhance a city’s climate resilience and facilitate the coordinated, optimal management of water resources amid environmental changes. Full article

(This article belongs to the Special Issue "Watershed–Urban" Flooding and Waterlogging Disasters)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Water, Volume 18, Issue 2 (January-2 2026) – 157 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI