Water

19 pages, 3333 KB

Open AccessArticle

Spatial Distribution and Environmental Impacts of Soil Nitrogen and Phosphorus in the Downstream Daliao River Basin

by Tianxiang Wang, Yexin Liu, Zixiong Wang, Tianzi Wang, Zipeng Zhang, Runfa Cui, Rongyue Ma and Guangyu Su

Water 2025, 17(22), 3267; https://doi.org/10.3390/w17223267 (registering DOI) - 15 Nov 2025

Abstract

Soil nitrogen (N) and phosphorus (P) loss in watersheds is a critical source of water pollution. This study explores the spatial distribution, release potential, and environmental impacts of soil N and P in the downstream Daliao River basin by integrating field investigations and [...] Read more.

Soil nitrogen (N) and phosphorus (P) loss in watersheds is a critical source of water pollution. This study explores the spatial distribution, release potential, and environmental impacts of soil N and P in the downstream Daliao River basin by integrating field investigations and simulation experiments. Results showed that total nitrogen content in soils ranged from 256.09 to 3362.75 mg/kg, while that in sediments ranged from 114.85 to 1640.54 mg/kg. Total phosphorus content in soils varied from 250.18 to 1142.69 mg/kg, whereas in sediments it ranged from 327.23 to 586.24 mg/kg. The ammonia nitrogen release potentials of soils collected from rice paddies, corn farmlands, roadsides, and reed wetlands were 0.75, 0.86, 0.70, and 8.65 mg/L, respectively, with corresponding total phosphorus release potentials of 0.61, 1.01, 0.31, and 1.52 mg/L. For sediments, ammonia nitrogen and total phosphorus release potentials ranged from 0.96 to 1.21 mg/L and 0.44 to 0.52 mg/L, respectively. Temperature, pH, and dissolved oxygen were important factors influencing nitrogen and phosphorus release from soils and sediments. The export of nitrogen and phosphorus from soil reached 50.50 t/a and 21.63 t/a, respectively. During the soil erosion process in the Daliao River Basin, phosphorus exhibited a high release potential and served as the primary pollutant, whereas the release mechanism of ammonia nitrogen was more complex, showing seasonal variability. Soils in the downstream Daliao River basin have large specific surface areas and may pose a high pollution risk after discharge into water bodies due to prolonged adsorption of pollutants. It is recommended to propose promoting soil testing-based fertilization, constructing ecological engineering projects, developing sponge cities, and conducting environmental dredging to reduce N and P release from agricultural lands, construction areas, natural wastelands, and sediments. Full article

(This article belongs to the Special Issue Application of Smart Technologies in Integrated Water Quality Modeling, 2nd Edition)

30 pages, 11720 KB

Open AccessArticle

Assessment of Groundwater Quality for Irrigation in the Semi-Arid Region of Oum El Bouaghi (Northeastern Algeria) Using Groundwater Quality and Pollution Indices and GIS Techniques

by Norelhouda Messaid, Ramzi Hadjab, Hichem Khammar, Aymen Hadjab, Nadhir Bouchema, Abderrezzeq Chebout, Mourad Aqnouy, Ourania Tzoraki and Lahcen Benaabidate

Water 2025, 17(22), 3266; https://doi.org/10.3390/w17223266 (registering DOI) - 15 Nov 2025

Abstract

Groundwater quality in the semi-arid region of Oum El Bouaghi, Northeastern Algeria, was assessed for irrigation suitability using hydrogeochemical analyses, water quality indices, and GIS techniques. The study analyzed 23 groundwater samples during dry and wet seasons in 2022–2023, several physicochemical parameters were [...] Read more.

Groundwater quality in the semi-arid region of Oum El Bouaghi, Northeastern Algeria, was assessed for irrigation suitability using hydrogeochemical analyses, water quality indices, and GIS techniques. The study analyzed 23 groundwater samples during dry and wet seasons in 2022–2023, several physicochemical parameters were measured. Results revealed neutral to slightly alkaline pH levels, except for one acidic sample, with salinity (EC: 527–5001 µS·cm⁻¹) exceeding WHO guidelines, particularly during the dry season due to evaporation and anthropogenic activities. Hydrogeochemical facies showed dominance of Na⁺-HCO₃⁻ and Ca²⁺-Cl⁻/SO₄²⁻ water types, indicating rock–water interactions and evaporation control, as confirmed by Gibbs plots. The IWQI classified water into five categories, with severe restrictions (IWQI < 40) in 13% of samples during the dry season, improving slightly in the wet season. Indices such as SAR, Na%, and RSC indicated low to moderate sodium hazard, while KR and PS highlighted salinity risks in specific areas. Spatial analysis revealed localized pollution hotspots, with the (GPI) identifying minimal to high contamination levels, linked to agricultural and geogenic sources. These findings underscore needs for sustainable groundwater management, including monitoring, optimized irrigation practices, and mitigation of anthropogenic impacts, to ensure long-term agricultural viability in this water-scarce region. Full article

(This article belongs to the Special Issue Research on Hydrogeology and Hydrochemistry: Challenges and Prospects)

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25 pages, 3960 KB

Open AccessArticle

Spatial Structure and Temporal Dynamics in Clear Lake, CA: The Role of Wind in Promoting and Sustaining Harmful Cyanobacterial Blooms

by David A. Caron, Alle A. Y. Lie, Brittany Stewart, Amanda Tinoco, Isha Kalra, Stephanie A. Smith, Adam L. Willingham, Shawn Sneddon, Jayme Smith, Eric Webb, Kyra Florea and Meredith D. A. Howard

Water 2025, 17(22), 3265; https://doi.org/10.3390/w17223265 (registering DOI) - 15 Nov 2025

Abstract

Clear Lake in Lake County, CA, USA has experienced highly toxic cyanobacterial blooms for more than a decade, with multiple cyanobacterial taxa and cyanotoxins appearing sporadically, typically throughout much of the early-spring to late-fall seasons. Recurring blooms have been attributed to high internal [...] Read more.

Clear Lake in Lake County, CA, USA has experienced highly toxic cyanobacterial blooms for more than a decade, with multiple cyanobacterial taxa and cyanotoxins appearing sporadically, typically throughout much of the early-spring to late-fall seasons. Recurring blooms have been attributed to high internal nutrient loads within the lake, with hydrography and hydrology playing important but still poorly documented roles in controlling the availability of growth-limiting elements to the phytoplankton community. The lake is approximately 180 km² in areal extent and composed of three somewhat disjointed lobes, or ‘Arms’. The large size of the lake presents a formidable task for synoptic lakewide surveys and for understanding the specific features that stimulate the development and magnitude of harmful blooms. We conducted a study in August of 2020 that involved the use of an autonomous underwater vehicle and deployment of a hand-held water column profiler to describe the lakewide status of various biological, chemical, and physical features. Discrete water samples were also collected from ten stations located throughout the lake to produce a near-synoptic depiction of lake status. Additionally, a mechanically driven, continuously monitoring water-column profiler was deployed at a central lake location to document short-term temporal (minutes to months) changes in water-column structure and chemistry. Wind was a dominant feature affecting the lake’s chemistry and biology during the study, resulting in massive concentrations and dramatic spatial heterogeneity of phytoplankton biomass and cyanotoxins in the eastern and southeastern Arms of the lake, and confirmed by the analysis of discrete water samples. Unique insight into the processes leading to or prolonging blooms was revealed by the water column profiler, which demonstrated rapid development (within a few hours) of suboxic conditions during periods of calm winds. We speculate that these quiescent periods are fundamental events in the lake’s ecology, resulting in episodic ‘pulses’ of nutrient release from the sediments, which can stimulate or refuel blooms of cyanobacteria in the water column. Full article

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

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16 pages, 2103 KB

Open AccessArticle

Hydrological and Geochemical Responses to Agricultural Activities in a Karst Catchment: Insights from Spatiotemporal Dynamics and Source Apportionment

by Le Cao, Qianyun Cheng, Shangqing Wang, Shaoqiang Xu, Qirui He, Yanqiu Li, Tao Peng and Shijie Wang

Water 2025, 17(22), 3264; https://doi.org/10.3390/w17223264 (registering DOI) - 15 Nov 2025

Abstract

Karst aquifers, vital freshwater resources, are highly vulnerable to agricultural pollution, yet their hydro-geochemical responses remain poorly understood due to high spatial heterogeneity. This study aimed to unravel these complex responses in a subtropical karst agricultural catchment to provide a basis for its [...] Read more.

Karst aquifers, vital freshwater resources, are highly vulnerable to agricultural pollution, yet their hydro-geochemical responses remain poorly understood due to high spatial heterogeneity. This study aimed to unravel these complex responses in a subtropical karst agricultural catchment to provide a basis for its sustainable management. We employed high-frequency monitoring at a headwater spring (background), a depression well (hotspot), and the catchment outlet (integrated) in Southwest China. Using hydrological and geochemical data from 2017, we applied Principal Component Analysis (PCA) to apportion natural and anthropogenic sources. The main findings revealed significant spatial heterogeneity, with the depression well acting as a contamination hotspot characterized by rapid hydrological responses and elevated SO₄²⁻ and Cl⁻ concentrations. PCA successfully decoupled an “anthropogenic factor” (PC1, 40.5%) from a “natural weathering factor” (PC2, 25.2%). Critically, agricultural SO₄²⁻ at the hotspot was counter-intuitively higher during the wet season than the dry season, opposing the typical dilution pattern of background ions and revealing that depressions act as contaminant-concentrating pathways, whose risks are severely underestimated by traditional outlet monitoring. The anomalous sulfate dynamics reveal a cross-seasonal “storage-and-release” mechanism (legacy effect) within the karst Critical Zone, demonstrating that these systems can buffer and “remember” contaminants. Full article

(This article belongs to the Section Hydrogeology)

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16 pages, 1602 KB

Open AccessArticle

Boosting Denitrification in Pyrite Bioretention Through Biochar-Mediated Electron Transfer

by Ying Xu, Xiaoqin Yang, Fanxiao Luo, Haiyuan Ma, Cong Huang, Zheng Xu, Rui Liu, Lu Qiu and Haifa Zu

Water 2025, 17(22), 3263; https://doi.org/10.3390/w17223263 - 14 Nov 2025

Abstract

The pyrite bioretention system has been increasingly used to control dissolved nutrients in stormwater runoff. However, its low electron supply rate cannot adapt to the demand for denitrification under high nitrogen-loading conditions. To address this limitation, we constructed a mixed biochar–pyrite bioretention system [...] Read more.

The pyrite bioretention system has been increasingly used to control dissolved nutrients in stormwater runoff. However, its low electron supply rate cannot adapt to the demand for denitrification under high nitrogen-loading conditions. To address this limitation, we constructed a mixed biochar–pyrite bioretention system (BP) by optimizing the structural composition of the fill media. Under simulated complex rainfall conditions, the nitrogen removal efficiency, by-product generation, and filler physicochemical properties of system were evaluated. Results demonstrated that the BP system significantly enhanced denitrification performance, achieving average NO_x⁻-N and TN removal rates of 63.3% and 67.8%, respectively. This represented improvements of 79.1% and 45.9% over the conventional pyrite bioretention system. Moreover, the composite system exhibited a sustained and effective denitrification even under low C/N ratio conditions. This enhancement is attributed to biochar’s dual role as an electron shuttle and an electron reservoir, which facilitated microbial nitrate reduction. XPS analysis further confirmed that biochar addition effectively reduced the oxidation degree of pyrite, thereby protecting it from rapid oxidative degradation. Microbial analysis revealed that biochar supplementation in the BP system increased microbial diversity in the saturated zone, which contributed to improved ecosystem function and stability, including the promotion for key denitrification processes. Full article

(This article belongs to the Special Issue Urban Drainage Systems and Stormwater Management)

16 pages, 2704 KB

Open AccessArticle

Study on Operational Stability of the Hydro-Turbine Governing System for Three-Turbine Shared Tailwater Tunnel

by Dong Liu, Yanbo Xue, Jiejie Lv and Xiaoqiang Tan

Water 2025, 17(22), 3262; https://doi.org/10.3390/w17223262 - 14 Nov 2025

Abstract

As a key power source for peak regulation and frequency control, hydropower units frequently adjust their output to maintain grid stability. In shared tailrace tunnel systems, hydraulic coupling between units significantly influences system stability. This study investigates a three-unit system with a common [...] Read more.

As a key power source for peak regulation and frequency control, hydropower units frequently adjust their output to maintain grid stability. In shared tailrace tunnel systems, hydraulic coupling between units significantly influences system stability. This study investigates a three-unit system with a common tailrace tunnel, establishes its mathematical model, and employs linear stability analysis to examine its stability characteristics under small disturbances. The research focuses on the impacts of total power output and power allocation strategies on system stability. Key findings reveal that (1) the stable domain of each unit decreases with greater penstock water inertia, and the instability of any single unit propagates through hydraulic coupling, causing system-wide instability; (2) the control parameters of individual units primarily affect their own stability, with negligible cross-unit impact, and the system’s overall stable domain is determined by the unit with the smallest stability region when uniform parameters are adopted; (3) increasing the total power output reduces system stability, and equally distributing power among units is more conducive to stable operation than concentrating it on a single unit. These results provide a theoretical basis for the optimized dispatch and stability control of multi-unit hydropower systems with shared hydraulic structures. Full article

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

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21 pages, 1858 KB

Open AccessArticle

Delineation Using Multi-Tracer Tests and Hydrochemical Investigation of the Matica River Catchment at Plitvice Lakes, Croatia

by Tihomir Frangen, Ivana Boljat, Hrvoje Meaški and Josip Terzić

Water 2025, 17(22), 3261; https://doi.org/10.3390/w17223261 - 14 Nov 2025

Abstract

In the Plitvice Lakes National Park, several hydrogeological catchments can be distinguished, but their boundaries are not clearly defined. This study focused on the Matica River catchment area, which covers the main contributors to the lake system and its overall water balance. An [...] Read more.

In the Plitvice Lakes National Park, several hydrogeological catchments can be distinguished, but their boundaries are not clearly defined. This study focused on the Matica River catchment area, which covers the main contributors to the lake system and its overall water balance. An initial assessment indicated that the Matica River catchment is among the most vulnerable areas due to the anticipated land-use expansion related to agriculture and tourism. This research provides critical hydrogeological data supporting sustainable management in response to the increasing extremes of floods and droughts induced by climate change. Two separate campaigns (March 2023 and April 2025) were carried out, each involving three simultaneous tracer injections using different fluorescent dyes. The results of earlier tracer tests were evaluated; furthermore, a hydrochemical analysis of the spring water offered valuable insights into subsurface processes and anthropogenic impacts. Tracing in the southwest clarified the boundary between the Plitvice Lakes and Una River catchments. In the Homoljac polje, the tracer responses highlighted a triple junction between the Plitvice Lakes, Gacka, and Una River catchments. In the southeastern Brezovac polje, the boundary between the Crna Rijeka and Bijela Rijeka catchments was delineated in detail. Full article

(This article belongs to the Special Issue Water Management and Geohazard Mitigation in a Changing Climate)

25 pages, 1563 KB

Open AccessArticle

AI-Augmented Water Quality Event Response: The Role of Generative Models for Decision Support

by Stephen Mounce, Richard Mounce and Joby Boxall

Water 2025, 17(22), 3260; https://doi.org/10.3390/w17223260 - 14 Nov 2025

Abstract

The global water sector faces unprecedented challenges from climate change, rapid urbanisation, and ageing infrastructure, necessitating a shift towards proactive, digital strategies. Historically characterised as “data rich but information poor,” the sector struggles with underutilised and siloed operational data. Traditional machine learning (ML) [...] Read more.

The global water sector faces unprecedented challenges from climate change, rapid urbanisation, and ageing infrastructure, necessitating a shift towards proactive, digital strategies. Historically characterised as “data rich but information poor,” the sector struggles with underutilised and siloed operational data. Traditional machine learning (ML) models have provided a foundation for smart water management, and subsequently deep learning (DL) approaches utilising algorithmic breakthroughs and big data have proved to be even more powerful under the right conditions. This paper explores and reviews the transformative potential of Generative Artificial Intelligence (GenAI) and Large Language Models (LLMs), enabling a paradigm shift towards data-centric thinking. GenAI, particularly when augmented with Retrieval-Augmented Generation (RAG) and agentic AI, can create new content, facilitate natural language interaction, synthesise insights from vast unstructured data (of all types including text, images and video) and automate complex, multi-step workflows. Focusing on the critical area of drinking water quality, we demonstrate how these intelligent tools can move beyond reactive systems. A case study is presented which utilises regulatory reports to mine knowledge, providing GenAI-powered chatbots for accessible insights and improved water quality event management. This approach empowers water professionals with dynamic, trustworthy decision support, enhancing the safety and resilience of drinking water supplies by recalling past actions, generating novel insights and simulating response scenarios. Full article

(This article belongs to the Special Issue Application of Artificial Intelligence (AI) in Water Quality Monitoring)

27 pages, 15079 KB

Open AccessArticle

Elucidating the Spatial Patterns and Influencing Mechanisms of Traditional Villages in Shanxi Province, China: Insights from a River Basin Perspective

by Shiyan Huo, Jinping Wang, Jinxi Hua, Benjamin de Foy and Ishaq Dimeji Sulaymon

Water 2025, 17(22), 3259; https://doi.org/10.3390/w17223259 - 14 Nov 2025

Abstract

Shanxi Province hosts a rich diversity of traditional villages. From a river basin perspective, adherence to natural laws and the removal of administrative barriers are essential for reshaping the conservation paradigm. Using spatial analysis and multiscale geographically weighted regression, this study revealed the [...] Read more.

Shanxi Province hosts a rich diversity of traditional villages. From a river basin perspective, adherence to natural laws and the removal of administrative barriers are essential for reshaping the conservation paradigm. Using spatial analysis and multiscale geographically weighted regression, this study revealed the spatial patterns of 619 traditional villages and how environmental, socioeconomic, and historical–cultural factors shape the spatial heterogeneity. Villages clustered within the Yellow River Basin and the Haihe River Basin, forming an agglomeration belt and three high-density cores. Distance to rivers was a key factor in village siting, with 70.8% located within 3 km of the nearest river. Village density exhibited a U-shaped relationship with distance to roads, and an inverted U-shaped relationship with distance to county-level administrative centers. The interaction between intangible cultural heritage density and average annual precipitation showed the strongest explanatory power, with positive local regression coefficients exceeding 95% and 72%, respectively. Traditional villages constitute an evolving human–environment system in which water resources underpin spatial patterns and intangible cultural heritage sustains endogenous cultural vitality. These findings provide a theoretical framework for graded conservation and resource coordination at the river basin scale. Full article

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

22 pages, 3358 KB

Open AccessArticle

First Evidence of Mesoplastic Pollution in Beach Sediments of the Moroccan Mediterranean Coast

by Soria Azaaouaj, Noureddine Er-Ramy, Driss Nachite and Giorgio Anfuso

Water 2025, 17(22), 3258; https://doi.org/10.3390/w17223258 - 14 Nov 2025

Abstract

The problem of marine plastic pollution is multifaceted and poses a serious threat to the ecosystem and human health. This work is the first investigation of mesoplastics (MEPs, 5 mm–2.5 cm) along the most representative beaches of the whole Mediterranean coast of Morocco. [...] Read more.

The problem of marine plastic pollution is multifaceted and poses a serious threat to the ecosystem and human health. This work is the first investigation of mesoplastics (MEPs, 5 mm–2.5 cm) along the most representative beaches of the whole Mediterranean coast of Morocco. Surface sediment samples (0–5 cm), with 3 replicates each, were collected from thirty-three beaches to identify mesoplastic item characteristics (concentration, weight, type, size, color, and nature). The samples were collected between October and November 2021 and a total of 1998 mesoplastics (59.99 g kg⁻¹) were collected from the thirty-three beaches studied. The average concentrations ranged from 20.18 ± 13.93 MEP kg⁻¹ to 0.61 ± 0.61 g kg⁻¹, showing a great variability within each beach and between the beaches investigated. Mesoplastic fragments accounted for 43.92% of the total mesoplastic items, showed sizes from 5 to 10 mm (56.64%) and were predominantly white/transparent (43.36%). Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that Polyethylene (PE), Polypropylene (PP), Polystyrene (PS), and Polyvinyl chloride (PVC) were the most common polymers. The present results revealed a moderate level of mesoplastics pollution along the beaches investigated. Fishing, coastal activities, and wastewater discharges were probably the main sources. Furthermore, this study is likely to serve as a scientific baseline for monitoring and tracking mesoplastic pollution on Moroccan beaches. Full article

(This article belongs to the Special Issue Aquatic Microplastic Pollution: Occurrence and Removal)

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17 pages, 3997 KB

Open AccessArticle

Hydrogeochemical Characterization, Processes, and Water Quality Assessment of Groundwater in an Agricultural Reclamation Area of the Sanjiang Plain, China

by Min Wang and Mingguo Wang

Water 2025, 17(22), 3257; https://doi.org/10.3390/w17223257 - 14 Nov 2025

Abstract

Understanding groundwater quality and its controlling mechanisms is vital for the sustainable use of water resources in agriculturally intensive regions. This study evaluates the hydrochemical characteristics, controlling geochemical processes, and overall water quality of 226 groundwater samples collected from a typical agricultural reclamation [...] Read more.

Understanding groundwater quality and its controlling mechanisms is vital for the sustainable use of water resources in agriculturally intensive regions. This study evaluates the hydrochemical characteristics, controlling geochemical processes, and overall water quality of 226 groundwater samples collected from a typical agricultural reclamation area in the Sanjiang Plain, northeastern China. Major ion compositions indicate that groundwater is predominantly of the Ca–HCO₃ type, with bicarbonate, calcium, and magnesium as the dominant constituents. Spatial and statistical analyses reveal that rock weathering—particularly the dissolution of carbonates and silicates—is the primary natural process influencing groundwater chemistry, while cation exchange contributes moderately. Anthropogenic inputs, especially from fertilizers, livestock waste, and wastewater discharge, were found to elevate concentrations of NO₃⁻, Cl⁻, and SO₄²⁻ in localized zones. The entropy-weighted water quality index (EWQI) was applied to assess overall groundwater suitability. Results show that 89.8% of samples fall into “excellent” or “good” categories, though 6.6% of samples indicate poor to very poor water quality. This study identified the hydrochemical characteristics, sources of substances, and water quality of groundwater in the reclamation area, providing a basis for scientific prevention and control, rational utilization, and protection of groundwater resources. Full article

(This article belongs to the Special Issue Contaminants in Aquatic Systems: Biogeochemical Processes, Ecological Impacts)

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20 pages, 4976 KB

Open AccessArticle

Influence of Step Height on Turbulence Statistics in the Non-Aerated Skimming Flow in Steep-Stepped Spillways

by Juan Pablo Toro, Sebastián Sepúlveda, Fabián A. Bombardelli, Patricio A. Moreno-Casas, Inês Meireles, Jorge Matos and Alex Blanc

Water 2025, 17(22), 3256; https://doi.org/10.3390/w17223256 - 14 Nov 2025

Abstract

The classical assumption of self-similarity in flow velocities and turbulence statistics has been successfully validated for fully developed flows in open channels, pipes, and boundary layers. However, its application in developing boundary-layer flows in channels with steep slopes and large roughness elements has [...] Read more.

The classical assumption of self-similarity in flow velocities and turbulence statistics has been successfully validated for fully developed flows in open channels, pipes, and boundary layers. However, its application in developing boundary-layer flows in channels with steep slopes and large roughness elements has not yet been thoroughly scrutinized. This study investigates whether turbulence statistics exhibit self-similar behavior when properly scaled in steep-stepped spillways. Specifically, it explores the influence of roughness height (

k_{s}

)—representing the cavity size of a steep-stepped spillway—on turbulence statistics in the non-aerated skimming flow region. Numerical simulations, extensively validated against experimental data, were conducted for a stepped spillway with a fixed slope angle of 51.34°, using five roughness heights (

k_{s}

= 6.25, 3.12, 1.56, 0.78 and 0.39 cm), corresponding to step height-to-length ratios of 10:8, 5:4, 2.5:2, 1.25:1 and 0.625:0.5, respectively. The results show that the dimensionless profiles of turbulent kinetic energy (TKE) at the step edges collapse onto a single curve when rescaled by a factor of

{(δ / k_{s})}^{n}

with

n ~ 0.4

. Likewise, the dissipation rate of TKE follows a similar collapse with

n ~ 0.3

. For the turbulent eddy viscosity, an exponent of

n ~ 0.5

was adopted based on dimensional analysis, although the values for the smoothest configuration deviate from the curve. Full article

(This article belongs to the Special Issue Computer Modelling Techniques in Environmental Hydraulics and Water Resource Engineering)

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25 pages, 3531 KB

Open AccessArticle

A Physics-Guided Optimization Framework Using Deep Learning Surrogates for Multi-Objective Control of Combined Sewer Overflows

by Tianyu Li, Jiabin Gao, Mengge Wang and Yongwei Gong

Water 2025, 17(22), 3255; https://doi.org/10.3390/w17223255 - 14 Nov 2025

Abstract

Combined sewer overflow (CSO) pollution threatens urban water environments, yet optimizing integrated green–grey infrastructure solutions remains computationally intensive, often making robust, large-scale multi-algorithm comparisons impractical. This study’s primary contribution is the development of an innovative physics-guided optimization framework that overcomes this computational barrier. [...] Read more.

Combined sewer overflow (CSO) pollution threatens urban water environments, yet optimizing integrated green–grey infrastructure solutions remains computationally intensive, often making robust, large-scale multi-algorithm comparisons impractical. This study’s primary contribution is the development of an innovative physics-guided optimization framework that overcomes this computational barrier. By coupling a deep learning surrogate (trained on 60,000 scenarios generated in 7.7 h) with evolutionary algorithms, this framework provides a 6.2- to 7.7-fold acceleration in total project time (approximately 13 h vs. 80–100 h) compared to direct SWMM optimization. This significant speedup enabled a comprehensive comparative analysis of four multi-objective evolutionary algorithms (MOEAs), which established NSGA-II’s superiority in discovering a larger and more diverse set of optimal trade-off solutions. The physics-guided surrogate achieved an R² of 0.9965 and a Mean Absolute Error (MAE) corresponding to 0.5% of the baseline overflow volume. The validated framework successfully identified Permeable Pavement as the dominant control variable and a critical knee-point scenario. This solution, requiring a 426 million CNY investment, achieved a 67.0% overflow volume reduction and a 74.4% COD load reduction under the 5-year design storm. Furthermore, the optimized system demonstrated high resilience to extreme events, contrasting sharply with the failure of a cost-minimized approach, which underscores the importance of designing for resilience. This framework provides urban planners with a validated, efficient, and reliable methodology for designing resilient, cost-effective CSO control systems. Full article

(This article belongs to the Special Issue Urban Drainage Systems and Stormwater Management)

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23 pages, 6839 KB

Open AccessArticle

Source Apportionment and Potential Health Risks of Trace Metals in a Contaminated Urban River in New York/New Jersey Harbor System

by Md Shahnul Islam, Sana Mirza, Huan Feng, Tapos Kumar Chakraborty, Yu Qian and Shinjae Yoo

Water 2025, 17(22), 3254; https://doi.org/10.3390/w17223254 - 14 Nov 2025

Abstract

The Lower Passaic River (LPR), located within the New York/New Jersey Harbor Estuarine System, has experienced long-term industrial activities, resulting in elevated concentrations of trace metals in sediment and water. This study aims to assess the bioaccumulation behavior, potential human health risks, and [...] Read more.

The Lower Passaic River (LPR), located within the New York/New Jersey Harbor Estuarine System, has experienced long-term industrial activities, resulting in elevated concentrations of trace metals in sediment and water. This study aims to assess the bioaccumulation behavior, potential human health risks, and sources of copper (Cu), lead (Pb), and mercury (Hg) in the LPR. Trace metal concentrations were measured in water, sediment, and seven edible aquatic species. Data were analyzed using statistical approaches, and evaluated by bioaccumulation factors (BAFs) and human health risk assessments based on U.S. Environmental Protection Agency (USEPA) guidelines. Results showed that Hg exhibited the highest bioaccumulation potential among the studied metals, except for Cu in Callinectes sapidus. Non-carcinogenic risks from the consumption of aquatic species followed the order Cu > Hg > Pb, with total target hazard quotient (TTHQ) values below 1, suggesting the non-carcinogenic health risk is negligible for adults and for most species in children, except C. sapidus and Morone americana. Carcinogenic risks for all species were within the acceptable threshold (Target Risk < 1 × 10⁻⁴). Sensitivity analysis indicated that body weight and exposure duration primarily influenced children’s carcinogenic risk, whereas trace metal concentrations were more significant for adults. Overall, this study provides insight into contaminant dynamics and health implications in a legacy-contaminated urban river system. Full article

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

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21 pages, 1485 KB

Open AccessArticle

Potential of Single-Cell Protein as Novel Biosorbents for the Removal of Heavy Metals from Seawater

by Chiara Maraviglia, Silvio Matassa, Alessandra Cesaro and Francesco Pirozzi

Water 2025, 17(22), 3253; https://doi.org/10.3390/w17223253 - 14 Nov 2025

Abstract

This study aimed to explore innovative sorbent materials for the remediation of contaminated marine environments, with a focus on metal removal from seawater. Adsorption tests were carried out to evaluate the performance of single-cell proteins (SCPs), a protein-rich biomass derived from industrial by-products, [...] Read more.

This study aimed to explore innovative sorbent materials for the remediation of contaminated marine environments, with a focus on metal removal from seawater. Adsorption tests were carried out to evaluate the performance of single-cell proteins (SCPs), a protein-rich biomass derived from industrial by-products, in comparison with commercial activated carbon (AC). Given the increasing need for sustainable and effective approaches in sediment remediation and water treatment, identifying alternatives to conventional sorbents is of particular relevance. Results showed that SCPs exhibited higher affinity for Cr than for Zn, while multi-metal solutions improved adsorption, suggesting synergistic interactions possibly linked to surface charge effects and ternary complex formation. Importantly, SCPs demonstrated competitive and, in some cases, superior performance compared to AC, highlighting their potential as an innovative and sustainable material. Moreover, when the absorbent materials were combined, SCP and AC mixes outperformed both the individual adsorbents and the expected additive efficiencies, achieving significantly higher removal yields for both metals, particularly at low concentrations. Overall, these findings suggest that SCPs, alone or in combination with AC, represent a promising strategy for the removal of heavy metals from marine systems, offering new opportunities for the treatment of contaminated sediments and seawater. Full article

(This article belongs to the Topic Soil/Sediment Remediation and Wastewater Treatment)

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18 pages, 9958 KB

Open AccessArticle

An Enhanced Machine Learning Approach for Regional Total Suspended Matter Concentration Retrieval Using Multispectral Imagery

by Xiuxiu Chen, Ge Lou, Hongbo Li, Xiaoyi Zhang, Shixuan Liu, Qingshan Gao, Conghui Tao and Qiuxiao Chen

Water 2025, 17(22), 3252; https://doi.org/10.3390/w17223252 - 14 Nov 2025

Abstract

Accurate monitoring of total suspended matter (TSM) concentration is essential for aquatic ecosystem protection and water quality assessment. Multispectral remote sensing provides an effective approach for large-scale TSM monitoring. However, robust retrieval models are difficult to develop due to limited in situ data. [...] Read more.

Accurate monitoring of total suspended matter (TSM) concentration is essential for aquatic ecosystem protection and water quality assessment. Multispectral remote sensing provides an effective approach for large-scale TSM monitoring. However, robust retrieval models are difficult to develop due to limited in situ data. This study presents a Deep Feature Extraction–Machine Learning fusion framework that integrates a pre-trained back-propagation neural network (BPNN) with support vector regression (SVR) to enhance TSM retrieval. High-level spectral features extracted by BPNN are used as inputs to SVR (termed DFE-SVR) for regional TSM retrieval, using in situ measurements from five inland lakes in Jiangsu and Anhui Provinces, China. The generated TSM maps showed spatial patterns consistent with TSM concentration distributions visually observed in true-color imagery. Validation results demonstrated that DFE-SVR outperformed BPNN and SVR models, achieving R² of 0.85 and 0.90 and RMSE of 7.95 and 4.76 mg/L for GF-1 and Sentinel-2 imagery, respectively. Compared with SVR models using principal component analysis or band combinations, DFE-SVR reduced RMSE by over 20%. Under reduced training samples, the DFE-SVR model also maintained higher stability and accuracy. These findings showed its potential for multispectral water quality monitoring with limited in situ data. Full article

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

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11 pages, 7898 KB

Open AccessArticle

Identification of a PCE Contamination Source in an Intergranular Aquifer Using a Simulation–Optimisation Framework: A Case Study of Ljubljana Polje, Slovenia

by Mitja Janža

Water 2025, 17(22), 3251; https://doi.org/10.3390/w17223251 - 14 Nov 2025

Abstract

Identification of contamination sources is critical for effective remediation planning in contaminated aquifers. This study presents a simulation–optimisation framework that was developed to reconstruct the release history and identify the potential source location after tetrachloroethene (PCE) concentrations that exceeded regulatory limits were detected [...] Read more.

Identification of contamination sources is critical for effective remediation planning in contaminated aquifers. This study presents a simulation–optimisation framework that was developed to reconstruct the release history and identify the potential source location after tetrachloroethene (PCE) concentrations that exceeded regulatory limits were detected in production and monitoring wells at the Hrastje well field. The approach integrates a physically based groundwater flow and solute transport model with an evolutionary algorithm to estimate unknown source parameters. The method was tested under realistic field conditions, accounting for the complexity and uncertainty of the subsurface environment. In the optimisation procedure, parameter values converged towards optimal estimates, and the simulated PCE concentrations in monitored wells showed good agreement with the observed values. The delineated source location and the reconstructed temporal and spatial dynamics of PCE contamination in the aquifer provide essential guidance for decision makers in designing and prioritising remediation strategies. By narrowing the potential source area, more targeted and cost-effective field investigations can be planned. The developed model offers a practical tool for evaluating alternative remediation scenarios, supporting adaptive water resource management and safeguarding the drinking water supply. Full article

(This article belongs to the Special Issue Water Management and Geohazard Mitigation in a Changing Climate)

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21 pages, 3524 KB

Open AccessReview

Italy’s Contribution to Artificial Reef Research: A Comprehensive Review (1970–2025)

by Alessandra Spagnolo and Carmen Ferrà

Water 2025, 17(22), 3250; https://doi.org/10.3390/w17223250 - 14 Nov 2025

Abstract

Italy represents one of the most prominent European countries in artificial reefs (ARs) research, with over 50 years of history and the construction of the second artificial reef in Europe designed according to scientific criteria. A review of 560 documents on Italian artificial [...] Read more.

Italy represents one of the most prominent European countries in artificial reefs (ARs) research, with over 50 years of history and the construction of the second artificial reef in Europe designed according to scientific criteria. A review of 560 documents on Italian artificial reefs (ARs) from 1970s to 2025—including 404 scientific papers and 156 gray literature sources—together with an in-depth web-search allowed the identification of 118 artificial reefs deployed in the Italian seas. Concrete represents the most used material for AR construction, due to its durability over time, and ductility to build modules of different shapes and dimensions. More than 70% of the Italian ARs are made of concrete utilized alone or with other associated materials. Habitat protection and finfish enhancement have been the main scopes for AR deployment. Most scientific papers on Italian artificial reefs refer to the zoobenthic communities settled on the manmade substrates or living in the surrounding soft bottom, finfish assemblage, ecology, and general themes, such as history and management of the reefs. Recommendations include the need for a multidisciplinary panel of experts to comprehensively assess the environmental, biological, and socio-economic characteristics of an area selected for a new AR, and for development of eco-designed structures. Full article

(This article belongs to the Topic Conservation and Management of Marine Ecosystems)

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32 pages, 3804 KB

Open AccessArticle

Water Networks Management: Assessment of Heuristic and Exact Approaches for Optimal Valve Location and Operation Settings Schedule

by Maria Cunha, João Marques and Enrico Creaco

Water 2025, 17(22), 3249; https://doi.org/10.3390/w17223249 - 14 Nov 2025

Abstract

This paper deals with the optimal design-for-control of water distribution networks (WDNs) with the objectives of minimizing pressure-induced background leakage and maximizing resilience. This problem entails defining locations for installing valves and/or pipes and for simultaneously determining valve settings and belongs to the [...] Read more.

This paper deals with the optimal design-for-control of water distribution networks (WDNs) with the objectives of minimizing pressure-induced background leakage and maximizing resilience. This problem entails defining locations for installing valves and/or pipes and for simultaneously determining valve settings and belongs to the class of non-convex mixed-integer nonlinear problems. Solving highly complex infrastructure problems, such as WDNs, raises a fundamental question about the accuracy of the solutions to be implemented for sound water management. Therefore, two kinds of optimization methods are applied and assessed on two case studies. While the first is an exact global optimization method, the second is the metaheuristic based on the concept of simulated annealing. This paper proposes an innovative methodological analysis to interpret and discuss the results provided by both methods, as well as to identify their impact on the performance of the WDN. This type of analysis may help in highlight how the integration of the best features of both solution methods can promote a step forward in solving WDN problems. Full article

(This article belongs to the Special Issue Advances in Management and Optimization of Urban Water Networks)

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