Water

17 pages, 870 KB

Open AccessArticle

Investigation of the Impact of Wastewater from Waste Oil In-Stallation on the Activated Sludge Process, to Ensure the Proper Operation of Municipal Wastewater Treatment Plant

by Agnieszka Bluszcz, Krzysztof Barbusiński, Barbara Pieczykolan and Mohamed Alwaeli

Water 2026, 18(1), 108; https://doi.org/10.3390/w18010108 (registering DOI) - 1 Jan 2026

Abstract

The study evaluated the feasibility of using the activated sludge process to treat real wastewater from used oil installations containing petroleum hydrocarbons, boron (B), and adsorbable organic halides (AOX). The aim was to determine the maximum ratio of this wastewater that could be [...] Read more.

The study evaluated the feasibility of using the activated sludge process to treat real wastewater from used oil installations containing petroleum hydrocarbons, boron (B), and adsorbable organic halides (AOX). The aim was to determine the maximum ratio of this wastewater that could be added to the influent without impairing treatment efficiency. Tested shares ranged from 0.50% to 1.90%. An initial 1.30% of the tested share caused process instability, reflected in the elevated total nitrogen (TN) levels in treated wastewater. After reducing the share to 0.50%, an adaptation of the activated sludge was observed, manifested by a decrease in TN concentration to below 15.0 mg N/L. For the most favorable share of 1.60% (0.38 ± 0.10 kg_BOD5/kg_MLSS d, 0.51 ± 0.14 kg_COD/kg_MLSS d), the removal efficiencies of chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), TN, and total phosphorus (TP) were 95.0% ± 1.5, 99.1% ± 0.2, 89.3% ± 2.7, and 94.0% ± 5.0, respectively. Increasing the share to 1.90% decreased treatment efficiency and exceedances of COD, BOD₅, TN, and TP occurred. At this ratio, an increase in ammonium nitrogen (NH4⁺-N) and TN concentrations was observed, indicating the inhibition of nitrification. However, the average concentrations of mineral oil index, AOX and B in the treated wastewater remained within permissible levels throughout the study. Full article

(This article belongs to the Special Issue Sustainable Biodegradation and Bioremediation of Organic Contaminants in Aquatic and Terrestrial Environments)

14 pages, 7422 KB

Open AccessArticle

Morphometric Analysis and Evolutionary Implications of Badland Basins in Southern Italy

by Marco Piccarreta, Giacomo Prosser and Mario Bentivenga

Water 2026, 18(1), 107; https://doi.org/10.3390/w18010107 (registering DOI) - 1 Jan 2026

Abstract

This study introduces the Badland Dissection Index (BDI), a new morphometric parameter that quantifies the internal dissection and drainage maturity of badland basins. The index was applied to 87 calanchi basins developed on marine clays in the Ionian sector of Basilicata (southern Italy). [...] Read more.

This study introduces the Badland Dissection Index (BDI), a new morphometric parameter that quantifies the internal dissection and drainage maturity of badland basins. The index was applied to 87 calanchi basins developed on marine clays in the Ionian sector of Basilicata (southern Italy). BDI values range from 0.13 to 0.62, with approximately 65% of the basins exhibiting values lower than 0.30, indicating mature geomorphic stages dominated by organized fluvial incision. Pearson correlation analysis shows that BDI is strongly correlated with compactness and shape indices (r = −0.71 with circularity ratio, r = 0.74 with Gravelius compactness index, GCI), and moderately with relief (r = 0.46 with Melton ratio), highlighting the primary control exerted by basin geometry on badland dissection. A principal component analysis shows that compactness-related variables and BDI dominate the first component, which explains 38.6% of the variance, while hydrological indices define an independent second component; together the first two components account for 57.4% of total variance. A multiple regression model confirms GCI as the dominant predictor of BDI (R² = 0.58), with relief variables playing a secondary role. Owing to its simplicity, limited data requirements and clear geomorphic meaning, BDI provides a robust and scalable tool for comparing badland morphodynamics across semiarid settings and for monitoring landscape evolution where only medium-resolution topographic data are available. Full article

(This article belongs to the Special Issue Impact of Climate Changes on Humid and Arid Geomorphic Systems)

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22 pages, 2084 KB

Open AccessArticle

Unraveling Nitrate Source Dynamics in Megacity Rivers Using an Integrated Machine Learning–Bayesian Isotope Framework

by Jie Ren, Guilin Han, Xiaolong Liu, Xi Gao and Shitong Zhang

Water 2026, 18(1), 106; https://doi.org/10.3390/w18010106 (registering DOI) - 1 Jan 2026

Abstract

Rapid urbanization has intensified nitrate pollution in megacity rivers, posing severe challenges to urban water governance and sustainable nitrate management. This study presents nitrate dual-isotope signatures (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻) from surface water samples collected [...] Read more.

Rapid urbanization has intensified nitrate pollution in megacity rivers, posing severe challenges to urban water governance and sustainable nitrate management. This study presents nitrate dual-isotope signatures (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻) from surface water samples collected during the wet season from the Yongding River (YDR) and Chaobai River (CBR) in the Beijing–Tianjin–Hebei megacity region of North China. Average concentrations of nitrate (as NO₃⁻) were 8.5 mg/L in YDR and 12.7 mg/L in CBR. The δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ values varied from 6.1‰ to 19.1‰ and −1.1‰ to 10.6‰, respectively. The spatial distribution of NO₃⁻/Cl⁻ ratios and isotopic data indicated mixed sources, primarily sewage and manure in downstream sections and agricultural inputs in upstream areas. Isotopic evidence revealed widespread nitrification processes and could have potentially localized denitrification under low-oxygen conditions in the lower YDR. Bayesian mixing model (MixSIAR) results indicated that sewage and manure constituted the main nitrate sources (49.4%), followed by soil nitrogen (23.7%), chemical fertilizers (19.2%), and atmospheric deposition from rainfall (7.7%). The self-organizing map (SOM) further revealed three nitrate regimes, including natural and agricultural, mixed, and sewage dominated conditions, indicating a clear downstream gradient of increasing anthropogenic influence. The results suggest that efficient nitrogen management in megacity rivers requires improving biological nutrient removal in wastewater treatment, regulating fertilizer application in upstream areas, and maintaining ecological base flow for natural denitrification. This integrated framework provides a quantitative basis for nitrate control and supports sustainable water governance in highly urbanized watersheds. Full article

(This article belongs to the Special Issue From Rainfall to Aquatic Ecosystems: Hydrological Processes and Environmental Effects)

16 pages, 1990 KB

Open AccessArticle

Hydrochemical Evolution and Pollution Source Apportionment of Groundwater in Arid Regions: A Case Study of the Datong River Basin, Northwest China

by Tao Liu, Jian Kang, Youwei Yu, Yue Qi and Zizhao Zhang

Water 2026, 18(1), 105; https://doi.org/10.3390/w18010105 (registering DOI) - 1 Jan 2026

Abstract

Understanding hydrochemical evolution and apportioning pollution sources are prerequisites for effective groundwater protection at the regional scale; nevertheless, the governing processes and anthropogenic drivers in arid regions remain poorly constrained. Here, we present a comprehensive geochemical survey of the Datong River Basin, a [...] Read more.

Understanding hydrochemical evolution and apportioning pollution sources are prerequisites for effective groundwater protection at the regional scale; nevertheless, the governing processes and anthropogenic drivers in arid regions remain poorly constrained. Here, we present a comprehensive geochemical survey of the Datong River Basin, a representative arid catchment in north-western China. Thirty-seven groundwater samples were analyzed with hydrochemical methods and Positive-Matrix Factorization (PMF) to delineate natural controls and contaminant sources. Results showed that the aquifer is dominated by HCO₃–Ca(Mg) water controlled predominantly by silicate and carbonate weathering, modified locally by evapo-concentration and human activities. Water-quality indices classify 70.3% of the samples as excellent, but spatially restricted degradation is evident. PMF resolved three independent sources: a natural end-member enriched in Mn, Na⁺ and Cl⁻; a mixed source reflecting domestic wastewater, agricultural fertilizers and rock weathering; and an industrial source dominated by Fe. The mixed source contributes most major ions and chemical oxygen demand (COD), whereas the industrial source accounts for 75.7% of total Fe. These findings provide a robust scientific basis for groundwater management and pollution mitigation in arid regions under similar hydrogeological settings. Full article

(This article belongs to the Special Issue Pollution Mechanisms and Source Apportionment of Typical Pollutants in Aquatic Environments)

35 pages, 2273 KB

Open AccessReview

Microplastics in Wastewater Systems of Kazakhstan and Central Asia: A Critical Review of Analytical Methods, Uncertainties, and Research Gaps

by María-Elena Rodrigo-Clavero, Javier Rodrigo-Ilarri, Kulyash K. Alimova, Natalya S. Salikova, Lyudmila A. Makeyeva and Meiirman Berdali

Water 2026, 18(1), 104; https://doi.org/10.3390/w18010104 (registering DOI) - 1 Jan 2026

Abstract

Microplastics are increasingly recognized as contaminants of emerging concern in wastewater systems, where treatment plants act both as sinks and as point sources. However, Central Asian wastewater infrastructures are under-represented in the literature, and global syntheses are hindered by strong methodological heterogeneity (sampling [...] Read more.

Microplastics are increasingly recognized as contaminants of emerging concern in wastewater systems, where treatment plants act both as sinks and as point sources. However, Central Asian wastewater infrastructures are under-represented in the literature, and global syntheses are hindered by strong methodological heterogeneity (sampling regimes, size cut-offs, QA/QC). This PRISMA-guided critical review compiles and harmonizes data from 63 WWTP studies worldwide (402 matrix-stage observations), including the few available case studies from Kazakhstan and neighboring countries, to benchmark Central Asian plants against a global envelope and identify methodological and infrastructure gaps. Globally, influent concentrations cluster around a median ≈65 particles/L, while final/tertiary effluents show a median ≈2.2 particles/L. Median removal efficiency is 85.5% for secondary and 95.0% for tertiary/advanced trains, with ≈10³–10⁵ particles/kg DW typically retained in sludge. Across influent, effluent and sludge, fibers and fragments of PE, PP and PET dominate polymer morphology patterns, with similar PET/PE/PP signatures also reported in downstream river water. Central Asian influents fall within global interquartile ranges, but secondary-only facilities tend to yield effluents in the upper half of the global distribution. Overall, the review provides a first integrated, methodologically explicit assessment of WWTP microplastics in Central Asia and underscores the need for protocol harmonization, longitudinal monitoring, and targeted upgrades of polishing steps and sludge management in arid hydrosystems. Full article

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

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28 pages, 4882 KB

Open AccessArticle

Seasonal Changes of Extreme Precipitation in Relation to Circulation Conditions in the Sudetes Mountains

by Irena Otop and Bartłomiej Miszuk

Water 2026, 18(1), 103; https://doi.org/10.3390/w18010103 (registering DOI) - 1 Jan 2026

Abstract

Heavy precipitation, and its dependence on atmospheric circulation, is one of the most important weather features in Central Europe. The Polish–Czech Sudetes Mountains and their northern foreland are one of the regions where such precipitation, under certain circulation conditions, often results in floods. [...] Read more.

Heavy precipitation, and its dependence on atmospheric circulation, is one of the most important weather features in Central Europe. The Polish–Czech Sudetes Mountains and their northern foreland are one of the regions where such precipitation, under certain circulation conditions, often results in floods. The main goal of this paper is to examine multiannual changes in seasonal heavy precipitation between 1961–2020 and to assess their relationship with atmospheric circulation. The data were derived from the Polish and Czech meteorological stations, representing various altitudes and geographical regions. For the purposes of the study, several indices were used, including 1-, 3-, and 5-day maximum precipitation, as well as two indices based on the 90th and 95th percentile thresholds. In the analysis concerning atmospheric circulation, the Lityński classification was considered. The results show that the changes in heavy precipitation usually do not indicate homogeneous directions and are strongly affected by applied indices, seasons, and various geographic factors. Those include the northern/southern slope exposition, which significantly determines heavy precipitation under circulation conditions typical for individual seasons. This particularly concerns heavy precipitation for the north and northeast types, which contribute to higher rates of the considered index, especially in the northern part of the mountains. Full article

(This article belongs to the Special Issue Analysis of Extreme Precipitation Under Climate Change)

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19 pages, 1175 KB

Open AccessArticle

Research on the Performance Evaluation System for Ecological Product Value Realization Projects: A Case Study of the Comprehensive Water Environment Management Project for a Drinking Water Source

by Yuan-Hua Chen, Chang Chai, Qing-Lian Wu and Nan-Nan Wang

Water 2026, 18(1), 102; https://doi.org/10.3390/w18010102 (registering DOI) - 1 Jan 2026

Abstract

Establishing a mechanism for ecological product value realizing (EPVR) is a critical component of China’s ecological civilization strategy, aimed at translating the concept that “lucid waters and lush mountains are invaluable assets” into actionable economic policies. Although central government investments in the form [...] Read more.

Establishing a mechanism for ecological product value realizing (EPVR) is a critical component of China’s ecological civilization strategy, aimed at translating the concept that “lucid waters and lush mountains are invaluable assets” into actionable economic policies. Although central government investments in the form of project for EPVR have increased significantly, surpassing CNY 700 billion by 2024, studies rarely focus on these projects and how to evaluate them. Evaluating the performance of EPVR projects is essential for optimizing resource allocation, enhancing project accountability, and ensuring the sustainable realization of ecological, economic, and social values. This study innovatively defines the conceptual connotation of EPVR projects and constructs a comprehensive performance evaluation system based on a “benefit-cost” analysis, comprising a multi-dimensional indicator system, quantifiable calculation methods, and explicit evaluation criteria. As water source protection projects are typical EPVR projects, the comprehensive water environment management project of Hongfeng Lake is selected for an in-depth empirical study. The results reveal that (1) the total annual benefits amount to CNY 923.66 million, dominated by ecological benefits (84.04%); (2) with an investment of CNY 1194.66 million, the project yields a net loss and a moderate performance index (PCPI = 0.77); (3) the project performance is primarily affected by weak economic value conversion stemming from restrictive zoning policies and underdeveloped market mechanisms for ecological services; and (4) integrated development pathways—such as ecotourism, eco-aquaculture, and ecological branding—are proposed to enhance the long-term sustainability of the project. The Hongfeng Lake case establishes a replicable framework for global assessment of analogous projects and delivers actionable insights for enhancing benefit–cost ratios in public ecological initiatives, with costs confined to data collection, modeling, and validation. Therefore, this study contributes a quantifiable and reproducible tool for the full lifecycle management of EPVR projects, thereby facilitating more informed government decision-making. Key findings reveal the following: (1) A comprehensive “Benefit-Cost” performance evaluation framework, pioneered in this study and tailored specifically for individual EPVR projects, surpasses regional-scale accounting methodologies like Gross Ecosystem Product (GEP). (2) A novel consolidated metric (PCPI) is introduced to integrate ecological, economic, and social dimensions with cost input, thus enabling direct cross-project comparison and classification. (3) The framework operationalizes evaluation by providing a detailed, adaptable indicator system with explicit monetization methods for 26 distinct benefits, thereby bridging the gap between theoretical value accounting and practical project assessment. (4) The empirical application to a drinking water source protection project addresses a critical yet understudied category of EPVR projects, offering insights into “protection-oriented” models. Full article

(This article belongs to the Special Issue Economic Approaches to Sustainable Water Management: Policy, Innovation, and Global Challenges)

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34 pages, 97071 KB

Open AccessArticle

Analysis of the Impact of Coastal Development and Utilization on the Ecological Environment of the Nearshore Area in the Liaohe River Estuary

by Lianyi Zhou, Yueyin Cai, Guangshuai Zhang, Xinchen Yue, Ying Liu, Hesong Zhou and Na Shen

Water 2026, 18(1), 101; https://doi.org/10.3390/w18010101 (registering DOI) - 1 Jan 2026

Abstract

Based on an analysis of monitoring data from the Liaohe estuary, the distribution of inorganic nitrogen and active phosphate is related to the type of shoreline. The pollutant concentrations in the port area are 16% (inorganic nitrogen) and 59% (active phosphate) higher than [...] Read more.

Based on an analysis of monitoring data from the Liaohe estuary, the distribution of inorganic nitrogen and active phosphate is related to the type of shoreline. The pollutant concentrations in the port area are 16% (inorganic nitrogen) and 59% (active phosphate) higher than those in the control area. The phytoplankton diversity index in the aquaculture area is 20% lower than in the mixed estuary area, which confirms the gradient effect of human disturbance. The constructed dual-mode distance effect model shows that, for a homogeneous shoreline, the goodness of fit is 40.1% in the non-estuary area, but radial basis function correction needs to be introduced for the estuary area. This study suggests that, in the port area, it is necessary to implement a combined policy consisting of ‘total nitrogen and phosphorus control + ecological compensation’, and artificial reefs should be built in the aquaculture area to maintain the number of benthic species. Full article

(This article belongs to the Special Issue Study on Environmental Hydrology and Hydrodynamic Characteristics of Basins, Estuaries and Offshore)

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22 pages, 1512 KB

Open AccessArticle

Leakage Modelling in Water Distribution Networks: A Novel Framework for Embedding FAVAD Formulation into EPANET 2.2

by Zahreddine Hafsi, Carlo Giudicianni and Enrico Creaco

Water 2026, 18(1), 100; https://doi.org/10.3390/w18010100 (registering DOI) - 1 Jan 2026

Abstract

This paper proposes a novel framework for embedding the Fixed And Variable Area Discharge (FAVAD) equation into the software EPANET 2.2 for the simulation of water distribution networks (WDNs). This framework yields a realistic model of leakage outflows that accounts for the expansion [...] Read more.

This paper proposes a novel framework for embedding the Fixed And Variable Area Discharge (FAVAD) equation into the software EPANET 2.2 for the simulation of water distribution networks (WDNs). This framework yields a realistic model of leakage outflows that accounts for the expansion of the leak area as a function of service pressure. Without altering the source code of EPANET, this is accomplished by using node emitters and by iteratively adjusting emitter coefficients in the Matlab^® (R2023a) environment to mimic the effects of the FAVAD equation along WDN pipes. An additional benefit consists of preventing backflow occurring under negative pressure conditions in EPANET 2.2. The application to two benchmark WDNs under various leakage configurations demonstrates the robustness and the numerical efficiency of the framework, as well as the impact and benefits of the FAVAD formulation. For instance, for pipes with higher elasticity, omitting the expansion of the leak area leads to an underestimation of the total leakage rate that exceeds 30% for one of the studied cases. Furthermore, the algorithm successfully prevents leakage backflow under both demand-driven and pressure-driven analyses. Full article

(This article belongs to the Section Urban Water Management)

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19 pages, 3509 KB

Open AccessArticle

Determining Water Resource Formation at the “Delegen” Nuclear Test Site Using Stable Isotope Analysis

by Almira Aidarkhanova, Ainur Mamyrbayeva, Anastassiya Nadeyeva, Alibek Iskenov, Assan Aidarkhanov, Natalya Larionova and Rinata Yermakova

Water 2026, 18(1), 99; https://doi.org/10.3390/w18010099 - 31 Dec 2025

Abstract

Despite the closure of the Semipalatinsk nuclear test site (STS) more than 30 years ago, water continues to transport radioactive contamination beyond the boundaries of the “Degelen” test site. Therefore, assessing the formation of water resources at this test site is highly relevant, [...] Read more.

Despite the closure of the Semipalatinsk nuclear test site (STS) more than 30 years ago, water continues to transport radioactive contamination beyond the boundaries of the “Degelen” test site. Therefore, assessing the formation of water resources at this test site is highly relevant, particularly in terms of forecasting the development of radioactive contamination at the STS. In this case, isotope hydrology is the most promising method for understanding these processes. The aquatic environment at the “Degelen” test site consists of radioactively contaminated tunnel water, streams, and groundwater. This paper presents the research results regarding the determination of stable isotopes of hydrogen and oxygen for the aquatic environment of the “Degelen” test site. ³H concentrations and the chemical composition of water at the site were also determined. Analysis of the water’s isotopic composition (δ₂H and δ¹⁸O) showed that the tunnel and stream water are formed by precipitation (snowmelt and rain). In summer, when precipitation is low, atmospheric condensation contributes significantly to recharge at the “Degelen” test site. The high radionuclide content of tunnel water leads to the contamination of stream water, and, to a lesser extent, groundwater. The ³H content of tunnel water can reach 260 kBq/L, and that of stream water can reach 58 kBq/L, both of which exceed the established standards in the Republic of Kazakhstan. Full article

(This article belongs to the Section Hydrology)

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20 pages, 6530 KB

Open AccessArticle

Monthly Temperature Prediction in the Han River Basin, South Korea, Using Long Short-Term Memory (LSTM) and Multiple Linear Regression (MLR) Models

by Chul-Gyum Kim, Jeongwoo Lee, Jeong-Eun Lee and Hyeonjun Kim

Water 2026, 18(1), 98; https://doi.org/10.3390/w18010098 - 31 Dec 2025

Abstract

This study compares and evaluates the performance of a statistical model, Multiple Linear Regression (MLR), and a deep learning model, Long Short-Term Memory (LSTM), for predicting monthly mean temperature in the Han River Basin, South Korea. Predictor variables were dynamically selected based on [...] Read more.

This study compares and evaluates the performance of a statistical model, Multiple Linear Regression (MLR), and a deep learning model, Long Short-Term Memory (LSTM), for predicting monthly mean temperature in the Han River Basin, South Korea. Predictor variables were dynamically selected based on lagged correlation analysis between climate indices and temperature over the past 40 years, identifying the top ten variables with the highest correlations for lag times ranging from 1 to 18 months. The MLR model was developed through stepwise regression with cross-validation, while the LSTM model was constructed using an 18-month input sequence to capture temporal dependencies in the data. Model performance was evaluated using percent bias (PBIAS), Nash–Sutcliffe efficiency (NSE), Pearson’s correlation coefficient (r), and tercile-based probability metrics. Both models reproduced the seasonal variability of monthly temperature with high accuracy (NSE > 0.97, r > 0.98). The LSTM model showed slightly higher predictive skill in several periods but also exhibited larger prediction variance, reflecting the sensitivity of nonlinear architectures to variations in predictor–response relationships. In contrast, the MLR model demonstrated more stable predictive behavior with narrower uncertainty bounds, particularly under low signal-to-noise conditions, owing to its structural simplicity. These findings indicate that the two approaches are complementary; the LSTM model better captures nonlinear temporal dynamics, while the MLR model provides interpretability and robustness. Future work will explore advanced hybrid architectures such as CNN–LSTM and Transformer-based models, as well as multi-model ensemble methods, to further enhance the accuracy and reliability of medium-range temperature prediction. Full article

(This article belongs to the Section Hydrology)

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21 pages, 1198 KB

Open AccessArticle

pH-Dependent Reactivity, Radical Pathways, and Nitrosamine Byproduct Formation in Peroxynitrite-Mediated Advanced Oxidation Processes

by Zhe Chen, Dandan Rao, Jian Zhang and Bo Sun

Water 2026, 18(1), 97; https://doi.org/10.3390/w18010097 - 31 Dec 2025

Abstract

Peroxynitrite (ONOOH/ONOO⁻) is increasingly recognized as a key intermediate in advanced oxidation processes (AOPs), yet its role in water treatment remains insufficiently defined. This study provides mechanistic insights into peroxynitrite-mediated AOPs through competition kinetics method, demonstrating that both decomposition and pollutant [...] Read more.

Peroxynitrite (ONOOH/ONOO⁻) is increasingly recognized as a key intermediate in advanced oxidation processes (AOPs), yet its role in water treatment remains insufficiently defined. This study provides mechanistic insights into peroxynitrite-mediated AOPs through competition kinetics method, demonstrating that both decomposition and pollutant degradation are strongly pH-dependent, with ONOOH dominating stability and radical pathways across pH 5.0−9.0, while its decay rate decreases from 1.2 s⁻¹ to 0.0022 s⁻¹. The interplay of HO^• and diverse reactive nitrogen species (RNS, including reactive nitrogen radicals and peroxynitrite) dictates pollutant-specific degradation efficiencies, with RNS showing a unique reliance in degrading bisphenol A—contributing up to 66.7% at pH 8.0. Buffer chemistry further modulates these pathways: bicarbonate accelerates peroxynitrite decay via CO₂ and CO₃^•−-mediated acceleration (resulting in a 361.9% increase at pH 9.0), while borate promotes reactive nitrogen radical formation but suppresses HO^• contributions. Importantly, peroxynitrite was shown to facilitate N-nitrosodimethylamine formation in the presence of dimethylamine, with yields maximized under alkaline conditions and attenuated by bicarbonate. These quantitative findings underscore the critical roles of pH and buffer chemistry in optimizing peroxynitrite-based water treatment while mitigating byproduct risks. Full article

(This article belongs to the Special Issue Novel Advanced Oxidation Technology for Water Treatment)

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16 pages, 731 KB

Open AccessReview

Neglected Genetic Coefficients for Bacterial Diversity as a Supporting Tool for Public Health and Wastewater-Based Epidemiology

by Karol Korzekwa, Oliwia Obuch-Woszczatyńska and Małgorzata Krzyżowska

Water 2026, 18(1), 96; https://doi.org/10.3390/w18010096 - 31 Dec 2025

Abstract

In the review, the collection of population genetics papers from 1973 to 2025 comprises 400 publications, 81 of which were significant and consulted with representatives from water and sewage companies. Reviewed Proteobacteria (mean H_S = 0.42), Firmicutes (mean H_S = 0.43), [...] Read more.

In the review, the collection of population genetics papers from 1973 to 2025 comprises 400 publications, 81 of which were significant and consulted with representatives from water and sewage companies. Reviewed Proteobacteria (mean H_S = 0.42), Firmicutes (mean H_S = 0.43), Actinobacteria (mean H_S = 0.33), and Spirochaetes (mean H_S = 0.54) represent the 60 species under investigation through the lens of “h” coefficients related to gene diversity and expected heterozygosity. The research also included ESKAPE, emerging pathogens, bacterial indicators of wastewater treatment efficiency, environmental sanitary surveillance and public health. The restoration of the expected heterozygosity for haploids “h” was proposed in wastewater-based epidemiology as an innovative tool for public health. The unique “h” coefficient allows for the comparison of genetic variability in various organisms, regardless of their ploidy, using multiple markers and traits. The parameter represents a noble character for both the variability of phenotypes (proteins) and genotypes (nucleic acids). Leveraging the genetic diversity highlighted by the “h” coefficient can support wastewater-based epidemiology, offering the ability to predict the stages and trajectories of disease outbreaks. Full article

(This article belongs to the Special Issue Evaluation of Microbiological Indicators for Water and Wastewater Treatment and Reuse)

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15 pages, 2230 KB

Open AccessReview

A Comparative Trends of Watershed Health and Its Driving Forces

by Ning Mao, Zitong Yin, Tanveer M. Adyel, Jun Hou and Lingzhan Miao

Water 2026, 18(1), 95; https://doi.org/10.3390/w18010095 - 31 Dec 2025

Abstract

In recent decades, rapid socioeconomic development and population growth have led to the degradation of river and lake health worldwide, posing severe challenges to watershed ecological management. The growing intensity of land-use has significantly contributed to the accelerated deterioration of aquatic ecosystems. River [...] Read more.

In recent decades, rapid socioeconomic development and population growth have led to the degradation of river and lake health worldwide, posing severe challenges to watershed ecological management. The growing intensity of land-use has significantly contributed to the accelerated deterioration of aquatic ecosystems. River and lake health assessment has evolved from single-parameter metrics (e.g., water quality) to multidimensional frameworks integrating hydrological, biological, and anthropogenic factors. This research conducted a bibliometric analysis of 1302 publications from 1996 to 2023 in the Web of Science database to identify research trends and hotspots. Results showed that publications exhibited a three-phase growth incubation (1996–2000), expansion (2001–2012), and acceleration (2013–2023), with the U.S., China, and Australia as leading contributors characterized by regionally clustered international collaborations. Research themes have shifted from single water quality parameters to integrated assessments. “Land-use”, “water quality”, and “biotic integrity” have emerged as core hotspots, forming a synergistic assessment framework that combines physicochemical, biological, and socioeconomic factors. The research scale underwent a spatial refinement process from the whole watershed to the buffer zone of rivers and lakes, and land-use effects on aquatic ecosystems vary significantly across spatial scales (entire watershed and riparian zones). Fine-scale studies better capture localized pollution pathways, supporting targeted conservation strategies. This review systematically outlines research status, hotspots, and development directions for river and lake health studies, highlighting the need for integrated watershed management, emphasizing conservation through fine-scale land-use monitoring, and providing scientific support for integrated refined governance of watershed ecology. Full article

(This article belongs to the Special Issue NBS for Watershed Management: From Ecological Health Assessment to Ecosystem Restoration)

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16 pages, 4982 KB

Open AccessArticle

Evaluation of Sediment Deposition Processes in Hydroelectric Plant: Case Study of Espora Reservoir, Brazil

by Assunção Andrade de Barcelos, João Batista Pereira Cabral, Fernanda Luisa Ramalho, Patrícia da Silva Gomes, Hudson Moraes Rocha, Valter Antonio Becegato and Alexandre Tadeu Paulino

Water 2026, 18(1), 94; https://doi.org/10.3390/w18010094 - 31 Dec 2025

Abstract

Studying sedimentary distribution in water reservoirs is essential to understand the depositional processes and develop sustainable environmental management strategies. Characterization of deposited sediments provides information about the sources of particulate matter, transport patterns and predominant deposition mechanisms in different compartments of the reservoir. [...] Read more.

Studying sedimentary distribution in water reservoirs is essential to understand the depositional processes and develop sustainable environmental management strategies. Characterization of deposited sediments provides information about the sources of particulate matter, transport patterns and predominant deposition mechanisms in different compartments of the reservoir. This study aimed to evaluate active deposition processes and to improve the understanding of sedimentation in water reservoirs. In this case, the Espora hydroelectric power plant, located on the Corrente River, southwestern Goiás, Brazil, was employed as a model environment. Sediment cores were collected at 29 points along the reservoir, covering different aquatic compartments. Particle-size analysis of the sediments was performed based on established methodologies using textural classification to identify sedimentary facies. The results indicated the predominance of stream deposits (sandy material) in areas where water flow velocity was higher, and bed deposits, composed predominantly of clays and silts, in regions of lower water flow velocity and greater depth. Full article

(This article belongs to the Special Issue River Channel Hydraulics, Fluvial Dynamics and Re-Opening Floodplains)

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18 pages, 1187 KB

Open AccessArticle

Detection of Water Quality COD Based on the Integration of Laser Absorption and Fluorescence Spectroscopy Technology

by Hanyu Zhang, Zhaoshuo Tian, Xiaohua Che, Ying Guo and Zongjie Bi

Water 2026, 18(1), 93; https://doi.org/10.3390/w18010093 - 30 Dec 2025

Abstract

Chemical oxygen demand (COD) serves as a critical indicator for assessing the extent of water pollution caused by organic matter. This study proposes an integrated COD detection methodology that combines laser absorption spectroscopy with laser-induced fluorescence spectroscopy, enabling accurate measurement of COD parameters [...] Read more.

Chemical oxygen demand (COD) serves as a critical indicator for assessing the extent of water pollution caused by organic matter. This study proposes an integrated COD detection methodology that combines laser absorption spectroscopy with laser-induced fluorescence spectroscopy, enabling accurate measurement of COD parameters across a wide concentration range. For high-concentration COD, conventional ultraviolet absorption spectrophotometry based on the Lambert–Beer law is employed. However, since laser absorption spectrophotometry exhibits substantial errors in detecting low-concentration COD, laser-induced fluorescence spectroscopy is adopted for the precise quantification of trace-level COD. By integrating these two laser-based approaches, a spectroscopic COD detection system has been developed that simultaneously records absorbance after the laser passes through the sample and quantifies fluorescence intensity perpendicular to the beam with an image sensor, thereby achieving comprehensive COD analysis. Laboratory validation using COD standard solutions demonstrated relative errors below 11% across the concentration range of 2–220 mg/L. Further application to natural water samples confirmed that the integrated laser absorption–fluorescence spectroscopy approach achieves wide-range COD measurement with high sensitivity, a compact configuration, and rapid response, demonstrating strong potential for real-time online water quality monitoring. Full article

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

25 pages, 16923 KB

Open AccessArticle

A Framework for Refined Hydrodynamic Model Based on High Resolution Urban Hydrological Unit

by Pan Wu, Tao Wang, Zhaoli Wang, Haoyu Jin and Xiaohong Chen

Water 2026, 18(1), 92; https://doi.org/10.3390/w18010092 - 30 Dec 2025

Abstract

With the accelerating pace of urbanization, cities are increasingly affected by rainstorm and flood disasters, which pose severe threats to the safety of residents’ lives and property. Existing models are increasingly inadequate in meeting the accuracy requirements for flood simulation in highly urbanized [...] Read more.

With the accelerating pace of urbanization, cities are increasingly affected by rainstorm and flood disasters, which pose severe threats to the safety of residents’ lives and property. Existing models are increasingly inadequate in meeting the accuracy requirements for flood simulation in highly urbanized regions. Thus, it is urgent to develop a new method for flood inundation simulation based on high-resolution urban hydrological units. The novelty of the model lies in the novel structure of the high-resolution Urban Hydrological Units model (HRGM), which replaces coarse sub-catchments with a fine-grained network of urban hydrological units. The primary innovation is the node-based coupling strategy, in which the HRGM provides precise overflow hydrographs at drainage inlets as point sources for LISFLOOD-FP, rather than relying on diffuse runoff inputs from larger areas. In this paper, a high-resolution hydraulic model (HRGM) based on urban hydrological units coupled with a 2D hydrodynamic model (LISFLOOD-FP) was constructed and successfully applied in the Chebeichong watershed. Results show that the model’s simulations align well with observed data, achieving a Nash efficiency coefficient above 0.8 under typical rainfall events. Compared with the SWMM model, the simulation results of HRGM were significantly improved and more consistent with measured results. Taking the rainstorm event on 10 August 2021 as an example, the Nash coefficient increased from 0.7 to 0.85, while the peak flow error decreased markedly from 15.8% to 3.1%. It should be emphasized that urban waterlogging distribution is not continuous but appears as patchy, discontinuous, and fragmented patterns due to the segmentation and blocking effects of roads and buildings in urban areas. The framework presented in this study shows potential for application in other regions requiring flood risk assessment at urban agglomeration scales, offering a valuable reference for advancing flood prediction methodologies and disaster mitigation strategies. Full article

(This article belongs to the Topic Basin Analysis and Modelling)

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23 pages, 4147 KB

Open AccessArticle

Physicochemical Conditions Shaping Phytoplankton Development in Shallow Lakes of Bellsund During the Ablation Season, West Spitsbergen

by Marta Ziółek, Małgorzata Poniewozik, Łukasz Franczak and Magdalena Kończak

Water 2026, 18(1), 91; https://doi.org/10.3390/w18010091 - 30 Dec 2025

Abstract

The small freshwater lakes of Spitsbergen remain poorly studied compared to surrounding marine ecosystems despite their sensitivity to rapid environmental changes. During the short ablation season, these shallow lakes exhibit physicochemical variability influenced by the harsh Arctic climate, local geology, and hydrology. This [...] Read more.

The small freshwater lakes of Spitsbergen remain poorly studied compared to surrounding marine ecosystems despite their sensitivity to rapid environmental changes. During the short ablation season, these shallow lakes exhibit physicochemical variability influenced by the harsh Arctic climate, local geology, and hydrology. This study analyzed six lakes located on marine terraces, moraine areas, and outwash plains in the Bellsund region to assess how physicochemical variability in their waters affects phytoplankton development. The lakes exhibited local and temporal variations in temperature, conductivity, ion composition, and nutrient levels, with generally low nutrient availability limiting biological productivity. Phytoplankton communities were quantitatively and qualitatively poor, dominated by green algae, either flagellates or mixed communities, including cyanobacteria. Green algae clearly dominated in lakes closest to the fjord shoreline, while dinoflagellates and cryptophytes dominated in inland lakes. Phytoplankton abundance and biomass were extremely low in one of the lakes situated on the raised marine terraces within the tundra vegetation zone (3 × 10³ ind L⁻¹ and 0.004 mg L⁻¹, respectively). In contrast, the much larger lake situated within the tundra zone nearer the fjord shoreline had values that were comparable to fertile lakes in the temperate zone (~30 thousand × 10³ ind L⁻¹ and ~28 mg L⁻¹, respectively). It should be noted that Monoraphidium contortum and Rhodomonas minuta dominated some of the lakes almost entirely. Phytoplankton abundance was related to physicochemical conditions: green algae increased with increasing ion concentrations (Cl⁻, Na⁺, K⁺, SO₄²⁻), P_min, Fe, and Mn; flagellates preferred colder waters with higher N_min and low TOC; cyanobacteria occurred in waters with lower COND, TOC, Ca²⁺, Si, Cu, and Zn. Phytoplankton biomass increased in July with increasing water temperature. Bird activity likely facilitated phytoplankton dispersal, increasing taxonomic diversity in frequently visited lakes. Full article

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

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18 pages, 10160 KB

Open AccessArticle

Hydrogeochemistry of Thermal Water from Lindian Geothermal Field, Songliao Basin, NE China: Implications for Water–Rock Interactions

by Yujuan Su, Fengtian Yang, Xuejun Zhou, Junling Dong, Ling Liu, Yongfa Ma, Minghua Chen and Chaoyu Zhang

Water 2026, 18(1), 90; https://doi.org/10.3390/w18010090 - 30 Dec 2025

Abstract

To explore the hydrogeochemical characteristics and dominant water–rock interaction processes of thermal water in Lindian geothermal field (northern Songliao Basin, NE China), this study analyzed 16 thermal water samples (1900–3000 m depth) and 3 shallow groundwater samples using hydrochemical indices, water isotopes, and [...] Read more.

To explore the hydrogeochemical characteristics and dominant water–rock interaction processes of thermal water in Lindian geothermal field (northern Songliao Basin, NE China), this study analyzed 16 thermal water samples (1900–3000 m depth) and 3 shallow groundwater samples using hydrochemical indices, water isotopes, and statistical methods (Pearson Correlation and Principle Component Analysis). Results show that the thermal water originates from precipitation and exhibits an “oxygen shift” indicating a long-time water–rock interaction under low to medium reservoir temperature. The thermal water is alkaline with a high TDS and dominated by Na⁺, Cl⁻, and HCO₃⁻, and its hydrochemical facies changes from HCO₃·Cl–Na to Cl·HCO₃–Na and Cl–Na along the groundwater flow path. Leaching of halite, silicates, and carbonates is the primary process controlling solute accumulation. The geothermal reservoir is in a relatively closed, strong reducing environment, and thermal water reached water–rock equilibrium with respect to Na-, K-, Ca-, and Mg-alumino silicates. Principle Component Analysis identifies three key controlling factors, including mineral leaching, organic matter degradation, and sulfate reduction/mineral precipitation. This study establishes a hydrogeochemical baseline for the initial exploitation stage, providing a scientific basis for predicting long-term water quality changes and formulating differentiated sustainable development strategies for the Lindian geothermal field. Full article

(This article belongs to the Special Issue Groundwater Environment Evolution and Early Risk-Warning)

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