Water

25 pages, 14882 KB

Open AccessArticle

Tracing the Origin of Groundwater Salinization in Multilayered Coastal Aquifers Using Geochemical Tracers

by Mariana La Pasta Cordeiro, Johanna Wallström and Maria Teresa Condesso de Melo

Water 2026, 18(2), 252; https://doi.org/10.3390/w18020252 (registering DOI) - 17 Jan 2026

Salinization represents a significant threat to freshwater resources worldwide, compromising water quality and security. In the Vieira de Leiria–Marinha Grande aquifer, salinization mechanisms are a complex interaction between seawater intrusion and evaporite dissolution. Near the coast, groundwater is mainly influenced by seawater, evidenced [...] Read more.

Salinization represents a significant threat to freshwater resources worldwide, compromising water quality and security. In the Vieira de Leiria–Marinha Grande aquifer, salinization mechanisms are a complex interaction between seawater intrusion and evaporite dissolution. Near the coast, groundwater is mainly influenced by seawater, evidenced by Na-Cl hydrochemical facies, high electrical conductivity, and Na⁺/Cl⁻, Cl⁻/Br⁻ and SO₄^2−/Cl⁻ molar ratios consistent with marine signatures. In areas affected by diapiric dissolution, besides elevated electrical conductivity, groundwater is enriched in SO₄²⁻ and Ca²⁺ and in minor elements like K⁺, Li⁺, B³⁺, Ba²⁺ and Sr²⁺, and high SO₄²⁻/Cl⁻ and Ca²⁺/HCO₃⁻ molar ratios, indicative of gypsum/anhydrite dissolution. The relationship between δ¹⁸O and electrical conductivity further supports the identification of distinct salinity sources. This study integrates hydrogeochemical tracers to investigate hydrochemical evolution in the aquifer with increasing residence time and influence of water–rock interaction, as well as the accurate characterization of salinization mechanisms in multilayer aquifers. A comprehensive understanding of these processes is essential for identifying vulnerable zones and developing effective management strategies to ensure the protection and sustainable use of groundwater resources. Full article

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

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30 pages, 13681 KB

Open AccessArticle

Atmospheric and Hydrospheric Characteristics in Contrasting Arctic and Intracontinental Regions of Northern Eurasia and Possible Mutual Influences

by Terry V. Callaghan, Andrey N. Romanov, Ilya V. Khvostov, Ivan V. Ryabinin, Vasiliy V. Tikhonov and Olga M. Shaduyko

Water 2026, 18(2), 251; https://doi.org/10.3390/w18020251 (registering DOI) - 17 Jan 2026

Abstract

Floods and droughts have increased in Northern Eurasia, probably caused by hydrological changes in other regions. We explore such hypothetical teleconnections by investigating environmental changes in two contrasting harsh environments: the Arctic Kara Sea and the arid Aral–Caspian region. Using long-term data from [...] Read more.

Floods and droughts have increased in Northern Eurasia, probably caused by hydrological changes in other regions. We explore such hypothetical teleconnections by investigating environmental changes in two contrasting harsh environments: the Arctic Kara Sea and the arid Aral–Caspian region. Using long-term data from daily remote microwave sensing, we describe seasonal dynamics of temperature and moisture regimes in the two regions and hypothesize their inter-relationships from new analyses of wind data. For the first time, daily L-band satellite data were used to determine open water in the Kara Sea and long-term seasonal dynamics of brightness temperatures were used to relate variations in the ongoing aridization of the Aral Sea area and abnormal spring floods in the south of Western Siberia. Using soil moisture and Ocean Salinity satellite data, we discovered a previously unrecorded 4-year cyclicity of open-water periods for the Arctic seas and northern parts of the Caspian and Aral Seas. This cyclicity could impact climate forecasting in Northern Eurasia with significant societal implications. The main aim of this paper is to present new analyses that suggest possible mechanisms for teleconnections between the two contrasting harsh environments of Northern Eurasia. The hypothetical teleconnections now need to be tested. Full article

(This article belongs to the Special Issue Climate Change Impacts on Water Resources and Ecosystem Dynamics in Mountainous and Cold-Region Ecosystems)

25 pages, 11789 KB

Open AccessArticle

Impact of Climate and Land Cover Dynamics on River Discharge in the Klambu Dam Catchment, Indonesia

by Fahrudin Hanafi, Lina Adi Wijayanti, Muhammad Fauzan Ramadhan, Dwi Priakusuma and Katarzyna Kubiak-Wójcicka

Water 2026, 18(2), 250; https://doi.org/10.3390/w18020250 (registering DOI) - 17 Jan 2026

Abstract

This study examines the hydrological response of the Klambu Dam Catchment in Central Java, Indonesia, to climatic and land cover changes from 2000–2023, with simulations extending to 2040. Utilizing CHIRPS satellite data calibrated with six ground stations, monthly precipitation and temperature datasets were [...] Read more.

This study examines the hydrological response of the Klambu Dam Catchment in Central Java, Indonesia, to climatic and land cover changes from 2000–2023, with simulations extending to 2040. Utilizing CHIRPS satellite data calibrated with six ground stations, monthly precipitation and temperature datasets were analyzed and projected via linear regression aligned with IPCC scenarios, revealing a marginal temperature decline of 0.21 °C (from 28.25 °C in 2005 to 28.04 °C in 2023) and a 17% increase in rainfall variability. Land cover assessments from Landsat imagery highlighted drastic changes: a 73.8% reduction in forest area and a 467.8% increase in mixed farming areas, alongside moderate fluctuations in paddy fields and settlements. The Thornthwaite-Mather water balance method simulated monthly discharge, validated against observed data with Pearson correlations ranging from 0.5729 (2020) to 0.9439 (2015). Future projections using Cellular Automata-Markov modeling indicated stable volumetric flow but a temporal shift, including a 28.1% decrease in April rainfall from 2000 to 2040, contracting the wet season and extending dry spells. These shifts pose significant threats to agricultural and aquaculture activities, potentially exacerbating water scarcity and economic losses. The findings emphasize integrating dynamic land cover data, climate projections, and empirical runoff corrections for climate-resilient watershed management. Full article

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

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12 pages, 3500 KB

Open AccessArticle

Hydrogeochemical Characteristics and Formation Mechanism of Metasilicic Acid Mineral Water at Taoping Water Source Area

by Dian Liu, Ximin Bai, Xuegang Wang, Shengpin Yu, Tian Li and Fei Deng

Water 2026, 18(2), 249; https://doi.org/10.3390/w18020249 (registering DOI) - 17 Jan 2026

Abstract

Northwestern Jiangxi Province is rich in metasilicic acid (as H₂SiO₃) mineral water resources. Investigating their hydrogeochemical characteristics and formation mechanism is crucial for the rational utilization of water resources and the sustainable development of the local mineral water industry. [...] Read more.

Northwestern Jiangxi Province is rich in metasilicic acid (as H₂SiO₃) mineral water resources. Investigating their hydrogeochemical characteristics and formation mechanism is crucial for the rational utilization of water resources and the sustainable development of the local mineral water industry. Taking the Taoping water source area in northwestern Jiangxi as a case study, 11 sets of groundwater and surface water samples were systematically collected. By comprehensively applying mathematical statistics, ionic ratios, and isotopic analyses, the hydrogeochemical characteristics and formation processes of metasilicic acid-type mineral water were examined. The results indicate that: (1) The mineral waters in the area are weakly alkaline and belong to the metasilicic acid type, with concentrations ranging from 22.0 to 67.0 mg/L, of which 75% exceed 30 mg/L. (2) The primary hydrochemical types are HCO₃⁻–Ca·Na, HCO₃⁻–Ca·Mg, and HCO₃⁻–Ca. Analysis of stable isotopes (δ¹⁸O and δ²H) and tritium (³H) indicates that metasilicic acid mineral water is primarily recharged by atmospheric precipitation, with an apparent groundwater age of approximately 60 years. (3) The enrichment of metasilicic acid primarily results from the weathering and leaching of silicate minerals, coupled with cation exchange. K⁺ and Na⁺ are mainly derived from silicate minerals such as feldspars and halite, whereas Ca²⁺ and Mg²⁺ originate primarily from carbonate minerals like calcite and dolomite. During recharge, atmospheric precipitation infiltrates the aquifer, dissolving aluminosilicate and siliceous minerals in the surrounding rocks, thereby releasing metasilicic acid into the groundwater and ultimately forming the metasilicic acid-type mineral water. Full article

(This article belongs to the Section Hydrogeology)

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18 pages, 3377 KB

Open AccessArticle

Enhancing Osmotic Power Generation and Water Conservation with High-Performance Thin-Film Nanocomposite Membranes for the Mining Industry

by Sara Pakdaman and Catherine N. Mulligan

Water 2026, 18(2), 248; https://doi.org/10.3390/w18020248 (registering DOI) - 17 Jan 2026

Abstract

Recycling water offers a powerful way to lower the environmental water impact of mining activities. Pressure-retarded osmosis (PRO) represents a promising pathway for simultaneous water reuse and clean energy generation from salinity gradients. In this study, the performance of a thin-film nanocomposite (TFN) [...] Read more.

Recycling water offers a powerful way to lower the environmental water impact of mining activities. Pressure-retarded osmosis (PRO) represents a promising pathway for simultaneous water reuse and clean energy generation from salinity gradients. In this study, the performance of a thin-film nanocomposite (TFN) membrane containing functionalized multi-walled carbon nanotubes (fMWCNTs) within a polyacrylonitrile (PAN) support layer, followed by polydopamine (PDA) surface modification, was investigated under a PRO operation using pretreated gold mining wastewater as the feed solution. Unlike most previous studies that rely on synthetic feeds, this work evaluates the membrane performance under a PRO operation using a real mining wastewater stream. The membrane with fMWCNTs and PDA exhibited a maximum power density of 25.22 W/m² at 12 bar, representing performance improvements of 23% and 68% compared with the pristine thin-film composite (TFC) and commercial cellulose triacetate (CTA) membranes, respectively. A high water flux of 75.6 L·m⁻²·h⁻¹ was also obtained, attributed to enhanced membrane hydrophilicity and reduced internal concentration polarization. The optimized membrane, containing 0.3 wt% fMWCNTs in the support layer and a PDA coating on the active layer, produced a synergistic enhancement in the PRO performance, resulting in a lower reverse salt flux and an improved flux–selectivity trade-off. Furthermore, the ultrafiltration (UF) and nanofiltration (NF) pretreatment effectively reduced the hardness and ionic content, enabling a stable PRO operation with real mining wastewater over a longer period of time. Overall, this study demonstrates the feasibility of achieving both reusable water and enhanced osmotic power generation using modified TFN membranes under realistic mining wastewater conditions. Full article

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

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17 pages, 2006 KB

Open AccessArticle

A Hybrid Inorganic–Organic Schiff Base-Functionalised Porous Platform for the Remediation of WEEE Polluted Effluents

by Devika Vashisht, Martin J. Taylor, Amthal Al-Gailani, Priyanka, Aseem Vashisht, Alex O. Ibhadon, Ramesh Kataria, Shweta Sharma and Surinder Kumar Mehta

Water 2026, 18(2), 247; https://doi.org/10.3390/w18020247 (registering DOI) - 16 Jan 2026

Abstract

An inorganic–organic hybrid nano-adsorbent was prepared by chemical immobilisation of an organic Schiff base Cu (II) ion receptor, DHB ((E)-N-(1-(2-hydroxy-6-methyl-4-oxo-4H-pyran-3-yl) ethylidene) benzohydrazide), a selective dehydroacetic acid-based chemosensor, onto a mesoporous silica support. In order to prepare the sorbent, the silylating agent was anchored [...] Read more.

An inorganic–organic hybrid nano-adsorbent was prepared by chemical immobilisation of an organic Schiff base Cu (II) ion receptor, DHB ((E)-N-(1-(2-hydroxy-6-methyl-4-oxo-4H-pyran-3-yl) ethylidene) benzohydrazide), a selective dehydroacetic acid-based chemosensor, onto a mesoporous silica support. In order to prepare the sorbent, the silylating agent was anchored onto the silica. During this procedure, 3-Chloropropyl trimethoxy silane (CPTS) was attached to the surface, increasing hydrophobicity. By immobilising DHB onto the CPTS platform, the silica surface was activated, and as a result the coordination chemistry of the Schiff base generated a hybrid adsorbent with the capability to rapidly sequestrate Cu (II) ions from wastewater, as an answer to combat growing Waste Electrical and Electronic Equipment (WEEE) contamination in water supplies, in the wake of a prolonged consumerism mentality and boom in cryptocurrency mining. The produced hybrid materials were characterised by FTIR, proximate and ultimate analysis, nitrogen physisorption, PXRD, SEM, and TEM. The parameters influencing the removal efficiency of the sorbent, including pH, initial metal ion concentration, contact time, and adsorbent dosage, were optimised to achieve enhanced removal efficiency. Under optimal conditions (pH 7.0, adsorbent dosage 3 mg, contact time of 70 min, and 25 °C), Cu (II) ions were quantitatively sequestered from the sample solution; 93.1% of Cu (II) was removed under these conditions. The adsorption was found to follow pseudo-second-order kinetics, and Langmuir model fitting affirmed the monolayer adsorption. Full article

(This article belongs to the Special Issue The Application of Adsorption Technologies in Wastewater Treatment)

13 pages, 1003 KB

Open AccessArticle

Exploring and Documenting Wadi Phycodiversity: Cosmarium yassinii sp. nov. (Desmidiaceae, Charophyta)—A New Desmid Species from Egypt

by Abdullah A. Saber, Mostafa M. El-Sheekh, Forough Salehipour-Bavarsad, Hoda H. Senousy, Nicola Angeli, Frans A. C. Kouwets and Marco Cantonati

Water 2026, 18(2), 246; https://doi.org/10.3390/w18020246 - 16 Jan 2026

Abstract

A new desmid microalga species, Cosmarium yassinii A.A. Saber, El-Sheekh, Kouwets et Cantonati sp. nov., was isolated from two hyper-arid mountain valleys, so-called “wadis”, in the Eastern Desert of Egypt. The distinctive morphological features of this new species were established using light and [...] Read more.

A new desmid microalga species, Cosmarium yassinii A.A. Saber, El-Sheekh, Kouwets et Cantonati sp. nov., was isolated from two hyper-arid mountain valleys, so-called “wadis”, in the Eastern Desert of Egypt. The distinctive morphological features of this new species were established using light and scanning electron microscopy observations, and also by documenting its life-cycle stages. Taxonomically, C. yassinii is characterized by a cell wall sculpture consisting of isolated granules or small warts arranged circularly in the swollen mid-region of each semicell, never forming parallel vertical ridges or costae as in morphologically similar species, and the interesting shape of the marginal granules appears as small emarginate “combs” or crenae, including its knobby zygospores. Similarities and differences with the morphologically most closely related species are discussed in detail. Ecologically, C. yassinii seems to prefer alkaline freshwater environments with lower nutrient concentrations and a NaCl/HCO₃ water type. The detailed assessment and documentation of the biodiversity of these peculiar freshwater ecosystems are a fundamental prerequisite to adequately inform their protection strategies. Full article

(This article belongs to the Special Issue Protection and Restoration of Freshwater Ecosystems)

19 pages, 2476 KB

Open AccessArticle

Coagulation Coupled with the Contact Oxidation Biofilter Process for Malodorous Blackwater Treatment

by Ping Kuang, Hengheng Jiao, Yingxue Sun, Juan Peng and Xiaolei Zhang

Water 2026, 18(2), 245; https://doi.org/10.3390/w18020245 - 16 Jan 2026

Abstract

With accelerating urbanization, rivers have been severely polluted, resulting in widespread black and odorous waterways. The coagulation–sedimentation and contact oxidation bypass treatment process is characterized by low operational cost and simple operation and management. In this study, a coagulation–sedimentation–contact oxidation biofilter process was [...] Read more.

With accelerating urbanization, rivers have been severely polluted, resulting in widespread black and odorous waterways. The coagulation–sedimentation and contact oxidation bypass treatment process is characterized by low operational cost and simple operation and management. In this study, a coagulation–sedimentation–contact oxidation biofilter process was developed to treat heavily polluted malodorous blackwater. Among the tested biofilm carriers, rigid aramid fiber exhibited the fastest biofilm formation and the best pollutant removal performance. Based on a comprehensive evaluation of effluent quality and treatment capacity, the optimal operating conditions of the proposed process were identified as a PAC dosage of 50 mg/L, an air-to-water ratio of 7:1, and a hydraulic retention time (HRT) of 2 h. Under these conditions, the effluent concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and suspended solids (SSs) were consistently maintained below 30, 5, and 5 mg/L, respectively. Moreover, the optimized system demonstrated strong resistance to shock loading, maintaining stable operation at influent COD and SS concentrations of approximately 150 mg/L and 40 mg/L, respectively, while complying with the Class A Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants. This study provides an efficient treatment strategy for malodorous blackwater remediation. Full article

(This article belongs to the Topic Wastewater Treatment Based on AOPs, ARPs, and AORPs)

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21 pages, 1881 KB

Open AccessArticle

Geometry-Driven Hydraulic Behavior of Pressure-Compensating Emitters for Water-Saving Agricultural Irrigation Systems

by Mohamed Ghonimy, Abdulaziz Alharbi, Nermin S. Hussein and Hisham M. Imam

Water 2026, 18(2), 244; https://doi.org/10.3390/w18020244 - 16 Jan 2026

Abstract

Water-saving agricultural irrigation systems depend heavily on the hydraulic stability of pressure-compensating (PC) emitters, whose performance is fundamentally shaped by internal flow-path geometry. This study analyzes six commercial PC emitters (E1–E6) operated under pressures of 0.8–2.0 bar [...] Read more.

Water-saving agricultural irrigation systems depend heavily on the hydraulic stability of pressure-compensating (PC) emitters, whose performance is fundamentally shaped by internal flow-path geometry. This study analyzes six commercial PC emitters (E1–E6) operated under pressures of 0.8–2.0 bar to quantify how key geometric descriptors influence hydraulic parameters critical for efficient water use, including actual discharge (q_act), discharge coefficient (k), pressure exponent (x), emission uniformity (EU), and flow variability. All emitters had discharge deviations within ±7% of nominal values. Longer and more tortuous labyrinths enhanced compensation stability, while emitters with wider cross-sections and shorter paths produced higher throughput but weaker regulation efficiency. Linear mixed-effects modeling showed that effective flow area increased k, whereas normalized path length and tortuosity reduced both k and x. Predictive equations derived from geometric indicators closely matched measured values, with deviations below ±0.05 L/h for k and ±0.05 for x. These results establish a geometry-based hydraulic framework that supports emitter selection and design in water-saving agricultural irrigation, aligning with broader Agricultural Water–Land–Plant System Engineering objectives and contributing to more efficient and sustainable water-resource utilization. Full article

(This article belongs to the Special Issue Agricultural Water-Land-Plant System Engineering, 2nd Edition)

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17 pages, 4945 KB

Open AccessArticle

Effects of Simulated Water Depth and Nitrogen Addition on Phragmites australis Root Anatomy

by Mingyu Zhang, Changwei Zhang, Guijun Wang, Zhenwen Xu and Yanjing Lou

Water 2026, 18(2), 243; https://doi.org/10.3390/w18020243 - 16 Jan 2026

Abstract

Root anatomy serves as a critical indicator for understanding wetland plant adaptation strategies to environmental changes. Since water depth determines root oxygen demand while nitrogen addition regulates nutrient acquisition, the two factors exert significant and interactive effects on root anatomical structure. In this [...] Read more.

Root anatomy serves as a critical indicator for understanding wetland plant adaptation strategies to environmental changes. Since water depth determines root oxygen demand while nitrogen addition regulates nutrient acquisition, the two factors exert significant and interactive effects on root anatomical structure. In this study, we established a controlled experiment employing three water depth treatments (W1: −10 cm; W2: 10 cm; W3: 30 cm), two nitrogen (N) forms (ammonium-N, nitrate-N), and four N addition levels (N0: 0 mg/L; N1: 40 mg/L; N2: 80 mg/L; N3: 160 mg/L). This design enabled us to analyze the effects of water–nitrogen interactions on the anatomical structure of reed roots to reveal wetland plants’ adaptive strategies to water-nitrogen fluctuations. The results indicate that (1) under nitrogen-free treatment, compared to the control group, the W1 treatment reduced the root aerenchyma proportion and the stele-to-root diameter ratio by 15.8% and 37.0%, respectively. In contrast, exodermis thickness increased by 32.4%, while epidermis thickness decreased by 33.7%. Under the W3 treatment, the aerenchyma proportion increased by 21.0%, the stele-to-root diameter ratio decreased by 22.2%, and exodermis thickness increased by 35.3%. (2) Compared to the nitrogen-free treatment, nitrate addition increased the root aerenchyma proportion under W1, W2, and W3 by 18.8%, 6.9%, and 18.3%. The stele-to-root diameter ratio increased by 27.9% and 12.7% under W1 and W2, but decreased by 10.8% under W3. Exodermis thickness increased by 26.3% under W2, whereas it decreased by 10.8% under W3. Epidermis thickness increased by 36.1% and 22.2% under W1 and W3, while a decrease of 12.7% occurred under W2. (3) Compared to the nitrogen-free treatment, ammonium addition increased the root aerenchyma proportion under W1, W2, and W3 by 13.6%, 13.2%, and 10.0%. The stele-to-root diameter ratio increased by 28.1% under W1 but decreased by 10.4% under W3. Conversely, exodermis thickness decreased by 20.2% under W1 while increasing by 12.6% under W3. Epidermis thickness increased by 26.3% and 20.8% under the W1 and W3 treatments. In summary, the root anatomical structure of P. australis adaptively responds to variations in water depth, nitrogen forms, and nitrogen concentrations by modulating aerenchyma proportion, the stele-to-root diameter ratio, exodermis thickness, and epidermis thickness. Future research should strengthen the study of the relationship between root anatomical traits and plant functions, to more comprehensively explore the adaptation mechanisms of wetland plants to global environmental change. Full article

(This article belongs to the Section Ecohydrology)

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14 pages, 2829 KB

Open AccessArticle

Study on the Characteristics of Horizontal Well Air Sparging and the Behavior of Pollutant Retention

by Hui Su, Hao Wang, Jianbo Yin, Benhang Li, Wenyue Lu, Qiang Xu, Xiaoping Liu, Haicui Wang and Xuebin Zhang

Water 2026, 18(2), 242; https://doi.org/10.3390/w18020242 - 16 Jan 2026

Abstract

Horizontal well air sparging (HAS) technology provides a promising approach for pollution remediation. In this study, a model experiment assessed the airflow distribution characteristics of HAS under varying air sparging (AS) pressure, tube burial depth, and groundwater flow conditions, while evaluating the retardation [...] Read more.

Horizontal well air sparging (HAS) technology provides a promising approach for pollution remediation. In this study, a model experiment assessed the airflow distribution characteristics of HAS under varying air sparging (AS) pressure, tube burial depth, and groundwater flow conditions, while evaluating the retardation effects of HAS on dissolved groundwater contaminants. The results indicated that airflow velocity and diffusion range increased markedly with elevated AS pressure. Deeper AS tube burial depths resulted in more uniform airflow distribution and broader coverage. Groundwater flow significantly affected airflow distribution, as greater water head differences induced a downstream shift in the airflow pattern, resulting in an asymmetric diffusion range. Regarding pollutant retardation, airflow created a physical barrier by reducing permeability and interfacial resistance, effectively hindering pollutant diffusion. Airflow from the AS tube aligned parallel to the flow direction reduced Rhodamine B concentration by 53.1% over 300 min, preventing deeper pollutant migration into the sand layer. Conversely, airflow from the AS tube oriented perpendicular to the flow direction reduced Rhodamine B concentration by 84.38% over the same period, demonstrating superior effectiveness in limiting horizontal pollutant diffusion. These findings provide valuable theoretical insights and practical guidance for implementing HAS technology in groundwater pollution management. Full article

(This article belongs to the Section Hydrogeology)

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13 pages, 2173 KB

Open AccessArticle

Daily Streamflow Prediction Using Multi-State Transition SB-ARIMA-MS-GARCH Model

by Jin Zhao, Jianhui Shang, Qun Ye, Huimin Wang, Gengxi Zhang, Feng Yao and Weiwei Shou

Water 2026, 18(2), 241; https://doi.org/10.3390/w18020241 - 16 Jan 2026

Abstract

Under the combined influences of climate change and anthropogenic activities, the variability of basin streamflow has intensified, posing substantial challenges for accurate prediction. Although Generalized Autoregressive Conditional Heteroskedasticity (GARCH) models characterize volatility in time series, many previous studies have neglected changes in series [...] Read more.

Under the combined influences of climate change and anthropogenic activities, the variability of basin streamflow has intensified, posing substantial challenges for accurate prediction. Although Generalized Autoregressive Conditional Heteroskedasticity (GARCH) models characterize volatility in time series, many previous studies have neglected changes in series structure, leading to inaccurate identification of the form of volatility. Building on tests for structural breaks (SBs) in time series, this study first removes the series mean using an Autoregressive Integrated Moving Average (ARIMA) model and then incorporates Markov-switching (MS) to develop a multi-state MS-GARCH model. An asymmetric MS-GARCH (MS-gjrGARCH) variant is also incorporated to describe the volatility of streamflow series with SBs. Daily streamflow data from five hydrological stations in the middle reaches of the Yellow River are used to compare the predictive performance of SB-ARIMA-MS-GARCH, SB-ARIMA-MS-gjrGARCH, ARIMA-GARCH, and ARIMA-gjrGARCH models. The results show that daily streamflow exhibits SBs, with the number and timing of breakpoints varying among stations. Standard GARCH and gjrGARCH models have limited ability to capture runoff volatility clustering, whereas MS-GARCH and MS-gjrGARCH effectively characterize volatility features within individual states. The multi-state switching structure substantially improves daily streamflow prediction accuracy compared with single-state volatility models, increasing R² by approximately 5.8% and NSE by approximately 36.3%.The proposed modeling framework offers a robust new tool for streamflow prediction in such changing environments, providing more reliable evidence for water resource management and flood risk mitigation in the Yellow River basin. Full article

(This article belongs to the Special Issue Advances in Research on Hydrology and Water Resources)

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27 pages, 2979 KB

Open AccessArticle

A Study on the Measurement and Spatial Non-Equilibrium of Marine New-Quality Productivity in China: Differences, Polarization, and Causes

by Yao Wu, Renhong Wu, Lihua Yang, Zixin Lin and Wei Wang

Water 2026, 18(2), 240; https://doi.org/10.3390/w18020240 - 16 Jan 2026

Abstract

Compared to traditional marine productivity, marine new-quality productivity (MNQP) is composed of advanced productive forces driven by the deepening application of new technologies, is characterized by the rapid emergence of new industries, new business models, and new modes of operation, and [...] Read more.

Compared to traditional marine productivity, marine new-quality productivity (MNQP) is composed of advanced productive forces driven by the deepening application of new technologies, is characterized by the rapid emergence of new industries, new business models, and new modes of operation, and is marked by a substantial increase in total factor productivity in the marine economy. It has, therefore, become a new engine and pathway for China’s development into a maritime power. The main research approaches and conclusions of this paper are as follows: ① Using a combined order relation analysis method–Entropy Weight Method (G1-EWM) weighting method that integrates subjective and objective factors, we measured the development level of China’s MNQP from 2006 to 2021 across two dimensions: “factor structure” and “quality and efficiency”. The findings indicate that China’s MNQP is developing robustly and still holds considerable potential for improvement. ② Utilizing Gaussian Kernel Density Estimation and Spatial Markov Chain analysis to examine the dynamic evolution of China’s MNQP, the study identifies breaking the low-end lock-in of MNQP as crucial for accelerating balanced development. Spatial imbalances in China’s MNQP may exist both at the national level and within the three major marine economic zones. ③ To further examine potential spatial imbalances, Dagum Gini decomposition was employed to assess regional disparities in China’s MNQP. The DER polarization index and EGR polarization index were used to analyze spatial polarization levels, revealing an intensifying spatial imbalance in China’s MNQP. ④ Finally, geographic detectors were employed to identify the factors influencing spatial imbalances in China’s MNQP. Results indicate that these imbalances result from the combined effects of multiple factors, with marine economic development emerging as the core determinant exerting a dominant influence. The core conclusions of this study provide theoretical support and practical evidence for advancing the enhancement of China’s MNQP, thereby contributing to the realization of the goal of building a maritime power. Full article

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

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27 pages, 11028 KB

Open AccessArticle

Integration of Satellite-Derived Meteorological Inputs into SWAT, XGBoost, WGAN, and Hybrid Modelling Frameworks for Climate Change-Driven Streamflow Simulation in a Data-Scarce Region

by Sefa Nur Yeşilyurt and Gülay Onuşluel Gül

Water 2026, 18(2), 239; https://doi.org/10.3390/w18020239 - 16 Jan 2026

Abstract

The pressure of climate change on water resources has made the development of reliable hydrological models increasingly important, especially for data-scarce regions. However, due to the limited availability of ground-based observations, it considerably affects the accuracy of models developed using these inputs. This [...] Read more.

The pressure of climate change on water resources has made the development of reliable hydrological models increasingly important, especially for data-scarce regions. However, due to the limited availability of ground-based observations, it considerably affects the accuracy of models developed using these inputs. This also limits the ability to investigate future hydrological behavior. Satellite-based data sources have emerged as an alternative to address this challenge and have received significant attention. However, the transferability of these datasets across different model classes has not been widely explored. This paper evaluates the transferability of satellite-derived inputs to eleven types of models, including process-based (SWAT), data-driven methods (XGBoost and WGAN), and hybrid model structures that utilize SWAT outputs with AI models. SHAP has been applied to overcome the black-box limitations of AI models and gain insights into fundamental hydrometeorological processes. In addition, uncertainty analysis was performed for all models, enabling a more comprehensive evaluation of performance. The results indicate that hybrid models using SWAT combined with WGAN can achieve better predictive accuracy than the SWAT model based on ground observation. While the baseline SWAT model achieved satisfactory performance during the validation period (NSE ≈ 0.86, KGE ≈ 0.80), the hybrid SWAT + WGAN framework improved simulation skill, reaching NSE ≈ 0.90 and KGE ≈ 0.89 during validation. Models forced with satellite-derived meteorological inputs additionally performed as well as those forced using station-based observations, validating the feasibility of using satellite products as alternative data sources. The future hydrological status of the basin was assessed based on the best-performing hybrid model and CMIP6 climate projections, showing a clear drought signal in the flows and long-term reductions in average flows reaching up to 58%. Overall, the findings indicate that the proposed framework provides a consistent approach for data-scarce basins. Future applications may benefit from integrating spatio-temporal learning frameworks and ensemble-based uncertainty quantification to enhance robustness under changing climate conditions. Full article

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

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17 pages, 1188 KB

Open AccessArticle

Simulation Experiment on the Effect of Saline Reclaimed Water Recharge on Soil Water and Salt Migration in Xinjiang, China

by Jiangwen Qin, Tao Zhou, Jihong Zhang, Tao Zhao, Ankun Wang, Hongbang Liang, Wenhao Li and Meng Li

Water 2026, 18(2), 238; https://doi.org/10.3390/w18020238 - 16 Jan 2026

Abstract

This study investigates the effects of saline reclaimed water recharge on soil salt accumulation and water migration in Xinjiang, China, aiming to provide scientific guidance for the sustainable utilization of reclaimed water in arid regions. Indoor vertical infiltration simulation experiments were conducted using [...] Read more.

This study investigates the effects of saline reclaimed water recharge on soil salt accumulation and water migration in Xinjiang, China, aiming to provide scientific guidance for the sustainable utilization of reclaimed water in arid regions. Indoor vertical infiltration simulation experiments were conducted using reclaimed water with varying salinity levels (0, 1, 2, 3, and 4 g L⁻¹) to evaluate their impacts on soil water–salt distribution and infiltration dynamics. Results showed that irrigation with saline reclaimed water increased soil pH and significantly enhanced both the infiltration rate and wetting front migration velocity, while causing only minor changes in the moisture content of the wetted zone. When the salinity was 2 g L⁻¹, the observed improvement effect was the most significant. Specifically, the cumulative infiltration increased by 22.73% after 180 min, and the time required for the wetting peak to reach the specified depth was shortened by 21.74%. At this salinity level, the soil’s effective water storage capacity reached 168.19 mm, with an average moisture content increase of just 6.20%. Soil salinity increased with the salinity of the irrigation water, and salts accumulated at the wetting front as water moved downward, resulting in a characteristic distribution pattern of desalination in the upper layer and salt accumulation in the lower layer. Notably, reclaimed water recharge reduced soil salinity in the 0–30 cm layer, with salinity in the 0–25 cm layer decreasing below the crop salt tolerance threshold. When the salinity of the reclaimed water was ≤2 g L⁻¹, the salt storage in the 0–30 cm layer was less than 7 kg ha⁻¹, achieving a desalination rate exceeding 60%. Reclaimed water with a salinity of 2 g L⁻¹ enhanced infiltration (wetting front depth increased by 27.78%) and desalination efficiency (>60%). These findings suggest it is well suited for urban greening and represents an optimal choice for the moderate reclamation of saline-alkali soils in arid environments. Overall, this study provide a reference for the water quality threshold and parameters of reclaimed water for urban greening, farmland irrigation, and saline land improvement. Full article

(This article belongs to the Special Issue Synergistic Management of Water, Fertilizer, and Salt in Arid Regions)

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21 pages, 13519 KB

Open AccessArticle

Development and Application of a Distributed Hydrological Model Ensemble (DHM-FEWS) for Flash Flood Early Warning

by Xiao Liu, Kaihua Cao, Ronghua Liu, Yanhong Dou, Min Xie, Delong Li, Hongqing Xu and Yunrui Zhang

Water 2026, 18(2), 237; https://doi.org/10.3390/w18020237 - 16 Jan 2026

Abstract

Mountain floods, one of the most common and destructive natural disasters worldwide, pose significant challenges to disaster prevention due to their sudden onset, high destructive power, and severe localized impacts. This study proposes an innovative flash flood early warning system based on a [...] Read more.

Mountain floods, one of the most common and destructive natural disasters worldwide, pose significant challenges to disaster prevention due to their sudden onset, high destructive power, and severe localized impacts. This study proposes an innovative flash flood early warning system based on a distributed hydrological model ensemble. The main objective is to improve the prediction and early warning accuracy of flash flood disasters by integrating multi-source data and regional modeling. The system simulates flood flow and risk levels under different rainfall scenarios to provide timely warnings in mountainous areas. A case study of a heavy rainfall event in Ma Jia Natural Village, Jiangxi Province was used to validate the system’s performance. Through regionalized parameter calibration within the ensemble, the system achieved Nash–Sutcliffe Efficiency (NSE) values exceeding 0.88, while the simulated peak discharges deviated from observed values by only 1.5%, 9.5%, and 4.8% under 3 h, 6 h, and 24 h rainfall scenarios, respectively, demonstrating the improved quantitative accuracy of flood prediction enabled by the ensemble-based framework. The system showed high consistency with observed data, accurately predicting flood responses at 3, 6, and 24 h time scales and providing reliable risk warnings. This approach not only enhances warning accuracy across multiple temporal scales but also supports risk-level early warnings at both river-section and village scales, offering significant practical value for the prevention of mountainous flood disasters. Full article

(This article belongs to the Section Hydrology)

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5 pages, 159 KB

Open AccessEditorial

Agricultural Water-Land-Plant System Engineering—Updated Achievements to Improve Crop Growth

by Haijun Liu

Water 2026, 18(2), 236; https://doi.org/10.3390/w18020236 - 16 Jan 2026

Abstract

To meet the needs of an estimated 9 [...] Full article

(This article belongs to the Special Issue Agricultural Water-Land-Plant System Engineering)

19 pages, 2956 KB

Open AccessArticle

Mechanisms and Efficacy of Thermally Modified Dolomite-Rich Phosphate Tailings as a Novel Adsorbent for Phosphorus Removal

by Yongjie Guo, Caixia Guo, Jiangli Li, Yuanchong Huang, Shuai Xu, Xing Zhao and Kunzhi Li

Water 2026, 18(2), 235; https://doi.org/10.3390/w18020235 - 16 Jan 2026

Abstract

The global environmental challenges of solid waste accumulation and aquatic eutrophication demand innovative and sustainable strategies. This study introduces a circular “waste-treats-waste” approach by converting dolomite-rich phosphate tailings (PT), a widespread industrial by-product, into a high-value adsorbent for phosphorus (P) removal. Thermal modification [...] Read more.

The global environmental challenges of solid waste accumulation and aquatic eutrophication demand innovative and sustainable strategies. This study introduces a circular “waste-treats-waste” approach by converting dolomite-rich phosphate tailings (PT), a widespread industrial by-product, into a high-value adsorbent for phosphorus (P) removal. Thermal modification at 950 °C for 1 h dramatically enhanced the adsorption capacity by approximately 45 times, from 2.52 mg/g (raw PT) to 112.41 mg/g. This performance is highly competitive with, and often superior to, many engineered adsorbents. The calcination process was pivotal, decomposing carbonates into highly active CaO and MgO while developing a porous structure. Using a multi-technique characterization approach (X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), TESCAN VEGA3 tungsten filament scanning electron microscope (SEM), the Brunauer–Emmett–Teller method (BET)), the key immobilization mechanism was identified as hydroxyapatite formation, driven by Ca²⁺/Mg²⁺-phosphate precipitation and surface complexation. Nonlinear regression analysis revealed that the adsorption kinetics obeyed the pseudo-second-order model, and the equilibrium data were best described by the Freundlich isotherm. This indicates a chemisorption process occurring on a heterogeneous surface, consistent with the complex structure created by thermal modification. Notably, post-adsorption pore structure expansion suggested synergistic pore-filling and surface reorganization. This work not only demonstrates a circular economy paradigm for repurposing industrial solid waste on a global scale but also offers a cost-effective and high-performance pathway for controlling phosphorus pollution in aquatic systems, contributing directly to resource efficiency and sustainable environmental remediation. Full article

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

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22 pages, 6124 KB

Open AccessArticle

High-Resolution Monitoring of Badland Erosion Dynamics: Spatiotemporal Changes and Topographic Controls via UAV Structure-from-Motion

by Yi-Chin Chen

Water 2026, 18(2), 234; https://doi.org/10.3390/w18020234 - 15 Jan 2026

Abstract

Mudstone badlands are critical hotspots of erosion and sediment yield, and their rapid morphological changes serve as an ideal site for studying erosion processes. This study used high-resolution Unmanned Aerial Vehicle (UAV) photogrammetry to monitor erosion patterns on a mudstone badland platform in [...] Read more.

Mudstone badlands are critical hotspots of erosion and sediment yield, and their rapid morphological changes serve as an ideal site for studying erosion processes. This study used high-resolution Unmanned Aerial Vehicle (UAV) photogrammetry to monitor erosion patterns on a mudstone badland platform in southwestern Taiwan over a 22-month period. Five UAV surveys conducted between 2017 and 2018 were processed using Structure-from-Motion photogrammetry to generate time-series digital surface models (DSMs). Topographic changes were quantified using DSMs of Difference (DoD). The results reveal intense surface lowering, with a mean erosion depth of 34.2 cm, equivalent to an average erosion rate of 18.7 cm yr⁻¹. Erosion is governed by a synergistic regime in which diffuse rain splash acts as the dominant background process, accounting for approximately 53% of total erosion, while concentrated flow drives localized gully incision. Morphometric analysis shows that erosion depth increases nonlinearly with slope, consistent with threshold hillslope behavior, but exhibits little dependence on the contributing area. Plan and profile curvature further influence the spatial distribution of erosion, with enhanced erosion on both strongly concave and convex surfaces relative to near-linear slopes. The gully network also exhibits rapid channel adjustment, including downstream meander migration and associated lateral bank erosion. These findings highlight the complex interactions among hillslope processes, gully dynamics, and base-level controls that govern badland landscape evolution and have important implications for erosion modeling and watershed management in high-intensity rainfall environments. Full article

(This article belongs to the Section Water Erosion and Sediment Transport)

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