Search Results (1,336)

This study focuses on the calibration and verification of a large-scale coupled numerical model to simulate the complex hydrodynamic–wave–sediment transport processes in the coastal and estuarine regions of the Mekong River Delta (MRD), Vietnam. Using the MIKE 21/3 modeling system, the research integrates Hydrodynamics (HD), Spectral Wave (SW), and Mud Transport (MT) modules across a computational domain of 270 × 300 km. The models were rigorously tested using field measurement data from three distinct periods: May 2004 (dry season calibration), September 2017 (first verification), and June 2024 (second verification). The results from the hydrodynamic model demonstrated high accuracy in predicting water levels, with the average Root Mean Square Error (RMSE) values ranging between 4.4% and 5.8%. The wave spectral model showed reliable performance, with the average RMSE values for wave height ranging from 15.1% to 18.0%. Furthermore, the Mud Transport module successfully captured suspended sediment concentrations (SSC), yielding average RMSE values between 26.0% and 32.1% after the fine-tuning of site-specific parameters such as critical shear stress for erosion and deposition. The study highlights the critical importance of utilizing site-specific sedimentological parameters to accurately predict morphological changes in highly dynamic estuarine environments. This validated model provides a robust tool for assessing coastal erosion and developing protection measures in regions that are increasingly vulnerable to climate change and human activities. Full article

In the effort to mitigate climate change, the Marine Hydrokinetic (MHK) energy from ocean currents emerges as an important renewable source due to its large potential, although it remains underexploited. In the Southwestern Tropical Atlantic, surface potentials linked to the North Brazil Current (NBC) are known, but the subsurface North Brazil Undercurrent (NBUC) remained unquantified. This study addressed this gap by applying a two-step approach using more than 20 years of high-resolution (1/12°) climatological and daily reanalysis data to estimate current power density (CPD) throughout the water column along the Brazilian shelf (4° N–12° S), with focus on energetic hotspots where maximum CPD exceeds 1000 W m⁻². The climatological analysis revealed 12 persistent hotspots (H1–H12). Daily analyses show highly energetic but seasonally variable surface hotspots north of 4° S linked to the NBC (H4–H12; >885 W·m⁻²) and weaker but more stable subsurface hotspots south of 4° S associated with the NBUC at depths of 130–266 m (H1–H3; 831–808 W·m⁻²). These patterns are likely influenced by flow–topography interactions along the continental margin. Overall, subsurface resources exhibit greater reliability than surface counterparts, highlighting the importance of incorporating subsurface dynamics in future MHK assessments and development along the Brazilian margin. Full article

The Santos Estuarine System, one of the most anthropogenically impacted coastal regions in Brazil, was studied using benthic foraminiferal assemblages to determine four distinct stages of organic pollution. Predictive models combined with the Ecological Quality Status (EcoQs) index were applied to relate pollution stages to abiotic parameters (total organic carbon, mud content, and salinity variability) and organic contaminants, including aliphatic (AHs) and aromatic hydrocarbons (PAHs), linear alkylbenzenes (LABs), and coprostanol. The pollution gradient ranged from low (São Vicente Channel and Santos Bay, characterized by Ammonia tepida and medium coprostanol concentrations), to moderate (Santos Channel, with Bulimina elongata and Triloculina sp.1), high (Bertioga Channel, showing Cribroelphidium poeyanum, Paratrochammina sp.1, high levels of LABs, and TOC), and severe (Upper Estuary, marked by Ammonia sp.1 and high concentrations of PAHs and coprostanol). A linear discriminant analysis (LDA) demonstrated an overall accuracy of 70%, suggesting that the discriminant model performs reasonably well in predicting the predictive ability of foraminifera species to distinguish between areas with varying pollution status based on organic pollutants. Also, the potential use of the EcoQs index in assessing the environmental quality of a subtropical estuary subjected to organic pollution was demonstrated. Full article

Dissolved organic matter (DOM) is central to biogeochemical cycles in estuarine-coastal zones, with its source-sink dynamics linking regional ecological functions to global carbon budgets. As a typical semi-enclosed bay in southern China, Zhanjiang Bay (ZJB) features intense tidal mixing and significant seasonal runoff variations, making it a representative system for understanding DOM dynamics in complex land–sea interaction zones. The migration of dissolved organic carbon (DOC) is crucial for bay carbon budgets, yet its estimation is constrained by land–water interface dynamics and in situ observation limitations. To clarify the regulation of DOM’s fate and exchange flux in ZJB, this study integrated in situ observations, ultraviolet spectroscopy, and three-dimensional fluorescence techniques to analyze DOM tidal dynamics and net DOC exchange flux. Results indicated terrestrial runoff dominated rainy-season DOC sources, resulting in slightly higher concentrations (1.86 ± 0.46 mg·L⁻¹) compared to the dry season (1.82 ± 0.20 mg·L⁻¹). Terrestrial inputs endowed rainy-season DOM with high molecular weight and aromaticity, with microbial humic substances (C2) accounting for 36%. Tidal fluctuations affected DOC via water exchange: ebb tides diluted concentrations with low-DOC open-ocean seawater, while flood tides increased them through high-DOC bay water discharge. Dry-season DOM relied on in situ biotransformation, characterized by low molecular weight and aromaticity, with the protein-like fraction (C4) accounting for 24.3%. Fluorescence index (FI = 1.77–1.79) confirmed DOM as a mixture of allochthonous and autochthonous sources, with significant in situ contributions and weak humification. Net DOC exchange flux, regulated by terrestrial runoff, was 3.6–4.6 times higher in the rainy season, decreasing from the estuary to the coast. In conclusion, the joint regulation of terrestrial runoff-driven seasonal dynamics and tidal water exchange governs ZJB’s DOM dynamics, providing valuable insights for biogeochemical research in semi-enclosed bays. Full article

Anthropogenic increases in nitrogen and phosphorus inputs have intensified coastal water pollution, leading to economic losses and even threats to human health. Dissolved Inorganic Nitrogen (DIN) and Dissolved Inorganic Phosphorus (DIP), as key indicators of water quality, are essential for formulating environmental protection strategies. While deep learning has advanced the retrieval of these nutrients in coastal waters, existing models remain constrained by limited accuracy, insufficient interpretability, and poor regional transferability. To address these issues, we developed a Transformer-based model for retrieving DIN and DIP in the Jiangsu-Zhejiang-Shanghai (JZS) Offshore, integrating satellite observations with reanalysis data. Our model outperformed previous studies in this region, achieving high retrieval accuracy for DIN (R² = 0.88, RMSE = 0.16 mg/L, and MAPE = 33.69%) and DIP (R² = 0.85, RMSE = 0.007 mg/L, and MAPE = 31.59%) with strong interpretability. Based on this model, we generated a long-term (2005–2024) dataset, revealing clear seasonality and spatial patterns of DIN and DIP. Specifically, the concentrations have a distinct seasonal cycle with winter minima and autumn maxima, as well as estuarine-to-offshore decreasing gradient. Water quality assessment further showed that the areal extent of medium-to-high eutrophic waters increased by 3.94 × 10² km²/yr (2005–2016) but decreased by 4.45 × 10² km²/yr (2016–2024). Overall, the proposed Transformer-based framework provided a robust, accurate, and interpretable tool for nitrogen and phosphorus nutrient retrieval, supporting sustainable management of marine water quality in the JZS coastal ecosystems. Full article

Under the dual pressures of rapid urbanization and climate change, urban expansion in high-density estuarine urban agglomerations has intensified economic–ecological trade-offs in the aquatic–terrestrial ecotone, necessitating land-use planning that reconciles economic growth with ecological protection. Here, we integrated linear programming with the CLUE-S model and incorporated marine–terrestrial integration objectives and typical natural disturbance factors. With this approach, a landscape pattern simulation framework capable of jointly optimizing ecological and economic benefits was developed. The framework was applied to the estuarine aquatic–terrestrial ecotone of the Pearl River Delta. This study drew on a land-use dataset, landscape dynamics, socioeconomic and biophysical drivers, and regional planning constraints to conduct simulation experiments under alternative development scenarios. The model achieved a Kappa coefficient of 0.904. From 2010 to 2020, built-up land expanded rapidly and encroached on ecological space. Simulations indicated that the natural evolution scenario increased fragmentation and ecological conflicts despite economic gains, whereas the sustainable development scenario balanced expansion and protection, reduced forestland fragmentation, safeguarded key ecological spaces, and improved ecological benefits while maintaining economic growth. Ecological benefits in the coastal aquatic–terrestrial ecotone from −0.2 to 0 km increased by 283.3%. The framework embeds land-use dynamics and spatial constraints, providing decision support for territorial spatial planning and ecological security pattern optimization. Full article

The phytoplankton community structure is regulated by environmental conditions, influencing ecosystem stability and productivity. In August 2023, a survey was conducted at 28 stations in the Yellow River Estuary (YRE) and adjacent coastal waters, where phytoplankton communities, nutrients, chlorophyll-a, and other environmental factors were synchronously analyzed. Across-site comparison, redundancy analysis (RDA), and K-means clustering were applied to characterize spatial patterns and identify key factors controlling diatom to dinoflagellate ratios and dominant taxa. The nutrient structure, particularly DIN/PO₄³⁻, corresponded closely with the spatial shift between diatom and dinoflagellate dominance. Offshore areas dominated by diatoms (Cerataulina, Chaetoceros) exhibited higher salinity and more balanced nutrient ratios, whereas nearshore zones influenced by Yellow River inputs had high DIN, low PO₄³⁻, and evident phosphorus limitation, favoring dinoflagellates (Noctiluca, Heterodinium). These results indicate that nutrient imbalance and salinity gradients are likely the main drivers of diatom-to-dinoflagellate transitions and shape the phytoplankton composition in the estuary coastal waters. This study provides insights linking nutrient imbalance to phytoplankton community succession and advances the understanding of estuarine phytoplankton dynamics. Full article

A macrotidal estuary with mountain-stream inputs (MEMSs) is characterized by strong hydrodynamic forcing, high turbidity, and complex channel morphology. This study combines field measurements (2005–2020) with a 2D hydrodynamic–sediment model to examine estuarine turbidity maximum (ETM) dynamics, erosion–deposition patterns, and the effects of engineering interventions in the Jiaojiang Estuary (JJE). Results show that the coupled influence of upstream floods and downstream macrotides produces highly seasonal and spatially variable water–sediment processes: mountain-stream floods exhibit sharp hydrodynamic fluctuations, and the estuary displays pronounced tidal-wave deformation. Over the 15-year observation period, the riverbed experienced alternating erosion (up to −3.5 m) and deposition (up to +4.2 m), with net erosion of 0.5–1.2 m occurring in most Ling River sections during high-discharge years. The ETM migrated about 30 km during spring tides, with near-bed suspended sediment concentrations reaching 50–60 kg/m³. Human activities—particularly historical sand mining—modified channel geometry and sediment composition, intensifying the exchange between bed material and suspended sediment and facilitating the formation and migration of the ETM. Extreme events further enhanced geomorphic adjustment: the post-Lekima (2019) flood produced maximum scour of −5.8 m in the upper Ling River and deposition of +3.2 m in the Jiaojiang main channel within weeks. Channel curvature and junction morphology strongly controlled flood-level distribution. Model experiments indicate that lowering shoal elevations and widening the cross-section at key constrictions can effectively reduce flood levels. Collectively, these findings clarify the morphodynamic evolution mechanisms of a MEMS system and provide quantitative guidance for flood-mitigation and estuarine-management strategies. Full article

Biochemical Oxygen Demand (BOD) is a key indicator of organic pollution and a proxy indicator reflecting organic loading that can indirectly influence eutrophication processes in aquatic systems. This study presents a spatially explicit, physically based modeling framework for simulating BOD dynamics in the urbanizing Chao Phraya and Tha Chin Rivers Basin in central Thailand. The framework integrates the Personal Computer Storm Water Management Model (PCSWMM) with GIS-based datasets to represent pollutant sources, hydraulic flow, and land use. The model was calibrated and validated using data from 36 monitoring stations (2021–2022), achieving strong performance: an NSE of 0.72 and an MAE of 0.35 mg/L for the Chao Phraya River, and an NSE of 0.88 and an MAE of 0.12 mg/L for the Tha Chin River. Scenario simulations for 2032 projected BOD concentrations exceeded 4 mg/L in several downstream segments under the baseline (no-intervention) scenario, indicating elevated organic pollution and potential oxygen depletion that may indirectly exacerbate eutrophication risk in the Upper Gulf of Thailand, particularly in tidal zones with low dilution and nutrient accumulation. Model projections suggest that effective mitigation would require a 20–30% reduction in BOD loads, achievable through enhanced wastewater treatment and stricter pollution controls. Although BOD reduction alone cannot eliminate eutrophication, it supports broader nutrient management efforts by improving baseline water quality conditions. The proposed model offers a robust tool for identifying pollution hotspots, evaluating management strategies, and informing integrated river basin policies under continued urban growth. Full article

Estuarine organisms experience frequent fluctuations in salinity and temperature, facing major challenges to their physiological homeostasis. Such variability can promote high energetic costs for osmoregulation, potentially reducing tolerance to additional stressors. We investigated the effect of salinity on the thermal tolerance of the estuarine amphipod Melita palmata (Montagu, 1804), a species of growing interest for aquaculture, either as live feed or as a potential source for essential fatty acids in formulated diets. The critical thermal maximum (CTmax) was determined for males and females collected from three sites within a temperate coastal lagoon (Ria de Aveiro, Portugal) characterized by different salinity regimes (15, 20, and 30). Individuals from lower-salinity environments exhibited significantly lower CTmax values than those from higher salinities, indicating that osmoregulatory costs may restrict thermal resistance. No significant sex-based differences in CTmax were detected. However, thermal safety margins (TSMs) increased with salinity, indicating greater thermal tolerance under higher salinity conditions, and differences in body condition index (BCI) between sites suggest salinity-related effects on growth performance. These results highlight that the elevated energetic demands of osmoregulation under hypo-osmotic conditions can constrain the thermal limits of M. palmata, underscoring the complex trade-offs between environmental variability and physiological performance in estuarine habitats. Beyond its ecological implications, understanding the physiological responses of M. palmata to salinity and temperature is key, optimising its use in aquaculture. The species’ physiological plasticity under such variable conditions reinforces its suitability for aquaculture production, particularly in earthen ponds in estuarine environments. Full article

The new estuarine goby Eugnathogobius ganuensis n. sp. is described from 5 specimens (4 males: 27.0–31.5 mm standard length; 1 female: 27.5 mm standard length) collected from a small ditch in the lower reach of the Terengganu River basin, east coast of Peninsular Malaysia. The new species is easily distinguished from other congeners, except E. kabilia, by the following a combination of characteristics: 16 segmented caudal-fin rays; 30 or 31 longitudinal scale lows; high first dorsal fin (especially in males); no head pores; shoulder with oblique black band; transverse black markings on each scale; paired black blotches on caudal-fin base; and distinct black dots on upper caudal fin. Although E. kabilia is very similar to the new species, the latter has a shorter jaw in males (well-extended in the former), high first dorsal fin (low), first dorsal-fin second spine length > 16.8% of standard length (<13.6%), throat yellowish in the fresh condition (whitish), and a yellowish second dorsal fin (reddish in males of E. kabilia). Because the type locality of the new species is clearly not a natural environmental feature and no salinity during the low tide, despite being included in the tidal area, the true habitat is suggested as being the upper reaches of estuarine areas. Full article

The differentiated responses of biological groups to environmental change are central to river ecosystem management; however, the shared and distinct environmental selection processes that shape their spatial patterns remain understudied. We investigated two adjacent rivers with contrasting environmental conditions and applied eDNA metabarcoding to characterize the eukaryotic plankton and fish communities. The alpha diversity showed no significant river-to-river difference for either group, but beta diversity differed strongly, indicating high spatial turnover. Both groups exhibited distance–decay relationships, which were stronger in plankton, whose community assembly was mainly stochastic; in contrast, fish assembly was predominantly deterministic. Community variation in both groups was significantly associated with physical and chemical factors—electrical conductivity (EC), the potential of hydrogen (pH), water temperature (WT), dissolved oxygen (DO), chemical oxygen demand (COD), and biochemical oxygen demand (BOD5)—while plankton also responded to nutrient variables, including total phosphorus (TP), total nitrogen (TN), and ammonium nitrogen (NH4-N). Collectively, our results emphasize differential environmental selection across biological groups and provide a basis for designing targeted river restoration and water quality improvement strategies. Full article

The transplanting of juvenile and adult mussels onto soft sediments is an emerging technique for the ecological restoration of the biogenic habitat formed by mussels. While these habitats are often found within estuarine systems, the spatial suitability of these environments for restoration is poorly described. The dynamic and variable environmental conditions characteristic of estuaries could represent challenges to the persistence of restored mussel beds. To assess whether there are spatial differences in mussel responses to transplantation within an estuarine environment, six experimental mussel beds of adult green-lipped mussels (Perna canaliculus) were established along an environmental gradient in a small estuarine harbour in northern New Zealand. Transplanted mussel beds were sampled immediately after installation and again at 3 and 9 months later. Minor differences in the density, length and condition index of mussels were identified among the six sites over the course of the study; however, their responses were typically similar across sites. These results suggest that these mussels have the capacity to establish themselves within estuarine environments and that their subsequent performance once transplanted onto the seafloor appears to be determined by other site-specific factors, such as the presence of predators and the degree of exposure to storm waves. Full article

Tidal inundation is a key factor determining the structure and function of estuarine salt marsh ecosystems. However, due to the influence of microtopography (small-scale topographic variations), the fine-scale spatial variations in tidal inundation have not been fully studied. To fill this research gap, this study focuses on the Luanhe Estuary—a region highly sensitive to topographic changes—and explores in depth the physical mechanisms regulating tidal inundation in this area. The study integrates long-term data from the Sentinel-1 Synthetic Aperture Radar (SAR) and Sentinel-2 Multispectral Instrument (MSI), spanning the period from 2016 to 2025, to construct a high-resolution time series dataset of Apparent Inundation Frequency (AIF). Subsequently, this dataset is correlated with a high-precision microtopographic Digital Elevation Model (DEM) obtained through Unmanned Aerial Vehicle (UAV) surveys. The analysis reveals a strong nonlinear relationship between AIF and topographic elevation, which is best described by an exponential decay model (R² = 0.903). The results show that the average inundation probability in the study area has shown a fluctuating but overall upward trend, increasing from 16.74% in 2016 to 29.02% in 2025 (peaking at 31.39% in 2024). Quantitative modeling confirms that microtopography is the primary controlling factor for fine-scale variations in tidal inundation levels. The integrated research approach proposed in this study provides a reliable framework for coastal vulnerability assessment. Against the backdrop of increasingly severe impacts from climate change and human activities, the high-resolution quantitative data generated by this study provides scientific support for formulating disaster mitigation and geomorphological management strategies. Full article

The Yangtze River Estuary is one of the most productive estuarine ecosystems in the western Pacific, supporting diverse fish communities that sustain ecosystem functioning. This study investigated the seasonal patterns and community structure of intertidal fish assemblages to provide a baseline for future habitat assessments. Seasonal surveys conducted from May to December 2024 recorded 47 fish species belonging to 10 orders, 18 families, and 37 genera. Cyprinidae contributed the highest proportion of species (42.55%). Dominant species identified by the index of relative importance-including Cynoglossus gracilis, Coilia nasus, and Lateolabrax japonicus—characterized the seasonal assemblage structure. The assemblages were dominated by sedentary species (82.98%), and demersal fishes accounted for 48.94% of the species. Carnivorous taxa (57.45%) dominated the trophic guilds. Diversity indices indicated moderate diversity (H′: 1.797–2.441; C: 0.788–0.892; D: 1.724–4.770; J′: 0.6318–0.8642). Similarity analysis based on Jaccard’s index (Cj) showed the highest overlap between spring and summer (Cj = 0.5000) and the lowest between spring and winter (Cj = 0.1714); spring–autumn and summer–autumn were approximately 0.30, indicating moderate overlap. ABC curves yielded slightly negative W values in spring and summer and positive values in autumn and winter (W = −0.066 to 0.276), indicating moderately disturbed assemblages in spring–summer and less disturbed communities in autumn–winter. Overall, the study provides a seasonal baseline of intertidal fish assemblages in nearshore waters of the southern branch of the Yangtze River Estuary, which can provide useful ecological context for future assessments of nursery and feeding habitats of juvenile Chinese sturgeon (Acipenser sinensis). Full article