Search Results (598)

A three-dimensional Computational Fluid Dynamics (CFD) model is developed to simulate an Ocean Brick System (OBS) placed in a wave tank. When stacked, ocean bricks are designed to withstand wave forces and ocean currents, enhancing the stability of offshore support structures, such as base supports of offshore wind turbines. In this study, the commercial software Ansys Fluent 2022 R1 is used for the simulations. A user-defined function (UDF) is developed to generate numerical waves that closely replicate those observed in experimental conditions. The numerical wave model is first validated against theoretical wave data, showing good agreement. The CFD model is then validated using experimental data from OBS tests conducted in the wave tank. Subsequently, the study investigates how OBS structures influence tidal waves—specifically, how they reduce the wave amplitude, and the pressure exerted on the bricks. Specifically, the wave amplitude reduction is more effective for waves with shorter wavelengths than for those with longer wavelengths, achieving up to a 70% reduction for waves with an amplitude of 0.785 m, a period of 5 s. Finally, a modification to the original brick geometry is proposed to further reduce wave amplitude and improve the stability of OBS platforms. For the same wave input, the modified brick geometry reduces wave energy effectively, achieving an 89.2% decrease in wave amplitude. Full article

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are promising molecular biomarkers widely applied in paleoenvironmental reconstructions, including temperature and pH. However, knowledge of the microorganisms responsible for brGDGT production in marine environments remains limited, which constrains the further development and application of brGDGT-based proxies for reconstructing past marine conditions. In this study, both ‘living’ intact polar lipid-derived brGDGTs (IPL-brGDGTs) and ‘fossil’ core brGDGTs (CL-brGDGTs), together with bacterial community compositions, were analysed in multiple sediment cores collected along a nearshore-to-offshore transect in the East China Sea (ECS). The potential correlations between brGDGT distributions and bacterial community compositions at varying sediment depths across an environmental gradient were also explored. Results revealed that IPL-brGDGTs were predominantly biosynthesised in situ, whereas CL-brGDGTs reflected a mixture of marine autochthonous production and terrestrial inputs. Potential brGDGT-producing bacteria in nearshore environments were primarily composed of chemolithoautotrophic taxa (e.g., Gammaproteobacteria and Dehalococcoidia) and chemoheterotrophic taxa (e.g., Alphaproteobacteria, Bacilli, and Actinobacteria). In contrast, offshore regions were dominated by chemoheterotrophic hypoxic bacteria (e.g., Anaerolineae and Phycisphaerae) and facultatively anaerobic chemolithoautotrophic bacteria (e.g., Gammaproteobacteria and Desulfobacteria). A significant difference in bacterial community composition and IPL-brGDGT distribution was observed at a depth of 17 cm, likely due to physical disturbance in near-surface sediments, such as wave action, tidal forces, and storm events. Variance partitioning analysis (VPA) revealed that the bacterial community composition alone accounted for 14.1% of the variation in IPL-brGDGTs and 6.5% in CL-brGDGTs, further suggesting that the distribution of brGDGTs is primarily influenced by the composition of the bacterial community in the nearshore-to-offshore sedimentary ecosystems of the ECS. These findings regarding the potential biosynthesis of brGDGTs in coastal habitats advance our understanding of the microbial mechanisms that regulate brGDGT distribution in marine ecosystems. Moreover, they emphasise the importance of considering physical disturbance effects when interpreting sedimentary brGDGT records for paleoenvironmental reconstructions in marginal seas, such as the ECS. Full article

Urban estuarine environments face increasing water safety risks due to microbial contamination from combined sewer overflows (CSOs), particularly during heavy rainfall events. In megacities like Tokyo, where waterfronts are widely used for recreation, such contamination poses significant public health risks. The challenge is compounded by the variability in both intensity and spatial distribution of rainfall across the catchment, combined with complex tidal dynamics making effective water quality management difficult. To address this challenge, we conducted a series of hydrodynamic–microbial fate simulations to examine the spatial and vertical behavior of Escherichia coli (E. coli) under different rainfall–tide conditions. Focusing on the Sumida River estuary, rainfall data from eight drainage areas were classified into six event types using cluster analysis. Two contrasting events were selected for detailed analysis: a light rainfall (G2, 15 mm over 13 h) and an intense event (G6, 272 mm over 34 h). Vertical water quality profiling was performed along an 8.5 km transect from the Kanda–Sumida River confluence to the Tokyo Bay Tunnel, illustrating E. coli and salinity. The results showed that the rainfall intensity and tidal phase at the event onset are critical in shaping both the magnitude and vertical distribution of microbial contamination. The intense event (G6) led to deep microbial intrusion (up to 6–7 m) and major salinity disruption, while the lighter event (G2) showed surface-layer confinement. Salinity gradients were more strongly affected during G6, indicating freshwater intrusion. Tidal phase also influenced transport: the flood-high condition retained E. coli, whereas ebb-low tides facilitated downstream flushing. These findings highlight the influence of rainfall intensity and tidal timing on microbial distribution and support the use of vertical profiling in estuarine water quality management. They also support the development of dynamic, event-based water quality risk assessment tools. With appropriate local calibration, the modeling framework is transferable to other urban estuarine systems to support proactive and adaptive water quality management. Full article

Plastic pollution in river systems is a growing concern, especially in the Mekong Delta, where complex tidal dynamics facilitate downstream transport of plastic waste into the marine environment. This study assessed the density, composition, and temporal variability of floating plastic waste in the Hau River, approximately 30 km upstream of the Tran De River estuary. Floating net traps were deployed during both ebb and flood tides to quantify plastic waste with simultaneous meteorological and hydrological monitoring. The findings highlight that key meteorological factors, such as air temperature, humidity, wind speed, and wind direction, were found to indirectly influence plastic transport by altering surface currents and promoting plastic degradation. Meanwhile, hydrological conditions, especially tidal variability, play a direct and dominant role in determining the spatial and temporal distribution of plastic waste. Plastic debris was diverse in terms of items during both tidal phases. Although the number of plastic pieces was higher at ebb tide (134.33 pieces/h), the volume and concentration of plastic were greater at flood tide (1.22 kg/h and 0.73 kg/m³) than at ebb tide (0.81 kg/h and 0.29 kg/m³). Macroplastic debris was almost dominant during both ebb tide (97.29%) and flood tide (93.96%) compared to megaplastic and mesoplastic size. These findings highlight the importance of integrating tidal and climate factors into plastic waste management and support targeted interventions to reduce plastic discharge into coastal ecosystems. Full article

Blackwater rivers are enriched in humic acids and impoverished in nutrients, sometimes discharging into oceans. Brazil has a coastal zone of about 8700 km, with several blackwater rivers discharging into the Atlantic Ocean, in addition to the Rio Negro of the northern Amazon basin, which is the largest (about 1700 km long) and best-known tropical backwater river. On the other hand, only a few attempts have been made to deal with their hydrochemical composition and how it is related to the hydrochemistry of different water bodies nearby. This paper focuses on a sector of the Atlantic Ocean shore occurring in São Paulo State, enclosing two important Ecological Reserves, i.e., the Restinga State Park of Bertioga and the State Park of Serra do Mar–São Sebastião Nucleus, located at Bertioga and São Sebastião cities, respectively. Physicochemical parameters such as pH and electrical conductivity, as well as the composition of major constituents like sodium, potassium, calcium, magnesium, bicarbonate, chloride, sulfate, nitrate, etc., have been evaluated in two blackwater rivers and one blackwater stream to compare their relative inputs into the Atlantic Ocean. Traditional hydrogeochemical diagrams such as the Piper, Schoeller, Gibbs, van Wirdum, and Wilcox graphs were utilized for investigating the major features of the blackwater’s composition, revealing in some cases that they suffer an accentuated influence of the constituents occurring in the Atlantic Ocean waters, due to backward currents (coastal upwelling or tidal currents). Another highlight of this paper is the measurement of an enhanced concentration of dissolved iron in one blackwater sample analyzed, reaching a value of 1.9 mg/L. Such a finding has also been often reported in the literature for blackwater rivers and streams, as humic and fulvic acids are used to bind Fe³⁺, keeping it in solution. Nowadays, iron in solution has been considered a very important element acting as a natural fertilizer of the coastal ocean because it is an essential nutrient to marine phytoplankton. Full article

This study aimed to evaluate how tidal modulation influences breaking waves on a macrotidal beach along the Amazonian coast under varying climatic conditions. The study utilized medium-term data (2006–2018) from national and international institutions and short-term data (2012–2014) from in situ measurements at Ajuruteua Beach. Offshore winds and waves, predominantly from the northeast, were influenced by severe storms associated with La Niña and El Niño events. During these periods, wave heights exceeded 5 m, with wave periods ranging from 12 to 20 s. Tidal fluctuations (typically 5.0–6.0 m) modulated nearshore wave heights and periods, with variations determined by offshore conditions and climatic influences. Wave heights decreased from 2–5 m offshore to 1–2 m nearshore. At low tide, sandbanks dissipated wave energy, resulting in significantly smaller breaking waves (0.1–0.5 m) compared with high tide (1–1.8 m). The northern part of Ajuruteua Beach experienced a progressive retreat, with a total area loss of 0.15 km² and a shoreline retreat of 0.360 km between 2007 and 2021. The combination of high hydrodynamic energy and unregulated development led to the destruction of 43 buildings between 2007 and 2013 and an additional 44 houses between 2013 and 2021 within the intertidal zone. Moreover, the absence of coastal management strategies has exacerbated erosion, underscoring the urgent need for planning and regulatory frameworks. Based on the findings of this study, it is recommended that land use be regulated and both short- and long-term physical processes be systematically integrated into future coastal protection planning. Full article

The increasing prevalence of chronic metabolic diseases poses a significant challenge in the modern world, impacting healthcare systems and individual life expectancy. The World Health Organization (WHO) recommends that older adults (65+ years) engage in 150–300 min of moderate-intensity or 75–150 min of vigorous-intensity physical activity, alongside muscle-strengthening and balance-training exercises at least twice a week. However, nearly one-third of the adult population (31%) is physically inactive, which increases the risk of developing obesity, type 2 diabetes, cardiovascular diseases, hypertension, and psychological issues. Physical activity in the form of aerobic exercise, resistance training, or a combination of both is effective in preventing and managing these metabolic diseases. In this review, we explored the effects of exercise training, especially on respiratory and pulmonary factors, including oxygen consumption, pulmonary ventilation, and blood gas analyses among adults. During exercise, oxygen consumption can increase up to 15-fold (from a resting rate of ~250 mL/min) to meet heightened metabolic demands, enhancing tidal volume and pulmonary efficiency. During exercise, the increased energy demand of skeletal muscle leads to increases in tidal volume and pulmonary function, while blood gases play a key role in maintaining the pH of the blood. In this review, we explored the influence of age, body composition (BMI and obesity), lifestyle factors (smoking and alcohol use), and comorbidities (diabetes, hypertension, neurodegenerative disorders) in the modulation of these physiological responses. We underscored exercise as a potent non-pharmacological intervention for improving cardiopulmonary health and mitigating the progression of metabolic diseases in aging populations. Full article

Plastic debris is a pervasive and persistent threat to marine ecosystems. Microplastics (plastics < 5 mm) are increasing in a variety of marine habitats, including open water systems, shorelines, and benthic sediments. It remains unclear how microplastics distribute and accumulate in marine systems and the extent to which this pollutant is accessible to marine taxa. We examined subtidal benthic sediments and beach sediments in critical nearshore habitats for forage fish species—Pacific sand lance (Ammodytes personatus), Pacific herring (Clupea pallasi), and surf smelt (Hypomesus pretiosus)—to quantify microplastic concentrations in the spawning and deep-water habitats of these fish and better understand how microplastics accumulate and distribute in nearshore systems. In the San Juan Islands, we examined an offshore subtidal bedform in a high-flow channel and beach sites of protected and exposed shorelines. We also examined 12 beach sites proximate to urban areas in Puget Sound. Microplastics were found in all samples and at all sample sites. Microfibers were the most abundant, and flakes were present proximate to major shipyards and marinas. Microplastics were significantly elevated in Puget Sound compared to the San Juan Archipelago. Protected beaches had elevated concentrations relative to exposed beaches and subtidal sediments. Microplastics were in higher concentrations in sand and fine-grain sediments, poorly sorted sediments, and artificial sediments. Microplastics were also elevated at sites confirmed as spawning habitats for forage fish. The model results indicate that both current speed and proximate urban populations influence nearshore microplastic concentrations. Our research provides new insights into how microplastics are distributed, deposited, and retained in marine sediments and shorelines, as well as insight into potential exposure in benthic, demersal, and shoreline habitats. Further analyses are required to examine the relative influence of urban populations and shipping lanes and the effects of physical processes such as wave exposure, tidal currents, and shoreline geometry. Full article

High-resolution mooring observations captured diverse upper-ocean responses during typhoon passage, showing strong agreement with satellite-derived sea surface temperature and salinity. Analysis indicates that significant wind-induced mixing drove pronounced near-surface cooling and salinity increases at the mooring site. This mixing enhancement was predominantly governed by rapid intensification of near-inertial shear in the surface layer, revealed by mooring observations. Unlike shear instability, near-inertial horizontal kinetic energy displays a unique vertical distribution, decreasing with depth before rising again. Interestingly, the subsurface peak in diurnal tidal energy coincides vertically with the minimum in near-inertial energy. While both barotropic tidal forcing and stratification changes negligibly influence diurnal tidal energy emergence, significant energy transfer occurs from near-inertial internal waves to the diurnal tide. This finding highlights a critical tide–wave interaction process and demonstrates energy cascading within the oceanic internal wave spectrum. Full article

This study investigates the flow dynamics and local scour around a Reef Cube^® artificial reef deployed in Torbay, UK, using computational fluid dynamics. The flow is modelled using Reynolds-Averaged Navier–Stokes (RANS) equations with a k-ω SST turbulence model. A novel hydro-morphodynamic model employing the generalized internal boundary method in HELYX (OpenFOAM-based) is used to simulate scour development. Model performance was validated against experimental data for flow fields, bed shear stress, and local scour. Flow simulations across various scenarios demonstrated that parameters such as the orientation angle and arrangement of Reef Cubes significantly influence flow patterns, bed shear stress, and habitat suitability. The hydro-morphodynamic model was used to simulate scouring around a reef cube in the Torbay marine environment. Results indicate that typical tidal flow velocity flow in the region is barely sufficient to initiate sediment motion, whereas extreme flow events, represented by doubling the mean flow velocity, significantly accelerate scour development, producing holes up to ten times deeper. These findings underscore the importance of considering extreme flow conditions in scour analyses due to their potential impact on the stability and failure risk of AR projects. Full article

Vegetation succession is a critical indicator of ecosystem structure and function and is often disrupted by the expansion of invasive species. However, ecosystem-scale studies elucidating invasion-driven succession mechanisms remain limited. This research focused on the Yancheng coastal salt marsh and analyzed the distribution variation of invasive species (Spartina alterniflora) and native species (Suaeda salsa and Phragmites australis) from 1987 to 2022 via the Google Earth Engine and random forest method. Logistic/Gaussian models were used to quantify land–sea distribution changes and vegetation succession trajectories. By integrating data on soil salinity, invasion duration, and fractional vegetation cover, generalized additive models (GAMs) were applied to identify the main factors influencing vegetation succession and to explore how Spartina alterniflora invasion affects the succession of salt marsh vegetation. The results indicated that the areas of Spartina alterniflora and Phragmites australis significantly increased by 3787.49 ha and 3452.60 ha in 35 years, respectively, contrasting with Suaeda salsa’s 82.46% decline. The FVC in the area has significantly increased by 42.10%, especially in the coexisted areas of different vegetation communities, indicating intensified interspecific competition. The overall trend of soil salinity was decreasing, with a decrease in soil salinity in native species areas from 0.72% to 0.37%. From the results of GAMs, soil salinity, tidal action, and invasion duration were significant factors influencing the distribution of native species, but salinity was not a significant factor affecting the Spartina alterniflora distribution. The findings revealed that the expansion of Spartina alterniflora changed the soil salinity and interspecific interactions, thereby altering the original plant community structure and establishing a new vegetation succession. This study enhances the understanding of the impacts of invasive species on ecosystems and offers theoretical support for salt marsh restoration. Full article

The Ganges–Brahmaputra–Meghna (GBM) delta, characterized by complex topography and hydrological conditions, is highly susceptible to recurrent flooding, particularly in its coastal regions where tidal dynamics hinder floodwater discharge. This study integrates Synthetic Aperture Radar (SAR) imagery with machine learning (ML) techniques to assess near real-time flood inundation patterns associated with extreme weather events, including recent cyclones between 2017 to 2024 (namely, Mora, Titli, Fani, Amphan, Yaas, Sitrang, Midhili, and Remal) as well as intense monsoonal rainfall during the same period, across a large spatial scale, to support disaster risk management efforts. Three machine learning algorithms, namely, random forest (RF), support vector machine (SVM), and K-nearest neighbors (KNN), were applied to flood extent data derived from SAR imagery to enhance flood detection accuracy. Among these, the SVM algorithm demonstrated the highest classification accuracy (75%) and exhibited superior robustness in delineating flood-affected areas. The analysis reveals that both cyclone intensity and rainfall magnitude significantly influence flood extent, with the western coastal zone (e.g., Morrelganj and Kaliganj) being most consistently affected. The peak inundation extent was observed during the 2023 monsoon (10,333 sq. km), while interannual variability in rainfall intensity directly influenced the spatial extent of flood-affected zones. In parallel, eight major cyclones, including Amphan (2020) and Remal (2024), triggered substantial flooding, with the most severe inundation recorded during Cyclone Remal with an area of 9243 sq. km. Morrelganj and Chakaria were consistently identified as flood hotspots during both monsoonal and cyclonic events. Comparative analysis indicates that cyclones result in larger areas with low-level inundation (19,085 sq. km) compared to monsoons (13,829 sq. km). However, monsoon events result in a larger area impacted by frequent inundation, underscoring the critical role of rainfall intensity. These findings underscore the utility of SAR-ML integration in operational flood monitoring and highlight the urgent need for localized, event-specific flood risk management strategies to enhance flood resilience in the GBM delta. Full article

As with wind turbines, marine tidal turbines are expected to be deployed in arrays of multiple turbines. To optimize these arrays, a more profound understanding of the interactions between turbines is necessary. This paper employs the Actuator Line Method alongside the Lattice Boltzmann Method and Large Eddy Simulation to develop a numerical model of tidal turbine arrays. It studies a vertical-axis turbine manufactured by HydroQuest/CMN that is equipped with two counter-rotating columns, each comprising two rotors. The ambient turbulence and upstream velocity profiles correspond to the characteristics of a tidal site such as the Alderney Race. Six turbine layouts are modeled: three aligned layouts with three turbines and three staggered layouts with four turbines. The spacing between turbines varies depending on the layout. This study yields several observations regarding array configuration. A minimum distance of 300 m, or $12D_{eq}$, between aligned turbines is necessary for full wake recovery. At shorter distances, the accumulation of velocity deficits significantly decreases the efficiency of the third turbine in the array. Pairs of counter-rotating vortices are observed in the wake of turbines. The evolution of these vortices and their influence on the wake depend greatly on the array configuration. An optimal configuration is observed in which the overall averaged power is not impaired by the interactions. Full article

The 2019 Antarctic sudden stratospheric warming (SSW) is well captured by the specified dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD-WACCM-X). This SSW is dominated by a strong quasi-stationary planetary wave with zonal wavenumber 1 (SPW1) activity, and nonmigrating tides show great variations. The nonlinear interactions between SPW1 and diurnal, semidiurnal and terdiurnal migrating tides triggered by this SSW also have significant impacts on the variabilities of corresponding nonmigrating tides. This is clearly proven by the fact that the variations of the secondary nonmigrating tides, generated by the nonlinear interaction, show higher correlation during this SSW than those during the non-SSW period. Meanwhile, the SPW1 dominates the nonlinear interactions with diurnal, semidiurnal and terdiurnal migrating tides, and the corresponding secondary nonmigrating tides show concurrent increases with SPW1. In the ionosphere, the nonmigrating tidal oscillations exhibit consistent temporal variabilities with those shown in the neutral atmosphere, which demonstrates the neutral–ion coupling through nonmigrating tides and that nonmigrating tides are significant sources for the short-term ionospheric variability during this SSW event. Specifically, the enhancement of the ionospheric longitudinal wavenumber 4 structure coincides with the increase of the eastward-propagating diurnal tide with zonal wavenumber 3 (DE3), semidiurnal tide with zonal wavenumber 2 (SE2) and terdiurnal tide with zonal wavenumber 1 (TE1). Also, DE3 dominates the influence of nonmigrating tides on the ionospheric longitudinal wavenumber 4 structure during this SSW. Full article

This study developed a coupled hydrodynamic-sediment-vegetation model to investigate the effects of Spartina alterniflora management and Suaeda salsa restoration on coastal wetland geomorphological evolution and vegetation distribution. Special attention is paid to the regulatory roles of tidal dynamics, sea-level rise, sediment supply, and sediment characteristics. The study shows that the management of Spartina alterniflora significantly alters the sediment deposition patterns in salt marsh wetlands, leading to intensified local erosion and a decline in the overall stability of the wetland system; meanwhile, the geomorphology of wetlands restored with Suaeda salsa is influenced by tidal range, sediment settling velocity, and suspended sediment concentration, exhibiting different deposition and erosion patterns. Under the scenario of sea-level rise, when sedimentation rates fail to offset the rate of sea-level increase, the wetland ecosystem faces the risk of collapse. This study provides scientific evidence for the ecological restoration and management of coastal wetlands and offers theoretical support for future wetland conservation and restoration policies. Full article