Search Results (146)

Estuarine turbidity fronts are narrow transition zones where suspended particulate matter concentrations change sharply. Their detection from remote sensing imagery remains challenging because conventional methods rely on empirical thresholds, are sensitive to mixed pixels, and often lack transferability and physical interpretability. Here, we evaluate the potential of foundation-model representations by integrating AlphaEarth 64-dimensional embeddings with Sentinel-2 spectral and multi-scale spatial features. A 229-dimensional feature set is constructed and fed into a two-step framework combining random forest classification with an empirically calibrated optical mask based on low red-band reflectance. The fused feature set achieves an overall accuracy of 91.2%, an F1 score of 87.5%, and a Kappa coefficient of 0.807, outperforming both spectral–spatial features alone and AlphaEarth embeddings alone. To elucidate the contribution mechanism of AlphaEarth embeddings, we conduct two complementary SHAP analyses: one evaluating each dimension’s direct contribution to front classification, and the other assessing its capacity to predict Sentinel-2 band reflectance. Only nine dimensions overlap between the respective top 20 lists, revealing a clear functional division within the embedding space—some dimensions primarily encode spectral reflectance information, while others encode spatial context, edge patterns, or topological structures that are not directly accessible from local spectral features. This division represents the added value of AlphaEarth beyond conventional optical data. The empirically calibrated optical mask reduces candidate frontal area by 59.09% in turbid estuaries and restores linear front morphology. However, leave-one-estuary validation yields F1 scores ranging from 0.33 to 0.84, substantially below the within-estuary score of 0.93, demonstrating limited cross-region transferability and challenging the assumption of domain invariance in foundation-model embeddings. These findings highlight both the value of fusing foundation-model representations with local spectral–spatial features and the critical need for domain-adaptation strategies to improve generalization across contrasting estuarine hydrodynamic regimes. Full article

The management of estuarine ecosystem sustainability is a complex problem that requires models that are physically sound, socially meaningful, and interpretable from a mechanistic standpoint. Even though classical AI has demonstrated promise in environmental forecasting, black-box models typically fall short of meeting basic conservation requirements or accounting for anthropogenic stresses that alter water quality. This work introduces a novel framework based on Deep Physics-Informed Neural Networks (Deep PINNs) to predict the dynamics of dissolved oxygen (DO) in the Bouregreg Estuary (Morocco). We advance baseline standards by directly integrating the non-linear advection–diffusion–reaction (ADR) transport equations into the loss function of a deep residual architecture (ResNet with 12–20 layers). This integration ensures that the model takes into account two important aspects of estuarine hydrodynamics: gravitational circulation and the salt wedge effect. The incorporation of a socio–hydro–physical nexus, which uses regional water-pricing indices and urban wastewater discharge volumes from the Rabat-Salé municipal area $(\sim \mathrm{120,000} {\mathrm{m}}^3/\mathrm{d}\mathrm{a}\mathrm{y})$ as proxy variables for anthropogenic pressure, is a unique aspect of this work. The Deep PINN achieves a better coefficient of determination ($R^2=0.998$) and a Nash–Sutcliffe efficiency ($\mathrm{N}\mathrm{S}\mathrm{E}=0.997$), outperforming the traditional ANFIS and ANN baselines by $89.1\%$ in terms of predictive error reduction ($\mathrm{R}\mathrm{M}\mathrm{S}\mathrm{E}=0.041\pm 0.002 \mathrm{m}\mathrm{g}/\mathrm{L}$). In situations where unconstrained data-driven models fall short, the framework exhibits physical robustness in capturing vertical DO stratification in addition to numerical accuracy. Urban effluent volumes have a significant impact on predictive variance, accounting for 28% of the model internal attribution—more than the relative influence of thermal solubility, according to mechanistic feature attribution analysis using SHAP (Shapley Additive exPlanations). Finally, exploratory management scenarios suggest that summer hypoxia could hypothetically be mitigated through a $20\%$ reduction in discharge volumes. This study bridges the gap between scientific modeling and policy implementation by providing a physics-consistent digital twin framework for environmental stewardship in support of UN SDG 6 and Morocco’s National Water Plan. Full article

River networks influenced by tides represent dynamic, hydrologically complex systems where fluvial inflows interact with oceanic tidal forcing. Conventional flow-based indica-tors of hydrologic alteration (IHA) inadequately capture tidal-driven dynamics, including diurnal water level fluctuations, flow reversals, and tidal asymmetry. This study develops an augmented IHA (AIHA) framework comprising 96 indicators derived from hourly-resolution hydrodynamic simulations (1960–2019) in the Pearl River Delta (PRD), China. The AIHA extracts four daily series—ebb-peak flow and residual, highest, and lowest water levels—supplemented by tidal characteristic metrics. A moving t-test identified 1991 as the significant regime shift, enabling comparison of reference (1960–1991) and altered (1992–2019) periods. Three-dimensional alteration was assessed as follows: deviation from the range of variability (RVA), shift in central tendency (RCM), and change in dispersion (RCD). Indicator importance was integrated via CRITIC weighting and multi-site Borda scoring. Results show that range shifts and central-tendency shifts were generally dominated by low-intensity alteration, accounting for 58.3–71.9% and more than 85% of the indicators, respectively, whereas dispersion shifts were more pronounced, with medium- and high-alteration indicators accounting for an average of 42.4%. Water level indicators exhibited substantially greater alteration sensitivity than flow indicators, particularly in estuarine zones where the alteration degrees of some indicators exceeded 90%. Among hydrological elements, ebb-peak flow indicators responded more strongly in range shifts, with an average comprehensive alteration degree of 29.6%, while water level indicators showed more pronounced changes in central tendency and dispersion; the lowest water level indicators were especially sensitive, with average comprehensive alteration degrees of 19.6% and 77.3%, respectively. Spatially, center-of-distribution shifts (RCM) diverged: positive in western/northern tributaries (increased flows) versus negative in the eastern PRD (decreased flows). Integrated Borda scoring identified low-flow extremes during dry seasons, event timing, and tidal modulation as the most sensitive responses to hydrological stress. The AIHA framework demonstrates that tidal river alteration is characterized by intensified low-flow volatility and amplified tidal influence, with water level metrics providing a superior detection capacity than achieved by discharge alone. This process-integrated approach offers robust quantitative support for ecological flow management and estuarine restoration in tidal environments globally. Full article

Accurate quantification of ecological losses in estuarine environments is often hindered by the mismatch between coarse-resolution biological surveys and fine-scale physical disturbances from engineering activities. While numerical models can simulate high-resolution environmental shifts, the inherent sparsity of ecological monitoring points limits the precision of spatial impact assessments. This study develops an integrated spatial-downscaling framework to transform sparse monitoring data into a high-resolution spatial continuum. A three-tiered modeling approach was used: first, the estuarine domain was partitioned into five eco-hydrodynamic zones using an entropy-weighted Support Vector Machine (SVM); second, localized chained Generalized Additive Models (GAMs) were established within each zone using MIKE-simulated hydrodynamic and water-quality data as proxy drivers; and third, these localized response functions were propagated across the study area to quantify multi-trophic biomass and economic losses. The framework revealed substantial spatial non-stationarity. Dredging operations locally altered the estuarine hydrodynamic regime. In northern channels, decreases in flow velocity were statistically associated with phytoplankton biomass to decline by 5.0% to 23.42%. Conversely, southern velocity increases enhanced water exchange and plankton growth. Using silt curtains as a mitigation strategy reduced the loss of phytoplankton by 11.4% and zooplankton by 9.6%. As a result, the total economic loss decreased from 26.54 million CNY to 25.34 million CNY, equivalent to a 4.5% reduction in economic loss. These results indicate that the proposed downscaling method can generate spatially explicit biological estimates. By offering a systematic pathway for impact evaluation and compensation in data-limited coastal regions, this framework supports more ecologically sustainable dredging operations. Nevertheless, the framework remains dependent on the representativeness of sparse monitoring stations, and future applications should integrate cross-estuary validation to improve transferability and uncertainty control. Full article

Daily hydropower regulation and mainstem backwater generate complex hydrodynamic conditions in the Min River estuary, posing significant challenges to navigation safety. To analyze the impact of mainstem backwater on tributary navigation safety, this study focuses on the lower Min River reach affected by backwater from the Jinsha River. A depth-averaged 2D hydrodynamic model is established, and a water level difference parameter is used to construct the stage–discharge relationship at the estuary based on long-term measured water level and discharge data. Indicators including backwater distance, water surface slope, hydrodynamic axis migration, flow velocity, and cross-flow are used to delineate navigation risk zones. The results indicate the following: (1) The backwater intensity and extent are primarily governed by the mainstem and tributary discharges and by the distance from the estuary. High discharge and water levels produce significant backwater effects and reduced flow velocity. Empirical formulas for backwater length under various discharge conditions are established to support navigation decision-making, with RMSE values ranging from 0.42 km to 0.92 km. (2) Variations in estuarine water level induce oscillations in the hydrodynamic axis. When the upstream discharge is 900 m³/s and the estuarine water level is 258.4 m, the maximum oscillation amplitude reaches 20.33 m. (3) During periods of medium and low water, the reach exhibits significant navigation-obstructing behavior, with high-risk zones concentrated in Tongluowan, Yangjiaoshi, and other shoals 5–8 km being found from the estuary. (4) Under the design discharge condition, the minimum estuarine water level required to ensure adequate channel depth, appropriate flow velocity, and manageable ship resistance for safe navigation is 267.96 m. This study provides a scientific basis for navigation safety and channel regulation in the Min River estuary and similar reaches affected by mainstem backwater, thereby supporting sustainable waterborne transport. Full article

Tidal energy assessment in tropical estuaries is constrained by low current velocities and high spatial variability, which limit conventional evaluation approaches. This study proposes a methodological framework adapted to velocity-constrained environments. The framework integrates ADCP-calibrated hydrodynamic modeling, velocity-exceedance-based site selection, low cut-in tidal turbine compatibility analysis, and a localized Levelized Cost of Energy evaluation within a unified decision-support structure. The methodology is applied to Buenaventura Bay, Colombia, where numerical simulations reproduce the mixed tidal regime with errors of approximately 0.30 m in water levels and 0.022 m/s in current velocities, enabling consistent characterization under low-flow conditions. Results at three locations indicate average available power densities of 64 W/m² at La Bocana, 19 W/m² at Buoy 29, and negligible values at Aguadulce, supporting the identification of marginal and non-viable sites based on velocity distributions. Under a low-velocity turbine configuration (10 m rotor diameter, 0.4 m/s cut-in speed), annual energy production is about 18 MWh per unit, while a 300-turbine array would generate approximately 5.4 GWh per year. The results indicate that annual energy production and capital expenditure are the main drivers of techno-economic feasibility in low-energy estuarine systems. Full article

This study investigates the distribution and concentration of microplastics (MPs) across the littoral profile of a beach, from dune base to offshore sector, including an estuarine channel and Sabellaria alveolata bioconstructions. The research was conducted at Pino di Lenne beach (Taranto, Ionian Sea), a wave-dominated, microtidal littoral system representing a unique natural laboratory with minimal anthropogenic pressure. An eco-friendly extraction protocol was used, combining methods that were already known in the literature. Olive oil proved highly effective in isolating a wide range of MP densities from sediment samples. Statistical analysis identified key accumulation zones, with the highest mean concentrations found in the submerged sandbar (2435 MPs/kg), Sabellaria bioconstructions (2324 MPs/kg), and the base of the dune (2065 MPs/kg). Fibres were the predominant morphology across all sub-environments. Distribution is interpreted as controlled by hydrodynamic processes and biological activity. The submerged beach drives MP transport, with the sandbar and shoreface acting as dynamic sinks. Sabellaria bioconstructions function as biological trap, actively incorporating MPs into their tubular structures. The dune base acts as a sink for wind-blown and storm-deposited plastics. These sub-environments function as critical littoral traps for MPs, essential for developing targeted monitoring and remediation strategies in similar coastal systems. Full article

Large-scale disasters can result in chronic pollution of coastal environments with unanticipated and poorly quantified impacts, such as the reshaping of marine connectivity. A recent example is the collapse of the Fundão tailings dam in 2015, which released about 50 million m³ of mine waste into the Doce River, affecting one of Brazil’s largest estuarine–mangrove systems. Here, we combine a high-resolution CROCO hydrodynamic simulation with an individual-based Lagrangian model (Ichthyop) to track the dispersal of mangrove crab (Ucides cordatus) larvae from four estuaries along the southeastern Brazilian margin between 2022 and 2024. Trajectories crossing seasonal msPAF fields derived from in situ water-quality measurements were used to quantify larval exposure to contaminants from mine waste. These fields were based on measured concentrations of As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V, Zn, and Al. Results show that surface shelf flow and mesoscale activity in the vicinity of the Doce River mouth contribute to offshore export of larvae, while the reef-dominated Abrolhos shelf promotes retention. Interannual variability alternates between long-distance export and local retention, associated with regional climate variability. Larval mortality rates caused by offshore advection and lethal temperature are high (65–75%). In addition to these modeled mortality sources, surviving cohorts frequently crossed areas with elevated msPAF values during transport, indicating potential exposure to metal(loid) mixtures. This suggests that the regional connectivity of U. cordatus is under chronic stress that likely compromises the integrity and resilience of coastal populations, since southern estuaries depend strongly on northern larval sources. The integration of Lagrangian simulations with in situ contaminant monitoring and spatially explicit exposure metrics demonstrates that transport pathways regulate not only connectivity among estuaries but also the duration and intensity of larval exposure to pollutants. Full article

Microplastics have become a ubiquitous environmental contaminant in natural waters, raising significant concerns regarding aquatic ecosystem health and potential human exposure. A comprehensive synthesis of current knowledge on microplastic pollution in freshwater and marine systems is presented, focusing on sources, distribution patterns, environmental behavior, and associated risks. In freshwater environments, microplastic inputs are closely linked to human activities and land use, with wastewater treatment plant effluent, urban runoff, and agricultural drainage serving as major pathways. In marine systems, microplastics undergo dynamic transport influenced by particle properties, hydrodynamic conditions, and biological interactions such as biofouling and aggregation, leading to widespread distribution from coastal zones to deep sea sediments. Importantly, the role of the freshwater–estuarine–marine continuum is emphasized, highlighting the coupled processes of transport, retention, and remobilisation that govern the spatiotemporal distribution and ultimate fate of microplastics across interconnected aquatic systems. Toxicological effects on aquatic organisms are further examined, particularly immunotoxicity and neurotoxicity, alongside potential human health risks via ingestion, inhalation, and dermal exposure. Attention is drawn to the discrepancy between experimental exposure conditions and environmentally relevant concentrations, which constrains robust risk assessment. Current mitigation strategies, including source reduction, wastewater treatment upgrades, transport interception, and degradation technologies, are critically evaluated in terms of effectiveness and limitations. A clear distinction is made between apparent removal and actual degradation, with further consideration of the environmental implications associated with sludge retention and degradation byproducts. Finally, key research priorities are identified, including the need for standardized detection methods, improved exposure assessment, development of environmentally benign alternatives, and strengthened policy-driven source control. These insights provide a basis for advancing sustainable management strategies for microplastic pollution in natural waters. Full article

This study aimed to assess the species diversity and genetic structure of Meretrix clams around Hainan Island using mitochondrial cytochrome c oxidase subunit I (COI) DNA barcoding. The genus Meretrix is a common and economically important group of bivalves in the intertidal zones of Hainan Island, widely distributed in estuarine and nearshore sandy habitats and playing a significant role in local fisheries and aquaculture. In recent years, studies on Meretrix in Hainan have mainly focused on morphological identification and species records from limited coastal areas; however, due to the high phenotypic plasticity of shell morphology and the relatively subtle differences among species, traditional morphology-based identification remains challenging. Meanwhile, molecular systematic investigations of Meretrix in Hainan are still limited, particularly systematic studies using DNA barcoding to assess species diversity and geographic distribution patterns. A total of 141 individuals were collected from ten intertidal sites. Four species were identified—M. lyrata, M. lamarckii, M. meretrix and M. petechialis—with interspecific genetic distances (17.6–22.7%) far exceeding intraspecific variation (0.3–0.9%). Phylogenetic analysis based on COI sequences clearly distinguished four Meretrix species from the waters around Hainan Island, with each species forming a well-supported monophyletic clade, supporting their status as independent evolutionary lineages. In addition, two markedly divergent genetic lineages were detected within M. petechialis, suggesting that this species may possess a relatively complex population structure, one of which is typically found in northern Chinese waters, suggesting possible human-mediated introduction. Species richness was higher on the eastern coast, potentially influenced by regional hydrodynamic conditions. This study provides baseline DNA barcode data for Meretrix species in Hainan and supports the need for integrative management of this economically important resource. Full article

This study provides the first characterization of the acoustic signals emitted by Lahille’s bottlenose dolphins (Tursiops gephyreus) in Argentine waters, establishing a baseline for the species’ southern distribution limit. Passive acoustic monitoring was conducted in the inner channels of the Bahía Blanca Estuary using a broadband hydrophone and F-POD detectors. We documented a diverse acoustic repertoire consisting of echolocation clicks, whistles, bray-calls, and chirps. Acoustic presence was predominantly diurnal and showed a marked synchronization with the tidal cycle, with peak activity occurring during the ebbing tide. Whistles had a mean center frequency of 8.1 kHz, showing spectral overlap with other regional populations in the Southwestern Atlantic. Echolocation clicks were broadband, with peak frequencies ranging from 18 to 127 kHz and a mode around 40 kHz. These results suggest that dolphin movement in the estuary’s internal channels is structured by hydrodynamics, likely reflecting foraging opportunities associated with tidal flow. Given the endangered status of this species, these data establish a technical framework for non-invasive monitoring and habitat-use assessments in complex estuarine environments. Full article

Tropical estuarine hydrodynamic processes are governed by complex interactions between tides, monsoons, and fluvial runoff. To obtain long-term (≥30 years) hydrodynamic conditions of the Mekong River Estuary, this study established a Finite Volume Coastal Ocean Model (FVCOM) coupled with validated Weather Research and Forecast (WRF) wind forcing for a 32-year (1988–2019) high-resolution simulation. Validation against in situ observations confirms the model’s robustness. Temporal–spatial patterns of water level and current were analyzed, and extreme parameters for 1–100 year return periods were derived via the Pearson-III probability distribution. Results indicate the study area is a mesotidal environment (tidal range = 3.58 m) dominated by SSE-NNW reciprocating tidal currents. Relative to Vietnam’s national elevation datum, 100-year return period extreme high/low water levels are 2.15 m and −2.03 m, with a maximum storm surge setup of 2.09 m. The 100-year return period maximum current velocity reaches 4.58 m/s (A21 station), and Mekong River runoff exerts a negligible influence (<5% velocity change). This study provides high-precision baseline data for offshore wind farm engineering and disaster risk assessment, offering a methodological reference for tropical estuarine hydrodynamic simulations. Full article

The coupling of physical transport and phase-transfer processes represents a fundamental mechanism governing metal cycling in estuarine systems under tidal oscillations. Taking Quanzhou Bay as a model system, we conducted continuous observations and sample collection at the river channel (Q1), the turbidity maximum zone (Q2), and the outer bay channel (Q3). The metals (Al, Ti, Ba, Cu, Mn, and Zn) were measured by ICP-MS to systematically investigate the distribution, transport, and inter-media transfer across multiple water layers under varying estuarine processes. Our findings demonstrate that particulate metal concentrations in Quanzhou Bay exhibit strong synchrony with suspended sediment concentrations (SSC) over tidal cycles, displaying a distinct sediment-following pattern controlled by alternating end members. Particulate metal fluxes during flood and ebb-tides generally followed the hierarchy Q1 > Q2 >> Q3. Notably, stations Q1 and Q2 were dominated by flood-tide fluxes with net transport directed landward, whereas Q3 was characterized by ebb tide dominance with net flux directed seaward—revealing a spatial division of labor between “inner bay retention/reallocation” and “outer bay channel export”. In contrast, dissolved metals exhibited marked element-specific responses to tidal forcing: Al and Ti increased during flood tides at stations Q1 and Q2, while Ba and Cu showed opposite trends, and Mn and Zn displayed more conservative behavior. Concurrently, solid/liquid partition coefficient (logKd) values for Al, Ti and Ba, Cu exhibited inverse patterns over tidal cycles, suggesting divergent adsorption–desorption regulation under identical hydrodynamic conditions that drives differential phase-transfer dynamics. These disparities likely reflect intrinsic chemical properties and source variations among the elements. This study elucidates, at the tidal timescale, the coupled processes of “alternating end-member control—estuarine filter modulation—concurrent channelized export and inner bay retention” in Quanzhou Bay, providing critical process-level insights for metal flux quantification and bay pollution remediation initiatives in an ecological restoration project. Full article

Acrylate-based self-polishing copolymer antifouling paint particles (SPC-APPs) are persistent micropollutants that act as carriers for biocidal heavy metals, posing significant ecological hazards to aquatic ecosystems. Despite their toxicity, the occurrence, characterization, and metal-leaching risks of SPC-APPs in estuarine environments remain largely understudied. This study investigated the contamination characteristics of SPC-APPs in surface sediments from the Yangtze River Estuary, a hotspot of shipping activity. A multi-technique analytical protocol was employed, combining density separation with scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS), and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) to characterize the morphology, quantify particle abundance, and assess the correlation between SPC-APPs and sedimentary heavy metals. SPC-APPs were ubiquitously detected across all sampling sites, with abundances ranging from (0.82 ± 0.15) × 10³ to (3.65 ± 0.42) × 10³ particles g⁻¹ dry sediment. A distinct distribution property (South Branch > North Branch > offshore shoal) was identified, primarily driven by shipping density and hydrodynamic sorting. Morphologically, particles exhibited irregular, abraded surfaces, with EDS confirming Cu (1.76~5.63 wt%) and Zn (0.27~3.65 wt%) as major metallic components. Py-GC/MS analysis identified specific mass fragments (m/z 41, 69, 87) as diagnostic markers. Strong positive correlations were observed between SPC-APP abundance and sediment Cu (r = 0.82, p < 0.01) and Zn (r = 0.76, p < 0.01) concentrations, indicating that these particles are a primary source of metal contamination. Ecological risk assessment based on sediment quality benchmarks showed that Cu in the South Branch reached 82~91% of the probable effect concentration (PEC), highlighting potential risks to benthic organisms. This study provides critical baseline data on the distribution and speciation of SPC-APPs, underscoring their role as vectors for toxic metals and the need for targeted pollution control in high-shipping-intensity estuarine regions. Full article

Tidal turbines have emerged as a promising alternative to fossil-fuel-based energy generation, with estuarine environments identified as potential sites for their deployment. However, estuaries are sensitive ecosystems, and understanding the impacts of turbine installation on local hydrodynamics and sediment transport is critical. While previous studies have shown the influence of turbines on seabed morphology under steady current conditions, the effects of combined wave–current loading remain insufficiently explored. In this study, we present a novel numerical modeling framework to predict seabed evolution in the vicinity of tidal turbines subjected to wave–current interactions. The approach integrates Blade Element Theory (BET) to represent turbine-induced forces, an Euler–Euler multiphase model for sediment transport, and the first-order wave theory to capture wave dynamics, all implemented within the OpenFOAM-based solver. Wave effects are incorporated as source terms in the momentum equations, and wave velocities are added to the current field at the velocity inlet boundary condition. Results demonstrate that wave–current loading induces oscillatory sediment transport, but net scouring remains significant in the vicinity of the turbine. The proposed framework is validated component-wise (wave forcing and rotor loading) and then demonstrated on mobile-bed simulations to quantify how oscillatory wave–current forcing modifies near-bed transport and early-stage scour development around a tidal turbine. While the present simulations focus on short morphodynamic times, the approach provides a physics-based basis for exploring wave effects on turbine-induced sediment dynamics. Full article