Search Results (1,770)

This study presents integrated Cladoceran, plant macrofossil and diatom-based environmental reconstruction from the Čepkeliai Bog (Southern Lithuania), covering the Late Glacial–Early Holocene transition. The objective was to assess palaeoenvironmental changes with a focus on trophic state, acidification, and water-level fluctuations and to explore the applicability of these assemblages as temperature-sensitive indicators. The findings of our study revealed that sedimentation started at about 13,200–13,000 cal yr BP in a deep, oligotrophic and cold-water palaeobasin. Inferred palaeoenvironment changes correlate with the GI-1b event (Gertsenzee oscillation). A significant ecological shift to a shallow, warm, ecologically diverse environment occurredat about 13,000 cal yr BP and is consistent with the GI-1a (Allerød) period. The Younger Dryas (12,850–11,650 cal yr BP) is characterised by a rise in lake level and oligo-mesotrophic and high-water transparency conditions. At the end of the Younger Dryas (around 12,000 cal yr BP), climate warming and a drop in water levels were recorded. Intensive palaeobasin swamping processes began around 9700 years cal yr BP, during the Boreal period. A short-lived “9.2” cooling event was fixed at about 9200–9000 cal yr BP. The results obtained provide new insights into postglacial palaeoenvironmental dynamics in the southeastern Baltic region. Full article

The Jordan Valley is a heavily modified, data-limited transboundary river basin where water availability is constrained by both climate conditions and intensive human intervention. This study applies an integrated hydrological and hydrogeochemical modeling framework using the Soil and Water Assessment Tool (SWAT) to quantify basin-scale water availability and quality and to assess climate change impacts for the period 2000–2021. Results indicate that the basin is strongly evapotranspiration-dominated, with mean annual precipitation of 298.9 mm and precipitation-derived evapotranspiration accounting for 66.3% of rainfall. When externally supplied irrigation water is included, total evapotranspiration increases markedly, highlighting the strong dependence of agriculture on imported surface water and groundwater abstractions. Only a small fraction of total water input contributes to river discharge toward the Dead Sea, indicating a very limited internal water surplus. Hydrological dynamics are largely controlled by upstream dams and transboundary diversions, while nitrate and sediment simulations demonstrate a close coupling between hydrology, land use, and water quality. Climate projections suggest further reductions in water availability during the 21st century, exacerbating existing water scarcity. Overall, the study illustrates how intensive regulation and irrigation dependency constrain water availability in the Jordan Valley and in similar heavily modified transboundary river basins. Full article

Parasitism affects nearly half of all animal species and strongly influences ecosystem dynamics. Despite their sentinel value, parasitic infections in cetaceans remain understudied. This study assessed the diversity, prevalence, and burden of gastrointestinal and pulmonary parasites in seventy-five stranded cetaceans from six species along the central and northern Portuguese coastline. Coprological methods included Mini-FLOTAC^®, Willis-flotation, natural sedimentation, modified Ziehl–Neelsen staining, direct immunofluorescence, and adapted spontaneous sedimentation. Overall, 61.3% of samples tested positive for at least one parasitic taxon, with 22.7% showing coinfections. Anisakidae and Ascaridida were the most prevalent (36%), followed by Pseudaliidae larvae (5.3%), unidentified trematode eggs (8.0%), Odhneriella spp. (5.3%), Nasitrema spp. (2.7%), Zalophotrema spp. (2.7%), and Synthesium spp. (1.3%). Nematode eggs exhibited the highest mean burden, with anisakids reaching 4862 eggs per gram of feces (EPG), whereas trematodes showed a markedly lower burden, exemplified by Zalophotrema spp. with 90 EPG. All samples assessed were negative for Cryptosporidium spp. and Giardia spp. Unidentified ovoid structures were present in 76% of samples. Macroscopic sedimentation revealed anisakid larvae, one cestode, over fifty Ogmogaster antarctica specimens, and six marine arthropods. These findings provide baseline data for cetacean parasitology and support future integrative research for conservation and ecosystem health. Full article

Suspended sediment concentration (SSC) strongly influences estuarine erosion–deposition processes, navigation safety, and coastal engineering stability. However, conventional remote sensing techniques are limited to surface SSC and cannot characterize vertical sediment structures. In this study, Landsat 8 OLI imagery was combined with in situ SSC profiles from six stations in the Guan River Estuary–Haizhou Bay system to retrieve full-depth sediment distributions. A band-combination inversion model using (B3 + B2)/B1 achieved the highest accuracy (R² = 0.679), and an improved vertical distribution model was developed by incorporating turbulent shear (G) into the Rouse framework. Results indicate that surface SSC ranged from 0.15 to 0.86 kg/m³, while middle- and bottom-layer SSC reached up to 1.20 kg/m³ and 1.77 kg/m³, respectively, exhibiting a consistent east–high and west–low spatial pattern. Settling velocity (SSV) varied from 3 × 10⁻⁶ to 1.49 × 10⁻² m/s and showed a positive correlation with SSC at low concentrations and a negative correlation at high concentrations due to flocculation effects. This integrated framework provides a rapid, low-cost method for full-water-column sediment assessment in estuaries and coastal zones, supporting engineering design, navigation maintenance, and sediment management. A better understanding of sediment transport processes in Haizhou Bay is important for maintaining shoreline stability and ecological balance in this semi-enclosed coastal system. The findings of this study provide a scientific basis for sediment management and environmental regulation, which can contribute to the long-term sustainable development of coastal environments in the Yellow Sea region. Full article

The monitoring of harmful algal blooms (HABs) constitutes a vital component of marine environmental protection and the sustainable development of the marine economy. However, the highly dynamic nature of these small targets, compounded by the complex water color interference prevalent in the coastal waters where HABs frequently occur, has resulted in traditional remote sensing monitoring methods, particularly those relying on fixed spectral index thresholds and pixel-wise binarization, suffering from imprecise identification in turbid coastal waters where suspended sediments, cloud cover, and sun glint create spectral confusion. These methods also exhibit low automation due to manual threshold adjustment requirements and poor transferability across different spatiotemporal conditions. Consequently, these methods struggle to meet practical application requirements. This study establishes a U-net model-based remote sensing identification framework for red tides using HY-1D CZI imagery (50 m resolution, 1–3 day revisit), targeted negative sample strategies, and event-level accuracy validation methods to achieve efficient marine red tide detection. Targeted negative sample selection involves purposefully selecting spectrally ambiguous regions as negative samples, aiming to enhance recognition accuracy and sample selection efficiency. The combination of targeted sampling with deep learning enables portability to new spatiotemporal contexts by learning invariant spectral–spatial features rather than relying on scene-specific thresholds. Experimental results demonstrate that the targeted negative sample strategy reduces event-level model false negatives by 27%, false positives by 36%, and increases the F1 score by 0.3217. Using an identical sample size, the targeted sample selection strategy yields an F1 score 0.0479 higher than random sampling. To achieve equivalent recognition accuracy, an increased number of random samples would be required. Comparative experiments reveal that the proposed method enhances sample selection efficiency by 87.5%. Transferability is demonstrated through successful identification of red tide patches in Wenzhou waters on 13 April 2022, without model retraining. This demonstrates that red tide remote sensing recognition based on targeted sample selection enables efficient, precise, and automated identification without human intervention, providing a reliable technical solution for operational marine red tide monitoring. Full article

Artificial seawater lakes constructed in estuarine environments are highly susceptible to the intrusion of water containing high concentrations of suspended sediment, which can degrade water quality and threaten ecosystem stability. To clarify the settling mechanisms and sedimentation efficiency under high-turbidity conditions, this study investigated the Baishawan Artificial Lake in the Jiaojiang Estuary, eastern China, through field observations, controlled still-water sedimentation experiments, and a multi-particle size sedimentation efficiency model. Field measurements revealed significant spatiotemporal variability in suspended sediment concentration (SSC), with higher SSC during spring tides than neap tides and a spatial gradient decreasing from the near-estuary zone to the artificial lake and offshore waters. Grain-size analysis showed that suspended sediment was dominated by clay and silt (>98%). Laboratory experiments indicated a two-stage settling process characterized by rapid initial sedimentation followed by gradual stabilization; under high concentration (1.32 kg/m³), SSC decreased by about 85% within 40 min due to concentration-enhanced flocculation, whereas under low-concentration conditions (0.24 kg/m³) approximately 14 h were required to reach the target concentration of 0.01 kg/m³. Model validation demonstrated that the multi-component sedimentation model effectively reproduced the temporal attenuation of SSC. Model application further suggested that when the initial SSC was 0.70 kg/m³ and the water depth was 5.7 m, the sedimentation tank could reduce the SSC to 0.01 kg/m³ within about 16–17 h, with an estimated annual sedimentation volume of ~65,000 m³ and a recommended dredging interval of five years. These results provide quantitative guidance for sedimentation tank operation and sediment management in estuarine artificial lakes and other high-turbidity coastal environments. Full article

Dust and sand storms occurring in northern China are strongly controlled by near-surface aerodynamics, yet the spatial heterogeneity of these processes remains poorly understood. We obtained field measurements of the wind above gobis, sandy surfaces, and dry lakebeds in the Hexi Corridor Desert and Heihe River Basin, and sandy surfaces in northern China. First, the slope of wind profile (a₁) reveals distinct drag reversal with increasing wind speed: under low winds, a₁ increases from sandy to dry lakebed to gobi surfaces, whereas under high winds, actively saltating sandy surfaces exhibit the highest a₁, surpassing gobi and dry lakebed. Second, the dynamic feedback between sediment transport and aerodynamics is clear: at below-threshold winds, friction velocity ($u_{*}$) and aerodynamic roughness length (z₀) are lowest for sand; however, as wind speed increases to initiate significant saltation, the sandy surface develops the highest $u_{*}$ and z₀, highlighting the dominant role of grain-borne roughness. Third, the focal height (z_f) shows regional disparity, varying by up to two orders of magnitude for both sandy and gobi surfaces, with a strong correlation to local gravel coverage. This work provides spatially explicit parameterizations of surface type, offering a physical basis for modeling dust emission and transport in northern China and similar arid regions globally. Such parameterizations are essential for developing reliable early warning systems and evidence-based land management strategies. These advances contribute directly to ecosystem sustainability and community resilience in vulnerable arid and semi-arid regions under climate change. Full article

Intrabasinal low uplifts in lacustrine rift basins are key targets for sedimentological and petroleum geological research, as they can act as local source areas and exert critical controls on intrabasinal “source-to-sink” systems. Due to the discontinuous sediment supply, these systems often demonstrate the subtle and intermittent nature, and their roles in the development of depositional systems are usually overlooked. To clarify the controlling effect of intrabasinal local provenances on sedimentary system evolution, this study reconstructed the dynamic tectonic evolution of the Weixinan Low Uplift in the Beibuwan Basin, and systematically analyzed its control on “source-to-sink” systems and sedimentary filling using integrated high-resolution 3D seismic, core, well logging and geochemical data. Our results demonstrate that the activity of Fault 3 dominated the paleogeomorphic evolution of the Weixinan Low Uplift and its surrounding areas, which further governed the spatiotemporal development of the “source-to-sink” system and the distribution of sedimentary systems, with distinct evolutionary stages as follows: During the Ls2 Member stage (48.6–40.4 Ma), Fault 3 was inactive, the Weixinan Low Uplift was manifested as a gently dipping subaqueous slope under the influence of regional lacustrine transgression, and only small-scale braided river deltas were developed on the slope belt with weak sediment supply from the Qixi Uplift. During the Ls1 Member stage (40.4–33.9 Ma), the Ls13 Sub-member stage (lower Ls1 Member stage) was characterized by initiation of Fault 3 with segmented activity, triggering the formation of the Eastern Sub-sag of the Haizhong Sag and subaqueous uplift of the Weixinan Low Uplift; clastic sediments from the central Qixi Uplift were transported northeastward, developed braided river deltas and large-scale basin-floor lacustrine fans. In the Ls12 Sub-member stage (middle Ls1 Member stage), Fault 3 continued to propagate and was gradually linked, leading to further uplift of the Weixinan Low Uplift and expansion of the Haizhong Sag; Clastic materials from the central Qixi Uplift were almost entirely trapped in the Eastern Sub-sag of the Haizhong Sag. During the Ls11 Sub-member stage (upper Ls1 Member stage), further intensification of Fault 3 activity caused the Weixinan Low Uplift to be subaerially exposed and evolve into an intrabasinal local provenance, which supplied clastic sediments to surrounding sags and developed braided river deltas on the gentle slope belts and small-scale lacustrine fans on the lower slope. This study demonstrates that the tectonic evolution of the Weixinan Low Uplift has induced prominent changes in the basin paleogeomorphology, which in turn triggered dynamic shifts in the provenance and sediment transport pathways, and thus gave rise to complex local “source-to-sink” systems and depositional styles. Full article

To investigate the drag reduction mechanism of shark skin placoid scales and develop high-efficiency drag-reducing surfaces, this study designed and fabricated a biomimetic shark skin surface featuring staggered microscale groove structures. The fabrication process involved laser etching on silicon wafers to create a placoid microstructure template, followed by polydimethylsiloxane (PDMS) replication to obtain biomimetic shark skin samples. Sedimentation experiments demonstrated that the biomimetic surface significantly reduced settling time compared to a smooth surface, achieving a drag reduction rate of 5.65%. Further computational fluid dynamics (CFD) simulations were conducted to analyze the near-wall flow characteristics around the biomimetic surface. The results revealed that the drag reduction mechanism primarily stems from the effective regulation of near-wall laminar flow by the micro-groove structures: a low-velocity fluid layer formed within the grooves reduces the near-wall velocity gradient, thereby decreasing frictional drag, while stable recirculation zones develop within the grooves, contributing to momentum redistribution and reduced energy dissipation. Additionally, the staggered arrangement of the grooves promotes a smoother pressure distribution along the flow direction, mitigating pressure drag by reducing the pressure differential between windward and leeward surfaces. The experimental and simulation results showed excellent agreement (simulated drag reduction rate: 5.08%), collectively verifying the feasibility and effectiveness of the proposed biomimetic placoid structure in achieving fluid drag reduction. Full article

To address the feasible issues in water treatment facilities such as low particle removal and overuse of chemical in flocculation–sedimentation treatment of complex sediment-laden particles in snowmelt and high-intensity rainfall water, this research presents a new multi-layered separation tank. Combining a multi-layer structural design and a synergistic enhancement mechanism flocculation–centrifugation, it is possible to engineer the tank to achieve improvement in the coexistence of the sediment and water. This study methodically examines the impact of the agitator speed, agitator height, and the number of blades on the flow field qualities and the effectiveness of the agitator in removing particles in the multi-layer separation tank. Computational fluid dynamics (CFD) simulation validation in comparison with hydro-calculations and laboratory experiments are used in a combined method. The findings show that there is strong agreement between numerical representation and experimental values in determining the optimal conditions of operation and the exact rate of dosage of polyaluminum chloride (PAC) and polyacrylamide (PAM). At these optimized conditions, the system achieves at a 75.25 percent removal rate of particles whose size ranges are 20–50 μm and turbidity of the effluent decreases to 10.6 NTU in 30 min of settling time. The proposed technology is more efficient than conventional coagulation processes in that effluent turbidity is reduced by 22.1% with same dosages of chemical additive indicating a higher performance of the proposed technology. Full article

The increasing demand for energy and the continued reliance on fossil fuels pose important environmental and social challenges, particularly for rural and isolated communities in developing countries that lack reliable access to the grid. Gravitational water vortex turbines (GWVT) are a run-of-river technology for low-head and moderate-flow sites that can provide decentralized electricity without the construction of large reservoirs. The expected environmental impacts are lower; nevertheless, to increase acceptance by the community, there is a necessity to identify and analyze the potential environmental impacts of GWVT in all its life-cycle phases (installation, operation, maintenance, and dismantling). The present study applies the Conesa cause–effect matrix to identify, classify, and analyze the potential environmental impacts associated with GWVT phases. Key identified impacts include removal of vegetation coverage and site disturbance (−32), sediment dynamics alterations (−39), formation of a depleted stretch (−45), accidental releases of hazardous maintenance products (−42), and remobilization of retained sediments (−46). These impacts can produce habitat alteration and fragmentation and loss of ecological connectivity. The relevant significance of energy generation that can have multiple benefits in the local communities was also identified. Primary mitigation measures include the incorporation of environmental flows in the design, sediment management, and strict protocols for hazardous materials. The findings underscore the necessity to conduct site-specific baseline surveys to preserve environmental, socio-economic, and cultural conditions in the local ecosystem and communities. Full article

Pondweeds, an important component of macrophyte vegetation, are influenced by various ecological factors of the aquatic ecosystem. In turn, pondweeds affect the nutrient and sediment dynamics and provide food and shelter for other organisms. As different species have specific environmental preferences and tolerances, they can serve as indicators of the ecological status of water bodies. Here, the ecological preference of the seven most frequent pondweeds in Croatia (Potamogeton berchtoldii, P. crispus, P. lucens, P. natans, P. nodosus, P. perfoliatus and Stuckenia pectinata) for chemical and physical water parameters was studied using 218 vegetation relevés and the accompanying water parameters. CCA revealed the main environmental gradients described by six parameters (chemical oxygen demand, total nitrogen, total phosphorus, electrical conductivity, dissolved oxygen and pH), while ecological responses of the species were further explored by GAMs. Potamogeton berchtoldii, P. lucens, P. natans and P. perfoliatus prefer clean, oxygenated, oligo- to mesotrophic water, and P. crispus and S. pectinata thrived in eutrophic water with low oxygen levels, while P. nodosus is a widespread generalist. The results of this study explain the distribution patterns of Potamogeton and Stuckenia species in Croatia, and add to the general knowledge on their role as bioindicators. Full article

High-precision sediment distribution maps are indispensable for nearshore sediment dynamics and ecology and nearshore resource management. Using grain-size data of surface sediments from the nearshore waters of Lianyungang and auxiliary datasets including bathymetric and hydrodynamic conditions, this study assessed Random Forest (RF), eXtreme Gradient Boosting (XGBoost), and Support Vector Regression (SVR) for predicting sediment grain-size fractions and mapping sediment substrate types. All three models capture the spatial gradient of sediment grain size from fine to coarse from the nearshore to the offshore regions, but differ in preserving local heterogeneity and defining transition boundaries: XGBoost delivers the most balanced performance by preserving grain-size variability, reducing boundary mixing, and improving the identification of classes with limited samples; RF excels in robust delineation of gradual transitions, whereas SVR tends to produce fragmented boundaries and unstable performance for classes with limited samples. Feature importance reveals that hydrodynamic drivers dominate the spatial distribution of sand, whereas terrain indices are more influential for the clay distribution pattern, confirming the role of microtopography in modulating fine-sediment trapping. Overall, this study improves mapping accuracy and supports marine spatial planning and coastal infrastructure design. Full article

The distribution of nutrients and microorganisms in sediments is not uniform, as it results from the complex interactions between chemical, biological, and physical transport processes. This study investigates, through a simplified model, the dynamics of a microbial population and its nutrients, accounting for the active metabolic state of the bacteria. Using the nutrient diffusion coefficient $d_2$ as a bifurcation parameter, we demonstrate that a Turing bifurcation, leading to spatial patterning, occurs at a critical value. Sufficient conditions for the stability of the resulting pattern are also established. Furthermore, by treating time delay as a bifurcation parameter, we prove the occurrence of Hopf bifurcation near the positive constant equilibrium solutions at a sequence of critical values, showing that time delay can induce spatially homogeneous and inhomogeneous periodic oscillatory patterns. Numerical simulations and solutions are provided to illustrate the theoretical findings. Full article

Marine ranching, as a pivotal strategy for enhancing the ocean’s carbon sequestration potential, offers significant potential to mitigate nearshore fishery depletion and restore marine ecosystems amid the global carbon neutrality agenda. However, the mechanistic pathways linking sediment total organic carbon (TOC) to various environmental factors in tropical marine ranches remain insufficiently quantified. This study selected the Wuzhizhou Island Marine Ranch in Hainan Province—a representative tropical marine ranch—as the research site. Field investigations and sampling were conducted during the dry (March 2024) and wet (September 2024) seasons to quantify TOC in surface sediments and associated environmental variables. A two-step analytical framework, integrating Principal Component Analysis (PCA) and Generalized Additive Models (GAM), was employed to elucidate the environmental drivers governing the spatiotemporal dynamics of TOC. The results show that the surface sediment TOC at Wuzhizhou Island Marine Ranch exhibits a distinct spatial gradient—Core Reef > Atoll > Control > Estuarine, and a pronounced seasonal pattern with elevated concentrations in the dry season relative to the wet season. The spatiotemporal differentiation of TOC is mainly driven by a gradient (explaining 52.1% of variation) that encompasses processes related to carbon accumulation from terrestrial inputs and primary production, as well as organic matter degradation promoted by nutrients and higher water temperatures. Sediment total nitrogen (TN) emerges as the primary environmental driver of TOC distribution, contributing up to 46.9% of the variance at an extremely significant level (p < 0.001). Furthermore, total phosphorus (TP), pH, and water temperature (WT) have relatively minor influences on the distribution of sedimentary TOC. Our study offers a crucial reference for elucidating the key processes governing the carbon cycle in tropical marine ranches and provides essential theoretical support for optimizing ocean carbon sink strategies in the context of global climate change. Full article