Search Results (487)

Aquatic macrophytes are a vital component of lake ecosystems, profoundly influencing ecosystem structure and function. Under future scenarios of more frequent extreme floods and intensified lake eutrophication, aquatic macrophytes will face increasing challenges. Therefore, understanding aquatic macrophyte responses to flood disturbances and nutrient enrichment is crucial for predicting future vegetation dynamics in lake ecosystems. This study focuses on Huangmaotan Lake, a Yangtze River floodplain lake, where we reconstructed 200-year successional trajectories of macrophyte communities and their driving mechanisms. With a multiproxy approach we analyzed a well-dated sediment core incorporating plant macrofossils, grain size, nutrient elements, heavy metals, and historical flood records from the watershed. The results demonstrate a significant shift in the macrophyte community, from species that existed before 1914 to species that existed by 2020. Unlike the widespread macrophyte degradation seen in most regional lakes, this lake has maintained clear-water plant dominance and experienced continuous vegetation expansion over the past 50 years. We attribute this to the interrelated effects of floods and the enrichment of ecosystems with nutrients. Specifically, our findings suggest that nutrient enrichment can mitigate the stress effects of floods on aquatic macrophytes, while flood disturbances help reduce excess nutrient concentrations in the water column. These findings offer applicable insights for aquatic vegetation restoration in the Yangtze River floodplain and other comparable lake systems worldwide. Full article

The continuous deposition of coal fine in the well can lead to complex problems, such as pump blockage and reduced capacity. The traditional critical velocity model applicable to rigid spherical particles, such as sand grains and glass beads, finds it difficult to accurately predict the migration behavior of coal fine in the wellbore. Therefore, this study aims to reveal the sedimentation law of coal fine particles, establish a critical velocity prediction model applicable to pulverized coal, and provide a theoretical basis for effectively preventing pump blockage and capacity decline problems. This paper analyzes the particle characteristics of coal fine in different mining areas and conducts experiments on the static settling of coal fine particles and the critical transport velocity. The experimental results showed that the larger the mesh size of coal fine, the lower the static settling velocity of coal fine particles. The critical velocity of coal fine increased with the particle size and concentration of the coal fine particles, as well as with the increase of the pipe column inclination. A new empirical formula for calculating the critical velocity of coal fine particles was derived by considering the effects of the coal fine concentration and pipe inclination. Full article

Hydrotechnical structures reshape sandy coasts by altering hydrodynamics and sediment transport, yet their long-term effects on sediment texture remain underexplored, particularly in the Baltic Sea. This study investigates the spatial and temporal variations in sediment grain size near two ports (Šventoji and Klaipėda) on the sandy Baltic Sea coast, considering the influence of jetties, nourishment, and geological framework. A total of 246 surface sand samples were collected from beach and foredune zones between 1993 and 2018. These samples were analyzed in relation to shoreline changes, hydrodynamic data, and geological context. The results show that sediment texture is most affected within 1–2 km downdrift and up to 4–5 km updrift of port structures. Downdrift areas tend to contain coarser, poorly sorted sediments because of erosion and the exposure of deeper strata, while updrift zones accumulate finer, well-sorted sands via longshore transport. In the long term, the geological framework controls sediment characteristics. In the medium term, introduced material that differs in grain size from natural beach sediments may alter the texture of the sediment, either coarsening or refining it. The latter slowly returns to its natural texture. Short-term changes are driven by storm events. These findings highlight the importance of integrating structural interventions, nourishment practices, and geological understanding for sustainable coastal management. Full article

This study presents the first detailed analysis of a Late Pleistocene cliff-front dune in northern Mallorca (Western Mediterranean). The research is based on sedimentological fieldwork conducted in a disused coastal quarry, where stratigraphic columns were recorded and facies were described in detail. Grain size analysis was performed using image-based measurements from representative samples, and palaeowind conditions were reconstructed through the analysis of cross-bedding orientations and empirical wind transport equations. The dune, corresponding to Unit U4, exhibits three distinct evolutionary stages: initial, intermediate, and final. During the initial stage, sediment mobilisation required wind speeds of approximately 10 m/s from the south-southwest (SSW). The intermediate stage was characterised by variable wind velocities between 5 and 8 m/s from the west-southwest (WSW). In the final stage, average wind speeds reached 7 m/s from the west (W), with intermittent peaks up to 10 m/s. These findings underscore the critical influence of wind regime and topographic constraints on aeolian sedimentation processes. By reconstructing wind dynamics and analysing sedimentary architecture, this work provides key insights into the interplay between climatic drivers and geological context in the development of coastal aeolian systems. Full article

Optically stimulated luminescence (OSL) dating is an important method for determining the ages of late Quaternary sediments. However, partial bleaching of quartz in fluvial sediments remains a challenge, with debates on grain-size effects in different sedimentary environments. The aim of this paper is to explore the bleaching degree and its influencing factors of different grain-size quartz in fluvial sediments from the Yanchi section in the Daluze area, North China Plain. According to sedimentological methods and grain size analysis, lacustrine and fluvial layers were identified, and the ages of sediments were determined by OSL and ¹⁴C methods. The key findings are as follows: (1) Fine-grained quartz can be better bleached than coarse/medium-grained quartz for early–middle Holocene fluvial sediments. (2) The OSL method can yield reliable ages for early–middle Holocene fluvial sediments, while it overestimates these for late Holocene fluvial sediments. This probably results from variations in sediment sources and hydrodynamic conditions. (3) The dating results show that there are three fluvial activity periods in the Daluze area: 10.8~10.2 ka, 5.3~4.7 ka, and after 1 ka. This paper provides a reliable chronological framework for the evolution of regional sedimentary environments and offers references for luminescence dating of fluvial sediments in similar environments. Full article

Radionuclides and heavy metals pose potential risks to marine ecosystems and human health. Daya Bay, the site of China’s first commercial nuclear power plant, has experienced significant anthropogenic impacts, yet the extent of radionuclide and heavy metal contamination remains unclear. Nineteen surface sediment samples were collected in January 2024 and analyzed for natural (²¹⁰Pb, ²²⁸Th, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) and anthropogenic (¹³⁷Cs) radionuclides, heavy metals (Cu, Pb, Zn, Cd, Cr, Mn, Hg, and As), grain size, and total organic carbon (TOC). The surface sediments of Daya Bay were predominantly fine-grained, with TOC levels ranging from 0.41% to 1.83%, influenced significantly by riverine input from the Dan’ao River. Natural radionuclides exhibited distinct spatial patterns: ²¹⁰Pb and ²²⁸Th activity levels were higher in fine-grained sediments, and correlated with TOC, indicating adsorption and sedimentation controls. In contrast, anthropogenic ¹³⁷Cs activity was low and showed no significant impact from the nuclear power plant. Notably, the absence in the samples of key anthropogenic radionuclides typically associated with nuclear power plant operations further confirmed the negligible impact of the power plant on local sediment contamination. The results indicated that the baseline levels of both natural and anthropogenic radionuclides and heavy metals were predominantly influenced by natural processes and local anthropogenic activities rather than the operation of the nuclear power plant. This study establishes critical baselines for radioactivity and heavy metals in Daya Bay, underscoring effective pollution control measures and the resilience of local ecosystems despite anthropogenic pressures. Full article

The present study focuses on the dynamics of trace metals (TM) in two European rivers, the Mosel and the Meuse. A deterministic description of hydro-sedimentary processes has been performed. The model used to describe pollutant transport and dilution at the watershed scale has been enhanced with the implementation of the MicMod sub-model. The objective of this study is to characterise the dynamics of TM in the water column and bed sediment. A multi-class grain size representation has been developed in MicMod. The dissolved and particulate TM phases have been calculated with specific partitioning coefficients associated with each suspended sediment (SS) class. The processes involved in TM fate have been calibrated in MicMod, including settling velocity, TM releases from the watershed (point and diffuse loads), etc. Following the calibration of the parameters involved in TM transport within the river ecosystem, the main goal is to describe TM dynamics using a pressure–impact relationship model. It was demonstrated that the description of at least one class of fine particles is necessary to obtain an adequate representation of TM concentrations. The focus of this study is low flow periods, which are characterised by the presence of fine particles. The objective is to gain a deeper understanding of the processes that control the transport of TM. This paper establishes consistent pressure–impact relationships between TM loads (urban, industrial, soils) from watersheds and concentrations in rivers. Full article

Warm conditions during typically cold winters impact runoff and resulting hydraulic processes in channels where ice-cover would typically dominate. This field study on a short, low-slope reach in Southern Ontario, Canada, examined hydrologic and hydraulic processes with a focus on winter runoff events and subsequent bed shear stress variability. Through winter 2024, six cross-sections over a ~100 m reach were monitored near-weekly to measure hydraulic geometry and velocity profiles. These data characterized channel processes and estimated bed shear stress with law of the wall. In this channel, velocity increased more rapidly than width or depth with rising discharge and influenced bed shear stress distribution. Bed shear stress magnitudes were highest (means ranged ~2–6 N/m²) and most variable over gravel beds compared to the exposed bedrock (means ranged ~0.05–2 N/m²). Through a rain-on-snow (ROS) event in late January, bed shear stress estimates decreased dramatically over the rougher gravel bed, despite minimal changes in water depth and velocity. Pebble counts before, during, and after the event, showed that the proportion of finer-sized particles (i.e., <5 cm) increased while median grain size did not vary. These observations align with findings from both flume and field studies and suggest that milder winters reduce gravel-bed roughness through finer-sized sediment deposition, altering sediment transport dynamics and affecting gravel habitat suitability. Additionally, limited ice-cover leads to lower bed shear stresses and thus finer-sized materials are deposited, further impacting gravel habitat suitability. Results highlight the importance of winter hydrologic variability in shaping channel processes and inform potential stream responses under future climate scenarios. Full article

This study contributes new mineralogical, whole-rock geochemical, and magnetic susceptibility data to the well-established petrogenesis of the Miocene of Limnos volcanic rocks in the Aegean region. The combined examination of volcanic samples from the Katalakon, Romanou, and Myrina units demonstrates that they belong to a genetically related high-K calc-alkaline to shoshonitic suite that was formed by fractional crystallization in a continental arc setting and derived from a subduction-modified mantle source, contaminated by continental sediments. Different magmatic processes and crystallization conditions are reflected in modest compositional differences in magnetite (Ti, Al substitution) and ilmenite (Mg, Al, Fe–Ti ratios), as well as variations in trace elements between the units (e.g., elevated Nb–Zr in Romanou, high LREE in Myrina, and Ba in Katalakon). According to the magnetic data, bulk magnetic susceptibility is largely determined by magnetite abundance, whereas magnetic domain states are influenced by the grain size and shape, as euhedral grains are associated with stronger responses. The coupled geochemical and magnetic results indicate the diversified and transitional character of the Agios Ioannis Subunit in the Katalakon Unit. Full article

The Huangshan site in Nanyang, situated at the junction of the Nanyang Basin and the Jianghan Plain, represents a critical region for understanding the northward expansion of rice farming in China. Due to the scarcity of suitable organic material, the dating of the channel section at Huangshan relies primarily on cultural relics. By employing grain-size analysis, pollen analysis, and phytolith analysis on sediment samples from the site’s river section, we established a comprehensive framework of hydrology, climate, vegetation, and agricultural activities during the Yangshao to Qujialing periods (ca. 7000–4600 BP). The findings indicate a relative decline in temperature during the Yangshao period, followed by a return to warm and humid conditions during the Qujialing period, which coincided with the peak intensity of rice farming. The continuous expansion of rice farming at the Huangshan site during prehistoric times is likely linked to the northward spread of Qujialing culture. The large-scale production of rice not only provided an economic foundation for the growth of the Huangshan settlement but also facilitated its development into a regional hub for jade production and trade. This study offers new environmental archaeological insights into the interactions between the middle Yangtze River region and the Central Plains during the late Neolithic period. Full article

Coastal erosion poses a significant threat to small tropical island regions, where coastal tourism and infrastructure play vital economic roles. However, the processes affecting tropical beaches, particularly in Central America, remain underexplored due to a lack of data on waves and atmospheric conditions. We propose a novel approach that utilises low-cost smartphone and satellite imagery to characterise beach ecosystems, where typically expensive and technologically intensive monitoring strategies are impractical and background data are scarce. As a test of its performance under real conditions, we apply this approach to four contrasting beaches in the low-lying islands of the Bocas del Toro Archipelago, Panama. We employ Earth Observation data and field-based monitoring to enhance understanding of beach erosion. Optical flow tracking velocimetry (OFTV) is applied to smartphone camera footage to provide a quantitative metric of wave characteristics during the high wave energy season. These data are combined with satellite-derived shoreline change data and additional field data on beach profiles and grain size. The results reveal distinct patterns of accretion and erosion across the study sites determined by wave climate, beach morphology, and grain size. Accreting beaches are generally characterised by longer wave periods, more consistent wave velocities, and finer, positively skewed sediments indicative of swell-dominated conditions and dissipative beach profiles. Conversely, more erosive sites are associated with shorter wave periods, more variable wave velocities, coarser and better-sorted sediments, and a shorter, steeper beach profile. Seasonal erosion during the high-energy wave season (January–April) and subsequent recovery were observed at most sites. This work demonstrates how foundational data for evidence-based coastal management can be generated in remote locations that lack essential baseline data. Full article

Two properties that are commonly used in the analysis of debris-flow motion and behavior are viscosity and yield strength; however, many of the techniques to measure these properties are tedious, highly theoretical, and use only the finer fraction of debris. The purpose of this study is to develop a practical and consistent method of determining the influence that coarse particles, up to 25.4 mm, have on the viscosity and yield strength of debris flows, using more accessible testing methods. Samples were tested at various sediment concentrations and with increasing maximum grain sizes of particles. Values for viscosity and yield strength of each mixture were measured and compared using four separate, previously derived laboratory tests: an inclined flume box, a slump test, a simple inclined plane, and a rolling sleeve viscometer. The slump test and rolling sleeve viscometer produced the most consistent and reasonable results, particularly as the maximum grain size was increased. In general, the sediment concentration required to produce a given yield strength increased as coarser particles were added to a slurry. While viscosity changes with grain size distribution, its variation can be predicted by sediment concentration alone. Both yield strength and viscosity could be predicted from the finer fraction of sediment, and a proposed method to predict the addition of coarse material is described. Including coarse material, yield strength and viscosity values are expected to be within 25 and 100%, respectively, of values measured by other methods. Full article

This paper is a contribution to the ongoing debate on the nature and drivers of the abrupt environmental shift at the onset of the Younger Dryas. The goal of this study is to identify key parameters that characterize the Allerød–Younger Dryas boundary, 12.9–12.8 ka in sedimentary sections, and are representative of broader paleobasin dynamics in the eastern Baltic region. Two new Late Glacial sediment archives, the Kulikovo and Sambian, provide data on this time interval. Geochronological and lithological (grain size and loss on ignition) analyses of the sequences indicate a change in sedimentation during 12.9–12.8 ka, which is manifested by a peak of terrigenous, coarser-grained material and an accompanying peak of organic matter in sediments. A review of the published data shows that this lithological situation is also characteristic of other paleobasins in the eastern Baltic region and beyond for layers dated to the onset of the Younger Dryas. This probably indicates an environmental event that caused a short-term increased input and deposition of organic matter, accompanied by a surge in erosional processes. The environmental shift triggered by the event is also recorded in a remarkable drop in pollen concentration and species diversity in the overlying layer. The sediment horizon in Late Glacial (Allerød–Younger Dryas) sequences corresponding to these parameters can be considered an important and reliable geochronological marker of the 12.9–12.8 ka interval. The organic-rich layer in the Kulikovo section, as well as other similar layers in the Baltic, can be considered a “black mat” phenomenon related to the onset of the Younger Dryas. Full article

This study investigates sediment transport processes in the Kelani River Basin, Sri Lanka, focusing on the formation of bed material sediment size distributions. Sediment transport processes during the flood events in 2016 and 2018 are evaluated using two approaches: assuming an equilibrium condition (Case 0) and evaluating basin-scale sediment transport using a distributed Rainfall–Sediment–Runoff (RSR) model based on the unit channel (Cases 1 and 2). Case 1 considers sediment transport only inside river channels, while Case 2 considers sediment supply at upstream end unit channels. The results indicate significant sediment deposition in the downstream reach, particularly downstream of Location 7. In Case 1, the sediment size distribution downstream rapidly coarsens, while in Case 2, considering sediment supply, the bed sediment size distribution downstream is close to the observed one, regardless of flood magnitude. This suggests that with sufficient sediment supply, the bed sediment size distribution forms based on channel conditions such as width and slope. Case 0 shows a similar trend in sediment transport rate to Case 2, demonstrating the applicability of this simple approach. In conclusion, this study has revealed the formation process of the present sediment bed conditions, which provides insight into effective and sustainable river management, including sand mining activities. Full article

This study introduces a spatial encoder network designed to estimate sand size distribution from optical images of sediments. The model achieves sufficient network capacity by stacking two-dimensional convolution-based encoder blocks to learn the spatial features that relate sediment images to grain size distribution. Additionally, to improve robustness and reliability, data augmentation techniques, including horizontal and vertical flipping, are used during training. The proposed model was applied to 41 littoral systems located along the eastern coast of the Korean Peninsula and was developed using grain size distribution data through sieve analysis and images obtained from 2010 to 2024. The proposed model demonstrated an impressive correlation of 98% for the estimated mean diameter of grain size and improved root mean square error across all measures of grain size distribution when compared to previous deep learning-based methods. The improvement in the accuracy of grain size distribution estimation using the proposed image-based deep learning model is expected to contribute to the advancement of conventional approaches, which are labor-intensive and time-consuming. Full article