Sediment Particles Research Articles

Impact of sediment uniformity from steep tributary on transport in main Channels: A CFD-DEM study

During flash flood events, a prominent size segregation phenomenon often occurs in the mixture of sediment particles of varying diameters moving with the floodwaters. However, the impact of the inherent inhomogeneity of the sediment on its transport process continues to be unclear. This study evaluates the sorting phenomenon in the transport behavior of flood-impacted, loosely deposited sediment particles originating from steep tributary feeders in mountain channels. To achieve this objective, a computational framework integrating Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) was utilized to directly simulate the detailed paths of all particles. After validating the CFD-DEM model, we investigated the influence of the sediment particles’ coefficient of uniformity (Cu) on sediment transport characteristics. The results suggest that under different Cu values, coarse particles initially accelerate rapidly but later slow down and converge to a consistent speed, whereas fine particles demonstrate a more uniform speed increase and eventually maintain a constant velocity. With rising Cu, the peak degree of sorting between coarse and fine particles first increases and then stabilizes. The temporal variation of the dimensionless sediment transport rate of any sediment component at a given section can be represented using a modified dual-branch Weibull function. The overall transport process can be determined through linear superposition based on mass proportion. Additionally, we found that the heterogeneous characteristics of the sediment provide a mode of overall sediment transport where fine particles roll at the bottom, while coarse particles slide and saltate at the top, leading to reduced frictional dissipation in the movement of coarse particles. This phenomenon is commonly observed in mountain flood channels with slopes less than 60 degrees. These findings bolster the explanation for the poor application of existing sediment transport rate formulas in flash flood channels.

Tracing microplastic pollution in Mahi River estuary, Gulf of Khambhat, Gujarat, and their influence on functional traits of macrobenthos.

Most maritime habitats contain microplastic (MPs) contamination. The quality of the benthic ecosystem's habitat is declining as MPs accumulate in marine system. The contamination of MPs must therefore be investigated. We studied MPs pollution in the Mahi River, estuary, and macrobenthos. In the present study, the abundance of MPs fragments gradually decreased from the high tide zone to the low tide zone and muddy sediment has high MPsconcentrations due to sediment characteristics and particle size. The majority of sediment and biota MPs were fibrous and black. MPs in both silt and biota have identical chemical compositions (modified cellulose), shapes, and colors. A significant source of pollutants and MPs fluxing into the ocean is well within the river system. Perinereis aibuhitensis ingested the most MPs out of 11 species, whereas Amphipods did not show any presence of MPs. Our findings showed that functional characteristics are essential for macrobenthos MPs intake. MPs in macrobenthos are high due to biological functions such as feeding, ecological groups, feeding mechanisms, body size, and bioturbation. MPs in marine sediment and organisms aretracked down to the Mahi River exceeding 50km. The present work has investigated the idea that the macrobenthos that live in the sediment are ingesting the MPs that are building up there and this ingestion relies on the macrobenthos' functional characteristics.

Dynamics and sorting of run-and-tumble particles in fluid flows with transport barriers

We investigate the dynamics of individual run-and-tumble particles in a convective flow which is a prototype of fluid flows with transport barriers. We consider the most prevalent case of swimmers denser than the background fluid. As a result of gravity and the effects of the carrying flow, in the absence of swimming the particles either sediment or remain in a convective cell. When run-and-tumble also takes place, the particles may move to upper convective cells. We derive analytically the probability of uprise. Since that probability in a given fluid flow can vary strongly across species, our findings inspire a purely dynamical mechanism for species extraction in the dilute regime. Numerical simulations support our analytical predictions and demonstrate that a judicious choice of the fluid flow’s parameters can lead to particle sorting with an arbitrary degree of purity.

Spatial heterogeneity, sediment-water exchange, and diffusion mechanisms of organophosphate esters from river to coastal aquatic system in a typical economic circle of northern China

Organophosphate esters (OPEs) have proven to be pervasive in aquatic environments globally. However, understanding their partitioning behavior and mechanisms at the sediment-water interface remains limited. This study elucidated the spatial heterogeneity, interfacial exchange, and diffusion mechanisms of 14 OPEs (∑14OPEs) from river to coastal aquatic system. The transport tendencies of OPEs at the sediment-water interface were quantitatively assessed using fugacity methods. The total ∑14OPEs concentrations in water and sediments ranged from 154 ng/L to 528 ng/L and 2.41 ng/g dry weight (dw) to 230 ng/g dw, respectively. This result indicated a descending spatial tendency with moderate variability. OPE distribution was primarily influenced by temperature, pH, and dissolved oxygen levels. As the carbon atom number increased, alkyl and chlorinated OPEs transitioned from diffusion towards the aqueous phase to equilibrium. In contrast, aryl OPEs and triphenylphosphine oxide, which had equivalent carbon atom counts, maintained equilibrium throughout. Diffusion trends of individual OPE congener at the sediment-water interface varied at the same total organic carbon contents (foc). As the foc increased, the fugacity fraction values for all OPE homologs showed a declining trend. The distinct molecular structure of each OPE monomer might lead to unique diffusive behaviors at the sediment-water interface. Higher soot carbon content had a more pronounced effect on the distribution patterns of OPEs. The sediment-water distribution of OPEs was primarily influenced by total organic carbon, sediment particle size, dry density, and moisture content. OPEs displayed the highest sensitivity to fluctuations in ammonium and dissolved organic carbon. This study holds significant scientific and theoretical implications for elucidating the interfacial transport and driving forces of OPEs and comprehending their fate and endogenous release in aquatic ecosystems.

Distribution of 137Cs specific activity in river sediments of the Barents Sea basin (Nenets Autonomous Okrug, Russian Arctic).

This article focuses on the study of the distribution of 137Cs in the bottom sediments of Arctic rivers of the Barents Sea basin (using the example of the Nenets Autonomous Okrug, Russian Arctic). This research is relevant due to the poorly studied region and the significant number of radiation-hazardous facilities in the Arctic zone of Russia, both those currently in operation and those that are "nuclear heritage sites". The study of 137Cs specific activity in bottom sediments was carried out in the period from 2020 to 2023 in the rivers Chizha, Nes, Vizhas, Oma, Pechora (river delta), as well as the rivers Kolva and Usa (first and second order tributaries, respectively, of the Pechora River). A total of 199 samples were collected. In addition to 137Cs specific activity, the samples were analysed for sediment particle size distribution, organic matter content, carbonate content and ash content. The 137Cs specific activity mainly ranged from the minimum detectable specific activity to 5.4 ± 0.8Bq·kg-1. In the Nes River basin (Kaninskaya tundra), the 137Cs content in bottom sediments reached 36.0 ± 3.2Bq·kg-1 (in the case of lake sediments) and 22.9 ± 3.7Bq·kg-1 (in the case of river sediments), values that are higher than those of the North-West of Russia. Considering the large area of the study area (Kaninskaya tundra, Pechora river delta, southern part of Bolshezemelskaya tundra) and the similarity of physical and chemical parameters of the studied rivers, it is possible to assume the existence of a zone of increased radionuclide content in the Nes river basin. This may be due to the runoff from the Nes River catchment area, its hydrological features, and the accumulation of 137Cs in the small fractions of bottom sediments. The results confirm the conclusions of previous soil studies in the Nes river basin. The main sources of elevated 137Cs content are global atmospheric deposition and the Chernobyl Nuclear Power Plant accident.

The Characteristics of Adsorption of Di-n-Butyl Phthalate by Surface Sediment from the Three Gorges Reservoir.

Phthalic acid esters (PAEs), recognized as endocrine disruptors, are identified as predominant organic pollutants in the Three Gorges Reservoir (TGR). Di-n-butyl phthalate (DBP), a representative PAE, has been extensively studied for its sources, distribution and ecological risks. However, there are few studies on the adsorption of DBP by sediment from the TGR, and the adsorption characteristics of surface sediment on DBP are not clear. Therefore, based on the actual sediment contents and particle sizes in the TGR, the kinetics and isothermal adsorption characteristics of surface sediment on DBP were investigated in this study. The results showed that the equilibrium time was 120 min, the adsorption kinetics were more in line with the pseudo-second-order kinetic model, and the sediment in water from the Yangtze River exhibited a higher adsorption rate and maximum adsorption amount on DBP than that observed in deionized water. Additionally, a decrease in DBP adsorption was observed with increasing sediment content, while sediment particle size and specific surface area had a slight influence. Analysis using SEM, TGA and FTIR revealed that organic matter on the sediment surface significantly contributed to DBP adsorption. This study contributes valuable insights into the adsorption characteristics of DBP by the surface sediment from the TGR, providing a scientific foundation for understanding the migration and transformation of DBP in this critical reservoir in China.

Experimental study on direct shear properties and shear surface morphologies of hydrate-bearing sediments

The safe production of methane gas requires a comprehensive understanding of the geomechanical behavior for hydrate-bearing sediments (HBS). Currently, there is a lack of detailed exploration of the shear surface failure characteristics of specimens. To address this, direct shear tests were performed to observe shear surfaces at the microscopic level. This study mainly focuses on the mechanical parameters of HBS and the morphological characteristics of shear surfaces, aiming to elucidate the deformation modes and failure mechanisms. Results reveal that shear load-displacement curves illustrate three stages: elastic deformation, strain softening, and stability stage. The shear strength increases from 12.65 KPa to 153.86 KPa with hydrate saturation rising from 12% to 72%, while decreases versus shear rate. Shear surfaces exhibit concave, convex, and S-shape patterns with remarkable differences in crack number and orientation. The shear load-displacement curves and shear surface morphology are closely correlated with shear rates, especially shear strength and shear surface roughness. Furthermore, the shear surface roughness varies between 2.02 mm and 3.61 mm with hydrate saturation increasing from 12% to 72%, which are also influenced by the shear rate. Empirical formulas were established based on test data to predict the shear strength and surface roughness. The failure mechanism of the specimens mainly depended on the movement modes of the sediment particles, hydrate strength, and hydrate-sediment cementation strength. Findings of this study provide a theoretical reference for evaluating geo-mechanical stability and predicting the destabilization of natural gas hydrate reservoirs.

Experimental investigation of pressure drop of spherical and non-spherical coarse particles in pneumatic conveying in horizontal pipes

In this work, the conveying flow pattern and pressure drop of spherical and non-spherical coarse particles in a horizontal pipe were measured experimentally. The experimental results show that when coarse particles are conveyed in stratified flow and sedimentation and dune formation, the rate of increase of pressure drop with superficial velocity is related only to the particles and not to the conveying conditions. The rate of increase of pressure drop with velocity is larger for spherical particles than for non-spherical particles in stratified flow, and the rate is smaller for spherical particles than for non-spherical particles in sedimentation and dune formation. The pressure drop varies linearly with the solid-gas ratio, and the slope of the linear relationship characterises the friction of the conveying pipe and the interaction parameters between the particles. The reduction in pressure drop for spherical particles is greater than that for non-spherical particles when the solid-gas ratio is increased by the same magnitude. In addition, to verify the experimental results of this work the data cited in the published literature were compared and the results were in good agreement. On the one hand, the variation rule of pressure drop with superficial velocity obtained in this investigation is an enrichment of the classical phase diagram. On the other hand, the experimental results are of guiding significance for the design and engineering application of coarse particle pneumatic conveying systems.

Prevalence of Microplastics in Coastal Area of Samae San, Thailand and Its Possible Source

This research explored the abundance, morphology, and polymer composition of microplastics (MPs) in various environmental samples within the Samae San subdistrict involving surface soil nearby the dumping site, road dust soil, beach sand and sediment in the area with distinct land- based activities. Dumping site soil exhibited the highest concentration in items per kg of dry weight at 93,734.3, followed by road dust soil (573.0 ± 583.7), beach sand (99.8 ± 75.3), and sediment (83.1 ± 50.4). Morphological traits revealed similarities between transparent fiber-shaped particles in beach sands and sediment, and those in nearby road dust soil, while green sheet-shaped particles dominated in dumping site soil. Predominant polymer types included PE, PET, and PP, associated with daily plastics, fishing gear, and fishing nets. In beach sand and sediment samples, transparent polyamide (nylon) fibers shaped like microplastics (MPs) were notably observed, as it is a common material used in fishing nets. Cluster analysis indicated a resemblance between MPs in beach sand, sediment, and nearby road dust soil, implying that plastic debris, comprising single-use plastics and fishing equipment, could be a potential source of MPs in coastal areas.

Characterizing the Stoichiometry of Individual Metal Sulfide and Phosphate Colloids in Soils, Sediments, and Industrial Processes by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Size and purity of metal phosphate and metal sulfide colloids can control the solubility, persistence, and bioavailability of metals in environmental systems. Despite their importance, methods for detecting and characterizing the diversity in the elemental composition of these colloids in complex matrices are missing. Here, we develop a single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS) approach to characterize the elemental compositions of individual metal phosphate and sulfide colloids extracted from complex matrices. The stoichiometry was accurately determined for particles of known composition with an equivalent spherical diameter of ≥∼200 nm. Assisted by machine learning (ML), the new method could distinguish particles of the copper sulfides covellite (CuS), chalcocite (Cu2S), and chalcopyrite particles (CuFeS2) with 75% (for Cu2S) to 99% (for CuFeS2) accuracy. Application of the sp-icpTOF-MS method to particles recovered from natural samples revealed that iron sulfide (FeS) particles in lake sediment contained ∼4% copper and zinc impurities, whereas pure pyrite (FeS2) was identified in hydraulic fracturing wastewater and confirmed by selected area electron diffraction. Colloidal mercury in an offshore marine sediment was present as pure mercury sulfide (HgS), whereas geogenic HgS recovered from an industrial process contained ∼0.08 wt % silver per Hg, enabling source apportionment of these colloids using ML. X-ray absorption spectroscopy confirmed that Hg was predominantly present as metacinnabar (β-HgS) in the industrial process sample. The determination of impurities in individual colloids, such as zinc and copper in FeS, and silver in HgS may enable improved assessment of their origin, reactivity, and bioavailability potential.

Mechanism of the impact of sediment particles on energy loss in mixed-flow pumps

Numerical simulations were performed on the fluid domain of the mixed-flow pump with different solid-phase volume fractions to examine the influence of the sediment particles on internal energy dissipation. The energy properties of the mixed-flow pump were analyzed using the entropy production theory, considering the various flow rates and the solid particle conditions. The research examined the impact of the proportion of the solid particles in the flow on the performance and effectiveness, uncovering the complexities of the energy dissipation in the channel. The results showed that incorporating solid particle media resulted in the decrease in both the performance and effectiveness of the mixed-flow pump compared to water conditions. The mixed-flow pump's head decreased by 0.56 % and its efficiency declined by 2.74 % due to the change in particle volume fraction (Cv) from 5 % to 7.5 %. Upon transitioning from Cv = 7.5 % to Cv = 10 %, the head exhibited a 2.54 % decrease, coupled with a 7.22 % efficiency reduction, signifying pronounced energy loss. The findings highlight that the increase in the quantity of the solid particles enhances the pump's energy dissipation. Solid particles tend to be mainly concentrated in the impeller inlet, blade outer edge, guide vane inlet, and guide vane outer edge regions at varying solid-phase volume fractions. The main dissipation in the fluid region of the mixed flow pump mainly occurs in the impeller and the guide vane, the total energy loss in the guide vane is more than 500 W under the three volume fractions, the total energy loss in the impeller is also about 500 W, and the inlet and outlet losses are small. These research outcomes lay the groundwork for further enhancements in the energy characteristics of mixed-flow pumps.

Effect of gravel pack permeability on horizontal well productivity loss under secondary methane hydrate formation: Experimental optimization of 3D randomly distributed mixed sand pack

Horizontal well productivity is limited by secondary hydrate formation (temperature drop results from endothermic of hydrate dissociation) during production. Seepage capacity as one of the key indexes for evaluating production efficiency, and efficiency is declined by sand production. Sand control is achieved by using gravel pack technology (selected sands for hindering the sediments particles migration), which extends the production time. However, forecasting the productivity decline trend from quantifying the permeability of the gravel pack after secondary formation remain challenges. To address these issues, a randomly distributed 3D normalized permeability (Kr) model was developed to describe the seepage capacity of gravel pack composed by various particle sizes of mixed glass beads. The theoretical modelling was established by observing micro spatial structure of glass beads with hydrate formation. The new model considered three consolidation modes of hydrate in pores (cementing + bearing, pore filling, and grain coating) and linked them with the productivity ratio equation of a horizontal gas well. To confirm the viability of the model, a series of permeability measurement experiments with various size ratios (α) from 1 to 10 were conducted. Finally, errors comparison and all parameters of the model were analyzed. The results showed that the productivity ratio declined clearly after saturation is >0.79, when α = 4. For long-term production, α = 10 would be better. The new model can help hydrate horizontal wells increase production from laboratory to industrial exploitation. KeyPoints•Secondary hydrate formation permeability model in gravel pack was established.•After secondary saturation's effect on horizontal well production was developed.•Gravel pack was simulated by random non-coincident particles with varies size ratios.•When the size ratio is 4, productivity ratio of horizontal well was extended.

Particle size distribution of total suspended sediments in urban stormwater runoff: Effect of land uses, precipitation conditions, and seasonal variations

Understanding particle size distribution (PSD) of total suspended sediments in urban runoff is essential for pollutant fate and designing effective stormwater treatment measures. However, the PSDs from different land uses under different weather conditions have yet to be sufficiently studied. This research conducted a six-year water sampling program in 15 study sites to analyze the PSD of total suspended sediments in runoff. The results revealed that the median particle size decreased in the order: paved residential, commercial, gravel lane residential, mixed land use, industrial, and roads. Fine particles less than 125 μm are the dominant particles (over 75%) of total suspended sediments in runoff in Calgary, Alberta, Canada. Roads have the largest percentage of particles finer than 32 μm (49%). Gravel lane residential areas have finer particle sizes than paved residential areas. The results of PSD were compared with previous literature to provide more comprehensive information about PSD from different land uses. The impact of rainfall event types can vary depending on land use types. A long antecedent dry period tends to result in the accumulation of fine particles on urban surfaces. High rainfall intensity and long duration can wash off more coarse particles. The PSD in spring exhibits the finest particles, while fall has the largest percentage of coarse particles. Snowmelt particles are finer for the same land use than that during rainfall events because the rainfall-runoff flows are usually larger than the snowmelt flows.

Mesh-free SPH modelling of sediment scouring and flushing considering grains transport and transformation

Sediment scour numerical simulation plays a critical role in the design of water-resistant foundation engineering, and this paper addresses a significant gap in most related studies, which often overlook the transformation of sediment and struggle to identify the actual riverbed obscured by yielding bed and suspended load. To tackle this challenge, a comprehensive sediment model based on the meshless Smoothed Particle Hydrodynamics (SPH) method was developed. Firstly, to enhance computational efficiency and mitigate the high cost of Fluid-Solid Interaction (FSI) between water and sediments, cohesionless sediment grains were modelled as non-Newtonian fluids, with yield strength determined according to a combined strength criterion. Subsequently, sediment transformation and identification were determined based on sediment particle velocity and shear stress, with the seepage force driving yield sediment particle motion at the interface. The effectiveness of this comprehensive sediment model was validated through comparison with three scour experiments. The results show better agreement between the model and experimental data, with a root-mean-square error of less than 2.17% in scour morphology simulation and successful identification of the actual post-scouring bed surface in each case. However, the free surface simulation in this model still exhibits slight error, with a root-mean-square error of less than 8.35%.

Local hydrography and interactions with benthic megafauna explain fish assemblage structure on the shallow inner shelf of Paraná, southern Brazil

An important objective of fish ecology is to understand pure and shared effects of abiotic, biotic, and spatial predictors of fish assemblages’ structure on continental shelves. This study aims to assess the structure of the bottom-associated fish assemblage on the shallow inner continental shelf of Paraná, southern Brazil, in response to physicochemical, biological, and spatial factors. We hypothesize that this structure is associated with the benthic megafauna, particularly with the distribution of the Brazilian seabob shrimp Xiphopenaeus kroyeri, an abundant fishing resource on the shallow coast of Paraná. We used uni and multivariate analyses to examine the distribution of abundance, richness, and composition of ichthyofauna in the region. Using variance partitioning analysis, we determined the pure and shared effect of spatial (latitude and longitude), physicochemical, and spatiotemporal distribution patterns of crustaceans, echinoderms, and mollusks as potential predictors of the structure of the fish assemblage. The data were obtained monthly from a one-year bottom trawl survey, comprising five transects and four depths (six, nine, 12 and 15 m) in a 60 km long section of the inner continental shelf, under the influence of estuaries. We captured 57578 demersal fish, comprising 37 families and 88 species. The average abundance of fish per haul was 387 individuals at a depth of 6 m, decreasing to 114 individuals per haul at 15 m. Average richness also decreased along the bathymetric profile, from 15 to 10 species per haul. Fish abundance and richness responded positively to a seasonal estuarine discharge pattern that was stronger in summer and autumn. High biomass of juvenile seabob shrimp in shallower regions also explained the higher abundances and richness. The results also suggest the existence of two fish assemblages in the region, associated with the distribution of the megafauna and segregated by depth, water surface transparency, and sediment particle size composition. Despite significant seasonal variations, controlled by precipitation and bottom water temperature, the structure of fish assemblages responded to the pure and shared effects of the three predictive components in all seasons. In particular, local coastal hydrography and the prey-predator relationship between fish and seabob shrimp were ecologically relevant processes for structuring fish assemblages at the inner continental shelf of Paraná. This study highlights the complexity of ecological interactions within demersal fish assemblages and the importance of considering biotic and abiotic factors in understanding fish distribution patterns at the spatial scale of inner continental shelves that are influenced by estuaries.

Experimental investigation on methane hydrate-bearing sediment permeability under a wide range of conditions

Depressurization exploitation of hydrate in methane hydrate-bearing sediments (MHBS) causes changes in sediment effective stress, deformation, and hydrate content, often resulting in decreased permeability which reduces gas production efficiency. To investigate the evolution of MHBS permeability subjected to these changing conditions, permeability tests on MHBS of different methane hydrate saturation level were performed during isotropic compression and drained triaxial shearing under a wide range of effective stress conditions. The results obtained from compression tests indicate that with increasing effective stress, MHBS permeability first decreases rapidly and then tends to stabilize, and the influence of hydrate saturation on permeability gradually reduces. The permeability during the triaxial shear process is closely related to volumetric deformation, with shear-contraction specimen exhibiting continuous decrease in permeability and shear-dilation specimens experiencing an increase in permeability. Unique correlation between permeability with effective void ratio (affected by hydrate saturation) was observed at low confining pressure and early stage of shear. However, this relationship becomes nonunique under increased pressure and shear strain. Thus, a unified MHBS permeability model for a range of conditions is established based on the observed relationship between MHBS permeability and effective void ratio, considering the influence of confining stress, shear strain, and the breakage of sediment particles.

13C evidence for the selective loss of active and inert organic carbon in soil aggregates under rain-induced overland flow erosion

Due to the hierarchical structure of aggregates, raindrops cause changes in the composition, distribution and state of aggregate-wrapped organic carbon (OC) fractions during erosion, greatly affecting soil carbon turnover and sequestration. To explore these regulatory mechanisms, the selective transport of light (LFoc) and heavy (HFoc) fraction OC within aggregates of varying sizes was traced via the 13C/12C carbon isotope ratio (δ13C) under splash and sheet erosion conditions. A “three-zone” variable-slope soil pan was filled with loess soil with a high aggregate concentration to monitor rainfall erosion on a slope. The OC aggregate composition, aggregate stripping and δ13C values of the sediment aggregates of various particle sizes were measured. When the erosion intensity was low, the splash-eroded sediment was mainly enriched in 13C-rich HFoc, and as the rainfall intensity increased, the concentrations of 12C-rich LFoc and HFoc gradually increased. That is, under heavy rainfall, aggregate fragmentation exposed more large fragments rich in younger HFoc and LFoc, and these fragments underwent saltation. There was no obvious correlation between the trends in splash erosion and OC, so runoff transport was an important factor influencing the correlation between δ13C and OC (P < 0.05). Raindrop impact exposed HFoc-rich aggregate fragments of different sizes, e.g., stable mineral-associated OC. Runoff promoted the obvious preferential transport of LFoc and the redistribution of particulate OC (POC) among different sediment particles. Mineral-associated OC and 2–0.05 mm easily decomposable LFoc or POC were preferentially transported, causing OC with the highest and median δ13C values to be preferentially transported. Overall, the transport order of aggregate-exposed OC particles was clay + silt particle-bonded OC, POC, POC-bonded aggregate fragments and silt-bonded aggregate fragments. These results verified the selective loss of aggregate-detached OC fragments during erosion, which led to a change in the OC sequestration and reaggregation potential of OC in the eroded and deposited soil.

Improving the accuracy of sediment source fingerprinting under particle sorting

Sediment fingerprinting has proven highly efficient and rapid in identifying the sources and hotspots of sediment, thereby facilitating the targeted implementation of control measures. However, the unpredictable effect of particle sorting during sediment transport on source identification has increased the uncertainty associated with this method. Here, laboratory sieving experiments were carried out to simulate particle sorting during sediment transport. The conservatism of the five widely used tracers (geochemical elements, mid-infrared, near-infrared, visible, and color properties) and the accuracy of sediment source fingerprinting were investigated in the process of sorting. The results highlight that selected tracers exhibited high source contribution prediction accuracy (mean MAE 6.6 %) without particle sorting, with the exception of the color tracer. In contrast, the predictive ability of all tracers significantly reduced (mean MAE 16.2 %) in simulated particle sorting groups (especially for 125–31 μm) due to the enrichment of fine particles. Moreover, the correction factor failed to improve the accuracy of source contribution prediction in this study. The uncertainty caused by particle sorting can be effectively resolved by narrowing the source and sediment particle sizes to <63 μm (for all five tracers) or <31 μm (except for color tracer). This study contributes a deeper understanding of the role of particle size in sediment source fingerprinting, providing valuable insights to guide future tracer selection and associated particle size criteria.

Centennial Records of Microplastics in Lake Cores in Huguangyan Maar Lake, China.

Microplastic records from lake cores can reconstruct the plastic pollution history. However, the associations between anthropogenic activities and microplastic accumulation are not well understood. Huguangyan Maar Lake (HML) is a deep-enclosed lake without inlets and outlets, where the sedimentary environment is ideal for preserving a stable and historical microplastic record. Microplastic (size: 10-500 μm) characteristics in the HML core were identified using the Laser Direct Infrared Imaging system. The earliest detectable microplastics appeared unit in 1955 (1.1 items g-1). The microplastic abundance ranged from n.d. to 615.2 items g-1 in 1955-2019 with an average of 134.9 items g-1. The abundance declined slightly during the 1970s and then increased rapidly after China's Reform and Opening Up in 1978. Sixteen polymer types were detectable, with polyethylene and polypropylene dominating, accounting for 23.5 and 23.3% of the total abundance, and the size at 10-100 μm accounted for 80%. Socioeconomic factors dominated the microplastic accumulation based on the random forest modeling, and the contributions of GDP per capita, plastic-related industry yield, and total crop yield were, respectively, 13.9, 35.1, and 9.3% between 1955-2019. The total crop yield contribution further increased by 1.7% after 1978. Coarse sediment particles increased with soil erosion exacerbated microplastics discharging into the sediment.

Response of macrobenthic communities to a Spartina alterniflora management project on tidal flats in Hangzhou Bay, China

Spartina alterniflora is one of the most invasive plants on Chinese tidal flats. To explore the responses of macrobenthic communities to the removal of S. alterniflora and the restoration of tidal flats, a survey of macrobenthic and sediment environmental factors was carried out in June 2022 in the mudflat recovery area (MRA) of tidal flats on the south bank of Hangzhou Bay, China. A proximate natural mudflat area (NMA), S. alterniflora area (SAA) and Scirpus mariqueter area (SMA) were selected for comparison with the MRA. A total of 48 macrobenthic species were identified, with 13, 28, 22 and 21species in the MRA, NMA, SAA and SMA, respectively. Cluster, multidimensional scaling (MDS) and SIMPER analysis suggested that the similarity between macrobenthic communities in the MRA and the NMA was high, whereas the similarity between macrobenthic communities in the MRA and SAA and the MRA and SMA was very low. The similarity between macrobenthic communities in the SAA and the SMA was high. ANOSIM analysis suggested that the differences between regions were greater than those within regions (R = 0.881). The sediment factors in the MRA were substantially different from those in the other three habitats, while the sediment factors in the SMA and the SAA were the most similar. Macrobenthos were mainly affected by the mean diameter of the sediment particles. After 1 year of natural recovery in the MRA, the macrobenthos approached the pre-project levels, but to ensure the effectiveness of the treatment project and prevent the recurrence of S. alterniflora, continuous monitoring should be carried out.