Sediment dynamic responses of coastal salt marsh to wind waves and swells in a semi-open tidal flat.

Coastal salt marshes provide effective protection to the coastal environments they front against coastal erosion by reducing the incoming wave energy. Understanding sediment dynamic processes in coastal salt marshes environments is of crucial importance for coastal defense. The objective of this study is to assess the impact of Spartina alterniflora (S. alterniflora) marshes on wave attenuation, sediment transport, and morphodynamics through extensive field records on the Cixi tidal flat in Hangzhou Bay. Results demonstrate that wave attenuation by S. alterniflora marshes increases proportionally with the intensification of wind waves at a consistent water depth or significant wave height. Moreover, wave attenuation in the context of wind waves surpasses that of swells. On average, the wave attenuation provided by S. alterniflora marshes during both wind waves and swells is more than six times greater than that offered by the adjacent mudflat. Additionally, net sediment fluxes within S. alterniflora marshes decrease by 37 % in the presence of swells and 84 % with wind waves, in comparison to the mudflat. The influence of S. alterniflora marshes on tidal flat accretion is more pronounced with wind waves than swells. Notably, observed from summer to winter, the surface accretion of tidal flats is highest (∼26 cm) at the edge of S. alterniflora marshes. This study contributes valuable insights into the complex interactions between salt marshes and hydrodynamic forces, essential for informing coastal management strategies.

The roles of geometry and viscosity in the mobilization of coarse sediment by finer sediment.

In rivers, the addition of finer sediment to a coarser riverbed is known to increase the mobility of the coarser fraction. Two mechanisms have been suggested for this: a geometric mechanism whereby smaller sizes smooth the bed, increasing near-bed velocity and thus mobility of the larger sizes, and a viscous mechanism whereby a transitionally smooth turbulent boundary layer forms, rendering the coarser grains more mobile. Here, we report on experiments using two sediment mixtures to better understand these proposed mechanisms. In Mixture 1, we used 0.5 and 5 mm grains, and in Mixture 2, we used 2 and 20 mm grains. If the entrainment of coarse gravel by finer sediment is a purely geometric effect, then the addition of finer material should produce the same effect on the mobility of the coarser material for both mixtures because they have the same size ratio. We show that addition of finer material has a different effect on the two mixtures. We observed an increase in the mobility of the coarse fraction for both mixtures, but the increase in coarse fraction mobility for Mixture 1 was almost twice that for Mixture 2. Our experiments show that in addition to the geometric effect, enhancement of coarse gravel transport by finer sediment is also driven by a viscous effect.

Assessing the possible influence of human activities on sediment transport in the Saskatchewan River and its delta.

Sediment transport is a complex, multi-dimensional process. With the advancement in computing power and sophistication of computer applications over recent decades, it has become possible to conduct detailed analysis and simulations of soil erosion and sediment transport. The primary objective of this study was to examine and predict the potential influence of human activities on sediment transport. This was achieved by analyzing sediment transport in the Saskatchewan River beneath the E.B. Campbell Dam and in the Saskatchewan River Delta. The Hydrologic Engineering Center's-River Analysis System (HEC-RAS) was deployed to ascertain the sediment transport capacity and estimate erosion, sedimentation, and riverbed changes. Cross-sectional data, flow data, and sediment data were used in conjunction with HEC-RAS. The simulation results reveal that sediment transport below the E.B. Campbell Dam is limited, leading to notable sediment erosion. The selected study area has witnessed significant erosion during high-flow periods, particularly in the event of floods. Between 2012 and 2019, the riverbed elevation at the selected survey site decreased by approximately 0.45 m. The study findings corroborate that the Saskatchewan River and its delta have been impacted by human activities. Potential erosion and deposition below the E.B. Campbell Dam have been simulated for the selected site. The aim is to provide decision-makers or related stakeholders with insight into how dam operations can be adjusted to decrease erosion while sustaining hydrological, ecological, and environmental outcomes from human activities.

Deep-sea mining rock-fragment dispersal scenarios associated with submesoscale forcings: A case study in the Atlantic.

In the last few years, the exploitation of deep-sea regions for minerals extraction raised international attention as an economically viable source for the mining industry. However, most of these minerals are found close to sensitive ecosystems that can be harmed by mining activities. Given the potential impact, there is a need for the establishment of best practices towards the adoption of preventive strategies for the sustainable management and exploitation of deep-sea environments. To accomplish this objective, numerical models have proven to be reliable tools to support decision-making. In the present study, a high-resolution eddy-resolving ocean numerical model was configured and integrated with a semi-Lagrangian model aiming to map the transport of rock-fragments associated with mining activities. The model was applied to an area rich in polymetallic sulphides at the Northern Mid-Atlantic Ridge (NMAR). Model results showed that local topography and circulation dynamics played an important role for the dispersion and settling of the rock-fragments. In the presence of local submesoscale processes, the residence time do not follow the neutral relation H/vs. It was demonstrated that, depending on the local hydrodynamics, rock-fragments released at sub-surface depth can impact wider areas, with a predicted impact on pelagic and benthic organisms.

Spatial-temporal variations of sediment transport rate and driving factors in Shule River Basin, northwest China.

The sediment content and transport rate of rivers are crucial indicators reflecting soil erosion, water quality, and water resource management in a region. Studying changes in river sediment transport rates within a basin is essential for evaluating water quality, restoring water ecosystems, and implementing soil and water conservation measures. This study focused on the Shule River Basin and utilized various methods such as moving average, cumulative anomaly, Mann-Kendall mutation test, Mann-Kendall (M-K) trend test, Sen's slope estimation, Correlation analysis, wavelet analysis, R/S analysis, ARCGIS10.7 interpolation, non-uniformity coefficient, and concentration to analyze data from hydrologic stations at Changmapu (CMP), Panjiazhuang (PJZ), and Dangchengwan (DCW). The research examined the temporal and spatial characteristics of sediment transport rates and identified key driving factors. Findings revealed significant increases in annual sediment transport rates at CMP and PJZ by 12.227 and 4.318 kg/s (10a)-1, respectively, while DCW experienced a decrease of 0.677 kg/s (10a)-1. The sediment transport rate of the three stations had a sudden change around 1994. The average annual sediment transport rates displayed distinct cycles, with CMP, PJZ, and DCW showing cycles of 51a, 53a, and 29a respectively. Additionally, while CMP and PJZ exhibited a continuous upward trend in sediment transport rates, DCW showed a consistent decline. The annual average sediment transport rates of CMP, PJZ, and DCW were 1305.43 kg/s, 810.06 kg/s, and 247.80 kg/s, respectively. These research findings contribute to enhancing the comprehension of sediment dynamics in the arid region of northwest China and offer a theoretical basis for the restoration and management of ecological environments in similar areas in the future.

Design of a sensor to estimate suspended sediment transport in situ using the measurements of water velocity, suspended sediment concentration and depth.

- The sediment transport plays a major role in every aquatic ecosystem. However, the lack of instruments to monitor this process has been an obstacle to understanding its effects. We present the design of a single sensor built to measure water velocity, suspended sediment concentration and depth in situ, and how to associate the three variables to estimate and analyse sediment transport. During the laboratory calibrations, the developed instrument presented a resolution from 0.001 g/L to 0.1 g/L in the 0-12 g/L range for the measurement of suspended sediment concentration and 0.05 m/s resolution for 0-0.5 m/s range and 0.001 m/s resolution for 0.5-1 m/s range for the measurement of water velocity. The device was deployed for 6 days in an estuarine area with high sediment dynamics to evaluate its performance. During the field experiment, the sensor successfully measured the tidal cycles and consequent change of flow directions, and the suspended sediment concentration in the area. These measurements allowed to estimate water discharge and sediment transport rates during the different phases of tides, and the daily total volume of water and total amount of sediment passing through the estuary.

Simulating liquefaction-induced resuspension flux in a sediment transport model.

Wave-induced liquefaction is a geological hazard under the action of cyclic wave load on seabed. Liquefaction influences the suspended sediment concentration (SSC), which is essential for sediment dynamics and marine water quality. Till now, the identification of liquefaction state and the effect of liquefaction on SSC have not been sufficiently accounted for in the sediment model. In this study, we introduced a method for simulating the liquefaction-induced resuspension flux into an ocean model. We then simulated a storm north of the Yellow River Delta, China, and validated the results using observational data, including significant wave heights, water levels, excess pore water pressures, and SSCs. The liquefaction areas were mainly distributed in coastal zones with water depths less than 12 m, and the simulated maximum potential soil liquefaction depth was 1.39 m. The liquefaction-induced SSC was separated from the total SSC of both liquefaction- and shear-induced SSCs by the model, yielding a maximum liquefaction-induced SSC of 1.07 kg·m-3. The simulated maximum proportion of liquefaction-induced SSC was 26.2% in regions with water depths of 6-12 m, with a maximum significant wave height of 3.4 m along the 12 m depth contour. The erosion zone at water depths of 8-12 m was reproduced by the model. Within 52.5 h of the storm, the maximum erosion thickness along the 10 m depth contour was enhanced by 33.9%. The model is applicable in the prediction of liquefaction, and provides a new method to simulate the SSC and seabed erosion influenced by liquefaction. Model results show that liquefaction has significant effects on SSC and seabed erosion in the coastal area with depth of 6-12 m. The validity of this method is confined to certain conditions, including a fully saturated seabed exhibiting homogeneity and isotropic properties, small liquefaction depth, residual liquefaction dominating the development of pore pressures, no influence by structures, and the sediment composed of silt and mud that experiences frequent wave-induced liquefaction.

Evaluating the effects of laver cultivation on tidal flat erosion: Toward sustainable environmental practices.

The rapid expansion of laver (Porphyra yezoensis) cultivation on lower tidal flats has become integral to the local economy, yet it also raises concerns regarding its potential impact on the morphological evolution due to increasing human activities. This study utilizes integrated near-bed field measurements to assess morphological dynamics and quantify sediment erosion processes, highlighting the significant impact of laver harvest on tidal flat stability. Our results show that erosion and bed coarsening in the cultivated areas experienced a notable intensification immediately after harvest, with net erosion in cultivated areas reaching approximately -38.2 mm during the first tide post-harvest, markedly higher-more than an order of magnitude-compared to adjacent uncultivated areas. The erosion rate notably spiked with the average bed level change rate increasing to -13.8 × 10-4 mm/s, compared to a rate of +0.3 × 10-4 mm/s during the unharvest period. Subsequently, the cultivated areas entered a recovery phase with a deposition amount of +12.5 mm, while the net cumulative erosion thickness throughout the entire observation period was -25.2 mm. The cultivation method, characterized by consistent harvests every 10 days, means that even minor erosion from continuous harvests can escalate into significant degradation. This study suggests that long-term cultivation cycle practices may result in irreversible changes to the depositional environment, potentially jeopardizing the habitat viability and ecological function. Sustainable agricultural strategies, including site selection, infrastructure planning, monitoring environmental changes, ecological assessments and sustainable practices, are recommended to mitigate the negative impacts of cultivation on regional stability and preserve the coastal ecological balance.

Flow rate influence on sediment depth estimation in sewers using temperature sensors.

Enhancing sediment accumulation monitoring techniques in sewers will enable a better understanding of the build-up processes to develop improved cleaning strategies. Thermal sensors provide a solution to sediment depth estimation by passively monitoring temperature fluctuations in the wastewater and sediment beds, which allows evaluation of the heat-transfer processes in sewer pipes. This study analyses the influence of the flow conditions on heat-transfer processes at the water-sediment interface during dry weather flow conditions. For this purpose, an experimental campaign was performed by establishing different flow, temperature patterns, and sediment depth conditions in an annular flume, which ensured steady flow and room-temperature conditions. Numerical simulations were also performed to assess the impact of flow conditions on the relationships between sediment depth and harmonic parameters derived from wastewater and sediment-bed temperature patterns. Results show that heat transfer between water and sediment occurred instantaneously for velocities greater than 0.1 m/s, and that sediment depth estimations using temperature-based systems were barely sensitive to velocities between 0.1 and 0.4 m/s. A depth estimation accuracy of ±7 mm was achieved. This confirms the ability of using temperature sensors to monitor sediment build-up in sewers under dry weather conditions, without the need for flow monitoring.

Assessment of soil erosion in the Upper Citarum watershed for sustainability of the Saguling reservoir: unmixing model approach.

The Citarum watershed and the Saguling reservoir are vital natural resources in Indonesia, affecting the livelihood of West Java and the DKI Jakarta population. This study aimed to assess the soil erosion in the Upper Citarum watershed and identify its source. The study used the fallout radionuclide technique, geochemical tracers, and an unmixing model to measure soil erosion and the contribution of suspended sediment sources due to erosion. Soil bulk transects and surface soil were sampled using a coring tool on the Ciwidey and Cisangkuy sub-watersheds. Riverbank and suspended sediment samples were collected from tributaries and rivers. With 137Cs, 40% of the samples had values below the minimum detectable activity, and vice versa for 210Pbex, all samples are detectable. For mitigation, bare land needs to be recovered due to its erosion (25.6 t ha-1 year-1) exceeding the tolerance erosion value (17 t ha-1 year-1). Statistically, Mg and Na were the most appropriate composite tracers for suspended sediment contribution. The unmixing model predicted the sediment contributors from bare land (58%), the riverbank (32.7%), and plantation land (9.3%). Proper land conservation could reduce sediment supply by almost 14.7% and extend the reservoir's life. This is the first study to report the feasibility of the unmixing model in Indonesia.

Understanding the dynamics of microplastics transport in urban stormwater runoff: Implications for pollution control and management.

The transport of microplastics (MPs) from urban environments to water resources via stormwater runoff poses significant concerns due to its adverse impacts on water safety and aquatic ecosystems. This study presents a modeling approach aimed at understanding the transport mechanisms of MPs in an urban residential setting, considering settling and buoyant MPs. To consider the effect of MP shapes, the settling velocity of various settling MPs in shapes of fibers, films, and fragments was calculated. Using an analogy of sediment transport, a Rouse number criterion was used to analyze the transport of MPs. For buoyant MPs, it was assumed that they transport as wash-load as soon as they float in the water and the travel time for them to reach the storm drain was determined. The calculation of settling velocity revealed the influence of shape on the settling velocity of MPs was particularly pronounced as the equivalent diameter of the MPs increased. The transport mechanism for the smallest settling MPs, irrespective of their shapes, density, and depth of flow, was wash-load. However, for larger MPs, the shape and size distribution of settling MPs, along with the depth of flow and slope significantly influenced their transport mechanisms compared to sediment particles. The influence of weathering on the MPs' transport mechanisms depended on their sizes and shapes. The site-specific characteristics, including slope and surface friction, significantly influenced the velocity of stormwater runoff and, consequently, the extent of MP transport during rain events. Moreover, an evaluation of the transport mechanism of settling MPs was conducted using the reported field data on MP abundance in road dust collected from residential and traffic sites. This study underscores the complexity of MP transport dynamics and provides a foundation for developing targeted strategies to mitigate MP pollution in urban environments.

Spatio-temporal variations of methane fluxes in sediments of a deep stratified temperate lake.

Spatio-temporal variability of sediment-mediated methane (CH4) production in freshwater lakes causes large uncertainties in predicting global lake CH4 emissions under different climate change and eutrophication scenarios. We conducted extensive sediment incubation experiments to investigate CH4 fluxes in Lake Stechlin, a deep, stratified temperate lake. Our results show contrasting spatial patterns in CH4 fluxes between littoral and profundal sites. The littoral sediments, ∼33% of the total sediment surface area, contributed ∼86.9% of the annual CH4 flux at the sediment-water interface. Together with sediment organic carbon quality, seasonal stratification is responsible for the striking spatial difference in sediment CH4 production between littoral and profundal zones owing to more sensitive CH4 production than oxidation to warming. While profundal sediments produce a relatively small amount of CH4, its production increases markedly as anoxia spreads in late summer. Our measurements indicate that future lake CH4 emissions will increase due to climate warming and concomitant hypoxia/anoxia.

Storm and tidal interactions control sediment exchange in mixed-energy coastal systems.

Storms can have devasting effects on shorelines, causing flooding and the destruction of property and infrastructure. As global warming and the frequency and magnitude of tropical storms increase, barrier islands comprising 10% of the world's coast may undergo significant change caused by beach erosion, loss of dunes, and formation of washovers and tidal inlets. Understanding how storms affect sediment transport at tidal inlets is an understudied subject that directly influences barrier island erosional-depositional processes and long-term sediment budgets. This study models hydrodynamics and sediment transport at a conceptualized mixed-energy, mesotidal inlet system using 10 synthetic storm tracks. We investigate the provenance and the role of various storm characteristics and timing between the peak storm surge and high tide on sediment fluxes for different grain sizes. We find that most storms (38 of 40) cause a net import of sediment into the basin that is sourced primarily from the updrift and downdrift nearshore and secondly from the ebb-delta. Very little sediment comes from inlet channel scour. Cumulative (net) transport correlates well with peak significant wave height because wave height influences bottom shear stresses and sediment suspension on the ebb-tidal delta and in the nearshore. The duration of the storm surge also correlates with net transport because it controls the period of flood-directed currents. Our findings help explain the formation of flood deltas inside tidal inlets and the formation of sand shoals in backbarrier regions. Storm-induced enlargement of these deposits represents a permanent long-term loss of sand from barrier islands that will lead to erosion.

Microplastic infiltration into mobile sediments.

This study investigates the dynamics of microplastic infiltration into non-stationary sandy sediments, a pressing environmental concern due to the rising prevalence of microplastics in aquatic ecosystems. An annular flume was used to simulate riverine bedform motion, examining the suspension and infiltration of denser-than-water microplastic particles, including polyvinyl chloride (PVC), polyamide (PA), and polylactide (PLA). The experiments focused on various particle sizes (ranging from 0.2 to 5 mm in diameter) and bedform migration speeds, known as celerities. The findings indicate that particle size is a significant factor influencing the depth of infiltration and distribution within sediment layers, whereas the impact of bedform celerities and particle densities appears less significant. This research provides novel insights into the behavior of microplastics in dynamic sedimentary environments, highlighting the intricate interaction between microplastic characteristics and sedimentary processes. The results contribute to an enhanced understanding of microplastic distribution and accumulation in riverine systems, offering crucial data for developing predictive models and formulating potential remediation strategies for microplastic pollution.

Numerical model study on stability of a micro-tidal inlet at Muttukadu along the east coast of Bay of Bengal.

The complexity of micro-tidal inlets arises from the combined action of littoral drift and tidal range on their stability. Consequently, understanding and evaluating their stability poses a significant challenge. This study aims to shed some insight on the assessment of inlet stability by employing Delft 3D model. The stability of the inlet between the ocean and estuary relies on the balance between the longshore transport rate and the spring tidal prism. Disrupting this equilibrium results in the closure of the inlets. The movement of sediments in the surf zone is primarily driven by longshore velocity, which acts as the driving force for littoral drift, which is estimated using Delft 3D wave model. The longshore transport rate is estimated by employing empirical relationships and numerical codes based on the obtained driving force. Subsequently, the stability of the inlet is assessed based on these estimations. The spring tidal prism refers to the discharge of water flowing into the ocean from inlets and estuaries. Flow velocity is determined using Delft 3D flow model. The input data for nearshore circulation resulting from waves and currents is primarily collected through field measurements and data collected from Indian National Centre for Ocean Information Services (INCOIS). For the current study, Muttukadu (12°47'13″N, 80°15'01″E) inlet, Kovalam along the East Coast of the Indian Peninsula is investigated by assessing its seasonal variations. This study contributes to the management of marine biological ecology, the expansion of small-scale artisanal fishing, the promotion of water sports-related tourism, the advancement of fishing harbor development, and the execution of coastal engineering projects.

Morphodynamics of a composite sand-cobble beach in response to extratropical cyclone Fiona and seasonal wave variability.

Climate change is driving higher coastal water levels, and models project accelerated future sea-level rise and coastal storm intensification. These dynamics paired with anthropogenic coastal alterations will drive drastic coastal change worldwide. Composite beaches with mixed sediment sizes warrant detailed study as these exhibit complex morphodynamics in response to changing hydrodynamics due to the distinct transport thresholds of different sediment types. This study uses a novel multi-method approach to investigate a composite sand-cobble beach in Atlantic Canada experiencing a shortening seasonal sand-covered period. Hydrodynamic forcing and associated beach changes were monitored over a focused eight-month period, while satellite-based visual imagery and reconstructed wave data were analyzed over longer periods. Results show that intra-annual wave energy changes drive sand dynamics, with reduced summer wave energy facilitating short-term deposition. Long-term positive trends were identified in late spring wave heights, which likely contribute to the shortening sand-covered period. Seasonal dynamics were overwhelmed by extratropical cyclone Fiona, which made landfall on September 24, 2022, generating significant wave heights up to 6.8 m in the bay, mobilizing sediment, and steepening cobble berms. A new index approach based on visual imagery facilitated the investigation of beach sand appearance/disappearance using the relative redness of sand compared to cobble. Finally, the UAV-based surveys yielded high-resolution orthomosaics and LiDAR-based elevation mapping, and highlighted pronounced longshore variability in erosion and deposition during Fiona. The beach mostly recovered to pre-storm conditions in <4 months, which indicates that proposed beach nourishment activities may only experience temporary success. The longer-term results showing a conversion of sand to cobble suggest that loss of sandy beach habitat is likely to increase, even without shoreline migration or coastal squeeze driven by sea-level rise.

Quantifying microplastic dispersion due to density effects.

An experimental study was conducted on how polymer density affects the transport and fate of microplastics in aquatic flows. For the first time, polypropylene (PP), polyethylene (PE), polymethyl methacrylate (PMMA), polyetheretherketone (PEEK), and polyvinyl chloride (PVC) were chemically stained and tested using solute transport techniques and velocities found among rivers in the natural environment (0.016 - 0.361 m/s). The movement of 3D-polymers with densities ranging from 0.9 - 1.4 g/cm³ was quantified in a laboratory flume scaled to simulate open-channel flows in fluvial systems. Except for PP, in most conditions microplastics exhibited similar transport characteristics to solutes regardless of density and established solute transport models were successfully implemented to predict their transport and fate. Mass recoveries and ADE routing model demonstrated microplastic deposition and resuspension was associated with polymer density below critical velocity thresholds ≤ 0.1 m/s. When density becomes the dominant force at these slower velocities, concentrations of denser than water microplastics will be momentarily or permanently deposited in channel beds and microplastics follow the classical Shields sediment transport methodology. This data is the first to provide microplastic suspension and deposition thresholds based on river velocity and polymer density, making a key contribution to research predicting microplastic fate and organismal exposure.

Assessment of sediment transport in Luxiapuqu watershed using RUSLE-TLSD and InSAR techniques: Yarlung Tsangpo River, China.

The Yarlung Tsangpo River Basin is characterized by its intricate topography and a significant presence of erosive materials. These often coincide with heavy localized precipitation, resulting in pronounced hydraulic erosion and geological hazards in mountainous regions. To tackle this challenge, we integrated the RUSLE-TLSD (Revised Universal Soil Loss Equation-Transportation-limited sediment delivery) model with InSAR (Interferometric Synthetic Aperture Radar) data, aiming to explore the sediment transport process and pinpoint hazard-prone sites within mountainous small watershed. The RUSLE-TLSD model aids in evaluating multi-year sediment transport dynamics in mountainous zones. And, the InSAR data precisely delineates changes in sediment scouring and siltation at sites vulnerable to hazards. Our research estimates that the potential average soil erosion within the watershed stands at 52.33 t/(hm2 a), with a net soil erosion of 0.69 t/(hm2 a), the sediment transport pathways manifest within the watershed's gullies and channels. Around 4.32% of the watershed area undergoes sedimentation, predominantly at the base of slopes and within channels. Notably, areas (d) and (e) emerge as the most susceptible to disasters within the watershed. Further analysis of the InSAR data highlighted four regions in the typical area (e) from 2017 that are either sedimentation- or erosion-prone, referred to as "hotspots." Among them, R1 exhibits a strong interplay between water and sediment, rendering it highly sensitive to environmental factors. In contrast, R4, characterized by a sharp bend in siltation, remains relatively impervious to external elements. The NDVI (normalized difference vegetation index) stands out as the pivotal determinant influencing sediment transport within the watershed, exerting a pronounced impact on the outlet section, especially in spring. By employing this approach, we gained a deeper understanding of sediment transport mechanisms and potential hazards in small watershed in uninformative mountainous areas. This study furnishes a robust scientific framework beneficial for erosion mitigation and disaster surveillance in mountainous watersheds.

A cockle-induced bioturbation model and its impact on sediment erodibility: A meta-analysis.

Modelling the dynamics of an estuary and the evolution of its morphology requires a process-based description not only of the physical processes, but also of the influence of benthic fauna on sediment characteristics at ecosystem scale. A meta-analysis was tested as an approach for modelling the effect of bioturbation exerted by the cockle Cerastoderma edule on sediment erodibility. Six different erosion flume datasets were collected to ensure a broad range of experimental conditions including bed shear stress, population characteristics, and sediment composition. First, a model was built to describe the biogenic fluff layer created by C. edule activity in relation to (i) bioturbation activity using the population metabolic rate [mW·m-2] as a proxy for faunal metabolic energy, and (ii) the silt content [%] of the sediment. Second, different erosion models were compared by testing parameterization steps incorporating both erosion of the fluff layer and/or mass erosion of the sediment bed. Structural differences in the flumes and in the preparation of samples in the six different datasets makes it difficult to propose a single model that satisfactorily simulates all the data and encompasses both types of subsequent erosion, that of the fluff layer and that of the underlying consolidated bed. However, a generic model is proposed for the surficial fluff layer erosion covering a moderate range of bed shear stress (<1 Pa). This study shows that including several datasets covering a wide range of environmental conditions is a key to the robustness of this model, and that new insights can be gained by integrating the complexity of sediment features. We expect that this two-part model can be used in broad contexts in terms of cockle populations, estuarine habitats, and climatic conditions and can combined with various hydro-morpho-sedimentary models that include these biological effects.

Insights into mineralogical distribution mechanism and environmental significance from geochemical behavior of sediments in the Yellow River Basin, China.

Mineralogical investigations on fluvial sedimentary sequences could provide historical environmental information on the effects of human activities and natural events. This study aims to identify the mineralogical distribution mechanism and environmental significance of sediments of the Yellow River Basin based on topographic analysis, statistics, weathering and recycling indices. In total, 107 samples were collected from sedimentary sequences in the source area, and the upper, middle, and lower reaches and analyzed for grain size, major elements, and mineral composition. The results showed that the climate conditions were cold and arid, where weak hydrolysis under continental weathering and strong erosion accelerated physical weathering. Clay minerals in the upper reaches primarily originated from the Tibetan Plateau, whereas the middle and lower reaches received input of aeolian deposits from Northern China. Quartz and feldspar in the middle and lower reaches may derive from the source area and upper reaches. Meanwhile, calcite and dolomite formed through diagenesis, with loess input from the Chinese Loess Plateau. Regarding heavy minerals, the dominant determinative factors of pyrite were post-depositional diagenesis and leaching. Hematite and amphibole primarily formed through magnetite conversion and contribution from regional sources, respectively. Moreover, the mineral distribution mechanism significantly affected the mobility and distribution of geochemical elements through diagenesis and alteration. The findings are instrumental in reconstructing the environmental evolution of large-scale watersheds across multiple climatic zones.