Fine Sediment Research Articles

Lateral Erosion of Bedrock Channel Banks by Bedload and Suspended Load

AbstractBedrock rivers carry large amounts of fine sediment in suspension. We developed a mechanistic model for erosion of bedrock channel banks by impacting bedload and suspended load particles that are advected laterally by turbulent eddies (advection‐abrasion model). The model predicts high lateral erosion rates near the bed, with rates decreasing up to the water surface. The model also predicts greater erosion within the suspended load layer than the bedload layer for many typical sediment supply and transport conditions explored. We compared the advection‐abrasion model with a previously derived model for lateral erosion of bedrock banks by bedload particles deflected by stationary bed alluvium (deflection‐abrasion model). Erosion rates predicted by the deflection‐abrasion model are lower, except within limited conditions where sediment is transported near the threshold of motion and the bed is near fully covered in sediment. Both processes occur in bedrock rivers at the same time, so we combined the advection‐abrasion and deflection‐abrasion models and found that the lateral erosion rate generally increases with increasing transport stage and relative sediment supply for a given grain size. Application of our combined‐abrasion model to a natural bedrock river with a wide distribution of discharge and supply events, and mixed grain sizes, indicates that finer sediment dominates the lateral erosion on channel banks in low sediment supply environments and can be as important as coarser sediment in high sediment supply environments.

The role of non-skeletal carbonate component in Mediterranean Coralligenous: new insight from the CRESCIBLUREEF project

In the frame of the project FISR_04543 “CRESCIBLUREEF - Grown in the blue: new technologies for knowledge and conservation of Mediterranean reefs”, we present preliminary data on the ecological and depositional implications of micritic sediments in a coralligenous bioconstruction formed along the Mediterranean shelf in front of the Marzamemi village (Sicily, Italy). The framework of the build- up is mainly built by crustose coralline algae, which in turn create the substrate for a high-diversified epi- and infaunal community. Two types of microcrystalline calcite, tentatively interpreted as allochthonous and autochthonous micrite, strictly related to fine skeletal debris, have been detected. The allochthonous micrite derive from abiotic accumulation of fine sediments in the framework cavities. The autochthonous micrite is deposited in situ through organic-mediated processes. The occurrence of this component allows hypothesizing a possible contribution of non-skeletal carbonate in the strengthening of the primary framework due to its syndepositional cementation.

Modeling anthropogenic affected sediment transport in a mid-sized European river catchment–extension of the sediment rating curve equation

Land use and water resource management influence the suspended sediment concentration (SSC) in rivers. Fine sediments are an important driver for river development, even in coarse-material-rich rivers. In this study, the sediment rating curve approach is modified to predict SSC several river-km downstream of a sampling site. Further, the prediction is improved by adding sediment input, storage, and dilution effects through relevant anthropogenic measures through a model identification approach. Thus, the impact of the most severe anthropogenic measures, damming and changes in the length of a channel section for the Rur River, could be identified. Further, the impact of describing parameter changes for those measures on the SSC can be computed and considered in future water resource management. In this approach, particle swarm optimization was used to fit parameters in permutable test- and training data sets to identify linear extensions to the sediment rating curve. The input data consists of (1) SSC, which was obtained by sampling along the river section four times a year over approximately two years, (2) discharge data from river gauges supplemented by rainfall-runoff modeling between stations, (3) rainfall data from meteorological stations, and (4) sub-catchment characteristics like river section length and erosivity obtained with GIS. Via incorporating the river section length and sediment deposition in response to damming, we reduced the RMSE (root mean squared error) from 152.27 to 131.83% with a p-value of 0.073 in the Wilcoxon Signed Rank Test. Further integration of sub-catchment parameters like erosivity led to overfitting and decreased prediction accuracy. A catchment-wide prediction was achieved, but sub-catchments operate on different spatial scales with different connectivity behavior, which restricts the transferability of the equation. SSC-Q hystereses provide the first indications of characteristic sediment sources and were used to discuss connectivity behavior within the study area. They are recommended as part of a (sub-) catchment characterization for further studies.

Geochemistry aspects of modern mercury accumulation in bottom sediments from the south-western Chukchi Sea

Mercury (Hg) having a high migration capacity reach the Arctic region via the atmosphere. The absorbers for Hg are sea bottom sediments. Sedimentation in the Chukchi Sea occurs under the influence of highly productive Pacific waters entering through the Bering Strait and the inflow of a terrigenous component from the western direction with the Siberian Coastal Current. The Hg concentrations ranged from 12 μg kg−1 to 39 μg kg−1 in bottom sediments of study polygon. Based on dating sediment core the background concentration was 29 μg kg−1. Concentration of Hg in fine sediment fractions was 82 μg kg−1, in sandy fractions (>63 μm) varied from 8 to12 μg kg−1. In recent decades the Hg accumulation in bottom sediments has been controlled by the biogenic component. The Hg in the studied sediments presents as sulfide form.

Contrast of fine sediment dynamics between shoals and channels in a microtidal estuary with mixed semi-diurnal tides

Estuaries usually feature complex bathymetries, where shoals and channels are co-existent. Due to the differences in water depth, current, density gradient and therefore stratification, sediment dynamics on the shoal and in the channel demonstrate significant variations. In this study, field measurements were carried out during spring and neap tides in both wet and dry seasons in the Huangmaohai Estuary, a microtidal estuary located in the southwest of the Pearl River Delta. Harmonic analysis was conducted for the timeseries data of current and suspended sediment concentration (SSC) for each deployment. Sediment transport flux was decomposed into an advective component, and tidal pumping fluxes by different tidal constituents. During the neap tides, sediment transport is primarily controlled by the advective flux, whereas during the spring tides, tidal pumping fluxes become comparable to, sometimes even exceeding, the advective one. For a 25-hr period, the M1 component of SSC usually denotes the maximum SSC associated with the highest bottom stress, while the M2 component signifies the two highs of the SSC. The M4 component is generally insignificant. The M1 and M2 components can be induced by both the advection and bottom resuspension. For the resuspension part, the M1 component is mostly induced by tidal velocity asymmetry, while the M2 component is generated by tidal straining effect. Sediment transport at the shoal is mostly controlled by the advective flux and the tidal pumping due to tidal velocity asymmetry, while that in the channel is dictated by advective transport and the tidal pumping due to tidal mixing asymmetry.

Spatial variability of erodibility of fine sediments deposited in gravel river beds: from field measurements to 2D numerical models

Spatial variability of erodibility of fine sediments deposited in gravel river beds: from field measurements to 2D numerical models

Industrial impacts on vanadium contamination in sediments of Chinese rivers and bays

Vanadium, like many trace metals, is persistent and detrimental to ecosystems at elevated concentrations. Likewise, it is versatile, functional, and used in many industries. Jiaozhou Bay (JZB) and Laizhou Bay (LZB) are valuable coastal ecosystems in China coexisting with several of these vanadium-related industries; however, limited studies have been conducted regarding vanadium occurrence, distribution, sources and risks in sediments. 208 surface sediment samples were collected from rivers and bays over two years and analyzed using inductively coupled plasma optical emission spectrometry. Overall, sediments near vanadium-related industries have significantly higher vanadium concentrations than those near traditional industries, with 30.3% and 22.9% higher average concentrations of vanadium in sediments of JZB and LZB, respectively. Vanadium accumulation at LZB is positively correlated with fine sediment, oxides (e.g., Fe, Ti, Mn), and organic matter content, while temporal changes in parts of JZB highlight the impacts of oxides, pH, and redox conditions on its accumulation. After geochemical normalization, the concentrations in marine samples from LZB showed slightly polluted sediments under the Modified Nemerow pollution index. Likewise, the elevated concentrations of vanadium in JZB, rivers and bay, were classified as slightly polluted and correlated with anthropogenic activities, such as the coal and petrochemical industries. Temporal changes indicated higher enrichments in 2019. Last, humans could be responsible for up to 46.8% and 16.2% of the vanadium accumulation in JZB and LZB, respectively, yet risks to species remain limited.

Impact of Bottom-Sediment Removal on 137Cs Contamination in an Urban Pond

Many irrigation ponds in Fukushima Prefecture were decontaminated due to the contamination of radiocesium released from Fukushima Daiichi Nuclear Power Plant. To evaluate the impact of decontamination on 137Cs dynamics in an urban pond in Koriyama City, Fukushima Prefecture, Japan, temporal changes in 137Cs concentrations in bottom sediments and pond water were investigated before and after bottom-sediment removal. Post-decontamination, 137Cs inventories in bottom sediments decreased by 46–89%. 137Cs inventories in bottom sediments were relatively high in fine sediments before decontamination, and were also high at points near the water inlet after decontamination. Following decontamination, the mean 137Cs concentration in suspended solids (SS) and the mean dissolved 137Cs concentration in pond water decreased by 52% and 5%, respectively. Even after decontamination, the normalized 137Cs concentrations in SS and in water, which were calculated by dividing the 137Cs concentrations by the mean 137Cs inventories in each area, were higher than those in rivers, dam reservoirs, and ponds elsewhere in Fukushima. The positive correlations between δ15N values, an indicator of the source contribution to bottom sediments, and 137Cs concentrations in the upper 5 cm of bottom sediments after decontamination implied that SS from urban areas gradually increased the 137Cs inventories in the pond. The results underline the importance of secondary inputs of 137Cs from highly urbanized catchments.

Hierarchical Milankovitch and sub-Milankovitch cycles in the environmental magnetism of the lower Shahezi Formation, Lower Cretaceous, Songliao Basin, northeastern China

SK-2 borehole in Songliao Basin provides unprecedented geological materials for investigating the Early Cretaceous continental paleoenvironment and paleoclimate in northeastern China. The lacustrine successions of the lower Shahezi (K1sh) Formation at the depth from 4,542 to 5,695 m was systematically studied using environmental magnetism and cyclostratigraphy in this study. Magnetic analysis reveals an inverse correlation between magnetic susceptibility (MS) and lithological ranks in fine clastic sediments, with the highest values in mudstones and the lowest in sandstones. The main magnetism carriers in the lower K1sh are pseudo-single-domain (PSD) and/or multi-domain (MD) magnetite with minor presence of hematite. MS was used to further explore the genesis of the environmental and climatic variations through cyclostratigraphic analysis. Sedimentary cycles of 113 m, 34 m, 13 m and 6 m can be identified in the power spectrum, which were interpreted as long and short eccentricity, obliquity, and precession cycles, demonstrating the impact of astronomical cyclicity on sedimentary rhythmicity. Floating astronomical time scale (FATS) of 4,090 kyr and 4,148 kyr were established by tuning the inferred long and short eccentricity cycles to the artificial 405-kyr and 105-kyr orbital eccentricity curves respectively. The estimated sediment accumulation rate around 28 cm/kyr confirms the rapid deposition process within the faulted lacustrine basin. Based on this study, the lake level oscillations in Songliao Basin are assumed to be shaped by long and short eccentricity, precession and semi-precession cycles during Early Cretaceous. This study also indicates that the sand-mudstone alternations deposition in K1sh is most likely driven by the seasonal discrepancies of summer insolation during semi-precession periods.

Fine sediment dynamics over a gravel bar. Part 2: Impact of hydro-meteorological conditions

In this study, the temporal evolution of fine sediment deposits on a gravel bar is analysed during a two-year period. The time-series of fine deposit surface area is obtained using the methodology proposed in Part 1 of this work. By combining the hydro-meteorological data, the main evolutions of the fine deposits observed on the bar surface are found to be triggered by events such as natural floods, dam flushes, and strong wind valley breezes, and are quantified for each of these events. A simple processed-based flow model is proposed to investigate the sediment dynamics during the flood events, which balances the erosional/depositional processes of fine sediments. Variability in the fine deposit evolution after floods is mainly due to the different flow and sediment concentration conditions. For small events for which the gravel bar is not totally submerged, a slight erosion generally occurs. For larger events for which the gravel bar is totally submerged, a large net deposition is often observed. The fine deposit surface area time-series also shows sharp decreases of the surface deposit coverage after some strong valley breeze events, with an evolution of the same order of magnitude than floods. The application of a wind transport model shows that strong wind valley breezes can transport fine particles from the bar surface to the river channel, thus leading to a loss of fine deposits on the bar surface. Also, the deposit initial moisture is a crucial element having impact on the fine sediment transport on the bar surface. Dry deposits are much more likely to be transported than wet deposits. A discussion is also provided on the potential impact of wind and vegetation on the long-term dynamics of fine sediment deposits.

Fine sediment dynamics over a gravel bar. Part 1: Validation of a new image-based segmentation method

In this paper, we present a new image processing algorithm to analyse fine sediment deposits on gravel bars. The method is based on pictures taken from the river bank with an average resolution of a few centimetres per pixel. The proposed image processing algorithm consists of two steps. In the first step, the raw image is orthorectified with a 5 cm pixel size. In second step, we used an original combination of two well-known image techniques to classify pixel. First, a high-pass filter is applied in the Fourier domain to correct grey-value potential bias, i.e. to merge wet and dry deposits. Then, an unsupervised classification process based on K-means clustering is conducted to partition image pixels into K classes. The area of fine sediment deposits is calculated by summing the area of each class multiplied by weighting parameters (surface area percentage of fine deposits for each class). The value of K and the weighting parameters are calibrated using local close range photos of the bar surface representing the spatial variation of surface fine sediment distribution. The algorithm is then validated with field measurement using the finest class (d<4 mm) of Wolman pebble count method. The impact of image resolution is investigated: the algorithm was found suitable for pixel size between 1 and 10 cm. The robustness of the present algorithm to images taken at different times and with different illuminations is studied by comparing it to two methods from the literature. The new method yields the most robust results with an average standard deviation lower than 5%. It yields larger surface of fine sediment since it includes all possible patches around coarse particles. Such results imply that the algorithm can be applied on a long image series to help us understand the temporal dynamics of fine sediment deposits on the bar surface.

Catchment-scale deer exclusion changes longitudinal patterns of macroinvertebrate communities through soil runoff mitigation

Deer overpopulation is occurring worldwide, and deer-induced soil runoff into streams increases levels of suspended sediment and fine sedimentation. While deer-induced fine sedimentation in depositional habitats including first- and fourth-order streams is known to alter macroinvertebrate communities, effects of drifting suspended sediment in erosional habitats between the stream orders are poorly understood. Here, habitat and macroinvertebrate community structures in first- to third-order streams were compared between deer-excluded and grazed catchments of a Japanese headwater system. Fine sediment cover on the streambed was significantly greater in the grazed catchments than the deer-excluded catchment only for first-order streams, while macroinvertebrate community structure differed distinctly between the deer-excluded and grazed catchments at all stream orders. Burrowing collector-gatherers, which inhabit fine streambed sediments, were less abundant in first-order streams in the deer-excluded catchment than the grazed catchments, while clinging collector-filterers, which are vulnerable to suspended sediment inputs, were more abundant in second- and third-order streams of the deer-excluded catchment than the grazed catchments. These results suggest that the effect of deer exclusion on stream ecosystems varies with longitudinal changes in sediment deposition and transport capacity. Hydro-geomorphological processes are thus fundamental to assessing the restoration of forest-stream ecosystems, particularly in spatiotemporally dynamic headwater systems.

Near‐surface temperatures and potential for frost weathering in blockfields in Norway and Svalbard

AbstractBlockfields remain enigmatic regarding their origin, internal structure, surface processes, and glaciological implications. In Scandinavia, blockfields are found on high‐elevation, low‐relief mountains (plateaus) across the Arctic and Subarctic. In this study, we present a 1D numerical model that uses near‐surface temperatures measured between summer 2018 and summer 2020 to calculate frost‐cracking intensities (FCI) within the ground column in three different blockfields in Norway and Svalbard. Eighty‐nine miniature temperature loggers were distributed on Tron Mountain (1650 m a.s.l.) in Alvdal, Gamlemsveten (780 m a.s.l.) near Ålesund in southwestern Norway and on Platåberget (460 m a.s.l.) near Longyearbyen, Svalbard. We modelled FCI by scaling the time spent in the frost cracking window (between −3 and −8°C) with the temperature gradient and a penalty function for distance to available water. At Tron and Gamlemsveten, ground temperatures never reached the frost cracking window at one third of our sites due to insulation by a thick snow cover in depressions and on the lee sides of summits. The highest FCI (0.05–0.4 K m) are obtained where the subsurface consists of boulders and stones in a matrix of relatively fine sediment (sand, silt, gravel). In contrast, very low FCI (0.003–0.02 K m) were modelled for blocky layers with large air‐filled pores because of the low water availability. On Platåberget, all sensors reached the frost‐cracking window during the annual temperature cycle, but FCI are extremely low (0.0004–0.15 K m) as water availability is limited due to (i) permafrost and (ii) near‐surface temperatures remaining below the frost‐cracking window for 3/4 of the year. This indicates that boulder‐rich blockfields with air‐filled hollows are preserved in very cold climates, whereas warmer, maritime settings with higher availability of fine interstitial material place blockfields in the fast lane for frost weathering.

Fluxes of settling sediment particles and associated mercury in a coastal environment contaminated by past mining (Gulf of Trieste, northern Adriatic Sea)

PurposeAs the result of historical mining at Idrija (Slovenia), mercury (Hg) contamination in the Gulf of Trieste (northern Adriatic Sea) is still an issue of environmental concern. The element has been conveyed into the coastal area by the Isonzo/Soča River inputs of freshwater and suspended particles for centuries. This research aims to investigate the occurrence of Hg bound to the settling sediment particles (SSP) in the coastal water and to assess the sedimentary Hg fluxes.MethodsSettling sediment particles were collected at four sites located in the innermost sector of the Gulf, a shallow and sheltered embayment where the accumulation of fine sediments is promoted. Six sampling campaigns were performed under different environmental conditions in terms of discharge from the Isonzo River and 12 sediment traps were installed in the upper and bottom water column for SSP collection. Settling sediment particles (SSP) were collected approximately every 2 weeks and analysed for grain size and total Hg.ResultsSettling sediment particles (SSP) consisted predominantly of silt (77.7 ± 10.1%), showing a concentration of Hg ranging overall between 0.61 and 6.87 µg g−1. Regarding the daily SSP fluxes, the minimum (7.05 ± 3.26 g m−2 day−1) and the maximum (92.4 ± 69.0 g m−2 day−1) values were observed under conditions of low and high river discharge, respectively. The daily Hg fluxes displayed a notable variability, up to an order of magnitude, both in the surface water layer (3.07–94.6 µg m−2 day−1) and at the bottom (11.3–245 µg m−2 day−1), reaching the maximum values following periods of high river flow.ConclusionsThe Isonzo River inputs of suspended particulate matter continue to convey Hg into the Gulf of Trieste, especially following river flood events, which represent one of the most relevant natural factors affecting the variations of the Hg flux in the investigated area.

Stability criteria for Bayesian calibration of reservoir sedimentation models

AbstractModeling reservoir sedimentation is particularly challenging due to the simultaneous simulation of shallow shores, tributary deltas, and deep waters. The shallow upstream parts of reservoirs, where deltaic avulsion and erosion processes occur, compete with the validity of modeling assumptions used to simulate the deposition of fine sediments in deep waters. We investigate how complex numerical models can be calibrated to accurately predict reservoir sedimentation in the presence of competing model simplifications and identify the importance of calibration parameters for prioritization in measurement campaigns. This study applies Bayesian calibration, a supervised learning technique using surrogate-assisted Bayesian inversion with a Gaussian Process Emulator to calibrate a two-dimensional (2d) hydro-morphodynamic model for simulating sedimentation processes in a reservoir in Albania. Four calibration parameters were fitted to obtain the statistically best possible simulation of bed level changes between 2016 and 2019 through two differently constraining data scenarios. One scenario included measurements from the entire upstream half of the reservoir. Another scenario only included measurements in the geospatially valid range of the numerical model. Model accuracy parameters, Bayesian model evidence, and the variability of the four calibration parameters indicate that Bayesian calibration only converges toward physically meaningful parameter combinations when the calibration nodes are in the valid range of the numerical model. The Bayesian approach also allowed for a comparison of multiple parameters and found that the dry bulk density of the deposited sediments is the most important factor for calibration.

Gas-saturated carbon dioxide hydrates above sub-seabed carbon sequestration site and the formation of self-sealing cap

Storing CO2 in sub-seabed sediments is a promising CO2 sequestration method to reduce atmospheric CO2 concentrations and mitigate climate change. Leaked CO2 from the sequestration site can form CO2 hydrates in the sediment and reduce the effective permeability of the sediment layer, developing a self-sealing cap above the storage site. Previous studies usually treat the CO2 hydrate layer similarly to a methane hydrate reservoir. However, unlike methane, CO2 has a larger solubility that increases significantly with depth, leading to high gas saturation levels in the sediment. Near the base of the CO2 hydrate stability zone, CO2 free gas, CO2 hydrate and dissolved CO2 coexist, and elevated surface energies of the curved surfaces of bubbles and hydrate crystals in pores shift the phase equilibria. The bubbles entrapped in the three-phase zone help to reduce the effective permeability besides accumulate CO2 hydrates. We simulate the three-phase zone in a shallow seabed using Monte Carlo methods in packed synthetic mono-dispersed spherical sediment grains, taking into account of the surface curvatures of the gas–liquid and hydrate–liquid interfaces in irregular pore spaces constrained by the sediment grains, and estimate the permeability reduction caused by entrapped CO2 bubbles. Finer sediment grains, larger geothermal gradients and shallower seawater all tend to broaden the zone, and the effective permeability in the three-phase zone can be further reduced by up to an order of magnitude than that with hydrates only. We also analyze the sensitivity of the three-phase zone due to temperature and pressure perturbations, and the results suggest possible thickness and depth variations of the zone due to cyclic temperature and sea level changes. This work demonstrates the difference between the CO2 hydrate-bearing sediment layer and the methane hydrate reservoir, and provides insight into the formation mechanism of the self-sealing cap above the sequestration sites.

Post-Formation of Oil Particle Aggregates: Breakup and Biodegradation.

Spilled oil slicks are likely to break into droplets in the subtidal and intertidal zones of seashores due to wave energy. The nonliving suspended fine particles in coastal ecosystems can interact with the dispersed oil droplets, resulting in the formation of Oil Particle Aggregates (OPAs). Many investigations assumed that these aggregates will settle due to the particles' high density. Recent studies, however, reported that some particles penetrate the oil droplets, which results in further breakup while forming smaller OPAs that remain suspended in the water column. Here, we investigated the interaction of crude oil droplets with intertidal and subtidal sediments, as well as artificial pure kaolinite, in natural seawater. Results showed that the interaction between oil droplets and intertidal sediments was not particularly stable, with an Oil Trapping Efficiency (OTE) < 25%. When using subtidal sediments, OTE reached 56%. With artificial kaolinite, OPA formation and breakup were more significant (OTE reaching up to 67%) and occurred faster (within 12 h). Oil chemistry analysis showed that the biodegradation of oil in seawater (half-life of 485 h) was significantly enhanced with the addition of sediments, with half-lives of 305, 265, and 150 h when adding intertidal sediments, subtidal sediments, and pure kaolinite, respectively. Such results reveal how the sediments' shape and size affect the various oil-sediment interaction mechanisms, and the subsequent impact on the microbial degradation of petroleum hydrocarbons. Future studies should consider investigating the application of fine (several microns) and sharp (elongated-sheeted) sediments as a nondestructive and nontoxic technique for dispersing marine oil spills.

Simulation of debris flow-barrier interaction using the smoothed particle hydrodynamics and coupled Eulerian Lagrangian methods

Debris flow events occur when fine soils and sediments are mixed with water, transporting coarse objects such as boulders and woody vegetation (debris) in a fast-moving down-slope flow. As such, debris flow can have catastrophic consequences for the environment, surrounding infrastructure and human life. The mitigation of damage caused by debris flow events is often addressed by rigid and flexible barriers placed in key locations to impede flow. The numerical simulation of interactions between large debris flow events and protective structures necessitates computational methods that model large deformation and flow behaviour as well as barrier performance. Although various numerical methods exist for debris flow modelling, the benefits of each method remain unclear when coupled with the analysis of protective structures. This research investigates debris flow-barrier interaction using two distinct numerical methods – the Coupled Eulerian-Lagrangian Method (CEL) and Smoothed Particle Hydrodynamics (SPH). The capabilities and limitations of each method are presented, highlighting the differences in computational cost. The results of simulations indicate preferable methods for modelling fluid-structure interaction for assessing the performance of debris flow-protective barrier structures. • The application of CEL and SPH methods in modelling of debris is investigated. • The capabilities and limitations of each method are studied. • Simulation of debris flow-boulders-barrier interactions is presented. • The effect of mesh and particle density is explained.

The Effect of Annealing Temperature on the Structural and Magnetic Properties of Lanthanum Doped Cobalt Ferrite with the Bengawan Solo River Fine Sediment as the Source of Fe&lt;sup&gt;3+&lt;/sup&gt;

The effect of annealing temperature on the structural and magnetic properties of a rare earth (La3+) doped cobalt ferrite with fine sediment from the Bengawan Solo River as the source of Fe3+ has been studied. Co-presipitation method is use for preparation nanoparticles whole this experiment. In order to modified the physical properties, the annealing treatment of 2000C, 3000C, and 4000C are performed. The obtained nanoparticles are characterized their structural properties by using X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Then, magnetic properties evaluated by using Vibrating Sample Magnetometer (VSM). XRD results have shown that there is an increase in crystallite size with an increase in the given annealing temperature from 24.56 nm to 27.83 nm. The increase in crystallite size can be attributed to the increase in the internal energy of the crystal structure which promotes atomic diffusion. Meanwhile, there is a decrease in the value of the lattice parameter with an increase in the given annealing temperature. The decrease in lattice parameters with increasing crystallite size is generally due to the lattice parameters reaching a minimum energy with increasing crystallite size. The formation of La3+-O2- for the incorporation of rare earth ions into the lattice requires high energy. The FTIR results show an absorption that appears at the peak around ~580 cm-1. This indicates that the La3+ cation has successfully replaced the original structure of cobalt ferrite. The VSM results show that there is an increase in the value of Hc with an increase in the annealing temperature given from 100 Oe to 160 Oe. This is supported by the increase of anisotropy constant and increasing temperature annealing.

Effects of microplastics pollution on the abundance and composition of interstitial meiofauna

Introduction: Pollution by microplastics is a global problem in marine environments, and impacts microorganisms and ecosystems at several spatial levels. Sandy beaches are depositional environments where microplastics tend to accumulate in large quantities. The co-occurrence of interstitial meiofauna and microplastics in sand grains raises the question on whether the accumulation of microplastics in the sediments affects the abundance and composition of the meiofaunal communities. Objective: To test the hypothesis that microplastics affect the meiofauna of urban sandy beaches. Methods: We studied the three main urban sandy beaches of Santa Marta, Colombia: El Rodadero, Santa Marta Bay, and Taganga. All are similar in morphology and external pressures and differ from other beaches in the region. In April 2019 we collected 81 sand samples, equally distributed in the intertidal zone (upper, mid, and lower intertidal levels). We applied generalized linear models to abundance, and multivariate permutational tests to community composition. Results: We identified 17 taxonomic groups of meiofauna, and microplastic particles (mainly 45-500 micron fibres) evenly distributed across beaches and intertidal levels. There was more meiofauna at the mid intertidal level, and in fine and medium grain sediment. At the lower intertidal level, sites with more microplastics had less meiofauna. Microplastics “explained” 39 % of the variation in meiofaunal communities at lower intertidal levels. Conclusions: The accumulation of microplastics has a negative impact on these meiofaunal interstitial communities. This is not surprising: microplastics occupy the same physical space as these animals, presumably modifying the structure of sediments and the composition of interstitial water. Objective: As a step forward on that direction, we have here analysed the distribution of the abundance of microdebris and major interstitial meiofaunal groups in three urban sandy beaches in Santa Marta region, Colombia, and possible relation among both factors. Methods: We selected the three main urban sandy beaches in Santa Marta, Northern Colombia: El Rodadero, Bahía de Santa Marta, and Taganga. All of them are very similar to each other due to its morfolophy and extern pressions, and differ starkly from other beaches in the region. Sampling was performed in April 2019 with a 81 samples in total equitably distributed in the supratidal zone, intertidal zone, and subtidal zone. In each point, we collected samples for microplastics quantification, meiofaunal community characterization, and granulometric analysis. Results: We extracted a total of 1131 debris particles, dominated by fibres ranging between 45-500 microns. Generalised linear models showed that microdebris were uniformly distributed across beaches and tidal levels, whereas meiofaunal abundances were significantly affected by the granulometry and tidal level. We detected a significant correlation between the abundance of microplastics and meiofauna at those levels, although with a very small estimate. Furthermore, our permutational multivariate tests showed that the abundance of microdebris significantly explained the 39.3% of the variation of the meiofaunal communities at the lowest tidal levels. Conclusions: Our result suggested that microdebris accumulating amongst the beach sand grains negatively impact meiofaunal diversity. This is not surprising, given that microdebris occupy the same physical space than these animals, presumably modifying the structure of the sediments and the composition of the interstitial water.