Coarse Silt Research Articles

Modelling the transport of sediment discharged by Colombian rivers to the southern Caribbean Sea

The three-dimensional transport of sediments released by the main rivers in the Colombian Caribbean basin is investigated using numerical model simulations. Different types of sediments (fine sands, very fine sands and coarse silts) were tracked by implementing SedimentDrift software, a subclass of the OpenDrift open-source trajectory framework. The simulations were forced with climatological winds from ERA-5 and currents from the Copernicus Marine Environment Monitoring Service (CMEMS). In situ measurements from the area were utilised in the evaluation of the forcing fields. The diagnostic analysis of ERA-5 and CMEMS at the evaluated stations in the Colombian basin led to the conclusion that these datasets are reliable; hence, they can be used for several oceanographic and coastal engineering studies. The sediment transport of non-cohesive particles at each river mouth is subject to the variability of local hydrodynamics, morphological features and the grain size, which determines the settling velocities. These factors were considered and evaluated in detail. Given the lack of available in situ information, the performance of the Lagrangian model is evaluated by comparing the resulting simulations with previous studies reported in the area for river plume dynamics. However, this study presents an initial analysis of the pathways that sediments of different sizes follow, from the river mouth to the seafloor. This approach is convenient given that the Colombian rivers deliver large amounts of sediment of various grain sizes, there are insufficient in situ data to assess the seasonal cycle of sediment transport and many aspects of the sediment dynamics are not fully resolved. The resulting simulations provide evidence of the importance of high-resolution ocean current data, given that this is the main factor determining the trajectories and dispersion patterns at seasonal scales.

ГРАНУЛОМЕТРИЧЕСКИЙ СОСТАВ ДОННЫХ ОТЛОЖЕНИЙ ОЗЕРА АНАШКИНО (ЮГО-ЗАПАДНОЕ ПРИОНЕЖЬЕ)

The lithostratigraphy and grain-size composition of sediments in Lake Anashkino (south-western Onego area) are described. The younger, upper sediment layers showed a prevalence of very fine sand. Further down the sediment, there dominate coarse and medium silt fractions, and down from the depth of 10.03–10.16 m — medium and fine silt. The oldest sediments (at 10.19–10.20 m) feature a prevalence of very coarse and coarse silt, and further below (10.30–10.31 m) there prevail very fine sand and very coarse silt fractions. The prevalent activity in the palaeo-hydrodynamic environments in which the ancient sediments (9.96–10.31 m) were deposited was turbidite flows. Younger sediments (9.32–9.92 m) were deposited in the environment of low-velocity flows. The sediment formation pattern in Lake Anashkino during the change from a nival to a humid climate suggests there happened five shifts in dynamic water regimes.

Spatial Availability of Nitrogen and Pesticides in the Surface Layers of Agricultural Soils of Tropical Hydrosystems in the Wet Season: Case of the Béré Watershed in Côte d’Ivoire (West Africa)

The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C?te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), i.e. 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g·kg-1) in contrast to those of the BDW (1.2 g·kg-1). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg·kg-1) in front of those of the BDW (94.81 μg·kg-1). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection; 79.37 μg·kg-1) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection; 13.17 μg·kg-1). However, in the BDW, urea substitute (100% detection; 44.02 μg·kg-1) dominate, including the active substance chlortoluron (84.62% detection; 10.12 μg·kg-1). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.

Effects of Stone Barriers on Soil Physicochemical Characteristics under Cotton (<i>Gossypium hirsutum</i> L.) Cropping Fields Northern of Côte d’Ivoire

In the north of Cote d’Ivoire, the rural economy is heavily dependent on cotton cultivation which is characterized by low yield. One of the main causes of low productivity is low level of soil fertility caused by erosion. The stone barriers technique is used to fight against erosion and to improve soil fertility. This work was carried out to assess the effects during 1-year-old stone barriers on selected soil physicochemical properties on two geographical locations where soil samples from 0 to 30 cm depth were selected. A total of 60 composite soil samples (30 × 2) were collected. One year after installing the stone bunds in cotton cultivation, the soil was sampled under the same conditions. The soil samples were analyzed for pH (H2O), organic carbon (SOC), total nitrogen (TN), available phosphorus (Av.P), cation exchange capacity (CEC), exchange bases (Ca, K, Mg, Na) and particle size (clay, coarse silt and sand) contents. The results show that the stone bunds significantly increased the water pH, the soil levels of calcium, magnesium, silt and coarse sand. On the other hand, they significantly lowered the levels of assimilable phosphorus, clay and fine sand in soils. CEC and soil carbon, nitrogen, potassium, sodium and fine silt content did not vary significantly. This study must be repeated in the years to come in order to determine the impact of stone barriers in the medium and long term on soil fertility in the north of Côte d’Ivoire.

Major Characteristics of Surface Sediments Within the Shallow Water of the Cat Ba Island, North Vietnam

The Cat Ba is one of the largest Islands offshore North Vietnam, which is characterized by an abundance of coral reefs in the East and Southeast of the island. The surface sediments are considered the basic elements for the coral ecosystem development. In this study, the authors present some new results studying pH, Eh, mineral composition, and grain size as the basic information for environmental assessment of this area. The results show that the pH value of the surface sediment varies from 6.90 to 8.09, with an average of 7.24 while the Eh value of the sediment ranges from -121.10 to -48.20mV, an average of -68.39mV, demonstrating a reducing environment. The surface sediments have been classified into 8 size classes: the coarse silt > very coarse silt > medium sand, very fine sand > very coarse sand, fine sand > coarse sand, very fine gravel. Most of the sediments are poorly sorted - very poorly sorted, only a few sedimentary samples are well sorted, moderately sorted, and moderately well sorted. The average mineral composition of the surface sediments consists of: 25% quartz, 17% illite, 16% aragonite, 13% kaolinite, 10% calcite, 5% chlorite, 4% gothite, 3% halite, 2% feldspar and less montmorillonite, and dolomite. These results allowed the researcher to interpret that the sediments have been deposited in a relatively calm environment and the terrigenous sediment sources are dominant over the marine sources. Source marine sediment groups are characterized by coarse grains, high pH, and are rich in carbonate minerals, which have been produced by biological materials. In contrast, the terrigenous sediment group is dominated by fine-grained sediments, rich clay minerals, quartz, and gothite. These fine-grained sediments are commonly distributed in the area and are favorable places for pollutant accumulation.

Effects of ryegrass canopy and roots on the distribution characteristics of eroded sediment particles during heavy rainfall events on steep loess‐cinnamon slopes in Zhangjiakou, China

AbstractTo evaluate the effects of ryegrass (Lolium perenne) canopy and roots on eroded sediment particle distribution characteristics, simulated rainfall tests were implemented on grass caopy, roots, and bare slopes. The grass coverage density were 0, 20, 40, and 60%. The results showed that ryegrass canopies mainly contributed to runoff reduction and ryegrass roots primarily contributed to erosion reduction. With increasing rainfall duration, smaller particles (clay and fine silt particles) increased and larger particles (coarse silt and sand particles) decreased in the eroded sediment on the grass slope while the opposite trend was observed for the roots and bare slopes. Moreover, the clay and sand particles were eroded as aggregates and most silt particles were transported in the form of primary particles. Compared to the original soil, larger particles in the eroded sediment mainly occurred on the grass slopes because smaller particles were intercepted by the grass canopies, while smaller particles primarily occurred in the eroded sediment of the root slopes because grass roots inhibited soil erosion. These results illustrate that grass cover can prevent the loss of small particles in the topsoil and avoid soil coarsening, which provides guidance for the comprehensive control of soil erosion.

Acoustic backscatter analysis of ground-fishing activity in the German North Sea sector

The physical impact of demersal fishing was studied in three different areas of the German North Sea sector by use of a multibeam echosounder. The areas represent typical shallow seas siliciclastic habitats in variable distance to the coastline. Their seabed substrate is dominated by coarse silt close to the shore and by fine sand in the most distal area on the Dogger Bank. The study documents the utility of the multibeam as a suitable tool to map large seafloor areas, as well as to quantify and qualify the footprints of the fishing groundgear. Besides the depth and amplitude information, the multibeam data allows the analysis of the incidence angle-dependent variation of the backscatter signal that provides additional information on the seabed impedance, roughness, volume scatter and substrate type. Two main types of destructive seafloor pattern were observed in the three areas. The dominant type are pairs of parallel furrows exhibiting widths of 6–9 m and depths of 2–6 cm and is related to beam trawling. Separation distance of the pair furrows is 16–23 m. The second type are pairs of narrow furrows (3–4 m) with much larger separation distance of 110–120 m. They are attributed to otter board trawling.A comparison of their mechanical ramification shows that the fishing gear incises the seafloor and modifies seafloor structures and properties. Our investigation documents that beam trawling has the greatest physical impact and exhibits the highest furrow density in the three study areas. The created furrows can persist for at least 4 months in a substrate of very fine sand. Depending on the hydrodynamic regime, the furrows can be later refilled by finer sediments, or levelled out by storm wave-induced turbulence reaching the seafloor. The hydrofoils used in otter trawl to spread the net likewise incise the seafloor, but the furrows are much narrower. However, the ground rope of the net towed between the boards scratches the seafloor and levels the microscale topography along track widths of ca. 100 m.

Assessing local acid mine drainage impacts on natural regeneration-revegetation of São Domingos mine (Portugal) using a mineralogical, biochemical and textural approach

São Domingos sulfide mine was shut down more than 50 years ago leaving behind eroded and depositional surfaces due to acid mine drainage (AMD). The aim of this study was to assess six selected sites subjected to AMD, considered phytotoxic regions characterized by vegetation scarcity. Two main criteria, nature and composition of soluble fractions and total chemistry of surficial products related to jarosites presence, enabled to set up an overall dichotomy between superficial proximal/discharge and distal/sedimentation areas. Wet and dry sieving results comparison revealed that samples have a predominant sandy texture and lithic (phyllite, quartzite and volcanic country rocks) composition. Quartz, and subordinate feldspar enrichment is also detected in the coarse silt fraction. The results also suggest that the materials under study, when subjected to the local torrential hydrologic regime, have a high mechanical vulnerability, facilitating erosion and mud transport, both critical for vegetation support, and triggering contamination transfer and dispersion. The vicinity and ground-level surfaces of discharging areas are enriched in the jarosite group minerals whereas the sedimentation ones present hypersaline aluminous tendency. The formation of jarosite is considered as an efficient positive environmental contribution to metals and metalloids sequestration/immobilization. The remediation/revegetation solutions to be adopted in each location must have into consideration these differentiating aspects.

Sediment dynamics of estuarine Holocene incised-valley fill deposits recorded by Siphonichnus (ancient Red River, Gulf of Tonkin)

The Holocene muddy infill of the valley incised by the ancient Red River during Pleistocene sea-level lowstand records a change from fluvial to estuarine and finally marine depositional conditions. Siphonichnus, a mainly vertical trace fossil produced by burrowing bivalves, documents otherwise unrecorded episodes of enhanced erosion, bypass and deposition of, on average, rapidly aggrading (> 1 m kyr−1), mainly completely bioturbated sediments within the fluvial-marine transition zone (FMTZ), supposedly within the polyhaline domain. The producers of Siphonichnus moved nearly 1 m downward or upward in response to erosional or depositional phases, respectively. The fill of Siphonichnus burrows, in addition, records erosion and/or bypass of sediment: The traces were produced in mud, but many of them are filled with coarse silt and sand that is otherwise not present in the studied intervals in distinct layers. Obviously, this material was available when Siphonichnus was produced and connected to the sediment surface. In addition to seasonal erosion and deposition during freshet and its waning stage, Siphonichnus records exceptional events that displace the sediment surface by >0.5 m. Such events occurred episodically at an estimated frequency of 1 event per several hundreds of years. The complete bioturbation of the deposits suggests apparent continuous accumulation, but in fact they represent a pile of stacked event deposits resulting from depositional phases and intermittent severe erosion.

Paleoceanographic changes in the Southern Ocean off Elephant Island since the last glacial period: Links between surface water productivity, nutrient utilization, bottom water currents, and ice-rafted debris

To understand past changes in ocean–cryosphere interactions in the Southern Ocean off the Antarctic Peninsula, multi-proxy analyses of three sediment cores located off Elephant Island were used to reconstruct changes in paleoproductivity, nutrient utilization, bottom current intensity, and iceberg calving since the last glacial period. The glacial period was characterized by low surface water productivity with high nutrient utilization, indicating surface water stratification. During the deglaciation, surface water productivity increased with decreasing nutrient utilization, implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing Antarctic Circumpolar Current (ACC) influence as fronts migrate southward with warming. Abundant occurrence of grains >1 mm during the deglacial period indicates rapid ice sheet retreat with large-scale melting and calving. During the glacial period, however, coarse silt–fine sand-sized fraction represented ice-rafted debris (IRD). The different IRD grain size characteristics are thought to be related to the IRD source material characteristics. Regardless of IRD input, the running downcore correlation (5 to 9-point) between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current. However, the cross plot of them showed different temporal relationships. Sediments were sorted by the ACC and southwestward flowing bottom current. Along with southward migration of fronts and the ACC, southwestward flowing bottom current influence diminished, whereas the ACC influence increased particularly from 7 ka. Our results indicate that the sedimentary processes in the Scotia Sea largely depend on the regional interactions between the ocean and the cryosphere.

Pedosedimentary and geoarcheological archives from clay-dominated sinkhole infillings in Middle Franconia, Germany

Sinkholes in the karstified Middle Keuper gypsum of Middle Franconia, Germany reveal numerous archeological findings and contain unique pedosedimentary records of landscape development and human-environment interaction during the Holocene. Mudstone-derived high clay contents result in a unique set of sedimentary and pedogenic properties of these archives in that all units exhibit vertic properties. Since the horizons have a polygenic history, detailed field and micromorphological observations, together with laboratory analyses (grain-size, color, iron-pedochemistry) are the basis for a classification of the pedosediments. 14C dating provides a chronological framework for geomorphological stability phases and thus, identified soil-forming processes. The first anthropogenic colluvial sediments of the studied archive date to the Early Bronze Age and accumulated in an initial karst depression. Water saturation caused iron reduction of these early infillings. In the pedosediments above, oxidation and iron release are largely related to changes in the parent material. Here, the soil material contains coarse silt indicating an admixture of nearby periglacial slope deposits. Furthermore, fossil root traces point to a longer time with stable conditions, which we interpret as absence of humans or at least an extended period of fallow land. The superimposed sediments from the Urnfield period are more inhomogeneous and consist of material from the eroded agricultural soils of the surrounding. The characteristics of these pedosediments point to intensified human land use. Pedogenic processes such as iron release, reduction of iron, swelling-shrinking, and short-distance translocation of clay intensively overprinted all soil sediments. In this context, micromorphology proved to be an essential tool for the characterization of polygenesis in terms of soil-forming as well as redepositional processes that lead to the formation of these complex archives. The present study reflects a multi-methodological approach to a rather disregarded type of polygenic terrestrial records. It constitutes an example for the investigation of clayey pedosediments in karstic environments under moderate climate in the frame of a prehistoric geoarcheological setting.

Quaternary influx of proximal coarse-grained dust altered circum-Mediterranean soil productivity and impacted early human culture

AbstractThe carbonate mountainous landscape around most of the Mediterranean is karstic, is almost barren, and has thin soils. Erosion of preexisting thicker soils is a common hypothesis used to explain this bare terrain. An alternative hypothesis is that in the Mediterranean region, thin soils are attributed to long-distance transport of very fine, silty clay dust, resulting in low mass accumulation rates. Even if accreted over millennia, such dust cannot produce thick, highly productive soils. A pronounced anomaly in the Mediterranean is the thick, more productive soil of the semiarid southern Levant (SL). These soils contain order-of-magnitude coarser grains than the characteristic thin soils in the Mediterranean and a high proportion (>70%) of coarse silt quartz sourced from the nearby Sinai-Negev erg, the primary contributor of the Negev loess. This proximal intense dust supply produced greatly thicker soils. However, influx of coarse silt quartz loess is a geologically recent phenomenon in the SL. Pre-loess (i.e., older than 200 ka, pre-coarse-silt influx) SL soils are much finer and were generated by long-distance dust from the Sahara and Arabia like most other Mediterranean soils. Thus, we hypothesize that the geologically recent Negev Desert loess interval caused a drastic change in mountainous soil properties within the SL, enriching the Levant’s ecology and affecting early human development. The high amounts of coarse silt deposited on the landscape have contributed to the unique sustainable agriculture in the SL, which assisted in transforming the Levant into “the land of milk and honey” and a cradle of civilizations.

Dynamics, thermodynamics, and mechanism of perfluorooctane sulfonate (PFOS) sorption to various soil particle-size fractions of paddy soil

Soil is an important sink for perfluorooctane sulfonate (PFOS) that is a typical persistent organic pollutant with high toxicity. Understanding of PFOS sorption to various particle-size fractions of soil provides an insight into the mobility and bioavailability of PFOS in soil. This study evaluated kinetics, isotherms, and mechanisms of PFOS sorption to six soil particle-size fractions of paddy soil at environmentally relevant concentrations (0.01–1 μg/mL). The used soil particle-size fractions included coarse sand (120.4–724.4 mm), fine sand (45.7–316.2 mm), coarse silt (17.3–79.4 mm), fine silt (1.9–39.8 mm), clay (0.5–4.4 mm), and humic acid fractions (8.2–83.7 mm) labeled as F1~F6, respectively. PFOS sorption followed pseudo-second-order kinetics related to film diffusion and intraparticle diffusion, with speed-limiting phase acted by the latter. PFOS sorption isotherm data followed Freundlich model, with generally convex isotherms in larger size fractions (F1~F3) but concave isotherms in smaller size fractions (F4 and F5) and humic acid fraction (F6). Increasing organic matter content, Brunner−Emmet−Teller surface area, and smaller size fractions were conducive to PFOS sorption. Hydrophobic force, divalent metal ion-bridging effect, ligand exchange, hydrogen bonding, and protein-like interaction played roles in PFOS sorption. But hydrophobic force controlled the PFOS sorption, because its relevant organic matter governed the contribution of the soil fractions to the overall PFOS sorption. The larger size fractions dominated the PFOS sorption to the original soil because of their high mass percentages (~80%). This likely caused greater potential risks of PFOS migration into groundwater and bioaccumulation in crops at higher temperatures and ce values, based on their convex isotherms with an exothermic physical process.

Response of grain-size components of loess-paleosol sequence to Quaternary climate in the Southern Loess Plateau, China

A new, thick, and complete loess-paleosol sequence is a good response to climate changes. In this paper, the distribution and parameters of grain size in the Xiushidu (XSD) sequence in the southern Loess Plateau were systematically investigated. A comparative analysis of the sediment granularity with different areas was also conducted. The results show that the XSD sequence is primarily constituted by coarse silt (52.18%), clay (21.71%), and fine silt (20.27%), and the contents of colloidal particles (3.63%) and fine sand (2.21%) are relatively small. The contents of 1~5 μm and < 5 μm show a slight increase from S9 to S5, while the contents are clear downward from L5 to L0, indicating that the climate is gradually getting colder after S5. Grain-size distribution curves show a bimodal pattern for loess/paleosol. The grain-size component and peak pattern illustrate that dust materials were not only transported by wind but also experienced pedogenesis. Moreover, the changes of grain-size indicator Mz values indicate climatic instability. Comparing with the Beglitsa, Oitak (AYTK), Lanzhou (LZ), Pengyang (PY), Luochuan (LC), and XSD sequences, we can infer that the XSD sequence not only has experienced the strong pedogenesis and the warm and humid climate but also has influenced by the Himalayas, the Tibetan Plateau, the QM, and the LPM. These analyses help to clarify the climatic and environmental context of loess-paleosol sequence deposition phases and regional environmental evolutions.

Effect of aggregate breakdown on the unevenly enriched organic carbon process in sediments under a rain-induced overland flow

Soil organic carbon (SOC) could be enriched in sediments for rain-induced overland flow. However, the features of the enriched SOC distribution in each size of sediment particles and the effect of aggregate breakdown on SOC enrichment features have not been completely investigated. Thus, the SOC concentration of different sizes of sediment aggregates was tested for all samples obtained for 27 simulated rainfall experiments conducted with 5°, 10°, and 15° gradients at rainfall intensities of 45, 90, and 120 mm h−1, respectively. The changes of SOC composition in aggregates from the original soil to sediments were estimated through the ratios of the variation percentage of the effective and dispersed each size of class sediment particle to that of the original soil particles (Ap). The contribution percentage of aggregate breakdown to the SOC enrichment in sediments (Ca) was also quantified. Results showed that Ca was above 50 % even when under an extremely high rainfall intensity of 120 mm h−1 on a 15° slope, but Ca decreased with the increase in overall rainfall intensity and slope. When the soil erosion rate is not high enough, Ca decreases with time because of the increase in the soil erosion rate. The absolute values of Aps of all size class particles were increased with the rainfall intensity and slope. However, the absolute values of Aps of clay- or fine silt-sized class particles changing between 0.11 and 0.68 were generally lower than those of coarse silt, fine sand, and coarse sand changing from −3.11 to 1.38, −0.35 to 0.06, and −1.3 to 0, respectively. This result indicates that 0.05–0.25-mm aggregates were more easily broken than other size particles, and the different sizes of particulate organic carbon chippings were more preferred transport than clay/silt-bonded aggregate fragments. The preferred transport of large amounts of 0.25–2-mm-size particulate organic carbon resulted in higher SOC enrichment ratios (ERocs) of 2.58 in 0.25–2-mm particle size class than others. The preferred transport of light particles, for example, mineral-associated and particulate organic carbon chippings exposed by aggregate stripping, caused the uneven enrichment of SOC in sediments. Last, a significantly negative correlation is observed among the mean weight diameter, the enrichment ratio (Er) of each size class particles in sediments, and Ca and ERocs of sediments (P < 0.05). If the rainfall intensity and slope are small, then many aggregates will be broken, and the uneven enrichment of SOC will be enhanced. Overall, our research provides an important reference to further understand the SOC loss mechanisms of soil aggregate induced by water erosion.

Particle-size dependent magnetic properties of Scotia Sea sediments since the Last Glacial Maximum: Glacial ice-sheet discharge controlling magnetic proxies

The strong glacial–interglacial similarity between the magnetic susceptibility (MS) of Southern Ocean sediments and Antarctic ice core dust records has often been used to reconstruct Southern Hemisphere atmospheric variability. Although evaluation of various magnetic properties is essential for identifying the magnetic carriers linked to sedimentological variation, detailed magnetic studies are not sufficient in the Scotia Sea. Here we investigate the bulk and particle-size dependent magnetic properties of Scotia Sea sediments over the past ~22 kyr, to determine the main sediment transport mechanism driving bulk magnetic proxies including MS. In bulk sediments, MS is highest during the last glacial period and is accompanied by an increase in the concentration and grain size of ferrimagnetic and antiferromagnetic minerals. For magnetic mineral assemblages, coarse detrital magnetite is dominant. Of three particle-size fractions (>63, 16–63, and <16 μm), the coarse silt fraction (16–63 μm) is responsible for the magnetic properties of bulk glacial sediments. Such dominant contribution of coarse silts rules out a major input of dust, which is expected as finer silt and clay. The silt fraction exhibits a co-varying magnetic mineral concentration with that of the sand fraction (>63 μm) throughout the last deglaciation, indicating a close linkage between their input mechanisms. Thus, the sediment particles ranging from sand to coarse silt, which control the bulk glacial magnetic proxies, are most plausibly transported by iceberg-rafted debris (IRD). As hematite is relatively concentrated in the sand fraction, the hematite contribution in the bulk sediment can highlight IRD-related magnetic signals rather than magnetite. The bulk hematite contribution simultaneously varies with the deglacial influx of coarse IRD particles (>1 mm) in Scotia Sea sediments, although their glacial inconsistency possibly suggests a different IRD input mechanism during the advancement and retreat of the ice sheet. Consequently, the glacial increase in the bulk magnetic concentration indicates vigorous iceberg calving activity in the Scotia Sea and further suggests the coupled cryosphere–atmosphere system.

Particle Size Imbalance Index from Compositional Analysis to Evaluate Cereal Sustainability for Arid Soils in Eastern Algeria

For homogeneous fertilization and crop management practices, this work hypothesized that texture could influence cereal yield, particularly in dry regions. Particle size analysis could help improve knowledge of the soil-plant relationship to obtain favorable conditions for better yield. The objective of this work is to develop a single granulometric index for durum wheat (Triticum durum) that is well correlated with yield. For this purpose, 350 independent samples of cereal soils from eastern Algeria were taken and the recorded yields were linked to these samples. The cutoff yield, which separates sub-populations with acceptable yield from those with less acceptable yield, was determined from the inflection point of the cumulative variance ratio functions related to yield by the Richards’ equation. The result obtained is 2.0 Mg.ha−1, with a theoretical critical chi-square value of 4.2, close to 4.6, which is the critical value of r2granulo as obtained by the Cate-Nelson procedure. The five-granulometric indices were found to be symmetrical around zero as follows: ±0.83 for clay (IC), ±1.73 for fine silt (IFL), ±0.31 for coarse silt (ICL), ±0.44 for fine sand (IFS), and ±1.30 for coarse sand (ICS). The two fractions that most influence the textural imbalance are fine silt (IFL) and coarse sand (ICS), with a contribution of 41% and 37%, respectively. The critical single imbalance index r g r a n u l o 2 can be used for determining cereal suitability for soils in the arid region of eastern Algeria. The lower the r g r a n u l o 2 is, the better the soil for cereal crops.

Infiltration Behavior of Microplastic Particles with Different Densities, Sizes, and Shapes-From Glass Spheres to Natural Sediments.

In this study, the infiltration behavior of 21 microplastic particles with different densities, diameters, and shapes was investigated using columns of glass spheres with different grain diameters. The glass spheres were considered as an analogy for natural sediment and the results were afterward transferred to natural sediment and compared to fine sediment infiltration. The infiltration depth of the microplastic particles increased with decreasing diameter of the microplastic particles (dMP) and with increasing diameter of the glass spheres (dGS). At ratios of dMP/dGS > 0.32, hardly any infiltration could be observed. In regard to the particle shape, the data shows that spherical particles infiltrate deeper than fragments and fibers. In case of fibers, the fiber diameter, in particular, influences the depth of infiltration, with thinner fiber diameters leading to deeper infiltration depths. Fragments, such as tire abrasion, infiltrated less deeply than spherical particles, probably due to the entanglement of the angular particles in the pores. Finally, based on the experiments, this study provides initial indications of reasonable sampling depths in dependence of the grain sizes of the bottom sediment and the microplastic particles. According to this, microplastics in detectable particle sizes (>100 μm) are only found on the surface of sediment consisting of coarse silt and fine sand, while the particles might infiltrate up to 13 cm into sediment consisting of coarse sand, fine gravel, and medium gravel. A statement of depth-variable microplastic concentrations is therefore mainly useful for these sediment types. Accordingly, in future sediment samples, the grain size distribution of the sediment should always be indicated to better evaluate the detected microplastic concentrations.

Data on the soilscape and vegetation properties at the key site in the NW Caspian sea coast, Russia.

Research on the environment in recent soils is important to understand geochemical processes in coastal landscapes and the rate of pedogenesis. In this article, we present original data on Gleyic Solonchaks (Loamic) and vegetation described at the eastern part of the Terek–Kuma lowland (Northern Dagestan, Russia). At the key site of 45 × 30 m released from water 293±13 years calBP, we described vegetation at 345 plots of 2 × 2 m (4 m2) and soil properties in 58 auger holes and 2 pedons, the latter characterizing a typical microhigh with Tamarix and a microlow with saltworts. The flora of the sites amounts to 32 species (predominantly, halophytes) belonging to 11 families. Shrubs represented by tamarixes are the dominant. Under their crowns, dense herb and grass microcommunities with a predominance of tall Puccinellia gigantea occur. Sparse stunted halophytic plants (Petrosimonia, Frankenia, Puccinellia) occupy open habitats between shrubs. In soil water extracts from auger holes (696 samples in total), we measured electrical conductivity (EC) and pH. In 49 soil samples from pedons, we described particle size distribution, total concentration of macro elements (Al, Ca, Fe, K, as well as Mg, Mn, P, Ti, and Si) and trace elements (As, Co, Cr, Cu, Ni, Pb, Sr, and Zn), EC, pH, basicity (HCO3– and CO32–) as well as the content of cations (Ca2+, Mg2+, Na+, and K+) and anions (SO42– and Cl–) in soil water extracts. Gleyic Solonchaks (Loamic) with bulk density of 1.35±0.12 g/cm3 (mean and standard deviation) contain SiO2 69±8%> Al2O3 11.8 ± 3.5 and CaO 7.5 ± 2.5%, Fe2O3 3.6 ± 1.4%, K2O 2.0 ± 0.3 and MgO 1.9 ± 0.4%> TiO2 0.62±0.25%> P2O5 0.14±0.06% and MnO 713±268 mg/kg> Sr 481±262 mg/kg > Cr 79±9 mg/kg > V 76±36, Zn 68±31, Cu 62±10, and Ni 50±17 mg/kg, Co 32±6 mg/kg> Pb 11±6 mg/kg> As 5.6 ± 1.4 mg/kg. The particle-size distribution is (WRB system,%): clay 13±5, fine silt 34±12, coarse silt 30±18, as well as very fine sand 11±10, fine sand 7.3 ± 10.5, medium sand 3.5 ± 5.8, coarse sand 0.9 ± 3.2, and very coarse sand 0.08±0.31 (n = 38). Soil water extract has EC 9.4 ± 4.1 dSm/m (soils: water ratio of 1:2.5, n = 713), contains Na+ 15.9 ± 7.0 > Ca2+7.3 ± 5.0 and Mg2+ 7.3 ± 3.1 > K + 0.30±0.20 cmol(eq)/kg, as well as Cl– 15.7 ± 7.3 and SO42– 14.6 ± 7.9 > HCO3– 0.55±0.15 > CO32–< 0.01 cmol(eq)/kg, and has pH 7.9 ± 0.3 (soils: water ratio of 1:5, n = 21). In soil paste, pH is 8.3 ± 0.2 (n = 461). Data obtained can be used for more confident identification of pollution sources and pollutants’ migration routes and more effective conservation and remediation of human-affected soils at the Caspian Sea coast.

Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.