Sand Fraction Research Articles

Large-scale assessment of characteristic plant species on Eurasian saline and alkaline soda ecosystems

From an ecological standpoint, saline and alkaline habitats are considered as extreme environments for vascular plants because salinity and alkalinity serve as primary structuring factors that significantly influence the species richness of vegetation cover. The non-alkaline salinity stress on plants primarily results from interactions of NaCl, Na2SO4, and other neutral salts, whereas alkalinity stress is caused by NaHCO3 and Na2CO3, accompanied by an increase in pH. Some halophytes and salt-tolerant plants are well-adapted to such permanent abiotic stress. Surprisingly, they are able to survive and reproduce under environmental conditions of more than 200 mM NaCl concentration and are also able to live permanently in extreme conditions. The aim of this study was to identify characteristic and indicator plant species for permanently alkaline soda and non-alkaline saline wetland habitats, and to analyze the relationship between the chemical composition of water and the plant’s saturation index. Based on the obtained results we can conclude that plant species identified to live in high saline conditions may also grow under high alkaline conditions. Two groups were distinguished based on the salinity and alkalinity: “Saline group” includes all types of halophytes and halotolerant species, while “Soda group” includes obligate alkalophytes and alkalotolerant species. However, the diversity of plants in alkaline environment is bigger than in saline environment, and most of the halotolerant species grow in both alkaline soda and saline habitats. It is possible to identify three indicator species requiring alkaline soda habitats to live in (Aster tripolium, Puccinellia limosa, Suaeda pannonica) and three indicator species that dominantly grow in non-alkaline saline habitats (Juncus maritimus, Salicornia prostrata, Suaeda salsa). Different independent variables have been identified and analyzed to understand their influence on the species saturation index by calculating percentage of characteristic plant species of the entire region. It was identified that the plant saturation index has a significant positive relationship with the Mean Temperature of the Warmest Quarter, Topsoil Sand, and Clay fraction variables, and there is a significant negative relationship with the Solid Earth surface heat flow, as the heating can increase the extremity of the environment. Identification of indicator species of salinity and alkalization makes it possible to determine the type of soil, water bodies and habitats as a rapid biomonitoring method as a visual observation, without the use of expensive equipment and chemical laboratory tests.

Contribution of Sentinel-2 spring seedbed spectra to the digital mapping of soil organic carbon concentration

Soil organic carbon (SOC) is central to the functioning of terrestrial ecosystems, has climate mitigation potential and provides several benefits for soil health. Understanding the spatial distribution of SOC can help formulate sustainable soil management practices. Digital soil mapping (DSM) uses advanced statistical and geostatistical methods to estimate soil properties across large areas. DSM integrates climate data, topographic features, geology, legacy soil maps, land management and remote sensing data. Bare soil spectra may reflect the presence of particular soil components, making satellite derived spectra suitable predictors of SOC. Bare soil spectra derived from Sentinel-2 were used to estimate SOC concentration (SOC%) and granulometric fractions in the plough layer (0–30 cm) of agricultural parcels in northern Belgium. Thereafter, the estimation performance of SOC% was compared for three DSM models: one with bare soil spectra, one with environmental covariates (topography, granulometry and vegetation), and a combined model with bare soil spectra and environmental covariates. The estimation performance of sand, silt and clay fractions using bare soil spectra from the spring seedbed (R2: 0.53–0.74; RPD: 1.49–2.05; RPIQ: 1.52–2.39) was higher than that of SOC% (R2: 0.16; RPD: 1.08; RPIQ: 1.32). The highest estimation performance of SOC% was obtained for a DSM model including all covariates (R2: 0.28; RPD: 1.18; RPIQ: 1.44), but the contribution of spring seedbed spectra to a model containing environmental covariates was small. The results provide valuable insights for refining soil property estimation using DSM with spectral and environmental covariates.

Context specific effects of substrate composition on the taxonomic and functional diversity of macroinvertebrate communities in temperate lowland streams.

Substrate composition has been widely recognised as a primary variable shaping lotic macroinvertebrate communities at the habitat unit level. However, fundamental understanding of how communities inhabiting mineralogical habitats (i.e., gravel, sand and silt) are structured across differing rivers is lacking. Moreover, research largely focusses on gravel beds and fine sediment in general (<2 mm) and as a result detailed field observations specifically of the sand and silt fractions are lacking. Using data from five UK streams collated from published studies, we assess taxonomic and functional biodiversity (alpha and beta diversity) at the habitat unit level (as defined by substrate composition of sand, silt and gravel). We found that the composition of taxonomic communities were clearly different in all habitat units for each individual stream (and at the landscape scale), with comparable, but less strong, distinctions between substrates for functional macroinvertebrate community composition. However, alpha diversity metrics and Local Contribution to Beta Diversity (LCBD) recorded among the different habitat units varied significantly across individual rivers, and the amount of variation explained by the habitat unit for taxonomic and functional composition demonstrated considerable differences suggesting strong context dependence. The depositional fine sediment habitats of sand and silt were found to support a discrete community composition and differing levels of alpha and beta diversity within and between rivers. We advocate that care should be taken when seeking to generalise biodiversity patterns at a landscape scale as our study highlights the high degree of context dependency when considering the role of the habitat template. Moreover, our results provide evidence that discriminating between the size fractions of fine sediment habitats (sand or silt) is important to fully elucidate the wider ecological importance of these habitats and the distinct taxonomic and functional biodiversity they support.

Chemometric heavy metal contamination in tropical Indian estuaries: Implications for source identification

The impact of urban and industrial effluents in the tropical Indian estuaries (Ariankuppam backwater and Chunnambar River), east coast of India have been investigated in the present study by determining the degree of heavy metals contamination of the estuarine sediments. A total of 30 surface sediment samples were collected from both estuaries and were analyzed for trace metals, grain size and organic matter. The granulometric analysis reveals that both the estuaries are predominated by silty sand to sandy silt. The significant amount of organic matter (OM) in the Ariankuppam estuary sediment is due to natural (mangroves) and anthropogenic (pollution) organic input. Pearson correlation analysis reveals that there was a strong negative correlation of sand fraction with other sediment variables (silt, clay, and organic matter) and heavy metals, whereas a positive correlation was observed between silt+clay, organic matter, and heavy metals. The significant positive correlation of Fe with Ni, Cu, Pb and Zn presents Fe-Mn oxyhydroxides are the main controlling factor of heavy metals in both estuarine sediments. Cluster analysis and PCA helped to discriminate the station groups along both estuaries according to their sediment components and heavy metals. This study also revealed that sediment grain size is a key factor influencing organic matter and heavy metal accumulation in surface sediments. The calculated pollution indices such as Contamination factor (CF), Geoaccumulation Index (Igeo) and Pollution Load Index (PLI) values indicate that both estuaries are moderate to highly contaminated by Co and low to moderately contaminated by Pb and Zn. Based on the factor analysis, it is presumed that river runoff and industrial and untreated domestic wastes from lands are responsible for increased heavy metal concentration in both estuaries. Increased levels of metal contamination along the Union Territory of Puducherry coastline may increase the risk of human exposure to metals through the consumption of seafood, making the need for tougher regulations on the discharge of metals into the environment even more important.

Impacts of climate-smart soil and water conservation practices and slope gradient on selected soil chemical properties in Eastern Ethiopia: A case study of the Kulkullessa Sub-watershed, Goro Gutu District

The productivity and sustainability of agricultural systems are heavily influenced by soil fertility and physicochemical properties. This study investigated the effects of climate-smart soil and water conservation (SWC) practices and slope gradient on selected soil physicochemical properties and soil organic carbon stock (SOCS) in the Kulkullessa Sub-Watershed of Goro Gutu District, Eastern Ethiopia. The research focused on farmland conserved by stone bunds (SB), bench terraces (BT), and grass strips (GS) five years post-implementation, across two slope gradients (15-20% and 21-30%). Twenty-four composite soil samples were collected from a depth of 0-20 cm and analyzed at the Haramaya University soil laboratory. Results demonstrated that climate-smart SWC practices significantly improved soil physicochemical properties and SOCS in the study area. Slope gradients also induced considerable variations in these parameters. Conserved farmland and areas with lower slope gradients exhibited higher clay content and lower sand fractions. Bench terraces were associated with lower bulk density (BD) and significantly higher total porosity (p ≤ 0.05). Conserved farmlands showed higher electrical conductivity (EC) and lower pH values, both statistically significant (p ≤ 0.05). Stone bunds were most effective in increasing soil organic matter (SOM) content and total nitrogen (TN). Climate-smart SWC practices also enhanced exchangeable bases in the farmlands. Cation exchange capacity (CEC) was significantly improved (p ≤ 0.05) on farmland conserved by SB and BT. In conclusion, climate-smart SWC practices demonstrated substantial potential for improving agriculturally and environmentally relevant soil physicochemical properties and organic carbon stocks. These findings underscore the importance of such conservation measures in enhancing soil quality and promoting sustainable agriculture in the region.

The distribution and drivers of tree cover in savannas and forests across India

The distribution of forest and savanna biomes and the role of resources (climate and soil) and disturbances (fire and herbivory) in determining tree-grass dynamics remains elusive and variable across geographies. This is especially problematic in Indian savannas which have been historically misclassified as degraded forests and are targeted for tree-planting. Here, we examine biome distribution and determinants through the lens of tree cover across India. Our analyses reveal four distinct zones of differing tree cover, with intermediate zones containing savanna vegetation. Rainfall seasonality determines maximum possible tree cover non-linearly. Once rainfall seasonality is factored out, soil sand fraction and topography partially explain residual variation of tree cover. High domestic livestock herbivory and other anthropogenic pressures reduce tree cover. Lastly, lack of detectable fires precludes robust conclusions about the relationship between fire and tree cover. By considering these environmental drivers in restoration planning, we can improve upon simplistic tree planting initiatives that may be detrimental to Indian savannas.

Separation of Brick Particles from the Sand Fraction of Masonry Construction and Demolition Waste on the Basis of Their Magnetic Susceptibility

Separation of Brick Particles from the Sand Fraction of Masonry Construction and Demolition Waste on the Basis of Their Magnetic Susceptibility

A Sediment Budget for a Sand Bed River Partitioned by Sand Fractions

AbstractSediment budgets are widely used to measure reach‐scale sediment accumulation and evacuation. Such measurements, however, cannot determine when the disturbance is major and the measured sediment mass imbalance is reflective of a river adjusting to a new equilibrium state, as opposed to situations when the disturbance is minor, and the mass imbalance is reflective of a river adjusting within its existing behavioral regime. Sediment sorting among channels and floodplains can have a large effect on how a river responds to a disturbance. Fine sediment may accumulate in the floodplains while coarser sediment erodes from the channel bed. We demonstrate that if a sediment budget does not account for the different behavior and destination of grain sizes, the budget cannot reveal important channel adjustments. In this study, we evaluated how a sand bed river responded to increases in sediment supply by partitioning a sediment budget among silt/clay and five sand fractions. On average, 12 metric tons/meter (downstream)/year of sand was evacuated from the system, but sorting caused channel margins to behave differently from vegetated islands, revealing how a river can slightly narrow while in deficit. Floodplain shaving and bed coarsening evacuated sediment while channel geometry barely changed, consistent with a river adjusting to a minor disturbance within its behavioral regime. This study is an important reminder that sediment mass imbalance does not always lead to channel change. Mechanisms such as floodplain shaving and bed textural change help rivers absorb minor disturbances and resist channel change.

Irrigation-Initiated Changes in Physicochemical Properties of the Calcisols of the Northern Part of Fergana Valley

Agriculture in Central Asia and in the Fergana Valley in general strongly depends on irrigation and drainage of agricultural lands. The Fergana Valley includes about 45% of the irrigated area in the Syr Darya River basin. Active use of irrigation in agriculture can lead to changes in the soil’s natural composition, as well as pollution and changes in the soil’s physical and chemical properties. Soil degradation in the process of irrigation can lead to a decrease in crop yields and, as a consequence, to a decrease in food security in the region. In this study, a comparative analysis of three main types of Calcisols (Dark, Light, and Typical) before (uncultivated soil) and after agricultural use (surface-irrigated agricultural soil) was carried out. Irrigation leads to increment of SOC stocks in Typical (from 113.8 to 126.3 t/ha) and Light (from 62.8 to 100.1 t/ha) Calcisols and to decreasing of SOC stocks in Dark Calcisols (from 160.1 to 175.3 t/ha). In general, the content of biophilic elements (SOC and TN) is lower in irrigated soils, and their distribution in the soil profile is close to the functional relationship (r2 0.98 to 0.99). In uncultivated Calcisols, the profile distribution of SOC and TN is more heterogeneous (r2 0.67 to 0.97). Changes in the humification processes of soil organic matter are also identified; in soils after irrigation the carbon ratio of humic/fulvic acids (CHA/CFA) is lower (&lt;1) compared to their uncultivated counterparts (~1). The alteration of the soil water regime also resulted in transformation of the individual compositions of amino acids. All studied types of Calcisols are characterized by changes in particle-size distribution of soils especially in the number of the silt fraction (0.01–0.05 mm) and the difference between uncultivated and irrigated soils, 10–20%, which is associated with the processes of colmatage by accumulation of a fine fraction and replacement of sub-fractions in the fraction of sand. The highest concentrations of nutrients are characteristic of the upper soil horizons (P up to 231, K up to 2350 mg/kg), which indicate their pedogenic and agrogenic origins rather than inheritance from the parent material. Soil P and K availability is rather high, with non-labile forms prevailing, although of near reserve. The surface irrigation results in apparent accumulation of water-soluble Mg2+ (1.6–2.1 meq/100 g) and K+ (0.6–0.9 meq/100 g), but the cation of Ca2+ predominates in the base cations’ composition, which is the most favorable in terms of soil agrogenic property formation. Data obtained will be useful for development of strategies for effective land use in arid, subtropical, overpopulated regions of Central Asia that have deficient water sources and intensive soil degradation.

MINERALOGIA, GEOQUÍMICA, FERTILIDADE E ORIGEM DOS SEDIMENTOS DE PRAIA (BARRA EM PONTAL) DAS BACIAS DOS RIOS PURUS E JURUÁ NOS TERRENOS DO ESTADO DO ACRE

The Acre state is in the southwestern part of the Brazilian Amazon region with an area of 164.123.738 km2 and a low population density (5.52 inhabitants/km2 for 2021). The geological context is mainly related to recent units that outcrop at the Acre basin and associated with the Solimões Formation, besides old alluvial terraces that follow main drainages. The Solimões Formation comprises fossil-bearing clayey siltstones intercalated to fine sandstones. The old alluvial terraces are composed by sand, silt, clay, and occasionally fossil fragments. The area of the Acre state is crossed by two main hydrographic basins: The Purus and Juruá rivers in the eastern and western part, respectively. Both rivers are the so-called “white-water rivers”. They exhibit a typical dendritic drainage pattern and are extremely meandering what give rise to lakes formed after abandoned meanders. During dry season, several beaches (point bars) are exposed on river‘s meanders, frequently used for swimming but also playing a very important role in the small-scale agriculture. These beaches are also used for planting corn (Zea-Mays) and beans (Vigna unguiculata (L) Walp). The main purpose of this work is to investigate the mineralogical and geochemical aspects of those beach sediments to understand their high fertility and to identify their primary source. Fourteen stations were selected for sampling purposes throughout the river valley close to BR-364 highway. Laboratory analyses were carried out as follow: grain sizes, x-ray diffraction, scanning electron microscopy and optical microscopy of heavy minerals concentrates; sediment whole chemistry (major and traces elements analyses including rare-earth elements) by means of ICP-MS; macronutrients (P, Mg, Ca, and K) besides available Na and Al and organic matter. The river sediments are mainly fine-grained, angular sub-angular and selected moderately. Mineralogical assemblage is represented by quartz, clay minerals (smectite, illite and kaolinite) and feldspars (K-feldspars and albite). The heavy minerals contents ranged from 0.5 to 4.6% and are mainly represented by zircon, epidote, kyanite, tourmaline, garnet, rutile, apatite, staurolite, ilmenite and hematite. Chemical results shown that the sediments are mainly composed by SiO2, besides minor amounts of Al2O3, Fe2O3, K2O, CaO and MgO, what is compatible with mineralogical composition. High SiO2 contents are mainly related to quartz and Al2O3 contents reflects the presence of clay minerals. Contents for alkaline and alkali-earths are relatively high for such beach environment related to feldspars and smectites. P2O5 is related to apatite and can also be adsorbed on smectite. Fe2O3 contents are mainly associated to smectite and a minor amount to ilmenite and hematite, the most common opaque minerals found in the beach sediments. Strong correlation coefficients were observed between Al2O3 and most major and trace elements, except for Zr, Hf, Ni and As. On the other hand, strong negative correlation was obtained between SiO2 and major and trace elements what points to the importance of smectites as scavenger of trace elements in such environment. The chemical results were compared with the mean of the Upper Crust and post-Archean Australian Shales (PAAS) and show that they are impoverished in MgO, CaO, Na2O and K2O in comparison with the former and MgO, in comparison with the latter. Such impoverishment is higher in samples enriched on sand fraction. The same comparison was carried out with the Chinese Changliang and Huanghe river sediments, showing impoverishment in CaO and MgO in comparison with the Changjiang River and MgO, CaO, Na2O and Sr, in comparison with the Huanghe River. The small value obtained for the Chemical Index of Alteration (CIA) shows that these sediments have experienced small degree of chemical weathering and consequently, physical weathering has prevailed in the source area. The beach sediments also exhibit high immature index as evidenced by the following very low rations: SiO2 / Al2O3 (11,64) and K2O/ Na2O (2,08). Rare-earth elements were normalized to the Upper Crust and to the PAAS patterns. They show similar patterns of LREE depletion and HREE enrichment. On the other hand, normalized to the chondrites present enrichment in LREE and horizontalization of the HREE, with similar standards of distribution between each other, presenting typical Eu negative anomalies of granitic and intermediary nature rocks. Analytical results for macronutrients exhibited high concentrations for P, Mg, Ca and K, and low contents of available Na and Al. Organic matter contents in below 1%. The sediments show high cation exchange capacity, base saturation over 70% and low Na and Al saturation. Accordingly, those sediments can be interpreted as representing a redistribution of the recent Miocene sediments (Solimões Formation) and the own sediments that were deposited in old alluviums. Chemical and mineralogical characteristics with a silty granulometry indicate that beach sediments are like the eutrophic cambisols.

Fine Sediment in Mixed Sand‐Silt Environments Impacts Bedform Geometry by Altering Sediment Mobility

AbstractGeometric characteristics of subaqueous bedforms, such as height, length and leeside angle, are crucial for determining hydraulic form roughness and interpreting sedimentary records. Traditionally, bedform existence and geometry predictors are primarily based on uniform, cohesionless sediments. However, mixtures of sand, silt and clay are common in deltaic, estuarine, and lowland river environments, where bedforms are ubiquitous. Therefore, we investigate the impact of fine sand and silt in sand‐silt mixtures on bedform geometry, based on laboratory experiments conducted in a recirculating flume. We systematically varied the fraction of sand and silt for different discharges, and utilized an acoustic Doppler velocimeter to measure flow velocity profiles. The final bed geometry was captured using a line laser scanner. Our findings reveal that the response of bedforms to an altered fine sediment percentage is ambiguous, and likely depends on, among others, bimodality‐driven bed mobility and sediment cohesiveness. When fine, non‐cohesive material (fine sand or coarse silt) is mixed with the base material (medium sand), an increased dune height and length is observed, possibly caused by the hiding‐exposure effect, resulting in enhanced mobility of the coarser material. However, weakly cohesive fine silt suppresses dune height and length, possibly caused by reduced sediment mobility. Finally, in the transition from dunes to upper stage plane bed, there are indications that the bed becomes unstable and dune heights vary over time. The composition of the bed material does not significantly impact the hydraulic roughness, but mainly affects roughness via the bed morphology, especially the leeside angle.

Investigation of the Strength of Fine-grained Concrete with a Plasticizing Additive

The article is devoted to the analysis of the effect of plasticizing additives and various sand fractions on the compressive strength of fine-grained concrete. Special attention is paid to the study of the effect of the Master Phebuild 1000 K superplasticizer on the strength of concrete when using various sand fractions. The experimental results confirm that this additive and aggregates with fractions of 0.63 mm, 1.25 mm and 2.5 mm have a positive effect on strengthening the strength of fine-grained concrete. It was found that with the combined use of aggregates and 0.5% of the cement weight of the Master Phebuild 1000 K superplasticizer, it can increase the strength at the age of 7 calendar days by 35%, at the age of 28 calendar days – by 30%. These results indicate the prospects of using this plasticizing additive to improve the characteristics of fine-grained concrete.

Soil fertility based on mineralogical properties to support sustainable agriculture management

&lt;p&gt;Detailed information on soil mineral composition has been crucial in providing the basis for designing sustainable agricultural practices, as this information offers long-term insights into natural soil fertility. This research aimed to further investigate the characteristics of soil mineral composition as a basis for managing soil fertility. Three soil profiles representing three different parent materials have been examined in the field, and soil samples have been collected for laboratory analysis. Profile 1 originates from the Raung Volcano Rock Formation (Qhvr). Profile 2 originates from the Sukamade Formation (Toms). Profile 3 originates from Puger Formation (Tmp). The presence of Mount Raung volcanic influence results in distinct soil characteristics in Profiles 2 and 3 compared to typical sedimentary and karst rock soils. The sand fraction minerals in all three profiles are predominantly composed of opaque minerals, followed by rock fragments, ferromagnesian mineral series (olivine, augite, hypersthene, and hornblende), plagioclase minerals (anorthite, biotite, and labradorite), iron concretions, epidote, and tourmaline. The clay fraction minerals in all three profiles consist of illite, kaolinite, and quartz. The minerals illite and ferromagnesian groups in all three profiles play a significant role in increasing the availability of potassium, calcium, and magnesium nutrients, thereby reducing the need for fertilizers for these elements. The soils in all three profiles naturally possess good fertility; however, designing a sustainable agricultural system requires consideration of the morphology, landform, and climate of all three profiles.&lt;/p&gt;

Hubungan komunitas moluska dengan parameter lingkungan di kawasan mangrove Pulau Penyu, Tanjung Benoa, Bali

Mangroves are plants in coastal and estuary areas that are influenced by tides. Mangroves provide essential habitats as spawning, nursery and food sources for various biota, including mollusks. Mollusks have a reciprocal relationship with mangrove plants, play an important role in maintaining the balance of the food chain in mangrove ecosystems. The objective of the research is to establish the structure of the mollusk community and its correlation with environmental conditions in the Pulau Penyu mangroves. The study was carried out in September 2023. The method employed the 1x1m quadrat transect with 15 points per station. Salinity, pH, temperature and substrate type are all measurements of environmental conditions. The research revealed 24 species, including 20 gastropod species and 4 bivalvia species from 12 mollusk families. Families found include Potamididae, Cerithiidae, Batillariidae, Ellobiidae, Mitridae, Neritidae, Littorinidae, Naticidae, Muricidae, Veneridae, Cyrenidae and Corbulidae. Mollusk abundance ranged from 0,07 to 13,07 ind/m2 at the research site, with Cerithium coralium being the most abundant species and Corbula macgillivrayi being the least abundant. The results of diversity index is 1,90 to 2,25; evenness index is 0,68 to 0,78; dominance index is 0,18 to 0,25; indicating moderate species diversity, high individual numbers each species, and no dominant species. The range of environmental parameter values obtained were; temperature ranges from 34,1 to 35,37 oC; pH ranges from 6,43 to 6,68; and salinity ranges from 35,2 to 36,3 ppt. The substrate type at the research site was sandy clay and clayey sand. PCA analysis results indicate a strong relationship between mollusk abundance and pH, salinity and sand fraction, but very weak relationship with temperature, dust and clay fraction.

A detailed quartz and feldspar luminescence chronology for the Khonako II loess section (Southern Tajikistan)

Parts of Central Asia have been dominated by high dust flux since the start of the Quaternary. The resulting loess-palaeosol deposits are important archives for landscape and climate changes, but there is a lack of chronological data for the subaerial deposits of Southern Tajikistan. Our study presents a high-resolution luminescence chronology for the Khonako II section in the Khovaling region. Thirty-seven samples were collected from the first ∼8 m of the section, corresponding to the Holocene soil and the upper part of the Loess 1 (L1) unit. We applied quartz OSL dating to the coarse-silt fraction (40–63 μm) and polymineral pIRIR200,290 dating to the very fine sand fraction (63–90 μm). The polymineral pIRIR200,290 signal has satisfactory characteristics. The quartz dose response curve displays a non-single exponential growth above ∼100 Gy, thus, the De values were estimated by fitting a single exponential function plus linear component to the dose response data. To assess the pIRIR200,290 residual dose at deposition, we used the offset between our quartz and polymineral chronologies from Khonako II and equivalent doses measured on modern dust samples from Tajikistan and Uzbekistan. The resulting 9.2 ± 0.4 Gy dose was then subtracted from the pIRIR200,290 doses for final age calculation. The quartz OSL and pIRIR ages are then generally consistent. The obtained high-resolution luminescence chronology shows that the upper part of the L1 unit accumulated during the end of marine isotope stage (MIS) 3 and through MIS 2 (39–20 ka). The average dust accumulation rates (DAR) increased from ∼31 cm ka−1 to 41 cm ka−1 between MIS 3 and MIS 2. The DAR reached a peak of ∼71 cm ka−1 at 21 ka. A hiatus of ∼7–9 ka was then identified between the end of the last glacial maximum (LGM) and the beginning of the Holocene, and the average DAR decreased during the Holocene. Our results indicate a continuous high dust flux in the Khovaling plateau over the last 39 ka, but reworking processes and potential deflation events mark the LGM-Holocene transition. High-resolution luminescence dating studies in Tajikistan are therefore important to detect potential discontinuities in the sequences and provide an independent timescale for interpreting the climate proxies and calculating dust accumulation rates.

Optimising Pavement Performance in Douala City Using a Mixture of Clay and Sand Fractions

Pavements are complex structures composed of multiple layers, designed to withstand various types of stress, including mechanical, organic, and climatic. The pavement is constantly subjected to cyclic, dynamic-mechanical actions caused by road traffic and different axle loads. Classified as engineering structures, the standard theoretical durability of this type of construction is generally estimated to be around one hundred years. However, this objective may not be achieved if the designer does not take into account certain specific factors that are endogenous and exogenous to the structure. Therefore, the durability of a road can be achieved through an optimized design that meets the needs defined by the public authorities and the context of its socio-economic framework. This passage discusses the factors that affect the performance of pavements, including soil type, machinery used, users, and climatic conditions. Exceeding axle loads, which form the basis of pavement design calculations, is also a disruptive factor from a civic perspective. A pavement consists of multiple layers, each made up of materials that must meet strict quality criteria and respect the anthropological, economic, social, and natural environment. It is important to consider all of these factors when constructing a pavement to ensure its longevity and avoid any negative impacts on the surrounding area. Additionally, it is crucial to maintain the pavement to prevent any loss of economic or infrastructural development opportunities. Several road infrastructures in urban and inter-urban areas experience issues that result from a combination of causes, each with varying degrees of impact. Douala is one such city where civil engineering projects are subject to an environment that is not conducive to the longevity of infrastructure, especially road infrastructure. The city is situated on a surface layer covered by a predominantly sandy-clay soil. This study aims to propose a proportional mixture of clay and sand soil fractions to create an anvil effect during compaction. The objective is to create a hybrid backfill material that can achieve a high compaction rate. Good compaction is crucial for achieving optimal pavement layer performance. The thickness of the material to be laid is greatly affected by this characteristic, which in turn affects the volume of equipment depreciation and user comfort. This has a significant impact on a wide range of socio-economic benefits. Based on soil mechanics and geotechnical tests, a new material is proposed to combat the early onset of disorders such as potholes, ruts, erosion, or pavement collapse in bad weather or heavy traffic.

Contribution of Saharan dust to chemical weathering fluxes and associated phosphate release in West Africa

Huge amounts of mineral dust are produced in northern Africa, representing the largest source of aerosols worldwide. Transatlantic dust transport is known to fertilize soils as far as in the Amazon Basin. Yet, the influence of Saharan dust on chemical weathering fluxes and associated nutrient release in West Africa remains largely overlooked. To address this issue, we analysed clay fractions (<2 µm) of river sediments (n = 37) from across the Niger River basin - the largest river system in West Africa - using neodymium and hafnium isotope compositions as proxies for provenance (εNd) and chemical weathering (ΔεHf CLAY).Compared to previously published data for corresponding sand fractions, measured εNd values indicate significant size-dependent decoupling for Nd isotopes in most samples, with εNd differences between clay and sand fractions yielding values as great as ∼26 ε-units. Using mixing models, we show that this discrepancy reflects the overwhelming presence in the studied clay fractions of Harmattan dust blown from the Bodélé Depression in Chad, which we estimate to account for about 40 % of the fine-grained sediment load exported to the Gulf of Guinea. Additionally, significant ΔεHf CLAY variability occurs across the Niger catchment, partly explained by the presence of zircon in clay-size fractions, but also by preferential alteration of dust-borne accessory phosphate minerals in the subtropical regions of the watershed.Based on these results, we propose that Saharan dust plays a major role in controlling regional patterns of chemical weathering in West Africa, suggesting that enhanced wet deposition of mineral dust in shield areas dominated by transport-limited weathering regime can result in a large increase in weatherability and associated release of phosphorus. These findings have general implications for the importance of mineral aerosols in controlling sediment yield and the supply of weathering-derived nutrients to continental areas bordering large subtropical deserts worldwide.

Combined effects of geological heterogeneity and discharge events on groundwater and surface water mixing

Stream water (SW) infiltration to the subsurface and subsequent mixing with groundwater (GW) is crucial for controlling water quality in river-corridors. Mixing of solutes from SW and GW triggers biogeochemical reactions, which can attenuate contaminant influx from upstream SW or from GW that eventually enters the river in downstream regions. It is known that geological heterogeneity affects SW-GW exchange fluxes (EF), however, the combined effects of both hydrological and geological aspects (e.g., sand fraction present in the aquifer material) on EF and on SW-GW mixing in strong contrasting bimodal aquifer units remain unclear. Here, we examined this gap by combining geostatistical realizations, fully-integrated numerical flow simulations, and a mixing-cell routine to assess the major controls on EF and to evaluate how mixing develops and is affected by stream discharge events with different magnitudes and durations. Results show that subsurface heterogeneity at the river-reach scale mainly affects EF magnitudes rather than EF patterns. Yet, both EF magnitudes and SW-GW mixing increased with the introduction of subsurface heterogeneity and with the increase of average hydraulic conductivity (K) values and sand fraction in the models. The simulations further indicated a larger potential for mixing under more frequent, short events regardless of the aquifer material, however, mixing values were generally higher for sandier and heterogeneous models. Lastly, for a high K contrast between subsurface units, these effects were more pronounced. This characterization is critical for river restoration strategies and for downstream management of dam-regulated rivers. Our study elucidates the interplay between hydrological and geological controls on the development of SW-GW mixing at intermediate scales and highlights the importance of considering aquifer characteristics in future studies.

Interrelation between compressibility and permeability of reconstituted sandy clays with different sand fractions

It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays, including the hosted clay and sand particles. However, interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported. For this, a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions (), initial void ratio of hosted clays () and void ratio at liquid limit of hosted clays (). The roles of in both the relationships of permeability coefficient of hosted clay () versus effective vertical stress () and void ratio of hosted clay () versus were analyzed. The results show that the permeability coefficient of reconstituted sandy clays () is dominated by hosted clay (). Both and affect the of sandy clays by changing the at any given . Due to the partial contacts and densified clay bridges between the sand particles (i.e. structure effects), the in sandy clays is higher than that in clays at the same σ′v. The relationship of sandy clays is independent of and , but is a function of . The types of hosted clays affect the of sandy clays by changing the . Based on the relationship between permeability coefficient and void ratio for the reconstituted clays, an empirical method for determining the is proposed and validated for sandy clays. The predicted values are almost consistent with the measured values with = 0.6 - 2.5.

Baseline Inventory of Benthic Macrofauna in German Marine Protected Areas (2020-2022) before Closure for Bottom-Contact Fishing.

The response of benthic habitats and organisms to bottom-contact fishing intensity is investigated in marine protected areas (MPAs) of the German EEZ in the North and Baltic Seas. We examined the current state of macrofauna biodiversity in 2020-2022. Comparative analysis for macrofauna (in- and epifauna) inhabiting nine Natura 2000 MPAs constitutes a baseline to assess the effects of bottom-contact fishing exclusion in the future. Aspects of spatial and temporal variability are briefly summarized and discussed. We provide a species list for each region, including 481 taxa, of which 79 were found in both regions, 183 only in the North Sea, and 219 only in the Baltic Sea. The Baltic Sea dataset surprisingly included higher numbers of taxa and revealed more Red List species. The share of major taxonomic groups (polychaetes, bivalves and amphipods) in species richness showed peculiar commonalities between the two regions. In the North Sea, multivariate analysis of community structure revealed significantly higher within-similarity and stronger separation between the considered MPAs compared to the Baltic MPAs. Salinity, temperature and sediment fractions of sand were responsible for over 60% of the variation in the North Sea macrofauna occurrence data. Salinity, mud fraction and bottom-contact fishing were the most important drivers in the Baltic Sea and, together with other considered environmental drivers, were responsible for 53% of the variation. This study identifies aspects of macrofauna occurrence that may be used to assess (causes of) future changes.