Medium Sand Fraction Research Articles

The influence of soil factors on the different vegetation formations of the Dunas Park, Salvador, Bahia, Brazil

This article was conducted in a restinga ecosystem on quaternary sandy deposits of Parque das Dunas, Salvador, Bahia, Brazil; located north of Salvador, this area comprises a landscape formed by different edaphic gradients with varied vegetation formations. An edaphic characterization of the sections of these remnants was carried out to understand the influence of edaphic factors on the distribution of the plant composition of this environment. For this purpose, a transect was delimited perpendicular to the coastline. In this transect, 08 plots of 25x25m were implanted, 100m apart. In the Centre of each plot, a 1m wide and 60 cm deep trench was opened, where soil samples were collected to determine edaphic and granulometric parameters. These samples in each plot followed the distribution of the vegetation formations of this environment. It was found that the different water regimes and topography of the area influence the soil factors, which interferes with the distribution and heterogeneity of the vegetation. The highest levels of fine, very fine and medium sand fractions and calcium and phosphorus were found in the highest portions. These areas, with better drainage, have a higher plant density. There is a lower vegetation density with open sandbanks in lower areas, lower levels of fine, very fine and medium sand fractions, and lower nutrient retention. In these environments, some areas are partially flooded with adapted species. It was also found that most of the plots had a very acidic pH with the presence of exchangeable Al, which could indicate high nutrient unavailability. Thus, the sandbanks' soil conditions influence the vegetation's development, inducing the plant species to develop adaptive mechanisms to maintain their biological organization.

Control of Sediment Grainsize on Lead (Pb) Content in the Reef Sediment Systems: A Case Study of Panjang Island, Banten Bay, Indonesia

Sediments are known to accumulate pollutants from terrestrial and coastal waters, and can be used as an indicator to monitor metal pollution in the biosphere and the effects of anthropogenic events in the environment. Eight samples of reef surface sediments were collected from the north and east coasts of Panjang Island. Panjang Island, located to the north of Banten Bay, was chosen for this study because of its proximity to many industrial areas. Nevertheless, the island supports a natural ecosystem, including coral reefs, seagrass, and mangroves. The samples were analyzed for the grainsize, component analysis, and Pb concentrationusing AAS flame method. The result indicated Pb concentration in the grain-supported surface sediment in Panjang Island is varied. The detected Pb concentrations were 0-28.68 mg/kg in dry weight. The study indicated that the different concentration of Pb value is mainly controlled by the different of sediment grainsize. The highest Pb accumulation occurs in the areas with very fine sediment grainsize, which have better adsorption capabilities for heavy metals. This study also suggests that the medium sand fraction may accumulate different Pb values. The result indicated that, according to the classification of ANZECC/ARMCANZ, all sediment samples in the study area is in the low risk of toxicant level. Additionally, the SQG-Q (Sediment Quality Guidelines) quotient analysis indicates that Pb concentration in the study area posed a low-moderate impact to adverse biological effect.

Understanding the impact of sand extraction on benthic ecosystem functioning: a combination of functional indices and biological trait analysis

Marine aggregates have been intensively extracted in the North-East Atlantic over the past decades. This study aimed to assess the effect of sand extraction on benthic ecosystem functioning using a combination of biological traits and functional indices (the bioturbation (BPc) and irrigation potential (IPc) and secondary production (SPc) of the macrobenthic community). Data on macrobenthos, sediment properties and extraction intensity were collected over a time period of ten years (2010 – 2019) for three coarse sediment extraction areas in the Belgian Part of the North Sea, each with a different extraction regime. Sediment parameters such as the medium sand fraction (250 – 500 µm) and median grain size showed a significant effect on all functional indices. Whilst sand extraction variables only significantly affected secondary production estimates. The secondary production of the macrobenthic community decreased following a high yearly extraction intensity, whereas a high cumulative (10-year period) extraction intensity resulted in a slightly increased secondary production. Species-specific responses revealed that these high cumulative extraction volumes increased the abundance of opportunistic species, which could have contributed to the higher SPc values observed in cumulative disturbed areas. Response traits such as tube-living and sessile individuals with a pelagic egg development were positively influenced by a long-term disturbance, an indication of a more disturbance-tolerant community. A short-term disturbance rather seemed to favor a macrobenthic community characterized by a higher burrowing capability. In terms of effect traits, both short- and long-term extraction clearly favored deposit feeders, which can structure organic matter distribution and thus indirectly influence nutrient and oxygen fluxes as well. Future in situ measurements in sand extraction areas could help to unravel and strengthen our understanding of the ecosystem processes linked to these trait-based observations.

Mineral chemistry in apatite from heavy mineral concentrate samples as a prospecting tool for carbonatites in the Angico dos Dias region, BA/PI border, Brazil

Apatite is one of the most common minerals found in a wide variety of rocks. It has variations of minor and trace elements in its composition that allow the recognition of its host lithotype. In this study, apatite grains identified in rock samples and grains recovered from heavy mineral concentrates in the Angico dos Dias Carbonatite Complex region, located on the border between the State of Bahia and the south of the State of Piauí, Brazil, were analyzed using an electron probe microanalyzer. These concentrates come from alluvial sediments downstream of the carbonatitic body from drainage channels. Sampling was guided by regional geochemical analytical results for the chemical elements of apatite. Grains were detected in alluvial covers for up to 9.5 km downstream in all fraction including coarse sand (1.0 mm) in proximal samples and up to medium sand fractions (0.50 mm) in distal samples. The 96 analytical results on 48 apatite grains show that most have chemical signatures characteristic of metacarbonatitic lithotypes (SrO 0.88–1.7 wt%) and that some host lithotypes were affected by the substituition processes (Si + LREE (Ce+La+Nd) 0.15–0.59 apfu), which may be an alternative to metasomatic fenitization. Statistical analysis by principal component analysis (PCA) helped the visualization and interpretation of the data by constructing clusters of the different compositions of apatite. The apatite fields of carbonatitic and silicate source rocks were separated and associated with the results obtained for alluvial apatite grains, resulting in carbonatitic derivation. The results of using this prospecting tool were satisfactory. Thus, it was possible to classify and detect the sources of alluvial apatite grains relating them to the Angico dos Dias carbonatite body, in addition to proposing a new potential area for the occurrence of carbonatitic bodies northeast of the Angico dos Dias phosphate deposit.

Granulometry, carbonate and glauconite content as stratigraphic tools to distinguish the Kiel Member and lower Antwerpen Member (Berchem Formation) in the City of Antwerp area (Belgium)

Granulometric, carbonate and glauconite analyses were performed on samples of the Kiel and Antwerpen members (Berchem Formation) in temporary exposures and boreholes in the area of the City of Antwerp. Since the upper part of the Antwerpen Member is only locally preserved from post-depositional erosion, this study focuses on the much more frequently sampled lower part of the Antwerpen Member. The granulometric results show that the Kiel Member and lower part of the Antwerpen Member are both dominated by the fine sand fraction, with an overall finer grain size for the lower Antwerpen Member compared to the Kiel Member. The Kiel Member is relatively enriched in the fine and medium sand fractions, whereas the lower Antwerpen Member is relatively enriched in the very fine sand to silt fraction. Both members show a similar, low clay content. Measurements of clay content are higher in boreholes (on average 3.9–5.2%) than in temporary exposures (less than 1%), which might be explained by the crushing of the glauconite into the clay fraction during drilling. In borehole samples, especially those analysed by sieving, the Antwerpen Member often shows a higher amount of coarse grains than the Kiel Member, which represent shell fragments present in the Antwerpen Member and nearly absent in the Kiel Member. Like the amounts of shells, also the measured carbonate content—measured outside the shell beds—is lower for the Kiel Member than for the lower Antwerpen Member (3% vs 4.2%). The average glauconite content—based on the >63 µm fraction—displays similar, strong fluctuations between 35% and 60% for both members. On top of these fluctuations, a general downward decrease in glauconite content is noticed in the Kiel Member.

Characteristics of Sediment and Physical Oceanography at Shoreline Movement of Rhu Bay Riau Province Indonesia

Rhu Bay is located in Rupat Island, Bengkalis Regency, Riau Province, Indonesia, under influence of the Malacca Strait. The main purpose of this study is to analyze shoreline changes in the Rhu Bay Coastal Area for 18 years, from 2012 to 2022 based on characterstics of sediment and physical Oceanography. Analysis of shoreline changes using Google Earth (Landsat Copernicus) covering the entire Rhu Bay area in 2002, 2008, 2014 and 2020. This research was carried out in Rhu Bay in June 2022 through two research stages:1) processing of secondary data in using Lansat Imagery Data and 2) the sediment samples were collected using sediment grab and oceanographic observation (currents, tides and waves) was also carried out at the coast. Digital Shoreline Analysis System (DSAS) is empowered in processing spatial data to calculate the rate of abrasion and accretion in Rhu Bay, using the methods applied of Net Shoreline Movement (NSM) and End Point Rate (EPR). The results of the study show that the coastline changes dominantly in Rhu Bay experiencing abrasion of 7.87 - 11.24 meters/year in a period of 18 years. The oceanographic parameters in Rhu Bay showed that the waves had a height of 0.2 m with a period of 3 second, current velocity of 0.36 m/s to the northwest. The change in shoreline is thought to be due to the current that flows from the Malacca Strait at high and low tide, as well as the transport of coastal sediment (dominated by medium sand fraction) towards the Malacca Strait by the currents.

Pycnometry for assessing porosity of fine recycled aggregates

The study extended the applications of powder pycnometry (PP) replacing the commercial enveloper for alternative envelopers (ceramic and carbon microspheres) to determine the envelope density of fine recycled aggregates (FRA) sand fraction. The properties of enveloper material such as particle size distribution, skeletal density and shape (aspect ratio and sphericity) affect the envelope density determination consequently impacts in porosity results by the association of PP and Helium pycnometry (HePyc). The porosity determination by association of HePyc and PP are comparable with mercury intrusion porosimetry analysis for medium sand fraction (0.300–1.180 mm).

THE EFFECTS OF WATER-SATURATED SAND-FRACTIONS ON THE SAND-BOILING PHENOMENON

Understanding the stress distribution behaviors along a soil cross-section have been the challenging topics in geotechnical engineering for the last two decades. Stress analysis by considering saturated sand without upward flow of water has been well studied. However, stress analysis in saturated sand-fraction with upward flow of water, which causes the sand-boiling phenomenon still needs a better understanding. In this paper, the relative density is used to indicate the denseness and looseness of sand fraction. The sand-boiling behaviors are then investigated through two scenarios. The first scenario uses a fine sand-fraction, called the FS scenario. The second scenario uses a mixture of coarse and medium sand-fractions, called the CS-MS scenario. For the FS scenario, the fine sand-fraction only consists of one layer, while for the CS-MS scenario, it consists of two layers where the coarse sand-fraction is above the medium one. The use of the relative density values of the fine sand, medium sand, and coarse sand in both scenarios are 7.6%, 12.4%, and 5%, respectively. As a result, all sand fractions used are categorized as very loose sand because their relative densities are less than 15%. The FS scenario shows that the effective stress is equal to zero obtained within 10 seconds at a depth of 0.12 m under the ground surface. This indicates that the sand boiling has occurred in the FS scenario. Whereas in the CS-MS scenario, the variation of effective stress with depth for a soil layer with upward seepage has a value greater than zero. This indicates that the sand boiling never occurred in the CS-MS scenario. Furthermore, both scenarios also show that the addition of coarse sand-fraction above medium sand-fraction could prevent the sand-boiling phenomenon.

Partitioning, leachability, and speciation of chromium in the size-fractions of soil contaminated by chromate production

Soil particle size significantly affects the distribution and migration of chromium (Cr) in soil. Limited studies have investigated the impact of soil particle size on Cr partitioning at chromate contaminated sites. In this study, the physicochemical properties of coarse sand, medium sand, fine sand, and silt-clay were analyzed. And the particle size effects on partitioning, leachability, and bioaccessibility of total Cr and Cr(VI) were determined. The results showed the distribution factor (DF) of Cr(VI) in the coarse sand, medium sand, fine sand, and silt-clay fractions were 0.70, 0.79, 1.35, and 1.60, respectively. The total Cr DF values also had the similar result. The leached concentrations of total Cr and Cr(VI) in silt-clay (562.89 mg/L and 551.71 mg/L) was higher than in coarse sand (238.55 mg/L and 228.68 mg/L) fraction. The bioaccessibility of total Cr and Cr(VI) in silt-clay (77.72% and 88.58%) was higher than in fine sand (60.72% and 79.55%) fraction. The total Cr proportion of the exchangeable fraction (45.92%–73.67%) was relatively high in the four soil particle size fractions and gradually increased as soil particle size decreased. These implied that finer soil particles are more capable of enriching, mobilizing, and bioaccessibility of Cr and Cr(VI) than the coarse particles, which was related to the higher organic matter, cation exchange capacity, specific surface area, and clay components in smaller particles. The results suggested that higher environmental risk occurred in the finer fraction than in the coarser fraction for the chromate production contaminated soil.

The use of mineral interfaces in sand-sized volcanic rock fragments to infer mechanical durability

The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at a modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea (Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli Island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural (e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47,386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl (Plagioclase)/Glgr (Glassy groundmass) > > Px (Pyroxene)/Glgr > > Ol (Olivine)/Glgr > > Op (Opaque)/Glgr > > Hbl (Hornblende)/Glgr> > Bt (Biotite)/Glgr > > Idd (Iddingsite)/Glgr > > Rt (Rutile) / Glgr; b) stable interfaces, categorized as Pl/Migr (Microlitic groundmass) > > Op/Migr > > Px/Migr > > Ol/Migr; c) moderately stable interfaces, categorized as Op/Px > > Op/Hbl > > Px/P > > Ol/Pl> > Bt/Op; and d) unstable interfaces, categorized as Pl/Pl > > Px/Px > > Ol/Ol > > Op/Op > > Hbl/Hbl > > Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass, Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.

Pedogenesis and Mineralogy of Alluvial Soils from Semi-arid Southeastern Part of Rajasthan in Aravalli Range, India

Abstract Three representative alluvial soils were studied from Kothari river basin of Bhilwara district in southeast Rajasthan to assess degree of chemical weathering and pedogenesis. Morphological, geochemical, mineralogical and other analytical investigations were carried out. Soils were classified as Entisols and Inceptisols. These soils are mostly sandy with more than 50% of fine and medium sand fractions, silt to clay ratio more than 0.45 and little textural variation suggesting more uniform weathering. These soils are slight to strongly alkaline with high exchangeable sodium (>15%) and cation exchange capacity less than 10 cmol(+)kg-1. Mineralogical investigations showed the dominance of micas and smectites in Pedon 1 (P1) and Pedon 2 (P2) and increase of smectites and micas in Bw3 horizon of P3 under strong alkalinity and high silica activity with limited lessivage. The low chemical index of alteration (CIA) in soils further indicated an incipient pedogenesis with a relative proportion of mica-smectite composition. The A-CNK-FM diagram shows abundance of CaO + Na2O + K2O as against Fe2O3+ MgO components under limited leaching environment and chemical weathering. The results of bivariate plot of SiO2 to (Al2O3 + K2O + Na2O) indicated the past weathering which influenced by prevailing arid climate in the region.

Compositional and textural study of modern beach sands in the active volcanic area of the Campania region (southern Italy)

The association among volcanism, tectonics and sedimentation may be critical for interpreting the paleogeographic and plate tectonic settings of the past. In modern and ancient sedimentary systems, volcaniclastic fragment classes have been distinguished on the basis of texture and composition. Criteria adopted for their temporal and spatial correlation with source volcanic areas, in terms of type of volcanism and particle-forming processes are still not well constrained and often a topic of controversy and misinterpretation. Here, we present data for volcaniclastic fragments occurring in modern beach sands of the Campanian coast of southern Italy, where there are two active volcanic areas, the Phlegrean Fields and Mt. Vesuvius. Despite their geographical proximity, these volcanoes are characterized by different magma compositions and eruptive mechanisms. We set out to test whether this translates into different textural and compositional characteristics of their associated volcaniclastic detritus in order to better constrain the criteria relating the type of volcanism to the nature of volcaniclastic sand fragments in the sedimentary record. Along a ~100 km coastal stretch, from the Volturno River mouth to Sorrento, 72 sand samples were collected mainly in beach berm environments. Detrital modes were defined for the medium sand fraction of each sample, where monocrystalline and lithic grains are easily identified. The analyzed samples show a mixed sedimentary and volcanic provenance. Samples from the northernmost coastal stretch show a sedimentary petrofacies at the Volturno River mouth. Bacoli marks the transition between the Apennine sedimentary and Phlegrean volcanic petrofacies. Along the Portici-Sorrento coastal stretch, volcanic lithic fragments dominate. Leucite and sanidine crystal components indicate that detritus from the Phlegrean Fields extends south from Licola to Naples Bay, whereas the Vesuvius provenance extends from Naples/Portici south to Castellammare di Stabia. Phlegrean Fields and Mt. Vesuvius volcaniclastic petrofacies have been discriminated through a different distribution of both compositions of the volcanic lithic fragments, leucite and K-feldspars content. Volcanic lithics with lathwork texture and leucite, are Mt. Vesuvius provenance source sensitive detrital grains, whereas volcanic lithics with vitric texture and K-feldspars marks the transition to the Phlegrean Fields petrofacies. The results formalize three different sandy petrofacies which were mapped from north to south as Sedimentary, Phlegrean (volcanic) and Vesuvius (volcanic) petrofacies.

Physical Properties of Urban Soils in Rostov Agglomeration

Transformation of particle-size composition, structure, and density of soils upon urbopedogenesis is considered for Rostov agglomeration. Various soils are compared by horizons. It is found that the share of sand fractions increases in upper and middle horizons of migration–segregation chernozems (Calcic Chernozem (Hyperhumic, Loamic)), above all, at the expense of particles of 0.05—0.001 mm in size; with the coarse medium sand fraction 1–0.25 mm being diagnostic for urbopedogenesis. The reason is the introduction of sandy particles upon urban construction, arranging water conduits and other utility lines, as well as the use of icing-control sandy mixtures. The Dolgov-Bakhtin schedule appears to be the most appropriate for assessing the structure of urban soils. Dry sieving testified to the decreasing amount of agriculturally valuable aggregates in all compared pairs of horizons in the sequence of urban soils: under forest vegetation → under steppe vegetation → in the buried massif of urbosoils. The water stability of aggregates decreases in the sequence: soils under steppe vegetation → buried horizons of urbosoils → soils under forest vegetation. The following sequence of urbic horizons (UR and RAT) shows a decrease in the share of agriculturally valuable fractions and an increase in their water stability: heavy-textured UR → light-textured UR → RAT. The density of natural soils varies insignificantly within the city territory, with its urbostratified soils (Calcic Chernozem Novic (Technic Loamic) in residential areas often manifesting the maximal density.

Tensile strength in horizons with and without cohesive character: Variability and relation with granulometry

Soils of Coastal Tablelands are important for the economic and social development of the coastal region of Brazil. However, these soils appear to have a number of chemical and physical limitations. One of the most expressive physical limitations is the occurrence of cohesive character, whose genesis is still not fully understood. Thus, considering that the tensile strength is a direct measure of the cohesion of particles, this research was undertaken to discover how the size of soil particles influences the genesis of the cohesive character in Bt horizons of the Coastal Tablelands of Ceará, Brazil. The study was carried out in the municipality of Aquiraz-CE, where samples of two soils were collected (Argissolo Vermelho-Amarelo Distrófico típico – PVAd; Argissolo Amarelo Eutrocoeso abrúptico – PAex) in the horizons Bt1 (cohesive) and Bt2 (non-cohesive) in the top, middle and bottom portions. The results demonstrated that the size of the particles led to sandy clay loam texture in horizons of PVAd and sandy clay texture in the horizons of PAex. Regarding sand sorting, for all investigated horizons and in the three positions (top, middle and bottom), the medium sand fraction prevailed, followed successively by fine and very fine sands together, coarse and very coarse sands. Tensile strength values were higher in cohesive horizons, with reduction in the tensile strength of aggregates from top to bottom. It was concluded that tensile strength was a useful indicator for differentiating cohesive properties in the different soil horizons. There was significant variation of tensile strength in the soil horizon defined by the pedologist – which suggests that it is necessary to include as a valuable addition to the diagnostic tools available to the working pedologist, a tensile strength scale for the identification of cohesion to avoid subjectivity in the definition of the cohesive horizon. For the studied set of horizons, tensile strength decreased from top to bottom. Sand and clay fractions, despite not being the only determinant factor, influenced the genesis of the cohesive character in soils. For the sand fraction, poor degree of sand sorting led to a denser packing of particles, significantly contributing to the cohesion of aggregates. Our experiment strongly suggests that the packing of particles allows the increase of cohesion provided there is a cementing agent even in small quantity.

Modelling of bed sediment composition changes at the lower shoreface of the Sand Motor

Large perturbations in the coastline, such as the 'Sand Motor' nourishment (∼21 million m3) at the Holland coast, can initiate considerable spatial and temporal changes in the median grain size (D50) of the sea bed on the lower shoreface. The relevance of hydrodynamic conditions for the development of the heterogeneity in D50 at large-scale nourishments was assessed with a numerical model (Delft3D), which required a validation against 2.5 years of D50 measurements. A good representation of the observed spatial pattern of D50 was obtained independent of a 2DH or 3D approach and initial condition for the D50 of the bed. Five sediment size fractions and a multi-layer administration of the bed composition were used. The extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide, while a far less pronounced coarsening takes place during energetic conditions (i.e. Hm0≥ 3 m). Differential suspension behaviour between the size fractions, which are all mobilized at the bed, causes a preferential transport of fine sediment (in alongshore direction) away from the Sand Motor at the lower shoreface (i.e. seaward of MSL -6 m). Storm conditions may induce a partial removal of the coarse top-layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material. Simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions. Models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large-scale coastal structures or land reclamation's and sediment transport on the lower shoreface.

Metals in 1–0.25 mm grain-size fraction in the soils of the mixed forest zone of the Russian plain

For an improved understanding of metal behavior in soils, studies on geochemical changes occurring in a specific grain-size fraction during pedogenesis and lateral translocation of soil material are needed. In the present research we analyzed the concentrations and vertical distributions of Fe, Mn, Cu, Ni, Co, Cr, Zn, Pb, Ti, Zr in coarse and medium sand fraction of the major soil types of the middle Protva basin, situated in the mixed forest zone of European Russia, and described patterns of downslope (lateral) distribution of metals in the humus horizons along two catenas and two types of small erosional systems. The observed concentrations for all metals in the fraction 1–0.25mm, except of Mn, conform to the natural geogenic concentrations reported previously in literature. The majority of the metals exhibit high natural variability in concentrations in the sand fraction. Higher metal concentrations are found either in the topsoil horizons or in parent material and underlying stratum. Studying lateral aspects of metal distribution in the sand fraction of humus horizons revealed a decrease in Mn, Zn, Pb, Co, Ti and an increase in Fe, Cr and Ni levels of the lower sections of the slopes. The similarity of metal concentrations in the sand fraction in these positions across two catenas implies the importance of the geochemical convergence processes operating in downslope direction. The small erosional landforms, a gully and a dry U-shaped valley, show similar patterns in lateral distribution of Fe, Cu, Ni, Cr, Zr, Zn, but they differ in terms of Pb, Co and Mn behavior across their elementary units: adjacent areas, slopes and bottom. The results imply that the features of vertical (within the soil profiles) and lateral (along catenas and small erosional systems) distributions of metals are significantly controlled by the provenance of the sand fraction, although at the same time some variations in metal contents seem are attributed to chemical transformations of the sand fraction due to pedogenic processes and during downslope translocation of soil material.

Influence of gradation and proportion of sand on stress–strain behavior of clay–sand mixtures

To investigate the influence of proportion of sand as well as its gradation on the undrained strength behavior of soils, undrained tests on statically compacted specimens of clay–sand mixtures were carried, with two extreme clay minerals, namely commercially available kaolinite and bentonite mixed with specimens of three grades of sand fractions, and also varying their proportion from 10 to 80%. This work was extended to two natural soils, viz., Red earth (kaolinitic type) and B.C. soil (montmorillitic type) by using fractionized fine portion from these soils obtained by sedimentation process, and later mixed with different proportions and grades of sand fractions. Results from this experimental investigation reveals that, at optimum sand content in clay–sand mixtures, use of medium sand fractions is more beneficial to improve the undrained strength of the mixtures irrespective of the clay mineral type being present in the mixture. It thus implies that proper selection of grade of sand is also important along with the optimum content to obtain higher strength of a clay–sand mixture. This has practical implications in understanding the performance of embankments or any ground improvement applications involving strength of clayey natural soils for better load carrying capacity, stability, and good performance of the structure supported by soil. It is also very useful in the geo-environmental applications like proper selection of proper grade of clay–sand mixtures as liners for better performance.

Preference of antlion and wormlion larvae (Neuroptera: Myrmeleontidae; Diptera: Vermileonidae) for substrates according to substrate particle sizes

Sand-dwelling wormlion and antlion larvae are predators with a highly specialized hunting strategy, which either construct efficient pitfall traps or bury themselves in the sand ambushing prey on the surface. We studied the role substrate particle size plays in these specialized predators. Working with thirteen species of antlions and one species of wormlion, we quantified the substrate particle size in which the species were naturally found. Based on these particle sizes, four substrate types were established: fine substrates, fine to medium substrates, medium substrates, and coarse substrates. Larvae preferring the fine substrates were the wormlion Lampromyia and the antlion Myrmeleon hyalinus originating from desert habitats. Larvae preferring fine to medium and medium substrates belonged to antlion genera Cueta, Euroleon, Myrmeleon, Nophis and Synclisis and antlion larvae preferring coarse substrates were in the genera Distoleon and Neuroleon. In addition to analyzing naturally-occurring substrate, we hypothesized that these insect larvae will prefer the substrate type that they are found in. Specifically, we tested substrate preference in a choice experiment for four species of antlions. This was then compared to the substrate that the larvae were naturally found in. Larvae of the four antlion species were allowed to choose among eight substrates differing according to their particle size. Our findings show that the majority of M. hyalinus larvae built pits in the finest sand fraction, and the majority of N. microstenus larvae were found in a coarser fraction. The other two species, M. immaculatus and E. nostras, constructed majority of their pits in a medium sand fraction. These results support the hypothesis that neuropteran larvae prefer specific substrates for pitbuilding or ambushing prey, and that this - in combination with other abiotic and biotic factors - may drive selection of appropriate habitats.

Erosion rates in and around Shenandoah National Park, Virginia, determined using analysis of cosmogenic 10Be

We use cosmogenic 10Be analysis of fluvial sediments and bedrock to estimate erosion rates (104-105 year timescale) and to infer the distribution of post-orogenic geomorphic processes in the Blue Ridge Province in and around Shenandoah National Park, Virginia. Our sampling plan was designed to investigate relationships between erosion rate and lithology, mean basin slope, basin area, and sediment grain size. Fifty-nine samples were collected from a variety of basin sizes ( Inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3.0 to 21 m/My. The area-weighted mean erosion rate for single-lithology basins in the Park is 12.2 m/My. Single-lithology erosion rate ranges for fluvial samples are: granite, 7.0 to 20 m/My; metabasalt, 3.8 to 21 m/My; quartzite, 3.8 to 15 m/My; and siliciclastic rocks, 5.2 to 15 m/My. Multilithology basins erode at rates between 3.0-16 m/My. The Shenandoah River basin (3305 km2) is eroding at 6.6 m/My. Bedrock erosion rates range from 1.8 to 11 m/My across all lithologies, with a mean of 6.5 ± 4.3 m/My. Grain-size specific 10Be analysis of four samples showed no consistent trend of concentration with grain size. Cosmogenic analysis of bedrock and sediment from the Shenandoah National Park area allows us to speculate about why some parts of the Appalachian Mountains erode more slowly and some more rapidly. Overall, it appears that steep drainage basins erode more rapidly than gently sloped basins. Climate and lithology may also influence basin-scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite- and granite-dominated basins. Data are conflicting in regards to the evolution of relief over time. Analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins (Susquehanna River, Shenandoah National Park region) or at similar rates (Great Smoky Mountains) providing a mechanism for growing relief at the scale of individual ridgelines. However, considering relief on a landscape or physiographic province scale, by comparing erosion rates of the highlands versus the lowlands, suggests that relief of the range as a whole is either steady or very slowly decreasing over multi-millennial timescales. The presence of significant erosion rate/slope relationships negates a broad Hackian view of the landscape because there is not uniform erosion across this landscape. The aspect-erosion rate and slope-erosion rate relationships present in the Shenandoah area suggest that the landscape is not fully adjusted to rock strength.

Physical and Chemical Properties of Complex and Compound Nabkhas in Kadhma Area Northern Kuwait Bay

The accumulation of aeolian sand around single plant is known as nabkhas, if it is around two plants it is called compound nabkhas, while if it is around more than two plants it is then called a complex nabkha and all are classified as anchored dunes. The compound and complex nabkhas are formed around dominant native plants in open desert and sabkhas in Kuwait. Morphological measurements were taken from a field of nabkhas formed around the plant “Nitraria retusa” in Khadhma area. Around 120 surface and core samples (down to a depth of 100 cm at each 10 cm) were collected in order to identify the morphological, sedimentological and chemical properties. The particle size, organic and moisture content, biological activity, acidity, electrical conductivity were measured for compound and complex nabkhas. The particle size for compound and complex nabkhas are varying upon location in the body of nabkhas and each type has its own distinguishing properties. There is reality that all nabkha deposits contain more fine sand in the wind ward (tail) sides compared to the mid of nabkhas. Graphical and inter-relation figures succeed in distinguishing between compound and complex nabkhas. The complex nabkha is characterized by normal distribution with increase in medium and coarse sand fractions with a percentage reaching more than 50%. The volume of the sand body in complex and compound nabkhas are 376.7 m3 and 14 m3 respectively. The complex dune is composed of a coalescence of 51 nabkhas with average 40 degree from north towards west, parallel to the dominant wind direction in the area. The sediment samples from the compound and complex dune is basic, dry with normal electrical conductivity and low organic matter content. The sample are with a medium mean size distribution, poorly sorted, normal skewness and very platy kurtic. This study showed that the importance of the sand body in the nabkhas is as nutrient and water storage rather than as a shield protecting the nabkhas from sand blasting. This sand body attracts native animals to a marvellous ecological interaction especially in complex nabkhas. the nabkhas use drought periods to catch more mobile sand in order to increase the volume size and to increase in water body.