Silt Fractions Research Articles

Chemical Fractionation and Risk Assessment of Some Heavy Metals in Soils, Assiut Governorate, Egypt

Toxic elements behavior in Egyptian soil need more studies for the enhancement of soil quality and human health protection. The current study focuses on the mobility assessment of chemical species of As, Pb, Cr, Ni, Cu and Co in soils due to anthropogenic emission using sequential extraction (SE) and risk assessment code (RAC). Generally, the studied soils are alkaline calcareous loam soil. It has a low organic matter (OM) that ranges from 1 to 3.8% and is enriched with As, Pb, Cr, Ni, Cu and Co, which preferentially accumulate in soil clay and silt fraction. SE revealed that the non-residual (bioaccessible) fraction contains about (70.7%) As, (65.2%) Co, (58.8%) Cr, (28.4%) Cu, (6.8%) Ni and (64.5%) Pb, indicates the risk of pollution with As, Co, Cr, and Pb. RAC values indicated a high risk of soil pollution with As, medium risk of Co and Pb, low risk of Cu and Ni, and no risk of Cr. The results pointed out the geogenic source of Cr, mixed source of Co, Cu, and Ni and the anthropogenic source of As and Pb. The spatial distribution analyses of these metals indicated the role of urbanization, traffic, and industry on the releasing of toxic metals into the environment.

Occurrence and Contamination of Rare Earth Elements in Urban Mangroves of Shenzhen, South China

Mangroves acted as sinks of terrestrial pollutants, but the occurrence and contamination of rare earth elements (REEs) in urban mangroves lacked systematic evaluation. In rapidly developing Shenzhen, China, four typical urban mangroves were selected to determine the REEs in urban mangroves, including Baguang mangrove (BGM) and Futian mangrove (FTM) featured with ecological preserve and central business district, respectively; Xixiang mangrove (XXM) and Shajing mangrove (SJM) both featured with industry district. The mean concentrations of total REEs (TREEs) in sediment (0–25 cm depth, μg g−1) were SJM (465.28) > FTM (411.25) > XXM (342.76) > BGM (118.63), with Ce to be the dominant REEs element. The depositions of REEs in urban mangroves were significantly affected by sediment sulfur accumulation and fine sediment, including silt and clay fractions. The main fractionation pattern of REEs in urban mangroves was the enrichment of light REEs (LREEs) and loss of heavy REEs (HREEs). Geo−accumulation index, modified degree of contamination, pollution load index, and potential ecological risk index showed the moderately contaminated level of REEs in FTM, followed by SJM, and XXM, with uncontaminated level in BGM. This study provided important information on REEs in urban mangroves for pollution prevention and remediation in the future.

GEOGRAPHICALLY WEIGHTED REGRESSION AND MULTIPLE LINEAR REGRESSION FOR TOPSOIL TEXTURE PREDICTION

Land resource management requires extensive land mapping. Conventional soil mapping takes a long time and is expensive; therefore, geographic information system data as a predictor in soil texture modeling can be used as an alternative solution to shorten time and reduce costs. Through digital elevation model data, topographic variability can be obtained as an independent variable in predicting soil texture. Geographically weighted regression is used to observe the effects of spatial heterogeneity. This study uses a data set of 50 observation points, each of which had soil particle-size fraction attributes and eight local morphological variables. The covariates used in this study are eastness aspects, northness aspects, slope, unsphericity curvature, vertical curvature, horizontal curvature, accumulation curvature, and elevation. Prediction using geographically weighted regression shows more results compared to multiple linear regression models. The spatial location can affect product Y, with the R2 value of 0.81 in the sand fraction, 0.57 in the silt fraction, and 0.33 in the clay fraction.

Status and Speciation of Silicon and Its Interaction with Physico-Chemical Properties

The effectiveness of three different extractants soil mixtures—HCl, HCl + H2S04, and DTPA-TEA, in order to determine Si from soil and the forms of Silicon as influenced by different parent materials under acidic medium.
 Seven forms of Silicon; namely water soluble, specifically adsorbed, oxides bound, organic matter bound, exchangeable, residual, total viz sequential fractionation.
 Extractable Si value established in this study was (50.0 mg kg-1), indicating negative effect on plant physiology. The physico-chemical properties decreased significantly with increase in soil depth vs soil parent materials. In addition, the forms of Si in the parent materials decreased in the pattern RES, bound residual fractions > EXC, soluble & exchangeable fractions > OM, organic matter fraction.
 Among the properties the silt fraction, pH & OM significantly and positively correlated with the forms of silicon, with negative correlation vs clay which maybe due to silicon adsorption by clayey fraction of the soil (redox). Therefore the soil maybe be maintained and conserved for farming activities.

Seasonal Changes of Soil Nitrogen Mineralization Along Restoration Gradient of Sandy Grassland, Northern China

Soil nitrogen mineralization strongly affects N availability, thus impacting the primary productivity in ecosystems. The seasonal environmental changes affect soil mineralization in restored sandy grasslands such as a studied mobile dune (MD), a semi-fixed dune (SFD), a fixed dune (FD) and a grassland (G). During the growing season, we examined the association of soil N mineralization rate with vegetation characteristics, soil properties and climatic factors through the multivariate stepwise regression model. The vegetation cover, species diversity, above- and belowground biomass, soil carbon, nitrogen, soil water content (SWC), pH, electrical conductivity, very fine sand, clay and silt fractions increased during sandy grassland restoration. The NH4+-N concentration in MD and SFD was higher than that in FD and G, while NO3--N and inorganic N concentration showed a reverse trend. The NH4+N, NO3--N and inorganic N concentrations in MD, SFD and FD reached to the highest values in June, while in G they were highest in May. The net mineralization and nitrification rates increased with sandy grassland restoration; both of these rates were much greater in June than in other months at all sites. Regression analysis showed that the NO3--N concentration, SWC, pH of the soil and precipitation could explain 75% of the total variation in net nitrification rate, and the NO3--N concentration and precipitation could explain 59% of the total variation in the net mineralization rate. These results illustrate that the sandy grassland restoration can enhance the soil N availability, with soil N mineralization mainly determined by the changes of the NO3--N concentration and precipitation.

Effect of Granulometric Composition of the Soil on the Occurrence of Carrion Beetles (Coleoptera: Silphidae)

The entomological material was collected in the years 2009–2012 and 2014 from 13 different habitat types from three localities in south-eastern Poland. In total, 11,095 Silphidae were collected. This study examined whether the percentage of individual soil granulometric fractions was significantly related to the total abundance of collected Silphidae and individual carrion beetle species. A positive correlation and a statistically significant correlation were found between the total number of specimens collected and the share of the mechanical fraction with a diameter of 0.05–0.002 mm (silt fraction). In three species, a statistically significant correlation was demonstrated between the number of collected Silphidae and the share of the mechanical fraction with a diameter of 2–0.05 mm (sand fraction). The two species Phosphuga atrata atrata and Nicrophorus vespilloides the correlation was positive. A statistically significant relationship was also observed for Thanatophilus sinuatus, but the correlation was negative. With regard to the mechanical fraction with a diameter <0.002 mm (clay fraction), a statistically significant relationship was demonstrated for Oiceoptoma thoracicum and for Nicrophorus vespilloides for which the correlation was negative. However, a positive correlation was found for T. sinuatus in this case.

Controls on the abundance, provenance and age of organic carbon buried in continental margin sediments

Continental margins play a fundamental role in the carbon cycle as primary oceanic locations of organic carbon (OC) burial. However, gaps remain in our understanding of factors controlling the distribution and preservation of organic matter (OM) in these heterogeneous and dynamic systems. In particular, the impact of hydrodynamic processes on the age, abundance, and stable isotopic composition of sedimentary OC is poorly constrained. Here, we characterize the OC present in bulk and grain-size sediment fractions from seven continental margin settings. Our results reveal that hydrodynamic particle sorting processes exert a ubiquitous influence on the radiocarbon age of OC. Both, hydrodynamic characteristics of mineral particles and the nature of their interactions with OM influence sedimentary OC content, whereas no significant influence of either effect is manifested in corresponding δ13C values. Since OC preferentially resides within the fine silt fraction (2-8 μm), and this fraction accounts for a substantial fraction of the bulk sediment mass, translocation and subsequent re-deposition of distant fine silt has the greatest potential to distort local OC signatures relative to those associated with clay or coarse silt fractions. We suggest that the magnitude of differences in 14C-age and OC content among grain-size fractions, determined by the interplay of hydrodynamic sorting and other site-specific processes, allow three different categories of depositional environment to be defined: initial, stable, and mature. Each domain is characterized by different degrees of vertical and lateral OC supply that reflect influences of local biological productivity and carbon export from overlying surface waters and physical forcing that drive hydrodynamic processes. This generic framework may serve as a guide to refine assessment of OC burial and to constrain the magnitude of potential aliasing among co-eval proxy signals in continental margin sedimentary sequences.

АГРОХИМИЧЕСКИЕИАГРОФИЗИЧЕСКИЕОСОБЕННОСТИКАШТАНОВЫХ ПОЧВ ЗОНЫ СУХОЙ СТЕПИ АЛТАЙСКОГО КРАЯ

The mathematical models of regional soil standards for the dry steppe zone were developed. Four soil regions were identified in the dry steppe zone in accordance with the soil-geographic zoning of the Altai Region. It is shown that the taxonomic boundaries of the agrochemical proper-ties of the soil standards may differ in different soil regions. On that ground, the regional soil classification at the level of soil regions was differentiated. Significant differences of the agrochemical properties of the Kashtanozem soil sub-types in four soil regions are shown. These differences are due to the geochemical features of their genesis and agro-genic transformations. The agrochemical properties reflect the changes associated with the long-term agricultural use of dry steppe soils: agricultural depletion of mobile nutrient АГРОНОМИЯВестник Алтайского государственного аграрного университета No 8(202), 202145content, absorbed bases and the changes of agrophysical properties -the degradation of Kashtanozems caused by deflation. This is proved by the decreased content of clay and silt fractions in the particle-size composition of the plowing soil horizon. It is proposed to use the classification boundaries of regional soil standards for monitoring their agrochemical and ecological state.

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.

Modeling of Compaction Trends of Anisotropic Elastic Properties of Shales

AbstractModeling of anisotropic elastic moduli of shales is a long‐standing problem in rock physics. Every year, industry and academia conduct hundreds of measurements of elastic and geomechanical properties of shales complemented with detailed mineralogical analysis, electron microscopy, and microtomographic images. However, a predictive theoretical model, which would be able to predict elastic properties of shale based on its detailed characterization, is still lacking. This is due to the complex multicomponent nature of shales which leads to multiparametric character of the modeling. It is extremely challenging to separate and investigate effects of these multiple parameters individually on natural shale samples. In this work, we analyze a unique data set of elastic properties measured on two artificial shales compacted with carefully controlled mineralogy, microstructure, and porosity. We developed a new modeling approach that consists of four steps that take into account effects of (1) the orientation of clay particles, (2) porosity, (3) silt fraction, and (4) the stiffness of contacts between clay particles. Three of these four steps require only measurable parameters and, only at the final step, the effect of unknown parameters (namely, contact properties of clay platelets) are accounted for. Further, the obtained contact properties are shown to be in a good agreement with the contact properties estimated for natural shale samples. Finally, we demonstrate the effect of each of these identified parameters on elastic coefficients and Thomsen's anisotropic parameters.

Soil organic carbon sequestration potential of Pampean soils: comparing methods and estimation for surface and deep layers

Estimates of soil carbon sequestration potential can help identify areas where appropriate use and management practices can be applied to convert them into carbon sinks. We estimated the carbon capacity of Pampean soils using previously developed models and compared the results with a local model developed by simultaneous quantile regression. We also modelled the effects of the factors controlling the carbon saturation deficit using artificial neural networks and mapped the topsoil and subsoil saturation deficit of the region. Data from a soil survey, in which 296 sites were sampled to 1 m depth, were used. Paired sites in grassland, cropland and lowland areas were selected. The total organic carbon was measured, and the proportion stabilised in the clay + silt (<20 µm) fraction was estimated. The saturation deficit could be predicted (R2 = 0.78) by neural networks and was greater in cropland, followed by lowland and then grassland. It was higher in fine textured soils, in soil surface layers and in humid and colder environments. The saturation deficit of the region is 8.8 Gt carbon (average 196 Mg C ha–1), approximately double the current organic carbon content of the region, indicating that there is considerable room for carbon sequestration in the Pampas. Efforts to increase soil carbon levels must focus on the finely textured soils in the humid part of the region.

ПОЛИЦИКЛИЧЕСКИЕ АРОМАТИЧЕСКИЕ УГЛЕВОДОРОДЫ ПОВЕРХНОСТНОГО СЛОЯ ДОННЫХ ОТЛОЖЕНИЙ В БАЛАКЛАВСКОЙ БУХТЕ

The contamination level of sea bottom sediments with polycyclic aromatic hydrocarbons in the Balaklava Bay (the Black Sea) was estimated depending on sediments particle size distribution. The total content of these pollutants in the studied water area was averagely 2459,58 ng/g. The increased concentrations of polycyclic aromatic hydrocarbons are confined to the eastern coast and the central part of the bay. Fourteen polyaromatic hydrocarbons were totally identified in 2018, four of which (naphthalene, 2-methylnaphthalene, fluorene, anthracene) had a trace content. Four- and fivecyclic aromatic hydrocarbons made the main contribution to the pollution of sea bottom sediments. In particular, it was chrysene (40,1 %), fluoranthene (17,5 %), benz(b)fluoranthene (15,1 %). The concentration of benz(a)pyrene in bottom sediments of the Balaklava bay ranged from 0,05 - 121,0 ng/g. Its increased concentrations are confined to the central part of the bay in the eastern coast. The amount of polyarenes correlated with the part of silt fraction (0,05 - 0,1 mm)...

Undrained shear strength of glacial till soils and its determining factors

This article presents results of the test conducted on the undrained shear strength of till clayey soils of Eastern Lithuania, which are characterized by rigid and very stiff consistency and low plasticity. According to the classification of soils presented in LST EN ISO 14688–2:2018 Geotechnical Investigation and Testing – Identification and Classification of Soil − Part 2: Principles for a Classification, the tested soils are classified as sandy low plasticity clays. The undrained shear strength was tested using the triaxial compression (unconsolidated undrained) method. The test results showed that peculiarities of the particle size distribution had a crucial impact on the undrained strength of these soils, i.e. on the correlation of clay and fine silt fractions with the rest of soil components.

Updating the Australian digital soil texture mapping (Part 2

Malone and Searle (2021) described a new approach to convert field measured soil texture categories into quantitative estimates of the proportion of clay, silt and sand fractions. Converted data can seamlessly integrate with laboratory measured data into digital soil mapping workflow. Here, we describe updating the Australian national coverages of clay, sand and silt content. The approach, based on machine learning, predicts each soil texture fraction at 90 m grid cell resolution, at depths 0–5 cm, 5–15 cm, 15–30 cm, 30–60 cm, 60–100 cm and 100–200 cm. The approach accommodates uncertainty in converting field measurements to quantitative estimates of texture fractions. Existing methods of bootstrap resampling were exploited to predict uncertainties, which are expressed as 90% prediction intervals about the mean prediction at each grid cell. The models and the prediction uncertainties were assessed by an external validation dataset. Results were compared with Version 1 Soil and Landscape Grid of Australia (v1.SLGA) (Viscarra Rossel et al. 2015). All predictive and functional accuracy diagnostics demonstrate improvements compared with v1.SLGA. Improvements were noted for the sand and clay fraction mapping with average improvement of 3% and 2%, respectively, in the RMSE estimates. Marginal improvements were made for the silt fraction mapping, which was relatively difficult to predict. We also made comparisons with recently released World Soil Grid products (v2.WSG) and made similar conclusions. This work demonstrates the need to continually revisit and if necessary, update existing versions of digital soils maps when new methods and efficiencies evolve. This agility is a key feature of digital soil mapping. However, without a companion program of new data acquisition through strategic field campaigns, continued re-modelling of existing data does have its limits and an eventual model skill ceiling will be reached which may not meet expectations for delivery of accurate national scale digital soils information.

Distribution of silty fraction and slurry by profile of arable soils of the central forest-steppe

The work is devoted to the study of granulometric composition of soils of 120-year and 240-year agricultural development of meadow-steppe landscape on the example of Belgorod region. In the lateral distribution of the silt fraction contained in the arable horizon, a significant increase in its proportion in the lower parts of the soil catenas of the 120-year arable, for the 240-year arable the lateral variations of the silt fraction are less noticeable. The averaged values of silt content over slope profiles of 240-year arable land showed local maximum of silt confined to subsoil horizon. An inverse relationship was found for slopes on 120-year-old arable land, namely the fact that the percentage of silt fraction increases at depth does not lead to an increase of the same fraction in the subsoil layer. Numerous blindfolds were found in the soil sections studied by caten, especially many of them were detected at a depth of up to one meter. Average area occupied by mole crusts on the walls of averaged transects is 80-90% on the 120-year arable and 70-80% on the 240-year arable. On soils of background catenas, 30-40% of the walls of soil transects are occupied by mole-rats. Blistergrasses are more often found in soils of catens of northern exposition - both 120-year and 240-year arable land.

Sediments Quality based on Geo-Accumulation Index in Heavy Metals (Pb, Cu, and Cd) of Cengkok Coastal Waters, Banten Bay

This area, which is located near the Banten Bay, is quite active with anthropogenic activities such as industry, fisheries, settlements, and shipyards that have the potential to pollute the environment with heavy metals. This study aims to determine the chemical environmental conditions of the waters and the concentration of heavy metals in the sediments of Banten Bay. Sediment samples were taken at five stations consisting of river and bay sections in April, May, July, August, and September 2019. Heavy metal content in sediments was analyzed according to APHA 2012 using hydrochloric acid and nitric acid destruction methods. The results of heavy metal concentrations in sediments were compared with ANZECC 2000 regulations and sediment quality was determined using the Geo-accumulation Index. The sediment at the observation site is dominated by the silt fraction. The concentration of heavy metals in this study was obtained in the form of lead (Pb) ranging from <0.05 to 6.408 mg / Kg, copper (Cu) ranging from 0.059 to 8.791 mg / Kg, and cadmium (Cd) ranging from 0.042 to 0.605 mg / K. While based on The level of heavy metal contamination in sediments using the Geo-accumulation index (I Geo), the value of all metal types in each month has a value <0.000 at all observation stations. Thus it is concluded that the concentration of heavy metals in the sediment is lower than the threshold determined during the observation. So that the metal concentration weight in the sediment has no significant effect on the environment.

Assessment of Some Geotechnical Properties for Soils of Euphrates River Banks (Kufa- Mishkhab), Middle of Iraq

Twelve stations in the cities of Kufa and Mishkhab were selected for studying the geotechnical, including physical, engineering, chemical and mineralogical, properties of soils in the river banks along the Euphrates River. Grain size distribution of the bank soils showed higher silt than clay and sand percentages. Soil samples from the 12 stations were classified according to the USCS standards. Silt with low plasticity constituted 91% of the silt fraction, whereas that with high plasticity composed 9%. The saturated density values ranged between 1.75-2.073 g/cm3 with an average of 1.953 g/cm3, while the dry density values ranged between 1.307-1.740 g/cm3 with an average of 1.553 g/cm3. The values of the dry and saturated density are within the permissible limits. Direct shear test showed cohesion values (C) that ranged between 15-55 kN/m2 with an average value of 34.8 kN/m2. The values of the internal friction angle (Ø°) of the clay type of soil with low plasticity ranged between 8.5°-17° with an average of 9.91°. The Ø° values of the other soil types ranged between 9°-17° with an average of 25°. Therefore, clay with high plasticity had higher Ø° values than the permissible limits. The results of unconfined compression test showed a range of 22.802-58.587 kN/m2 with an average of 38.173 kN/m2, with water percentage of 30%. The mineralogical tests of the bank soil performed using XRD analysis showed that the analyzed soil samples are composed mainly of quartz, calcite, chlorite, palygorskite, and montmorillonites. The pH value ranged between 6.4-7.55 with an average of 7.10, indicating low basicity. Gypsum concentrations ranged between 0.049-12.75 % with an average of 3.99 %, while that for carbonate ranged between 5-45 % with an average of 26.16%. Sulphates concentration ranged between 0.23-5.93 % with an average of 1.85%. Several treatment measures are proposed to stabilize the soil of the studied area.

The manifestation of VIS-NIRS spectroscopy data to predict and map soil texture in the Triffa plain (Morocco)

The use of standard laboratory methods to estimate the soil texture is complicated, expensive, and time-consuming and needs considerable effort. The reflectance spectroscopy represents an alternative method for predicting a large range of soil physical properties and provides an inexpensive, rapid, and reproducible analytical method. This study aimed to assess the feasibility of Visible (VIS: 350-700 nm) and Near-Infrared and Short-Wave-Infrared (NIRS: 701-2500 nm) spectroscopy for predicting and mapping the clay, silt, and sand fractions of the soils of Triffa plain (north-east of Morocco). A total of 100 soil samples were collected from the non-root zone of soil (0-20 cm) and then analyzed for texture using the VIS-NIRS spectroscopy and the traditional laboratory method. The partial least squares regression (PLSR) technique was used to assess the ability of spectral data to predict soil texture. The results of prediction models showed excellent performance for the VIS-NIRS spectroscopy to predict the sand fraction with a coefficient of determination R2 = 0.93 and Root Mean Squares Error (RMSE) =3.72, good prediction for the silt fraction (R2=0.87; RMSE = 4.55), and acceptable prediction for the clay fraction (R2 = 0.53; RMSE = 3.72). Moreover, the range situated between 2150 and 2450 nm is the most significant for predicting the sand and silt fractions, while the spectral range between 2200 and 2440 nm is the optimal to predict the clay fraction. However, the maps of predicted and measured soil texture showed an excellent spatial similarity for the sand fraction, a certain difference in the variability of clay fraction, while the maps of silt fraction show a lower difference.

Late Pleistocene sediment accumulation in the lower slope off the Rio Grande terrace, southern Brazilian Continental Margin

Here are described the analyses of sediments from the lower slope of the Pelotas Basin in the southern Brazilian continental margin, southwestern Atlantic. The samples were obtained from the core SIS-249, collected adjacent to the Rio Grande Terrace (RGT) at a water depth of 2091 m, an area poorly known in terms of sedimentary characteristics compared to the oil and gas-rich basins to the north. The age model indicates that the sampled sediments were accumulated during the last glacial period, between 112.5 and 34.47 ka (MIS 5 to MIS 3). The fine (<63 μm) fraction is dominated by silt with subordinate clay, whereas the coarse (sandy) fraction is chiefly composed of biogenic carbonate (tests of foraminifers) with subordinate very fine (63–125 μm) lithogenic sand. The composition of the lithogenic sand is essentially uniform downcore, dominated by quartz with glaucony as the dominant accessory mineral, and the presence of augite, derived from Mesozoic volcanic rocks, points to a source from the adjacent coastal plain. The uniform mineral composition indicates continuous input of sediments removed from the RGT by action of the Brazil Current (BC) and transferred to the lower slope by gravity flows. The higher proportion of lithogenic sand from the upper RGT along the intervals corresponding to MIS 5 and MIS 3 points to erosion of the terrace due to a more landward position of the BC, related to sea-level highstand and falling stage tracts. The higher amount of silt along the MIS 4 interval suggests increased transfer of sediments from the flanks of the RGT as the result of a more downslope position of the BC driven by the sea-level lowstand. Winnowing of the sortable silt fraction during MIS 5 and 3 points to influence of the southward-flowing North Atlantic Deep Water (NADW). The higher estimated accumulation rates and less negative peaks of δ13C in benthic foraminifers Uvigerina peregrina during MIS 4 could have been caused by oscillations of water masses with distinct isotopic compositions, but also by increased burial and decomposition of organic matter as a result of high ocean surface primary productivity, indicated by the correspondence between the δ13C oscillations and higher accumulation rates and proportion of biogenic sand in the core. Higher productivity was apparently driven by episodes of increased eolian transport of dust from Patagonia and central-western Argentina in milenial timescales, coeval with oscillations in strength and position of the southern westerly winds (SWW) system.

Influence of site-classification approach on geochemical background values

AbstractThis study of peri-urban minerogenic topsoil on glacigenic or post-glacial deposits shows the influence of the site-classification approach on the differentiated median background (DMB) values of major elements and the potentially harmful elements (PHEs) Ba, Cr, Cu, Mn, Ni, Pb and Zn. Composite samples from forests and meadows were taken in 25 sites, each of which had five sub-sites. A fraction of &lt;2 mm was used to determine the organic matter by loss on ignition (LOI), grain size by laser diffraction and the elemental contents by X-ray fluorescence. The following five site-classification approaches are compared: geochemical (G), using relative median contents of Al, K, Ti; textural (T), according to mean percentages of clay-sized fraction (CLF) and silt fraction (SIF); lithological (L), based on soil parent material texture from the soil database; soil type (S), presented in the soil database; and parent material (P), generalising the underlying Quaternary deposits. Sites were classified into four level groups in which the DMB values were estimated after eliminating anomalies. The average ranks of three scores according to SIF, CLF, LOI, Al, K, Ti, Fe, Mg, Ca and S in the respective groups revealed the highest value for the G approach. It better eliminates the CLF and SIF influences on the median assessment indices of PHEs in sites.