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The foothill areas of eastern Turkey are an arid and semiarid region with natural salinization, where calcareous alluvial saline soils (Calcaric Fluvisols) are circulated as a result of floods of the Aras River. In this study, the effects of salinity and alkalinity on soil aggregate size distribution and enzyme activities at different aggregate size were investigated. For this purpose, soil samples were collected with three replicates at saline, alkaline, saline-alkaline and non-saline–alkaline areas and passed through into different sieves (2, 1, 0.850, 0.425, 0.106 and 0.02 mm) by dry sieving method for determining aggregate weight distribution in each macro (2–0.45 mm) and micro (0.45–0.02 mm) aggregates. For determining aggregate size distribution, sieves were shaken using a horizontal shaking machine (Retsch, AS 200 basic, Haan, Germany). The soil enzymes were determined in these aggregate sizes (2–1, 1–0.850, 0.850–0.425, 0.425–0.106, 0.106–0.02 mm) for all soil types. All soils belonged to the clay loam with the carbon content in the range of 0.5–0.8%, while the percentage of exchangeable sodium for the non-saline–alkaline and alkaline–saline soils was from 3.5 to 22%, but the pH diapason from 8.3 to 8.9. Results showed that soil salinity and alkalinity decreased the weight of macro aggregates and increased the weight of micro aggregates, besides soil salinity and alkalinity decreased soil enzyme activities. But soil salinity decreased enzyme activity more than alkalinity. Furthermore, the highest urease and catalase activities were in macro aggregates (0.850–0.425 mm aggregate size) for all soil types. The reason may be that macro aggregates contain higher organic matter and organic carbon than micro aggregates. Consequently, the highest enzyme (urease and catalase) activities were detected in macro aggregates. [ABSTRACT FROM AUTHOR]

• Soil type, topography and the legacy of land use are closely linked with OC stocks. • Topsoil OC stocks are strongly controlled by land use history. • Climatic factors were of minor importance for regional OC stocks. • Highest subsoil OC stocks in alluvial, colluvial and groundwater affected soils. • Legacy of human activities strongly influences whole soil profile OC storage. Agricultural soils are highly important organic carbon (OC) reservoirs in Central Europe. Their OC stocks are crucial for a wide range of ecosystem services such as food security or climate regulation through atmospheric CO 2 storage. There is increasing evidence that the controlling factors of OC stocks may differ between topsoil and subsoil, but distinct knowledge about the factors at a regional scale for temperate soils is scarce. In order to identify the controlling factors of OC storage in agricultural soils we implemented a random forest model on a data set of 692 soil profiles located in Bavaria, Southeast Germany. We differentiated between topsoil (0–30 cm profile depth) and subsoil (30–100 cm) and predicted OC stocks (kg OC m−2) using 13 predictor variables including soil type, topographical factors, climatic factors and information on land use. The explained variance of the topsoil random forest was higher than that of the subsoil (51 and 23%, respectively). The fact that major proportions of the variance in the modelling of subsoil OC remained unexplained, revealed high uncertainties that persist about subsoil OC storage. OC storage of both, topsoils and subsoils, was to a large extend determined by four factors: land use history, soil type, major landform and topographic wetness index (TWI). Climatic factors as well as clay content had surprisingly low impact on the model. Topsoil OC was mainly controlled by the legacy of the land use resulting in highest stocks under permanent grassland use. In contrast, soil type and topographical factors, i.e. major landform and TWI, largely determined subsoil OC stocks. The topography indicates the lateral transport of OC due to soil erosion and its subsequent deposition in low lying landform positions. There, high soil moisture as indicated by the TWI, hampers the decomposition of the OC. Human activities such as tillage amplify the lateral OC transport and therefore the amount of buried OC. As a result of these processes, highest subsoil stocks were found in alluvial, colluvial and groundwater affected soils. The findings demonstrate the close link between the generic soil type, topography, land use and OC stocks. We further conclude that the legacy of human activities affect both, topsoil and subsoil OC storage. [ABSTRACT FROM AUTHOR]

The geochemical fractionation and potential mobilization of Co, Cu, Ni, and Zn were studied in thirteen soil profiles originating from Germany and Egypt to assess the potential mobilization of these potentially toxic metals. The German soils were classified as Eutric Fluvisols, Tidalic Fluvisols, Haplic Gleysols, and Calcic Luvisols, and the Egyptian soils as Eutric Fluvisols, Sodic Fluvisols, and Haplic Calcisols. The geochemical fractions (acid soluble (F1), reducible (F2), oxidizable (F3), and residual (F4) fraction) of the metals were sequentially extracted using the sequential extraction technique of the Commission of the European Communities Bureau of Reference (BCR). The maximal total concentrations (mg kg − 1 ) of Cu (3242), Ni (105), and Zn (1672) were in the German Eutric Fluvisols, while the maximal concentrations of Co (37) were in the Egyptian Eutric Fluvisols, and those values exceeded the international maximum allowable soil concentrations. The values of enrichment and contamination factors exhibit a clear indication of dramatic contamination by Cu and Zn at the Eutric Fluvisols along the Wupper River, Germany. The acid soluble fraction of all metals (except for Ni in the Calcic Luvisols) was higher in the German soils than the Egyptian soils. The reducible fraction of Co, Cu, Ni, and Zn was the dominant non-residual fraction (as precentages of total) in all Egyptian soils and in the German Eutric Fluvisols as well as for Zn in the Tidalic Fluvisol and Co in the Calcic Luvisols. The potential mobile fraction (PMF = ∑ F1 − F3) of Co, Cu, Ni, and Zn accounted (% of total) for 39–61, 15–60, 21–57, and 6–44, respectively in the Egyptian soils, while it accounted for 14–70, 11–92, 2–73, and 8–89, respectively in the German soils. The high PMF of the metals in the German Eutric Fluvisols, Haplic Gleysols, and Sodic Fluvisols might reflect that the sources of these metals are of anthropogenic origin here. However, the dominance of the metals residual fraction in the Egyptian soils supports the assumption of the geogenic origin of these metals in these soils. The canonical discriminant analysis as a multivariate statistical procedure was applied and differentiated the soils according to their geochemical behavior into four clusters i.e., 1) Eutric Fluvisols, Calcic Luvisols, and Haplic Calcisols; 2) Egyptian Fluvisols (Eutric and Sodic); 3) Haplic Calcisols; and 4) Tidalic Fluvisols. In conclusion, the potential risk of the metals in the anthropogenic polluted soils is higher than in the soils naturally enriched with these metals. Therefore, remediation approaches may be needed in the German Eutric Fluvisols, Haplic Gleysols, and Sodic Fluvisols. [ABSTRACT FROM AUTHOR]

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the biogeochemical processes driving Si fractionation in these soils. Therefore, we applied for the first time a sequential Si extraction scheme to three floodplain soils (Mollic Fluvisols) to separate six Si fractions: mobile Si, adsorbed Si, Si bound to organic matter, Si included in pedogenic oxides and hydroxides, biogenic as well as minerogenic amorphous silica. Residual Si was calculated. The highest Si proportion apart from the residual fraction (Si bound in primary and secondary silicates) was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02–0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget (here periodic flooding with prolonged water saturation) on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous minerogenic as well as biogenic silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. These processes are more pronounced in floodplain than in terrestrial soils, thus implying different distributions of Si among soil fractions. [ABSTRACT FROM AUTHOR]

Abstract: The computer code FAST3D has been developed to calculate flow and sediment transport in open channels. In the code, the flow field is calculated by solving the full Reynolds-averaged Navier–Stokes equations with k–ε turbulence model; the bed-load transport is simulated with a non-equilibrium model containing an important parameter, the so-called non-equilibrium adaptation length, which characterizes the distance for sediment to adjust from a non-equilibrium state to an equilibrium state; the bed deformation is obtained from an overall mass-balance equation for sediment transport. The governing equations are solved numerically with a finite volume method on an adaptive, non-staggered grid. The former model assumed uniform bed material. In order to take into account the influence of grain-size distribution of the bed-surface on the evolution of the bed topography and consequently also on the flow field, a sediment transport module has been presently developed by the authors at the Institute of Hydraulic and Water Resources Engineering, Technische Universität München, Germany, for fractional sediment transport using a multiple layer model. This paper presents the numerical results for sediment sorting and the bed deformation in a curved alluvial channel under unsteady-flow conditions according to . The calculations were compared with data from laboratory measurements. Further, the sensitivity of the simulated results to the non-equilibrium adaptation length is investigated. [Copyright &y& Elsevier]

Abstract: Two- and three-dimensional element distributions in soils and sediments may be important for the identification of geomorphic processes and the reconstruction of landscape evolution. Field portable X-ray fluorescence (FPXRF) analysers provide new possibilities in the detection and quantification of these element distributions. Results from a research project studying the heavy metal contamination of alluvial soils in a historic mining area at the Vils River near Freihung (Eastern Bavaria, Germany) exemplify how FPXRF can be applied to quantify two- and three dimensional element distributions in a floodplain environment on different scales. The results show that two-dimensional lead distribution of topsoil bulk samples (0 to 20 cm depth) clearly depends on the geomorphology of the study area. Concentrations of more than 1000 mg kg−1 lead are restricted to the river floodplain. On a fluvial terrace lead concentrations of the topsoils are consistently far below 500 mg kg−1. Within the floodplain environment the lead contamination is not homogeneously distributed but forms areas of higher and lower lead concentrations. Micro fluvial structures (channels, ridges) are polluted on different levels, depending on the composition of the sediments or the water contents. This demonstrates that accurate assessments of floodplain metal contamination can only be made if small scale spatial variability has been considered. Analysis of the three-dimensional lead distribution shows that concentrations of the in situ measurements range from 500–6000 mg kg−1 subject to depth, geomorphology and distance from the Vils River. Although the absolute contents are higher, three-dimensional lead distribution derived from laboratory measurements is identical with the plotted results of the in situ investigations. By calculating a correction factor for further investigations, water content as one of the main causes for differing results between field and laboratory analyses can be diminished. In situ FPXRF analysis as a robust technique could be used to investigate metal contamination on floodplain soils at a range of spatial scales. It allows detailed sampling, which can yield important information on the geomorphological controls on metal contamination in such environments. [Copyright &y& Elsevier]

Two long-term submerged Eutric Gleysols (GLe) and two short-time flooded Eutric Fluvisols (FLe) at the Elbe River (Germany) with high organic carbon contents (Corg between 4.9 and 11.6%) were selected to evaluate dehydrogenase activity (DHA), soil microbial carbon (Cmic), Cmic/Corg ratio, and phospholipid fatty acids (PLFA) to characterize and discriminate these soils with microbial parameters. DHA, Cmic and PLFA-biomass as well as Cmic/Corg ratios are considerable lower in GLe's than in FLe's what seem to be an unspecific response of aerobic soil microorganisms on the long flooding period and the resulting short time for development after last flooding. Cmic/Corg ratios are low in comparison to terrestrial soils. PLFA profiles were dominated by saturated fatty acids (FA). Principal component analyses (PCA) with the identified FAs revealed a clear discrimination among the four floodplain soils. In GLe's, all groups of PLFA, inclusive monounsaturated FA, are lowest and in FLe's highest. Polyunsaturated FA fungi biomarker (18:2ω6,9c) was very low in GLe1 and could not be detected in GLe2. The environmental conditions which microorganisms are exposed seem to be disadvantageous for fungi in these long submerged soils. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the soil contamination caused by potentially toxic elements (Al, As, Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, V, and Zn) using various indices and the associated risk of human health for adults and children in selected soils from Germany (Calcic Luvisols, Tidalic Fluvisols, Haplic Gleysols, and Eutric Fluvisols) and Egypt (Haplic Calcisols, Sodic Fluvisols, and Eutric Fluvisols). Soil contamination degree has been assessed using indices such as contamination factor (CF), pollution load index (PLI), geo-accumulation index (I geo), and enrichment factor. We also assessed the health risk for children and for male and female adults. Chromium, Cu, As, Mo, Ni, Se, and Zn in the German Fluvisols had high CF of >6, while in the Egyptian Fluvisols Se, Mo, As, and Al revealed a high CF. The PLI (1.1–5.2) was higher than unity in most soils (except for Tidalic Fluvisols), while the most important contributor was Se, followed by Mo and As in the Egyptian Fluvisols, and by Cr, Cu, and Zn in the German Fluvisols. The median value of hazard index (HI) for children in the studied soils indicated an elevated health risk (higher than one), especially in the German Fluvisols (HI = 4.0–29.0) and in the Egyptian Fluvisols (HI = 2.2–5.2). For adults, median HIs in all soils were lower than unity for both males and females. The key contributor to HI was As in the whole soil profiles, accounting for about 59% of the total HIs in all three person groupings. Our findings show that in the studied multi-element contaminated soils the risk for children's health is higher than for adults; while mainly As (and Al, Cr, Cu, and Fe) contributed significantly to soil-derived health risk. Image 1 • German Eutric Fluvisols are highly polluted by Cu, Cr, Zn, Cd, Pb, and As. • Egyptian Fluvisols and Haplic Gleysols are highly polluted by Al, Se, Mo, and V. • The hazard index for children indicated an elevated health risk in all soils. • The risk for children's health is higher than for adults in all soils. • As, Cr, Al, Fe, and Cu contributed significantly to soil-derived health risk. Soil contamination was very high in the studied soils (pollution load index ranged from 1.1 to 5.2), especially in the German and Egyptian Fluvisols; health risk for children was higher than for adults, and As, Al, Cr, Cu, and Fe had a key role in soil-derived health risk. [ABSTRACT FROM AUTHOR]