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  • 1
    Language: English
    In: Catena, April 2016, Vol.139, pp.9-18
    Description: Riparian woodlands consist of different landscape units characterized by different hydroecomorphological site conditions that are reflected in the distribution of soils and tree species. These conditions are determined by flooding frequency and duration, distance to river channels, elevation and water flow velocity. The influence of these environmental drivers on the stabilization of soil organic matter (SOM) has as yet not been investigated. Hence, the aim of our study is to link soil formation and its drivers with stabilizing processes of SOM in riparian floodplain forests. We investigated soils and sediments at two sites in the ash–maple–elm–oak alluvial forest zone (AMEO sites) and two sites in the willow-poplar alluvial forest zone (WiP sites) within the riparian zone of the Danube near Vienna (Austria). Sediments and soils were characterized based on texture, contents of organic carbon (OC), nitrogen, Fe oxides, and soil pH. Density fractionation was used to separate OC fractions in terms of stabilization process and resulting organic matter (OM) turnover time: the free light fraction (fast turnover), the light fraction occluded in aggregates (intermediate turnover) and the heavy fraction of OM associated tightly to mineral surfaces (slow turnover). At both sites, soil and sediment properties reflect the hydroecomorphological site conditions for formation of the landscape units in the riparian zone: Soils at AMEO sites develop during constant deposition of fine-textured sediment while water flow velocity is low. Progressing soil development causes a continuous decrease in OC content with increasing soil depth, mainly from fractions with fast and intermediate turnover. As a consequence the heavy fraction clearly dominates with around 90% of OC. Temporally variable flooding conditions with occurring turbulences found at WiP sites result in a discontinuous change of soil properties with increasing soil depth. Former topsoil horizons buried by huge amounts of sediments seem to keep the OC fractionation typical for topsoil horizons with extraordinarily high amounts of light fraction OM (free and occluded) representing 20–40% of total OC. The presented results confirm that sedimentation and soil formation are simultaneous processes at AMEO sites. At WiP sites both processes seem uncoupled with alternate phases of sedimentation and soil formation. Thus, the frequent burial of topsoil material formed at WiP sites seems to enable the conservation of unstable organic matter fractions at this part of active floodplains.
    Keywords: Fluvisol Formation ; Soil Organic Matter ; Density Fractionation ; Riparian Floodplains ; Soil Aggregates ; Riparian Forests ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 2
    Language: English
    In: Plant and Soil, 2018, Vol.427(1), pp.53-69
    Description: Background and aims Phosphorus (P) availability is crucial for forest ecosystem productivity and soil organic matter (SOM) is an important source for P. This study was conducted to reveal carbon (C), nitrogen (N) and P distributions in functional SOM fractions. We hypothesised that (1) most of the organic P (P.sub.org) is part of the particulate SOM, (2) particulate SOM stores increasing share of P with decreasing soil P content and (3) the C:P.sub.org ratio of mineral-associated SOM is smaller than that of particulate SOM. Methods We analysed soil samples from five temperate forest sites (Fagus sylvatica) under different geological parent material with a wide range of total P concentrations. Density fractionation was used to separate free light fraction (fLF), particulate SOM occluded within soil aggregates (occluded light fraction; oLF), and mineral associated SOM (heavy fraction; HF). We determined the mass balance of P in these fractions, in addition to the C and N concentrations. Additionally, the P speciation of the topsoil was analysed by X-ray absorption near edge structure (XANES) spectroscopy at the P K-edge. Results The fLF contained 18-54% and the oLF 1-15% of total P (P.sub.tot). High percentage of P in these light fractions was associated to soil minerals. Phosphorous in particulate SOM within aggregates tend to increase with decreasing soil P. The HF containing mineral-associated OM, comprised 38-71% of P.sub.tot and their C:P.sub.org ratios were consistently lower than those of the fLF irrespective of the P status of the soil. Conclusions We show that all three functional SOM fractions contain variable amount of both organic and inorganic P species. The free light fraction shows no response to changing P stocks of soils.. Despite physically protected particulate SOM, oLF, becomes increasingly relevant as P cache in soils with declining P status.
    Keywords: Ecosystem nutrition ; Density fractions ; Soil organic matter ; C:N:P ratio ; Phosphorus ; P K-edge XANES
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 3
    Language: English
    In: Journal of Plant Nutrition and Soil Science, December 2018, Vol.181(6), pp.894-904
    Description: Sonication is widely used for disruption of suspended soil aggregates. Calorimetric calibration allows for determining sonication power and applied energy as a measure for aggregate disrupting forces. Yet other properties of sonication devices (., oscillation frequency and amplitude, sonotrode diameter) as well as procedure details (soil‐to‐water ratio, size, shape, and volume of used containers) may influence the extent of aggregate disruption in addition to the applied energy. In this study, we tested potential bias in aggregate disruption when different devices or procedures are used in laboratory routines. In nine laboratories, three reference soil samples were sonicated at 30 J mL and 400 J mL. Aggregate disruption was estimated based on particle size distribution before and after sonication. Size distribution was obtained by standardized submerged sieving for particle size classes 2000–200 and 200–63 µm, and by dynamic imaging for particles 45 W). Thus, these sonication device properties need to be listed when reporting on sonication‐based soil aggregate disruption. The overall small differences in the degree of disruption of soil aggregates between different laboratories demonstrate that sonication with the energies tested (30 and 400 J mL) provides replicable results despite the variations regarding procedures and equipment.
    Keywords: Disaggregation ; Particle Size Fractions ; Reproducibility ; Round‐Robin Test ; Ultrasound
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 4
    Language: English
    In: Geoderma, 2004, Vol.123(1), pp.153-162
    Description: Use of soil archives provides the opportunity to retrospectively analyze changes in soil properties. We used the distribution of heavy metals between the exterior and interior of aggregates in recent and archived samples to derive (1) temporal trends in metal concentrations and distribution across aggregates and (2) to assess aggregate turnover times. We collected 11 topsoils under grassland and forest along a transect from Moscow to a distance of 50 km from the city centre and at a background location. Furthermore, we analyzed six topsoils sampled between 1910 and 1954 at some of the locations. We fractionated aggregates 〉1 cm into interior and exterior portions. Except at one contaminated site, heavy metal concentrations were low (Cd: 0.09-0.33 mg kg (super -1) , Cu: 6.8-24 mg kg (super -1) , Pb: 6.7-31 mg kg (super -1) , Zn: 25-54 mg kg (super -1) ), comparable with background levels in central Europe. They were not related to the distance to Moscow indicating that Moscow was no point source for the studied soils. During the last century, contents of heavy metals in soils increased inside and decreased outside the city. In Moscow, the heavy metal accumulation in the aggregate exterior relative to the interior was more pronounced in recent than in archived samples reflecting a higher recent than historic deposition. However, there was also an increase in heavy metal concentrations in the interior of recent compared with archived aggregates. Thus, the studied aggregates were turned over at least once during the last 50-90 years at all sites. This limited the build-up of metal concentration gradients in aggregates.
    Keywords: Archived Soil Samples ; Heavy Metals ; Soil Aggregates ; Small-Scale Heterogeneity ; Aggregate Stability ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    In: European Journal of Soil Science, May 2019, Vol.70(3), pp.454-465
    Description: Soil structural traits provide links between soil structure and ecosystem functioning. The size and stability of soil aggregates are assumed to provide information on aggregate formation and turnover. A standard method to analyse these traits is to determine the mass distribution on sieves. The major drawback of this method is the small size resolution because of a small number of size classes. A promising, yet still unexplored, method for size distribution analysis in soil science, is dynamic image analysis, which foremost allows a much larger diameter resolution and the assessment of both size and shape distributions. The aim of our study was to validate the applicability of dynamic digital image analysis in combination with sonication to characterize the size and shape distribution and the stability of aggregates. We used two different heterogeneous reference materials and three different soil samples with different aggregate stabilities to test this method. The soil samples were chosen based on increasing clay, humus and calcium carbonate contents. The method yielded reproducible results for diameter and shape distributions for both reference materials and soil samples. The most important improvement compared to well‐established methods was the extremely large size resolution. This allows specification of the pattern of diameter‐dependent breakup curves by relating them to specific soil properties. The information on sphericity adds supplementary information on the aggregates released. We found much lower sphericity of 1‐mm aggregates mobilized from topsoil samples formed from the activity of living organisms than aggregates mobilized from subsoil samples formed mainly by physicochemical processes. Highlights Our aim was to validate dynamic digital image analysis to characterize soil aggregates.Dynamic image analysis allows high resolution and shape analysis compared to established methods.The method yielded reproducible results for diameter and shape distributions.We established high‐resolution disruption patterns of aggregates enabling new approaches in future research.
    Keywords: Aggregate Breakdown Dynamics ; Particle‐Size Distribution ; Ultrasonic Dispersion
    ISSN: 1351-0754
    E-ISSN: 1365-2389
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