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  • Geochemistry Of Rocks, Soils, And Sediments  (36)
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  • 1
    Language: English
    In: Geochimica et Cosmochimica Acta, 01 May 2016, Vol.180, pp.284-302
    Description: We evaluated the impact of nano-structural characteristics of allophanic compounds and Fe oxide speciation on the efficiency of organo-mineral interactions in an allophanic derived from volcanic ash (Eifel mountains, Germany). The samples selected for our work represented a gradient from: (i) a pure synthetic allophane and (ii) model organo-mineral mixtures to (iii) particle size fractions of the natural Andosol. We thus aimed to link the processes operating at the individual molecular scale to the phenomena active at the aggregate scale. For a non-destructive characterization of the samples, we applied Xe NMR spectroscopy of adsorbed Xe atoms (to identify the mineral nano-structure and surface acid centres), ESEM (verifying the nano-spherical structure of allophane), C CPMAS NMR (for the nature of the soil organic matter (SOM)), Fe Mössbauer spectroscopy (Fe oxide speciation), and N adsorption (contribution of micro- and mesoporosity). By using the atomic probe Xe, we obtained evidence for a mechanism of adsorption onto allophane requiring both the narrow pores (voids formed by the primary nano-spherules) and the acid centres located at the defect surfaces of the primary spherules. The validity of this coupled mechanism for the sorption of organic matter was confirmed by the concomitant blocking of acid centres ( Xe NMR data) and the decrease of the N -available pore volumes ( and ) in the model samples DOM/- and NOM/allophane (DOM = dissolved OM, NOM = natural OM). In the Andosol, the high resistance of SOM against oxidation (OC = 15–50%) was combined with preferential accumulation of certain organic compounds, e.g. potentially labile substrates such as carbohydrates, and the low molecular weight species such as amino acids. This feature was attributed to the peculiar microporous tortuous structure of allophane aggregates that likely impose certain criteria for the chemical nature and size of mineral-bound SOM. On the other hand, the revealed dominance of nanoparticulate Fe oxyhydroxides (57% ferrihydrite) and Fe-substituted allophane (supposedly formed due to co-precipitation of the Al, Si and Fe in the course of volcanic soil formation) may substantially contribute to the formation of highly resistant organo-mineral associations through the enhanced extent of reactive surface groups in nanoparticles, increased surface charge density and electron accepting properties of substituting Fe species that supposedly enhance the proportion of oxidised organic components.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 May 2012, Vol.85, pp.1-18
    Description: Interactions between organic and mineral constituents prolong the residence time of organic matter in soils. However, the structural organization and mechanisms of organic coverage on mineral surfaces as well as their development with time are still unclear. We used clay fractions from a soil chronosequence (15, 75 and 120 years) in the foreland of the retreating Damma glacier (Switzerland) and from mature soils outside the proglacial area (〉700 and 〈3000 years) to elucidate the evolution of organo–mineral associations during initial soil formation. The chemical composition of the clay-bound organic matter (OM) was assessed by solid-state C NMR spectroscopy while the quantities of amino acids and neutral sugar monomers were determined after acid hydrolysis. The mineral phase was characterized by X-ray diffraction, oxalate extraction, specific surface area by N adsorption (BET approach), and cation exchange capacity at pH 7 (CEC ). The last two methods were applied before and after H O treatment. We found pronounced shifts in quantity and quality of OM during aging of the clay fractions, especially within the first one hundred years of soil formation. The strongly increasing organic carbon (OC) loading of clay-sized particles resulted in decreasing specific surface areas (SSA) of the mineral phases and increasing CEC . Thus, OC accumulation was faster than the supply of mineral surfaces and cation exchange capacity was mainly determined by the OC content. Clay-bound OC of the 15-year-old soils showed high proportions of carboxyl C and aromatic C. This may point to remnants of ancient OC which were inherited from the recently exposed glacial till. With increasing age (75 and 120 years), the relative proportions of carboxyl and aromatic C decreased. This was associated with increasing O-alkyl C proportions, whereas accumulation of alkyl C was mainly detected in clay fractions from the mature soils. These findings from solid-state C NMR spectroscopy are in line with the increasing amounts of microbial-derived carbohydrates with soil age. The large accumulation of proteins, which was comparable to those of carbohydrates, and the very low C/N ratios of H O -resistant OM indicated strong and preferential associations between proteinaceous compounds and mineral surfaces. In the acid soils, poorly crystalline Fe oxides were the main providers of mineral surface area and important for the stabilization of OM during aging of the clay fractions. This was indicated by (I) the strong correlations between oxalate soluble Fe and both, SSA of H O -treated clay fractions and OC content, and (II) the low formation of expandable clays due to small extents of mineral weathering. Our chronosequence approach provided new insights into the evolution of organo–mineral interactions in acid soils. The formation of organo–mineral associations started with the sorption of proteinaceous compounds and microbial-derived carbohydrates on mineral surfaces which were mainly provided by ferrihydrite. The sequential accumulation of different organic compounds and the large OC loadings point to multiple accretion of OM in distinct zones or layers during the initial evolution of clay fractions.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    Language: English
    In: Soil Science Society of America Journal, 2011, Vol.75(6), p.2158
    Description: To characterize biogeochemical interface properties in soil with respect to oxide surfaces, the contribution of weakly crystalline and crystalline oxides to soil specific surface area (SSA) of particle size fractions was determined. Three arable topsoils with intermediate to high clay content were subjected to ultrasonic dispersion and particle size fractionation. The obtained silt and clay fractions were treated with hydrogen peroxide, extracted with oxalate and dithionite and the SSA of all fractions was determined using BET-[N.sub.2]. Results show that stable microaggregates were present in the coarse and medium silt fractions of all soils that could not be dispersed physically even at the highest ultrasonic dispersion energy and were probably stabilized by organic matter and iron oxides. Iron oxides were a major contributor to the SSA of all particle size fractions and the losses of carbon after oxalate and dithionite extraction showed that a major part of the organic matter in all particle size fractions was stabilized by iron oxides, even in these clay-rich soils. Weakly crystalline oxide surface area did not increase with decreasing partide size and calculated negative surface areas for some of the fine fractions indicated that weakly crystalline oxides were present as coatings on other minerals. The results demonstrate the importance of (iron) oxides for microaggregation and stabilization of organic matter in soil. However, the actual interface provided by these oxides depends on particle size and crystallinity due to the possible occlusion of mineral surfaces by organic matter and weakly crystalline oxides. Abbreviations: OC, organic carbon; OM, organic matter; SSA, specific surface area; XRD, X-ray diffraction. doi: 10.2136/sssaj2010.0455
    Keywords: Iron Oxides -- Chemical Properties ; Iron Oxides -- Environmental Aspects ; Loams -- Chemical Properties ; Loams -- Composition ; Soil Chemistry -- Research ; Geochemistry -- Research;
    ISSN: Soil Science Society of America Journal
    E-ISSN: 0361-5995
    E-ISSN: 14350661
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  • 4
    Language: English
    In: Geoderma, 15 December 2017, Vol.308, pp.350-362
    Description: When acid sulfate soils containing hypersulfidic material (pH 〉 4) dry, oxidation of pyrite causes strong acidification with the formation of sulfuric material (pH 〈 4), which may release high concentrations of metals and metalloids. Re-submerging of sulfuric material can lead to re-formation of pyrite and pH increase to re-form hypersulfidic and hyposulfidic materials due to the action of sulfate-reducing bacteria. However, low availability and/or low biodegradability of organic carbon (OC) may limit the activity of sulfate reducers in re-saturated sulfuric material. Our study investigated the content and composition of OC with specific emphasis on the proportion of readily available, non mineral-associated OC. Samples were taken from a non-acidifying pasture topsoil with hyposulfidic material and two re-submerged subsoils with hypersulfidic material derived from river sediments in South Australia. The sites experienced drying at depths between 0.5 and 4.5 m with severe acidification (pH 〈 4) during the Millennium drought from 2007 to early 2010. After re-submerging, sulfuric material at one site recovered to neutral pH values, whereas the other site remained acidic. Samples were analysed for total OC content and the proportion of available, non mineral-associated OC. Chemical composition of bulk soil OC and available fractions was determined by solid-state C NMR spectroscopy and neutral sugar analyses. The OC composition of re-submerged sulfuric material was generally characterised by small proportions of easily degradable carbohydrates and proteins, but high proportions of hardly degradable lignin and lipids. Lowest amounts of available OC fractions and lowest proportions of carbohydrates and proteins were found in hypersulfidic material which is still acidic. This indicates that slow pH recovery rates can be ascribed to low proportions of biodegradable OC. The OC composition can be explained by: (I) sedimentation of organic materials which were already highly biodegraded during formation of river sediments, and (II) selective preservation of lignin and lipids due to permanent waterlogging. Thus, the organic material is characteristic for wetlands, but hardly usable as substrate for microbes and may retard sulfate reduction and pH neutralisation of re-submerged sulfuric material.
    Keywords: Non Mineral-Associated OC ; Solid-State 13c NMR Spectroscopy ; Neutral Sugar Analysis ; Wetlands ; River Sediments ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    Language: English
    In: Geoderma, November 2012, Vol.189-190, pp.585-594
    Description: Soils represent a very complex material where mineral, organic and biological components interact together to form a large ‘biogeochemical interface’. In order to study this complex interface in a simplified system, a so-called ‘artificial soil’ incubation experiment was carried out. This experiment was used here specifically to study the effect of microbial activity and mineral interactions on the aggregation occurring during incubation. Artificial soils with different mineral composition but the same texture, were composed of well-defined model materials. The materials considered were quartz, illite, montmorillonite, ferrihydrite, boehmite and charcoal, manure as an organic matter (OM) source and a microbial inoculum extracted from a natural arable topsoil. The artificial soils were incubated for 3 to 18 months in the dark, under constant temperature and water content. The pH, organic carbon (OC) and nitrogen content, extractable Fe, Al and Si of the incubated artificial soils were measured, and the amount of macroaggregates 〉 2 mm was determined by sieving. Density fractionation was performed at densities of 1.8 and 2.4 g cm to separate particulate OM, organo-mineral associates and the mineral fraction. The specific surface area (SSA) of the organo-mineral associate fraction and the amount of OC associated with organo-mineral associates and minerals was determined. The SSA of the model materials and the artificial soils at the start of incubation was determined by BET-N . The artificial soils developed quickly and CO respiration occurred during the entire 18 month incubation time. The actual SSA of the ‘soils’ was significantly lower than the sum of the SSA of the pure model materials indicating that occlusion of mineral surfaces by interaction between OM and minerals occurred almost immediately after incubation started. Macroaggregates and organo-mineral associates were formed within 3 months of incubation. Macroaggregation decreased after 12 months of incubation probably due to decreasing biological activity. The turnover of macroaggregates and continuing formation of organo-mineral associates was consistent with the aggregate hierarchy model. Less macroaggregation was observed in the soil where no clay mineral was present, indicating that clay minerals were important for the formation of macroaggregates. Ferrihydrite and boehmite did not affect the aggregation or formation of organo-mineral associates in this experiment. The results of density fractionation indicate that OM was mainly associated with the clay minerals, probably due to the neutral pH of the artificial soils, leading to a low or negative surface charge of the oxides. The artificial soil incubation experiment showed that interface development and the building of macroaggregates and organo-mineral associates took place within a relatively short time scale. It offers a valuable model where the formation and interactions of soil properties and processes can be studied in a well-defined system.
    Keywords: Specific Surface Area ; Ferrihydrite ; Clay Mineral ; Aggregate Hierarchy ; Charcoal ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Organic Geochemistry, 2011, Vol.42(11), pp.1308-1314
    Description: ► X-ray microscopy (μ-XRF) reveals microheterogeneity of element distribution in an organic soil. ► Diatoms, clay minerals, and sulfide precipitates can be identified at the (sub)micron scale. ► X-ray spectromicroscopy (μ-XANES) reveals microheterogeneity of S speciation in an organic soil. ► Inorganic and organic S species of different oxidation state coexist at the (sub)micron scale. In recent years, the relevance of physico-chemical heterogeneity patterns in soils at the micron and submicron scale for the regulation of biogeochemical processes has become increasingly evident. For an organic surface soil horizon from a forested Histosol in Germany, microspatial patterns of element distribution (sulfur, phosphorus, aluminium, silicon) and S speciation were investigated by synchrotron-based X-ray spectromicroscopy. Microspatial patterns of S, P, Al and Si contents in the organic topsoil were assessed for a sample region of 50 μm × 30 μm by spatially resolving μ-XRF. Sulfur speciation at four microsites was investigated by focused X-ray absorption near edge structure (μ-XANES) spectroscopy at the S -edge. The results show a heterogeneous distribution of the investigated elements on the (sub)micron scale, allowing the identification of diatoms, aluminosilicate mineral particles and sulfide minerals in the organic soil matrix. Evaluation of the S -edge μ-XANES spectra acquired at four different microsites by linear combination fitting revealed a substantial microspatial heterogeneity of S speciation, characterized by the presence of distinct enrichment zones of inorganic sulfide and zones with dominant organic disulfide S within a few micrometers distance, and coexistence of different S species (e.g. reduced inorganic and organic S compounds) at a spatial scale below the resolution of the instrument (60 nm × 60 nm; X-ray penetration depth: 30 μm).
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 7
    Language: English
    In: Organic Geochemistry, 2010, Vol.41(6), pp.580-585
    Description: To understand plant–microbe relationships, a simple method is required for identification of the nature of soil polysaccharides. Acid hydrolysis, reduction of sugar monomers to the corresponding alcohols and subsequent derivatisation with acetic anhydride prior to gas chromatography has often been used for identification and quantification of hydrolysable sugars in plant and soil samples. In mineral soil samples, precipitation of iron hydroxides and dissolved organic substances after addition of ammonia may lead to co-precipitation of the analytes, leading to an underestimation of the neutral sugar content. The aim of this study was to adapt the derivatisation procedure for soil samples with large iron (hydr)oxide contents. This was done by omission of ammonia and addition of ethylenediaminetetraacetic acid (EDTA) to keep iron in solution and to avoid co-precipitation. Standard addition approaches show that the recovery of all sugars is enhanced with the modified method. Application of the EDTA method improves the recovery of added internal standard, increases yields of sugars in mineral soils and reduces the observed standard error compared to the ammonia method. This was shown for a set of various soil samples with different iron (hydr)oxide contents. The EDTA method is also applicable for mineral free samples and therefore suitable for routine use.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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  • 8
    Language: English
    In: Geoderma, September 2014, Vol.228-229, pp.90-103
    Description: We studied organic carbon (OC) accumulation in organo-mineral associations during soil development on calcareous parent material. Two chronosequences in the Zhejiang Province, PR China, were investigated; one under paddy cultivation with a maximum soil age of 2000 years, and the other under upland crops where the oldest soil was 700 years old. Bulk soils and soil fractions of the uppermost A horizons were analyzed for OC concentrations, radiocarbon ( C) contents, total pedogenic iron oxide concentration and oxalate extractable proportions of iron (Fe ) oxides. The specific surface area of soil minerals was measured with the Brunauer–Emmett–Teller (BET-N ) method on four conditions: untreated, after organic matter removal, after iron oxide removal and after removal of both. Initial soil formation on calcareous marine sediments includes soil decalcification and OC accumulation. Paddy soils are characterized by an accelerated decalcification, higher contents of OC and Fe oxides, and a pronounced accumulation of modern OC. The mineral constitution of the soil material indicated already a certain degree of weathering since the earliest stages of pedogenesis and remained unchanged in paddy and non-paddy soils. The study provides no evidence of formation of new clay-sized minerals during soil development, which could supply new surfaces for OC accumulation. However, the study revealed higher OC coverage on mineral surfaces in decalcified paddy soils. Therefore, we assume the specific surface area and the specific affinity of Fe oxides for OC storage to play an important role for OC accumulation in organo-mineral associations. In contrast, the surface area of minerals in non-paddy soils, in which decalcification and the proportion of Fe oxides were much lower, showed significantly lower OC coverage. Selective removal of SOM or iron oxides clearly showed that iron oxides and SOM protect each other in organo-mineral associations primarily in paddy fine clay-sized fraction. Thus, we explained the higher OC coverage on mineral surfaces by complex association between clay minerals, iron oxides and SOM in paddy soils.
    Keywords: Pedogenesis ; Chronosequence ; Paddy Rice Cultivation ; Iron Oxides ; Specific Surface Area ; Decalcification ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 9
    Language: English
    In: Catena, 2011, Vol.87(3), pp.376-385
    Description: Considerable amounts of soil organic matter (SOM) are stabilized in paddy soils, and thus a large proportion of the terrestrial carbon is conserved in wetland rice soils. Nonetheless, the mechanisms for stabilization of organic carbon (OC) in paddy soils are largely unknown. Based on a chronosequence derived from marine sediments, the objectives of this study are to investigate the accumulation of OC and the concurrent loss of inorganic carbon (IC) and to identify the role of the soil fractions for the stabilization of OC with increasing duration of paddy soil management. A chronosequence of six age groups of paddy soil formation was chosen in the Zhejiang Province (PR China), ranging from 50 to 2000 years (yrs) of paddy management. Soil samples obtained from horizontal sampling of three soil profiles within each age group were analyzed for bulk density (BD), OC as well as IC concentrations, OC stocks of bulk soil and the OC contributions to the bulk soil of the particle size fractions. Paddy soils are characterized by relatively low bulk densities in the puddled topsoil horizons (1.0 and 1.2 g cm ) and high values in the plow pan (1.6 g cm ). Our results demonstrate a substantial loss of carbonates during soil formation, as the upper 20 cm were free of carbonates in 100-year-old paddy soils, but carbonate removal from the entire soil profile required almost 700 yrs of rice cultivation. We observed an increase of topsoil OC stocks from 2.5 to 4.4 kg m during 50 to 2000 yrs of paddy management. The OC accumulation in the bulk soil was dominated by the silt- and clay-sized fractions. The silt fraction showed a high accretion of OC and seems to be an important long-term OC sink during soil evolution. Fine clay in the puddled topsoil horizon was already saturated and the highest storage capacity for OC was calculated for coarse clay. With longer paddy management, the fractions 〈 20 μm showed an increasing actual OC saturation level, but did not reach the calculated potential storage capacity. ► Chronosequence consisting of 50 to 2000 years of paddy soil evolution. ► OC accumulation during 2000 years of paddy pedogenesis. ► Soil fractions are responsible for OC accumulation. ► Fine mineral fractions showed an increasing actual OC saturation.
    Keywords: Soil Organic Carbon (Soc) ; Particle Size Fractionation ; OC Storage Capacity ; Pedogenesis ; Fine Mineral Fraction ; Cultivation History ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 10
    Language: English
    In: Organic Geochemistry, 2012, Vol.42(12), pp.1476-1488
    Description: ► NanoSIMS enables submicron analyses of in situ soil processes. ► Isotopic enrichment of organic matter can be tracked in soil aggregates. ► Submicron elemental composition of soil aggregates follows spatial patterns. The specific features of the nano-scale secondary ion mass spectrometry (NanoSIMS) technology with the simultaneous analysis of up to seven ion species with high mass and lateral resolution enables us to perform multi-element and stable isotope measurements at the submicron scale. To elucidate the power of this technique, we performed an incubation experiment with soil particles of the fine silt and clay fractions (from an Albic Luvisol), with occluded particulate organic material and intact soil aggregates (from a Haplic Chernozem), using a C and N labelled amino acid mixture as tracer. Before and during 6-day incubation after the addition of the label, samples were consecutively prepared for NanoSIMS analysis. For this purpose, two different sample preparation techniques were developed: (i) wet deposition and (ii) the sectioning of epoxy resin embedded samples. Single soil particles (fine silt/clay fraction) showed an enrichment of C and N after label addition that decreased over time. On aggregates of particulate organic matter, re-aggregated during the 6-day incubation experiment, we could show a spatially heterogeneous enrichment of C and N on the particle surface. The enrichment in N demonstrated the diffusion of dissolved organic matter into intact soil aggregate interiors. The prospects of NanoSIMS for three dimensional studies of stable C and N isotopes in organo-mineral associations is demonstrated by the recorded depth profiles of the organic matter distribution on mineral particles.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
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