Biological influences on the morphology and micromorphology of selected Podzols (Spodosols) and Cambisols (Inceptisols) from the eastern United States and north-east Scotland

Biological activities greatly influence the formation of many soils, especially forest soils under cool humid climates. The objective of this study was to investigate the effects of vegetation and soil biota on the formation of selected soils. Field morphology, micromorphology, and carbon and organic matter analysis were determined on six Podzols (Spodosols) and two Cambisols (Inceptisols) from the eastern United States and north-east Scotland. Humification of plant material by soil fauna and fungi occurs in all organic horizons. Thick organic coatings are observed on soil peds and rock fragments from the E1 to the Bs horizon in a Haplic Podzol from Clingmans Dome Mt., TN. Thin sections reveal large accumulations of root material in different stages of decomposition in the spodic horizons of a Haplic Podzol from Whiteface Mt., NY. Organic carbon ranges from 5.4 to 8.5% in the spodic B horizons of the Whiteface Mt. Podzol. Earthworms and enchytraeids have a great effect on the structure of the surface and subsurface horizons in the Dystric Cambisols from Huntly and Clashindarroch Forests, Scotland and a Cambic Podzol from the Corrie Burn Basin, Scotland. Podzols from Speymouth Forest, Scotland (Gleyic Podzol), Clingmans Dome Mt., and Whiteface Mt. have thick organic horizons. The Podzols from the Flatwoods in Georgia, the Pine Barrens in New Jersey, the Corrie Burn Basin, and the Cambisol from Huntly Forest have only A horizons at the surface. The Clashindarroch Forest soil has a very thin organic horizon. Warm and humid climates and sandy parent material are responsible for thick E horizons and lack of thick organic horizons in the Flatwoods (Carbic Podzol) and Pine Barrens (Ferric Podzol) soils. Earthworms and enchytraeids thrive in the Corrie Burn Basin and Huntly Forest soils due to the vegetation and the highly weathered basic parent material. The site at Clashindarroch once carried oak, and then birch forest, both of which produce a mild litter and also encourage earthworm and enchytraeids. This fauna is responsible for much mixing of the topsoil. The present conifer vegetation will eventually produce a deep litter and cause podzolization.     

A reassessment of podzol formation processes

Translocated (oxalate-soluble) Al and Fe are present predominantly in inorganic forms in the B₂ horizons of the five pcdzol profiles examined: A1 as imogolite and proto-imogolite allophanes, and Fe as a separate oxide phase. Below the top few cm of the B₂ horizon, over 75 per cent of the extractable (acid-plus alkali-soluble) organic matter is present as Al-fulvates, largely sorbed on allophanic material. The Bh horizons of the Iron Humus Podzol and Iron Podzol intergrades are distinguished by very high levels of organically bound Fe (soluble in EDTA solution), five to ten times more than in immediately adjacent A₂ or B₂ horizons, and also by larger humic acid contents than in comparable B₂, levels in typical Iron Podzols. Inorganic forms of translocated Al and Fe are probably absent from two of the three Bh horizons examined, and also from the Bhg horizon overlying the thin iron pan in the Peaty Podzol. The organic matter in this Bhg horizon is saturated with Al rather than Fe. Chemical and physical processes which could lead to evolution of a profile along the genetic sequence, Iron Podzol, Iron Humus Podzol, Peaty Podzol, are postulated. During the formation of an Iron Podzol, positively charged inorganic sols carry aluminium, silicon and iron from the A₂ and deposit them in the B₂ horizon; subsequently, with the development of an H layer, colloidal humus migrates through the A₂ and precipitates on the positive colloids at the top of the B₂ horizon to form a Bh horizon, in which remobilized ferric species are trapped by the organic matter. In higher rainfall areas, occasional waterlogging above the oxide-impregnated B₂ leads to a thin iron pan, separating permanently oxidizing conditions below from seasonally waterlogged and reducing conditions above.     

Soil organic matter composition and pesticide bonding in sandy soils in relation to groundwater protection in the Northwest German Lower Plain

In sandy gleyic soils with a low groundwater table under arboriculture in Northwest Germany, a wide variation of groundwater pollution by pesticides has been observed. We therefore examined data on microbial activity and soil organic matter composition by wet chemistry, cross-polarization magic-angle spinning and ¹³C nuclear magnetic resonance, and pyrolysis-field ionization mass spectromy. However, neither microbial activity nor the soil organic matter composition of cultivated topsoils explained the differences in xenobiotic leaching into the groundwater. Data from Anthrosols suggested that these soils have a higher capacity for pesticide bonding because of high amounts of aromatic and carboxylic C moieties in the soil organic matter. However, despite the same pesticide inputs and time of application, the leached output from these soils was higher than that from the Podzols. Initial data from subsoil investigations suggest that the presence of a spodic horizon most likely reduces groundwater pollution by pesticides. Studies to assess fixation capacity and desorption kinetics in Bh horison seem warranted.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol – Podzol sequence of the upper Amazon Basin

Hydrochemical processes involved in the development of hydromorphic Podzols are a major concern for the upper Amazon Basin because of the extent of the areas affected by such processes and the large amounts of organic carbon and associated metals exported to the rivers. The dynamics and chemical composition of ground and surface waters were studied along an Acrisol‐Podzol sequence lying in an open depression of a plateau. Water levels were monitored along the sequence over a period of 2 years by means of piezometers. Water was sampled in zero‐tension lysimeters for groundwater and for surface water in the drainage network of the depression. The pH and concentrations of organic carbon and major elements (Si, Fe and Al) were determined. The contrasted changes reported for concentrations of Si, organic carbon and metals (Fe, Al) mainly reflect the dynamics of the groundwater and the weathering conditions that prevail in the soils. Iron is released by the reductive dissolution of Fe oxides, mostly in the Bg horizons of the upslope Acrisols. It moves laterally under the control of hydraulic gradients and migrates through the iron‐depleted Podzols where it is exported to the river network. Aluminium is released from the dissolution of Al‐bearing minerals (gibbsite and kaolinite) at the margin of the podzolic area but is immobilized as organo‐Al complexes in spodic horizons. In downslope positions, the quick recharge of the groundwater and large release of organic compounds lead to acidification and a loss of metals (mainly Al), previously stored in the Podzols.     

Podzolization as a deferralitization process: a study of an Acrisol–Podzol sequence derived from Palaeozoic sandstones in the northern upper Amazon Basin

Morphological, geochemical and mineralogical studies were carried out in a representative soil catena of the low‐elevation plateaux of the upper Amazon Basin to interpret the steps and mechanisms involved in the podzolization of low‐activity clay soils. The soils are derived from Palaeozoic sandstones. They consist of Hydromorphic Podzols under tree savannah in the depressions of the plateaux and predominantly of Acrisols covered by evergreen forest elsewhere. Incipient podzolization in the uppermost Acrisols is related to the formation of organic‐rich A and Bhs horizons slightly depleted in fine‐size particles by both mechanical particle transfer and weathering. Weathering of secondary minerals by organic acids and formation of organo‐metallic complexes act simultaneously over short distances. Their vertical transfer is limited. Selective dissolution of aluminous goethite, then gibbsite and finally kaolinite favour the preferential cheluviation of first Fe and secondly Al. The relatively small amount of organo‐metallic complexes produced is related to the quartzitic parent materials, and the predominance of Al over Fe in the spodic horizons is due to the importance of gibbsite in these low‐activity clay soils. Morphologically well‐expressed podzols occur in strongly iron‐depleted topsoils of the depression. Mechanical transfer and weathering of gibbsite and kaolinite by organic acids is enhanced and leads to residual accumulation of sands. Organo‐metallic complexes are translocated in strongly permeable sandy horizons and impregnate at depth the macro‐voids of embedded soil and saprolite materials to form the spodic Bs and 2BCs horizons. Mechanical transfer of black particulate organic compounds devoid of metals has occurred later within the sandy horizons of the podzols. Their vertical transfer has formed well‐differentiated A and Bh horizons. Their lateral removal by groundwater favours the development of an albic E horizon. In an open and waterlogged environment, the general trend is therefore towards the removal of all the metals that have initially accumulated as a response to the ferralitization process and have temporarily been sequestrated in organic complexes in previous stages of soil podzolization.     

Physicochemical and Microbiological Characteristics of Tundra Soils on the Rybachii Peninsula

The Rybachii Peninsula is composed of Proterozoic sedimentary rocks and differs sharply from the rest of the Kola Peninsula in its geological structure, topographic forms, and parent rocks. It is dominated by Al–Fe-humus soils formed on moraines with an admixture of local rock fragments, including slates. Organic horizons of tundra soils in the peninsula are less acid than those on granitoids of adjacent mainland of the Kola Peninsula. The content of exchangeable calcium in the organic horizons varies from 17.4 to 68.0 cmolc/kg, and the content of water-soluble carbon reaches 400 mg/100 g amounting to 1–2% of the total soil organic matter content. The total number of bacteria in the organic horizons of tundra soils varies from 3.5 × 10⁹ to 4.8 × 10⁹ cells/g; and bacterial biomass varies from 0.14 to 0.19 mg/g. The length of fungal mycelium and its biomass in the organic horizons are significant (>1000 m/g soil). The biomass of fungal mycelium in the organic horizons exceeds the bacterial biomass by seven times in podzols (Albic Podzols) and by ten times in podbur (Entic Podzol), dry-peat soil (Folic Histosol), and low-moor peat soil (Sapric Histosol).     

EXTRACTABLE SESQUIOXIDES IN SIX MEDITERRANEAN SOILS DEVELOPED ON BASALT AND SCORIA

Iron, Al, and Mn were extracted by oxalate and dithionite from two Brown Mediterranean Soils, two Red Mediterranean Soils, one Vertisol and one Gley soil, all derived from basalt or scoria in the sub-humid and humid Mediterranean regions of the Golan Heights. Ratios of oxalate: dithionite extracted iron (Fe_o:Fe_d) were low in all soils, indicating that the predominant form of free iron is crystalline. Fe_o accumulates in the argillic B horizons of the Mediterranean soils, while Fe_d accumulates in the surface horizons. A large part of the free iron oxide in the surface horizons of Mediterranean soils is associated with non-clay fractions. While manganese behaves in a manner somewhat similar to that of iron, no definite trends could be discerned in the vertical distribution of free aluminium. In the Vertisol, Fe_o and Mn_o accumulate in the subsoil. Fe_d and Mn_d increase slightly with soil depth. In the Gley soil, amorphous iron accumulates in the surface horizon, total free iron in the bottom horizon. Both amorphous and total free Mn had been depleted from the upper horizons of the Gley soil.     

Rheological Properties of Automorphic and Semihydromorphic Cryometamorphic Northern Taiga Soils in Northeastern European Russia (Komi Republic)

Soil pastes at the water content corresponding to the maximum swelling of samples from different genetic horizons of cryometamorphic soils―surface-gleyic iron-illuvial svetlozem (Folic Albic Stagnosol) and peaty and peat humus-impregnated gleyic svetlozems (Histic Gleyic Stagnosols)―have been studied with an MCR-302 modular rheometer (Anton Paar, Austria). It has been found that the strongest interparticle bonds are formed in the horizons of cryometamorphic soils characterized by high contents of humic substances and organomineral Al–Fe–humus compounds. These are horizons of podzol microprofile (Eg and BHF) in iron-illuvial svetlozem and a humus-impregnated horizon (ELhi,g) in peaty and peat svetlozems. Organomineral Al–Fe–humus compounds, as well as the seasonal freezing of soils, determine the elastic-brittle character of interparticle interactions. The contents of clay fractions, exchangeable bases, and organic and organomineral substances impart viscoelastic properties to these contacts. An enhancement of elastic-brittle properties of soil is observed under the impact of gleying and freezing. The threefold decrease of the structural interaction parameter (∫Z) when going from automorphic to semihydromorphic conditions indicates a decrease in the resistance of peaty and peat svetlozems to mechanical loads under increasing hydromorphism compared to iron-illuvial svetlozems.     

Clay minerals in chernozem-like soils of mesodepressions in the northern forest-steppe of European Russia

In the northern forest-steppe of European Russia, under the conditions of surface waterlogging (freshwater) and a stagnant-percolative regime, gleyic podzolic chernozem-like soils with thick light-colored eluvial horizons are formed. These horizons are close or similar to the podzolic horizons of bog-podzolic soils in many properties of their solid phase. They are bleached in color and characterized by the removal of Ca, Mg, Fe, Al, and Mn and the relative accumulation of quartz SiO₂. These soils differ from leached chernozems in their acid reaction and very low CEC, the presence of Fe-Mn concretions and coatings, and the significant decrease in the clay content in the A2 horizon as compared to the parent rock. The soils studied differ significantly from loamy podzolic and bog-podzolic soils by the composition of the clay minerals in the A2 horizons: (1) no essential loss of smectite minerals from this horizon was found as compared to the rest of the solum, (2) pedogenic chlorites (HIV and HIS) are absent, and (3) the distinct accumulation of illites is observed as compared to the subsoil and parent material, probably, due to the process of illitization.     

Podzol: Soil of the Year 2007. A review on its genesis,occurrence, and functions

The Podzol has been elected “Soil of the year 2007” in Germany. This article reviews the present knowledge on the development, functions, and threats of Podzols. The main theories on mobilization and transport of organic matter, Fe, Al, and Si are (1) metal‐organic migration, (2) metal reduction, and (3) inorganic sol migration. Immobilization theories include precipitation or polymerization due to increasing pH/abundance of base cations with depth, mechanical filtering in soil pores, oxidation of metal‐organic complexes, biodegradation of the organic part, decreasing C‐to‐metal ratios during translocation, adsorption to soil particles, and flocculation at the point of zero charge. Podzolization is discussed also on the catena scale, where vertical and lateral translocation processes (across pedon boundaries) need to be considered to understand Podzol patterns in landscapes. Chronosequence studies show that incipient podzolization usually becomes visible between 100 and 500 y and mature Podzols develop in 1,000–6,000 y. The occurrence of Podzols worldwide is concentrated mainly on the boreal zone and mountain regions within the humid temperate zone. Smaller Podzol areas are found in some perhumid tropical and subtropical regions. In Germany, Podzols occur in the Alps, in the glaciofluvial valleys and heathlands of N Germany, and in the mountain ranges. They fulfil several ecological functions, especially for groundwater recharge. Main threats for these mostly sandy soils are wind erosion and surface mining of sand. Two pedons which were chosen to represent the “Soil of the year 2007” are presented. Finally, some conclusions about podzolization processes are drawn, which may explain the diverse observations reported in the literature.     

Element enrichment and migration within some soils on Fildes Peninsula (King George Island), the maritime Antarctic

Three soil profiles (Dystri‐gelic Cambisol, Fibri‐gelic Histosol, Relic Ornithosol) sampled from Fildes Peninsula of King George Island, Antarctica, were involved in this study to quantitatively demonstrate the enrichment, migration, loss of the elements Si, Al, Fe, Ca, Mg, Mn, K, Na, and P in soil horizons and their behaviors within profiles by introduction and application of the enrichment coefficient (calculated in relation to the abundance of Ti). Additionally, six other soil horizon samples taken randomly from the study area were examined for calculation of the redistributing enrichment coefficient: These coefficients were applied here for a better understanding of the element redistribution between soil and clay fraction along with soil development. The results show that the enrichment, migration and redistribution of the elements vary strongly amongst the investigated soils and horizons, due to the differences of weathering degrees, moisture status, and influences of sea bird activities etc.     

Mineralogic evolution in hydromorphic sandy soils and podzols in “landes du médoc”, France

Soils of the nearly level “Landes du Médoc” in southwestern France have a pattern of alternating bodies of hydromorphic podzols (Haplaquods) and low humic hydromorphic soils (Psammaquents). The soils are formed in a sedimentary mantle of coarse, quartzose sands with a slight microrelief consisting of low, elongated ridges and shallow, intervening troughs. The water table is at shallow depths throughout the plain, even at the surface in places. The podzols on the crests of the low ridges have distinct A₂ and cemented B₂ h horizons. Podzols persist down the sides of ridges but going downslope first lose the A₂ horizon and then the cementation of the Bh horizon. Soils in the shallow troughs have A₁ and Cg horizons without B horizons.The fine silt (2–20 μm) and clay (0–2 μm) fractions of the parent sand contain primary trioctahedral chlorite, mica, feldspars, and quartz, with the last mineral predominant. During soil development, the first three minerals undergo weathering at different rates and to different extents. Chlorite is most strongly weathered, followed in order by plagioclases and K-minerals. In the fine silt fraction, weathering seems to occur mostly by fragmentation of particles. In the clay fraction, the phyllosilicates successively form irregularly interstratified minerals with contractible but not expandable vermiculitic layers, interstratified minerals with contractible and expandable smectitic layers, and finally smectites.The extent to which the silicate minerals are weathered becomes progressively greater from the low humic hydromorphic soils to the podzols with friable Bh horizons to the podzols with cemented Bh horizons. Smectite is present only in the A₂ horizons of these last podzols.The aluminum release by weathering of silicate minerals is translocated in part in the form of organo-metal complexes into the Bh horizons of the podzols. Greatest concentrations of Al are associated with coatings of monomorphic organic matter on mineral grains in the cemented Bh horizons, in which some Al has also crystallized into gibbsite. That mineral was not detected in friable B horizons of podzols nor in the low humic hydromorphic soil. Contrary to expectations, the mobile Al did not enter interlayer spaces of expanding 2:1 clay minerals.     

南极Fildes半岛成土过程中主要元素的行为

Nine horizon samples of three soil profiles representative of Dystri-gelic Cambisol, Fibri-gelic Histosol and Relic Ornithosol were taken from Fildes Peninsula of King George Island, South Shetland Islands to quantitatively demonstrate the enrichment, migration and loss of the elements (Si, Al, Fe, Ca, Mg, Mn, K, Na and P) in soil horizons and their behaviour within profiles by application of the enrichment coefficient calculated in terms of the abundance of Ti. Six horizon samples of 4 other profiles randomly taken from the studied area were examined for calculation of the redistributing enrichment coefficient, which was applied for a better understanding of the element redistribution between soil and clay fraction along with soil development. The results showed that the enrichment, migration and redistribution of the elements varied strongly among the investigated soils and horizons, due to the differences of weathering degrees and moisture status, influences of sea bird activities, etc.     

Schwermetallverteilung und -bilanzen typischer Waldböden aus nordischem Geschiebemergel

Heavy metal distribution and balances of typical forest soils out of German and Danish till The total contents of Cd, Cu, Fe, Mn, Pb and Zn were determined in different horizons as well as in clay coatings, mottles and concretions from 4 Orthic and Gleyic Luvisols around the Baltic Sea. Profile balances resulted in very small losses of Fe, small losses of Cu, Pb and Zn but higher losses of Cd and Mn. All elements were translocated by clay migration but corresponding enrichments in the B-horizons were covered by translocations in soluble form. Only Fe and Mn had been enriched in mottles of the water logged soils.     

Podzol formation in sandy soils of Finland

Podzolization occurs quickly in acidic parent materials with addition of acidic litter from coniferous trees. This study was conducted to evaluate Podzol formation and estimate lengths of time required to meet morphological and chemical criteria of podzolic B horizon and spodic horizon in Finland. Soil color, organic C, ODOE, and extractable Al and Fe were measured in a seven-pedon chronosequence (230–1800 years) and four older pedons (8300–11,300 years). The bulk mineralogical composition of the BC and C horizons was uniform with quartz, plagioclase and K-feldspar as main components and amphibole, illite and chlorite as minor components. The fine (<5 μm) fraction of selected samples was primarily amorphous allophone-like material with some mixed-layered illite–vermiculite. All pedons in the study met the criteria for albic horizons according to the FAO–Unesco, World Reference Base (WRB) and Soil Taxonomy systems. According to the FAO–Unesco system, all pedons had spodic B horizons and were classified as Podzols. According to the WRB system, none of pedons of the chronosequence had spodic horizons, whereas the older pedons met the criteria for a spodic horizon. About 4780 years were required to form a spodic horizon according to the WRB system. The oldest pedon of the chronosequence and the older pedons had spodic horizons according to Soil Taxonomy, but the younger pedons failed to meet the spodic horizon criteria. About 1520 years were required to form a spodic horizon that met the color and organic C criteria of Soil Taxonomy, whereas it took about 4780 years to meet the required accumulation of Fe and Al. This study points out the discrepancy between the color criteria and the criteria reflecting the accumulation of Al, Fe and organic matter in the B horizon.     

Changes in soil morphology of Podzols affected by alkaline fly ash blown out from the dumping site of an electric power plant

Purpose

The impacts of fly ash on the chemistry of forest floors were previously described in literature, while impacts on soil properties were less recognised. Soil investigations were focussed mainly on increases of pH and base saturations in surface horizons. The purpose of this study was to describe the influence of alkaline fly ash blown out from the dumping site of a lignite-fired power plant on pH changes of ectohumus horizons of Podzols and the morphology of deeper horizons.

Materials and methods

We investigated the soil profiles of Podzols derived from loose quartz sand and developed under pine forest surrounding the dumping site of the power plant Be?chatów, central Poland. In the vicinity of the fly ash dumping site, five Podzol profiles located at a distance of 50 m from the dumping site were investigated, as well as soil profiles located along the transect set at distances of 50, 300, 800 and 2000 m from the dumping site. Control profiles were located at a distance of 7.3 km from the dumping site. Soil morphology was described in the field and the following properties were determined: soil texture, hydrolytic acidity, exchangeable cations, total organic carbon and total nitrogen content.

Results and discussion

The pH values of Podzol ectohumus horizons located close to the dumping site ranged from 6.01 to 7.34 compared to a range of 3.08–3.72 in the control. Ectohumus horizon located 300 m from the dumping site showed a pH range of 4.13–4.26, while at a distance of 800 m, the pH values did not differ from those of the control site. The upper part of the eluvial soil horizons located close to the dumping site had been transformed into transitional AE horizons in which humic substances translocated from ectohumus horizons were accumulated. Moreover, the organic carbon content of this horizon increased compared to the carbon content of the illuvial Bs horizon located below it. Under the influence of alkalisation of upper horizons, the illuvial Bhs horizons vanished and were transformed into Bs horizons.

Conclusions

Changes in soils affected by fly ashes are connected with alkalinisation of ectohumus horizons. Podzolisation processes can be reduced or even completely stopped regarding the distance from the dumping site. Eluvial Podzol horizons located close to the dumping site may be transformed into AE horizons in which humic substances translocated from ectohumus horizons are accumulated. Due to transformation and translocation of organic components, Bhs horizons can be transformed into Bs horizons.

     

Andic properties in soils developed from nonvolcanic materials in Central Bhutan

A number of soils are described in the literature as having andic and spodic soil properties, but have developed in nonvolcanic and nonallophanic materials and lack typical Podzol eluvial and illuvial horizons. They cover a wide range of parent materials and different types of climate. They have always been regarded as restricted to small areas. They were assigned to Andisols/Andosols, Podzols/Spodosols, or andic Inceptisols in the WRB and Soil Taxonomy and sometimes also named Cryptopodzols or Lockerbraunerden. Recent soil surveys in Bhutan, E Himalayas, show these soils are widespread at altitudes between 2200–3500 m asl and are spanning several bioclimatic zones. The aim of this study is the detailed characterization of specific properties and processes of formation by physical and chemical analyses, NMR spectroscopy, column experiments, SEM, XRD, and ¹⁴C dating in one of these soils in E central Bhutan. The results indicate advanced soil development with high amounts of oxidic Fe and Al compounds, low bulk densities (partly <0.5 g cm^–3), P retention >85%, and a dominance of Al‐hydroxy‐interlayered phyllosilicates. Scanning electron microscopy of sand fractions indicate microaggregates highly resistant to dispersion. Column experiments show podzolization with mobilization and translocation of DOM, Fe, and Al. Nuclear‐magnetic resonance spectroscopy and ¹⁴C ages of 16,000 BP indicate stabilization of DOM. Applying classification criteria, these soils appear to have andic and spodic features, but are neither Andosols nor Podzols senso strictu. Especially the role of Fe seems to be underestimated with regard to the specific soil‐forming processes. Because of their widespread occurrence and distinct properties, we suggest either a simplification of the criteria for existing soil types or a clearly defined separation of volcanic and nonvolcanic/nonallophanic Andosols.     

Soil mixing and genesis as affected by tree uprooting in three temperate forests

The purpose of this study was to identify general patterns of pedoturbation by tree uprooting in three different, forested landscapes and to quantify post‐disturbance pedogenesis. Specifically, our study illustrates how the effects of ‘tree‐throw’ on soils gradually become diminished over time by post‐uprooting pedogenesis. We studied soil development within 46 pit‐mounds in two regions of the Czech Republic, one on Haplic Cambisols and one on Entic Podzols. A third study site was in Michigan, USA, on Albic Podzols. Uprooting events were dated by using tree censuses, dendrochronology and radiometry. These dates provided information on several chronosequences of pedogenesis in the post‐uprooting pits and mounds, dating back to 1816 AD (dendrochronological dating, Haplic Cambisols), 322 AD (median of calibration age, ¹⁴C age = 1720 ± 35 BP, Entic Podzols) and 4077 BC (¹⁴C age = 5260 ± 30 BP, Albic Podzols). Post‐uprooting pedogenesis was most rapid in pits and slowest on mounds. Linear chronofunction models were the most applicable for pedogenesis, regardless of whether the soils were in pit or mound microsites. These models allowed us to estimate the time required for horizons in such disturbed sites to obtain the equivalent thicknesses of those in undisturbed sites. These ranged from 5 (O horizon in pits on the Haplic Cambisols) to > 16 000 years (E horizon on mounds on the Albic Podzols). On the Albic Podzols, development of eluvial and spodic horizon thicknesses suggested that pathways involving divergent pedogenesis may occur at these small and localized spatial scales.     

Sulfur K-edge XANES spectroscopy reveals differences in sulfur speciation of bulk soils, humic acid, fulvic acid, and particle size separates

X-ray absorption near edge structure (XANES) spectra at the sulfur (S) K-edge (E=2472 eV) were compared for bulk soil material, humic and fulvic acid fractions, and different particle size separates from Ah horizons of two arable Luvisols, from an O and a Bs horizon of a Podzol under Norway spruce forest, and from an H horizon of a Histosol (peat bog). In the bulk soil samples, the contribution of reduced organic S (organic mono- and disulfides) to total sulfur increased from 27% to 52%, and the contribution of ester sulfate and SO₄²⁻-S decreased from 39% to 14% of total S in the following order: arable Luvisols Ah—forested Podzol O—Histosol H. This sequence reflects the increasing organic carbon content and the decreasing O₂ availability in that order. Neither sulfonate nor inorganic sulfide was detected in any of the bulk soil samples. For all samples except the Podzol Bs, the XANES spectra of the bulk soils differed considerably from the spectra of the humic and acid fractions of the respective soils, with the latter containing less reduced S (16-44% of total S) and more oxidized S (sulfone S: 19-35%; ester sulfate S: 14-38% of total S). Also the S speciation of most particle size fractions extracted from the Ah horizon of the Viehhausen Luvisol and the Bs horizon of the Podzol was different from that of the bulk soil. For both soils, the contribution of oxidized S species to total S increased and the contribution of sulfoxides and organic mono- and disulfides decreased with decreasing particle size. Thus, sulfur K-edge XANES spectra of alkaline soil extracts, including humic and fulvic acids or of particle size separates are not representative for the S speciation of the original soil sample they are derived from. The differences can be attributed to (i) artificial changes of the sulfur speciation during alkaline extraction (conversion of reduced S into oxidized S, loss of SO₄²⁻ during purification of the extracts by dialysis) or particle size separation (carry-over of water-soluble S, such as SO₄²⁻), but also to (ii) preferential enrichment of oxidized S in hydrophilic water-soluble soil organic matter (ester sulfate) and in the clay fraction of soils (ester sulfate, adsorbed SO₄²⁻).     

Geochemical characterization of placic horizons in subtropical montane forest soils,northeastern Taiwan

Well‐developed placic horizons have been found in subalpine forest soils with large clay contents in Taiwan. We investigated their formation processes in five profiles in a subalpine ecosystem of northeastern Taiwan, using scanning electron microscopy (SEM), energy‐dispersive spectrometry (EDS), electron probe microanalysis (EPMA), differential X‐ray diffraction (DXRD) and chemical extractions. The placic horizons, ranging from 3‐ to 17‐mm thick, always occurred above argillic horizons with abrupt changes in pH and texture between the two horizons. When fully developed, the placic horizons were clearly differentiated between upper and lower sub‐horizons. EDS and chemical extractions revealed that the cementing materials in both were predominantly inorganic Fe oxides. However, contents of aluminosilicates and organically complexed Fe and Al were greater in the lower than in the upper placic sub‐horizon. Results of EPMA indicated that interstitial fine materials in the upper placic sub‐horizon were composed mainly of Fe oxides, whereas Fe oxides were codominant with illuvial clay in the lower sub‐horizon. These analyses identified the migration of Fe and clay as major formation processes in both sub‐horizons. We hypothesize that there is a pedogenic sequence that starts with clay illuviation, followed by podzolization. The resultant textural and permeability differentiation reinforces the tendency to profile episaturation that is already inherent from the heavy rainfall and clayey surface soils. Topsoil Fe is therefore reduced and mobilized, and then illuviated with clay and organically complexed Fe/Al to initiate the lower placic sub‐horizon. The poor permeability of this layer reinforces the moisture conditions in the surface soils, and the further reduction, illuviation and deposition of inorganic Fe to form the upper placic sub‐horizon.