Hydromorphic Conditions Research Articles

Origin and evolution of soil materials of the Paleo-Chadian linear-dune landscape in the Far North Region of Cameroon

The mineralogy and micromorphology of associated red Arenosols and both yellow and grey Gleysols of the Paleo-Chadian linear-dune landscape of the Far North Region of Cameroon were studied in order to obtain information about depositional environments and pedogenic processes. Differences between the red soils and both others include a significant difference in clay content, which is much higher in the grey and yellow soils. The composition of the clay fraction is also different, with kaolinite and illite as main mineral phases in the red soils, whereas smectite is strongly predominant in the grey soils and a major phase in the yellow soils. Mössbauer spectroscopy analysis reveals a predominance of hematite as iron oxide mineral in the red soils, in contrast to goethite-predominance in the yellow soils. Thin section observations reveal poor sorting of the coarse fraction, differences in feldspar content, and an absence of reworked clay aggregates, as well as the presence of pore-related carbonate features in the grey soils and iron oxide nodules in the grey and yellow soils. The obtained results indicate that the red soils are derived from a different parent material than the other soils. The grey soils developed on flood-related fluvial deposits in interdune depressions, whereas the red soils formed on aeolian sands and the yellow soils show a mixed origin. In the interdune depressions, hydromorphic conditions led to iron reduction and pedogenic carbonate enrichment.

Origin and properties of kaolinites from soils of a toposequence in Southern Brazil

ABSTRACT Kaolinite is the main clay mineral in most soils around the world and has been widely used for industrial purposes. This research aimed to study chemical, morphological and crystallographic characteristics of kaolinite, and establish the origin of kaolinitic samples on Serra do Mar and kaolinitic layers on peatlands, located at Southern Brazil. Samples were collected on different geomorphological positions: two samples at Serra do Mar (kaolinitic saprolite – SAP, and kaolinitic layers - KL); and two cores at the peatland with Sapric Histosols from Quaternary sedimentary basin. Granulometry and total organic carbon (TOC) were determined in soil samples. Kaolinite in silt and clay fractions was studied by chemical extractions, X-ray diffraction (XRD), thermal analysis (DTA/TG), and scanning electron microscopy with energy dispersive spectroscopy – SEM/EDS. Chemical and mineralogical characteristics of kaolinite were divided into two groups, according to the particle size and the location of the deposit in the relief. Silt fraction: i) SAP – genesis mainly derived from mica weathering; ii) peatland, containing pseudomorph crystals smaller than those found in Serra do Mar; Clay fraction: i) Serra do Mar – there was a larger contribution of K-feldspar weathering in the genesis of kaolinite from KL in relation to SAP; ii) peatland – the stronger weathering and the hydromorphic conditions resulted in less neoformed crystalline kaolinites. For both environments, the substitution of Al 3+ by Fe 3+ into the octahedral sheet led to a reduction in the mineral thickness and also increased the occurrence of structural deformations in clay kaolinite. Kaolinite in peatland is a combination of the following genesis processes: transportation from Serra do Mar (mainly in the silt fraction) and; formation in situ through neogenesis process (dominant in the clay fraction).

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

Spodosol formation on sandy ruins in a semi-arid climate in the Catimbau National Park, Northeast Brazil

The Catimbau National Park (CNP) is found in the Caatinga biome under a semi-arid climate. The soils of certain humid areas have horizons with morphology typical of Spodosols, and their occurrence in the CNP seems to be in discord with their formation model. This study aimed to investigate the genesis of Spodosols in the semi-arid climate of the CNP, testing the hypothesis that these soils are the result of local tectonic conditions associated with a past climate. As such, a sandy soils toposequence over sandstone of the Tacaratu Formation, under Caatinga vegetation and a semi-arid climate in northeast Brazil was studied. Sampling was based on the structural model of the pedological coverage, whereby physical and chemical analyses, Fourier transform infrared spectroscopy, X-ray diffraction, and soil micromorphological analysis were carried out. The results indicate that paludization of the soils occurred in two more humid phases, being compounded by the occurrence of distended faults/fractures related to the geology of the CNP. Microbiological decomposition under hydromorphic conditions led to humification of the organic constituents, which acidified the environment and increased Al solubility, forming organometallic complexes with fulvic and humic acids. The FTIR spectra and the presence of charcoal confirm the condensed aromatic nature and the abundance of carboxylic groups in the soils, these being related to the pyrolysis of biotransformed plant residues. Podzolization occurred in pulses promoted by intense rains under a dry climate and Fe-poor parent material, which favored the translocation of organometallic compounds of Al. The dense packing of fine organomineral material in the Bh horizons and the open matrix in the adjacent horizons indicate that the narrowing of the porous environment may be an important factor for the immobilization of translocated material. With the return of the current drier conditions in Brazil’s semi-arid, the podzolization process remains incipient.

Soil formation and hydrological evolution of Navazo del Toro small-lake ecosystem, Doñana National Park, Andalusia, Spain

The wetlands on the quartz sands aeolian sheet make up one of the ecosystems most recognized and important of the Doñana National Park and Doñana Biological Reserve (South Spain). More than 650 temporal small-lakes have been surveyed in the abundant sand depressions of the aeolian sheet, the most are a hydro-geomorphological dune-small-lake system. This paper studies the pedological diversity around Navazo del Toro (NVT) wetland, one of the biggest temporal small-lakes, through a geopedological catena along 230 m with five soil profiles (NVT-1 to NVT-5). In this context a major focus is displayed on pedological processes and the current hydrological situation of the depression in the Middle-Upper Holocene. The main processes are: translocation of materials (silt and clay) from the Arenosols developed in the slope dune (sand washing processes), sediment accumulation on the dune depression (current wetland bottom), and the development of tirsificated and vertic Luvisols with a chronology of more than 4.255 BP (OSL dating). The water body of the geoecosystem has modified the horizons morphology, creating new hydromorphic (gleyic and stagnic) conditions that have incorporated abundant organic material (sediment of diatoms and sponge spicules) in the higher profile layer and generated an incipient podzolization processes.

Iron isotope fractionation during the formation of ferromanganese nodules under different conditions of hydromorphism

Hydromorphic soils are often characterized by redoximorphic pedofeatures like ferromanganese nodules. As the highly varying properties of the nodules are sensitive indicators of the pedogenic processes and redox history of the soil, their isotopic study may get a deeper insight into the soil genesis. In this study, the Fe isotopic characteristics, fabric, and mineralogy of ferromanganese nodules formed in six hydromorphic soil profiles were investigated using MC-ICP-MS, EPMA, and XRD analyses. We aimed to relate the Fe isotopic composition of the bulk soils and nodules to the varying conditions of hydromorphism and the various properties of the nodules.Although the extent of hydromorphism could be related to the nodules' properties, such a relationship was not found with their Fe isotopic characteristics. The reductive dissolution of primary Fe minerals resulted in similar Fe isotope distribution characteristics for the bulk soils. However, specific features of hydromorphic conditions (like frequency of the redox cycles, relocation of water fluctuation zone, external Fe input, and inhibition of leaching) affected the Fe isotope characteristics of both bulk soils and nodules. The minimum δ 56Fe value within the soil profile indicated the deepest part where precipitation of light Fe may dominate over its leaching. Above this depth, the isotopically light Fe precipitated to form the nodules. However, the higher frequency of the reductive conditions was responsible for the higher mobilization of isotopically light Fe below this depth. The isotopic characteristics of the nodules supported that authigenic Fe-oxyhydroxides were enriched in the light Fe isotope.The Fe isotope composition of a given soil horizon and its nodules result from a complex interaction of different processes whose effect varies from profile to profile. The integrated study of the Fe isotope characteristics of hydromorphic soils and their nodules may help follow several pedogenic processes and conditions.

Litologie a paleopůdy klikovského souvrství ve vrtu 2140 01T1 Dunajovice, třebonská pánev

The 2140 01T1 borehole sampling the Late Cretaceous non-marine strata of the Klikov Formation in the central part of the Třeboň Basin in southern Bohemia provided ~ 70 m thick alluvial succession composed of alternating sandstone and mudstone intervals that overlays deeply weathered crystalline basement. The mudstone interval in the lower part of the Klikov Formation is separated by sandy layers into several 2–4 m thick fining-upward units. The sharp-based sandy layers with fusain, carbonized stems and rip-up clasts of underlying mudstone are interpreted as avulsion deposits. They grade upwards into heterolithic sand-silt sequence and mottled massive mudstone with burrows, rhizohalos and variably developed pedogenic features. Such cyclic arrangement probably reflects autogenic processes on distal floodplain with episodic deposition and upward increasing subaerial exposition and pedogenic overprint. In the middle to upper parts of the Klikov Formation up to 6 m thick channel sandbodies with sharp erosional bases cutting into the underlying laminated sand-silt heteroliths of channel levee deposits occur. The thickness of the single-storey sandbodies corresponds usually to c. 2 m which suggests up to 3 m deep channels during bankfull discharge. The thicker multi-storey sandbodies record channel amalgamation on the alluvial ridge or shallow paleovalley fillings. The sandbodies grade upwards to massive mudstones of abandoned channel fills and floodplain deposits. These floodplain units are up to 8 m thick and consist of variegated massive mudstones interrupted by discrete up to 1 m thick fining upward layers of rippled sandstone representing crevasse splay deposits. Depositional context including preserved levee deposits, abandoned channel fillings and floodplain finegrained deposits suggests rather higher sinuosity of the formative rivers. Palaeosol profiles represent pedogenically modified floodplain fines with gradational bases and sharp erosive top surfaces. At least 10 palaeosols were identified in the measured section, forming mostly discrete profiles up to 2 m thick consisting of several B-horizons that differ in the degree of the soil structure development, colour, mottling, grain size, presence of clay hypocoatings and bioturbation index. The most common Bw horizons form lower parts of the profiles and have no or only a weakly developed angular blocky structure (ABS). The typical mottling is caused by a hierarchical system of vermicular greenish-grey reduction rhizohalos, that may be filled by silt to sand or illuviated clay hypocoatings and probably follow the original plant root system. Some patches have diffuse orange rims of iron oxides, probably represented by goethite. Mudstone of Bsst horizons displays well-developed ABS with rare wedge-shaped peds and contains a number of illuviated clay skins and redox depletions. Vertic features like fine cracks filled by sand are common, and slickensides with clay hypocoatings occur rarely. Mudstones of Bt horizons contain a number of illuviated clay hypocoatings filling root channels or interpedal cracks, while the Bss horizons exhibit well-developed ABS with slickensides and contain a number of vertical cracks filled by sandy grains. Palaeosol profiles represent mainly argillisols and vertic argillisols with transitions to argillic vertisols. Poorly developed argillic to vertic protosols are also common. Palaeosol profiles differ mainly in the degree of structural development/maturity, which is given by various lengths of exposition to similar climatic conditions. Vertical distribution of palaeosols reflects their position in the alluvial landscape with locally specific hydromorphic conditions rather than a distinct climatic trend. Most of palaeosols exhibits downprofile translocation of clay (illuviation) leading to the formation of argillic horizon, which typically develop on stabilized landscape in humid climate with seasonal moisture deficit.

Formation of Solonchak in the Area of the Discharged Ancient Brine Wells (Perm Krai, Russia)

The change in soil-forming processes and, as a result, in the ecosystem due to nearly 300-year long outflow of highly saline waters from ancient brine wells is considered for Perm Krai in Russia for the first time. The study area is located in the high floodplain of the Usolka River valley. Sodium-chloride ancient brine wells with mineralization of about 30 g/L flow in streams over the soil surface and enter the Usolka River. The paper considers three soil types at various distances from a saline stream. The main pedogenic processes are the sod-forming process and gleying in alluvial soils. Soils in Gleyic Fluvisols (background)—Gleyic Fluvisols (Sulfatic) (transition)—Solonchak (affected by sodium-chloride brines) series were studied in terms of occurring soil-forming processes. All studied soils are formed under hydromorphic conditions. It is evidenced by gleization. However, the morphological and physicochemical properties of the soils differ. The presence of water-soluble ions in the solonchak suggests that salinization is occurring. The sum of toxic salts was 0.94% which was several times higher than in the transition and background soils. The sodium adsorption ratio (SAR) ranged from 10.4 to 21.6, with a рН of 8.3–9.1. The saline soils were more alkaline (pH average 8.8 and 9.3) than the background soil (pH 8.1). SAR decreased significantly in the Solonchak—transition—background soil series from 16.9 to 0.7. The aforementioned observations, as well as physical properties of the saline soil, clearly show the entry of sodium into the solonchak adsorption complex, indicating the solonization process. The study area is characterized by the presence of salt-tolerant species of herbaceous plants and an obligate halophyte. Salicornia perennans Willd, a halophyte, was discovered in the wells’ discharge area at a distance of 0.2–1.5 m from saline streams. The analysis of the long-term impact of highly mineralized waters on the natural environment will aid in revealing and forecasting ecosystem changes caused by potash mining in Perm Krai for environmental risk assessment for new and existing potash enterprises.

Times are changing: A new chronology for Holocene volcanic events and hydro-sedimentary history recorded in the Sarliève marsh (central France)

This paper presents the first well-dated palaeoenvironmental study from the Sarliève marsh, a unique sedimentary record in the Limagne plain of central France, where all previous studies suffered from unreliable chronologies. We developed an accurate radiocarbon-based age-depth model and performed high-resolution multi-proxy sedimentological and geochemical analysis on a new sediment core from the heart of the sedimentary basin, improving the chronology and Holocene palaeoenvironmental interpretations. We found six potential (crypto)tephra fallouts (c. 9750, 8500, 7500, 7400, 6300, and 5800 cal yr BP) that enrich the Holocene tephrostratigraphy in Limagne, five of which were not previously documented in the sediments of the marsh. We also detected, for the first time, an array of volcanic phenomena such as degassing episodes (c. 6950 and 6050 cal yr BP), ash leaching phases (10250–9750, 8500–7400, and 5800–5100 cal yr BP), and earthquakes (c. 6800, 6600, 6050, 6100, and 1600 cal yr BP), suggesting a hitherto unsuspected period of high volcanic activity in the area between 7500 and 5800 cal yr BP. This increased activity appears to have caused a massive forcing of hydrosedimentary dynamics in the catchment in the Middle Holocene, by supplying significant volumes of fine volcanic ash to the palustrine basin, and thereby questioning the current Holocene morpho-sedimentary narrative for Limagne. The basin became a permanent freshwater lake after the Mid-Holocene climatic shift, and detrital influxes likely due to anthropogenic soil erosion appeared c. 5500 cal yr BP and grew steadily after 5000 cal yr BP, with a marked lull between 3600 and 3000 cal yr BP, perhaps because of a phase of settlement abandonments during the middle and early-late Bronze age. A series of lacustrine low-stands (c. 4750–4600, 3750–3600, 3350–3200 and 2950–2800 cal yr BP) that correlate strongly with western alpine lake records do not seem to have caused significant changes in the anthropogenic impact on soils modifying the sedimentary supply. Our results suggest that this lake could have been artificially drained c. 2550 cal yr BP, several centuries earlier than previously estimated, allowing us to hypothesize that Early Iron age societies already had substantial capacity to modify the hydraulic environment. Hydromorphic conditions developed thereafter, including complex short-lived marshy phases in late Roman times.

Micromorphological features of cryogenesis in the structure of taiga soils on the West Siberian Plain

Morphological descriptions of cryogenic soils of the taiga zone are very important for diagnostics and classification of soils of northern regions. The development of geocryogenic processes depends on locally specific climatic and lithological factors. Previous studies on cryometamorphic soils (svetlozems) formed on Mid-Pleistocene loamy parent materials have been focused on their hydrological and thermal regimes. This article presents the results of meso-and micromorphological analyses of mesomorphous loamy soils formed in autonomous (interfluve) areas under seasonal freezing conditions. The permafrost features of the studied soils were formed during cold climatic cycles of the Pleistocene-Holocene period. The modern pedogenesis develops under increasingly hydromorphic conditions untypical for autonomous soils of the taiga zone of the West Siberian Plain. As a result, processes of peat accumulation and gleyzation have developed in such soils. However, gley features are absent in cryometamorphic soils. In their upper layers, iron undergoes oxidation and concentrates within granular peds during freezing. In their lower horizons (from the 40 cm depth), Fe-nodules are assimilated within platy peds (as a result of cryogenic restructuring of silty-clayey groundmass) and relic clay coatings are fragmented. The vertical differentiation of cryogenic features within the studied soil profiles can be associated with changes in climatic conditions during the Pleistocene-Holocene period.

Micro-analytical study of the distribution of iron phases in ferromanganese nodules

The differentiation of Fe and Mn within the nodules and its relation to the fabric is a well-known phenomenon. However, the relationship of this differentiation to the nodules mineralogy was not studied yet. This study aimed to fill this gap through the micro-mineralogical and geochemical investigation of nodules from soils with different hydromorphic conditions by electron probe microanalysis and micro-X-Ray diffractometry.Different conditions of hydromorphism resulted in the same nodule types and their similar vertical distribution in soils. In soils with shallow groundwater table, nodules exhibited more developed fabric, and crystalline hydrous Fe oxides (goethite) prevailed in them. Contrarily, nodules showed smaller size, lower Fe enrichment, and a higher frequency of non-crystalline hydrous Fe oxides in soils with regular flooding and stagnant surface water. The difference could be related to the lower intensity of water oscillation and the shorter redox periods in the latter soils. The formation of the nodules’ fabric may have been followed by the slow crystallization of Fe-oxyhydroxides when favorable redox oscillation conditions occur allowing subsequent recrystallization. The association of hydrous Fe oxides to clay minerals may have also affected the crystallization process within the nodules.Although the observation of assumed differentiation of hydrous Fe oxides failed within the nodules, soils with different conditions of hydromorphism could be characterized by different Fe-oxyhydroxide mineralogy, at least in the progression of their crystallization process.

Properties of Alluvial Soils of Taiga Forest under Anthropogenic Salinisation

The environmental impact of deposit development can be indirect and can cause combined geochemical processes in ecosystems. These must be taken into consideration under environmental forecasting and environmental risk assessment. Soil degradation in the Taiga Forest is considered, within the area of Verkhnekamskoye potash deposit (Russia), as an example of such environmental transformation. Here, the mechanism and characteristics of the anthropogenic salinisation of alluvial soils under potash deposit development are newly described. It was found that there is a strong anthropogenic impact of the potash industry on valley soils where the contaminated Na-Cl groundwater discharges or is close to the surface. The valley soils are characterised by high salinity, and the sum of toxic salts in soils has reached 26%. Alluvial gley humic clay chloride saline soil (Gleyic Fluvisols (Salic, Loamic, Technic)) and secondary solonchak on alluvial humic clay soil sulphate-chloride gypsum-containing surface-gleyed (Chloridic Gleyic Fluvic Solonchak (Hypersalic, Loamic, Technic)) were formed in hydromorphic conditions. Morphological, physicochemical and mineralogical analyses were carried out. Under hydromorphic conditions, Chloridic Gleyic Fluvic Solonchak (Hypersalic, Loamic) was described to show a hydrotroillite layer and reddish-yellow iron-rich precipitates on its surface. The top soil horizon has the highest content of iron minerals (up to 84.9%) and Fe-bearing plant residues (up to 20%). Additionally, the spongy and gel-like organic materials, as well as the siliceous remains of diatoms, are enriched in Ca, Fe, Cl, K, Na, S and P. The lower soil horizon consists of black gel-like phases and hydrogen sulphide settings with a high content of plant residues. The insoluble part of the samples contains up to 84% hydrogoethite. The sources of iron in soils and bottom sediments include the iron-enriched Sheshma sediments speckled rocks, slurry material, halite wastes and soil minerals of alluvial gley soils.

The origin of gley colors in hydromorphic vertisols: the study case of the coastal plain of the Río de la Plata estuary

This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Rio de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Rio de la Plata estuary were analyzed using routine and chemical analyses, Mossbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite).

ТРАНСФОРМАЦИЯ ПОЧВЕННО-РАСТИТЕЛЬНОГО ПОКРОВА В РЕЗУЛЬТАТЕ ВЛИЯНИЯ ИЗЛИВАЮЩИХСЯ ДРЕВНИХ РАССОЛОПОДЪЁМНЫХ СКВАЖИН НА ТЕРРИТОРИИ ПЕРМСКОГО КРАЯ

The article deals with the problem of changes in the soil and vegetation cover as a result of more than 300-year long salt load. The study was carried out in the area of brine wells outflow onto the soil cover within the area of a 16th-century settlement where a group of 5 wells with outflowing brines with sodium-chloride chemistry and water salinity of about 30 g/L has survived to this day. The impact of sodium chloride waters on the alluvial soils of the Usolka River led to the emergence of secondary solonchaks with sulphate-chloride sodium salinization (Chloridic Gleyic Fluvic Solonchak (Humic, Loamic)). In the course of research, morphological and physicochemical analyses were conducted. Chloridic Gleyic Fluvic Solonchak (Humic, Loamic) forms under hydromorphic conditions. Starting from the depth of 45 cm, a dark, almost black, gley horizon with a distinct smell of hydrogen sulphide was observed in the soil. The sum of toxic salts in the soil reached 1,23%; the sodium adsorption ratio (SAR) varied from 13,8 to 19,8; pH was 7,15–8,2. The study area is characterized by the presence of salt-tolerant herbaceous plants. The halophyte Salicornia perennans Willd. has appeared within the wells discharge zone at a distance of 0,2–1,5 m from salty streams. Analysis of the salt load impact on the soil and vegetation cover of taiga landscapes will make it possible to predict the environmental impact of the potash industry of Perm Krai.

Microeukaryotes in the Metagenomes of Late Pleistocene Permafrost Deposits

The analysis of metagenomes from four Late Pleistocene permafrost samples allowed us to recognize nearly four hundred genera of protists and fungi, as well as nematodes, in the microeukaryotic assemblage. The sample of the ancient oxbow lake sediments is characterized by the highest taxonomic diversity. Heterotrophic protists and autotrophs dominated the deposits that formed under hydromorphic conditions. Fungi, in turn, prevailed in the Ice Complex deposits. In general, metagenomic analysis characterizes the assemblages from permafrost deposits more entirely than the standard methods of enrichment cultivation.

The effect of hydromorphic processes on the soil organic matter in the Central Russia (case study of the Voronezh and Kursk regions)

The one of the main types of land degradation that cause the most damage to the state of soil cover is local waterlogging of soils. Only in Russia, about 9 million hectares are currently considered waterlogged, including 5 million hectares of agricultural land. On the lowland plains of the forest-steppe zone of the Central Black Earth Region of Russia, local over moistening of the soil cover creates significant difficulties in the use of arable land resources. Natural factors effects waterlogging are the amount of precipitation and the level of groundwater. The objects of research are virgin and arable soils with different hydromorphic conditions in the Central Russian Upland. The article presents results about humus content and reserves in Chernozems typical, Chernozems leached, Meadow-chernozemics soil, Chernozems-meadow soil and Chernozem wet-meadow soil. According to our investigations the most rich humus soils of the forest-steppe is semi-hydromorphic Meadow-chernozemics soils. Meadow-chernozemics leached and typical soils have an average thickness of the humus horizon of 88 and 85 cm and contain about 8.5 and 8.8% humus in the arable layer. Humus reserves in horizons A + AB is 623 and 629.5 t/ha and in a meter layer is 653.5 and 672.5 t/ha.

Free Iron and Iron-Reducing Microorganisms in Permafrost and Permafrost-Affected Soils of Northeastern Siberia

An agreement between the content of amorphous (oxalate-extractable) iron and morphochromatic features of gley attests to the modern activity of gleyzation processes in tundra soils of the Kolyma Lowland, especially within lower parts of gentle and steep slopes. A suprapermafrost reduced gley horizon thawing out in the warmest years is considered a relic of the warmer and wetter stage of soil formation. An integrated analysis of data on the contents of mobile iron and annotated metagenomes indicates that microorganisms affiliated with the Proteobacteria phylum capable of iron reduction predominate in sediments formed under hydromorphic conditions and in modern mineral soil. In laboratory experiments, the process of microbial iron reduction was more active at 5°C than at 20°C. Therefore, it can be assumed that the majority of cultivated communities of iron-reducing bacteria have been adapted to low Arctic temperatures. Under conditions of climate warming and an increase in precipitation, permafrost temperature, and thickness of the seasonally thawed layer, iron reduction processes in the soils rich in the total iron will play an even greater role and create favorable redox conditions for the formation of methane, one of the most important greenhouse gases.

Study of organic-matter intercalated vermiculitic phases in the hydromorphic red earth sediments

Al-hydroxy intercalated vermiculitic phases have been widely observed in pedogenic environment, but soil organic intercalations have rarely been reported. In the present study, mixed-layer illite–vermiculite (I/V) with organic matter (OM) intercalation under hydromorphic conditions in the Xuancheng red earth sediments was investigated in order to better understand the interlayer components occurring in mixed-layered clay minerals and the formation of this unusual OM interlayered mixed-layer clay species. Selective extraction of organic fillings by ammonium ethylene diamine tetraacetic acid (EDTA) and acid ammonium oxalate (NH4OX) showed that the components associated with organic complexes in the interlayer space of the 2:1 clays are mainly Fe- and A1-(oxy)hydroxides, which block substantial swelling after ethylene glycol solvation and complete collapse after heating. The OM interlayer filling contains CH3(CH2), CO, COO-, and NH functional groups and are resistant to H2O2 extraction although the binding intensity to the interlayer surface may change. Upon heating to ~300 °C the OM filling escapes from the interlayer space which causes the collapse of the 2:1 clay species. Alteration of primary illite during pedogenesis causes release of K and intercalation of hydrated cations in the interlayer space, and also leaching of Al and Fe. There is accumulation of exchangeable cations and Al and Fe oligomers in the interlayer region, which affects the behavior of I/V clays on glycolation and heating. Hydromorphic conditions favor the transformation of organic polymers into small size organic acids, and thus, favor the intercalation of interlayer OM filling into the 2:1 clays. Pedogenesis processes involves both the weathering of clay minerals and the decomposition of OM, leading to formation of interlayer clay-organic complexes in a hydromorphic soil.

Quality reference values for heavy metals in soils developed from basic rocks under tropical conditions

Soil Quality Reference Values (QRV) refer to the natural heavy metal concentrations that is not influenced or is minimally influenced by anthropogenic activities. Such values are unique of each environment, and their extrapolation to different locations becomes inadequate. This research aimed to determine the natural concentrations of metals in soils (QRV) developed on essentially basaltic lithology and tropical conditions in the south of Brazil. Seventy-two soil samples from the Forest Conservation Areas in the west of the state of Paraná, Brazil, were obtained. The extraction and dosage of Ag, As, Ba, Cd, Cr, Cu, Mo, Ni, Pb, Sb, V, and Zn were carried out employing methods USEPA 3051a and ICP-OES. The QRV was set to 75th percentile of each element, from the detection and exclusion of the outliers. The natural concentration of all heavy metals was related to the geological context of the basaltic area in Brazil. There was no influence of the pedogenetic degree of soils on the natural heavy metal concentration. The only relevant process for reducing the natural heavy metal levels was the Fe and Mn oxide solubility promoted by hydromorphic conditions. Fe oxides had a significant role in the maintenance of structural and adsorbed heavy metal forms in soils. The results may help the research and monitoring of environmental heavy metals in soils developed from basalt under tropical conditions.

Landscape evolution across the Cretaceous/Paleogene boundary in southwestern North Dakota, U.S.A.

The Hell Creek Formation and overlying Fort Union Formation record a geologically rapid base-level rise that was approximately contemporaneous with the K/Pg extinction and deposition of Chicxulub-impact indicators. An outstanding question that remains is whether this base-level rise is attributable to: 1) a multi-thousand-year transgression adjacent to a relatively low-relief coastal plain, causing a rise in the water table; or 2) catastrophic flooding due to upland denudation, rapid channel accretion, and hydrologic reorganization resulting from wildfires/deforestation consequential of the impact. Herein we aim to address which of these hypotheses is most consistent with a paleolandscape reconstruction at Mud Buttes, a locality where the boundary clay (BC) is coincident with the Hell Creek-Fort Union contact. One hundred twenty-seven trenches were examined laterally across ∼2 km transect of K/Pg boundary. The uppermost Hell Creek is comprised of three pedotypes: Pale-Silt Inceptisol (PSI), Olive-Clay Vertisol (OCV), and Chocolate-Clay Vertisol (CCV), which range from moderately well-drained, to variable to poorly drained, to very poorly drained, respectively. All of the BC occurs superjacent to the CCV, despite this pedotype accounting for only ∼50% of the pre-event landscape. The edaphic features preserved in the CCV pedotype are not attributable to Paleogene overprinting, which indicates that hydromorphic conditions began prior to the impact. Furthermore, 46% of BC is overlain by lignite, despite lignite occurrence on 17% of the earliest Paleogene landscape. This reveals that the poorest-drained landscape positions of the latest Cretaceous persisted across the boundary. These relationships are most consistent with a non-catastrophic base-level rise.