Hydromorphic Soils Research Articles

Monitoramento contínuo do potencial redox e de variáveis complementares em ambiente hipersazonal no Pantanal Norte

A análise conjunta do potencial redox com outras variáveis pode ser útil para o entendimento da dinâmica dos solos hidromórficos, ao longo de todo o ciclo hidrológico a que o Pantanal está submetido. Neste trabalho, foram estudados o potencial redox e algumas variáveis do solo (CO2, O2, temperatura, umidade e potencial matricial) pelo monitoramento contínuo e ininterrupto. Para isso, foram realizadas determinações nas profundidades de 10 e 30 cm num Planossolo Háplico alítico gleissólico, na fitofisionomia Cerrado sensu stricto. O trabalho foi realizado de fevereiro de 2010 a julho de 2011 na RPPN (Reserva Particular do Patrimônio Natural/Sistema Nacional de Unidades de Conservação - SNUC), Estância Ecológica SESC (Serviço Social do Comércio) Pantanal, município de Barão de Melgaço, nordeste do Pantanal de Mato Grosso. Os valores do potencial redox variaram de 636 mV (enchente) a -341 mV (cheia), caracterizando ambiente anaeróbico na estação da cheia e ambiente oxidado nas demais estações do ciclo hidrológico, o que indica que o potencial redox é ferramenta versátil para compreender as reações de oxirredução nos solos hidromórficos do Pantanal mato-grossense, pois os valores diminuíram quando o teor de umidade era elevado. Além disto, o estudo evidenciou também que o monitoramento contínuo de variáveis complementares pode ser importante por permitir análise mais aprofundada das condições de hipersazonalidade, em que esses solos estão submetidos. Neste contexto, o potencial matricial e a umidade foram as variáveis de maior importância para explicar a variação do conjunto de dados obtidos ao longo do ciclo hidrológico, o que indica que esses parâmetros físicos são determinantes nos processos biológicos desse solo tropical com hipersazonalidade hídrica.

Differential radial growth patterns between beech (Fagus sylvatica L.) and oak (Quercus robur L.) on periodically waterlogged soils

Climate scenarios for northern Central Europe project rising temperatures and increasing frequency and intensity of droughts but also a shift in precipitation pattern with more humid winters. This in turn may result in soil waterlogging during the following spring, leading to increasing stress for trees growing on hydric sites. The influence of waterlogging on growth of common beech and pedunculate oak has been studied intensively on seedlings under experimental conditions. However, the question remains whether results of these studies can be transferred to mature trees growing under natural conditions. To test this, we investigated general growth patterns and climate-growth relationships in four mature stands of beech and oak growing on hydromorphic soils (Stagnosols) in northeast Germany using dendrochronological methods. Our results confirmed the expected tolerance of oak to strong water-level fluctuations. Neither extremely wet conditions during spring nor summer droughts significantly affected its radial growth. Oak growth responded positively to warmer temperatures during previous year October and March of the current year of ring formation. Contrary to our expectations, also beech showed relatively low sensitivity to periods of high soil water saturation. Instead, summer drought turned out to be the main climatic factor influencing ring width of beech even under the specific periodically wet soil conditions of our study. This became evident from general climate-growth correlations over the last century as well as from discontinuous (pointer year) analysis with summer drought being significantly correlated to the occurrence of growth depressions. As ring width of the two species is affected by differing climate parameters, species-specific chronologies show no coherence in high-frequency variations even for trees growing in close proximity. We assume differences in rooting depth as the main reason for the differing growth patterns and climate correlations of the two species under study. Our results indicate that under the projected future climate scenarios, beech may suffer from increasing drought stress even on hydromorphic soils. Oak might be able to maintain a sufficient hydraulic status during summer droughts by reaching water in deeper soil strata with its root system. Wet phases with waterlogged soil conditions during spring or summer appear to have only a little direct influence on radial growth of both species.

A computer vision approach to quantify leaf anatomical plasticity: a case study on Gochnatia polymorpha (Less.) Cabrera

Inferences about leaf anatomical characteristics had largely been made by manually measuring diverse leaf regions, such as cuticle, epidermis and parenchyma to evaluate differences caused by environmental variables. Here we tested an approach for data acquisition and analysis in ecological quantitative leaf anatomy studies based on computer vision and pattern recognition methods. A case study was conducted on Gochnatia polymorpha (Less.) Cabrera (Asteraceae), a Neotropical savanna tree species that has high phenotypic plasticity. We obtained digital images of cross-sections of its leaves developed under different light conditions (sun vs. shade), different seasons (dry vs. wet) and in different soil types (oxysoil vs. hydromorphic soil), and analyzed several visual attributes, such as color, texture and tissues thickness in a perpendicular plane from microscopic images. The experimental results demonstrated that computational analysis is capable of distinguishing anatomical alterations in microscope images obtained from individuals growing in different environmental conditions. The methods presented here offer an alternative way to determine leaf anatomical differences.

Surface charge and growth of sulphate and carbonate green rust in aqueous media

We report the first determination of the point of zero charge of sulphated and carbonated green rust particles. Green rust has been recognised as a prevalent mineral in environments such as hydromorphic soils, groundwaters and anoxic Fe(II)-rich water bodies, and the evolution of its net surface charge with pH has direct implications for the uptake of contaminants, metals and nutrients in such settings. We find that the surface of both sulphated and carbonated green rust is positively charged at pH<8.3, whereas it is negatively charged at pH>8.3. Thus, alkaline settings will promote enhanced adsorption of metallic cations. However, the behaviour of ionic species surrounding green rust is more complicated than that predicted by simple pH-dependent adsorption, as our experiments suggest that green rust likely grows via dissolution–reprecipitation during Ostwald-ripening. This implies that adsorbed species are potentially subject to repetitive steps of release into solution, re-adsorption and co-precipitation during particle growth. The growth rate of green rust particles is highest within the first 50min of aging, and appears to decrease towards an asymptote after 200min, suggesting that particle growth controls on the uptake of dissolved species will be most important during the early steps of green rust growth. Our findings thus contribute to a better understanding of the controls that green rust may exert on dissolved ions in a variety of anoxic environments.

Survival and Speed of Escherichia coli Infiltration in a Hydromorphic Soil in Wet Tropical Zone

Survival and Speed of Escherichia coli Infiltration in a Hydromorphic Soil in Wet Tropical Zone

Biomobilization of Heavy Metals from the Sediments Affect the Bacterial Population of Al-Ghadir River (Lebanon)

Although there is no doubt about the importance of the bacterial activity on the solubilisation and the distribution of heavy metals in aquatic sediments, hydromorphic soils and ground waters; little is known about the involvement of bacterial dissolution in periodically anaerobic environments like that found in dredged sediments and little is known about the processes and the environmental factors controlling this process.The aim of this paper was to study the effect of the autochthonous bacterial activity on the biodegradation of organic matter and the mobilization of heavy metals in the sediments of Al-Ghadir river (Mount Lebanon). Sediments were incubated under standard anaerobic conditions and enriched with glucose to stimulate and accelerate microbial metabolism. The evolution of carbon metabolism (Organic matter evolved, carbon consumed and organic acids produced) and metals released in batch reactors were followed over time. Under the adopted conditions, analysis of the chemical parameters indicated that the incubated sediments showed a significant release of organic carbon corresponding to bacterial development. Mineral analysis showed an important solubilisation of Fe2+ and Mn2+ indicating the presence of Fe- and Mn-reducing bacteria in sediments. Pb, Cd and Cr solubilisation profiles were observed and appeared concomitant to the solubilisation profiles of Fe and Mn indicating that the redox cycle has been well installed and that Pb, Cd and Cr were associated to Fe and Mn oxides. The production of Cu appeared in parallel to the mineralization of the organic matter in the sediment indicating that Cu was associated to this fraction. Zn appeared associated to the sulphide fraction than to the Fe and Mn oxides fraction. Microbiological and genetic analysis showed a decrease and the disappearance of some bacterial strains due to the shift in the culture conditions and the toxicity of the released heavy metals but at the same time the development and the growth of many other populations which showed to be tolerant to the same conditions

Effect of livestock on soil structure and chemistry in the coastal marshes of the central Gulf Coast of Mexico

Wetlands are among the most productive ecosystems on earth because of their high ecological and economic value. On the central Gulf Coast of Mexico, there are numerous coastal wetlands, although 58% of their area has been lost or degraded due to management activities, among them raising livestock. Globally, little is known about the effect of this activity on hydromorphic soils of herbaceous wetlands, and in Mexico, there is even less knowledge. This study assessed the degree of impact of livestock on soil physicochemical properties of the coastal marshes of Alvarado, in the south of Veracruz. In four sampling sites (two organic and two with mineral soils) with different levels of impact, soil samples were taken during one year to obtain data on variables such as bulk density, total porosity, organic matter, pH, and nutrients. At sites where the stocking was low, cattle were rotated once a year and the hydrology was unaltered, and soil hydromorphic intrinsic properties were preserved. The results of this study should be considered in the development of strategies for the management and conservation of these tropical ecosystems, as a means to achieve sustainable livestock farming in wetlands.

O uso da terra e as implicações sócio-ambientais na zona úmida do Rio Araguaia, Estado de Goiás, Brasil

The Araguaia River is one of the largest in Brazil and certainly the most significant for the state of Goiás. It played a central role in the discovery of, and settlement in, the hinterlands of central Brazil. The Aruaguia river basin, in between its source and its mouth, is usually divided into three segments – High, Middle and Lower Araguaia – to which correspond different types of landscape. The present study focuses on a segment of the Middle Araguaia that stretches from the Registro do Araguaia district (municipality of Montes Claros) to the southern tip of the Bananal island (municipality of São Miguel do Araguaia). The study area occupies an area of 4,430 km² and is characterized by its smooth relief and hydromorphic soils, which are associated with a discontinuous strip of flood plain. Occupation of the study area intensified from the 1960s onwards, and was driven mostly by pastoralists who were attracted to the area by the low price of the land, the public policy of colonization and the physical characteristics of the region. This article presents an environmental characterisation of these wetlands, based on the interpretation of data acquired through remote sensing and a field work. It then discusses the predominant types of land use and their socio-environmental implications. The analysis refers to the year 2007 and indicates the existence of a number of serious threats to the integrity of the wetlands of the Araguaia River, whose relevance in terms of natural heritage has been acknowledged at the national level. In particular, the results show that 61% of the study area is allocated to either cattle farming or agriculture, and that the predominant economic activity, cattle farming, takes up 42% of that area.

Specific features of soil organic matter in forest landscapes of Karelia

The organic matter reserves and the soil humus state are assessed in three types of landscapes of the middle taiga (Karelia). Peat soils are the main organic matter reservoir. Hence, the greater their area, the higher the organic matter reserves in a particular landscape. The organic matter stocks in the group of semihydromorphic and hydromorphic soils clearly correlate with the degree of their waterlogging. The distribution of organic matter reserves within these soils depends on the ratio between the areas of boggy forests and open mires. The forest supporting quality of the soil is related to the organic matter composition and parent rock (the properties of the soil mineral horizons) rather than to the organic matter stocks. The data obtained may be used for assessing the forest supporting qualities of the soils and the basis for estimating the carbon budget in the landscapes.

Greater abundance of Fagus sylvatica in coniferous flood protection forests due to climate change: impact of modified root densities on infiltration

Climate change is expected to modify the spatial distributions of zonal forest communities and thus, their species compositions. The aim of this paper was to study the impact of higher abundance of beech on water storage capacity in current coniferous flood protection forests due to varying root densities of the main tree species. Two forest communities in the northern pre-Alps in Switzerland with similar soil properties but varying in species composition were investigated (space-for-time substitution). It was assumed that the Vaccinio myrtillii-Abieti-Piceetum (site A) will be replaced by a Luzulo-Abieti-Fagetum (site B). We irrigated 16 hydromorphic soils (1 m2, 70 mm/h, three consecutive irrigations) at site A and 10 at site B and recorded water-content variations with time domain—and frequency domain reflectometry. Roots were extracted from soil cores taken from the positions where the water-content probes were inserted, and digitally measured. Infiltration capacity ω I was mainly limited to the upper soil at site A but was approximately constant down to 0.7 m depth at site B. Between 0.3 and 1.0 m soil depth, root densities at site B exceeded those at site A. Root density was the main predictor for ω I (R 2 = 0.57) at site A as shown by a multiple linear regression analysis. Assuming that the root density in the current coniferous forest (A) will increase to that of the beech stand (B) due to the greater abundance of beech, the water storage capacity will increase by 9.2 mm in consequence of the expected forest transformation.

Individual organic compounds in water extracts from podzolic soils of the Komi Republic

The contents of organic compounds in water extracts from organic horizons of loamy soils with different water contents from the medium taiga zone of the Komi Republic were determined by gas-liquid chromatography and chromatography-mass spectrometry. The mass concentration of organic carbon in the extracts was in the range of 290–330 mg/dm3; the mass fraction of the carbon from the identified compounds was 0.5–1.9%. Hydrocarbons made up about 60% of the total identified compounds; acids and their derivatives composed less than 40%. Most of the acids (40–70%) were aliphatic hydroxy acids. The tendencies in the formation of different classes of organic compounds were revealed depending on the degree of the soil hydromorphism. The acid properties of the water-soluble compounds were studied by pK spectroscopy. Five groups of compounds containing acid groups with similar pKa values were revealed. The compounds containing groups with pKa < 4.0 were predominant. The increase in the surface wetting favored the formation of compounds with pKa 3.2–4.0 and 7.4–8.4.

Influence of hydromorphic soil conditions on greenhouse gas emissions and soil carbon stocks in a Danish temperate forest

Recent research has shown that wet or hydromorphic soils in forests are hotspots for greenhouse gas (GHG) emission of methane (CH4) and nitrous oxide (N2O), and that emission of these gases may offset the mitigation potential from carbon (C) sequestration. However, quantitative evidence at the forest scale is limited. We investigated the role of hydromorphic soils for N2O and CH4 fluxes at the forest district level (Barritskov, 348ha) by mapping the distribution of upland and hydromorphic soils, measuring the soil carbon and nitrogen stocks and field fluxes of N2O and CH4 for a period of 2years as well as in laboratory experiments.Field exchange rates of N2O (mean±standard error of the mean(SE), μgN2O–Nm−2h−1) were similar for hydromorphic (3.8±1.2) and upland soils (3.8±0.4). Although both soil types displayed net CH4 oxidation the average rate (μgCH4–Cm−2h−1) was significantly lower in hydromorphic soils (−5.8±2) compared to the upland soils (−23±1.2). Soil water content (SWC) was, as expected, higher in hydromorphic soils which was consistent with lower uptake of CH4 as well as significantly larger soil carbon stocks in O horizon plus 0–30cm mineral soil (86±6 versus 66±5MgCha−1 in hydromorphic versus upland). Oxidation rates of CH4 in laboratory incubations at ambient concentration (2μLL−1) were similar in the two soil types, but the hydromorphic soils oxidised CH4 fastest when incubated at 10,000μLL−1CH4: only hydromorphic soils produced CH4. Potential N2O production did not differ between soil types and N2 production was significantly higher in hydromorphic soils, which also had a higher pH>6.Based on four scenarios, we assessed how reduced ditching might affect the emissions of N2O and CH4 from upland soils. The CH4 sink of the soil decreased in all four reduced ditching scenarios from 1.3 to 7MgCO2-equivalent (eqv)y−1. The emissions of N2O and CH4 in the current state and all scenarios comprised only a minute fraction (<1%) of the global warming potential (GWP) of carbon stored in the soil.We conclude that hydromorphic soils are potential hotspots for CH4 production and reduced uptake of atmospheric CH4, but their limited area covered by such soils at Barritskov implies that upland soils are most important in terms of soil C stock and the non-CO2 GHG budget. Ceased drainage activities in upland soils are expected to increase the likelihood of CH4 emissions and reduce soil CH4 uptake.

Origin and K/Ar age of cryptomelane-bearing Sn placers on silcretes, SE Germany

During the early Miocene (Aquitanian–Burdigalian) an alluvial–fluvial drainage system evolved along the boundary fault of the Münchberg Gneiss Complex in SE Germany. The resultant NE–SW trending channel system collected debris from the enclosing Paleozoic country rocks and from gossans of cassiterite-bearing veins exposed to denudation in the roof rocks of the adjacent Late Variscan Sparnberg-Pottiga Granite. Three different types of placer minerals occur: (1) isolated grains of cassiterite, (2) armored relics of cassiterite and barite, (3) remobilized and redeposited silica aggregates. Silica is present in a zone of silcretes, in mechanically redeposited pebbles within this depression and in cobbles of quartz gangue derived from the nearby vein-type deposits. These silcretes developed from alkaline fluids and were redeposited under semiarid conditions with dryer (period of solution) and wetter seasons (period of redeposition) at ≥23Ma. Cryptomelane I formed under dry conditions around 23Ma when the pore space of the channel lag deposits was incompletely filled with water, whereas goethite points to more humid climatic conditions between 23 and 17Ma as the fluids were more acidic. Cryptomelane II filled the pore space of the clastic sediments to completeness on increasing humidity at ≤17Ma. The mineral association under study pertains to the group of supergene Fe–Mn deposits (Hunsrück-type) whose ore-forming processes span a wide range from pedological/ground water-related Fe–Mn concentration in hydromorphic soils to alluvial–fluvial pebble or placer-type concentrations. The current investigations involved geological mapping and geoelectrical DC deep sounding in the field and optical microscopy, SEM-EDX, and K/Ar age dating of cryptomelane in the laboratory.

Effect of long-term free-air CO2 enrichment on the diversity and activity of soil methanogens in a periodically waterlogged grassland

As atmospheric CO2 levels continue to rise researchers now identify concomitant changes in plant biomass and diversity, which are postulated to alter the quality and quantity of the organic carbon entering the soil. In anoxic soils, CH4 is the end product of the degradation of organic carbon and the system's terminal electron sink. Some soils (such as wetlands) are usually waterlogged and therefore constitute permanent CH4 sources, while others (hydromorphic soils) are only occasionally saturated with water and alternate between acting as net CH4 sources or sinks. Since methanogenesis is ultimately dependent on soil organic carbon, we hypothesized that a long term alteration of the latter will cause changes in type and magnitude of the former. To test this, we studied the effect of 10 years of atmospheric CO2 enrichment on the methanogenic potential and community in a hydromorphic temperate grassland soil at the experimental Free Air Carbon dioxide Enrichment (FACE) site in Giessen, Germany. While all soils demonstrated methanogenic potential, we detected no significant changes in CH4 production rates, lag times, methanogenic pathways, diversity, or population sizes in soils that were exposed to either 20 or 30% elevated ambient CO2. Our findings suggest that the methanogenic potential of the soil and the methanogenic community might be insensitive to changes in atmospheric CO2 concentrations, at least not on a decadal timescale. Thus, if our results can be extrapolated to other temporarily flooded or even wetland ecosystems, the often-observed increase in CH4 emissions under elevated CO2 may simply be due to an increase in labile-C input via living root and increasing fresh litter deposition, but not due to shifts in the microbial population characteristics. This could make it easier to model and extrapolate the global effect of elevated CO2 on terrestrial CH4 emissions.

Green Rust Formation during Fe(II) Oxidation by the Nitrate-Reducing Acidovorax sp. Strain BoFeN1

Green rust (GR) as highly reactive iron mineral potentially plays a key role for the fate of (in)organic contaminants, such as chromium or arsenic, and nitroaromatic compounds functioning both as sorbent and reductant. GR forms as corrosion product of steel but is also naturally present in hydromorphic soils and sediments forming as metastable intermediate during microbial Fe(III) reduction. Although already suggested to form during microbial Fe(II) oxidation, clear evidence for GR formation during microbial Fe(II) oxidation was lacking. In the present study, powder XRD, synchrotron-based XAS, Mössbauer spectroscopy, and TEM demonstrated unambiguously the formation of GR as an intermediate product during Fe(II) oxidation by the nitrate-reducing Fe(II)-oxidizer Acidovorax sp. strain BoFeN1. The spatial distribution and Fe redox-state of the precipitates associated with the cells were visualized by STXM. It showed the presence of extracellular Fe(III), which can be explained by Fe(III) export from the cells or extracellular Fe(II) oxidation by an oxidant diffusing from the cells. Moreover, GR can be oxidized by nitrate/nitrite and is known as a catalyst for oxidation of dissolved Fe(II) by nitrite/nitrate and may thus contribute to the production of extracellular Fe(III). As a result, strain BoFeN1 may contribute to Fe(II) oxidation and nitrate reduction both by an direct enzymatic pathway and an indirect GR-mediated process.

Structural and productive-developmental characteristics of white willow plantations of different density on humogley in Donji Srem

The study was conducted in two plantations of white willow (Salix alba L.) in Donji Srem on the humogley soil type (hydromorphic black soil), which belongs to a narrow-leaved ash forest with remote sedge (Carici remotae - Fraxinetum angustifoliae Jov. et Tom., 1979). The plantations are located in the same depression. The SP (sample plot)-1 plantation is 21 years old with a 6?6 m planting spacing, and the SP-2 plantation is 27 years old with a 3?3m planting spacing. Elements of stem growth in the SP-1 plantation showed that with the white willow planting spacing of 6?6 m and a planned 25-year production cycle it is possible to obtain about 250 m3?ha-1 of timber volume, with an 80% net share of technical wood and a 20 % share of pulp wood. The plantation in SP-2 is at the age, which is well above the optimum age in terms of rational management, and the total volume at the age of 27 years is about 300 m3?ha-1, with a 53.7% net share of technical wood and a 46.3% share of pulpwood.

État des ressources pastorales dans une terre d’accueil et de transit des pasteurs transhumants : le terroir de Kotchari (sud-est du Burkina Faso)

The condition of pastoral resources of a land of reception and transit for transhumant herders : the Kotchari territory (Southeastern Burkina Faso). Kotchari pasturelands, which include a portion of the W National Park, were characterized by three complementary methods : an analysis of a colour composition of an Aster image, a floristical analysis and a pastoral survey. Nine pastoral landscape units with diverse tree cover were described, they include ten agrostological groups. The landscape units located outside the protected area, especially on thin to fairly deep soils, show the highest density in ligneous species and the highest herbaceous richness as well as the least dominance between species. Conversely, herbaceous phytomass and ligneous cover are higher in the protected area, particularly on the deep hydromorphic soils units. In addition, these units are more or less heterogeneous, some containing several agrostological groups. In general, the pasture lands located outside the protected area tend to be the most degraded : in some of them there is a regeneration of trees and a decrease of perennial herbaceous species. In all, although the phytomass is rather abundant and the pastoral values are acceptable in most units, those located outside the W park appear not very interesting in terms of pastoral use. Their ability to produce herbaceous regrowth after vegetation fires is low, the landscape is highly fragmented and the access to some units is not possible all year long. The pastoral status of the pastoral units inside the protected area, which have the highest phytomasses and the best pastoral values, is clearly much better. The strong interest of transhumant herders in this region seems guided on the one hand by the quality and availability of forage that is better at the end of the dry season than in their home grazing territory, and on the other hand by the opportunity of illegal use of pastoral resources in protected areas.

Isolation of Phyllosilicate–Iron Redox Cycling Microorganisms from an Illite–Smectite Rich Hydromorphic Soil

The biogeochemistry of phyllosilicate–Fe redox cycling was studied in a Phalaris arundinacea (reed canary grass) dominated redoximorphic soil from Shovelers Sink, a small glacial depression near Madison, WI. The clay size fraction of Shovelers Sink soil accounts for 16% of the dry weight of the soil, yet contributes 74% of total Fe. The dominant mineral in the clay size fraction is mixed layer illite–smectite, and in contrast to many other soils and sediments, Fe(III) oxides are present in low abundance. We examined the Fe biogeochemistry of Shovelers Sink soils, estimated the abundance of Fe redox cycling microorganisms, and isolated in pure culture representative phyllosilicate–Fe oxidizing and reducing organisms. The abundance of phyllosilicate–Fe reducing and oxidizing organisms was low compared to culturable aerobic heterotrophs. Both direct isolation and dilution-to-extinction approaches using structural Fe(II) in Bancroft biotite as a Fe(II) source, and O2 as the electron acceptor, resulted in recovery of common rhizosphere organisms including Bradyrhizobium spp. and strains of Cupriavidus necator and Ralstonia solanacearum. In addition to oxidizing biotite and soluble Fe(II) with O2, each of these isolates was able to oxidize Fe(II) in reduced NAu-2 smectite with as the electron acceptor. Oxidized NAu-2 smectite or amorphous Fe(III) oxide served as electron acceptors for enrichment and isolation of Fe(III)-reducing microorganisms, resulting in recovery of a strain related to Geobacter toluenoxydans. The ability of the recovered microorganisms to cycle phyllosilicate–Fe was verified in an experiment with native Shovelers Sink clay. This study confirms that Fe in the native Shovelers Sink clay is readily available for microbial redox transformation and can be cycled by the Fe(III)-reducing and Fe(II)-oxidizing microorganisms recovered from the soil.

Transformation of the salt structure of soils of the stony steppe during agricultural use

The salt structure and structure of salt profiles of automorphic and hydromorphic soils of stony steppes on fallow land and arable land are studied. It is shown that during agricultural use of these soils the general maintenance of salts in a profile, including that in the root-inhabited layer, increases and the type of salt changes. In cation structures the quantity of Na+ and, to a lesser degree, of Ca2+, increase, and in the anion structure CO 3 2− increases. It is shown that the most significant transformation of the salt mode of soils during agricultural use is observed in soils with low humidity.

Iron compounds and oil biodegradation in overmoistened contaminated soils: A review of publications

In Russia, the areas of oil pollution gradually shift toward the north into the zone of increased moistening with widespread hydromorphic soils. In this zone, the role of the rapid aerobic degradation of hydrocarbons decreases, while that of slow anaerobic degradation increases. The biological reduction of Fe(III) only proceeds at the expense of the energy of oxidation of organic substances, including oil hydrocarbons, in the oil-polluted soils. This favors the development of technogenic gleying. In contrast to the uncontaminated background soils, in which gleying is correctly considered a degradation process, the same process in the oil-contaminated mineral soils plays a positive role, because it is accompanied by the oxidation of organic pollutants, which otherwise penetrate into rivers and lakes with water flows. The role of Fe(III) reduction may be significant: at one of the oil-spill sites, one-third of the organic pollutants degraded within twelve years after an accident in the anaerobic zone due to Fe(III) reduction. Both iron hydroxides and clay minerals enriched in Fe(III) participate in the reduction processes. In the anaerobic zone, the destruction of organic pollutants begins several years after the relevant natural microorganisms become active. The reduction of Fe(III) reaches its maximum faster than the process of methanogenesis. Upon the soil’s cooling in the winter, the reduction of Fe(III) is replaced by the spontaneous formation of iron oxides (oxidogenesis). Thus, alternating reduction ↔ oxidation reactions proceed in the soils with a contrasting temperature regime. Iron oxides formed in the winter are reduced to Fe(II) in the summer and, thus, resume the associated oxidation of organic pollutants upon the stagnant moisture regime. Therefore, upon monitoring of hydromorphic oilcontaminated soils, special attention should be paid to the forms of iron compounds.