T. A. Sokolova

Adsorption of sulfate ions by soils (A Review)

The literature data on the adsorption of sulfates by soils were reviewed. Factors affecting the adsorption of sulfates and the major mechanisms of sulfate adsorption were considered, including the most important of them: the ligand exchange with the formation of surface outer-and innersphere complexes and the Coulomb interaction with the surface of mineral particles. Equations describing the adsorption isotherms of sulfates are given; some methods for the mathematical simulation of sulfate ion behavior in the “soil solid phase-soil solution” system are discussed.

Pedogenic chlorites in podzolic soils with different intensities of hydromorphism: Origin, properties, and conditions of their formation

Minerals of the pedogenic chlorite group were studied in the clay fractions isolated from the mineral horizons of podzolic and gleyic peat-podzolic soils. In the AE and E horizons of the podzolic soil, pedogenic chlorites are thought to develop from vermiculite, whereas in the E horizon of the gleyic peat-podzolic soil, they can be formed from smectite minerals. For estimating the degree of chloritization (the degree of filling of the interlayer space of 2: 1 minerals with Al hydroxides), a numerical criterion was is proposed. The difference between the values of this criterion before and after the treatment of the preparations with NH4F indicated that the degree of chloritization in the pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the AE horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil. Another numerical criterion was proposed to estimate the degree of polymerization of Al-hydroxy complexes in pedogenic chlorites. This criterion was based on the thermal stability of soil chlorites and represented the temperature at which an increase in the intensity of the 1.0-nm peak after heating the K-saturated preparations exceeds 50% of its initial value. According to this criterion, the degree of polymerization of the Al-hydroxy interlayers in pedogenic chlorites decreases in the following sequence: the E horizon of the podzolic soil > the E horizon of the gleyic peat-podzolic soil ≥ the AE horizon of the podzolic soil. The distinct interrelation between the soil properties and the degrees of chloritization and polymerization of the Al-hydroxy interlayers attests to the modern origin of the pedogenic chlorites.

The role of soil biota in the weathering of minerals: A review of literature

Two methodological approaches used in the study of the mineral weathering in soils under the effect of biota were analyzed. According to one approach, which is based on the concepts of coordination chemistry, the dissolution of minerals is considered at the ion-molecule level and can be described using the terms and notions of classical thermodynamics. According to the other approach, the weathering of minerals in the supergenesis zone is considered at the ion-electron level within the framework of the corrosion model of supergenesis on the basis of anode-cathode processes, when the mineral in the electrolyte environment serves as an anode and is oxidized being an electron donor. Microorganisms act as a cathodic associate of minerals, i.e., an electron acceptor. The kinetic parameters related to the rate of the biological processes and the diffusion come out on top in this case. The review deals with the mechanisms of the direct and indirect effect of biota on the weathering of minerals in soils; the features of the soil in the rhizosphere and the ectomycorrhizosphere; the impact of fungi, bacteria, and higher plants on the minerals; and the generated synergistic effect.

Aluminum Compounds in Soil Solutions and Their Migration in Podzolic Soils on Two-layered Deposits

The fractional composition of aluminum compounds was studied in soil solutions obtained using vacuum lysimeters from loamy podzolic soils on two-layered deposits. The concentration of aluminum was estimated in brooks and a river draining the area with a predominance of these soils. In soil solutions, the concentration of aluminum was experimentally determined in the following compounds: (1) organic and inorganic monomers, (2) stable complexes with HAs and FAs together with polymers, and (3) the most stable complexes with HAs and FAs together with fine-crystalline and colloidal compounds. The total Al concentration in soil solutions from forest litter was 0.111–0.175 mmol/l and decreased with depth to 0.05 mmol/l and lower in solutions from the IIBD horizons. More than 90% of the Al in the solutions was bound into complexes with organic ligands. Some amount of Al in solution could occur in aluminosilicate sols. The translocation of Al complexes from the litter through the AE horizon to the podzolic horizon was accompanied by an increase in the ratio between the Al concentration in fraction 2 and the C concentration in the solution. The concentrations of Altot in the surface waters varied in the range from 0.015 to 0.030 mmol/l. Most of the Al came to the surface waters from the litter and AE horizons and partially from the podzolic horizon due to the lateral runoff along the waterproof IIBD horizon. Approximate calculations showed that the recent annual removal of Al from the AE and E horizons with the lateral runoff was 7 to 560 mg (3–21 mmol) from 1 m2.

Biotite weathering in podzolic soil under conditions of a model field experiment

The biotite changes in the 1–5 μm fraction after its occurrence in the F, H, AE, and E horizons of a pale-podzolic soil for five years under conditions of a model field experiment were assessed by X-ray diffraction analysis. It was found that the main changes of the biotite in all the horizons included the degradational transformation of its crystal lattice to interstratified mica-vermiculite structures and vermiculite. The intensity of this process gradually decreased from the F horizon down the profile in parallel with the decrease in the amount of roots and the abundance and activity of microbiota. Chloritized structures were present among the products of the biotite weathering in the H, AE, and E horizons; the degree of chloritization gradually increased from the H horizon to the E horizon. The main identified products of the biotite weathering in the AE and E horizons formed during the 5 years of the model experiment were identified in the clay and fine-silt fractions from these horizons of the native pale-podzolic soils. Therefore, the vermiculite, soil chlorite, and mixed-layer illite-vermiculite minerals in the soils studied could be considered as products of the recent soil functioning. The obtained results and literature data showed that the weathering of biotite resulted in the formation of K- and Al-buffer systems.

Specificity of Soil Properties in the Rhizosphere: Analysis of Literature Data

An analysis of literature is given on the following problems: a concept of the rhizosphere and its boundaries, a notion of border cells, the composition and the role of root exudates, the role of ectomycorrhyzal fungi and the biological activity of soils in the rhizosphere, and the specificity of some chemical and physical properties of soils in the rhizosphere. The soil of the rhizosphere is shown to differ significantly from the surrounding soil in most characteristics concerning both the composition of the solid phase and soil solution and the function of individual components of the soil system. The rhizosphere soil has a great number of microorganisms and they have high diversity. The most important specific features of soils in the rhizosphere are related to a continuous input of root exudates, metabolic products of microorganisms and border cells. The presence of these diverse substances leads to significant changes in the cycles of chemical elements, intensification of the carbon cycle, weathering, and decomposition of organic matter. Some compounds composed root exudates, which promote the microbial synthesis of ethylene—a signal controlling the development of plants—and can cause chemotaxis.

The acid-base buffer capacity of podzolic soils and its changes under the impact of treatment with the Mehra-Jackson and Tamm reagents.

The acid-base buffer capacity before and after the treatment with the Mehra-Jackson and Tamm reagents was assessed by continuous potentiometric titration for the main genetic horizons of two profiles of podzolic soils in the Central Forest State Reserve. The total buffer capacity was calculated in the pH range from the initial titration point (ITP) to 3 for the acid titration and from the ITP to 10 for the base titration, as well as the buffer capacities in the pH intervals of 0.25. It was found that both treatments abruptly decreased the base buffer capacity, which reached 70–90% in the E horizons. The high direct linear correlation of the difference between the total base buffer capacities before and after each treatment with the content of Fe in the Tamm extract was revealed. From the results obtained, a conclusion was drawn that finely dispersed Fe hydroxides were the main solid-phase constituents ensuring the base buffer capacity, and the deprotonation of hydroxyl groups on the surface of Fe hydroxides was the essential buffer reaction during the base titration.

Mobile aluminum compounds in soils of the southern taiga (soils of the central forest reserve as an example).

The profile distributions of aluminum extracted by the Tamm and Bascomb reagents and of the exchangeable aluminum were studied in soils of automorphic, transitive, and accumulative positions in the landscapes of the southern taiga. In the mineral horizons of the gleyic peaty-podzolic soils developed on poorly drained flat surfaces and in the floodplain soils, the distribution of oxalate- and pyrophosphate-soluble aluminum has a strongly pronounced accumulative character. In the podzolic soils of the automorphic positions and slopes, an eluvial-illuvial distribution was characteristic with the maximal aluminum content in the podzolic horizons. The strong differentiation of the upper part of the profile in the automorphic podzolic soils in terms of the Al content in the Tamm and Bascomb extracts is mainly related to an increase of the pedogenic chlorite content upon the transition from the AE to the E horizon. In the podzolic horizons of these soils, aluminum can accumulate in the form of proto-imogolite structures. The exchangeable aluminum displays an accumulative type of distribution. On the basis of calculating the reserves of the different aluminum compounds, two main accumulative zones for the mobile compounds of this element were recorded in the soils of the landscapes studied: the E horizon in the automorphic podzolic soils, where Al accumulates as soil chlorite or, probably, as proto-imogolite, and the A1 horizon of the floodplain soils, where Al accumulates in aluminoorganic complexes.

Laboratory simulation of the successive aerobic and anaerobic degradation of oil products in oil-contaminated high-moor peat

A model experiment has been performed on the successive aerobic and anaerobic degradation of oil products in samples of oil-contaminated peat sampled from a pine-subshrub-sphagnum bog near the Sutormin oilfield pipeline in the Yamal-Nenets autonomous district. During the incubation of oil-contaminated peat with lime and mineral fertilizers under complete flooding, favorable conditions are created for the aerobic oxidation of oil products at the beginning of the experiment and, as the redox potential decreases, for the anaerobic degradation of oil products conjugated with the reduction of N5+ and S+6 and methanogenesis. From the experimental data on the dynamics of the pH; Eh; and the NO3−, NO2−, and SO42− concentrations in the liquid phase of the samples, it has been found that denitrifiers significantly contributed to the biodegradation of oil products under the experimental conditions. After the end of the experiment, the content of oil products in the contaminated samples decreased by 21–26%.

Chemical and mineralogical characteristics of podzolic soils of the central forest reserve in the area of karst sinkholes

A specific feature of the soil developing near the edge of a sinkhole in comparison with the soil at a distance of 10 m from the sinkhole is the presence of calcareous horizon from the depth of 116 cm. The soil near the edge of the sinkhole is also characterized by the increased contents of exchangeable calcium and oxalatesoluble iron in the litter layers and in the AE horizon. This may be explained by a more active biological uptake of these elements under conditions of a shallow occurrence of carbonates. With respect to pH values; the contents and distribution of humus and exchangeable potassium, sodium, hydrogen, and aluminum; the mineralogical composition of the clay and fine silt fractions; and the distribution of oxalatesoluble iron compounds in the soil profiles, palepodzolic soils of the Central Forest State Biospheric Nature Reserve developing in karst areas do not differ from similar soils beyond karst areas.