No 2 (2023)

Physico-chemical properties and vertical distribution patterns of clay minerals in the weakly differentiated soils were studied. The soils are located in the Kolyma lowland plain; they have formed in a cold and ultracontinental climate. The study objects cover a broad range of the landscape diversity: the marsh and alas meadows and typical northern taiga landscapes. Despite the fact that weathering processes are weakly developed at high latitudes, mineral transformation represented by chlorite-illite association led to presence of (i) vermiculite in the acidic soil horizons of the alas meadow and the zonal northern taiga landscapes and (ii) iron hydroxide – lepidocrocite in the profile from the marsh meadow. It was shown that classification of the Kriozem located in the open woodland landscapes that are typical in the northern taiga does not cause difficulties based on the profile-genetic approaches of the national classification system. Oppositely, classification of the permafrost affected soils located in the intrazone landscapes of the marsh and alas meadows should be further clarified.

Using the method of sequential removal of various types of sorption surfaces, a qualitative assessment of the contribution of organic matter, non-silicate iron compounds, and clay minerals to the adsorption of Cu(II) by alluvial soddy-gley soil was carried out under the conditions of laboratory equilibrium experiments. It has been established that the contribution of each of the components is determined both by the ability to form surface inner-sphere complexes at pH-dependent positions, and by the availability of sorption centers in the places of localization of a constant charge of clay minerals. In the AY horizon, the main components sorbing Cu(II) are organic matter and nonsilicate iron compounds, while in the ABg and BDg horizons, clay minerals make the main contribution to Cu(II) adsorption under the experimental conditions. The main mechanism of Cu(II) adsorption in the AY horizon is ion exchange with H⁺ on functional groups of organic matter and surface hydroxyls of nonsilicate iron compounds. In the underlying horizons, Cu(II) is mainly sorbed as a result of ion exchange with cations that compensate for the constant charge of the crystal lattices of clay minerals. Soil treatment with 10% H₂O₂ and the Mehra-Jackson reagent leads to a change in the surface area, quality and quantity of sorption centers, and to the transformation of the crystal lattices of clay minerals. These changes should be taken into account when assessing the contribution of soil components to the sorption of metal ions.

Understanding the variability of stable carbon isotopic composition of organic matter in Cambisols, one of the most widespread soils in the temperate zone, can shed light on the response of forest soils to changes in environmental conditions. The studies were carried out in the foothills of the northeastern macroslope of the Eastern Sayan ridge. For the first time, the formation of Cambisols here was established. Investigated soils are one of the isotopically lightest soils of the Baikal region which is most associated with favorable moistening conditions for the vegetation that forms soil organic matter (δ¹³С values of the dominant species vary from –32.6 to –27.8‰). The variations in δ¹³С values from site to site do not exceed 1‰ (–25.81…–26.81‰) for the organic matter of surface soil horizons despite significant differences in the input and subsequent transformation of organic matter. At the same time, there is a significant intrasoil gradient of δ¹³С values (4–5‰). An analysis of differences in the intensity of carbon turnover, expressed through the slope of the linear regression (β) between δ¹³C values and log-transformed content of total carbon in the soil, which varies with depth, showed that, most likely, the isotope profile of the studied Cambisols is formed under the influence of microbial utilization of organic matter, which manifests itself with different intensity depending on the composition of organic-rich horizons. The increased intensity of mineralization of labile components of plant material in the upper part of the organic profile of soils with developed litter and organic-accumulative horizons can lead to a noticeable increase in δ¹³С values and a more pronounced β, in contrast to soils with a predominance of mineral horizons in the organic profile.

Soil stability in modern soil physics is divided into two directions: water stability and resistance to mechanical influences (compression, wedging). Both soil properties in water-saturated soil are based on the rupture of intra-aggregate interparticle bonds, however, no standard physically justified values have been proposed to characterize the stability of aggregates. The purpose of the article is to substantiate the physical concept of stability of soil aggregates and to propose a single methodological method for quantifying stability as a normative soil characteristic. A high-performance method has been developed based on the dissection of linearly arranged water-saturated aggregates using blades under controlled load. The main stages of the technique are vacuuming of aggregates to eliminate the uncontrolled influence of trapped air, saturation of aggregates in vacuum with water and subsequent determination of the aggregates stability to penetration of blades. Experimental stability values (mN/aggregate) were obtained for 17 soils, which made it possible to form normative ranges for mountainous arable heavy loamy soils: sod-podzolic – 17–19, gray forest –27–29, chernozems – 34–37 mN/agr and a number of other soils, which makes it possible to apply the obtained value as a soil characteristic of the stability of aggregates. The possibility of using the stability values as a methodological basis for monitoring soil stability and degradation, quantitative directions for assessing the state of physical characteristics of soil aggregates (first their main parameter, their stability) is discussed. Taking into account the highly correlative dependence of the proposed stability characteristic on the water stability values obtained by the Savvinov method (>85%) and the high performance of the stability determination method (the proposed method is about 20 times more productive than the Savvinov method), the possibilities of using the method and the obtained values of the stability of aggregates as a general physical characteristic and a separate well for quantifying water stability are discussed.

Diversity of cyanobacteria and eukaryotic algae was recovered from biological soil crusts formed on bare spots in tundras of the Ural mountains. The research was carried out in two typical tundra types, dominated by shrub-moss-lichen and dwarf birch-lichen-moss communities. In total, 46 species belonging to five divisions were identified: Cyanobacteria (19), Ochrophyta (1), Bacillariophyta (2), Chlorophyta (22), Charophyta (2). Core species of the biological crusts come from Cyanobacteria (Stigonema minutum, Gloeocapsopsis magma, Schizothrix fuscescens, Dasygloea cf. lamyi, Fischerella muscicola, Nostoc commune, Scytonema hofmannii) and Chlorophyta (Sporotetras polydermatica, Coccomyxa simplex, Elliptochloris bilobata, E. subsphaerica, Lobochlamys culleus, Pleurastrum terricola). The low diversity of algae and cyanobacteria results from harsh environmental conditions of their habitat: extreme fluctuation of upper ground temperatures, acidic soils with low base content, and reduced levels of nitrogen, phosphorus and other crucial biogenic elements. The total number of cyanobacterial and algal cells per g of soil was estimated at 0.03 to 34.19 million. Based on the acetylene reduction method, the average nitrogen fixation rates in biological crusts ranged from 0.009 to 0.015 mg С₂Н₄ m^–2h^–1. The activity varied between soil crust types from 1.48 to 2.25 mg С₂Н₄ m^–2h^–1. In future, regular observations are planned on the studied sites to reconstruct and predict succession processes in cryogenic landscapes under mountain tundra conditions.

In pot experiments, the effect of introducing rhizospheric bacteria promoting plant growth on the yield and chemical composition of spring wheat when grown in humus horizon of the Luvic Retic Greyzemic Phaeozems (Loamic) soil artificially contaminated with a water-soluble nickel compound was studied. Application of P. fluorescens 20, P. fluorescens 21, and P. putida 23 bacteria increased plant resistance to elevated nickel concentration and increased yields, significantly reducing or completely eliminating heavy metal phytotoxicity. The resistance of plants to impact of nickel stress when using bacteria is due to: a) stimulation of root growth and an increase in the accumulation of nickel in the root system, b) improvement in the mineral nutrition of plants – an increase in uptake of biophilic elements from contaminated soil due to an increase in yield, in general, without significant changes in the content of the most elements in plants, including grain. Application of bacteria increased uptake of nickel from the soil by above-ground organs of plants, thereby enhancing phytoextraction – purification from heavy metal and, consequently, soil remediation. The distribution of nickel in soil in fractions isolated by the method of consecutive selective extractions has been established. In the first half of the growing season, application of bacteria increased the content of nickel in the soil, mainly in the exchangeable and specifically sorbed fractions and, to a lesser extent, in fractions associated with organic matter and ferruginous minerals, and decreased content of the metal in the residual fraction. Increase of nickel accumulation in plants in application of bacteria corresponded to increased heavy metal content in soil, mainly in the composition of compounds associated with exchangeable and specifically bound fractions. At full maturity of plants, no significant changes were found in fractional composition of Ni in the soil. Application of bacteria can be recommended in the development of strategies for remediation of nickel-contaminated soils based on environmentally friendly technologies.

Highlighting the context of soils, we discussed the issues of environmental safety of using a synthetic highly toxic organic substance – heptyl (or unsymmetric dimethylhydrazine, UDMH), carried out a comparative analysis of Russian methods for its identification, characterized the behavior and interaction with ecosystem components, and summarized the existing experience in soil detoxification. Despite the long-term use of UDMH, analytical methods for its determination in soil are far from perfect, have a number of uncertainties and require further improvement, since the possibility of its reverse synthesis from transformation products during sample preparation does not let assess the degree of danger to ecosystems and humans unambiguously and objectively. Environmental pollution by heptyl during normal operation of launch vehicles is currently negligible. However, large amounts of heptyl can enter ecosystems due to launch vehicle accidents. In acidic peat soils (Histosols) at the regular falling sites of the first stages of launch vehicles in the Arkhangelsk region, heptyl pollution persists for at least 10 years. And in alkaline soils (Arenosols, Gypsisols, Solonetz) at the falling sites in the Ulytau region of Kazakhstan, due to rapid evaporation and transformation, it preserves no more than one year. In Russia, the existing soil remediation techniques can be grouped into thermal, sorption, biological, and others, some of which are based on the oxidation of heptyl with the formation of a number of derivatives, the properties and toxicity of which are poorly understood.

We studied the safety of sorbents based on zerovalent iron in the form of micro- and nanoparticles and their detoxifying activity in peat eutrophic soil (Eutric Histosol) polluted by emissions from a copper-nickel (Cu/Ni) plant (Kola Peninsula, Russia). Iron nanoparticles, as well as iron microparticles at a dose of 2%, turned out to be non-toxic according to the results of three standard bioassays based on the reactions of test organisms of different taxonomic affiliation. Toxicity was assessed by the change in the length of the roots of seedlings of plants Sinapis alba L. in uncontaminated peat, by the survival of Ceriodaphnia affinis Lilljeborg and the protozoan Parameciun caudatum Ehrenberg in water extracts of the samples. Fe-containing preparations significantly reduced the ecotoxicity of the soil due to the extremely high content of copper (6877 mg/kg) and nickel (2580 mg/kg). Differences in the remediating ability of the preparations were revealed. According to the results of soil phytotesting, iron nanoparticles significantly outperformed the detoxifying effect of microparticles (iron powder). When analyzing the water extract, the superiority of nanoparticles in reducing soil toxicity was not found. The dependence of the assessment of the detoxifying ability of zerovalent iron nanoparticles on soil properties and the plant species used in phytotesting is discussed.