Том 52, № 9 (2019)

The results of the study of cryogenic landforms (heave mounds and thermokarst depressions) and soils developed on them under conditions of the ultracontinental climate of Buryatia and relatively shallow permafrost are discussed. According to the analysis of data of a Tandem X radar and terrain geomorphic surveys, the spatial distribution of local heave mounds and depressions in the Eravna Basin in the south of the Vitim Plateau has been mapped. Heave mounds are mainly allocated to watersheds and foothill fans; soils formed on them are represented by gleyic cryoturbated chernozems (Haplic Chernozems (Stagnic, Turbic) and gleyic dark-humus soils (Stagnic Phaeozems). Thermokarst depressions are allocated to the bottom of the basin and to the wide leveled loamy watersheds. The soil cover here is formed by quasigley chernozems (Gleyic Chernozems) and calcareous quasigley humus soils on stratified lacustrine sediments (Calcaric Gleyic Phaeozems). The soils of heave mounds and thermokarst depressions are characterized by considerable variation in the thickness of horizons and their inversion because of frost heave and cryoturbation processes. They pronouncedly differ in morphology and physical and chemical properties. The distribution of carbon pools in the profiles of these soils differs considerably from that in the background quasi-gley chernozems (Gleyic Chernozems).

Isotopic composition of nitrogen in soils can be an informative indicator of N transformation processes and sources of N nutrition of plants, but data on δ¹⁵N of labile N compounds are scarce. It is shown that N transformation in meadow-alpine soils (Leptic Umbrisols) of the northwestern Caucasus (Teberda Reserve, Karachay-Cherkess Republic) leads to well-expressed differences in isotopic signatures of different N compounds: δ¹⁵N of extractable organic matter > δ¹⁵N_total > δ¹⁵N–\({\text{NH}}_{{\text{4}}}^{ + }\) > δ¹⁵N–\({\text{NO}}_{{\text{3}}}^{ - }.\) The range of δ¹⁵N in this sequence reaches 25‰. Differences in δ¹⁵N within the same pool of N in soils of different alpine ecosystems, as well as seasonal dynamics of δ¹⁵N–\({\text{NH}}_{{\text{4}}}^{ + },\) are much less pronounced (the range of δ¹⁵N is 2–4‰). The values of δ¹⁵N_total and δ¹⁵N–\({\text{NH}}_{{\text{4}}}^{ + }\) positively correlate with N mineralization and nitrification and demonstrate the accumulation of heavy N isotope in soils of the alpine ecosystems with more active N transformation processes. Obviously, nitrification is the key process controlling the isotopic signature of N–\({\text{NH}}_{{\text{4}}}^{ + }.\) The role of N mineralization in the fractionation of N isotopes is less obvious, and ¹⁵N accumulation in the extractable organic matter can be related to the significant content of “heavy” microbial N in extractable organic N pool.

The influence of biological and physicochemical soil properties on the variations in soil organic and inorganic carbon (OC and IC) contents at the soil surface was studied. Three-dimensional plots of variations in OC, IC and the correlated properties were obtained. Soils of the study area were classified as Aridisols and Entisols used as a rangeland. Soil samples were collected from 38 representative points with a wide range of physicochemical soil properties; in addition, three important microbiological indicators—dehydrogenase enzyme activity (DHA), soil basal respiration, and bacterial population—were analyzed. Variation partitioning analysis was carried out to assess the determining factors influencing soil OC and IC variations in soil surface. Additionally, the principal component analysis (PCA) was applied to explore the patterns of determinant soil variables. Variation partitioning demonstrated that the physicochemical soil properties were the determining variables in explaining the variations of both OC and IC. A remarkable portion of the variations remained unexplained by any of the two explanatory sets according to this analysis. Soil OC was not significantly related to the biological soil properties. Soil OC was inversely related to IC, clay, and sodium contents in the soil profiles. Soil type-specific vertical trends were observed for soil OC and IC. Soil conditions and pedogenic processes were deduced to have a major role in OC and IC spatial variations according to the results of soil type-specific trends of variation. The results of this study can be useful for better soil management and OC and IC prediction, or spatial distribution patterns modeling.

Chernozem humic acid (HA) fractions with nominal molecular sizes (MS) >100, 30–100, 5–30 and <5 kDa were obtained, using a combination of low-pressure preparative size exclusion chromatography with analytical polyacrylamide gel electrophoresis or multistep ultrafiltration. The initial HA and fractions were tested for the ability to destroy model aromatic compounds 2,4,6-trimethylphenol and furfurol in aqueous solution when illuminated with polychromatic light in the range 300–450 nm under laboratory conditions. It has been found that chernozem HA fractions with MS less than 5 kDa had the maximum ability to decompose the above-mentioned substances, while fractions with MS above 30 kDa practically did not perform this function. The data obtained allow us to explain partially the mechanisms of the photoinduced transformation of many organic pollutants by soil humic substances.

A destructive peat horizon T_md of bare peat circles on flat-topped peat mounds in the north of Western Siberia differs from peat horizons (T) of typical peat soils in its higher density, water content, and comminution of peat residues; lower microbial biomass; low mineralization and hydrolase activities; low physiological diversity of hydrolytic bacteria; and specific composition of the fungal complex with an uncharacteristically high proportion and quantity of psychrophilic yeasts Leucosporidium drummii. Specific respiration rate and hydrolase activity in the T_md and T horizons are relatively close, which indicates that, in general, the metabolic activity of microorganisms decomposing the organic matter of peat and increasing the degree of peat decomposition remains unchanged in the soils of bare peat circles.

The decomposition rate of four species of peat-forming plants typical of bog phytocenoses in the southern taiga subzone of Western Siberia—Sphagnum fuscum, Chamaedaphne calyculata, Eriophorum vaginatum, and Sphagnum angustifolium—was determined in the 3-yr field experiment. The research was performed by the method of partially isolated samples on the Timiryazevskoe and Bakcharskoe bogs, differing in their hydrological regime and temperature condition. Regardless of the chemical composition of the peat-forming plants, their decomposition was characterized by the most significant mass loss over the first year of studies. By the end of the third year, the destruction of plant residues was slowed down, and the decomposition constant value for all the studied plant species decreased by 1.2–2.8 times. The decomposition of peat-forming plants was the slowest under wetter conditions of the Bakcharskoe bog, where the mass losses of all the species studied, except for Eriophorum vaginatum, were 1.2–1.6 times lower than on the Timiryazevskoe bog. Over the three years of the experiment, the total mass loss and the decomposition constant value significantly differed for S. fuscum and Chamaedaphne calyculata, as well as for two sphagnum species (S. fuscum and S. angustifolium). Positive correlations between the mass loss of peat-forming plants (except for S. angustifolium) and the sums of temperatures of the peat deposit, exceeding 0, 5, and 10°C, were revealed. The lowering of the water table level resulted in a significant increase in the intensity of the decomposition processes for all the studied plant species, except for Eriophorum vaginatum.

The deconvolution procedure for splitting the initial particle-size distribution spectrum into constituent fractions makes it possible to refine the traditional indicators of particle-size distribution and gives us new information about the properties of individual particle-size fractions. Owing to the deconvolution, it is possible to identify fractions that remain “invisible” upon the traditional visual analysis of the initial particle-size distribution spectra. The new indicators include the average diameter of the particle-size fraction d_aver, the dispersion value D of each fraction, and the convergence index of the neighboring fractions h. Deconvolution helps us to characterize the fractions not by their size boundaries, but by the average particle diameter. Deconvolution has shown that the distribution of major particle-size fractions in Vertisols is consistent with the boundaries of the particle-size factions according to the international classification system and is not consistent with the boundaries of the particle-size classes in the classification by Kachinskii (Russia), in which the width of the classes is variable (index F is either 2 or 5). The advantage of the international classification of particle-size fractions is the same width of separate size classes with a constant F value (F = 3.2).

The postagrogenic dynamics of biological cycling and soil properties have been studied in three soil successions characterizing postagrogenic overgrowing of: (i) former cropland on a loamy sandy soil underlain by loam (Retic Albic Podzol (Anoarenic, Endoloamic, Ochric)), (ii) well-fertilized garden loamy sandy soil underlain by loam (Plaggic Podzol (Anoarenic, Endoloamic, Humic)), and (iii) loamy soil of a hayfield developed from the former arable land (Albic Retisol (Loamic, Ochric)). The dynamics of acidity and organic carbon content are determined by the rate of the succession depending on soil fertility during the agrogenic stage in the past. In case of overgrowing of poor sandy agrosoddy-podzols, the changes in soil acidity and organic carbon content are adequately reflected by the proportion between different ecological groups of plants in the herb–dwarf-shrub layer. In the case of reforestation of former croplands, the organic carbon stock in biogeocenoses increases from 30–40 to 120 t/ha after 35–40 years. The restoration of forest vegetation on well-manured soils of private vegetable gardens with the initial carbon stock of 100–120 t/ha is retarded for a long time, and the organic carbon stock remains unchanged for at least 35 years.

This study is devoted to the determination of the main types of soil cover patterns (SCPs) in anthropogenically transformed landscapes of Leningrad oblast for the purpose of medium-scale soil cover mapping. Sixteen different groups of anthropogenically transformed and anthropogenic SCPs are identified, and their characteristics are given. They are related to tree logging, forest reclamation, forest fire control, forest recreation, postwar effects, agroforest measures, forest nurseries, agrogenic impact, recreation loads in parks, agroreclamation, postagrogenic development, pipeline and power line construction, agrourban, highway and railroad, and mining quarry areas. A typology of SCPs of anthropogenically transformed landscapes in Leningrad oblast has been developed. It takes into account regularities of changes in the soil cover under the influence of the anthropogenic factor. The type and degree of transformation of the soil cover components, the degree of their contrast and heterogeneity, intercomponent links, and the geometric shape of SCPs are analyzed. The developed typology has a universal character for landscapes of the forest zone and can be used for medium-scale soil mapping in other regions of this zone.