Articles

Soils are the largest terrestrial reservoir of organic carbon, so even small changes in soil carbon stocks can have significant eff ects on the atmosphere and climate. To select effective strategies to mitigate climate change, predictions of how soils will respond to future changes in climate and land use are needed. Achieving meaningful predictions requires a deep understanding of the highly complex, open, multicomponent soil organic matter system. One of the most effective methods for predicting the dynamics of soil organic matter is mathematical modeling. Process-oriented (physically based) models make it possible to present the basic concepts about the mechanisms that determine the behavior of this system in a mathematically formalized form and conduct a quantitative analysis. The uncertainty of the forecasts depends on the level of development of the theory explaining the dynamics of soil organic matter, the models representing it and their experimental support. This review examines the achievements of the last decade in modeling the role of microorganisms in the stabilization of soil organic matter, the concept of soil saturation with organic carbon, temperature control, as well as the development of reactive transport models describing the dynamics of organic carbon in the soil profile, and the representation of the dynamics of soil organic matter in global climate models. Unsolved problems associated with the high variability in the structure of new generation soil organic matter dynamics models are discussed.

Winter temperature regime was studied for soils of thufur field formed on gazha sediments within the first terrace above the floodplain, and for the dark humus soil formed under the conditions which were closer to zonal ones. The temperature of atmospheric air, that of soil surface under snow and soil temperatures at the depths of 5–120 cm were measured with autonomous temperature recorders. The surface temperature of soil under snow depended on the snow depth. In the thufur center the sum of surface temperatures for the period from December 10 to March 30 was equal to –387°C, and in the microdepression this sum was smaller by absolute value and equal to –170°C. Soil temperature in thufur microelevation for different depths was lower than soil temperature in microdepression between the thufurs; soil temperature in zonal conditions was intermediate. The zero-isotherm penetration depth was 55 cm within the thufur, 25 cm in microdepression and 45 cm in the zonal soil. The microtopography of the thufur field is a factor of snow redistribution and formation of heterogeneity of snow depth, thus forming regular differences in the zero-isotherm penetration depth in different areas and spatial heterogeneities in the temperature field of the studied soils in winter.

The thermal diffusivity of the upper plow horizon of the urban soil from the territory of MSU Experimental soil station, lowland packed peat, and their mixtures was studied. The soil from Ap horizon was sieved through a 1 mm sieve and mixed with peat in various proportions; the content of peat in mixtures ranged from 1 to 80% by dry weight. Metal cylinders 10 cm high and 3.8 cm in diameter were filled with soil, peat, and soil-peat mixtures. The thermal diffusivity was measured using the unsteady-state method with a working temperature range of 20–26°C. The heating rate of the packed samples was measured after the samples were placed in a liquid thermostat with a constant water temperature. For each sample, a series of measurements was carried out with a step-by-step change in soil water content from the maximum one after capillary saturation of the sample to the minimum one, corresponding to the air-dry state. Within the studied range of water contents, the thermal diffusivity of different samples changed by a factor of 1.3–3.5; the greatest changes with water content were typical for mineral soil. The thermal diffusivity vs. water content dependence was almost linear for peat, and for soil it was an S-shaped curve with a weakly expressed maximum. The lowest thermal diffusivity was obtained for peat and mixtures with high peat contents; the highest one — for soil without peat additions. The non-linear character of the thermal diffusivity vs. peat content dependence was revealed. Small additions of peat to mineral soil resulted in a noticeable decrease in the thermal diffusivity of the mixture; small additions of soil to peat had practically no effect on thermal diffusivity. The thermal diffusivity of the studied substrates increased with increasing sample bulk density and decreased with increasing organic matter content. It was concluded that the patterns typical for soil-peat mixtures are similar to those earlier obtained for peat-sand mixtures, but in the case of soil-peat mixtures these patterns are less clearly expressed.

The main purpose of the work was to verify the applicability of the approach to assessing the ecological state of soils and the theoretical model of the response of a living being in the form of a vegetation index to the impact of a complex of heavy metals in the zone of impact of coal mining and processing facilities in the conditions of the Far Eastern taiga-forest soil-bioclimatic region. The research was carried out in conjunction with a geochemical assessment of natural environments, which made it possible to consider the size of the impact zones of coal mining and processing facilities on the territory of the emission quota experiment conducted by the Ministry of Natural Resources of the Russian Federation. Th e inventory of emission sources allowed us to identify several priority areas: the main industrial site, an industrial boiler house, an integrated industrial site, two coal mines, etc. According to the results of the summary calculations of the dispersion of pollutants, the following priority pollutants were identified: carbon (soot), inorganic and coal dust. The determination of soil and snow pollution levels made it possible to identify the localization of technogenic anomalies of heavy metals, as well as to determine the dust load on the studied area. The soil cover is characterized by a low level of pollution in terms of the total pollution index, however, the accumulation of trace elements in the surface layer of soils is typical for most of the studied metals and metalloids, as evidenced by concentration coefficients > 1. Centers of snow cover pollution have been identified, confined to the residential area. Areas with very high levels of snow pollution are located near municipal boiler houses. Based on a theoretical model of the response of a living in the form of a vegetation index to the effect of a complex of heavy metals of a certain set contained in the soils of the vicinity of a coal mining and processing enterprise, maximum permissible levels of their content have been established. The boundaries of the zone of influence of the main structural divisions of the coal mining enterprise, beyond which the territories of the natural and anthropogenic background are distributed, are determined. The soils in the vicinity of coal mining and processing facilities are characterized mainly by a background (undisturbed) condition or are poorly degraded, thus no harm has been done to the soils.

Influence of plastic trenchless and pottery trench drainage on physical and chemical properties of mineral ogleyed soils formed on carbonate-free loess-like loams with medium and low water permeability (Kf 0.1–0.3 m∙day-1) is estimated. The peculiarities of water regime of gray forest gleied soils of different degree of gleying in years of different moisture content were revealed. In profile of gleyed soils in spring and fall two-tiered top-water is formed that causes decrease of crop yield or their death. Drainage has been shown to eliminate topsoil water. Pottery trench and plastic trenchless drainage have close agroecological and hydrological influence on the considered soils. Transformation of physical and chemical properties as well as humus state of soils drained by different types of drainage has been established. Long-term studies of plastic and pottery drainage aft ereffects allow to study evolution of drained soils and adjacent landscape. On the basis of 30-year study of heavy loamy soils and ferromanganese nodules it is proposed for the first time to use the parameter «carbon content in Fe-Mn ortsteins»: firstly, for diagnostics of soil hydromorphism degree; secondly, for evaluation of drainage systems efficiency and expediency of their reconstruction.

A significant role in the movement of water in the soil profile belongs to the preferential vertical water flows, while less attention is paid to the study of lateral flows. We propose a method for studying lateral moisture flows at the microlandscape level using 137Cs of “Chernobyl” origin. For GIS modeling of lateral transport, the hydrological attributes of the microrelief were used, based on a digital relief model (DEM) at a scale of 1:200 with a horizontal section of 20 cm. The Catchment Areas, the Overland Flow Distance, the ephemeral Tricle Network (Strahler Order),
as well as the topographic humidity index (TWI) qualitatively characterize the intensity of soil moisture, as well as lateral flows at the microlandscape level. Th e idea of “preferential lateral flows” introduced by analogy with vertical “preferential moisture flows”. Due to the spatial features of the structure of the nano- and microrelief, lateral transfer forms ephemeral patterns with different humidification modes: “finger-like”, filamentous, and others. A weak level of lateral migration of 137Cs was revealed depending on DEM derivatives.

The contribution of organic matter content to the hydrosorption properties of soils is demonstrated. Hydrosorption properties have been studied for soils of different genesis and degree of technogenic loading. Among the technogenic soils, urban and arable soils are considered. Natural soils are represented by Albic Stagnic Retisol (Siltic) on varved clays, Luvic Greyzemic Phaeozem (Clayic, Humic) and Luvic Chernozem (Clayic, Humic) on brown clays. The sorption isotherms constructed using the BET method and the specifi c surface areas of the initial samples and samples after organic matter destruction were compared. The destruction of organic matter was carried out in a laboratory experiment using hydrogen peroxide. It was found that treatment with H2O2 resulted in a significant decrease in the sorption capacity of soils and a change in hysteresis phenomena. At the same time, the sorption capacity of the soils decreased in different ways. The specific surface area decreased from 1.9 to 2.8 times. Statistical analysis showed no correlation between the degree of reduction in specific surface area and the degree of reduction in organic matter content. However, a close correlation was found between the degree of reduction in specific surface area and the initial organic matter content. The higher the initial organic matter content of the soil, the greater the reduction in specific surface area as a result of the treatment. Treatment with H2O2 was found to have the most significant effect on equilibrium water contents during the capillary condensation interval. The sorption capacity of the urban soils was lower than that of their natural and arable counterparts. With a relatively high organic carbon content in the urban soils, the effect of its destruction on the specific surface was less than for the other soils, which allows us to consider it in relation to the qualitative composition of the organic matter.

The article presents a new methodological approach to modeling the soil water retention curve (WRC), based entirely on the Deryagin phenomenon of wedging pressure of water films in relation to the soil physical system. It operates with a variable mass fraction of the liquid phase (soil solution) with the parameters of the concentration and charge of electrolyte ions, the specific surface area of the solid phase, as well as limitations by porosity and the standard potential of a conditionally zero water content in the soil. The new model, validated according to the author’s and independent literature data for soils of various genesis and granulometric composition from sands to clays, showed good agreement with experimental data and a more adequate description of water retention with normalized root-mean-square errors 5–10 times smaller compared with the most common empirical van Genuchten model for describing the WRC. Along with an adequate description of WRC in the entire range from the state of water saturation to conditionally zero water content, the new model makes it possible to analytically calculate pore size distributions, estimate the generalized Hammaker constant for interphase molecular interactions of liquid and solid phases of soil, the Debye thickness of the double electric layer and the specific surface area of the solid phase of soil, alternatively to the standard BET method.

The paper presents the results of experiments to study changes in hydrological properties of soil substrates composing profiles of artificial soils (construktozems) 1-4 years aft er their creation. Constructozems are represented by two variants - layered soils including Ap horizon, lowland peat and quarry sand of the same thickness, and a mixture of these substrates in an identical amount by weight, as for layered constructozems. Water retention curves obtained by capillarimetric method on samples of undisturbed structure were compared. A decrease in the water-holding capacity of the peat layer and an increase in the mixture samples were found a year after their functioning as part of the artificial soils. Laboratory and field experiments showed a statistically significant difference in water filtration rates of the layered constructozems and the mixture. Sharp boundaries between soil horizons contrasting in their properties reduce water migration rates down to zero values. Obtaining breakthrough curves of potassium ions allowed us to establish that the formation of continuous paths of rapid movement of water and dissolved substances is observed after four years of functioning of artificial soils and is most pronounced in constructions with homogeneous soil profile structure.

The problems of determination and classification of soils by granulometric composition from the point of view of domestic and international soil science are considered. The development of methods and devices for granulometric analysis of soils was largely promoted by the works of the Department of Soil Physics and Reclamation, on the basis of which the necessity of two stages of granulometric analysis was shown, the all-Russian method of sedimentation analysis of particles by pipette method was founded, with the development of the classification of N.A. Kachinsky and names of soils by granulometry, which are fundamentally different from those generally accepted in the world practice. At present, at the first stage the method of pretreatment with 4% sodium pyrophosphate is widespread, at the second stage — measurement of granulometric composition two approaches are used — sedimentation method and laser diffractometry, which have different physical bases. The difference of final results on granulometric composition of soils is usually associated with different shape and density of solid phase of organic and mineral particles. This paper presents the studies of granulometric composition of agrodernovo-podzolic sandy loam soil (Tver region, VNIIMZ experimental site) with low content of organic matter in comparison of three methods of granulometric composition determination: laser diffractometer, sedimentometric methods of suspension pressure estimation on Pario - ISP+ (Integral Suspension Pressure) device and classical pipette method. Th e laser diffractometer for fine fractions showed systematically underestimated data with the same pretreatment procedure compared to ISP and pipette method. The ISP+ method compared to the classical pipette method gives similar results.