Nº 9 (2024)

The aim of the work is to present the results of a ground-based study of the erosion-accumulative soil cover pattern of a key area and to assess the information content of multi-temporal remote sensing data of the bare soil surface for its identification and mapping in the zone of distribution of dark chestnut soils (Kastanozems). The study area is located on the Millerovo-Morozovskaya inclined plain within the Don-Donetsk hilly-ridge plain in the Oblivsky district of the Rostov region. The soil cover of the key area is represented by a combination of different variations of low-contrast soils on convex and concave surfaces within an elongated ridge and its slopes, including agro-dark chestnut solonetzic and non-solonetzic soils, agrozems (eroded soils that have lost the xerometamorphic horizon), stratozems (heavily delivered soils). The formation of the soil cover pattern is determined by a combination of mesorelief forms and two types of parent material. The C coefficient map of the multi-temporal soil line reveals the heterogeneity of the soil cover due to erosion-accumulative processes. In study area, three contrasting soil combinations are confidently distinguished in the form of different variations and combination-variations, forming a kind of framework of the soil cover pattern. Soil combinations of eroded and delivered soils located between the above three groups of soil combinations are significantly different from their neighbors, but their interpretation has increased uncertainty.

The dynamism of carbon pools and flows in landscapes requires special attention to methods and means for measuring all carbon components. An important component of the carbon budget of carbonate geosystems is dissolved inorganic carbon, part of which is carried out by surface and lateral flows into water bodies, which requires attention to assessing the total alkalinity (TA) of soils. Analysis of soils of the Polar Urals with CaCO₃ content from 0 to 100% revealed factors influencing the value of their TA: a) method of soil preparation and water extract (ratio of soil mass and volume of distilled water $m_{\mathrm{S}} : V_{{\mathrm{H}}_2\mathrm{O}}$, quality of separation of solid and liquid phases); b) option of fixing the end point of titration of extracts with acid; c) the presence of organic acids with pK_a less than 4.4. The latter reduce the content of bicarbonate ion by converting it into carbonic acid, which is not measured titrimetrically. This mechanism is confirmed by: a) analysis of model solutions of sodium bicarbonate and formic (pK_a = 3.75), tartaric (pK_a1 = 3.04, pK_a2 = 4.37), malic (pK_a1 = 3.46) acids; b) cation-anion balance of water extracts from soils; c) a negative shift in the results of titrimetric measurement of TA (the sum of carbonate and organic alkalinity) relative to the amount of equivalents of dissolved inorganic carbon determined by high-temperature catalytic oxidation at the same $m_{\mathrm{S}} : V_{{\mathrm{H}}_2\mathrm{O}}$ in both methods. Comparison of the TA of soils obtained in different laboratories is possible only under strict observance of all conditions that can be performed experimentally. It is recommended to use a centrifuge to separate the solid and liquid phases of carbonate soils, as well as a pH meter or titrator to fix the end point of titration. The above considerations can be useful for forecasting and research modeling of soil carbonate dissolution as a result of global climate change and acidification.

Quantitative description of the water retention curve (WRC) of soils remains one of the most pressing problems in soil hydrophysics due to the importance of WRC for computer modeling of the transport of soil moisture and dissolved substances and for the development of the thermodynamic concept of physical soil quality. The article presents a new model of WRC as a functional dependence of the thermodynamic potential (pressure) of soil water and its content in the entire possible range from conditionally zero to total water capacity in a state of water saturation. Unlike well-known empirical analogues, the model is based on fundamental physical mechanisms of water retention, combining the capillary effect and the Deryagin disjoining water pressure. Limitations by porosity (total water capacity), the maximum height of capillary rise and the standard thermodynamic potential of conditionally zero water content at a temperature of 105°C are used to justify the domain of determination of the WRC, its inflection point and for its scaling. The analytical expression of the new model in the form of a combination of exponential and hyperbolic functions with the argument of soil water content is easily differentiated and makes it possible to calculate the differential water capacity, variable interfacial surface and pore size distribution with a maximum at the inflect point of the field capacity, as well as estimate the specific surface area of the solid phase. Validation of the model using average statistical WRCs of the main genetic types and textural classes of Eurasian soils confirms its good agreement with experimental data with a more adequate description of WRC in the vicinity of conditionally zero soil water content compared to the standard empirical van Genuchten model with the same number of parameters. The fundamental basis of the new model and its good approximation ability for the entire range of WRC create the prospect of its diverse use for assessing the physical quality of soil and for process modeling of water transport, especially in finely dispersed and highly drained arid soils, where the approximation capabilities of the model exceed the known empirical analogues.

The total content, forms and mineralogy of iron compounds of soils of forest-steppe, steppe and semi-desert zones from the central chernozem regions to the Caspian lowland and from the Southern Urals to the Kerch Strait have been studied. The subjects of the study were Сhernozems (n = 40), Kastanozems (n = 15), Solonetz (n = 7), Calcisols (n = 7). Based on the results obtained, characteristic features of the distribution of total iron content, mass balance (τ_Fe,Zr), forms of iron compounds, magnetic susceptibility ($\chi$) and mineralogy of iron in soil profiles were revealed. The distribution of τ_Fe,Zr in the studied soils reflects the processes and conditions of soil formation, as well as lithological features. For a more detailed understanding of the process of transformation of iron compounds in steppe soils, studies of granulometric fractions (<2, 2–5, 5–10, 10–50 μm) by the method of Mossbauer spectroscopy and magnetic susceptibility were carried out on samples of Luvic Chernozem, Haplic Kastanozem, Haplic Kastanozem (Endosalic, Cambic)) and Luvic Calcisol (Endosalic). It is shown that a large fraction of Fe³⁺ in the silt fraction is contained in highly dispersed oxides and hydroxides in the superparamagnetic state. In humus-accumulative horizons of steppe soils, a decrease in the Fe²⁺ fraction in aluminosilicates due to weathering processes is recorded. The revealed interrelation of the goethite/(hematite + goethite) ratio in humus-accumulative horizons of soils with climatic parameters allows to use it in future paleoclimatic reconstructions. The Mössbauer spectroscopy records a significant increase in non-silicate iron in the accumulative humus horizons of steppe soils in comparison with the soil-forming rock, which is an important confirmation of the formation of iron oxides during soil formation. When comparing methods for determining non-silicate iron in soils (Mössbauer spectroscopy and Mehr-Jackson extraction), significant differences in the results were revealed due to a decrease in free forms of iron when isolated by the chemical method.

The impact of land use and erosion-deposition processes on some physical, chemical, and biological soil properties in a small agricultural catchment in Kursk oblast is analyzed. Plowed Haplic Chernozems and stratozems (Fluvic Chernic Phaeozems (Loamic, Pachic)), as well as unplowed stratozems of a dry valley bottom have been studied. The proportion of large soil aggregates (clods) >10 mm in soils is high on plowed land and low in the dry valley bottom. Differences in the carbon and nitrogen content and in the C/N ratio have not been detected. The analytical pyrolysis has revealed 26 pyrolysates in the composition of soil organic matter (SOM). The relative abundances of pyrrole, pyridine, toluene, and indan among SOM pyrolysates are higher in plowed soils as compared to the soils at the dry valley bottom. Proportions of furfural and methyl furfural among SOM pyrolysates are higher in soils of the dry valley bottom than in plowed soils. Differences in the content of alkanes and phenol are absent. The biomass of microorganisms is mainly formed by fungi (97–99%), and their abundance is greater in soils of the dry valley bottom than in soils of the plowland. Differences in the respiratory activity of the studied soils have not been revealed. The significant influence of erosion-deposition processes and soil cultivation on the spatial heterogeneity of the SOM composition and microbiological parameters is shown. Plowed soils are characterized by the high relative abundance of nitrogen-containing SOM components, while soils at the dry valley bottom have a relatively high abundance of carbohydrate components of mature SOM. The accumulation of fungal biomass and an increase in the structure coefficient in soils of the dry valley bottom indicate the participation of material redeposited from slopes in soil aggregation.

The transformation of radioactive contamination of agricultural lands with the ¹³⁷Cs isotope is one of the evidences of soil erosion. Quantitative assessment of changes in radionuclide inventories and the corresponding rates of soil loss can be carried out by repeated sampling of integral soil samples at key sites over long time intervals. Due to the high labor intensity, such studies are relatively few and have not previously been conducted in the zone of intense Chernobyl contamination in Central Russia. The method of repeated sampling (re-sampling) was used in 2023 within the plowed slopes of a small catchment area in the southern part of the Tula region, 26 years after a similar procedure was carried out in 1997. The changes in ¹³⁷Cs inventories that occurred during this period turned out to be statistically significant, with an average reduction of more than 10%. According to a proportional erosion conversion model using relative changes in ¹³⁷Cs inventories, the average annual flushing rate was estimated at 11.7 t ha^-1 year^-1. Such values of soil losses are generally comparable with the previously published results of independent mathematical modeling for this area. Thus, the use of the re-sampling method, including at new sites, is promising for assessing the rate of soil loss, and in addition makes it possible to verify existing erosion models and track long-term trends in the spatial transformation of radioactive contamination.

Kerosene is widely used in various types of anthropogenic activities. Its environmental safety is mostly discussed in the context of aerospace activity. At all stages of its life cycle, aerospace activity impact the environment. In aviation, pollution of atmospheric air and terrestrial ecosystems is caused, first of all, by jet-fuel and the products of its incomplete combustion and is technologically specified for a number of models in case of fuel drainage due to an emergency landing. During the rocket and space activity, jet-fuel enters terrestrial ecosystems as a result of fuel spills from engines and fuel tanks at the fall sites of spent first stages of the launch vehicles. Jet-fuel does not enter terrestrial ecosystems from the second and third stages of launch vehicles. The component composition of aerosol emissions from aircraft engines and launch vehicles has been studied in sufficient detail. At the same time, regarding soils, there are practically no publications with representative data sets and their statistical processing not only for the kerosene content, but also for the total petroleum hydrocarbons in soils affected by aerospace activity. Nevertheless, the available data and the results of modeling allow us to assert that during the normal aerospace activity, an acceptable level of hydrocarbons entering is observed into terrestrial ecosystems, which does not exceed the assimilation potential. That is, the incoming amount of jet-fuel disappears quickly enough without causing irreversible damage.