Articles

Erosion-accumulation processes are realized through paragenetic processes of soil destruction, transport, redepo- sition and accumulation of pedosediments enriched in organic carbon. A promising approach in modern methods for substantiating permissible erosion losses of soils is the integration of assessments of the quality of soil resources, the rate of erosion and soil formation, including calculations of the balance of organic carbon in soils of agroeco- systems. The range of research tasks included: analysis of current integrated approaches to justify the permissible erosion losses of soils that are the most promising from the point of view of the completeness of reflection of ag- ropedogenesis; assessment of the effectiveness of the process of regeneration of the humus horizon under primary, recent and postagrogenic variants of soil reproduction; identification of patterns of formation of natural soil cover on dated and full Holocene erosional pedotopocatena; determination of the effectiveness of erosion-accumulation processes in the formation of pedosediments enriched with organic carbon in the thalwegs of runoff depressions during an extreme hydrological event and in accumulative elements of the landscape over a centuries-long period. The main objects of the study were soils of different ages in a state of renaturation, which were selected in anthropo- genically disturbed geosystems of the European forest-steppe. In addition, soil-geomorphological features within different-aged erosional pedotopocatenes and processes of accumulation of pedosediments at different scale levels were studied.
The results of mathematical modeling of the soil-forming process over time, based on an extensive database of soil-chronological data, show significant differences in the rate of formation of the humus horizon at the initial and quasi-final stages of pedogenesis, as well as the relationship between the ontogenetic maturity of the humus profile and the rate of pedogenesis, which must be taken into account when justifying acceptable erosion losses. Long-term studies of the processes of renaturation of disturbed soils in the forest-steppe zone have identified a special type of reproduction in Agroabrozems, when functional rehabilitation of the residual humus horizon occurs, which differs from primary pedogenesis during the formation of a humus profile on parent rocks. Depending on the erosional transformation of the predecessor soil profile, the average rates of formation of the postagrogenic humus horizon in forest-steppe Chernozems range from 3,6 to 6,0 mm·year–1. As shown by the results of studying different-age and full-Holocene pedotopocatenes, the natural soil cover, which reflects the processes of erosion-accumulation and landscape slope microzonality, and soil-geomorphological relationships can be adequately formalized by improving the formula for calculating the relief function in erosion models through the introduction of a variable power value for the slope length index.

In the paper spatial and temporal variability of soil erosion for the periods of 1958–1988 and 1989–2018 is estimated
on the basis of RUSLE in Crimea. Erosion rates vary from very slight to very high in the region. Strongly eroded
areas are found in the mountainous regions in the Southern Crimea, mainly attributable to a combination of a high
rainfall erosivity (R-factor) and relatively steep slopes (LS-factor). Soil loss in 1958–1988 exceeded the values in
1989–2018 on approximately 13%, while the share of moderate, high and very high-eroded areas varied within the
range of less than 1%. € ese changes are associated with both the reduction of agricultural cultivated lands and the
variability of soil erosion factors. € e soil erosion formation is mainly connected with the factors of rainfall erosivity,
slope steepness as well as the cover-management factor in Crimea. Comparison of actual suspended sediment yield
in the gauges with the values of soil erosion demonstrated that most rivers area characterized by the accumulation
of eroded material when 10–50% of the washed products reach the gauges.

The study of erodibility of model soils using the methodology of washing out soil samples with a water stream in a hydrodynamic tube has been carried out. In comparison to the traditional method of vertical loading of cartridges, the new method of soil samples formation using horizontal loading allowed to obtain more homogeneous resistance of samples in the process of their erosion by water flow, to which the formed layers of soil aggregates are located perpendicularly. The use of the «Poseidon» measuring device made it possible to obtain washout intensities in dynamics, to evaluate the quality of sample preparation and to analyze the data in order to cull them, especially in the beginning and the end of the experiments. In addition, the use of the device allowed to skip some operations needed to clarify the data of experiments at their early termination (remainder accounting that requires drying to determine the mass of washed out soil by difference). The data files generated by the device at the end of experiments significantly simplified their processing and considerably reduced the time required for it. The coefficient of varia- tion of the washout intensity value decreased by 12% on average when using the new method of sample preparation compared to the previous one. The moisture ranges with minimum erodibility have been established for model soils. Dependences of soil washing intensity on water flow velocity in the range from 0.5 to 2.5 m∙s–1 were demonstrated. The results confirm the correlation of soil washout intensity with the cube of the flow velocity. Soil erodibility was determined as a coefficient of proportionality between the intensity of soil washout and the cube of flow velocity. The maximum erodibility coefficient typical for agrogray soil equals to 179×10–6, and the minimum value obtained for agrochernozem was 53.0×10–6 s2∙m–2. Agrosod-podzol soil features the intermediate value of erodibility coefficient: 80.3×10–6 s2∙m–2. The proposed methodological approaches and obtained experimental results can be further used to assess the erodibility of soil and soil monoliths and model samples of polyfractional composition close to natural.

Land degradation is a global problem of humankind, where the greatest contribution belongs to aridity and soil erosion. The social consequences of land degradation are extremely important, but poorly conceptualized issues. This makes it difficult to create effective research programs to study them. The article provides an overview of the issues under consideration. An expert study was conducted to identify a problem field in the field of studying the social consequences of land degradation. By interviewing nine recognized scientific experts in the field of land degradation studies, the most stable judgments were identified, which served as a basis for highlighting the main forms of manifestation of the social consequences of land degradation. Private research concepts were compiled, which consist in highlighting the position of each expert on the main consequences of land degradation. As a result, a generalized expert model of the problem field of the social consequences of land degradation was formed. According the model all experts note the interdisciplinary nature of the study of the issues under consideration, which are placed at the intersection of environmental, economic and social problems. The overwhelming majority of experts noted the direct nature of the impact of land degradation on the formation of social consequences. Thanks to the integration of private concepts, it was possible to identify such aspects on which there are discrepancies. That provides an opportunity for a broader study of the social consequences of land degradation. However, there is an expert opinion that the social consequences are rather indirect and are realized through resource problems. Some experts draw attention to the fact that there are the extreme forms of land degradation that significantly increases the manifestation of social consequences. According to experts, land degradation can lead to a change in social status; a decrease in the recreational potential of land; hunger; a change in life expectancy, job loss; increased stratification of society; changes in the cost of housing and a change in the type of land use; reducing the use of land for agricultural needs and changing people’s attitudes to more individualistic ones. It was also noted that the use of products from degraded lands could lead to an increase in cancer incidence in the region. Conceptualization and identification of these problems could help to focus efforts in the field of studying the social problems of land degradation.

The paper considers the spatial heterogeneity of the flow of eroded soil material to the foot of the plowed slope and further to the side of the valley in the presence of a lyncahrt resulting fr om mechanical tillage on the lower border of arable land. A small catchment area in the area of intense Chernobyl pollution has been studied, wh ere the po- sition of the lower boundary of the arable land over the past few decades coincides with the upper boundary of the side of the valley. This made it possible to trace the spatial patterns of the distribution of eroded material with stable functioning of the lynchart as an important lithodynamic boundary accumulating and redistributing the slope runoff of sediments. The determination of the volume of material coming from arable slopes was carried out using mathematical modeling of erosion based on a high-precision digital terrain model, climate data, soil erodibility and crop rotations. To assess the intensity of accumulation, 137Cs of Chernobyl origin was used as a reliable tracer. The bulk of the eroded material enters the valley network through a system of slope hollows that concentrate the slope runoff and cut through the valleys. In the areas of the valleys sides outside the runoff concentration zones, the re- deposition of the material mainly depends on the morphology of the lyncahrt, occurs locally and is associated with episodic overflows as a result of the gradual filling of the depression before the lyncart. Under existing conditions, accumulation on the sides of the valley occupies a relatively small share in the total sediment balance of the studied catchment area. Significant changes may occur due to a gradual decrease in the barrier role of the soil as a result of sediment accumulation and climatic changes that contribute to an increase in erosion rates.

The aim of the work was to evaluate the effect of shallow–water flows on the morphometric characteristics of aggre- gates of typical Сhernozems of varying degrees of erosion. A number of model erosion experiments were carried out with capillary–moistened bulk samples of the upper 10–centimeter layer of the humus horizon of typical plowed Сhernozems of the Kursk region. The control variant is a comparable sample of chernozem from a typical site of the virgin steppe Chernozem in the Central Black Earth State Natural Biosphere Reserve named after Professor
V.V. Alekhin. Morphometric parameters of soil aggregates transported by model flows with minimum, average and maximum velocity (0,3, 0,41–0,45 and 0,54–0,58 m∙s–1, respectively) were determined. It was shown that smaller aggregates have higher form factor, roundness, and a lower edge unevenness. Larger aggregates, on the contrary, are less rounded and isometric and have higher unevenness. In erosion experiments with shallow–water flows, roundness and unevenness of the aggregate surface change inversely to each other. The change in form factor and unevenness is influenced by both the degree of soil erosion and the flow rate, and these factors mutually enhance the influence of each other. Aggregate roundness is mainly influenced by the degree of soil erosion, but its effect is enhanced by the addition of a flow rate factor. Depending on the flow rate, its effect on the morphometric parameters of aggregates varies: in the area of low speeds, a rolling effect occurs, in the area of high speeds, a destructive one. The continuation and expansion of such studies will expand the understanding of the mechanisms and patterns of formation of washed soils.

Kuznetsov’s formula relates the parameters of erosion resistance and soil water stability. However, the mechanism of occurrence of these properties is different: water stability is explained by the action of intra–aggregate hydrophobic bonds in organomineral soil gels, and erosion resistance is explained by water stable aggregates and their adhesion to each other. At the same time, the nature of the interaggregate bonds that ensure erosion resistance remains unclear. The purpose of the work was to clarify the mechanism of erosion resistance of soils and compare it with the mecha- nism of formation of water stability. The work used samples of humus-accumulative soil horizons: sod-podzolic and leached chernozem. To obtain samples with the same aggregate composition, but differing in erosion resistance, it is proposed to use soil polymer ameliorants (SPM). The erosion resistance of soils was determined on a hydrolotter and the critical rate of flushing was calculated. The water stability of the soils was assessed by the blade method. The particle size in the solutions was estimated by laser diffractometry. It was found that on soils treated with SPM, the results of the tray and blade methods correlate by 99%. The high correlation suggests a common nature of intra- and interaggregate bonds. To test the role of hydrophobic interactions in the formation of aggregates resistant to water, polymers of varying degrees of hydrophobicity were added to aqueous humate solutions in a model experiment: polyethylene glycol (PEG), polyacrylamide (PAA) and polyvinyl alcohol (PVA). In parallel, the water stability of soils treated with PEG, PAA and PVA was evaluated. The analysis of the results showed that the greatest water stability of the aggregates was noted when the most hydrophobic polymer, polyvinyl alcohol, was added to the soil, which formed the largest particles when interacting with humate in the model experiment. These results confirm the role of hydrophobic interactions in the formation of aggregates and indicate that when selecting polymer structures, their interaction should be taken into account not with clay minerals, but with soil gels, which include clay minerals and humic substances.

The dynamics of sedimentation in the bottoms of small catchments in the forest–steppe zone of the Central Russian Upland was assessed using the soil–morphological, radiocesium and magnetic tracer methods, which made it possible to calculate the rate of soil loss 1) since 1986, 2) since 1954, 3) since the launch and active operation of the railway, 4) since the mass plowing the entire catchment area. Two groups of small dry valleys have been identified: the catchment area of the first group includes tributaries of larger dry valleys, where the average rate of loss during the agricultural period is 2,1–2,4 t∙ha-1 per year and exceeds modern ones (since 1986) by 0,6–0,7 t∙ha-1 per year. The catchments of the second group include the sources of larger valleys, where the average rate of loss during the agri- cultural period is 0,6–0,9 t∙ha-1 per year and less than modern ones (since 1986) by 0.3–0.8 t∙ha-1 per year. The max- imum rates within all catchments were observed in the period 1954–1986, which is associated with soil compaction by heavy agricultural machinery, as well as the contribution of snowmelt runoff, which was regular for this period.

The article presents an analysis of the thickness of humus horizons of chernozems and gray forest soils, measured at more than a thousand survey points in three areas with an area of about 10 thousand hectares each in the northern (Oryol region), central (Kursk region) and southern (Belgorod region) forest-steppe on the Central Russian Upland. Th e measured thicknesses of the humus horizons was compared with the modeled thicknesses. Modeling of the thickness of humus horizons was carried out based soil erosion modelling and taking into account soils development. An assessment of soil erosion rates was carried out by WaTEM/SEDEM (rainfall erosion) and State Hydrological Institute in the Larionov modifi cation (snowmelt erosion), previously verifi ed on small catchments within or in close proximity to the study sites. Land use history was reconstructed using historical maps. Th e approach made it possible to model with suffi cient accuracy the average erosion losses of soils and calculate the average current thickness of the humus horizon. The obtained results of comparisons of measured and modeled thicknesses of the humus horizon clearly indicate the signifi cant role of soil development in the formation of erosion-accumulative structures of the soil cover. Insuffi cient consideration of soil development leads to a signifi cant underestimation of the calculated thickness of the humus horizon and, as a consequence, to an overestimation of the degree of soil degradation. The rate of development of chernozems and dark gray forest soils is about 0.4 mm∙year–1, which is consistent with literature data from case studies. An increase in diff erences between the modeled and measured thicknesses of the humus layer was noted in the series: chernozem - dark gray forest soil - gray forest soil - light gray forest soil. Perhaps the plowing of gray forest soils contributes to an increase in the fl ow of dissolved humus, as well as pedoturbations, which could potentially contribute to a measurement distortion of the thickness of the humus horizon and an underestimation of the degree of degradation of the soil cover in the northern forest-steppe.