Tatyana Vadimovna Prokofieva

Abundance and diversity of soil saprotrophic bacteria complexes were monitored for two years on the territory of one of the large industrial cities of the European North of Russia, Syktyvkar. The work was carried out before and after quarantine in connection with the COVID-19 pandemic. The capital of Komi is characterized by a high population, and by tense environmental conditions according to the ecological standard. Studies were conducted in 2019—2020. Topsoils (0—10 cm) of urbanozems, horizon A in the park area in the urban space, as well as zonal undisturbed podzolic soil were analyzed. Comparison of the two)year monitoring results demonstrated a marked increase in the number and diversity of saprotro) phic bacteria complexes in 2020 both in urban and control soils (topsoil, 0—10 cm).

Detailed studies of Enterobacteriaceae demonstrated a decrease in the share of opportunistic (Enterobacter agglomerans, Citrobacter europaeus, Klebsiella oxytoca, Serratia marcescens, etc.) as well as fecal coliforms (Escherichia coli, Enterococcus faecalis) in urbanozems in 2020 — a consequence of a sharp and prolonged decrease in the anthropogenic impact on the environment. It can be viewed as a manifestation of the soil ability to “self-purification” when anthropogenic impact on the environment reduces.

The functioning of stationary soil lysimeters is determined by a limited volume of soil in both horizontal and vertical directions. The areal spatial limitation and the proximity of phytocenoses to each other in the large lysimeters at the
Moscow State University Soil Station determines the interbiogeocenotic exchange of plant litter, while the vertical
one excludes the role of groundwater and their influence on soil formation. The absence of lateral runoff, which is
common in natural landscapes, and the increased supply of alkaline earth elements with atmospheric precipitation
and dust, reduces the manifestation of the eluvial-illuvial process. Comparison of lysimetric waters in 1967–1968
and 2014–2015 showed a significant increase over time in the concentration of elements such as calcium, sodium,
magnesium and potassium, and among the anions chloride and sulfate ions. The local spatial geochemical contrast
of lysimetric waters caused by the effect of anti-icing agents, however, does not change the relative migration ability
of elements. According to the level of biogeochemical accumulation of elements in the soil, macroelements form
a series of Ca > K > Al > Mg > Na, and trace elements — Zn > Sr > Cu > Ba, while maintaining the same type on all
types of lysimeters. An increase in the concentration of elements in the soil occurs in the following order: broad
leaf > spruce > mixed > pure fallow. The increased accumulation of elements in the soil profile of spruce forests in
comparison with mixed plantations correlates with the type of humus forming here, which is close to the moder
type, which is due to the combination of coniferous and deciduous litter.

The features of anthropogenic transformation of natural chestnut soils and genesis of urban soils and conditions of the dry-steppe natural zone on the territory of Volgograd were studied in detail. The study was carried out by comparing the morphological characteristics of natural soils and their anthropogenic-modified counterparts. A morphological description was carried out for each of the 16 transects. The morphological characteristics of urban soils and chestnut soils of the city outskirts were compared. Under the influence of urban pedogenesis, natural light humus horizons AJ disappear, and the average thickness of diagnostic xerometamorphic horizons BMK decreases. The upper boundary of accumulative-carbonate horizon BCA lowered relative to the surface by an average of 32 cm compared to natural chestnut soils. Under the influence of urban-techno-pedogenesis there appeared inclusions represented by debris of building materials and garbage, accumulated in the process of human settlements functioning, the structure, density, nature of boiling from HCl 10% have changed. Modern surface horizons often boil off HCl 10%. In the landscaped recreational areas of the city, carbonate leaching has occurred due to irrigation of the area. The variants of morphological transformation of chestnut soils formed on the territory of Volgograd as a result of urban pedogenesis have been revealed. The first variant - soils of initial stages of technotransformation, with changes at the level of the upper horizons. The second option — soils with thick urban horizons, overlapping the preserved diagnostic horizons. The third option — burial of natural rocks by man-made soils of varying thickness with almost complete destruction (removal) of natural soil horizons. The fourth option — soils with thick humus horizons formed at the expense of intensive infusion of organic matter in underpourings of compost. It is noted that most of the soils of the city have profiles, completely formed on man-made sediments, and do not contain natural soil horizons in the upper 1,5 m thickness. According to the Field Identification of Soils of Russia, the studied soils of the first variant of transformation are defined as urban-stratified. The soils of the other options of transformation can be attributed to man-made surface formations. The content of organic carbon in the urban, technogenic, and replanted horizons averages 1,1, 0,25, and 1,6%, respectively. Chemical analysis of urbic, reclamation, and technogenic horizons revealed a low content of readily soluble salts — 0,14% and carbonates — 0,9%. Density in UR and RAT horizons is on average 1,4─1,43 g/cm³, in TCH horizons — 1,55 g/cm³. Buried horizons average density is 1,43 g/cm³ in AJ, 1,49 g/cm³ in BMK, 1,62 g/cm³ in B, and 1,54 g/cm³ in BCA, which is higher than average density for native chestnut soils. Also for the buried horizons is characterized by leaching from salts (mid. 0,2%) lower values of calcium carbonate content than in the background, alkalinization of the environment, as well as a decrease in organic carbon by an average of 0,35% in the AJ, BMK, and B horizons, and by 0,28% in BCA. The average CaCO3 content in the upper humus and median horizons is 1,4% and in the carbonate horizon 4,3%. The obtained results allow us to study in more detail the peculiarities of the genesis of urban soils and the anthropogenic transformation of natural chestnut soils in urban conditions of the dry-steppe natural zone.