Moscow University Soil Studies Bulletin. 2021. 4.

The article discusses the existing methodological approaches used in Russian and foreign studies of urban soils. The analysis of methods for studying the soil cover as an object of landscape design, considering its formation and functioning on the example of the Moscow city. Information is provided on the territorial and functional organization of urban space. From the point of view of methodological approaches for the study of urban soils, it is proposed to divide them into two groups: uneven-aged soils with bulk surface horizons from various recultivants, formed according to design documents, and natural and surface-transformed soils without filling layer. The features of methodological approaches for studying each soil group are considered. It is noted that the material composition of the ground materials from which urban soils are formed has a significant impact on their structure, properties and functioning. The use of ground materials of different composition and properties for the formation of the upper part of urban soils, sometimes an unknown history of their functioning and land use, and possible numerous violations cause extremely high and most often unsystematic spatial and temporal variability of urban soils. With the increasing interest of the scientific community in the qualitative assessment of the urban environment, the most promising is the development of methods for studying the resulting ecological functions of urban soils using integral indicators, as well as the development of approaches, methods and technologies for creating urban soils that meet the criteria of green environmental management.

Key words: soils of Moscow city, zoning of urban areas, soil science methods, urban ecology, ecological functions of soils, ground materials.

We used sequential static chemical extraction methods for studying soil pollution with heavy metals. This allowed determining the amount of metals extracted with this reagent. The new equipment for dynamic extraction of HM and obtaining extractograms, opens up additional possibilities: to determine the number of particles’ groups that differ in resistance to this reagent and to determine the statistical indicators of each group of particles. The technique for decrypting extractograms is based on their deconvolution into a series of asymmetric Gaussians corresponding to a separate group of particles – carriers of HM. The statistical indicators of Gaussians include the relative stability of each group of particles to this reagent, their dispersion D, asymmetry As, and excess Ex. Statistical indicators of Ca-Mg particles of HM carriers in urban soils show a high heterogeneity in the resistance of particles to acetic acid compared to particles in non-urban soils. The probable reason for the difference between urban and non-urban soils is a different composition of Ca-Mg minerals: , most Ca-Mg minerals in non-urban soils are carbonates. Urban, initially carbon-free soils are contaminated with Ca-Mg-containing construction waste: cement, lime and asbestos, and also contain secondary carbonates formed from Ca-Mg-waste. Urban acetic soluble pollutants belong to the following groups of minerals: technogenic hydroxides, silicates and aluminates of calcium and magnesium, which greatly distinguishes their chemical properties from the properties of carbonates. The abundance of pollutant forms as carriers of HM determines the diversity and heterogeneity of groups of particles soluble by acetic acid in urban soils.

Complexes of cultured saprotrophic bacteria and yeasts from different components of soil constructions (humus soil horizon and peat) were studied simultaneously with the assessment of auxin-producing activity (synthesis of 3-indolylacetic acid, IAA), of some bacteria and yeast strains isolated. The study was conducted at the stage of laying two variants of constructions in Syktyvkar, formed from components of local origin (variant 1) and imported (humus soil horizon, Moscow, peat "Seliger-agro", Tver region) (variant 2).

The taxonomic structure of microbial complexes isolated from the studied substrates had significant features of similarity. At the same time, components of variant 1 revealed a greater diversity of cultivated saprotrophic bacteria (Bacillus species) species resistant to adverse environmental conditions as well as the presence of psychrophilic basidiomycete yeast Leucosporidium scottii, which was not found in the components of variant 2.

The average IAA production by the yeast strains studied was 647.6 µg/L and by saprotrophic bacteria - 741.3 µg/L. The highest values of IAA concentration were found in the culture liquid of the yeast Tausonia pullulans (strain Y-6) - 3362.6 µg/l, isolated from the humus soil layer of variant 1, and of the two saprotrophic bacteria Flavobacterium рsychrophilum (strain B-7 - 2616.8 µg/L and B-5 - 1056.3 µg/L), isolated from the humus soil horizon in variant 1 and from peat of variant 2. For strains of the yeast Leucosporidium scottii and the cultured saprotrophic bacteria Flavobacterium psychrophilum the ability to synthesize IAA was found for the first time. 

Urban soils contain a substantial pool of organic matter (OM), the decomposition of which leads to intensive CO₂ emission that important in terms of global climate change. The OM decomposition increases in line soil temperature, the magnitude of such effect largely depends on the soil physicochemical properties. At the same time, the contribution of the functional microbial diversity on the temperature sensitivity of OM decomposition (Q₁₀) is still poorly understood, and especially for urban ecosystems. Consequently, our study aimed to assess the effect of the microbial functional diversity on the Q₁₀ value for urban soils considering its physicochemical properties. In the St. Petersburg, Moscow, Voronezh and Krasnodar, located in different bioclimatic zones (southern taiga, mixed forests, forest-steppe and steppe, respectively), four parks were selected. In each park the samples were taken from the topsoil (0-10 cm layer). In soil samples, decomposition of OM was determined at the temperature 10, 20, 30, and 40°C for the subsequent calculation of Q₁₀ value. The soil physicochemical (moisture, texture, pH, content of C, N, P₂O₅, K₂O) and microbial (functional diversity, biomass) properties were determined as possible Q₁₀ index drivers. The Q₁₀ value in humus horizons of urban soils was mainly correlated with its texture, moisture C and N contents, while the microbial functional diversity was correlated with P₂O₅. The regular distribution pattern of Q₁₀ and the studied soil properties of urban parks along the latitudinal gradient has not been found, however a negative relationship between Q₁₀ and the microbial functional diversity has been revealed (R² = 0.50). Apparently, the high microbial functional diversity contributes to a decrease of the temperature sensitivity of OM decomposition.

It is shown that the cultural layers of urban ecosystems are distinguished by the accumulation of all groups (general, mineral, organic) phosphorus compounds. At the same time, the humus of the horizons of anthropogenic origin is enriched in organic phosphorus in comparison with natural analogues by 3-10 times. Due to the neutral and close to neutral character of soil acidity, the mobility of all groups of phosphorus compounds is reduced, which is the main reason for their fixation in the profile of stratozems. It was found that the group composition of phosphorus in the soils of settlements and settlements does not reflect the zonal patterns of accumulation and profile distribution of phosphorus, but it can serve as a reliable indicator of the presence of anthropogenic activity in the past.

Methodological problems of the quantitative assessment of pollution of urban soils by benzo(a)pyrene and their bioremediation are considered by the example of the Moscow metropolis. Available materials of scientific publications and official reports of the «Mosecomonitoring» municipal system about pollution of urban soils by benzo(a)pyrene and the patterns of its dynamics were used. The methodological basis of the study was mathematical modeling, including both non-linear regression analysis in the S-Plot-11 program and numerical computer simulation in the Matlab-7 software. Analysis of published materials reveals at least a double excess of the maximum permissible level of pollution of urban soils by benzo(a)pyrene at 70% of the territory of the Moscow metropolis, with a high probability of an extremely high degree of pollution in several dozen MPCs at 10% of the city's area. Unlike known works in this field, the study links such a negative situation not with the resistance of benzo(a)pyrene in soils, but with its high technogenic load. A simple kinetic model, verified for experimental information on biodegradation of benzo(a)pyrene in soils, makes it possible to assess the permissible limits of technogenic load, guaranteeing the self-cleaning of urban soils from this dangerous pollutant in the conditions of Moscow.