Variability of surface soil horizons in the city of Tyumen (Russia)

Urbanization is one of the main trends of the modern world. The growth of the urban population, and, as a consequence, the increase in the area of urban landscapes, leads to a significant transformation of the environment due to comprehensive human economic activity or anthropogenesis. Such changes affect not only natural landscapes as a whole, but also their individual components, such as soil cover. Anthropogenically transformed soils occupy significant areas within urbanized territories. The nature of the anthropogenic impact on soils is determined by the type of land use and is reflected in the profile of urban soils in the form of formation of corresponding anthropogenic horizons or changes in the properties of surface horizons. Field work was carried out within the boundaries of the city of Tyumen (57°09′ N, 65°32′ E), including both the core of dense urban areas and peripheral agricultural and recreational areas. The object of the study in this work is anthropogenically modified soils of the city of Tyumen. The description and diagnostics of horizons and characteristics were carried out on the basis of the “Classification and Diagnostics of Soils of Russia” [2004], taking into account proposals for the introduction of urban soils into the soil classification system of Russia. The research methods included morphological analysis of soils, determination of acidity, organic carbon content by the titrimetric method, soil texture by sedimentation method with pyrophosphate preparation. Statistical analysis of the data was carried out using the STATISTICA 12 “StatSoft” package (USA). The results showed that natural surface horizons are typical only for undisturbed soils of the recreational area. The soils of other functional zones demonstrated signs of anthropogenic impact, which were expressed in the form of changes in both the soil profile as a whole and surface horizon. The direction and intensity of anthropogenic impact correspond to the severity of the transition from natural to anthropogenic landscapes. The reaction of the surface horizons varies from acidic to strongly alkaline. The largest area within the city is occupied by alkaline soils. The Corg values fluctuate within 0.01-22.84%, with an average value of 2.7%. Loamic and siltic varieties predominate, among which silt loams are the most widespread. The composition of the major oxides is consistent with the soil texture. The contents of Fe2O3 and Al2O3 vary between 0.7-7.7 and 1.5-13%, their increased values are typical for soils on cover and loess-like loams. The SiO2 content in most urban soils is 60-70%. Within the urban area of Tyumen, 5 districts are distinguished according to with the morphology and properties of surface soil horizons. In the city center, urban stratified soils on sandy and silty loamy technogenic deposits with elevated pH and average content of Corg predominate. The northern part of the city is occupied mainly by peat soils on the site of mined-out areas of the Tarman bog massif with an alkaline reaction and а high content of Corg. In the western part on the city periphery, agrogenically transformed and postagrogenic soils with slightly acidic and neutral reaction and average content of Corg on loess-like loams can be found. In the northeast of the city alkaline agricultural soils predominate. In the southeastern part within the lacustrine-alluvial deposits, slightly altered soils with low pH values and low Corg content can be found.

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