Transformation of Kastanozems in the conditions of urban technopedogenesis within the city of Volgograd

Abstract

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.