The results of the Internet discussion on the classification of urban soils aimed at evaluating their possible inclusion into the modern Russian soil classification system adopted by a wide range of specialists are presented. The first step was to address the urban diagnostic horizons as the basis for identifying soil types according to the rules of the Russian soil classification. New diagnostic horizons were proposed for urban soils: urbic (UR), filled compost-mineral (RAT), and filled peat (RT). The combination of these horizons with other diagnostic horizons and layers of technogenic materials correspond to different soil types. At the subtype level, the diagnostic properties (qualifiers) that may reflect both natural phenomena (gley, alkalinity) and technogenic impacts on the soils (urbistratified; phosphatic; or poorly expressed urban-ur, rat, rt) are used. Some corrections were proposed for the system of parent materials in urban environments. Urban soils formerly described in another nomenclature-urbanozems, urbiquasizems, and culturozems-are corre lated with the taxa in all the trunks of the system. The proposals accepted can be used for the next updated version of the new Russian soil classification system.
Purpose The main aim of the study performed during 6 years was to determine the specific features of heavy metal contamination of soil cover in the city of Rostov-on-Don and its agglomeration. It was supposed to answer the question: Does soil inherit heavy metals mainly from the parent rocks, or they enter the soil mainly as a result of anthropogenes in the city condition. Materials and methods Seventeen soil profiles were established in different parts of the Rostov agglomeration, within the city and in the urbanized agricultural region. The following objects were studied: (1) calcareous ordinary chernozem under steppe vegetation (fallow) and under trees (parks): soils of natural structure insignificantly affected by urbanization processes; (2) urbostratozems: soils of natural structure overlain by loose anthropogenic deposits; (3) screened urbostratozems (or ecranozems): soils of natural structure overlain by asphalt and/or another impermeable surface. The contents of heavy metals were determined by X-ray fluorescence. The degree of soil contamination with heavy metals was assessed by comparing their content with the MPC values (danger coefficient method) or using the total contamination factor Zc. Results and discussion The comparison of chernozems under different plant covers shows that the woody plants capable of retaining moisture in the soil and more deeply wetting the soil layer decrease the accumulation of vanadium, chromium, cobalt, nickel, and copper in the surface layer. The accumulation coefficients of these metals in urbostratozems are still lower for some reason. At the same time, an increase in the accumulation of zinc and lead is observed in the surface layer of soils under the forest canopy, as well as in the urbostratozems. In the Urbostratozems, screened by dense surfaces, a high variation is observed, which is related to the different times of soil sealing with asphalt.Conclusions The results showed that the concentrations of most elements in the parent rock of Rostov-on-Don exceed the background values, and those of some elements exceed the MPC levels. The main source of accumulation of these elements in the soil profile is the parent rock. Additional input from anthropogenic sources is contributed by the accumulation of such elements as chromium, nickel, zinc, and lead.
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