Hydromorphic soils of natural and disturbed landscapes of the Tura-Tavda interfluve (south of Western Siberia)

The presented paper is devoted to the ecological and geochemical features of natural and anthropogenically disturbed soils of lake-wetland landscapes of the Tura-Tavda interfluve. Hydromorphic landscapes occupy a significant area within the territory under consideration and play a key role in ensuring the sustainable development of the entire region, performing a number of important ecosystem functions. The intensification of anthropogenic pressure in the south of the Tyumen Oblast, caused by an increase in the area and population of cities, as well as the intensification of agriculture, also affects lake and wetland ecosystems. A striking example of such an impact can be hydromorphic landscapes in the vicinity of the city of Tyumen, which underwent a radical transformation as a result of drainage melioration, peat extraction and subsequent agricultural activity and urbanization. The result of the following process was an intensive transformation of the soil and vegetation cover associated with both mechanical disturbances and drying out, and chemical pollution. The purpose of this study was to assess the evidence of characteristic soil-forming processes and their influence on the structure, properties and geochemical features of soils of hydromorphic landscapes of the Tura-Tavda interfluve. The novelty of the presented research lies in the fact that the combined behavior of inorganic pollutants in similar soils of the territory under consideration has been studied for the first time. The background soil, represented by Sapric Calcic Histosol under a linden-aspen forest, and the soil of a heavily disturbed area, Sapric Drainic Histosol, were studied. Research methods included methods of soil morphology when describing soil profiles, micromorphology of soil thin sections for analysis of expression and intensity of soil-forming processes, as well as chemical analysis of soil, including measurements of pH, Eh, electrical conductivity (EC) and total dissolved solids (TDS) by the potentiometric method in suspension, organic carbon content (Corg) by the titrimetric method, CaCO3 content by the gas-volumetric method, mass loss on ignition (LOI), exchange cations Ca2+ and Mg2+, particle size distribution by sedimentation method with pyrophosphate preparation. The macro- and microelement composition (Na, Mg, Al, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Sr, Pb) of the soils was determined using X-ray fluorescence analysis. Statistical analysis of the data was carried out using the STATISTICA 12 “StatSoft” package (USA). Signs of anthropogenic transformation of the profile in Sapric Drainic Histosol are noted, such as reduced thickness of organogenic and organomineral horizons and the absence of signs of carbonate formation (See Fig. 1), which, on the contrary, are manifested at the micro level in thin sections of Sapric Calcic Histosol (See Fig. 2). There are significant differences in the values of such parameters as pH, Eh, Corg, LOI, as well as sand fraction content for natural and disturbed soils (See Fig. 3). The levels of most elements in the two soils do not differ significantly: Mg (4.7 and 5.1 mg/kg), Ca (51.9 and 35.4 mg/kg), Mn (445.5 and 521.2 mg /kg), Fe (20.7 and 15.5 mg/kg), Cu (5.2 and 8.2 mg/kg), Zn (31 and 37.2 mg/kg), Sr (146.8 and 144.9 mg/kg), Pb (12.9 and 10.7 mg/kg) (See Fig. 4). Compared with the world-soil average, the disturbed hydro-morphic soils of the Tarman bog massif have higher contents of Cr, Mn, Co, As. Correlation analysis made it possible to identify associations of elements, characterized by close relationships (R > 0.576; p < 0.05), which indicates a similar nature of their behavior and a common origin in the hydromorphic soils of the Tura-Tavda interfluve (See Fig. 5). The levels and profile distribution of metals in the soils under consideration, despite significant differences and the history and nature of anthropogenic impact, demonstrated similar values and features. This fact indirectly indicates that even significant anthropogenic impact does not always transform the trends laid down as a result of long-term development of ecosystems and soils. In general, it is possible to note the presence of indirect interrelations between the prevailing set of soil-forming processes and their expression and the features of the radial geochemical structure of natural and disturbed soils. The article contains 5 Figures, 40 References. The authors express their gratitude to Sergei V. Loiko for participation in the field study. The Authors declare no conflict of interest.

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