Genesis features of the Nikolaevka ryam in the forest-steppe of Western Siberia

Native ecosystems of the forest-steppe zone are most sensitive to climate change, which determines their prospects as a scientific object of both paleoclimatic and paleoecological reconstructions. The forest-steppe raised bogs (ryams) are unique objects; their peat deposit contains information about the genesis and evolution of bogs, as well as environmental conditions throughout their lifetime. A lack of knowledge about forest-steppe bogs' life in the past and the present determines the necessity of the study for a possible forecasting of their evolution under the conditions of native and anthropogenic factors. The aim of this work was to study the peculiarities of the peat deposit formation of the Nikolaevka ryam which is a representative of raised bogs of the forest-steppe of Western Siberia. This research was carried out in the bog area in the Baraba forest-steppe near Nikolaevka-2 village (Ubinskiy district, Novosibirsk oblast). The main studies were conducted in August-September, 2008 and 2010. The object of the study was a pine-dwarf shrub-Sphagnum bog bog known as Nikolaevka ryam (N 55°09', E 79°02'), whose area is approximately 200 hectares. We studied the botanical composition, the degree of peat decomposition, the physicochemical properties (ash content, acidity), the age of the peats, as well as the content of microelements (B, Ga, Ce, Y) in the peat deposit. On the basis of quantitative assessment of microelement content, we calculated geochemical indicators of sedimentation - B/Ga and Ce/Y. The boron content and the B/Ga ratio are an indicator of the climate temperature change, while the Ce/Y ratio characterizes the moisture condition. We estimated the age of the peat deposit of the bog based on both the thickness of the bog peat and the average peat accumulation rate established earlier for other forest-steppe ryams. According to the obtained results, the Nikolaevka ryam is characterized by a large capacity of peat deposit (about 4 m), although it is younger in age (no more than 2.6 thousand years) as compared with similar bogs of the forest-steppe of the Baraba lowland. As for peat deposits of forest-steppe ryams, a thick layer of the oligotrophic peat, a thin layer of the eutrophic peat and a very small interlayer of the mesotrophic peat one are typical. The peat contribution to the formation of the Nikolayevka ryam deposit is determined as 3:1:18 for "eutrophic-mesotrophic-oligotrophic" peats (See Fig. 2). The genesis of the bog and other forest-steppe ryams differs by the eutrophic stage of peat accumulation, which is characterized by the bedding wood-grassy, cotton grass Sphagnum, grass-Sphagnum and Sphagnum (S. squarrosum) peats. It may indicate the predominance of birch-grassy and cotton grass-Sphagnum communities in the early stages of evolution of the studied bog. The dynamics of the change in geochemical indicators, which is connected with the sedimentation conditions during the all-time peat deposit formation, is in good agreement with the known changes in climate conditions on the territory of the modern forest-steppe of Western Siberia in the Holocene. It was revealed that the formation of the Nikolaevka raym occurred in a colder and wetter climate period. As noted, the climate changed from warmer and drier (about 2.0 thousand years ago) to colder and wetter (1.4-1.2 thousand years ago), and again, in the period of a small climate optimum, to a warm and dry climate (1.00.8 thousand years ago). Warming and aridization of climate conditions in the area of the bog occurs from 500 years to the present time. The obtained results highlight the uniformity of the formation and evolution of raised bogs of the forest-steppe of Western Siberia. The weak variability of the botanical composition throughout the depth of the column, despite the significant changes in climate conditions and other external impacts, indicates a significant stability of the ecosystem at the oligotrophic stage of evolution. Thus, forest-steppe ryams of Western Siberia are unique chronicles of the events in the past, bearing in themselves valuable information on the variability of climate changes and other external conditions in the Holocene. The article contains 3 Figures, 1 Table and 41 References.

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