Geoecological assessment of the current state of upper bogs (Ryams) of the Barabin forest steppe under anthropogenic impact
The two sampled peatlands of the Baraba steppe are compositionally heterogeneous and consist of bog and fen peat types. The Ubinskoe section is composed of Sphagnum fuscum peat and encloses layers of combusted transitional woody peat in the upper part (0-257 cm) and grass, woody-grass, and sphagnum peat in the lower part (257-347 cm). The Sherstobitovo section comprises Sphagnum magellanicum peat in upper 70 cm and diverse grass, woody-grass, and sphagnum peat species in the lower 70-250 cm interval. According to 14C constraints, peat accumulation in the two peatlands began, respectively, at 5.6 and 4.5 kyr BP. The uneven profiles of main biogenic elements record peat composition changes at different evolution stages. Deep peat intervals were deposited in the time span from 5.6 to 2.7 14C kyr BP at relatively high concentrations of S and N in organic matter. Both Ubinskoe and Sherstobitovo samples show significant correlation of C/N ratios with the degree of OM de-composition (r = -0.93 and -0.82, respectively) and with peat depth (r = -0.61 and -0.76), which confirms increasing OM degradation. The heterogeneity in the distribution of the main biogenic elements (C, H, N, S) along the peat bog sections marks the change in the botanical composition of peat at different stages of bog formation. All chemical elements can be conditionally divided into four main groups: 1. Li, Al, Na, K, Fe, Cr, Mn, Ni - included in the terrigenous (detrital) part of peat; 2. Ca, Sr, Mg; with maximum concentrations in the lower intervals of peat sections; 3. Pb, Sb, Hg, Cu, Zn - chalcophilic elements, with maxima in the upper intervals of peat sections. The profiles of iron-group elements (Fe, Mn, Cr, and Ni) stand out among other elements common to the clastic peat component. Judging by similarity of concentrations and Al, K, and Na patterns, silicate and aluminosilicate material had the same source: atmospherically-derived soil dust. The sampled sections show a tendency of increasing Ca (and partly Mg, Sr) downward from upper 60 cm of the Sherstobitovo peat and 112 cm of the Ubinskoe peat, which was reported also for other raised bogs. The greater concentrations of Cu, Zn, As, Se, Cd, Sb, Hg, and Pb in upper layers may be attributed to natural and man-caused atmospherically-derived dust inputs in the 20th and 21st centuries, which agrees with published evidence. An assessment of the pollution of bog waters based on a set of geochemical criteria shows that the highest concentration coefficients (Kc) of elements (As, Pb, Zn, Cu, Mn) involved in atmospheric transport during fires are found in the bog waters of the Ubinsky burnt ryam. Comparative analysis of the values of concentration coefficients (Kc) in the studied components of the Ubinsky burnt ryam ecosystem (forest litter, upper soil horizon, indicator biological objects - moss, lingonberry and birch leaves) indicates an intensive accumulation of chalcophilic elements (Pb, Sb, Cu, Hg) in them, which may be a consequence of the anthropogenic impact on the raised bog during fires.