Geochemical Peculiarities of the Peat Litter’s Morphometric Fractions in the Swamp Birch Forests of Western Siberia’s Southern Taiga

Peat litter of moss-woody composition was studied in swamp birch (Betula pubescens Ehrh.) forests of the grass-mossy forest types in the northern part of the Ob and Tom interfluve (geographical coordinates N 56°23′186″, E 084°32′519″). The litter samples are characterized by a low base saturation of 35.6%; an acidic reaction (\({\text{p}}{{{\text{H}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}\) 4.0); and an ash content of 8.9%. The average content of macro- and microelements forms the following descending series, mg/kg: Ca₅₁₀₅ > Fe₄₂₀₁ > Al₃₆₁₄ > K₉₈₆ > Mg₈₉₃ > Mn₄₆₈ > Sr₂₃₀ > Na₁₅₃ > > Zn₅₁ > Pb₁₃ > Cu_6.8 > Ni₅ > Cr_4.6 > Co_2.9 > Cd_0.2. According to the factor analysis, the mineral component composition of the litter during the plant residues destruction is 57% determined by the variability of the heavy metals content, 37% by the content of alkali, alkaline earth, Zn and Cd. Using the tree clustering method, the morphometric fractions of plant fragments (derivatives) were organized as follows: >10 mm, [(10–5) + + (5–3) + (3–2) + (2–1)] and [(1–0.5) + (0.5–0.25) + <0.25] mm. Discriminant analysis showed 100% fit in the corresponding group. Al and Ca make the greatest contribution to the prediction. As plant fragments decompose, heavy metals and aluminium gradually accumulate while alkali and alkaline earth metals get washed away, the processes being most active at the fermentation stage. The distribution of mineral components in litter derivatives is consistent with their humus state. In small morphometric fractions, compared to large fragments, the ratio (∑HA + ∑FA)/polysaccharides expands, the C/N value gets lower, humic and fulvic acids accumulation occurs mainly for the 1st fraction ones. Peat litter is characterized by an average, moderately dangerous level of pollution: the total pollution index (Zc) is 18. The toxicants composition is dominated by Pb and Zn – chemical elements of the hazard class I.