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Formation of the chemical composition of Histosols and histic soils in the forest lands of Estonia

The formation and vertical distribution of the chemical properties of fen (group I, five research areas) and transitional bog (group II, eight research areas) Histosols, and situated depressions of mineral landscape Histic Gleysols (group III, six research areas) and Histic Podzols (group IV, seven research areas) soil covers were studied. As a benchmark in the comparative analysis of Histosols, we used the 20 cm epipedon peat layers of eutrophic moderately acid (I) and mesotrophic very strongly acid (II) types. The thickness of histic soil epipedon peat varied from 10 to 30 cm and was classified as slightly acid peaty mull (IIIa) or strongly acid peaty moder (IIIb), and as very strongly acid peaty mor (IV). In forming the epipedon of the forest floor, aqua regia (mixture of hydrochloridic and nitric acids, 3:1)-extractable Fe, Cr, Al, Pb and Ni accumulated to a great extent (accumulation coefficient>2.5), and S, Na and Hg accumulated to a medium extent (accumulation coefficient 1.2–2.0); the amounts of Zn, K and Mn decreased to a great extent (accumulation coefficient<0.5), and those of Mg and P to a medium extent (accumulation coefficient 0.6–0.8); levels of Ca, Cu and Cd remained practically unchanged. Comparison of Histosol subsoil and substratum peats with a Histosol epipedon demonstrates considerable accumulation of Mn, Pb, Cd, Zn, Hg and Na in the thin (20 cm) superficial peat layer of mires.