Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia

Abstract The morphology and chemical characteristics of mineral soils underlying modern peaty (histic) and shallow peat soils (or histosols) are analyzed in pedoecological conditions of Estonia. The underlying shallow peat mantle gley soils have been formed on different geological origin (glaciolacustrine, glacial, glaciofluvial, marine) parent materials. The peat mantle overlying gley soils has accumulated in the process of landscape paludification during the post glacial period. Using the Estonian Soil Classification (ESC), the peat layer thickness of peaty soils is 10–30 cm and of shallow peat soils, 30–100 cm. The studied peaty soils may be characterized as polygenetic soils. Depending on parent material properties (calcareousness, acidity, texture) and feeding water the peaty soils are divided into two types specified by ESC as peaty gley soils and peaty podzols, and by WRB as Histic Gleysols and Histic Podzols. The mineral soils underlying peat soils may be defined as paleosols. The development of such soils has proceeded according to the chronosequence: gley soils or protosols → peaty soils → fen soils → transitional bog soils → bog soils, whereas mineral paleosols may be found under fen, transitional bog and bog soils. The peat soils studied in this research work, classified by ESC as drained shallow transitional (mesotrophic) bog soils and by WRB as Drainic Dystric Ombric Hemic Fibric Histosols, are located on the edges of bog areas and are fed mostly by mesotrophic surface seepage water. In comparative analysis of three soil groups (peaty gley soils, peaty podzols and shallow peat soils) (i) their location on the landscape, the geological origin of their parent materials and morphology of the mineral layers are characterized; (ii) the vertical distribution of organic carbon and total nitrogen contents, and different characteristics of soil acidity are analyzed, and (iii) their catenal position or associated soils are characterized. In the case of peaty soils, the three types of mineral soil profiles (eluvial, eluvio-accumulative and accumulative) which underlie the peat cover were elucidated. Under thicker peat layers, i.e. under shallow peat soils, mostly humus accumulative profiles were found. In all analyzed sites, in the course of progressive paludification (among this peatification) the peaty soils have been formed from gley soils. The formation of the peaty soil stage was followed by the fen soil stage. Depending on the feeding water, some of these soils developed in the direction of bog soils, with an intermediary transitional bog stage. Artificial drainage is of great importance in the development of peat cover, which influences first the decomposition of top layer peat.