Soils of Peatlands: Histosols and Gelisols

Peatlands are a subset of wetlands that have accumulated significant amounts of soil organic matter. Soils of peatlands are colloquially known as peat, with mucks referring to peats that are decomposed to the point that the original plant remains are altered beyond recognition (Chapter 6, SSSA 2008). Generally, soils with a surface organic layer >40 cm thick have been classified as Histosols in the U.S. soil classification system—Soil Taxonomy (Soil Survey Staff 2014). Permafrost-affected organic soils are classified as the Histels suborder in the Gelisols order (Soil Survey Staff 2014). Based on current calculations of earth’s land surface of 148,940,000 km2 and our estimate of peatland area (or the combined area of Histosols and Histels) (Table 10.1), peatlands occupy about 2.7% of the earth’s surface. Peatlands have historically been classified based on a number of criteria, such as topography, ontogeny (i.e., landscape developmental sequence), hydrology, soil and/or water chemistry, plant community composition, and degree of soil organic matter decomposition (Moore and Bellamy 1974; Cowardin et al. 1979; Gore 1983; Bridgham et al. 1996; National Wetlands Working Group 1997; Inisheva 2006; Vitt 2006). Given the confusion in peatland terminology and the emphasis of this chapter on soils, we will discuss here only the dominant ecological paradigm in peatlands—the ombrogenous–minerogenous gradient. Although the fundamental definition of this gradient is based on hydrology, it is often CONTENTS