than boreal or lowland tropical peats. (0.25 mm/year in Colorado Rocky Mountains vs. 1.3 mm/year in Ecuadorian páramo vs. 8 mm/yr in lowland tropics (Chimner and Karberg 2008)). There are three processes of peat formation. Primary peat formation permits peat to form directly over freshly exposed mineral soil without any open or standing water and no deposition of aquatic sediment. It occurs on poorly drained, flat expanses in shallow basins or slopes. Infilling or terrestrialization allows peat to develop on the margins of slow moving water then fill in towards the center. Open waters become partially or totally converted to bogs or fens. Paludification occurs when a shift in local hydrology promotes waterlogged conditions (i.e. change in climate or plant colonization); the term also refers to peat encroachment onto adjacent mineral soils (Charman 2002; Rydin and Jeglum 2006). All three processes are at work to create mire complexes in most valleys in HNP. General Physical and Chemical Characteristics In terms of physical characteristics, peatlands exhibit vertical and horizontal structure. The acrotelm is the top 10 – 15 cm of the mire including surface vegetation. The catotelm is the deeper layer where conditions are always anoxic. Soil in the catotelm is always darker, more decomposed and constantly waterlogged (Rydin and Jeglum 2006). Peat is known for high water storage capacity and most water is stored in the catotelm where hydraulic conductivity is low (Pfadenhauer et al. 1993). Mires can exhibit large and small-scale horizontal patterns, but these are more common in the boreal latitudes. Wide color variation exists, but peat is usually dark brown to black. Fibrosity depends on state of decomposition, bulk density, and porosity. All of these characteristics vary over time as the decomposition state changes. Chemically, peats have low pH levels, high cation exchange capacity, and low gas content (higher in the acrotelm than in the catotelm) (Rydin and Jeglum 2006). Carbon typically comprises ½ of the organic matter. Peatlands store tremendous volumes of carbon: the best current estimate of global carbon storage is 600 gigatons, most located north of 45° N (Yu et al. 2010). Peat is a source of methane and nitrous oxide. Peat chemistry is heavily influenced by the sources of water and throughflow patterns (Moore and Bellamy 1974).
Field Exercise – Von Post System of Humification Scale
Description
Plant structure
H1
Undecomposed
Unaltered
H2
Mostly undecomposed Very weakly decomposed Weakly decomposed Moderately decomposed Strongly decomposed Strongly decomposed Well decomposed Almost completely decomposed Completely decomposed
Distinct
H3 H4 H5 H6 H7 H8 H9
H10
Expressed fluid Colorless, clear Yellow-brown clear Turbid
Peat lost when squeezed None
Consistency in the hand n.d.
None
n.d.
None
Not mushy
Noticeably turbid Strongly turbid
None
Slightly mushy
Some
Very mushy
n.d.
Up to 1/3
Strongly mushy
n.d.
About 1/2
Gruel-like
n.d.
About 2/3
Almost indistinct
n.d.
Almost all
Only fibrous matter and roots remain Almost all peat escapes
Unrecognizable
n.d.
All
Distinct Distinct Clear, becoming indistinct Somewhat indistinct Indistinct but recognizable Vague
All peat escapes