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Peat and Peatlands

The formation of peat

The process of forming peat takes place over centuries and consists in the slow accumulation of vegetation debris in wetlands called peatlands. In Canada, this type of wetland developed after deglaciation on poorly drained soils and shallow depressions, under cool, moist and oxygen poor conditions. In this type of environment, bacterial action is much reduced resulting in a rate of plant production that exceeds the rate of decomposition. Over time, slowly decomposing vegetation debris accumulates leading to the development of a peat deposit that in places can exceed 6 m in thickness. The rate at which peat forms in Canadian peatlands ranges from 0.5 to 1 mm per year.

Steps in peatland formation

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The different types of peat

The nature of peat varies according to its original botanical components and its state of decomposition.

The vegetation types that make up the peat affect its physical properties. For example, sphagnum peat will be light and spongy, whereas sedge peat will be characterized by mats of linear fibres.

The colour of peat commonly reflects its age and degree of decomposition. Younger peat is pale yellowish brown and the plant remains are still readily identifiable. Older peat is more decomposed, darker in colour and its source parent material becomes harder or impossible to identify. The degree of decomposition of peat is measured using the Von Post scale, where for example H2 refers to lightly decomposed spongy fibrous peat and H8 to a much more decomposed black peat with the consistency of putty.

Von Post scale

H1 : The living layer and the first layer of undecomposed peat (blond or pale yellowish brown)
H2 - H4 : Blond to light brown / rough texture, spongy / distinct individual plant remains / slightly decomposed
H5 : Brown / slightly soapy texture / plant remains breaking up / moderatly decomposed
H6 - H9 : Dark brown to black / fine soapy to pasty texture / few identifiable plant remains / highly decomposed
H10 : Amorphous matter, completely decomposed