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
Poorly drained site on mineral soil
Accumulation of organic matter
Infilling of the depression and consolidation
Development of a raised dome of peat
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.