Publications

Survey of Energy Resources 2007

The Nature of Peatlands and Peat

Globally, peatlands are major stores of carbon. Peatlands are also vital environmental 'regulators'. Peat is accumulating on the ground all the time and the top layers of mires and peatlands form complex ecosystems.

Joosten and Clarke (2002) describe peatlands as analogous to living organisms because they grow, mature and may even die. Joosten and Clarke continue: peat is 'sedentarily accumulated material consisting of at least 30% (dry weight) of dead organic material'.

Peat is the partly decomposed remains of the biomass that was produced, mostly by plants, on waterlogged substrates; it is mostly water-saturated and therefore not compacted. The peat harvested today in the northern hemisphere was formed during the Holocene epoch (the last 10 000 years), after the retreat of the glaciers that once covered most parts of Europe. Those parent plant species, which formed the basal peat, are still forming peat today.

Peat used for fuel consists of different peat layers of different ages. The above-peat biomass (sedges, mosses, shrubs and trees), which is milled and mixed with the upper peat layer in the preparation of the production field, also contains the material freshly grown during the summer before milling. The surface part of peat below the living ground layer, being less than 300 years old, amounts on average to 10.2% of the total peat carbon volume (Mäkilä, 2006). Only the deeper and basal parts of the peat are thousands of years old.

Fig. 8-4 , 8-5 (milling process)
The harvested material thus consists of the living biomass above and below ground, the less-than-300 year old surface layer, which is comparable to wood biomass, (Mäkilä, 2006) and older middle and basal peat. This means that, on average, at least 10% of each peat fuel load consists of very young peat which, according to current criteria, is renewable biomass. This shows that peat is akin to biomass fuels and much closer to them than fossil fuels.