How does a peat bog form ?
A peat bog is a peat-building ecosystem; peat is dead organic matter that only partly decomposes. This process of partial decomposition, called humification, can be variable in intensity (weakly to highly humified peat).
There are different types of bogs, which are not detailed here. For all of them, the following two conditions are required :
required conditions |
propitious situations |
| - a positive water balance: the bog receives more water than it can lose | - annual precipitation (AND/OR spring- or runoff water) >> annual potential evaporation (without saesonal deficit) |
- a positive organic matter balance: organic matter production and accumulation is quicker than its decomposition |
- cool temperatures |
As an example, the formation of Sphagnum raised bogs, which are the most common bogs in the Hautes-Fagnes and are present in many areas of the world, is illustrated hereunder.
Peat mosses (Sphagnum) are very special mosses, made of two types of cells: small green (chlorophyllian) cells, and large, dead cells acting as water reservoirs.
When they colonize a propitious place (humid to aquatic, acidic), they form dense cushions. Sphagnum stalks continuously grow upwards, while their lower part dies. These dead Sphagnum, as well as other plants that grow on bogs, are progressively buried under living Sphagnum and partly decompose to form peat.
Remains of all objects that were formerly present at the surface of the bog can be found in peat: seeds, plant tissues, wood pieces, spores, pollens, insect or spider fragments, ash, volcanic dust,...
