There are two types of freshwater peatlands, fens and bogs. They are similar in many ways, because they both develop by the accumulation of peat (organic material). This peat accumulates because the soil in these wetlands is waterlogged and anoxic (lacking oxygen), creating an environment that is not favorable for most forms of decomposing bacteria. The bacteria that can survive (anaerobic bacteria) are very slow at decomposing the organic material found in the soil and thus the organic material will build up over time, forming peat.

The primary difference is in the source of mineral nutrients under which the upper layers of peat have formed. Bogs are obrotophic and fens are minerotrophic. For a more detailed discussion read my study "Is Orono Bog a True Bog?" and see table 2 for a list of the differences between fens and bogs.

Ombrotrophic - receives it's nutrients from the atmosphere.

Minerotrophic- nutrients received from ground water.

Fens are peat containing wetland that receive their nutrients from mineral waters (minerotrophic). The pH of fens is usually around neutral or even slightly alkaline, due to the presence of minerals. Fens have a much wider diversity of plants than do bogs and can be wooded or open.

A "True Bog" is a peat containing wetland, where more than half the bog receives it's nutrients from the atmosphere alone (Ombrotrophic). Bogs develop from the accumulation of peat in fens. The peat builds up to become raised above it's original layer. It becomes a bog when the raised portion becomes ombrotrophic. In some Maine bogs the peat has accumulated to "over 7 meters thick". (Davis 1992) When you walk out onto a bog the surface may bounce a little like a floating mat. The surface of bogs tends to be less productive than fens. The true bog also lacks pH buffering due to it's lack minerals; because of this bogs will be more acidic. The pH range can be as low as 3.5 to 4.5. These conditions severely limit the variety of plant life found in bogs.

Many of the plants you will see are the sundew, pitcher plant, sphagnum moss, sheep laurel, leatherleaf and larch. Click here to see some great pictures of these plants. There are also many hummocks (high spots) and hollows (low spots) in bogs that give the surface an interesting look. The vegetation will vary from hummock to hollow, with sphagnum moss and other bryophytes dominating the hollows and shrub heath dominating the hummocks.

The "true bog" is usually surrounded by other types of wetlands including fens.