Peat Bogs

A peat bog is a type of wetland whose soft, spongy ground is composed largely of living and decaying Sphagnum moss. Decayed, compacted moss is known as peat, which can be harvested to use for fuel or as a soil additive.

Peat bogs are found throughout the world where cool temperatures and adequate rainfall prevail. Estimates indicate that peatlands (bogs and fens) cover as much as 5 percent of the land surface, primarily in northern temperate and arctic regions. Canada contains approximately 130 million hectares of bogs, while the United States has approximately 7 million hectares.

Bogs are not just any type of wetland, and they require a particular sequence of events in order to form. A bog begins in a low spot where ground-water is close to or above the surface. Such a spot, sometimes called a fen, contains a wide mix of water-tolerant plants, including grasslike plants such as reeds and sedges, and trees such as alders. Groundwater has a relatively high mineral content, which helps support this variety of plant types. Because water in such low spots is still, oxygen is not replenished quickly, and normal decomposition of dead plants is slowed somewhat by the low oxygen content. When plant deposition exceeds plant decay, the fen begins to fill in, and the uppermost level of the fen loses contact with groundwater. In many wetland areas, this leads to drying out of the wetland and development of a field or woodland. However, if there is sufficient rainfall and other conditions are right, the fen may be transformed into a raised bog— a self-contained wetland that grows up to and even above the surrounding terrain.

Most plants cannot survive on the low mineral content of rainwater, but the several dozen species of mosses of the genus Sphagnum can, and these come to dominate the bog flora. Sphagnum removes positive ions from the water such as calcium and sodium, leaving positive hydrogen ions, which are acidic. As a result, the pH of bog water may be as low as 3.5, about the acidity of tomato juice. As new Sphagnum grows atop the partially decayed growth of previous years, it compacts the layers below it into the thick, crumbly, spongelike material known as peat. Other bog plants include the carnivorous sundews (Drosera spp.) and acid-tolerant reeds and sedges.

Peat has been harvested as a fuel for millennia, and it is still used this way today. Fuel peat is harvested both commercially and by individuals. Because bog peat is approximately 95 percent water, it must be dried before use. Dried peat is also used as a soil additive in gardens and nurseries, and its harvest and export for this purpose is economically significant to Canada, Sweden, Ireland, and several other countries.

Like other wetlands throughout the world, bogs are threatened by human activities, including draining and filling, and harvesting of peat. Estimates indicate that 90 percent or more of former boglands has been lost in several European countries.

see also Bryophytes; Carnivorous Plants; Wetlands.

Richard Robinson

Bibliography

Eastman John A. The Book of Swamp and Bog: Trees, Shrubs, and Wildflowers of the Eastern Freshwater Wetlands. Mechanicsburg, PA: Stackpole Books, 1995.

Feehan, John. The Bogs of Ireland: An Introduction to the Natural, Cultural and Industrial Heritage of Irish Peatlands. Dublin: The Environmental Institute, University College, 1996.