Peat is an accumulation of partially decayed vegetable matter. Peat forms in wetlands or peatlands, variously called bogs, moors, muskegs, mires, and fens.
Peat deposits are found in many places around the world, notably in Russia, Ireland, Scotland, northern Germany and Scandinavia, and in North America principally in Canada, Michigan and the Florida Everglades. The majority (around 80%) of peatlands are found in high latitudes; approximately 60% of the world's wetlands are peat. Peatlands cover a total of around 3% of global land mass or 3,850,000 to 4,100,000 km². About 7% of this total has been exploited for agriculture and forestry, with significant environmental repercussions.
Peat forms when plant material, usually in marshy areas, is inhibited from decaying fully by acidic conditions. It is composed mainly of peat moss or sphagnum, but may also include trees, grasses and other marshland vegetation. It also includes many other types of organic remains, including fungi, insects, pollen and even, on occasion, human corpses. Its growth and degree of decomposition (or humification) depends principally on its composition and on the degree of waterlogging. Peat formed in very wet conditions will grow considerably faster, and be less decomposed, than that in drier places. This allows climatologists to use peat as an indicator of climatic change. The composition of peat can also be used to reconstruct ancient ecologies by examining the types and quantities of its organic elements.
Under the right conditions, peat is the earliest stage in the formation of coal. Most modern peat bogs formed in high latitudes after the retreat of the glaciers at the end of the last ice age some 9,000 years ago. They usually grow very slowly, at the rate of only about a millimetre per year.
Types of peatland
Six principal types of peatland are widely recognised. These are:
- Blanket mires. Rain-fed peatlands generally 1 to 3 m deep. Many of the peatlands found in the United Kingdom are of this type, with the UK possessing around 13% of the total global blanket mire area. They generally develop in cool climates with small seasonal temperature fluctuations and over 1 m of rainfall and over 160 rain days each year.
- Raised mires: Rain-fed, potentially deep peatlands occurring principally in lowland areas across much of Northern Europe, as well as in the former USSR, North America and parts of the southern hemisphere.
- String mires: flat or concave peatlands with a string-like pattern of hummocks (hence the name), found principally in northern Scandinavia but occurring in the western parts of the former USSR and in North America. A few examples exist in northern Britain.
Tundra mires: peatlands with a shallow peat layer, only about 500 mm thick, dominated by sedges and grasses. They form in permafrost areas, covering around 110,000 to 160,000 km² in Alaska, Canada, and the former USSR.
- Palsa mires: a type of peatland typified by characteristic high mounds, each with a permanently frozen core, with wet depressions between the mounds. These develop where the ground surface is only frozen for part of the year, and are common in the former USSR, Canada and parts of Scandinavia.
- Peat swamps: forested peatlands including both rain- and groundwater-fed types, commonly recorded in tropical regions with high rainfall. This type of peatland covers around 350,000 km², primarily in south-east Asia but also occurring in the Everglades in Florida.
Characteristics and uses
Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as a fuel, and is traditionally used for cooking and domestic heating in many countries including Ireland and Scotland, where trees are often scarce. Stacks of drying peat dug from the bogs can still be seen in some rural areas.
Peat is also dug into soil to increase the latter's capacity to retain moisture and add nutrients. This makes it of considerable importance agriculturally, for farmers and gardeners alike. Its insulating properties make it of use to industry as well.
Peat fires are used to dry malted barley for use in Scotch whisky distillation. This gives Scotch whisky its distinctive smoky flavour, often referred to as "peatiness" by its afficianados.
Although peat has many uses for humans, it also presents severe problems at times. When dry, it can be a major fire hazard, as peat fires can burn, even underground provided there is a source of oxygen, almost indefinitely (or at least until the fuel source has been exhausted). Peat deposits also pose major difficulties to builders of roads and railways. When the West Highland Line was built across Rannoch Moor in western Scotland, its builders had to float the tracks on a mattress of tree roots, brushwood and thousands of tons of earth and ashes.
During prehistoric times, peat bogs had considerable ritual significance to Bronze Age and Iron Age peoples, who considered them to be home to (or at least associated with) nature gods or spirits. The bodies of the victims of ritual sacrifices have been found in a number of locations in England, Germany and Denmark, almost perfectly preserved by the tanning properties of the acidic water. (See Tollund Man for one of the most famous examples of a bog body).
Peat wetlands formerly had a degree of metallurgical importance as well. During the Dark Ages, peat bogs were the primary source of bog iron, used to create the swords and armour of the Vikings.
Many peat swamps along the coast of Malaysia serve as a natural means of flood mitigation. The peat swamps serve like a natural form of water catchment whereby any overflow will be absorbed by the peat. However, this is only effective if the forests are still present since they prevent peat fires.
Peat 'production' in Ireland
In Ireland, large-scale domestic and industrial peat usage is still widespread. A state-owned company called Bord na Móna, is responsible for managing peat production. It sells processed peat fuel in the form of peat briquettes which are used for domestic heating. These are oblong bars of densely compressed, dried and shredded peat. Peat moss is a manufactured product for use in garden cultivation. Turf (dried out peat sods) is not so commonly used in modern Ireland.
Environmental and ecological issues
Because of the challenging ecological conditions of peat wetlands, they are home to many rare and specialised organisms that are found nowhere else.
Some environmental organisation have pointed out that the large-scale removal of peat from bogs in Britain and Ireland is destroying precious wildlife habitats. In addition, harvesting peat at faster rate than it forms is unsustainable as it takes centuries for a peat bog to regenerate.
Further, recent increases in world carbon dioxide levels are thought to be attributed to the burning of Peat bogs in Borneo, with their large and deep growths containing more than 50 billion tons of CO2.
Peat Swamp Protection
In June 2002 the United Nations Development Programme launched the Wetlands Ecosystem and Tropical Peat Swamp Forest Rehabilitation Project. This project is targeted to last for 5 years till 2007 and brings together the efforts of various non-government organisations.