Peat is an accumulation of partially decayed vegetation matter. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world. By volume there are about 4 trillion m³ of peat in the world covering a total of around 2% of global land mass (about 3 million km²), containing about 8 billion terajoules of energy.
Peat deposits are found in many places around the world, notably in Ireland, Russia, Belarus, Ukraine, Finland, Lithuania, Latvia, Estonia, Scotland, Poland, northern Germany, the Netherlands, Scandinavia, New Zealand and in North America, principally in Canada, Michigan, Minnesota, the Florida Everglades, and California's Sacramento-San Joaquin River Delta. The amount of peat is smaller in the southern hemisphere, as there is less land, but peat can be found in New Zealand, Kerguelen, Southern Patagonia/Tierra del Fuego and the Falkland Islands. Asia, Indonesia (Kalimantan (Sungai Putri, Danau Siawan, Sungai Tolak, Rasau Jaya (West Kalimantan), Sumatra).
Approximately 60% of the world's wetlands are peat. About 7% of total peatlands have been exploited for agriculture and forestry. Under proper conditions, peat will turn into lignite coal over geologic periods of time.
Peat forms when plant material, usually in marshy areas, is inhibited from decaying fully by acidic and anaerobic conditions. It is composed mainly of marshland vegetation: trees, grasses, fungi, as well as other types of organic remains, such as insects, and animal remains. Under certain conditions, the decomposition of the latter (in the absence of oxygen) is inhibited, and archaeologists often take advantage of this.
Peat layer growth and the degree of decomposition (or humification) depends principally on its composition and on the degree of waterlogging. Peat formed in very wet conditions accumulates considerably faster, and is 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 constituents.
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 slowly, at the rate of about a millimetre per year.
Peat may contain traces of heavy metals such as mercury. The source of mercury may be methane upwelling from great depths, which interacts with the peat.
Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed, and comprise intact fiber. Hemic peats are somewhat decomposed, and sapric are the most decomposed. Phragmites peat is one composed of reed grass, Phragmites australis, and other grasses. It is denser than many other types of peat. Engineers may describe a soil as peat which has a relatively high percentage of organic material. This soil is problematic because it exhibits poor consolidation properties.
Peat is soft and easily compressed. Under pressure, water in the peat is forced out. Upon drying, peat can be used as a fuel. It has industrial importance as a fuel in some countries, such as Ireland and Finland, where it is harvested on an industrial scale. In many countries, including Ireland and Scotland, where trees are often scarce, peat is traditionally used for cooking and domestic heating. Stacks of drying peat dug from the bogs can still be seen in some rural areas.
Peat is important for farmers and gardeners, who mix it into soil to improve its structure and to increase acidity. The most important property of peat is retaining moisture in soil when it is dry and yet preventing the excess of water from killing roots when it is wet.
Peat can also store nutrients although it is not fertile itself.
Its insulating properties make it of use to industry.
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 almost indefinitely (or at least until the fuel is exhausted). Peat fires can even burn underground, reigniting after the winter, provided there is a source of oxygen. Peat deposits also pose major difficulties to builders of structures, roads, and railways, as they are highly compressible under even small loads. 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.
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, Ireland, and especially northern 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).
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 effective only if the forests are still present, since they prevent peat fires.
Peat is also an important raw material in horticulture. However it is recommended to treat peat thermally, e.g. through soil steaming, in order to kill inherent pest and reactivate nutrients. Furthermore peat is used in medicine and balneology to produce filters and textiles}.
Peat is sometimes used in freshwater aquaria, most commonly in soft water or blackwater river systems, such as those mimicking the Amazon River basin. In addition to being soft in texture and therefore suitable for demersal (bottom-dwelling) species such as Corydoras catfish, peat is reported to have a number of other beneficial functions in freshwater aquaria. It softens water by acting as an ion exchanger, it contains substances good for plants and for the reproductive health of fishes, and can even prevent algae growth and kill microorganisms. Peat often stains the water yellow or brown due to the leaching of tannins.
In Ireland, large-scale domestic and industrial peat usage is widespread. Specifically in the Republic of Ireland, a state-owned company called Bord na Móna is responsible for managing peat production. It produces milled peat which is used in power stations. 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. Briquettes are largely smokeless when burned in domestic fireplaces and as such are widely used in Irish towns and cities where burning non-smokeless coal is banned. Peat moss is a manufactured product for use in garden cultivation. Turf (dried out peat sods) is very commonly used in rural areas.
The climate, geography and environment of Finland favour bog and peat bog formation. Peat is available in considerable quantities: Some estimates put the amount of peat in Finland alone to be twice the size of the North Sea oil reserves. This abundant resource (often mixed with wood at an average of 2.6%) is burned in order to produce heat and electricity. Peat provides approximately 6.2% of Finland's annual energy production, second only to Ireland. The contribution of peat to greenhouse gas emissions of Finland can exceed a yearly amount of 10 million tonnes carbon dioxide, equal to the total emissions of all passenger car traffic in Finland.
Finland classifies peat as a slowly renewing biomass fuel as opposed to the stance of the European Union and Intergovernmental Panel on Climate Change which classify peat strictly as a fossil fuel. Peat producers in Finland often claim that peat is a special form of biofuel, because of the relatively fast retake rate of released CO2 if the bog is not forested for the following 100 years. Also, agricultural and forestry-drained peat bogs actively release more CO2 annually than is released in peat energy production in Finland (approx 30 TWh versus 25 TWh). The average regrowth rate of a single peat bog, however, is indeed slow, from 1,000 up to 5,000 years. Furthermore it is a common practice to forest used peat bogs instead of giving them a chance to renew, leading to lower levels of CO2 storage than the original peat bog.
At 106 g CO2/MJ, the carbon dioxide emissions of peat are higher than those of coal (at 94.6 g CO2/MJ) and natural gas (at 56.1) (IPCC). According to one study, increasing the average amount of wood in the fuel mixture from the current 2.6% to 12.5% would take the emissions down to 93 g CO2/MJ, though little effort is made to achieve this.
Peat extraction is also seen by some conservationists as the main threat to mire biodiversity in Finland. The International Mire Conservation Group (IMCG) in 2006 urged the local and national governments of Finland to protect and conserve the remaining pristine peatland ecosystems. This includes the cessation of drainage and peat extraction in intact mire sites and the abandoning of current and planned groundwater extraction that may affect these sites.
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 organisations and scientists have pointed out that the large-scale removal of peat from bogs in Britain, Ireland and Finland is destroying wildlife habitats. It takes centuries for a peat bog to regenerate.
Recent studies indicate that the world's largest peat bog, located in Western Siberia and the size of France and Germany combined, is thawing for the first time in 11,000 years. As the permafrost melts, it could release billions of tons of methane gas into the atmosphere.
The world's peatlands are thought to contain 180 to 455 petagrams of sequestered carbon, and they release into the atmosphere 20 to 45 teragrams of methane annually. The peatlands' contribution to long-term fluctuations in these atmospheric gases has been a matter of considerable debate.
Large areas of organic wetland (peat) soils are currently drained for agriculture, forestry and peat extraction. This process is taking place all over the world. This not only destroys the habitat of many species, but heavily fuels climate change. As a result of peat drainage, the organic carbon that was built up over thousands of years and is normally under water, is suddenly exposed to the air. It decomposes and turns into carbon dioxide (CO2), which is released into the atmosphere.
Peat has a high carbon content and can burn under low moisture conditions. Once ignited by the presence of a heat source (e.g. a wildfire penetrating the subsurface), it smolders. These smouldering fires can burn undetected for very long periods of time (months, years and even centuries) propagating in a creeping fashion through the underground peat layer. Peat fires are emerging as a global threat with significant economic, social and ecological impacts. Recent burning of peat bogs in Indonesia, with their large and deep growths containing more than 50 billion tons of carbon, has contributed to increases in world carbon dioxide levels. Peat deposits in Southeast Asia could be destroyed by 2040.
In 1997, it is estimated that peat and forest fires in Indonesia released between 0.81 and 2.57 Gt of carbon; equivalent to 13-40 percent of the amount released by global fossil fuel burning, and greater than the carbon uptake of the world's biosphere. These fires may be responsible for the acceleration in the increase in carbon dioxide levels since 1998.
More than 100 peat fires in Kalimantan and East Sumatra continue to burn since 1997. Each year the peat fires in Kalimantan and East Sumatra ignite new forest fires above the ground.
Some northern European acidic anaerobic peat bogs have proved to have the capability to preserve mammalian tissue for millennia. Examples of this conservation are Tollund Man and Haraldskær Woman, both recovered from peat bogs with remarkable intact skin, internal organs and skeletons. Also preserved were their clothes and personal effects.
In June 2002 the United Nations Development Programme launched the Wetlands Ecosystem and Tropical Peat Swamp Forest Rehabilitation Project. This project was targeted to last for 5 years until 2007 and brings together the efforts of various non-government organisations.
In November 2002, the International Peat Society and the International Mire Conservation Group (IMCG) published guidelines on the "Wise Use of Mires and Peatlands — Backgrounds and Principles including a framework for decision-making". The aim of this publication is to develop mechanisms that can balance the conflicting demands on the global peatland heritage, to ensure its wise use to meet the needs of humankind.