What is Peat?

Peat is an accumulation of partially decayed vegetation matter. Peat forms in wetlands or peatlands, variously called bogs, moors, muskegs, pocosins, mires, and peat swamp forests.

Geographic distribution

Peat deposits are found in many places around the world, notably in Russia, Ireland, Finland, Estonia, Scotland, Poland, northern Germany, the Netherlands and Scandinavia, and in North America, principally in Canada, Michigan, the Florida Everglades, and California's Sacramento-San Joaquin River Delta. 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. Under proper conditions, peat will turn into lignite coal over geologic periods of time.

Formation

Peat forms when plant material, usually in marshy areas, is inhibited from decaying fully by acidic and anaerobic conditions. It is composed mainly of peat moss or sphagnum, but may also include other marshland vegetation: trees, grasses, fungi, as well as other types of organic remains, such as insects, and animal corpses. 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 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 slowly, at the rate of about a millimetre per year.

The peat in the world's peatlands has been forming for 360 million years and contains 550 Gt of carbon.^[1]

Types of peat material

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.

Types of peatland

Six principal types of peatlands are widely recognized. These are:

• Blanket mires: Rain-fed peatlands generally 1 to 3 m deep. Many of the peatlands found in Ireland and the United Kingdom are of this type, with the UK alone 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 frozen only 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. 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 also dug into soil to increase the soil's capacity to retain moisture and add nutrients. This makes it important agriculturally, for farmers and gardeners. Its insulating properties make it of use to industry.

Peat fires are used to dry malted barley for use in Scotch whisky distillation. This gives Scotch whisky its distinctive smoky flavour, often called "peatiness" by its aficionados.

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), even underground, 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.

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, 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).

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 effective only if the forests are still present, since they prevent peat fires.

Peat is also an important raw material in horticulture, and it is used in medicine and balneology to produce filters, textiles etc.

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.^[2]

Peat is also used in cosmetic treatments, because they contain humic acids, which are able to absorb through skin and boost metabolism.

In Ireland

In Ireland, large-scale domestic and industrial peat usage is widespread. 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 no longer commonly used for home heating in Ireland, though it is still used, especially in rural areas.

In Finland

Thanks to the climate, geography and environment of Finland, bogs and peat bogs (turvesuo in Finnish) are widespread. Twenty-six percent of the land area of Finland is bog of some sort. Because of this abundance of sources, peat is available in considerable quantities: Some estimates put the amount of peat in Finland alone to be twice the size of North Sea oil reserves.^[3] 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.^[4] 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^[5] 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, unused (and conservatively used) peat bogs actively bind more CO₂ annually than is released in peat energy production in Finland (approx 40 TWh versus 25 TWh).^[6] 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.^[7]

The state-owned company VAPO is the world leader in peat production with 21.7 million cubic meters in 2003.^[8]

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.

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 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 tonnes of methane gas into the atmosphere, greatly exacerbating global warming. Such discoveries are causing climate scientists to have to revise upwards their estimates of the rate of increase in global temperatures.

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.^[9]

Fires

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 smoulders. 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.^[10][11]

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. 1997 was unusually high, however. These fires likely are responsible for the boost in the increase in carbon dioxide levels since being noticed in 1997.^[12][13]

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.

Tissue preservation

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.

Wise use and 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.

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.

See also

• Acid sulfate soil
• Abiogenic petroleum origin
• Histosols
• List of bogs
• Unified Soil Classification System

References

External links

• International Peat Society
• International Mire Conservation Group
• Gardening without peat information supplied by Kew gardens in London
• Peat-free gardens from the RSPB
• Massive peat burn is speeding climate change From The New Scientist
• Cutover and Cutaway bogs from IPCC

•  • [ e] Topics in geotechnical engineering
Soils	Clay Silt Sand Gravel Peat
Soil properties	Hydraulic conductivity Water content Void ratio Bulk density Thixotropy Reynolds' dilatancy Angle of repose Cohesion Porosity Permeability Specific storage
Soil mechanics	Effective stress Pore water pressure Shear strength Overburden pressure Consolidation Soil compaction Soil classification Shear wave
Geotechnical investigation	Cone penetration test Standard penetration test Exploration geophysics Monitoring well Borehole
Laboratory tests	Atterberg limits California bearing ratio Direct shear test Hydrometer Proctor compaction test R-value Sieve analysis Triaxial shear test
Foundations	Bearing capacity Shallow foundation Deep foundation Dynamic load testing Wave equation analysis Crosshole sonic logging
Retaining walls	Lateral earth pressure Mechanically stabilized earth Soil nailing Tieback Gabion Slurry wall
Slope stability	Mass wasting Landslide
Earthquakes	Soil liquefaction Response spectrum Seismic hazard Ground-structure interaction
Geosynthetics	Geotextile Geomembranes Geosynthetic clay liner