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Peat (/pt/), sometimes known as turf (/tɜːrf/), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs.[1][2] The peatland ecosystem covers 3.7 million square kilometres[3] and is the most efficient carbon sink on the planet,[2][4] because peatland plants capture CO2 naturally released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m [4.9 to 7.5 ft], which is the average depth of the boreal [northern] peatlands",[2] which store around 415 gigatonnes of carbon (about 46 times 2019 global CO2 emissions).[3] Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed 'habitat manipulation'.[5] Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition.[6]

Peatlands, particularly bogs, are the primary source of peat;[7] although less-common wetlands including fens, pocosins, and peat swamp forests also deposit peat. Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen. This allows the reconstruction of past environments and the study of changes in land use.[8]

Peat is harvested as a source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres (5.2 trillion cubic yards) of peat in the world, covering a total of around 2% of the global land area.[9] Over time, the formation of peat is often the first step in the geological formation of fossil fuels such as coal, particularly low-grade coal such as lignite.[10]

The Intergovernmental Panel on Climate Change (IPCC) classifies peat as neither a fossil fuel nor a renewable fuel, and notes that its emission characteristics are similar to fossil fuels.[11] At 106 g CO2/MJ,[12] the carbon dioxide emission intensity of peat is higher than that of coal (at 94.6 g CO2/MJ) and natural gas (at 56.1) (IPCC). Peat is not a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year,[13] and as it is also reported that peat regrowth takes place only in 30–40% of peatlands.[14]

Formation

Peat forms when plant material does not fully decay in acidic and anaerobic conditions. It is composed mainly of wetland vegetation: principally bog plants including mosses, sedges, and shrubs. As it accumulates, the peat holds water. This slowly creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds, ridges, and raised bogs.[7] The characteristics of some bog plants actively promote bog formation. For example, sphagnum mosses actively secrete tannins, which preserve organic material. Sphagnum also have special water retaining cells, known as hyaline cells, which can release water ensuring the bogland remains constantly wet which helps promote peat production.[15]

Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age.[16] Peat usually accumulates slowly at the rate of about a millimetre per year.[13] The estimated carbon content is 415 GtC (northern peatlands),[3] 50 GtC (tropical peatlands) and 15 GtC (South America).[17]

Types of peat material

Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed and

Peatlands, particularly bogs, are the primary source of peat;[7] although less-common wetlands including fens, pocosins, and peat swamp forests also deposit peat. Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen. This allows the reconstruction of past environments and the study of changes in land use.[8]

Peat is harvested as a source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres (5.2 trillion cubic yards) of peat in the world, covering a total of around 2% of the global land area.[9] Over time, the formation of peat is often the first step in the geological formation of fossil fuels such as coal, particularly low-grade coal such as lignite.[10]

The Intergovernmental Panel on Climate Change (IPCC) classifies peat as neither a fossil fuel nor a renewable fuel, and notes that its emission characteristics are similar to fossil fuels.[11] At 106 g CO2/MJ,[12] the carbon dioxide emission intensity of peat is higher than that of coal (at 94.6 g CO2/MJ) and natural gas (at 56.1) (IPCC). Peat is not a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year,[13] and as it is also reported that peat regrowth takes place only in 30–40% of peatlands.[14]

Peat forms when plant material does not fully decay in acidic and anaerobic conditions. It is composed mainly of wetland vegetation: principally bog plants including mosses, sedges, and shrubs. As it accumulates, the peat holds water. This slowly creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds, ridges, and raised bogs.[7] The characteristics of some bog plants actively promote bog formation. For example, sphagnum mosses actively secrete tannins, which preserve organic material. Sphagnum also have special water retaining cells, known as hyaline cells, which can release water ensuring the bogland remains constantly wet which helps promote peat production.[15]

Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age.[16] Peat usually accumulates slowly at the rate of about a millimetre per year.[13] The estimated carbon content is 415 GtC (northern peatlands),[3] 50 GtC (tropical peatlands) and 15 GtC (South America).[17]

Types of peat material

Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed and consist of intact fibre. Hemic peats are partially decomposed and sapric are the most decomposed.[18]

Phragmites peat are 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 – it cannot be easily compacted to serve as a stable foundation to support loads, such as roads or buildings.

Peatlands distribution

In a widely cited article, Joosten and Clarke (2002) defined peatlands or mires (which they claim are the same)[Notes 1][1] as,

...the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 4 million square kilometres [1.5 million square miles] or 3% of the land and freshwater surface of the planet. In these ecosystems are found one third of the world's soil carbon and 10% of global freshwater resources. These ecosystems are characterized by the unique ability to accumulate and store dead organic matter from Sphagnum and many other non-moss species, as peat, under conditions of almost permanent water saturation. Peatlands are adapted to the extreme conditions of high water and low oxygen content, of toxic elements and low availability of plant nutrients. Their water chemistry varies from alkaline to acidic. Peatlands occur on all continents, from the tropical to boreal and Arctic zones from sea level to high alpine conditions.

— Joosten and Clarke 2002
PEATMAP is a GIS shapefile dataset shows a distribution of peatlands that covers the entire world

A more recent estimate from an improved global peatland map, PEATMAP,[19] based on a meta-analysis of geospatial information at global, regional and national levels puts global coverage slightly higher than earlier peatland inventories at 4.23 million square kilometres (1.63 million square miles) approximately 2.84% of the world land area.[20] In Europe, peatlands extend to about 515,000 km2 (199,000 sq mi).[21] About 60% of the world's wetlands are made of peat.

Peat deposits are found in many places around the world, includin

Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age.[16] Peat usually accumulates slowly at the rate of about a millimetre per year.[13] The estimated carbon content is 415 GtC (northern peatlands),[3] 50 GtC (tropical peatlands) and 15 GtC (South America).[17]

Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed and consist of intact fibre. Hemic peats are partially decomposed and sapric are the most decomposed.[18]

Phragmites peat are 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

Phragmites peat are 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 – it cannot be easily compacted to serve as a stable foundation to support loads, such as roads or buildings.

In a widely cited article, Joosten and Clarke (2002) defined peatlands or mires (which they claim are the same)[Notes 1][1] as,

...the most widespread of all wetland typ

...the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 4 million square kilometres [1.5 million square miles] or 3% of the land and freshwater surface of the planet. In these ecosystems are found one third of the world's soil carbon and 10% of global freshwater resources. These ecosystems are characterized by the unique ability to accumulate and store dead organic matter from Sphagnum and many other non-moss species, as peat, under conditions of almost permanent water saturation. Peatlands are adapted to the extreme conditions of high water and low oxygen content, of toxic elements and low availability of plant nutrients. Their water chemistry varies from alkaline to acidic. Peatlands occur on all continents, from the tropical to boreal and Arctic zones from sea level to high alpine conditions.

— Joosten and Clarke 2002
[19] based on a meta-analysis of geospatial information at global, regional and national levels puts global coverage slightly higher than earlier peatland inventories at 4.23 million square kilometres (1.63 million square miles) approximately 2.84% of the world land area.[20] In Europe, peatlands extend to about 515,000 km2 (199,000 sq mi).[21] About 60% of the world's wetlands are made of peat.

Peat deposits are found in many places around the world, including northern Europe and North America. The North American peat deposits are principally found in Canada and the Northern United States. Some of the world's largest peatlands include the West Siberian Lowland, the Hudson Bay Lowlands, and the Mackenzie River Valley.[22] There is less peat in the Southern Hemisphere, in part because there is less land. That said, the vast Magellanic Moo

Peat deposits are found in many places around the world, including northern Europe and North America. The North American peat deposits are principally found in Canada and the Northern United States. Some of the world's largest peatlands include the West Siberian Lowland, the Hudson Bay Lowlands, and the Mackenzie River Valley.[22] There is less peat in the Southern Hemisphere, in part because there is less land. That said, the vast Magellanic Moorland in South America (Southern Patagonia/Tierra del Fuego) is an extensive peat-dominated landscape.[22] Peat can be found in New Zealand, Kerguelen, the Falkland Islands, and Indonesia (Kalimantan [Sungai Putri, Danau Siawan, Sungai Tolak], Rasau Jaya [West Kalimantan], and Sumatra). Indonesia has more tropical peatlands and mangrove forests than any other nation on earth, but Indonesia is losing wetlands by 100,000 hectares (250,000 acres) per year.[23]

About 7% of all peatlands have been exploited for agriculture and forestry.[24] Under proper conditions, peat will turn into lignite coal over geologic periods of time.

Traditionally peat is cut by hand and left to dry in the sun. But for industrial uses, companies may use pressure to extract water from the peat, which is soft and easily compressed, and once dry can be used as fuel. In many countries, including Ireland and Scotland, peat was traditionally stacked to dry in rural areas and used for cooking and domestic heating.

Peat can be a major fire hazard and is not extinguished by light rain.[25] Peat fires may burn for great lengths of time, or smoulder underground and reignite after winter if an oxygen source is present. Because they are easily compressed under minimal weight, peat deposits pose major difficulties to builders of structures, roads, and railways. When the West Highland railway line was built across Rannoch Moor in western Scotland, its builders had to float the tracks on a multi-thousand-ton mattress of tree roots, brushwood, earth and ash.

Peatland can also be an important source of drinking water providing nearly 4% of all potable water stored in reservoirs. In the UK, more than 28 million people use drinking water from water sources which rely on peatlands.[26]

In the Bronze and Iron Ages, people used peat bogs for rituals to nature gods and spirits.[27] Bodies of the victims of such sacrifices have been found in various places in Scotland, England, Ireland, and especially northern Germany and Denmark. They are 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 also used to have a degree of metallurgical importance in the Early Middle Ages, being the primary source of bog iron used to create swords and armour. Many peat swamps along the coast of Malaysia serve as a natural means of flood mitigation, with any overflow being absorbed by the peat, provided forests are still present to prevent peat fires.[citation needed]

Characteristics and uses by nation

Finland