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Peat (turf) is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands or mires.[1][2] The peatland ecosystem is the most efficient carbon sink on the planet[2] because peatland plants capture the CO2 which is naturally released from the peat, thus 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, which is the average depth of the boreal peatlands".[2] One of the most common components is Sphagnum moss, although many other plants can contribute. Soils that contain mostly peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs flows of oxygen from the atmosphere, slowing rates of decomposition.[3]

Peatlands, also known as mires,[Notes 1] particularly bogs, are the most important source of peat,[4] but other less common wetland types also deposit peat, including fens, pocosins, and peat swamp forests. Other words for lands dominated by peat include moors or muskegs. Landscapes covered in peat also have specific kinds of plants, particularly Sphagnum moss, ericaceous shrubs, and sedges (see bog for more information on this aspect of peat). Since organic matter accumulates over thousands of years, peat deposits also provide records of past vegetation and climates stored in plant remains, particularly pollen. Hence, they allow humans to reconstruct past environments and changes in human land use.[5]

Peat is harvested as an important source of fuel in certain parts of the world. By volume, about 4 trillion m³ of peat are in the world, covering a total of around 2% of global land area (about 3 million km²), containing about 8 billion terajoules of energy.[6] Over time, the formation of peat is often the first step in the geological formation of other fossil fuels such as coal, particularly low-grade coal such as lignite.[7]

Depending on the agency, peat is not generally regarded as a renewable source of energy, as its extraction rate in industrialized countries far exceeds its slow regrowth rate of 1 mm per year,[8] and as peat regrowth is also reported to take place in only 30-40% of peatlands.[9] Because of this, the United Nations Framework Convention on Climate Change (UNFCCC),[10] and another organization affiliated with the United Nations classifies peat as a fossil fuel.[11] However, the Intergovernmental Panel on Climate Change has begun to classify peat as a "slow-renewable" fuel.[12] This is also the classification used by many in the peat industry.[10]

At 106 g CO2/MJ,[13] 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).

Peat fires have been responsible for some large public health disasters, including the 1997 Southeast Asian haze.

Environmental and ecological issuesEdit

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Because of the distinctive ecological conditions of peat wetlands, they provide habitat for a distinctive fauna and flora. For example, whooping cranes nest in North American peatlands, while Siberian cranes nest in the West Siberian peatland. Such habitats also have many species of wild orchids and carnivorus plants. It takes centuries for a peat bog to recover from disturbance. For more on biological communities, see wetland, bog or fen.

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 billion metric tons of sequestered carbon, and they release into the atmosphere 20 to 45 million metric tons of methane annually. The peatlands' contribution to long-term fluctuations in these atmospheric gases has been a matter of considerable debate.[14]

One of the characteristics for peat is that bioaccumulations of metals are often concentrated in the peat, of significant environmental concern is accumulated mercury.[15]

Peat drainageEdit

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 also heavily fuels climate change. As a result of peat drainage, the organic carbon—which 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.[16] The global CO2 emissions from drained peatlands have increased from 1,058 Mton in 1990 to 1,298 Mton in 2008 (>20%). This increase has particularly taken place in developing countries, of which Indonesia, China, Malaysia, and Papua New Guinea, are the fastest growing top emitters. This estimate excludes emissions from peat fires (conservative estimates amount to at least 4,000 Mton/CO2-eq./yr for south-east Asia). With 174 Mton/CO2-eq./yr the EU is after Indonesia (500 Mton) and before Russia (161 Mton) the World's 2nd largest emitter of drainage related peatland CO2 (excl. extracted peat and fires). Total CO2 emissions from the worldwide 500,000 km2 of degraded peatland may exceed 2.0 Gtons (including emissions from peat fires) which is almost 6% of all global carbon emissions.[17]

Peat firesEdit

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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 smoldering 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.Script error Recent burning of peat bogs in Indonesia, with their large and deep growths containing more than 50 billion tons of C, has contributed to increases in world carbon dioxide levels.Script error Peat deposits in Southeast Asia could be destroyed by 2040.[1][2]

It is estimated that in 1997, peat and forest fires in Indonesia released between 0.81 and 2.57 Gt of C; 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.[3][4] More than 100 peat fires in Kalimantan and East Sumatra have continued to burn since 1997. Each year, the peat fires in Kalimantan and East Sumatra ignite new forest fires above the ground.

In North America, peat fires can occur during severe droughts throughout their occurrence, from boreal forests in Canada to swamps and fens in the subtropical southern Florida Everglades.[5] Once a fire has burnt through the area, hollows in the peat are burnt out, and hummocks are desiccated but can contribute to Sphagnum recolonization.[6]

In the summer of 2010, an unusually high heat wave of up to 40 °C (104 °F) ignited large deposits of peat in Central Russia, burning thousands of houses and covering the capital of Moscow with a toxic smoke blanket. The situation remained critical until the end of August 2010.[7][8]

See alsoEdit

Notes Edit

ReferencesEdit

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  3. Cat Lazaroff, Indonesian Wildfires Accelerated Global Warming, Environment News Service
  4. Fred Pearce Massive peat burn is speeding climate change, New Scientist, 6 November 2004
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External linksEdit

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