Peatland

Botanists and ecologists use the word "peatland" as a general term for any terrain dominated by peat to a depth of at least , even if it has been completely drained (i.e. a peatland can be dry). A peatland that is still capable of forming new peat is called a mire, while drained and converted peatlands might still have a peat layer but are not considered mires as the formation of new peat has ceased. A fen is located on a slope, flat, or in a depression and gets most of its water from the surrounding mineral soil or from groundwater (minerotrophic). Thus, while a bog is always acidic and nutrient-poor, a fen may be slightly acidic, neutral, or alkaline, and either nutrient-poor or nutrient-rich. All mires are initially fens when the peat starts to form, and may turn into bogs once the height of the peat layer reaches above the surrounding land. A '''''' is a floating (quaking) mire, bog, or any peatland being in a stage of hydrosere or hydrarch (hydroseral) succession; it yields underfoot (floating mats). Ombrotrophic types of quagmire may be called quaking bogs (quivering bogs); minerotrophic types can be labelled with the term "quagfen". Some swamps can also be peatlands (e.g. peat swamp forest), while marshes are generally not considered to be peatlands. Swamps are characterized by their forest canopy or by the presence of other tall and dense vegetation like papyrus. Like fens, swamps typically have a higher pH level and higher nutrient availability than bogs. Some bogs and fens can support limited shrub or tree growth on hummocks. A marsh is a type of wetland within which vegetation is rooted in mineral soil. == Global distribution ==

Peatlands are found around the globe, although are at their greatest extent at high latitudes in the Northern Hemisphere. Peatlands are estimated to cover around 3% of the globe's surface, The type of mire—bog, fen, marsh or swamp—depends also on each of these factors. The largest accumulation of mires constitutes around 64% of global peatlands and is found in the temperate, boreal and subarctic zones of the Northern Hemisphere. Mires are usually shallow in polar regions because of the slow rate of accumulation of dead organic matter, and often contain permafrost and palsas. Very large swathes of Canada, northern Europe and northern Russia are covered by boreal mires. In temperate zones mires are typically more scattered due to historical drainage and peat extraction, but can cover large areas. One example is blanket bog where precipitation is very high i.e., in maritime climates inland near the coasts of the north-east and south Pacific, and the north-west and north-east Atlantic. In the sub-tropics, mires are rare and restricted to the wettest areas. Mires can be extensive in the tropics, typically underlying tropical rainforest (for example, in Kalimantan, the Congo Basin and Amazon basin). Tropical peat formation is known to occur in coastal mangroves as well as in areas of high altitude. In the early 21st century, the world's largest tropical mire was found in the Central Congo Basin, covering 145,500 km2 and storing up to 1013 kg of carbon. The total area of mires has declined globally due to drainage for agriculture, forestry and peat harvesting. For example, more than 50% of the original European mire area which is more than 300,000 km2 has been lost. Some of the largest losses have been in Russia, Finland, the Netherlands, the United Kingdom, Poland and Belarus. A catalog of the peat research collection at the University of Minnesota Duluth provides references to research on worldwide peat and peatlands. == Biochemical processes ==

Peatlands have unusual chemistry that influences, among other things, their biota and water outflow. Peat has very high cation-exchange capacity due to its high organic matter content: cations such as Ca2+ are preferentially adsorbed onto the peat in exchange for H+ ions. Water passing through peat declines in nutrients and pH. Therefore, mires are typically nutrient-poor and acidic unless the inflow of groundwater (bringing in supplementary cations) is high. Generally, whenever the inputs of carbon into the soil from dead organic matter exceed the carbon outputs via organic matter decomposition, peat is formed. This occurs due to the anoxic state of water-logged peat, which slows down decomposition. Peat-forming vegetation is typically also recalcitrant (poorly decomposing) due to high lignin and low nutrient content. Topographically, accumulating peat elevates the ground surface above the original topography. Mires can reach considerable heights above the underlying mineral soil or bedrock: peat depths of above 10 m have been commonly recorded in temperate regions (many temperate and most boreal mires were removed by ice sheets in the last Ice Age), and above 25 m in tropical regions.[7] When the absolute decay rate of peat in the catotelm (the lower, water-saturated zone of the peat layer) matches the rate of input of new peat into the catotelm, the mire will stop growing in height.[8] Carbon storage and methanogenesis Despite accounting for just 3% of Earth's land surfaces, peatlands are collectively a major carbon store containing between 500 and 700 billion tonnes of carbon. Carbon stored within peatlands equates to over half the amount of carbon found in the atmosphere. The sequestration of carbon dioxide takes place at the surface via the process of photosynthesis, while losses of carbon dioxide occur through living plants via autotrophic respiration and from the litter and peat via heterotrophic respiration. Due to the continued sequestration over millennia, and because of the longer atmospheric lifespan of the molecules compared with methane and nitrous oxide, peatlands have had a net cooling effect on the atmosphere. The water table position of a peatland is the main control of its carbon release to the atmosphere. When the water table rises after a rainstorm, the peat and its microbes are submerged under water inhibiting access to oxygen, reducing release via respiration. Carbon dioxide release increases when the water table falls lower, such as during a drought, as this increases the availability of oxygen to the aerobic microbes thus accelerating peat decomposition. Levels of methane emissions also vary with the water table position and temperature. A water table near the peat surface gives the opportunity for anaerobic microorganisms to flourish. Methanogens are strictly anaerobic organisms and produce methane from organic matter in anoxic conditions below the water table level, while some of that methane is oxidised by methanotrophs above the water table level. Therefore, changes in water table level influence the size of these methane production and consumption zones. Increased soil temperatures also contribute to increased seasonal methane flux. A study in Alaska found that methane may vary by as much as 300% seasonally with wetter and warmer soil conditions due to climate change. Peatlands are important for studying past climate because they are sensitive to changes in the environment and can reveal levels of isotopes, pollutants, macrofossils, metals from the atmosphere and pollen. For example, carbon-14 dating can reveal the age of the peat. The dredging and destruction of a peatland will release the carbon dioxide that could reveal irreplaceable information about the past climatic conditions. Many kinds of microorganisms inhabit peatlands, due to the regular supply of water and abundance of peat forming vegetation. These microorganisms include but are not limited to methanogens, algae, bacteria, zoobenthos, of which Sphagnum species are most abundant. Humic substances Peat contains substantial organic matter, where humic acid dominates. Humic materials can store substantial amounts of water, making them an essential component in the peat environment, contributing to increased carbon storage due to the resulting anaerobic condition. If the peatland is dried from long-term cultivation and agricultural use, it will lower the water table, and the increased aeration will release carbon. Upon extreme drying, the ecosystem can undergo a state shift, turning the mire into a barren land with lower biodiversity and richness. Humic acid formation occurs during the biogeochemical degradation of vegetation debris and animal residue. The loads of organic matter in the form of humic acid is a source of precursors of coal. Prematurely exposing the organic matter to the atmosphere promotes the conversion of organics to carbon dioxide to be released in the atmosphere. == Use by humans ==

from derelict blanket bog, South Uist, Scotland. This old bog is no longer forming peat because the vegetation has been changed, and therefore it is not a mire. Records of past human behaviour and environments can be contained within peatlands. These may take the form of human artefacts, or palaeoecological and geochemical records. The use of this land by humans, including draining and harvesting of tropical peat forests, results in the emission of large amounts of carbon dioxide into the atmosphere. In addition, fires occurring on peatland dried by the draining of peat bogs release even more carbon dioxide. The economic value of a tropical peatland was once derived from raw materials, such as wood, bark, resin and latex, the extraction of which did not contribute to large carbon emissions. In Southeast Asia, peatlands are drained and cleared for human use for a variety of reasons, including the production of palm oil and timber for export in primarily developing nations. This releases stored carbon dioxide and prevents the system from sequestering carbon again. == Tropical peatlands ==

The global distribution of tropical peatlands is concentrated in Southeast Asia where agricultural use of peatlands has been increased in recent decades. Large areas of tropical peatland have been cleared and drained for the production of food and cash crops such as palm oil. Large-scale drainage of these plantations often results in subsidence, flooding, fire and deterioration of soil quality. Small-scale encroachment on the other hand, is linked to poverty and is so widespread that it also has negatively impacts these peatlands. The biotic and abiotic factors controlling Southeast Asian peatlands are interdependent. These peatlands are mostly located in developing regions with impoverished and rapidly growing populations. These lands have become targets for commercial logging, paper pulp production and conversion to plantations through clear-cutting, drainage and burning. The change in soil strongly affects the sensitive vegetation and forest die-off is common. The short-term effect is a decrease in biodiversity but the long-term effect, since these encroachments are hard to reverse, is a loss of habitat. Poor knowledge about peatlands' sensitive hydrology and lack of nutrients often lead to failing plantations, resulting in increasing pressure on remaining peatlands. In contrast to temperate wetlands, tropical peatlands are home to several species of fish. Many new, often endemic, species have been discovered but many of them are considered threatened. Greenhouse gases and fires . In 1997 alone, 73000 ha of swamp was burned in Borneo, releasing the same amount of carbon as 13-40% of the mean annual global carbon emissions of fossil fuels. The majority of this carbon was released from peat rather than overlying tropical rainforest. The tropical peatlands in Southeast Asia only cover 0.2% of Earth's land area but CO2 emissions are estimated to be 2 Gt per year, equal to 7% of global fossil fuel emissions. The 2015 El Niño event further exacerbated the condition of these peatlands, as wildfires burned approximately 3 million hectares of forests and peatlands on the east coast of Sumatra and in Central Kalimantan, emitting 11.3 teragrams of CO2 per day during the months of September and October that year. With a warming climate, these burnings are expected to increase in intensity and number. This is a result of a dry climate together with an extensive rice farming project, called the Mega Rice Project, started in the 1990s, which converted 1 Mha of peatlands to rice paddies. Forest and land was cleared by burning and 4000 km of channels drained the area. Drought and acidification of the lands led to bad harvest and the project was abandoned in 1999. Similar projects in China have led to immense loss of tropical marshes and fens due to rice production. Drainage, which also increases the risk of burning, can cause additional emissions of CO2 by 30–100 t/ha/year if the water table is lowered by only 1 m. The draining of peatlands is likely the most important and long-lasting threat to peatlands globally, but is especially prevalent in the tropics. Tropical peatlands are suggested to contain about 100 Gt carbon, == Northern peatlands ==

, Estonia. 65% of mires in Estonia have been strongly affected or damaged by human activity in recent years. Northern peatlands are associated with boreal and subarctic climates. Northern peatlands were mostly built up during the Holocene after the retreat of Pleistocene glaciers, but in contrast tropical peatlands are much older. Total northern peat carbon stocks are estimated to be 1055 Gt of carbon. Of all northern circumpolar countries, Russia has the largest area of peatlands, Nakaikemi Wetland in southwest Honshu, Japan is more than 50,000 years old and has a depth of 45 m. == Impacts on global climate ==

According to the IPCC Sixth Assessment Report, the conservation and restoration of wetlands and peatlands has large economic potential to mitigate greenhouse gas emissions, providing benefits for adaptation, mitigation and biodiversity. Wetlands provide an environment where organic carbon is stored in living plants, dead plants and peat, as well as converted to carbon dioxide and methane. Three main factors give wetlands the ability to sequester and store carbon: high biological productivity, high water table and low decomposition rates. Suitable meteorological and hydrological conditions are necessary to provide an abundant water source for the wetland. Fully water-saturated wetland soils allow anaerobic conditions to manifest, storing carbon but releasing methane. Wetlands make up about 5-8% of Earth's land surface, but contain about 20-30% of the planet's 2500 Gt soil carbon stores. Peatlands contain the highest amounts of soil organic carbon of all wetland types. Wetlands can become sources of carbon, rather than sinks, as the decomposition occurring within the ecosystem emits methane. Throughout the Holocene (the past 12,000 years), peatlands have been persistent terrestrial carbon sinks and have had a net cooling effect, sequestering 5.6 to 38 grams of carbon per square metre per year. On average, it has been estimated that today northern peatlands sequester 20 to 30 grams of carbon per square metre per year. Peatlands insulate the permafrost in subarctic regions, thus delaying thawing during summer, as well as inducing the formation of permafrost. Compared with untilled cropland, wetlands can sequester around two times the carbon. Carbon sequestration can occur in constructed wetlands as well as natural ones. Estimates of greenhouse gas fluxes from wetlands indicate that natural wetlands have lower fluxes, but man-made wetlands have a greater carbon sequestration capacity. The carbon sequestration abilities of wetlands can be improved through restoration and protection strategies, but it takes several decades for these restored ecosystems to become comparable in carbon storage to peatlands and other forms of natural wetlands. As such, drainage of mires for agriculture transforms them from net carbon sinks to net carbon emitters. When undertaken in such a way that preserves the hydrological state of a mire, the anthropogenic use of mires' resources can avoid significant greenhouse gas emissions. However, continued drainage will result in increased release of carbon, contributing to global warming. As of 2016, it was estimated that drained peatlands account for around 10% of all greenhouse gas emissions from agriculture and forestry. Palm oil has therefore become a popular cash crop in many low-income countries and has provided economic opportunities for communities. With palm oil as a leading export in countries such as Indonesia and Malaysia, many smallholders have found economic success in palm oil plantations. However, the land selected for plantations are typically substantial carbon stores that promote biodiverse ecosystems. Palm oil plantations have replaced much of the forested peatlands in Southeast Asia. Estimates now state that 12.9 Mha or about 47% of peatlands in Southeast Asia were deforested by 2006. In their natural state, peatlands are waterlogged with high water tables making for an inefficient soil. In their natural state, peatlands are resistant to fire. Drainage of peatlands for palm oil plantations creates a dry layer of flammable peat. As peat is carbon dense, fires occurring in compromised peatlands release extreme amounts of both carbon dioxide and toxic smoke into the air. These fires add to greenhouse gas emissions while also causing thousands of deaths every year. Decreased biodiversity due to deforestation and drainage makes these ecosystem more vulnerable and less resilient to change. Homogenous ecosystems are at an increased risk to extreme climate conditions and are less likely to recover from fires. Fires Some peatlands are being dried out by climate change. Drainage of peatlands due to climatic factors may also increase the risk of fires, presenting further risk of carbon and methane to release into the atmosphere. Fire events are predicted to become more frequent with the warming and drying of the global climate. == Management and rehabilitation ==

The United Nations Convention on Biological Diversity highlights peatlands as key ecosystems to be conserved and protected. The convention requires governments at all levels to present action plans for the conservation and management of wetland environments. Wetlands are also protected under the 1971 Ramsar Convention. Rehabilitation projects undertaken in North America and Europe usually focus on the rewetting of peatlands and revegetation of native species. This acts to mitigate carbon release in the short term before the new growth of vegetation provides a new source of organic litter to fuel the peat formation in the long term. Peat extraction is forbidden in Chile since April 2024. Global Peatlands Initiative == References ==