Peat
Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. 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'. 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. Peat properties such as organic matter content and saturated hydraulic conductivity can exhibit high spatial heterogeneity.
Peatlands, particularly bogs, are the primary source of peat; although less common, other 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. 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 land-use changes.
Peat is used by gardeners and for horticulture in certain parts of the world, but this is being banned in some places. By volume, there are about 4 trillion cubic metres of peat in the world. 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. The peatland ecosystem covers and is the most efficient carbon sink on the planet, because peatland plants capture carbon dioxide 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, which is the average depth of the boreal peatlands", which store around 415 gigatonnes of carbon. Globally, peat stores up to 550 Gt of carbon, 42% of all soil carbon, which exceeds the carbon stored in all other vegetation types, including the world's forests, although it covers just 3% of the land's surface.
Peat is in principle a renewable source of energy. However, its extraction rate in industrialized countries far exceeds its slow regrowth rate of per year, and is also reported that peat regrowth takes place only in 30–40% of peatlands. Centuries of burning and draining of peat by humans has released a significant amount of into the atmosphere, contributing to anthropogenic climate change.
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. 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.Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat usually accumulates slowly at the rate of about a millimetre per year. The estimated carbon content is , and .
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.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 described peatlands or mires as:the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 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.
A more recent estimate from an improved global peatland map, PEATMAP, based on a meta-analysis of geospatial information at global, regional and national levels puts global coverage slightly higher than earlier peatland inventories at approximately 2.84% of the world land area. In Europe, peatlands extend to about. 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.
There is less peat in the Southern Hemisphere, in part because there is less land. The world's largest tropical peatland is located in Africa. In addition, the vast Magellanic Moorland in South America is an extensive peat-dominated landscape. Peat can be found in New Zealand, Kerguelen, the Falkland Islands and Indonesia. Indonesia has more tropical peatlands and mangrove forests than any other nation on earth, but Indonesia is losing wetlands by per year. A catalog of the peat research collection at the University of Minnesota Duluth provides references to research on worldwide peat and peatlands.
About 7% of all peatlands have been exploited for agriculture and forestry. Under certain conditions, peat will turn into lignite coal over geologic periods of time.
General uses
Fuel
Peat can be used as fuel once dried. Traditionally, peat is cut by hand and left to dry in the sun. In many countries, including Ireland and Scotland, peat was traditionally stacked to dry in rural areas and used for cooking and domestic heating. This tradition can be traced back to the Roman period. For industrial uses, companies may use pressure to extract water from the peat, which is soft and easily compressed.Agriculture
Peat has been discouraged as a soil amendment by the Royal Botanic Gardens, Kew, England, since 2003. While bark or coir-based peat-free potting soil mixes are on the rise, particularly in the UK, peat is still used as raw material for horticulture in some other European countries, Canada, as well as parts of the United States.Drinking water
Peatland can also be an essential source of drinking water, providing nearly 4% of all potable water stored in reservoirs. In the UK, 43% of the population receives drinking water sourced from peatlands, with the number climbing to 68% in Ireland. Catchments containing peatlands are the main source of water for large cities, including Dublin.Metallurgy
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.Flood mitigation
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.Freshwater aquaria
Peat is sometimes used in freshwater aquaria. It is seen most commonly in soft water or blackwater river systems such as those mimicking the Amazon River basin. In addition to being soft and therefore suitable for demersal species such as Corydoras catfish, peat is reported to have many other beneficial functions in freshwater aquaria. It softens water by acting as an ion exchanger; it also contains substances that are beneficial for plants and fishes' reproductive health. Peat can prevent algae growth and kill microorganisms. Peat often stains the water yellow or brown due to the leaching of tannins.Balneotherapy
Peat is widely used in balneotherapy. Many traditional spa treatments include peat as part of peloids. Such health treatments have an enduring tradition in European countries, including Poland, the Czech Republic, Germany and Austria. Some of these old spas date back to the 18th century and are still active today. The most common types of peat application in balneotherapy are peat muds, poultices and suspension baths.Peat archives
Authors Rydin and Jeglum in Biology of Habitats described the concept of peat archives, a phrase coined by influential peatland scientist Harry Godwin in 1981.In Quaternary Palaeoecology, first published in 1980, Birks and Birks described how paleoecological studies "of peat can be used to reveal what plant communities were present, what period each community occupied, how environmental conditions changed, and how the environment affected the ecosystem in that time and place."
Scientists continue to compare modern mercury accumulation rates in bogs with historical natural archives records in peat bogs and lake sediments to estimate the potential human impacts on the biogeochemical cycle of mercury, for example. Over the years, different dating models and technologies for measuring date sediments and peat profiles accumulated over the last 100–150 years, have been used, including the widely used vertical distribution of 210Pb, the inductively coupled plasma mass spectrometry, and more recently the initial penetration.