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 3.7 million square kilometres (1.4 million square miles) and is the most efficient carbon sink on the planet, because peatland plants capture carbon dioxide (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", which store around 415 gigatonnes (Gt) of carbon (about 46 times 2019 global CO₂ emissions). 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 1 mm (0.04 in) 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 CO₂ into the atmosphere, contributing to anthropogenic climate change.

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.^{[citation needed]}

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 415 gigatonnes (457 billion short tons) (northern peatlands), 50 Gt (55 billion short tons) (tropical peatlands) and 15 Gt (17 billion short tons) (South America).

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.