Photo: Drainage ditch in 7m of peat with woody
peat at the top, near Palangkaraya, Central
Kalimantan, Indonesia in February, 1987. Photo
courtesy of Sandra Neuzil, USGS.
What is Peat?
Peat is a soft organic material consisting of partly decayed plant and, in some cases, deposited mineral matter. Peat mires cover nearly 3 percent of the earth’s surface (DNPI, 2010) and are a carbon sink (natural carbon sequestration) and a potential source of methane, carbon dioxide, and nitrous oxides (greenhouse gases), should they be drained, flooded, oxidized, or destroyed by fire. Many peat occurrences are undergoing rapid change or loss, so it is important to understand their contribution to the biosphere and hydrosphere, as well as their role in global carbon and climate cycles.
In peat, the floral composition, geochemistry, geometry, and relationships to sediments are influenced by depositional setting factors including climate, basin tectonics, sediment yield and dispersal patterns, and coastal dynamic processes (Coleman and Whelan, 1977; Schweinfurth, 2003; Cecil and Neuzil, 2009). Additionally, nutrient supply, acidity, bacterial activity, temperature and redox potential are significant factors (Thomas, 2002). ASTM originally defined peat (1969) as organic matter having less than 25 percent ash on a dry basis; for more than 25 percent ash yield, the proper term is peaty material. Definitions and analytical methods were examined and modernized (Jarrett, 1983) and are continuously reviewed and upgraded (ASTM, 2011a; 2011b).
Peat is generally classified into two end member hydrologic types: ombrogenous (owing origin to rainfall) and topogenous (owing origin to both surface and groundwater regimes). Modern definitions (Anderson, 1983; Gore, 1982; Jackson, 1997; Thomas, 2002 and Wust and others, 2003) of various types of peat environments include:
Bog – An ombrotrophic peat-forming ecosystem
Bog forest – Ombrotrophic forested vegetation, generally an upper story of coniferous trees with a ground layer of sphagnum moss
Fen – A topogenous rheotrophic ecosystem in which the dry season may lower the water table below the surface of the peat
Floating swamp – Develops around the fringes of lakes and estuaries and extends out into open water. In tropical areas, these can be thick and laterally extensive
Humus – Highly degraded peat; the humification process (transforming organic matter into humus) is active and yields a dark, spongy, organic matter of uniform appearance
Marsh – A topogenous wetland characterized by floating vegetation of various kinds (reeds, sedges, etc.), but controlled by rheotrophic (flowing) hydrology that rarely forms peat
Mire – General term for peat-forming ecosystems of all types
Peat swamp forest – A forest growing on peat that is formed from the partially decomposed forest plant matter, common in tropical Indonesia and Malaysia
Swamp – A rheotrophic ecosystem where the dry season water table is almost always above the surface of the sediment. This aquatic ecosystem is dominated by emergent vegetation (trees, shrubs)
A list of references [.docx] associated with the above overview of peat is available.
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