Peatlands
_ Peat is a product of peat forming wetlands; peatland is the
word used to describe a peat-covered landscape. Peat is essentially incompletely decayed organic matter; it is the remains of plant and animal parts that do not fully decompose because of their placement in water saturated, low temperature, highly acidic conditions. Peatlands occur on all continents;
most peatlands are found in the boreal regions of the world, although there are
subtropical and tropical peatlands in the south.
Ecological Succession
_ Wetlands
are vulnerable to man-induced and environmental changes because of their
changeable nature. There are distinct zones of different vegetation
that grown in rings in wetland areas. The fate of many wetlands that go through
natural succession, is to become permanent or semi-permanent shallow lakes.
Successive plant communities alter the ecosystem processes and functions, and
therefore habitat suitability for different species, as well as ecological
goods and services.
Submerged and floating leaved vegetation are the first to colonize a small pond area. The organic matter that accumulates because of these aquatic plants gradually deposits along the bottom of the pond. This can be a gradual process, which eventually fills the pond, making it shallow and advancing the shoreline into the lake area. When the substrate is composed of partially decomposed organics, this is when peat accumulates. As the water becomes shallower, emergent species will dominate the area, and they function to impede water movement, trap sediment and shade the under-water vegetation. Larger terrestrial plants, such as water-tolerable trees and shrubs, will begin to establish themselves along the edges of the basin in the areas that may flood on a seasonal basis. Domination of terrestrial trees changes the ecozone of the area from wetland to woodland ecosystem. There wetness of the area will change as the dominant vegetation changes. This succession process happens naturally to all wetland areas, but has been further described in the Van der Valk and Davis model of the wet-dry cycle of marshes.
Submerged and floating leaved vegetation are the first to colonize a small pond area. The organic matter that accumulates because of these aquatic plants gradually deposits along the bottom of the pond. This can be a gradual process, which eventually fills the pond, making it shallow and advancing the shoreline into the lake area. When the substrate is composed of partially decomposed organics, this is when peat accumulates. As the water becomes shallower, emergent species will dominate the area, and they function to impede water movement, trap sediment and shade the under-water vegetation. Larger terrestrial plants, such as water-tolerable trees and shrubs, will begin to establish themselves along the edges of the basin in the areas that may flood on a seasonal basis. Domination of terrestrial trees changes the ecozone of the area from wetland to woodland ecosystem. There wetness of the area will change as the dominant vegetation changes. This succession process happens naturally to all wetland areas, but has been further described in the Van der Valk and Davis model of the wet-dry cycle of marshes.
Accumulation of Peat
Peatlands can have several metres of peat that accumulates over thousands of years. Peat is essentially incompletely decayed organic matter; it is the remains of plant and animal parts that do not fully decompose because of their placement in water saturated conditions. Much of the plant matter that makes up peat has a low ability to decompose, and this also helps to slow the process; most of the plant material is from parts below the ground, such as roots and rhizomes. In swamps, because of the high density of trees, woody materials are a large component of the peat matter.
_ Not all wetlands have the correct conditions to allow peat to accumulate in large amounts. All wetlands may produce peat, but areas will only be considered peatlands if the underlying peat layer is greater than forty centimetres in depth. Anoxic conditions, combined with seasonally low temperatures, allows peat to form and accumulate in layers in specific wetland areas. Low oxygen and acidic conditions are required for the formation of peat; as peat accumulates, it causes more acid and nutrient poor conditions, proving positive feedback. _
_ Not all wetlands have the correct conditions to allow peat to accumulate in large amounts. All wetlands may produce peat, but areas will only be considered peatlands if the underlying peat layer is greater than forty centimetres in depth. Anoxic conditions, combined with seasonally low temperatures, allows peat to form and accumulate in layers in specific wetland areas. Low oxygen and acidic conditions are required for the formation of peat; as peat accumulates, it causes more acid and nutrient poor conditions, proving positive feedback. _
Formation of peat
_
All peat forming processes create drainage conditions that
facilitate peat production; these are positive feedback mechanisms.
Essentially, the more peat that is produced, the more peat that will be
produced.
Infilling is a primary process, meaning it occurs in an area where there has been no prior formation of peat. It occurs when aquatic vegetation completely fills in a pond or water filled depression. This is a result of an anaerobic environment where temperature and microbial activity are low. During the infilling process, peat accumulates on the edges or shallows of ponds, lakes, or other slow flowing water bodies. The infilling may continue to fill the basin completely, or it may process into a bog ecosystem. The final succession stage after infilling will depend on the hydrologic situation. Some basins that have rising water and continuous accumulation of peat may maintain themselves as wet, slowly growing peatlands, where others will transform into marsh or fen communities.
In primary peat formation, layers in the soil will prevent downward penetration of water; this is the humus or clay layer. This creates persistently wet conditions that allow for the accumulation of organic matter that will form into peat. Primary peat formation occurs on freshly exposed, wet soil.
Paludification the term for secondary processes of peat production. This is when peat forms on previously less wet mineral ground.
Infilling is a primary process, meaning it occurs in an area where there has been no prior formation of peat. It occurs when aquatic vegetation completely fills in a pond or water filled depression. This is a result of an anaerobic environment where temperature and microbial activity are low. During the infilling process, peat accumulates on the edges or shallows of ponds, lakes, or other slow flowing water bodies. The infilling may continue to fill the basin completely, or it may process into a bog ecosystem. The final succession stage after infilling will depend on the hydrologic situation. Some basins that have rising water and continuous accumulation of peat may maintain themselves as wet, slowly growing peatlands, where others will transform into marsh or fen communities.
In primary peat formation, layers in the soil will prevent downward penetration of water; this is the humus or clay layer. This creates persistently wet conditions that allow for the accumulation of organic matter that will form into peat. Primary peat formation occurs on freshly exposed, wet soil.
Paludification the term for secondary processes of peat production. This is when peat forms on previously less wet mineral ground.
Peat composition
_
Although peat matter itself is not a living organism, there
is a variety of microorganisms living within the peat that act to slowly
decompose the organic remains. The texture and decomposition of the organics
in the peat vary from very fibrous and poorly decomposed, to weak and very
decomposed; this is because of the varying rates of diffusion of oxygen and
water through the peat layer. The water saturated soil acts as an insulator
to the peat layer underneath and allows more peat to accumulate in cool
conditions.
The physical properties of peat that can be measured to determine quality include fibrosity and humification, density, porosity and water content. Botanical composition determines the fibrosity and humification of the peat. Fibrosity and humification are terms for how much of the original plant material is left at pre-decomposition state. Humification is the concept that determines how decomposed the peat is. A high-fibre content is associated with low humification. Bulk density is measured from dry peat matter, and water content is measured as a loss of mass from wet peat to dry peat.
The physical properties of peat that can be measured to determine quality include fibrosity and humification, density, porosity and water content. Botanical composition determines the fibrosity and humification of the peat. Fibrosity and humification are terms for how much of the original plant material is left at pre-decomposition state. Humification is the concept that determines how decomposed the peat is. A high-fibre content is associated with low humification. Bulk density is measured from dry peat matter, and water content is measured as a loss of mass from wet peat to dry peat.
ENVR 4000 Sustainable Water Management 2012