What are Wetlands?
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Wetlands can be characterized by low topography that causes unique hydrology in an area; the hydrology allows water to sit and accumulate in an area which leads to poorly aerated soil. The Ramsar Convention of 1987 provides a wide definition:
“…wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres”
Some sources define wetlands to a narrower scope, including the Canadian Wetland Classification where a wetland is defined as:
“…land that is saturated with water long enough to promote wetland or aquatic processes as indicated by poorly drained soils, hydrophitic vegetation and various kinds of biological activity which are adapted to a wet environment”
There are four ecosystem classes of wetlands identified in Canada: marsh, swamp bog and fen. Each of these terms are used for different wetland ecosystems that provide similar ecological goods and services. They meet the characteristics of wetland areas, but each type is different in its own way.
Wetlands can be characterized by low topography that causes unique hydrology in an area; the hydrology allows water to sit and accumulate in an area which leads to poorly aerated soil. The Ramsar Convention of 1987 provides a wide definition:
“…wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres”
Some sources define wetlands to a narrower scope, including the Canadian Wetland Classification where a wetland is defined as:
“…land that is saturated with water long enough to promote wetland or aquatic processes as indicated by poorly drained soils, hydrophitic vegetation and various kinds of biological activity which are adapted to a wet environment”
There are four ecosystem classes of wetlands identified in Canada: marsh, swamp bog and fen. Each of these terms are used for different wetland ecosystems that provide similar ecological goods and services. They meet the characteristics of wetland areas, but each type is different in its own way.
Marshes
_ Marshes are
characterized by slowly moving or standing water and are dominated by emergent
vegetation such as cattail, bulrush and reed grass; they can be seasonally or
permanently flooded with a high fluctuation in water levels. Marsh
ecosystems are sustained by sources of water other than just precipitation;
they are also nourished by overland flooding and ground water systems. Marshes
are not known as wetlands that accumulate large amounts of peat, and because of
this they are not considered peatlands. Freshwater marshes account for a large
percentage of the world’s temperate wetlands; they are found at all latitudes
where ground water, lakes or springs cause frequent flooding.
Depressions in floodplains left behind by glaciation are referred to as pothole
marshes. Saltmarshes are also common at estuaries and play an important
part in the spawning, nursery and feeding requirements of some marine organisms.
Swamps
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Swamps are thicketed wetlands, often characterized by the
presence of trees and tall shrubs; most swamps are often dominated by a single
woody species and named as such. The soils of swamps and swamp forests are
rich in organics, and can be considered peat forming wetlands, or a transition
between forested area and peatland. Swamps are flooded for most of the growing
season; this aids in the formation of peat because of the water saturated
conditions.
Bogs
Bogs are topographically high wetlands and are isolated from the ground and soil waters. Because bogs are ombrotrophic systems, there is less chemical variation than that of fens. Vegetation characteristic of bags are trees and shrubs with stunted growth, because of the extremely nutrient poor and highly acidic soils. The true meaning of ‘bog’ has been designated to mean ombrotrophic peatland, but is also a term used to describe Sphagnum-dominated peatlands. Bogs can be classified by different types of tree cover. They may be treeless, treed only on the edges, or treed throughout.
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Fens
__ Fens are considered peatlands because they accumulate a deep layer of peat. Fens are more open
than swamps, in the sense that fens are not characterized by tall or many
trees, instead mostly sedges, grasses and low shrubs. Fens accumulate
peat, similar to bogs, but they have a higher nutrient content than bogs, and
therefore more variation in vegetation. A mire is a term for
wet terrain that is dominated by peat forming plants that are still living. A mixed mire is a
type with bog and fen features.
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Ombrotrophic wetlands are purely
rain-fed water systems, and do not have contact with the ground water.
Wetlands that receive mineral nourishment from the ground water are known as
minerotrophic. Minerotrophic fens, swamps and marshes have a higher
pH and usually more nutrients. The higher nutrient availability and
variation in the pH allows for more biotic variation in the area as well.
Ombrotrophic bogs are considered to be peatland areas that are nutrient poor
and highly acidic. Northern temperate bogs tend to be more acidic due
to the dominant vegetation, Sphagnum sp.,
and the low amounts of incoming rainwater.
_ENVR 4000 Sustainable Water Management 2012