|Taiga, Boreal forests|
|Montane grasslands and shrublands|
|Temperate coniferous forests|
|Tropical and subtropical coniferous forests|
|Temperate broadleaf and mixed forests|
|Mediterranean forests, woodlands, and scrub|
|Tropical and subtropical moist broadleaf forests|
|Tropical and subtropical dry broadleaf forests|
|Temperate grasslands, savannas, and shrublands|
|Tropical and subtropical grasslands, savannas, and shrublands|
|Deserts and xeric shrublands|
|Flooded grasslands and savannas|
|Littoral, Intertidal zone|
A wetland is an area of land whose soil is saturated with moisture either permanently or seasonally. Such areas may also be covered partially or completely by shallow pools of water. Wetlands include swamps, marshes, and bogs, among others. The water found in wetlands can be saltwater, freshwater, or brackish. The world's largest wetland is the Pantanal which straddles Brazil, Bolivia and Paraguay in South America.
Wetlands are considered the most biologically diverse of all ecosystems. Plant life found in wetlands includes mangrove, water lilies, cattails, sedges, tamarack, black spruce, cypress, gum, and many others. Animal life includes many different amphibians, reptiles, birds, and mammals.
The study of wetlands has recently been termed paludology in some publications.
Wetlands have been categorized both as biomes and ecosystems. They are generally distinguished from other water bodies or landforms based on their water level and on the types of plants that thrive within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough season each year to support aquatic plants. Put simply, wetlands are lands made up of hydric soil.
Wetlands have also been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both."
Under the Ramsar international wetland conservation treaty, wetlands are defined as follows:
In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas". Some states, such as Massachusetts and New York, have separate definitions that may differ from United States federal laws.
Wetlands have important functions in relation to climate change. These functions are twofold: wetlands for mitigation of climate change, meaning the limiting of CO2 emissions coming from wetlands and wetlands as carbon sinks on the one hand; wetlands for adapting to climate change on the other.
Peatswamp forests and soils are being drained, burnt, mined, and overgrazed contributing severely to climate change. As Peatlands form only 3% of all the world’s land area, their degradation equal 7% of all fossil fuel carbon dioxide (CO2) emissions. As a result of peat drainage, the organic carbon that was built up over thousands of years and is normally under water, is suddenly exposed to the air. It decomposes and turns into carbon dioxide (CO2), which is released into the atmosphere. Peat fires cause the same process and in addition create enormous clouds of smoke that cross international borders, such as happen every year in Southeast Asia.
Through the building of dams, Wetlands International is halting the drainage of peatlands in Southeast Asia, thereby avoiding enormous CO2 emissions. Reforestation with native tree species as well as setting up community fire brigades are also part of an integral, very cost effective approach shown in Central Kalimantan and Sumatra, Indonesia. (from: www.wetlands.org)
Mangroves, floodplains, highland and other wetlands can reduce the impacts of increased precipitation, storms, glacier melting and even sealevel rise. The water regulating and storage functions of these wetlands are crucial in adapting to a changing climate. Therefore, in order to protect people living close or even far downstream from wetlands and their source of livelihoods, we must conserve and restore wetlands. In this way, they can continue to play their critical role. (from www.wetlands.org)
Wetlands have historically been the victim of large-scale draining efforts for real estate development, or flooding for use as recreational lakes. By 1993 half the world's wetlands had been drained. Since the 1970s, more focus has been put on preserving wetlands for their natural function — sometimes also at great expense. Wetlands provide a valuable flood control function. Wetlands are very effective at filtering and cleaning water pollution , (often from agricultural runoff from the farms that replaced the wetlands in the first place). To replace these wetland ecosystem services enormous amounts of money have been spent on water purification plants and remediation measures, constructing dams, leves and other artificial flood controls.
The USA came to understand how biologically productive wetlands are, so the USA passed laws limiting wetlands destruction, and created requirements that if a wetland had to be drained, developers at least had to offset the loss by creating artificial wetlands. One example is the project by the U.S. Army Corps of Engineers to control flooding and enhance development by taming the Everglades, a project which has now been reversed to restore much of the wetlands as a natural habitat for plant and animal life, as well as a method of flood control.
The South African Department of Environmental Affairs and Tourism in conjunction with the departments of Water Affairs and Forestry, and of Agriculture, supports the conservation and rehabilitation of wetlands through the Working for Wetlands program. The aim of this program is to encourage the protection, rehabilitation and sustainable use of South African wetlands through co-operative governance and partnerships. The program is also a poverty relief effort, providing employment in wetland maintenance.
The Convention on Wetlands of International Importance, especially as Waterfowl Habitat, or Ramsar Convention, is an international treaty designed to address global concerns regarding wetland loss and degradation. The primary purposes of the treaty are to list wetlands of international importance and to promote their wise use, with the ultimate goal of preserving the world's wetlands. Methods include restricting access to the majority portion of wetland areas, as well as educating the public to combat the misconception that wetlands are wastelands.
There are many remote sensing methods that can be used to map wetlands. Remote-sensing technology permits the acquisition of timely digital data on a repetitive basis. This repeat coverage allows wetlands, as well as the adjacent land-cover and land-use types, to be monitored seasonally and/or annually. Using digital data provides a standardized data-collection procedure and an opportunity for data integration within a geographic information system. Traditionally, Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM + ), and the SPOT 4 and 5 satellite systems have been used for this purpose. More recently, however, multispectral IKONOS and QuickBird data, with spatial resolutions of 4m by 4m and 2.44m by 2.44 m, respectively, have been shown to be excellent sources of data when mapping and monitoring smaller wetland habitats and vegetation communities.
A wide range of remote sensing studies has been undertaken in a variety of wetland environments. Remote sensing technology has permitted the acquisition of timely digital data on a repetitive basis. For example, the wetlands and vegetation within Detroit Lakes Wetland management District has been assessed using remote sensing. In mapping and monitoring large geographic areas, analysis of satellite images is less costly and time-consuming compared to visual interpretation of aerial photographs. Aerial photographs also require experienced interpreters to extract information based on structure and texture while remote sensing only requires the analysis of the spectral characteristics of data.
However, there are a number of limitations associated with image acquisition. Analysis of wetlands has proved difficult because to obtain the data, it has to be linked with practical purposes such as the analysis of land cover or land use. Wetlands, in particular are difficult to monitor, are often difficult to access, especially their inner reaches, and are sometimes home to dangerous wildlife and endemic diseases. Developing a global inventory of wetlands has proven to be a large and difficult undertaking. Current efforts are based on available data, but both classification and spatial resolution may be inadequate for regional or site-specific management decision-making. It is difficult to identify small, long, and narrow wetlands within the landscape. Current efforts using today’s remote sensing satellites may not have sufficient spatial and spectral resolution to monitor wetland conditions, although multispectral IKONOS and QuickBird data may offer improved spatial resolutions of 4m or higher. Majority of the pixels are just mixtures of several plant species or vegetation types and are difficult to isolate. Improved remote sensing information, coupled with good knowledge domain on wetlands will facilitate expanded efforts in wetland monitoring and mapping. This will also be extremely important because we expect to see major shifts in species composition due to both anthropogenic (land use) and natural changes in the environment caused by climate change. Methods to focus the classification on specific classes of interest so that identification can be done with very high accuracies should be looked into. The issue of the cost and expertise involved in remote sensing technology is still a factor hindering further advancements in image acquisition and data processing. Future improvements in wetland vegetation mapping could include the use of more recent and better geospatial data.
Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in temperate zones (midway between the North and South Poles and the equator). In these zones, summers are warm and winters are cold, but temperatures are not extreme. However, wetlands found in the tropic zone, which is around the equator, are always warm. Temperatures in wetlands on the Arabian Peninsula, for example, can reach 50 °C (122 °F). In northeastern Siberia, which has a polar climate, wetland temperatures can be as cold as −50 °C (−58 °F).
The amount of rainfall a wetland receives depends upon its location. Wetlands in Wales, Scotland, and Western Ireland receive about 150 cm (59 in) per year. Those in Southeast Asia, where heavy rains occur, can receive up to 500 cm (200 in). In the northern areas of North America, wetlands exist where as little as 15 cm (6 in) of rain fall each year.
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Ullah, S; Faulkner, SP. 2006. Denitrification potential of different land-use types in an agricultural watershed, lower Mississippi valley. ECOLOGICAL ENGINEERING 28 (2): 131-140.