Constructed wetlands are designed and built to treat municipal and industrial wastewater as well as to divert stormwater runoff. However, some wetlands are a significant source of methane emissions and some are also emitters of nitrous oxide. Wetlands can be important sources and sinks of carbon, depending on the specific wetland, and thus will play an important role in climate change and need to be considered in attempts to mitigate climate change. According to the UN Millennium Ecosystem Assessment, wetlands are more affected by environmental degradation than any other ecosystem on Earth. Wetlands are reservoirs of biodiversity and provide wetland products. These are called ecosystem services and include water purification, groundwater replenishment, stabilization of shorelines and storm protection, water storage and flood control, processing of carbon ( carbon fixation, decomposition and sequestration), other nutrients and pollutants, and support of plants and animals. Wetlands contribute a number of functions that benefit people. The world's largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, and the Sundarbans in the Ganges- Brahmaputra delta. Some wetlands have multiple types of plants and are fed by multiple sources of water, making them difficult to classify. Examples of wetlands classified by their sources of water include tidal wetlands ( oceanic tides), estuaries (mixed tidal and river waters), floodplains (excess water from overflowed rivers or lakes), springs, seeps and fens ( groundwater discharge out onto the surface), and bogs and vernal ponds ( rainfall or meltwater). For example, marshes are wetlands dominated by emergent vegetation such as reeds, cattails and sedges swamps are ones dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). The main wetland types are classified based on the dominant plants and/or the source of the water. The water in wetlands is either freshwater, brackish or saltwater. Wetlands occur naturally on every continent. These methods have contributed to wetland conservation partly by raising public awareness of the functions some wetlands provide. ![]() ![]() Methods for assessing wetland functions, wetland ecological health, and general wetland condition have been developed for many regions of the world. Wetlands are considered among the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal species. The primary factor that distinguishes wetlands from terrestrial land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique anoxic hydric soils. Flooding results in oxygen-free ( anoxic) processes prevailing, especially in the soils. Wetlands, or simply a wetland, is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). ![]() lacustrine zones Freshwater swamp forest in Bangladesh A freshwater cattail ( Typha) marsh that develops with standing water and high soil fertility Peat bogs are freshwater wetlands that develop in areas with standing water and low soil fertility. Wetlands come in different sizes, types, and locations.
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