Wetland

A wetland is a semi-aquatic ecosystem where the ground is covered by water—sometimes permanently, sometimes for years or decades, and sometimes only during certain seasons. This flooding creates oxygen-poor (anoxic) conditions, especially in the soil. Wetlands sit at the boundary between open water and dry land, and they differ from other ecosystems because the plants living there have roots that are specially adapted to survive in waterlogged, low-oxygen soil. These areas are among the most biologically rich ecosystems on Earth, providing homes for many aquatic and semi-aquatic plants and animals. They often improve water quality by filtering out excess nutrients like nitrates and phosphorus. Wetlands are found on every continent except Antarctica. The water in them can be freshwater, brackish, or saltwater. Common types are defined by their dominant plants and water source. Marshes, for instance, are dominated by emergent herbaceous plants like reeds, cattails, and sedges. Swamps are dominated by woody plants such as trees and shrubs (though reed swamps in Europe are mostly reeds, not trees). Mangrove forests are wetlands where mangroves and other salt-tolerant woody plants have evolved to thrive in salty water. Other examples, classified by water source, include tidal wetlands (fed by ocean tides), estuaries (fed by a mix of tides and river water), floodplains (fed by overflow from rivers or lakes), and bogs or vernal ponds (fed by rainfall or meltwater, sometimes via groundwater springs). 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. Wetlands provide many benefits to people, such as purifying water, stabilizing shorelines, protecting against storms, and controlling floods. They also process and store carbon (through carbon fixation and sequestration) and other nutrients and pollutants. Depending on the specific wetland, it can act as a carbon sink or a carbon source. If it functions as a sink, it can help mitigate climate change. However, wetlands can also release significant amounts of methane due to the anaerobic breakdown of soaked plant matter, and some emit nitrous oxide as well. Human activities are damaging wetlands in many ways, including oil and gas extraction, building infrastructure, overgrazing by livestock, overfishing, dredging and draining, nutrient pollution, and water pollution. According to the 2005 Millennium Ecosystem Assessment, wetlands are more threatened by environmental degradation than any other ecosystem on Earth. Methods exist to assess the ecological health of wetlands, and these have helped conservation efforts by raising public awareness of what wetlands do.