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Wetlands have decreased by as much as 50% since 1900 and in some parts of the world by 90%. [19] [20] Inland wetlands, freshwater marshes making up about 20-25% of all freshwater wetlands globally, [21] have been decreasing approximately 1.2% each year throughout the last century (since 1900). [22] [23]
Wetlands exist on every continent, except Antarctica. [19] The water in wetlands is either freshwater, brackish or saltwater. [18] The main types of wetland are defined based on the dominant plants and the source of the water. For example, marshes are wetlands dominated by emergent herbaceous vegetation such as reeds, cattails and sedges.
Plant community composition can change dramatically over a gradient of groundwater depth: plants that can only survive in wetland conditions can be replaced by plants that are tolerant of drier conditions as groundwater levels are reduced, causing habitat community shifts and in some cases complete loss of riparian species. [7]
The beaver is a keystone species, increasing biodiversity in its territory through creation of ponds and wetlands. [1] [2] As wetlands are formed and riparian habitats enlarged, aquatic plants colonize newly available watery habitat. Insect, invertebrate, fish, mammal, and bird diversities are also expanded. [3]
Wetland vary widely in their salinity levels, climate zones, and surrounding geography and play a crucial role in maintaining biodiversity, ecosystem services, and support human communities. [1] Wetlands cover at least six percent of the Earth and have become a focal issue for conservation due to the ecosystem services they provide.
Wetlands can be part of the lentic system, as they form naturally along most lake shores, the width of the wetland and littoral zone being dependent upon the slope of the shoreline and the amount of natural change in water levels, within and among years. Often dead trees accumulate in this zone, either from windfalls on the shore or logs ...
When the proliferation of newly introduces nutrients evoke plant and algae growth, oxygen levels in the water decrease. [citation needed] This process, known as eutrophication, suffocates plants and animals and leads to dead zones i.e. water habitats without any life. Chemicals and heavy metals from industrial wastewater are also toxic to ...
Coastal wetlands also reduce pollution from human waste, [41] [42] remove excess nutrients from the water column, [43] trap pollutants, [44] and sequester carbon. [45] Further, near-shore wetlands act as both essential nursery habitats and feeding grounds for game fish, supporting a diverse group of economically important species. [46] [47] [48 ...