Wetlands

Wetlands are distributed throughout the world except Antarctica. A key facet of a wetland is that water is the primary factor controlling the environment and its associated biota. Several definitions of wetlands have been described. The Ramsar definition of wetlands, which is widely used, is a broad one, encompassing not just marshes and lakes but also coral reefs, peat forests, temporary pools, riparian systems, underground caves, and other systems found everywhere from the mountains to the sea, including man-made habitats such as aquaculture ponds and irrigated agricultural lands. According to the U.S. Environmental Protection Agency, they are areas where water covers the soil or is present either at or near the surface of the soil all year or for varying periods of time during the year.

The Environmental Protection Agency defines two broad categories of wetlands: coastal or tidal wetlands and inland or nontidal wetlands. Coastal wetlands are distributed throughout almost the entire coastal zone, where saline water and the influence of tides are the defining factors. The salinity of saltwater wetlands is not a fixed value but, rather, changes with distance from the ocean, water depth, freshwater input (e.g., precipitation, runoff, ground water), and season. Nontidal or inland wetlands are most common on floodplains along rivers and streams—small to large portions of water surrounded by dry land, along the margins of lakes and ponds, and in other low-lying areas where the groundwater intercepts the soil surface or where precipitation sufficiently saturates the soil. Inland wetlands include marshes and wet meadows dominated by herbaceous plants, swamps dominated by shrubs, and wooded swamps dominated by trees.

About 6 percent of the world's surface is made up of a variety of wetlands, including swamps like this one at the Cypress Creek National Wildlife Refuge in southern Illinois.

Source: U.S. Fish & Wildlife Service

Wetlands and their functions are inextricably linked to the watershed and its surroundings, encompassing a vast and diverse range of ecosystems and, as such, representing a wide array of relationships and services to both people and biodiversity. Wetlands are valuable and among the most productive ecosystems on Earth, occupying about 6 percent of the world's land surface. They include a wide spectrum of habitats ranging from extensive peat bogs in northern latitudes to tropical mangrove forests, from seasonal ponds and marshes to floodplains and permanent riparian swamps, from freshwater shallow lakes and margins of large reservoirs to the salt lakes, brackish lagoons, estuaries, and coastal salt marshes. Extensive sea grass beds along coasts and coral reefs are also wetlands. Thus, wetlands show great differences in their habitat characteristics, hydrological regimes, water quality and soils, and the nature and diversity of their biota.

Wetlands are key to the life cycles of waterfowl and other wildlife and provide a variety of irreplaceable ecosystem services; filter our water and help provide clean, secure water sources; provide environmental and societal value by moderating the effects of droughts, floods, climate change, and erosion; maintain soil fertility; decompose and detoxify wastes; recycle essential nutrients; and provide recreation and learning opportunities for people of all ages. They are essential habitat for many species of wildlife, have the potential to remove and store greenhouse gases from the Earth's atmosphere, and are a key component of watershed management planning. One wetland acre is seven times more valuable than an acre of tropical forest in terms of ecosystem benefits. Wetlands provide numerous ecosystem goods and services not only to the local people living around them but also to communities living outside wetland areas. Mangroves are considered a natural barrier protecting the lives and property of coastal communities from storms and cyclones, flooding, and soil erosion. Values attributed to this service have been calculated by different authors to range from $3,700 per hectare to $7,700 per square kilometer.

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