Wetlands | Research & Encyclopedia Articles

Wetlands

Wetlands encompass an enormously diverse range of areas, with different water regimes, dominant plant species, and sediment or soil characteristics. However, all wetlands have water present for a significant period of time and plants adapted to their wet conditions. Wetlands encompass large areas along the shores of lakes and small prairie potholes found in the north central United States. Neither exclusively aquatic nor terrestrial, wetlands are in the zone between permanently wet and normally dry environments. While the crucial value of wetland ecosystems is widely recognized today, in the past they were considered swampland to be drained or filled in for agricultural and other uses. In the United States, some 117 million acres (47.4 million hectares) of wetlands, half the original acreage, have been lost to such conversion by the mid-1980s.

Modern society recognizes that wetlands play a major role in providing habitats for numerous plants and animals, including waterfowl and other birds, fur-bearing mammals, reptiles, fish, shellfish. From wetlands wood and fibers are obtained. Wetlands help maintain water quality by retaining nutrients, metals, and other substances. They act as water absorbing sponges that control flooding and provide long term storage of surface water. In addition to these and other ongoing functions, wetlands are also recognized as having played an important role in human history. In the past, humans have depended on wetlands for food, clothing, and shelter, as shown by archaeological sites where the bones of waterbirds and the remains of fish spears indicate that people in Europe and elsewhere drew sustenance from wetlands.

Most of the wetlands in temperate parts of the world are freshwater marshes, but the broader group of marsh wetlands also includes tidal saltwater and tidal freshwater marshes. Marshes can be found in many places where frequent flooding is caused by streams or lakes, ground water, or water. Ninety percent of the wetlands in the lower 48 states are freshwater marshes. Tidal salt marshes with their salt tolerant plant species can be found along the Arctic and Atlantic seaboards of North America, the Gulf of Mexico, and the European coastline. Mangrove forests, which are mostly concentrated in the Indian Ocean and West Pacific region, are the subtropical equivalent of tidal salt marshes.

Reeds, grasses, sedges, and rushes grow in these highly productive ecosystems, depending on the hydrology. For instance, many marshes are dominated by what are called emergents, which have stems partly submerged and partly above the water. Where the water is deeper, submerged and floating water plants thrive. These ecosystems contain tidal creeks that provide a link between the marsh, the estuary, and the sea. Many marine organisms rely on these wetlands for spawning and feeding. Further inland can be found tidal freshwater marshes, which contain more diverse plants than in the salt marshes, including flowering plants.

Swamps, which differ significantly from marshes, are low-lying depressions that are poorly drained and are dominated by a single plant species. These ecosystems include North American bottomland hardwoods and cypress swamps, the swamp forests of the Amazon, and the swamps found along the shores of many large tropical lakes in Zambia, Uganda, and other African countries. Some South American and Southeast Asian swamp forests contain many species of trees, including some that are important sources of timber.

Floodplain wetlands are those flat areas on the borders of rivers that flood periodically, sometimes creating grassy regions that sustain large grazing populations. Often these wetlands spread into wide deltas, usually along the lower reaches of rivers but sometimes far inland. South America possesses some of the largest floodplains, including an area along the Paraguay River called the Gran Pantanal and along tributaries of the Orinoco River in Venezuela. Along the Lower Mekong River in Indochina and the Lower Mississippi in the United States are also found major floodplain areas.

Peatlands are another type of wetland. Water saturation, lack of oxygen, and other conditions can cause organic matter to decompose less slowly than it is produced, resulting in the accumulation of deposited organic matter. Peat deposits occur in marshes, swamps, floodplains, and other wetland types. When more than a foot (300 millimeters) of peat accumulates, it forms wetlands known as bogs and fens. Bogs can be either raised bogs, where the peat continues to accumulate and forms a dome, or blanket bogs, where the peat has spread beyond the borders of a lake or pond. Peatlands can be found on every continent. In North America, a unique peatland called a pocosin can be found in the flat, elevated regions between two rivers.

Marshes, swamps, and other wetlands receive protection under national and international laws. In the United States, for instance, the Federal Water Pollution Control Act amendments of 1972 authorized the U.S. Army Corps of Engineers and the Environmental Protection Agency to regulate pollution of the nation's waters, including wetlands. The federal jurisdiction has broadened since then to cover increasingly more acreage of wetlands. This has caused a political backlash by private companies who state that the wetlands regulations constitute a governmental "taking" of their property, and that they ought to be fairly compensated. Critics also accuse government agencies of defining wetlands so broadly that many non-wetlands were coming within the agencies' regulatory jurisdiction. Political battles became so intense during the 1990s that in 1993 Congress requested that the National Academy of Sciences create a committee to evaluate scientific wetlands issues, including how they are defined. In a 1995 report, Wetlands Characteristics and Boundaries, the academy addressed the various hydrology, vegetation, soil, and other factors that define wetlands. The report did not resolve the political controversy, leaving Congress to find a legislative compromise to address the concerns of all parties. Worldwide efforts to protect these precious areas are occurring through the 1971 Convention on Wetlands of International Importance especially as Waterfowl Habitat, or the "Ramsar Convention" as it is called after the place in Iran where it was adopted. More than 500 wetland sites have been placed on the Ramsar list, which designates wetlands of international importance whose ecological characteristics the treaty nations agree to maintain.