Wetlands INTRODUCTION

Transcription

1 Wetlands INTRODUCTION Wetlands is a generic term for all the different kinds of habitats where the land is wet for some period of time each year, but not necessarily permanently wet. Natural wetlands are created by geological or ecological processes that supply water through tidal flows, rivers, or groundwater. Wetlands are covered or soaked by water for part or all of the year. They are a transitional zone between terrestrial and aquatic ecosystems and have charceristics of both. Some have fresh water, some have salt water, and some have brackish water, a combination of both. Wetlands can occur in many different places. Some occur where surface water collects after a rainstorm or snowmelt. Others occur where underground water discharges at the surface. Some wetlands are found in coastal areas. Salt marshes are an example of this type of wetland. Page 1 of 6

2 Courtesy of Marco Molinaro The San Francisco East Bay region has reclaimed much of its waterfront properties for restoration of wetlands. Courtesy of NOAA National Estuarine Research Reserve Collection, NOAA Photo Library The wetlands and tidal streams in the Ashe Island area, ACE Basin National Estuarine Research Reserve, South Carolina. The U.S. Clean Water Act defines wetlands as"areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support...a prevalence of vegetation typically adapted to saturated soil conditions." Wetlands generally include swamps, marshes, bogs, and similar areas. A morning mist hangs over the Florida Everglades. Wetlands serve to slow rivers as they wind their way through the marsh. Wetlands are an important biome for many reasons. They prevent floods by absorbing water and helping keep river levels normal. Wetlands filter and purify water from surface drainage. They help control erosion by slowing down water flow. They recycle nutrients into the ecosystem as they contribute to the decomposition of plant material and convert the resulting chemicals into usable forms. During dry periods, wetlands slowly release water to the surrounding area. They provide nesting, resting, and feeding habitats for a variety of animals. Just like our kidneys, wetlands help control water flow and cleanse the ecosystem. ABIOTIC DATA Wetlands vary greatly with their location. They are found in all climates from the poles to the tropics. There are even wetlands in the desert. The location determines the average temperatures and rainfall. Page 2 of 6

3 The Bosque del Apache National Wildlife Refuge is a wetland in central New Mexico. It occurs in the floodplain of the Rio Grande. Its riparian marshes are mostly grasses with a few scattered trees and shrubs. Swamps are areas of slow-moving rivers. Their wet soils support a variety of trees, shrubs, and other plants. Shrub swamps are covered by willows, alders, shrubby dogwoods, and buttonbush. Some shrub swamps are permanent. Others slowly become forested swamps. Bogs are wetlands that are usually fed by rainfall. They often do not have a stream flowing through them. Bogs are found in parts of the northeastern United States and Canada in depressions caused by glaciers that covered the area during the last million years or so. Peat may form when plants slowly decompose, especially in highly acidic soils and in poorly drained areas. Peat sometimes forms a floating mat of vegetation over water. It can become up to 12 meters (40 feet) thick. Evergreen trees and shrubs live in and around bogs. The bog surface may be covered by sphagnum moss. Grasses and water lilies grow in swamps. Water is slowly flowing through this area. A forested swamp has large stands of trees growing from the water. Vernal pools are low areas that fill up with water in spring and dry up in winter. Vernal pools are usually small, temporary, and isolated from other wetlands, streams, and other water bodies. They are an important breeding habitat for certain animals, such as fairy shrimp and some amphibians. These ponds have no fish. As the ponds dry up, a succession of wildflowers may bloom around the edges, creating a series of colorful rings. Salt marshes are found in low-lying coastal areas. The water level fluctuates with the tides. If the salt marsh is at the mouth of a river, the water grades from fresh to brackish to salt as it reaches the ocean. These marshes are also called estuaries. Other types of wetlands include forested floodplains, pocosins, prairie potholes, cienegas, and muskegs. BIOTIC DATA The wetland biome is both aquatic and terrestrial, depending on the season and the weather. Organisms that live in Page 3 of 6

4 wetlands have to be adapted to survive changing conditions. Many kinds of birds use wetlands as resting places and shelter during their annual migrations. You might find geese, herons, American coots, egrets, ducks, cranes, yellow-headed blackbirds, marsh hawks, rails, and kingfishers. Courtesy of Stefan Dobert, U.S. Fish and Wildlife Service Thousands of flamingos nest in a wetland in central Africa. These snow geese nest in the summer in the eastern Arctic and migrate south to wetlands in the United States for the winter. Amphibians, such as frogs, require wetlands for reproduction. Eggs and tadpoles need the wet environment as they develop and mature. Fish also thrive in wetlands, where they find food and protection from predators. Turtles such as pond sliders, snakes such as cottonmouths, other reptiles such as American alligators, and a variety of insects depend on wetlands for life. Muskrats, beavers, minks, marsh rabbits, nutrias, and other mammals also live in wetland areas. Courtesy of John and Karen Hollingsworth, U.S. Fish and Wildlife Service Nutrias are rodents that live near ponds, lakes, and swampy areas. They are skillful swimmers and spend most of their day in the water. Nutrias are an introduced species from Europe and South America. They are prized for their coats and are often raised on farms. Courtesy of National Estuarine Research Reserve Collection, NOAA Photo Library A Mississippi diamondback terrapin found in Weeks Bay National Estuarine Research Reserve, Alabama. A variety of plants provide shelter and food for animals living in wetlands. Through photosynthesis, plants add oxygen to the water. Some plants, like pickerelweed, grow along the water's edge. Other plants grow out of the water. They are called emergents. Emergents include broadleaf arrowhead, lotus, and soft rush. Other aquatic plants have adapted so that their leaves float on the water's surface. These plants include floating Page 4 of 6

5 pondweeds, spatterdock, and duckweed. Courtesy of Alison Robb, National Estuarine Research Reserve Collection, NOAA Photo Library Joe-pye weed (foreground) and cattails (middle) are emergents growing at Flat Pond, South Cape Beach, Massachusetts. Courtesy of Steve D. Eggers and Donald M. Reed, Northern Prairie Wildlife Research Center, U.S. Geological Survey A number of plants thrive in this Minnesota marsh, including broad-leaved arrowhead (foreground) and lotus (background), as well as Elodea, coontail, and giant bur reed. ISSUES Wetlands have often been underappreciated and their ecological functions overlooked. They were once thought to be useless wastelands places where pests breed and dangerous diseases are harbored. Today wetlands are disappearing at a rapid rate about 40,500 hectares (100,000 acres) each year in the United States alone. Some are lost as water is diverted for industrial, agricultural, and municipal water supplies. As cities along rivers grow, riparian wetlands are filled for housing and industrial parks. Courtesy of National Estuarine Research Reserve Collection, NOAA Photo Library Old rice fields 72 kilometers (45 miles) south of Charleston, South Carolina. Courtesy of Todd Voteller, Environmental Protection Agency Wetlands can be threatened by industrial pollution. Part of the U.S. Clean Water Act provides for the control of wetland development. But the laws are weak and contain loopholes. Few states have programs to protect wetlands. Some states have a "no net loss" plan for wetlands. This Page 5 of 6

6 means that, for every hectare of wetland that is lost to development, another hectare is created in some other place. But many scientists suggest this plan doesn't work very well, because it removes everything that lived and thrived in the old area. It is difficult to create a new wetland to match the old one. Courtesy of Paul McIver, U.S. Environmental Protection Agency Mining for peat destroys a valuable wetland habitat. Courtesy of Dick Gersib, U.S. Environmental Protection Agency This wetland is being drained to provide irrigation water. Wetlands are used by hunters, fishers, naturalists, and recreational users. Care must be taken that these intrusions by humans do not harm the environment. Trash and litter dropped may float long distances before it becomes entangled in vegetation. Exotic plants and animals sometimes are transported into wetlands via boats and vehicle tires. Vehicles can compress soil and disrupt water movement. Courtesy of National Estuarine Research Reserve Collection, NOAA Photo Library Crabbing in an estuary of North Carolina. Courtesy of National Estuarine Research Reserve Collection, NOAA Photo Library A winter wetland is an excellent place for birdwatching. Transportation by airboat can damage both plants and animals. Page 6 of 6