Changes in water level may be related to amount of runoff from surrounding land, the flooding and recession of water in nearby streams, or the ebb and flow of tides farther down an estuary.
Hydroperiods are defined as permanent when the wetland is flooded all year. Intermittent hydroperiods are those where standing water is absent only during exceptionally dry years. With a saturated hydroperiod standing water is rare, but the soil is saturated during growing season or even longer. Finally, a temporary hydroperiod occurs when the wetland is flooded for a short time at least a week during the growing season. Water holds and carries nutrients sediments, organic material, dissolved salts, and organisms so its rhythm of ups and downs is important for ecosystem functioning, development, and change.
Wetland soils are hydric soils. The upper layer develops anaerobic lacking oxygen conditions during the growing season. This means that decomposition of organic matter proceeds slowly and, especially in regions of low temperatures, more organic material may be added each year than is removed by decomposition.
Soils are described as either organic or mineral. They tend to hold water and be both acidic and nutrient-poor. Individual soil profiles may be described as peats, peaty muck, or muck. They exhibit low permeability; that is, water does not pass readily through them.
Anoxic low dissolved oxygen conditions develop rapidly during the growing season when they become saturated. Their pH is in the neutral range and nutrient availability can be rather high. Mineral soils assume a dull gray coloration often mottled with reddish areas resulting from iron oxides. Wetlands occur in every climate region and on every continent except Antarctica.
Marshes are dominated by non-woody herbaceous , emergent plants such as sedges and grasses and short, broadleaved perennials.
A great variety of freshwater marshes exists, including wet meadows, wet prairie, playas, and vernal pools. Vernal pools hold surface water in winter and spring, but lose it via evapotranspiration in summer, when the standing water disappears entirely.
In eastern North America they are important breeding grounds for salamanders, wood frogs, and spring peepers. Tidal freshwater marshes have a hydroperiod determined by daily tides.
They occur inland from saltwater marshes near the head of estuaries. Swamps are wetlands dominated by woody vegetation, either shrubs or trees, are classified according to the dominant woody species. For example, In North America, there are cypress swamps, cedar swamps, and red maple swamps. All have mineral soils.
Peat is the partially decomposed remains of dead plants. Bogs are also one of the stages of succession as a lake fills in. Fens are different from bogs in that they receive their water supply from either runoff or groundwater not rainfall. This usually results in a different water chemistry. Fens have either neutral or alkaline waters and are typically not stages in lake succession. Wetlands Wetlands are areas of standing water that support aquatic plants.
Types of Wetlands There are many types of wetlands. Scientists often divide them up into the following groups. Marshes Swamps Bogs Fens Marshes are characterized by the presence of soft-stemmed vegetation adapted to saturated soils. It is often the first step in the creation of coal , a fossil fuel. The fossils in coal are wetland plants. Some people living near bogs cut and dry squares of peat.
It is burned for heating and cooking, or used to insulate buildings. Bogs preserve more than the remains of plants, however. The bodies of dozens of prehistoric people have been found in bogs in Europe and Asia. Bog bodies are in such excellent condition that anthropologist s can examine clothes, tattoos, and hair color, and even investigate a cause of death. Most people found in bogs were killed, though historians and anthropologists debate whether they were murdered or sacrifice d as part of a religious ritual.
They are called quaking bogs because the surface quakes when a person walks on the spongy peat. The island of Ireland, with its cool, wet climate, has hundreds of quaking bogs. Unlike other wetlands, bogs usually are not agriculturally fertile. The amount of acid in the soil and water is generally higher than that in swamps or marshes.
The supply of nutrient s, especially nitrogen, is low. Only certain kinds of plants can grow in bogs. Some of the few plants harvested in the wet, acidic soil of bogs are cranberries and blueberries.
Plants are autotroph s, meaning they are able to create their own food from air, water, and sunlight. Many bog plants have adapted to the poor nutrients in the soil and water by expanding their food source. Pitcher plants and sundew, common in bogs, are carnivorous: They trap and consume insects.
Because of the limited species of plants, bogs do not have the biodiversity common in other types of wetlands. Insects, common in all wetlands, include butterflies and dragonflies. These insects feed on the nectar in bog flowers. Ireland has dozens of native butterflies found in bogs.
Birds, such as geese and pheasant, also make their homes in the bog, although it is unusual to find larger animals. In North America, moose are one of the few large animals that thrive in bog habitats. Moose, the largest species of deer, consume aquatic plants such as pond lilies. Vital Ecosystems Wetlands are some of the most valuable ecosystems on Earth. They act like giant sponges or reservoirs. During heavy rains, wetlands absorb excess water, limiting the effects of flooding.
Wetlands also protect coastal areas from storm surge s that can wash away fragile beaches and coastal communities.
Saltwater swamps and tidal salt marshes help secure coastal soil and sand. Wetland ecosystems also act as water-treatment facilities. The plants, fungi, and algae of a wetland filter wastes and purify water.
Nitrate s and other runoff chemicals often wash into wetlands from urban area s and farm s. Organisms there absorb the harmful chemicals. Pollutant s not absorbed by plants slowly sink to the bottom, where they are buried in sand and other sediment. Wetlands, especially marshes and swamps, are home to a wide variety of plant and animal life.
Some animals, such as shrimp, live in tidal marshes. Many marine fishes, such as striped bass, enter coastal wetlands to spawn. Bass swim from the ocean and into salt marshes to lay their eggs.
When the eggs hatch, the young bass find plenty of food and some protection in the grasses or tree roots. Oysters live in huge reefs in salt marshes.
All of these wetlands are home to economically valuable fisheries. Near the bay, the ecosystem is a tidal salt marsh. Farther from the Atlantic Ocean, freshwater marshes appear close to the Susquehanna River and its tributaries. Chesapeake Bay wetlands are home to an extraordinary variety of wildlife. Plants include grasses, wild rice, pond lily, cattail, alder, and button bushes. Chesapeake Bay wetlands are a major nesting area for the bald eagle, a symbol of the United States.
Bald eagles and ospreys feed on fish in the Chesapeake Bay. Many migratory birds, including swans and geese, spend winters in the Chesapeake wetlands. Other animals native to the Chesapeake Bay include muskrats, beavers, otters, turtles, frogs, and numerous shellfish, as well as the fox squirrel and bog turtle, which are endangered species. Economic Importance Wetlands are economically important to people.
They are popular places for recreational activities, such as hunting, hiking, canoeing, and bird-watching. According to the U. Images of blue crabs are on thousands of souvenirs, and many Maryland restaurants serve crab cakes.
For most of history, wetlands were looked upon as wastelands. They do not easily support development. The soil is wet, spongy, and difficult to build on.
Wetlands are also home to pests, from mosquitoes to alligators. Until recently, draining wetlands was accepted practice. Drained wetlands provided land for agriculture, housing, industry , schools, and hospitals. The capital of the United States, Washington, D. Almost half of U. Drainage and peat harvesting have destroyed wetlands in Ireland and Scandinavia.
Many fish that depend on wetlands have become rare. Some of these species, such as flounder, trout, and bass, are commercially important. Freshwater and ocean fisheries depend on wetlands to provide habitat for the next generation of fish. In the early s, governments began recognizing the enormous value of wetlands. To protect the vanishing ecosystems, hunting and fishing licenses were restricted. Living shoreline s and other restoration project s encouraged the development of coastal wetlands to protect communities from storm surges.
Fines and restrictions on agricultural and industrial runoff reduced the toxic chemicals spilling into wetlands. In some parts of the world, including the United States, it is now against the law to alter or destroy wetlands. Through management plans and stricter laws, people are trying to protect remaining wetlands and to recreate them in areas where they have been destroyed.
Case Study: Tres Rios The arid urban area of Phoenix, Arizona, serves an example of how wetlands support the economy, health, and wildlife of an area. In the early s, city leaders worked with the Army Corps of Engineers, the Environmental Protection Agency, and local environmental groups to create a wetland, the Tres Rios Demonstration Project.
Tres Rios receives its water from a wastewater facility serving the busy urban area of Phoenix, as well as the seasonal streams of the Gila, Salt, and Agua Fria rivers. More than two million gallons of wastewater flow into Tres Rios every day.
Thousands of birds flock to Tres Rios: waterfowl, such as ducks and cormorants; terrestrial species, such as sparrows and cardinals; and migratory species, such as blackbirds. Even raptors such as osprey inhabit Tres Rios. The habitat established at Tres Rios was so successful that wildlife managers were forced to relocate beavers, native to Arizona marshes, because multiplied too quickly for the wetland to sustain. Tres Rios cleans the wastewater that flows into it. The ecosystem acts as a filter for toxic chemicals.
Its position along the Salt River also makes Tres Rios a natural flood-control mechanism. Finally, Tres Rios was less expensive to construct than a new water treatment plant for the city of Phoenix. Ghost Airport In the s, Floridas Miami-Dade Aviation Department planned to build a square-kilometer square-mile airport complex and transportation corridor in the southern Florida wetlands. The Everglades Jetport would have blocked the flow of water into the Everglades, causing untold environmental damage.
A group of activists, helped by the first-ever environmental impact study, successfully stopped the venture. Soggy Cities Some of the biggest cities in the U. In fact, the "tidal basin" in front of the Jefferson Memorial in Washington, D.
Pantanal The Pantanal is the largest natural wetland in the world.
0コメント