Wetlands are areas covered or soaked by ground or surface water often enough and long enough to support special types of plants that have adapted for life under such conditions. Wetlands occur where the water table (the level of groundwater) is at or near the surface of the land, or where the land is covered by shallow surface water (usually no deeper than about 6 feet [1.8 meters]). They form the area between places that are always wet, such as ponds, and places that are always dry, like forests and grasslands.
Many wetlands are not constantly wet, experiencing what is called a wet/dry cycle. Some are wet for only part of the year, like those that are drenched during heavy seasonal rains. Some have no standing water but, because they are near the water table, their soil remains saturated (soaked with water). Others may dry out completely for long periods, sometimes years.
Wetlands are among the world’s most productive environments with high biodiversity (a large variety of life forms). Only rain forests and coral reefs have more biodiversity.
Wetlands are found all over the world, in every climate from the frozen landscape of Alaska to the hot zones near the equator, except Antarctica. In the continental United States, there are about 110,000,000 acres (44,500,000 hectares) of natural wetland, and some types are found in every state. Alaska contains about 175,000,000 acres (71,000,000 hectares) of wetlands.
Wetlands have a life cycle that begins with their formation and may involve many changes over time.
Many wetlands were formed when glaciers retreated after the last ice age, about 10,000 years ago. Some of the glaciers left depressions
|WORDS TO KNOW|
|Arroyo: The dry bed of a stream that flows only after rain; also called a wash or a wadi.|
|Biodiverse: Term used to describe an environment that supports a wide variety of plants and animals.|
|Bio-indicators: Plants or animals whose health is used to indicate the general health of their environment.|
|Dambo: Small marsh found in Africa.|
|Fen: A bog that lies at or below sea level and is fed by mineral-rich groundwater.|
|Hydric soil: Soil that contains a lot of water but little oxygen.|
|Hydrophytes: Plants that are adapted to grow in water or very wet soil.|
|Kettle: A large pit created by a glacier that fills with water and becomes a pond or lake.|
|Peat: A type of soil formed from slightly decomposed plants and animals.|
|Pocosin: An upland swamp whose only source of water is rain.|
|Prairie potholes: Small marshes no more than a few feet deep.|
|Submergent plant: A plant that grows entirely beneath the water.|
|Wadi: The dry bed of a stream that flows only after rain; also called a wash or an arroyo.|
in the ground, called kettles, which were perfect places for water to gather. In some places, buried ice melted to form kettle lakes that eventually turned into wetlands.
Wetlands are formed by overflowing river banks and changes in sea level (the average height of the sea) that leave behind waterlogged areas. Some wetlands are formed with help from beavers making dams that cause rivers or streams to back up and flood the surrounding area. Landslides or centuries of heavy winds may change the terrain or carve out depressions in the ground where water then collects.
Climate plays a key role in the formation of wetlands. Lots of rain and little drainage, for example, can cause the ground to become waterlogged.
Wetlands are constantly changing as their plant and animal life changes. This process is called succession. For example, one type of floating plant, such as pondweed, begins to fill up a pond or lake. The waste from these plants, such as dead stems and leaves, makes the water thick, shallow, and slower moving. As a result, plants that must be
anchored in soil, such as reeds and grasses, can grow. As waste matter continues to accumulate, the pond gradually becomes wetland. As succession continues, the wetland eventually disappears and is replaced by dry ground.
The three main types of wetlands are swamps, marshes, and peat-lands. They can be identified by size, soil type, plant populations, and the type and amount of water they hold. Some wetlands located inland are fresh water, while coastal wetlands may be fresh or salt water. Many areas contain several different types of wetlands. The Great Dismal Swamp in Virginia, contains both peat bogs and freshwater swamps.
A swamp is a wetland characterized by poorly drained soil and plant life dominated by trees. Swamp soil is usually saturated for most of the year. The water can range from 1 inch (2.5 centimeters) to more than 1 foot (30 centimeters) deep.
Because swamp ground is constantly waterlogged, trees and plants that grow must be able to tolerate having their root systems wet for long periods of time. The water is stagnant (without movement) and the dead plant matter that settles on the bottom receives little oxygen. Without oxygen, the dead matter cannot fully decay. This gives the swamp its characteristic brown water and unpleasant smell.
Swamps are usually found in low-lying areas near rivers or along coastal areas. They get water from the overflow of the river or from ocean tides. Inland swamps always contain fresh water, but coastal swamps may contain either fresh or salt water.
In the eastern United States, some swamps, called pocosins, form in upland areas. The term pocosin comes from the Algonquin phrase meaning “swamp on a hill.” Rain is usually their only source of water, meaning the soil is low in minerals and nutrients that come from ground water. Drainage is poor in pocosins and the saturated soil is acidic (high in acids). In this environment, decomposition (breaking down) of waste is slow, and decaying matter accumulates over time. Sometimes pocosins are flooded by slow-moving streams.
Freshwater swamps develop near the edges of lakes and next to rivers that overflow their banks. Partly decayed plant matter and stagnant water soon create swamp conditions. The Everglades in Florida, the Okefenokee Swamp in Georgia, and the Great Dismal Swamp in North Carolina and Virginia, are examples.
A saltwater swamp is formed by the ebbing (receding) and flowing of the ocean tides. (Tides are a rhythmic rising and lowering of the oceans caused by the gravitational pull of the sun and moon.) When the tide is low, flat areas of the swamp are not under water. Saltwater swamps can be found in New Guinea, Indonesia, Kenya, Zaire, along the Mekong River in Vietnam, and along the Ganges River in India.
In some low-lying coastal areas regularly flooded with sea water, mangrove swamps develop. A mangrove swamp is a coastal, saltwater wetland found in tropical and subtropical climates such as southern Florida and Puerto Rico. (Tropical and subtropical climates are found in areas close to the equator and are characterized by warm weather.) The mangrove swamp supports salt-loving shrubs and trees such as the man-grove, from which it takes its name. Few other woody plants grow there because of the high salt content.
Marshes are the most common type of wetland. They are dominated by nonwoody plants such as grasses, reeds, rushes, and sedges. Some marshes are so thickly covered with vegetation they look like fields of grass.
Marshes are usually found in temperate climates where summers are hot and winters are cold. They often form at the mouths of rivers (the point where a river enters into a larger river or ocean), especially those having large deposits of soil and sand, called deltas. They also form in flat areas frequently covered by shallow fresh or salt water.
Freshwater marshes are the most common of the world’s temperate wetlands. Some receive no rain, and most are found along the edges of lakes and rivers or where groundwater, streams, or springs cause flooding. The Camargue in the Rhône Delta in southern France is an example. Different types of freshwater marshes include prairie potholes, riparian areas, wet meadows, and washes.
Prairie potholes are small marshes found by the millions throughout the north central area of the United States and south central Canada. Usually no more than a few feet deep, they may cover as much as 10,000 acres (4,000 hectares). Prairie potholes are important to migratory waterfowl as places to rest, feed, and nest. In Africa, these small marshes are called dambos. In North America it is estimated that two-thirds of all waterfowl are hatched in prairie potholes.
Wet meadows are freshwater marshes that frequently become dry. They look like grasslands but the soil is saturated. They are common in temperate and tropical regions around the world, including the midwestern and southeastern United States. Their dominant plants are sedges, flowering plants that resemble grass.
Riparian wetlands are marshes found along rivers and streams. They range in width from a few feet (meters) to as much as 12 miles (20 kilometers). Smaller riparian wetlands are common in the western United States. Larger ones are located along large rivers, such as the Amazon in South America. Riparian wetlands are unique from others in that the vegetation and life forms found immediately adjacent to the river or streams differ from those of the surrounding area, usually a forest. This marked contrast produces a diversity and enhances the benefits for wild-life, both in food (grasses and sedges) and in shelter (shrubs and trees) in a relatively small place.
A wash is a dry streambed that becomes a wetland only after a rain. Washes are found in dry plains and deserts. The plant life they support usually has a short growing season and disappears during dry periods. In North Africa and Saudi Arabia washes are called wadis. In the American west they are called arroyos.
Saltwater marshes, also called salt marshes, are found in low, flat, poorly drained coastal areas. They are often flooded by salt water or brackish water (a mixture of both fresh and salt water). Saltwater marshes are especially common in deltas, along low seacoasts, and in estuaries (arms or inlets of the sea where the salty tide washes in and meets the freshwater current of a river). They can be found in New Zealand, in the Arctic, and along the Atlantic, Pacific, Alaskan, and Gulf coasts.
Saltwater marshes are greatly affected by tides, which raise and lower the water level on a daily basis. A saltwater marsh may have tidal creeks, tidal pools, and mud flats, each of which has its own ecosystem (a network of organisms that have adapted to a particular environment).
The high salt content of the sea water in the marsh makes it hard for plants to adapt. Grasses such as marsh grass, cord grass, salt hay grass, and the grasslike needlerush thrive here.
Peatlands are wetlands in which peat has formed. Peat is a type of soil made up of the partially decayed remains of dead plants, such as sphagnum moss and even trees. In peatlands, dead plant matter is produced and deposited at a greater rate than it decomposes. Over time, sometimes over thousands of years, a layer of this plant matter is formed that may be as deep as 40 feet (12 meters). Several conditions are necessary for peat to form. The soil must be acidic, waterlogged from frequent rains, and low in oxygen and nutrients. The bacteria responsible for decomposing plant matter cannot thrive under these conditions, resulting in accumulation of the layers of partially decayed plant matter.
Peatlands cover three percent of Earth’s land and freshwater surface area. Peatlands are located in colder, northern climates and in the tropics. They can be found in Russia (mainly Siberia), China, Scandinavia, northern Europe, England, Ireland, Canada, and the northern United States.
The types of peatlands are temperate bogs, fens, and tropical tree bogs.
Ninety percent of peatlands are found in northern temperate climates where they are called bogs. Bogs have a soft, spongy, acidic soil that retains moisture, which comes primarily from rainwater. Some bogs have taken as long as 9,000 years to develop and are sources of peat that can be burned as fuel.
Temperate bogs have been described as soft, floating carpets. The carpet is made mostly of sphagnum moss, which can be red, orange, brown, or green and may grow as long as 12 inches (30 centimeters). Sphagnum moss can grow in an acidic environment. It holds fresh rain-water in which other bog plants can grow. The high concentration of sphagnum moss has led other bog plants to develop unusual adaptations for obtaining nutrients. For example, the bog myrtle forms a partnership with the bacteria in its roots to get extra nitrogen. Other plants that grow in bogs include grasses, small shrubs such as leatherleaf, flowering plants such as heather, and poison sumac. Some rare wildflowers, such as the lady slipper orchid and the Venus flytrap, are found in bogs.
Most bogs lie in depressed areas of ground. Some, called raised bogs, grow upward and are about 10 feet (3 meters) higher than the surrounding area.
Blanket bogs are shallow and spread out like a blanket. They form in areas with relatively high levels of annual rainfall. Their average depth is 8 feet (2.6 meters). Blanket bogs are found mainly on lowlands in western Ireland and in mountain areas. After a heavy rainfall, bogs located on steep slopes can wash down like a huge landslide of jelly and cover cattle, farms, and even villages.
Sphagnum moss, which is found in bogs, can absorb many times its weight in water. At one time, certain Native Americans dried this moss and used it as diapers for their babies.
When a peatland is less acidic and is fed by mineral-rich groundwater, it is called a fen. Plants characteristic of fens are grasses, sedges, and reeds rather than sphagnum moss, and the soil does not become as acidic as in a bog. Less peat accumulates in a fen and it becomes only about 6 feet (2 meters) thick. As plant matter accumulates in a fen over time, it may form a raised bog.
Tropical tree bog
Bogs found in tropical climates are called tree bogs. These bogs produce peat from decaying trees rather than from sphagnum moss. The trees most commonly found in these bogs are broad-leaved evergreens. Temperatures are warmer than in temperate regions, causing decay to occur more rapidly. As a result, not as much peat develops. The only source of water is rain.
Tropical tree bogs can be found in South America, Malaysia, Africa, and Indonesia.
Unlike some other biomes, wetlands do not have a characteristic climate. They exist in polar, temperate, and tropical zones, but not usually in deserts. They are very sensitive to changes in climate, such as a decrease in precipitation (rain, sleet, or snow). The amount of precipitation and changes in temperature affect the growth rate of wetland plants. Some wetlands are seasonal, which means they are dry for one or more seasons of the year.
Temperatures vary greatly depending on the location of the wetland. Many of the world’s wetlands are in temperate zones (midway between the North and South Poles and the equator). In these zones, summers are warm and winters are cold, but temperatures are not extreme. Wetlands found in the tropic zone, which is around the equator, are always warm. Temperatures in wetlands on the Arabian Peninsula, for example, can reach 122°F (50°C). In northeastern Siberia, which has a polar climate, wetland temperatures can be as cold as –60°F (–51°C).
The amount of rainfall a wetland receives depends upon its location. The average rainfall for wetlands in Wales, Scotland, and western Ireland is about 59 inches (150 centimeters) per year. Wetlands in Southeast Asia, where heavy rains occur, can receive up to 200 inches (500 centimeters). In the northern areas of North America, wetlands exist where as little as 6 inches (15 centimeters) of rain fall each year.
The geography of wetlands involves landforms, elevation, and soil.
Landforms found in wetlands depend upon location, soil characteristics, weather, water chemistry, dominant plants, and human interference. Their physical features are often short-lived, especially if they are near floodplains or rivers, which can cause abrupt changes. Wetlands usually form in a basin where the ground is depressed, or along rivers and the edges of lakes.
Wetlands are found at many elevations (the height of an area in relation to sea level). Some wetlands in the Rocky Mountains in North America, for example, are at an elevation of 10,000 feet (3,048 meters).
Elevation is used to help classify some wetlands in Ireland. Bogs that are less than 656 feet (200 meters) above sea level are called Atlantic blanket bogs. Those that are more than 656 feet (200 meters) above sea level are called mountain blanket bogs.
An important characteristic of a wetland is its soil. Soil composition helps to determine the type of wetland and what plants and animals can survive in it. Almost all wetland soils are at least periodically saturated.
Wetland soils are hydric. This means they contain a lot of water but little oxygen. Only plants that that can adapt to these wet soils live in wetlands. The nutrients in the soil often depend upon the water supply. If the water source is primarily rain, the wetland soils do not receive as many minerals as those fed by groundwater. Soil in floodplains is very rich and full of nutrients, including potassium, magnesium, calcium, and phosphorus.
In some bogs associated with forests, decaying plant matter fully decomposes and is combined with sediments to form muck. This type of soil is dark and sticky. To be classified as muck, soil must contain not less than 20 percent organic (derived from living organisms) matter.
An important characteristic of any biome is its plant life or lack of plant life. More than 5,000 species of plants live in or near wetlands. Wet-lands have high biological productivity (the rate at which life forms grow in a certain period of time). The higher its plant productivity, the more animal life a wetland can support. The kinds of plants found in a wetland are determined by several factors, especially the type of soil and the quantity of water.
Some plants, called hydrophytes, grow only in water or extremely wet soil. Sedges are an example. Mesophytes, such as reeds, need moist but not saturated soil. When a wetland dries up,
A Useful Nuisance
People often grumble about the water hyacinth because it multiplies and spreads quickly in open water. The plants become so thick that boats have a hard time moving through them. The water hyacinth has an important use, though. It absorbs and neutralizes many pollutants that would otherwise contaminate the water. It also has a high nutrient content, which makes it a good fertilizer.
the area may fill with plants called xerophytes. These are plants adapted to life in dry habitats and can survive where other wetland plants would wilt.
A submergent plant grows beneath the water and is found in deep marshes and ponds. Even its leaves are below the surface. Submergents include milfoil, pondweed, and bladderwort, an insect-eating plant.
Found in deep marshes, floating aquatics float on the water’s surface. Some, like duckweed, have free-floating roots. Others, including water lilies, water lettuce, and water hyacinths, have leaves that float on the surface, stems that are underwater, and roots that are anchored to the bottom.
An emergent plant grows partly in and partly out of the water. The roots are usually under water, but the stems and leaves are at least partially exposed to air. They have narrow, broad leaves, and some produce flowers. Emergents include reeds, rushes, grasses, cattails, and water plantain.
Algae, fungi, and lichens
It is generally recognized that algae (AL-jee), fungi (FUHN-ji), and lichens (LY-kens) do not fit neatly into the plant category.
Most algae are one-celled organisms too small to be seen by the naked eye. They make their food by a process called photosynthesis (foh-toh-SIHN-thuh-sihs). Photosynthesis is the process by which plants use the energy from sunlight to change water and carbon dioxide from the air into the sugars and starches they need. Some wetland algae drift on the surface of the water, forming a kind of scum. Others attach themselves to weeds or stones. Some grow on the shells of turtles or inside plants or animals. Microscopic algae that can be found in saltwater marshes include diatoms and green flagellates (FLAJ-uh-lates). Desmids are a type of green algae found in bogs.
Fungi are plantlike organisms that cannot make their own food by means of photosynthesis; instead, they grow on decaying organic matter or live as parasites (organisms that depend upon another organism for food or other needs).
Fungi grow best in a damp environment, which makes wetlands a favorable home. Common wetland fungi include mushrooms, rusts, and puffballs.
Lichens are combinations of algae and fungi. The alga produces food for both itself and the fungi by means of photosynthesis. It is believed the fungus absorbs moisture from the air and provides shade. One of the most common wetland lichens is reindeer moss, an important food source for northern animals such as caribou.
Most green plants have several basic requirements: light, air, water, warmth, and nutrients. In a wetland, light and water are in plentiful supply. Nutrients, primarily nitrogen, phosphorus, and potassium, are obtained from the soil. Some wetland soils are lower in these nutrients and low in oxygen. As a result, many wetland plants have special tissues with air pockets that help them survive.
Trees that grow in swamps, such as the mangrove and bald cypress, have shallow roots. Due to the lack of oxygen in the soil, the roots remain near the surface. Other trees found in mild climates include willows and alders. Palms are found in warm climates.
Wetland plants are classified as submergents, floating aquatics, or emergents, according to their relationship with water.
Common green plants
Common wetland green plants include mangrove trees, insectivorous plants, reeds, rushes, and sedges.
Trees that live in wetlands must tolerate having their roots wet for a long period of time. One of the best examples of this is the mangrove tree, which grows in tropical and subtropical saltwater swamps. Mangroves have done so well adapting to wetland conditions that there are more than 34,000,000 acres (14,000,000 hectares) of them in the world. One of the largest mangrove forests is the Sundarban Forest in Bangladesh. Mangroves can also be found in southern Florida and other tropical and subtropical areas.
The Hat Thrower
An unusual fungus called a hat thrower grows on dung (animal waste) deposited in wetlands. The fungus forms a tiny black bulb that looks like a hat. The hat explodes under pressure and pieces get thrown outward from the fungus and attach to other plants. When an animal eats those plants, the hat thrower passes through its digestive system. When the animal defecates, a new fungus grows on the pile of dung.
Attack of the Killer Plant
Insectivorous (insect-eating) plants, such as the sundew, the pitcher plant, and the Venus flytrap, need nitrogen to survive. These plants live in bog areas where the soil is acidic and nitrogen and phosphorus are not readily available. In order to obtain the proper nutrition, they trap insects, dissolve them, and absorb their nutrients, which include these essential nutrients.
The Venus flytrap, for example, has toothed “jaws” at the end of its leaves. These jaws spring shut when an insect in search of nectar touches the sensitive hairs inside. The plant eats the insect by dissolving it with digestive juices and absorbing it through its leaves. After the insect has been digested, the plant opens its jaws again and waits for the next victim.
Venus flytraps are found in the marshy coasts of North and South Carolina. These plants grow only under certain conditions and are popular houseplants. As a result, they sometimes have been overharvested.
Some non-tropical mangroves have special membranes that reduce the entry of salt into their systems. Mangroves get some of their oxygen from pores in their roots, the largest portions of which are above ground, and from small gaps in their bark.
Mangrove flowers are pollinated by the wind, insects, birds, or bats. The seedlings begin to grow while they are still attached to the parent tree. Seedlings germinate (grow) within the fruit that contains them. The root, or roots, of the maturing seedling then break through the outer wall of the fruit. When the seedling reaches a mature enough stage, it is released from the parent plant, floats on the water, and then settles in mud, where it establishes roots and begins to grow.
Two common peatland plants eat insects. The sundew eats ants by catching them in a sticky liquid on its leaves. It then releases chemicals that break down the ant’s body so the plant can absorb the nutrients. The pitcher plant gets its name from the shape of its leaf, which looks like a pitcher. If an insect crawls down the leaf it cannot crawl back up because the leaves have downward pointing hairs and are too slippery. It is then digested by chemicals in the plant.
A reed is a type of grass with tall, feathery flowers, with round, hollow stems, and long, flat, narrow straplike leaves. Rushes and sedges are grasslike, but they are not true grasses. Rushes have round, solid stems and narrow, rigid leaves. Sedges have solid, triangular stems.
Reed mace and common reeds play a key role in wetland succession. They reproduce widely through their rhizomes (underground stems). As the plants spread out, they push aside other plants and quickly choke up a pond, slowing the water’s movement and trapping dead plant matter. As this matter accumulates, the pond fills up and becomes a marsh.
Climate and precipitation effect the length of the growing season in a wetland. Warmer temperatures and moisture usually signify the beginning of growth. In regions that are colder or receive little rainfall, the growing season is short. Growing conditions are affected by the amount of moisture in the soil, which ranges from saturated to dry. Although many wetland plants die during dry periods, their seeds remain in the soil all winter and sprout in the spring.
Green wetland plants reproduce by several methods. One is pollination, in which the pollen from a flowering plant’s male reproductive part, called the stamen, is carried by wind or insects to the flowering plant’s female reproductive part, called the pistil. Water lilies, for example, are closed in the morning and evening, but open during midday when the weather is warmer and insects are more active. It is usually at this time that the insects pick up the pollen and transfer it from the stamen to the pistil, allowing pollination to occur.
Some wetland plants send out rhizomes, which are stems that spread out under water or soil and form new plants. Reed mace and common reeds are examples.
One-third of the endangered plants in North America are dependent upon wetlands for their survival. As of January 2008, there were 1,046 endangered and 305 threatened plants in the United States protected under the U.S. Endangered Species Act.
Changes in the habitat, such as succession, pollution, and new weather patterns, endanger wetland plants. They are also endangered by people who collect them. Rare species of orchids are an example, as is the Venus flytrap, which has become a popular houseplant and has been overharvested. Peat moss is overharvested because it is popular as fuel, packaging material, and in gardens.
Wetlands have been called “biological supermarkets.” Besides animals that live there permanently, many nonwetland animals, such as opossums, raccoons, and skunks, visit for food and water. Wetlands provide shelter for mammals such as minks, moose, and muskrats. Wetland conditions make it necessary for the animals that live there permanently to adapt in special ways.
Microorganisms cannot be seen by the human eye. Those found in wetlands include protozoa and bacteria. Protozoa are single-celled animal-like protists that feed on bacteria and other microorganisms. Other protozoa are parasites that live on aquatic plants, on damp ground, or inside animals or plants. Protozoa are not capable of
The Persistent Marsh
For more than 2,000 years popes, emperors, and government officials tried to drain the Pontine Marshes where malaria-carrying mosquitoes like to live. Located in south-central Italy, the marshes are bordered by the Tyrrhenian Sea, the Lepini Mountains, and the Alban Hills.
All attempts to completely drain the marshes failed. The area survived and about 300 square miles (777 square kilometers) of the original marsh is now a national park with native vegetation intact. With the help of water from the marsh, the area is now one of the most agriculturally productive in Italy. Crops grown in the area include sugar beets, fruits, grains, and vegetables. Livestock is also raised here.
photosynthesis. Bacteria are also single-celled; most cannot make their own food and must obtain it from the environment. Blue-green bacteria are plantlike, photosynthetic algae that can make their own food.
Some protozoa cause malaria, a disease characterized by chills, fever, and sweating. Mosquitoes carry malaria and spread the disease to humans. Malaria is found in temperate, subtropical, and tropical regions. Spread of the disease has been greatly reduced due to the use of pesticides to kill mosquitoes, but it remains a problem in parts of Africa and southeastern Asia.
Invertebrates are animals without a backbone. They range from simple sponges to complex animals like insects, snails, and crabs.
Thousands of species of insects have adapted to life in wetlands. Some spend their entire lives in the water. Others live in the water while young, but leave it when they become adults. Still other insects have gills, just like fish, which enable them to obtain oxygen from the water; and some breathe air. For example, the diving beetle traps air in the hairs on its body or under its wings, which helps it to float. Water spiders create bubbles of air under the water in which they feed and lay eggs. The water spider even hibernates under water. When the weather gets cold, it constructs an air bubble in deep water and remains there until spring.
Some invertebrates, such as crabs, survive in wetlands by creating watertight holes in the mud or sand and hide there during high tide. Other species, like the African mangrove snail, feed in the mud and sand when the tide is low. When the tide comes in the snail climbs the mangrove trees to keep from drowning.
Perhaps the most well-known and unpopular wetland invertebrate is the mosquito. Mosquitoes breed in shallow wetland waters. In their larval form, they have tubes in their abdomens that stick out of the water, allowing them to breathe. Larvae are often eaten by frogs, fish, and aquatic insects. Those that survive face being eaten by bats, sprayed with pesticides, and swatted by humans. In spite of these hazardous conditions, mosquitoes in large numbers are responsible for diseases in both humans and animals.
The Marsh Treader
The marsh treader is an insect that can be found walking very slowly across the surface of marsh water. It has a long, skinny body about 0.3 inches (8 millimeters) in length. Its legs are as fine as threads and its body is covered with velvety hairs. As it moves across the water, it searches for food. Mosquito larvae are its favorite meal.
Insects may feed underwater as well as on the surface. The milkweed beetle feeds on insects found on wetland plants, while the diving beetle’s diet includes tadpoles and small fish. The dragonfly larva eats tiny floating organisms and water fleas. The larva of a certain species of caddisfly weaves a silk net under the water in which to catch floating algae.
Some snails are plant feeders, while others eat the eggs and larvae of other invertebrates, or even decaying matter. Crabs are often omnivorous, meaning they eat both plants and animals.
Most invertebrates are insects, which have a four-part life cycle. The first stage is the egg. The second stage is the larva, which may be divided into several steps as the insect increases in size, between which there is a shedding of the outer casing or skin. The third stage is the pupal stage, during which the insect lives in yet another protective casing. Finally, the adult emerges. Some wetland dragonflies lay their eggs in the tissues of submerged plants. The insects remain in the water as larvae. As they mature, they move to dry land.
More than 190 species of amphibians are found in wet-lands. Amphibians are vertebrates, which means they have a backbone. There are two kinds of amphibians, those with tails, like salamanders and newts, and those without tails, like toads and frogs.
Amphibians live at least part of their lives in water and are found in primarily freshwater environments. Most are found in warm, moist regions and in a few temperate zones. Because amphibians breathe through their skin, they must remain close to water so they can stay moist. Only moist skin can absorb oxygen. If they are dry for too long they will die. Their lower layer of skin, called the dermis, helps them to stay moist by producing mucous, a thick fluid that moistens and protects the body.
Amphibians are cold-blooded animals, which means their body temperature is about the same temperature as their environment. They need warmth and energy from the sun in order to be active. As temperatures grow cooler, they slow down and seek shelter. In cold or temperate
The Salamander that Never Grows Up
The axolotl, a type of salamander found in freshwater wetlands in Mexico and the western United States, spends its entire life as a tadpole. It can reach a size of 10 inches (25 centimeters) and is able to reproduce, but it never matures, so it never leaves the water. Scientists have determined that the diet of these salamanders is lacking the chemical iodine, which is in short supply in many parts of the world. This shortage is the reason why iodized table salt is used in most homes. Iodine has been added as an essential nutrient.
regions, some amphibians hibernate (become inactive) during the winter, hiding in mud or trees. When the weather gets too hot, they go through another period of inactivity called estivation.
The most common wetland amphibians are salamanders, frogs, and toads. Frogs and toads are found all over the world, at all altitudes, and in both fresh and salt water.
A frog spends half its life in the water and half out of it. Frogs can lay up to 3,000 eggs, which float beneath the water’s surface. The eggs hatch into tadpoles (larvae), which swim and breathe through gills, like those on a fish. The larvae feed on small plants and animals in the water. As they mature, legs and lungs develop, which they will need on land.
Adult frogs feed mainly on insects, especially mosquitoes, but bullfrogs have been known to eat birds and snakes. In the food web they, in turn, become meals for herons, raccoons, and other wetland animals.
Frogs are considered bio-indicators. This means that when many frogs are sick their entire environment may be in trouble. If they disappear from a habitat or if they do not sing, the area may be polluted and its resources may be dwindling. Frogs are totally absent from some wet-lands in the United States, indicating their environment was no longer a healthy place for them to live.
In their larval form, amphibians are usually herbivorous (plant-eating). Adult amphibians are usually carnivorous (meat-eating), feeding on insects, slugs, and worms. Salamanders that live in the water suck prey into their mouths. Those that live on land have long, sticky tongues that capture food.
Most frogs and toads lay many tiny eggs. Some are held together in a jellylike substance. As the female lays her eggs in the water, the male releases sperm, which is carried to the eggs by the water. Most salamanders and newts lay eggs that have been fertilized internally (within the female).
Reptiles are cold-blooded vertebrates that depend on the environment for warmth. Thousands of species of reptiles live in the temperate and tropical wetlands of the world. They include snakes, lizards, turtles, and crocodiles. Reptiles are more active when the weather and water temperature become warmer. Unlike amphibians, reptiles have skin that is waterproof, so they do not dry out. This allows them more freedom to move away from the wet areas.
Because they are so sensitive to their environment, reptiles often go through a period of hibernation in cold weather. Turtles bury themselves in the wetland mud. They barely breathe, and their energy comes from stored body fat. When the weather warms in spring, they come out of hibernation and become active. At the other extreme, when the weather becomes very hot and dry, some reptiles go through estivation, another inactive period.
Two well-known and dangerous wetland reptiles are the crocodile and the cottonmouth snake.
The Web of Life: Keystone Species
Species interact with one another in many ways. Those that play an important role in the survival of others are called keystone species. In the wetlands, a keystone species is the alligator, which lives in southern marshes such as the Florida Everglades.
Wetlands often dry up if rainfall is low. Alligators then dig holes with their powerful tails and bodies. Water collects in these holes and helps alligators, as well as birds, fish, frogs, turtles, and other marsh animals, survive during dry periods.
Crocodiles are found in warmer parts of North and South America, Africa, Australia, and Southeast Asia. They have inhabited Earth for more than 170,000,000 years. Their long survival may be due in part to the fact that they will eat almost anything or anyone. Crocodiles are responsible for killing at least ten humans every day in Africa, and a large crocodile will attack a 4,000-pound (1,816-kilogram) adult rhinoceros if given the chance. A crocodile’s teeth are rounded and made for holding, not cutting, and it first tries to swallow its prey whole. If the prey is too large, the crocodile pulls it underwater and stashes it where it can decay. When the meat is soft, the crocodile rips off a piece at a time.
The largest living crocodile officially recorded was 20.3 feet (6.2 meters) long. A crocodile continues to grow throughout its life, reaching average ages of 60-70 years; the oldest known crocodile was 115 years old. Their speed out of the water over short distances may be more than 35 miles (56 kilometers) per hour. By contrast, a very fast human may run 25 miles (40 kilometers) per hour over the same distance.
The cottonmouth snake inhabits marshes and swamps in the south and southeastern United States. A thick-bodied snake, it spends most of its life in or near water. It is active at night, when it preys on amphibians, fish, snakes, and birds. Its venom is extremely poisonous.
Some wetland reptiles, such as the dice snake, are carnivores that eat frogs, small fish, and crayfish. The pond turtle, which inhabits tropical swamps, is an omnivore. When it is young it feeds on insects, crustaceans, mollusks, and tadpoles. As an adult, it eats primarily wetland plants.
The eggs of lizards, alligators, and turtles are either hard or rubbery and do not dry out easily. Most are buried in the warm ground, which helps them hatch. In a few species of lizards and snakes the young develop inside the female’s body until birth.
The dice snake lays it eggs on land, close to the water. Crocodiles and alligators keep eggs in warm nests, which can be simple holes in the ground or constructions above the ground made from leaves and branches.
Like amphibians and reptiles, fish are cold-blooded vertebrates. They use fins for swimming and gills for breathing. Two-thirds of all fish used for human food depend on wetlands during some part of their lives. Most commercial game fish breed and raise their young in marshes and estuaries. When the wetlands are not healthy, the fish die, and the commercial and recreational fishing industries suffer.
Fish that commonly rely on coastal wetlands are striped bass, sea trout, African lungfish, mudskippers, and flounder. Brackish marshes, which contain both salt and fresh water, support sole, sardines, and common mackerel.
The African lungfish, which lives in pools surrounded by swampland, has adapted to the wet/dry cycle of wetlands. When there is plenty of water, the fish breathes through its gills. In the dry season, when the water disappears, the fish burrows into the mud and seals itself into a moist cocoon, breathing through special pouches on its underside. It can remain inactive in its cocoon for months or even years.
Also well adapted to life in the wetland is the mud-skipper, found in coastal areas of Bangladesh. This fish usually lives out of the water on exposed mud at low tides. Mudskippers breathe air through membranes at the back of their throats. Enlarged gill chambers hold a lot of water to help them remain on land for long periods. They keep water in their mouths, which they swish over their eyes and skin to help them stay wet. They feed on crabs that are easily caught during low tide.
Some fish eat plants while others depend upon insects, worms, crustaceans, or smaller fish. Some fish may simply grab an insect from the surface of the water or use a more elaborate scheme. The archerfish, for example, has grooves in the top of its mouth that lets it spit water at its prey. The force of the spit knocks the insect off its perch and into the water, where it is quickly eaten. Archerfish are found in the swamps of southeast Asia.
Fish that breed in wetlands include flounder, sea trout, striped bass, and carp. Some European carp live in rivers and move to the floodplains during spawning (breeding) season. Others live in the ocean and spawn in mudflats, marshes, or mangrove swamps.
Many different species of birds live in or near wetlands. These include many varieties of wading birds, waterfowl, shore birds, and perching birds. One of the special adaptations of birds to wetlands is their bill. Some bills, like those of the egret, are shaped like daggers for
stabbing prey such as frogs and fish. Other bills, like those of the spoonbill, are designed to root through mud in search of food.
Wetlands provide a variety of hiding places where birds can build nests and protect their young. Dense underbrush or hollows in the ground are good hiding places, especially when nests are made from reeds, flowers, and grasses, which help them blend into their surroundings. Wood ducks build their nests in hollow cavities in trees lining the wetland shores.
Birds found in wetland environments can be grouped as wading birds, shorebirds, waterfowl, and perching birds.
Wading birds, such as herons and egrets, have long legs for wading through the shallow water. They have wide feet, long necks, and long bills that are used for nabbing fish, snakes, and other food. Herons and egrets are the most common in freshwater marshes of North America. The great blue heron stands 4 feet (1.2 meters) tall. This is the tallest recorded wading bird in North America.
Shorebirds feed or nest along the banks of wetlands and prefer shallow water. Their feet are adapted for moving in water, and some have long, widely spread toes to prevent them from sinking in the mud.
The bills of shorebirds are designed to help them find food. The ruddy turnstone, for example, has a short, flattened, upturned bill, which helps it sift through mud or overturn pebbles and shells. A favorite food of the oystercatcher is the mussel. Each young oystercatcher learns from its parents a technique for opening the mussel shells to get at the meat. Some birds hammer a hole in the shell with their bills, and others prop the shells at an angle so they can pry them open. It may take the birds several years of practice to get the technique just right.
There are more than 200 species of shorebirds dependent on wetland habitats. These include sandpipers, which are found in marshes, wet woodlands, and on inland ponds, lakes, and rivers.
Waterfowl are birds that spend most of the time on water, such as ducks, geese, and swans. Their legs are closer to the rear of their bodies than those of most birds, which is good for swimming, but awkward for walking. Their bills are designed for grabbing wetland vegetation, such as sedges and grasses, on which they feed.
Perching birds can be found living along wetland areas where food and shelter are readily available. They are land birds, with feet designed for perching. Their feet usually have three long toes in the front and one in the back. The barred owl is commonly found in swamps, while red-winged blackbirds live in cattail marshes. Bogs are home to golden plovers, skylarks, and meadow pipits.
Plants and small animals in wetlands provide a ready food source for birds. Some birds feed on vegetation, while others are predatory. The marsh harrier, for example, feeds on mussels, small fish, or insects and their larvae. Herons and egrets feed on fish, frogs, and snakes.
All birds reproduce by laying eggs. Most male birds are brightly colored and sing to attract the attention of females. After mating, female birds lay their eggs in nests made out of many different materials. These nests may be found in a variety of places throughout the wetland area. Different species of birds lay varying numbers of eggs. The tufted duck, for example, lays six to fourteen eggs that hatch in less than a month. The ducklings begin to swim within days.
Mammals are warm-blooded vertebrates that are covered with at least some hair and bear live young nursed with milk. Aquatic mammals, such as muskrats, have waterproof fur that helps them blend into their surroundings and webbed toes for better swimming. Some of these mammals live permanently in wetlands and others, such as raccoons, visit for food, water, and shelter during part of their lives.
The Duck that Saved Wetlands
The Federal Duck Stamp Program began in 1934 when the U.S. Congress passed the Migratory Bird Hunting Stamp Act. The act required waterfowl hunters to purchase and carry Federal Duck Stamps that are attached to a hunting license or other document. The money was used to buy or lease waterfowl habitats from their owners and designate them as restricted areas. This helped save millions of acres of wetlands.
Over the years, efforts have also included saving wetland species that were declining in numbers, such as wood ducks, canvasback ducks, and pintail ducks. The program helps endangered species that rely on wetlands for food and shelter.
Anyone can own Federal Duck Stamps. State, international, and junior stamps are available. A duck stamp provides free admission to all National Wildlife Refuges where entrance fees are charged. To learn more about the duck stamps and to see pictures of them, visit http://www.nationalwildlife.com.
American beavers are well-adapted to the wet-land environment. They have webbed feet for powerful swimming
and warm, waterproof fur. Other mammals found in wetlands include the mink, the water shrew, and the Australian platypus. The sitatunga, a type of antelope, lives near swamps in central and east Africa. It feeds on emergent wetland plants.
Although peatlands generally do not support many species of animals, red deer live in the bogs. At 5 feet (1.5 meters) tall, it is the largest land mammal found in Ireland. It can be seen rolling in the peat in order to get rid of parasites and insects.
Muskrats resemble beavers. They are heavy-bodied rodents about 12 inches (30 centimeters) long, not including the long tail. They are native to North America and common to marshes all over the country. Their hind feet are webbed for swimming and they can often be seen floating on the water’s surface. Marsh plants such as sedges, reeds, and the roots of water plants provide most of their diet.
Muskrats build dome-shaped houses in water. They pile up mud, cattails, and other plants until the mound rises above the water’s surface. Tunnels lead into the mound where one or more rooms are hollowed out above the water’s surface.
These mammals are hunted for their fur, which is brown and consists of soft underfur and a dense coat. They are also sold as food, often labeled as “marsh rabbit.”
Some aquatic mammals, like the otter, are carnivores, eating rabbits, birds, and fish. Muskrats are omnivores, eating both animals, such as mussels, and plants, such as cattails. Beavers are herbivorous and eat trees, weeds, and other plants.
Mammals give birth to live young that have developed inside the female’s body. Some mammals are helpless at birth while others are able to walk and even run immediately. Some are born with fur and with their eyes and ears open. Others, like the muskrat, are born hairless and blind. After about three weeks young muskrats are able to see and swim.
Over half of the endangered or threatened fish and other wildlife in the United States (about 240 species altogether) rely partly on wetlands for food, water, shelter, or a place to reproduce. Over one-third of these live only in wetlands.
In North America, endangered species include the whooping crane and the manatee. The whooping crane lives in coastal swamps and feeds on roots and small reptiles. It has been threatened by hunting, pollution, and dredging (dragging a net along the bottom of a body of water to gather shellfish or plant specimens).
The manatee is a slow-moving, seal-like animal. Manatees live in shallow coastal wetlands in the Caribbean, the Amazon, and Africa. They have become endangered because of overhunting, being caught and strangled in fishing nets, or being killed by boat propellers. Pollution has disrupted their habitats and food sources.
In Ireland, the Greenland white-fronted goose, which relies on bogs for feeding and breeding, is endangered because many bogs have disappeared.
The Swimming Rabbit
The North American swamp rabbit has broad, flat feet so that it can move easily over wet, marshy soil. It can swim, and often escapes danger by staying submerged with only the tip of its nose exposed to the air in order to breathe.
After 13000 BC, wetlands played an important role in early civilizations. For prehistoric communities throughout the world they provided food, water, and materials for clothing, shelter, and tools. Wetlands are able to reveal many of these ancient civilizations’ secrets to scientists. Bodies of animals and humans, and artifacts (objects made by humans, including tools, weapons, jars, and clothing) have been well preserved in some wetlands and give information about how ancient people lived. Evidence of these ancient communities has been found in bogs. Conditions in bogs are excellent for preserving artifacts and bodies.
Impact of wetlands on human life
Wetlands have had an affect on the supply of food and water, on shelter, and on other resources.
The Bog People
Organic materials in peat bogs absorb and hold large amounts of water like a sponge. Bog soils are extremely acidic and have little oxygen. Because of these factors, decomposition takes place very slowly. Entire trees, animals, and even human bodies have been preserved for centuries.
The remains of more than 2,000 humans have been found in bogs, primarily in northwestern Europe. The bodies are in various stages of preservation, from skeletons to those with flesh intact. Sometimes only body parts such as heads or limbs are found. Often the skin has darkened and the hair has turned red from peat acids. The bodies found in Europe range in age from about 1,500 to 3,000 years old. The body of a woman, known as the Koelbjerg Woman, was found in Denmark and is believed to be 10,000 years old.
Many of these people appear to have died violent deaths. Perhaps they were killed as a punishment for a crime or were the victims of human sacrifice. Their deaths may have taken place at the bog because it was so isolated.
At a bog in Windover, Florida, 160 bodies have been found that are about 7,000 years old. Buried with them are food, tools, clothes, and weapons. Many of these items were made from wetland plants and from the bones of wetland animals.
Food and water
Wetlands are a source of water for drinking and crops. Areas near wetlands continue to provide food in a variety of ways for tribal cultures in Asia and Africa and for urban peoples elsewhere. Since wetlands are a habitat for much wildlife, hunting and fishing are common there.
Cattle can be raised near wetlands because water and grazing land are available. Crops such as sorghum (a cereal grain native to Africa and Asia) are commonly grown in wetland areas. Grain sorghums, such as milo, kafir, and durra, have adapted to the extremes of the wet/dry cycle of the wetland and are among the most drought-tolerant grains. Millions of people in China, India, and Africa rely on sorghum as a food staple. In the United States, sorghum is used mostly as livestock feed.
Besides sorghum, American farmers use wetland plants, such as marsh grass, reeds, and sedges, for feeding livestock. Wetlands are an excellent place to grow rice, which is a major food source for much of the world’s population.
Materials for dwellings are available from wetland sources. Roofs made from reeds are used on huts in Egypt and in stilt houses in Indonesia to keep the occupants cool and dry. A tightly woven reed roof can last for forty years. House frames are constructed from the timber of
Houses Without Walls
The Seminoles, a Native American people who once lived in the Florida Everglades, built homes with no walls. Called a chikee, the home was built on a platform, had a log framework, and a thatched reed roof. The absence of walls provided ventilation in the warm climate.
mangrove, and palm trees. Wetland sediments, such as clay and mud, may be used to produce bricks that are used for walls.
Wetlands provide other resources that humans rely on besides building materials. For example, dried peat is used in homes for heat and to fuel electric generators in countries such as Ireland, where coal is scarce. Peat is a source of protein for livestock feed, and chemically processed peat is used as a base for polishes and waxes. In horticulture, peat moss is used as ground cover, a soil conditioner, and a growing medium. Peat is also found in medicinal baths and cosmetics.
There are at least 120 distinct medicinal substances derived (made) from wetland plants. Wetland soils are sources of gravel and phosphate. Phosphate is used as a raw material for making fertilizers, chemicals, and other commercial products.
Wetlands prevent loss of human life and property during floods because they absorb and store water. The riparian wetlands along the Mississippi River once stored sixty days of floodwater. Since most of these wetlands have been filled or drained, they now only store twelve days of floodwater.
Impact of humans on wetlands
The important role of the wetland for plant and animal communities and for the environment in general has not always been understood. For more than 2,000 years, people in different countries have been draining wetlands to get rid of mosquitoes and disease, to increase land for farming, and to make room for development. By 1990, more than half of the wetlands in the United States were destroyed.
As the value of wetlands becomes more recognized, government agencies, such as the U.S. Department of the Interior and U.S. Fish and Wildlife Service, as well as environmental groups, are working to preserve existing wetlands and to create new ones. In 1989, U.S. president George Bush, asked that the United States work toward the goal of no net loss of wetlands. This means that if a natural wetland is destroyed by development, an artificial one must be built to replace it. As of July 1998, there were 97,000,000 acres (39,000,000 hectares) of artificial wetlands in the United States. In 1998, the Clinton administration issued an
An Earth-Friendly Architect
Architect James Cutler of Seattle, Washington, believes that the environment should be preserved when designing and building houses. He has gone to extremes to save the landscape, including building houses on stilts and placing sidewalks over the tops of forests. Cutler designed a home for Microsoft Chairman Bill Gates, where he reestablished wetlands on the property.
initiative calling for a net gain of 100,000 acres (40,500 hectares) of wetlands per year beginning in 2005.
The Convention on Internationally Important Wetlands was signed by representatives of many nations in Ramsar, Iran, in 1971. Commonly known as the Ramsar Convention, it is an intergovernmental treaty that provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources.
Use of plants and animals
When animals and plants are overharvested they may become endangered. Overharvesting means they are used up and destroyed at a faster rate than they can reproduce. When this happens, wetland, timber, fuel, medicines, and sources of food for humans and animals are all lost.
Use of natural resources
The two primary resources found in wetlands are water and peat. Wetlands often act as part of the ground-water system. When they are lost, the supply of drinking water may be affected.
It takes ten years to form less than half an inch of peat, and its overuse has caused significant peatland losses. Western European peat mining companies are rapidly using up local areas of peat and expanding their mining operations into eastern European countries. All natural peatlands in the Netherlands have been destroyed. Switzerland and Germany each have only 1,250 acres (500 hectares) of peatland remaining.
Quality of the environment
Wetlands are endangered by industrial and municipal (city) contaminants, by the accumulation of toxic chemicals, and from acid rain.
Acid rain is a type of air pollution especially dangerous to wetlands. It forms when industrial pollutants such as sulfur or nitrogen combine with moisture in the atmosphere and form sulfuric or nitric acids. These acids can be carried long distances by the wind before they fall either as dry deposits or in the form of rain or snow. Acid rain can significantly damage both plant and animal life. It is especially devastating to wetland amphibians such as salamanders, because it prevents their eggs from maturing.
Mining for minerals near a wetland can have a negative impact on the biome. Mercury, a poisonous liquid metal used in gold mining operations, often contaminates wetlands close to the mines. Mining operations also require large amounts of water, and nearby wetlands may be drained.
The world’s climate may be growing warmer because of human activity. As polar ice caps melt, there is a rise in sea level. As this happens, more salt water floods into coastal wetlands and increases the salinity not only of the wetlands, but of rivers, bays, and water supplies beneath the ground. As these habitats change, animal and plant life are affected, and some wetlands may be destroyed.
Artificial wetlands are those created by humans. Creating a wetland is very difficult; all the right conditions need to be met, including a water source and nutrient rich soil that contains a lot of water but not much oxygen. In Arizona, there are twenty-six artificial wetlands operational with twenty-four others under construction or awaiting approval.
An artificial wetland that works well and is extremely valuable worldwide is a rice paddy. A rice paddy is simply a field that is flooded for the purpose of growing rice, a food staple for about three billion people—nearly one half of the world’s population. Some are flooded naturally, by monsoon (tropical) rains or overflowing rivers. Others are flooded by irrigation (watering). Mud dams and waterwheels are built to bring in and hold the water level at approximately 4 to 6 inches (10 to 15 centimeters) while the rice grows. Ninety percent of rice paddies are in Asia, especially China and India. Some rice is also grown in Europe and the United States.
Artificial wetlands are found on the Arabian Peninsula where they are used for water storage and sewage treatment. Other human-made wet-lands have been created as winter homes for migrating waterfowl.
Adopt A Wetland
Both the federal government and individual states are working to protect wetlands. Some states sponsor “Adopt a Wetland” programs, in which groups of people agree to help support their local wetlands in a variety of ways, such as picking up litter. For information about adopting a wetland, contact the U. S. Environmental Protection Agency, Public Information Center, (202) 260-7756 or (202) 260-2080.
Marshes Clean Up Messes
A lot of contaminants seep into the environment every day from oil spills, sewage treatment plants, industrial waste, and old mines. In some areas, phytoremediation (fi-toh-rih-mee-dee-AY-shun) is being used to clean up these messes. (Phyto is a Greek word for plant and remediation means to make things right.) Phytoremediation uses plants to absorb pollutants.
One type of phytoremediation involves creating an artificial marsh containing cattails and water lilies. These wetland plants are able to absorb some water pollutants. Poplar trees can clean up water polluted with oil, and sunflowers are used to help clean up radioactive materials in the soil. Sunflowers are used near the Chernobyl nuclear power station in Pryp’yat near Kiev in the Ukraine. The power station exploded in 1986, releasing radioactive waste into the environment.
The Marsh Arabs of Iraq and the Nilotic peoples of Africa live in or near wet-lands that provide almost all of the resources they need.
Marsh Arabs of Iraq
The Mesopotamian wetland lies between the Tigris and Euphrates Rivers in southern Iraq. At almost 8,000 square miles (20,000 square kilometers), it is one of the largest wetlands in the world. The Marsh Arabs, or Ma’dan, have lived there for more than 6,000 years. The water there is clean, calm, and fairly shallow—about 8 feet (2.4 meters) deep.
The Marsh Arabs’ houses are made of reeds and built on islands that they make. To construct the islands, they create a fence from reeds and partially submerge it. Then they fill the area inside the fence with cut rushes, add layers of mud, and stamp it all down. When the pile reaches the water’s surface, they fold the top of the fence onto the pile and add more reeds to finish it. The completed island is big enough not only for the family to build a house and live on, but for their cattle as well.
Isolation from the outside world has allowed the Marsh Arabs’ way of life to remain the same for hundreds of years. Daily life consists of fishing, buffalo herding, and growing rice. Reeds are gathered every day to feed the buffalo. Transportation from house to house or to other villages is by means of small canoes called mashhufs.
Survival of the Marsh Arabs is threatened by irrigation practices, which have drawn water from their wetlands. Some of the marshes have already been drained for agricultural use and oil exploration.
Nilotic peoples live near the Nile River or in the Nile Valley in Africa. Two Nilotic tribes, the Dinka and the Nuer, live in southern Sudan. This area is a rich floodplain, and during the wet season, from July through October, the people live on high ground in permanent villages. From December through April, when the floodwater recedes, they move to the flood-plains. There, the Dinka build temporary villages along the banks of the Nile River. Their homes, made from reeds and grasses, are circular at the base and come to a point at the top, much like a teepee. Their neighboring tribe, the Nuer, lives in a similar fashion but in the marsh, savanna (grass-land), and swamp areas.
Wetland grasses and plants grow in the floodplain after the waters recede. The grasses provide food for cattle and attract wildlife, which is often hunted for food. Nilotic tribes fish, hunt, and grow some grains. The Dinka use their cattle for meat and milk, but the Nuer eat cattle only during religious ceremonies. For them, cattle represent wealth and are used for bridal dowries (gifts) and to sell. Animal hides are made into clothing and bedding, and dried cattle dung (waste) is used for fuel.
The transfer of energy from organism to organism forms a series called a food chain. All the possible feeding relationships that exist in a biome make up its food web. In the wetland, as elsewhere, the food web consists of producers, consumers, and decomposers. These three types of organisms transfer energy within the wetland environment.
At the bottom of the food chain are the producers, such as photo-synthesizing plants and algae, which use energy from the sun to produce sugars and starch from carbon dioxide and water. The shallow wetland water lets in lots of sunlight, which helps these organisms grow.
Primary producers are eaten by primary consumers such as the larval forms of frogs and toads, and larger animals such as shrimp and snails. Other primary consumers, such as small aquatic insects, shellfish, and small fish, feed on plant materials.
Primary consumers are food for predators such as larger fish, reptiles, amphibians, birds, and mammals, which are called secondary consumers. Tertiary consumers are the predators, such as owls, coyotes, and humans, that prey on both primary and secondary consumers.
The decomposers feed on dead organic matter and include fungi, bacteria, and crabs.
The Florida Everglades
The Florida Everglades, lying within the sub-tropical zone near the tropics, is one of the largest freshwater marshes in the world, stretching from Lake Okeechobee 100 miles (160 kilometers) south to Florida Bay. Within its boundaries are freshwater swamps and coastal (saltwater) mangrove swamps. In the northern portion of the Everglades is Big Cypress Swamp. This swamp covers 1,500 square miles (4,000 square kilometers) and gets its name from the many tall bald cypress trees that live there.
The Florida Everglades
Location: Southern Florida
Area: Approximately 1,506,539 acres (606,688 hectares)
Classification: Freshwater marsh, freshwater swamp, and saltwater swamp
The Everglades were formed during the last ice age, which ended about 10,000 years ago. During this period, glaciers melted and sea level was raised, which flooded the area and turned it into a wetland. Under the water and soil is a porous limestone rock formed during the last glacial period. This type of rock contains shells and skeletons of animals deposited in the sea. Hummocks (rounded hills or ridges) have formed in some areas, and hardwood trees can grow there. Otherwise, the terrain is flat.
The subtropical climate of the Everglades is mild, with temperatures ranging from 73° to 95°F (25° to 35°C) in the summer. Winters are mild, with an average high of 77°F (25°C) and a low of 53°F (12°C). The rains occur from June to October, with an annual accumulation of about 55 inches (140 centimeters). The region is often hit by severe tropical storms.
The grassy waters of the Everglades are actually very shallow, ranging from about 6 inches (15 centimeters) to 3 feet (94 centimeters) deep. They cover about 4,000 square miles (10,300 square kilometers). Water comes from rainfall and overflows from Lake Okeechobee.
Much of the Everglades are covered with sawgrass, a type of sedge. Tropical plants, such as ferns, orchids, and mosses, grow in freshwater areas. Saltwater aquatic plants include lilies and bladderworts. Cypresses, palms, live oaks, and pines grow on the hummocks.
Among the invertebrates, the Liguus tree snail can be found living on the hummocks, and Everglades reptiles include turtles, king snakes, water moccasins, and rattlesnakes. Alligators live in freshwater areas while American crocodiles live saltwater swamps.
Tourists are attracted by the bird life in the Everglades. Herons, egrets, spoonbills, ibises, eagles, and kites are a few of the birds in the area. The Everglades kite, a tropical bird of prey, has been named after the region. Mammals include white tailed deer, cougars, bobcats, black bears, and otters.
Many attempts have been made to drain the Everglades so the land could be used for farming and development. Drainage projects began in the early 1900s. Consequently, about 50 percent of the wetlands have been altered. Due to agriculture and development, only about 27 percent of the original area has been preserved as the Everglades National Park.
Draining the area has caused a loss of animal and plant life. Endangered species include the manatee, the round-tailed muskrat, and the mangrove fox squirrel. Early in the twentieth century, plume hunters nearly wiped out egrets and spoonbills for their feathers, which were used extensively as decorations on women’s hats.
The introduction of non-native species of plants is also a threat. The Australian melaleuca tree and the Brazilian pepper plant have spread throughout the area, using up water supplies and choking native plants.
Agriculture is the leading economic activity in the region. In the area south of Lake Okeechobee, farmers raise sugarcane, fruit, and vegetables, which are shipped north. Sport fishing, boating, hunting, and camping are popular in the area.
The Seminole Indians, who were driven out of the Okefenokee Swamp in northern Florida by American troops during the nineteenth century, found a safe home in the Everglades. They planted corn and vegetables and gathered roots and nuts. Fishing and hunting were also sources of food. Throughout the twentieth century, the number of Seminoles living in the area has decreased. Another tribe, the Miccosukee, still live in reservations near the center of the Everglades.
A growing concern for the environment has encouraged protection of the Everglades and its ecosystem. It became a national park in 1947 and is the third largest and the wettest national park in the United States. The park includes 10,000 islands off the Florida coast along the Gulf of Mexico, and more than one million people visit annually.
The word “Okefenokee” (oh-kee-fen-OH-kee) is taken from a Timucuan Indian word and means “trembling earth.” This refers to the small bushes and water weeds that float on the swamp’s open water and move when the water is disturbed. The swamp, which is 25 miles (40 kilometers) wide and 38 miles (61 kilometers) long, is one of the oldest and most well-preserved freshwater wetlands in the United States.
Location: Southeastern Georgia and northern Florida
Area: 438,000 acres (177,000 hectares)
Classification: Freshwater swamp, bog, marsh
The Okefenokee lies about 50 miles (80 kilometers) inland from the coast of the Atlantic Ocean in Georgia, but a sandy ridge prevents the swamp from draining directly into the ocean. The Suwannee River is the principal outlet of the swamp providing 85 percent drainage into the Gulf of Mexico.
The Okefenokee was formed almost 250,000 years ago when the waters of the Atlantic Ocean covered the area. When the ocean receded, some salt water was trapped in depressions in the ground. Over thousands of years, plants grew and filled the wetland. As they decayed, they turned into peat, which now forms the swamp floor. The peat is as deep as 15 feet (4.6 meters) in places.
Freshwater lakes, wet savannas (grasslands with scattered trees), cypress woods, hummocks, open grassy spaces, peat bog islands, and thick brush are also found in the Okefenokee. Many channels form a maze through the area. About 60 inches (152 centimeters) of rain falls annually.
The Okefenokee supports 621 species of plants, including rare orchids and lilies. The insectivorous pitcher plant, maiden cane, floating hearts, and golden club all add color. Freshwater regions support sphagnum moss, ferns, and rushes. Tupelo trees and giant bald cypress trees covered with Spanish moss add an eerie quality.
Insects, such as the mosquito and the yellow fly, are abundant, and 37 species of amphibians make the Okefenokee their home. At least 64 species of reptiles live here, including 5 kinds of poisonous snakes, and more than 10,000 alligators. Considered “kings” of the swamp, alligators are a major tourist attraction. About 40 species of fish live in the swamp, including bluegill, warmouth, golden shiners, and pumpkinseed sunfish. These fish have adapted to life in the acidic water. They are often dark with yellow undersides and they can see in low light.
The Okefenokee is home to 233 species of birds including the white ibis, the sandhill crane, the wood duck, the great blue heron, and the barred owl.
Bears, bobcats, deer, foxes, and raccoons live in the forested areas. Approximately thirty species of mammals can be found in the swamp, including the black bear.
The area surrounding the swamp was settled by Europeans in the late 1700s. The Seminoles once lived in the interior, but they were driven out by American troops in 1838.
During the 1800s, developers tried to drain the swamp by building a canal, but found the project larger than anticipated. The project was abandoned in 1893. After the turn of the century, logging companies built railroad tracks through the swamp; as a result 400,000,000 feet (120,000,000 meters) of timber, mostly cypress were cut down. In 1937, U.S. president Franklin Roosevelt (1882–1945) protected about 629 square miles (1,630 square kilometers) of the Okefenokee by designating it the Okefenokee National Wildlife Refuge. Despite these actions, the swamp continues to be threatened by developers, including those who want to mine titanium ore on its eastern rim. Due to public and government opposition, the mining project was terminated.
Fire is a natural part of the swamp’s ecosystem, which can occur as infrequently as every 30-50 years. The two most recent fires occurred in May 2002 and May 2007.
The Okefenokee offers walking trails for tourists and 120 miles (193 kilometers) of water trails that can be explored by canoe.
The Mekong Delta
The Mekong Delta extends from Phnom Penh, the capital of Kampuchea province in Vietnam, to the coastline bordering the South China Sea. The Mekong River, the longest in Southeast Asia, divides at Phnom Penh into two branches. As the branches pass through the delta they form nine channels. The name Mekong means “Nine Dragons” and refers to these channels.
The Mekong Delta
Area: 12,237 acres (49,712 square kilometers)
Classification: Freshwater swamp and saltwater swamp
The delta, which supports 15,000,000 Vietnamese, forms a 13,600,000 acre (5,500,000 hectares) triangular area including floodplain, freshwater, and saltwater swamps. Mangrove and melaleuca forests cover the remaining area.
Most of the delta is less than 16 feet (5 meters) above sea level. From May to October the area experiences heavy rains, ranging from 59 to 92 inches (150 to 235 centimeters). The average temperature is about 79°F (26°C), and the climate is very humid.
The Mekong Delta supports 35 species of reptiles, including crocodiles and the endangered river terrapin (a type of turtle), and 260 species of fish, many of which are sold commercially. Herons, egrets, ibises, and storks nest in the delta’s forested areas. Mammals include otters and fishing cats.
The delta is rich in agricultural produce, fish, and waterfowl. At one time it yielded 26 tons (23.5 metric tons) of fish per square mile. About half of the delta is devoted to rice paddies, which yield about 6,500,000 tons (5,900,000 metric tons) of rice each year.
During the Vietnam War (1959–1975), the Mekong Delta was seriously damaged when Agent Orange and other defoliants (chemicals that cause leaves to fall off plants and trees) destroyed over 50 percent of the mangrove forests. The object was to remove any hiding places used by the enemy, but Agent Orange also caused skin diseases, cancer, and birth defects. One-fifth of the country’s farmland was destroyed by direct bombing and machines used to clear land. The melaleuca forests were burned with Napalm, another chemical weapon, and almost destroyed. These chemicals made much of the soil infertile.
Of the 386 bird species supported by the Mekong Delta, 92 are waterfowl. The eastern Sarus crane, an endangered bird, disappeared during the war but has since returned. The giant ibis, the white-shouldered ibis, and the white-winged wood duck, all endangered, have not been seen here since 1980.
Hydroelectric dams, built for generating electricity, have a negative affect on the ecosystem. The dams reduce flooding, which decreases the freshwater flow to wetlands. Spawning areas for fish are declining and mangrove forests are being converted to artificial ponds by the farmed shrimp industry.
The Great Dismal Swamp
The Great Dismal Swamp is a freshwater wetland located in southeast Virginia and northeast North Carolina. Its soil contains few minerals and nutrients. Drainage is poor and the soil is saturated and acidic. In this environment, decomposition is slow and peat accumulates over time.
The Great Dismal Swamp
Location: North Carolina and Virginia
Area: 106,716 acres (42,686 hectares)
Classification: Peat bog and freshwater swamp
The fungus called armillaria, which grows on rotten wood in the swamp, gives off a luminescence (glow) called foxfire. Broad-leaved shrubs such as hollies and bayberries are found here. Bald cypress trees survive well in saturated soil and populate the area; some are as old as 1,500 years. Other native trees include the black gum, the juniper, and the white ash.
Seventy-three species of butterflies and more than 97 species of perching birds, including warblers, woodpeckers, and wood ducks, live in this area. Black bears, bobcats, minks, and otters also live in the region.
Many famous Americans were in some way associated with the Great Dismal Swamp. In 1763, U.S. president George Washington (1732–1799) set up a company to drain the swamp for agricultural purposes and to use its lumber. One hundred-forty-five miles of road were constructed to support the logging activities that continued until 1976. The American statesman, Patrick Henry (1736–1799), who participated in the American Revolution, owned land there. The swamp was used by American author Harriet Beecher Stowe (1811–1892) as the setting for her 1856 novel, Dred: A Tale of the Great Dismal Swamp. The forests of the swamp provided refuge to runaway slaves. In 2003, the Great Dismal Swamp became the first National Wildlife Refuge to be officially designated as a link in the Underground Railroad Network to Freedom.
Kakadu National Park
Kakadu National Park is the largest wetland in Australia and is marked by a great diversity in species and habitats. The area includes freshwater wetlands, mangrove swamps, and billabongs. The term billabong comes from an Australian Aboriginal (native) word meaning “dead river,” and describes standing, often stagnant, water near river channels. Billabongs are usually found only in the parts of Australia where the climate is hot and dry and interrupted by occasional flooding.
Kakadu National Park
Location: East of Darwin in the Northern Territory of Australia
Area: 7,700 square miles (20,000 square kilometers)
Classification: Freshwater wetlands, mangrove swamps
Average temperatures are high all year and range from 91°F (33°C) in July to 108°F (42°C) in October. Rivers flooded by January and February rains feed the freshwater areas. The coastal wetlands are fed by tides.
Kakadu includes many acres of forests, sedges, and grasslands. In April and May, when the dry season begins, bush fires destroy old growth and encourage new plant life.
When the thousands of acres of grassland flood during the wet season, plant and animal life abounds. In all, there are more than 200 species of plants, including 22 species of mangrove trees. Water lilies, woolybutt (Eucalyptus miniata), and spear grass, which grows to more than 6 feet (1.8 meters) tall, can all be found. Paperbark trees dominate freshwater swamp areas.
Numerous turtles and both freshwater and saltwater crocodiles live in the shallows. Barramundi fish travel between the waterholes and estuaries, depending on the season. Goannas, a type of monitor lizard, live here.
Millions of water birds live in the park. These include whistling ducks, magpie geese, radjal shelducks, and grey teals. Shorebirds migrate from as far away as the Arctic to winter in the mild climate of Kakadu.
The Australian native people, called Aborigines, once used the park’s wetland plants and animals as a source of food. Aborigines recognized six seasons in the Kakadu region instead of the traditional wet and dry seasons. Disposal of waste from uranium mines on the edge of Kakadu is threatening the area. Other dangers include tourism and the introduction of non-native plants and animals. Para grass, an exotic grass being tested as cattle feed, is currently choking Kakadu’s wetlands. The big-headed ant, a native of Africa, forms huge colonies that wipe out many native ants and other small creatures.
The Kushiro (koo-SHEE-roh) Marsh is one of the largest and most important natural wetlands in Japan. It is located in a floodplain and contains small freshwater lakes, reed beds, sedge marshes, and peat bogs. About 68,400 acres (27,700 hectares) have been designated as a national wildlife protection area and a national monument.
Location: The island of Eastern Hokkaido, Japan, along the Kushiro and Akan Rivers
Area: 112 square miles (290 square kilometers)
Classification: Marsh and peat bog
Annual rainfall averages about 44 inches (112 centimeters). The climate is on the cold side with winter temperatures sometimes falling below -4°F (-20°C). The average annual temperature is 42°F (5.6°C) encouraging slow decomposition and peat formation. Spring and summer are also cool.
The floodplain areas support reeds and sedges. The shallow marshes are extremely important for the endangered red-crowned crane, because they provide a place for the birds to breed and winter. More than 100 species of birds use the area, including geese, ducks, and swans. Mammals found in the marsh include the raccoon dog and the red fox. The marsh has an exceptional abundance of dragonflies.
The Llanos (YAH-nos), a Spanish word for “plains,” is a large grassland covering parts of western Venezuela and northeastern Colombia. Within its boundaries is one of the largest wetlands in South America; a combination of rivers, lakes, marshes, swamps, forests, and ponds. It is bordered by the Andes Mountains on the north and west, the Orinoco and Apure Rivers to the east, and the Amazonian wilderness to the south.
Location: Venezuela and Colombia, South America
Area: 220,000 square miles (570,000 square kilometers)
Classification: Riparian wetland and swamp
The Llanos is a temperate area, with year-round average temperatures of 75°F (24°C). Rain falls primarily between April and November, the central plains get about 45 inches (110 centimeters) annually. Areas closer to the Andes Mountains receive about 180 inches (457 centimeters). The summer is very dry. No growth takes place during these months and frequent fires drive animals to areas that are still wet. When the rains come in the winter, the growing season begins.
Although growth is limited by the long dry period, swamp grasses and sedges are common. Carpet grass is able to grow in drier areas. Oak and palm trees are found along the edges of the rivers.
The Llanos provides a habitat for many wading birds such as herons, storks, and ibises. The capybara, the world’s largest rodent, lives in the area. It grows up to 4 feet (1.3 meters) long and weighs as much as 100 pounds (50 kilograms). Armadillos, deer, and anteaters find shelter in the forest and feed in the grasslands. The green anaconda, the largest snake in the world, makes its home in the Llanos.
The most common economic activity is cattle ranching. Since most ranchers use traditional methods, the activity has had little effect on the area.
The Okavango Delta is considered an oasis in the Kalahari Desert. As the Okavango River flows from Angola into Botswana, it becomes choked with weeds and spreads out to create one of the world’s largest inland wetlands.
Location: Northwest Botswana, Africa
Area: 6,175 square miles (16,000 square kilometers) in the dry season increasing to 8,500 square miles (22,000 square kilometers) in the wet season
Classification: Freshwater marsh and swamp
Annual temperatures range from 21° to 105°F (-6° to 41°C). Average rainfall is about 18 inches (45 centimeters). In February and March, the river overflows and refills the marshes and swamp areas, making them desirable habitats for plants and animals. Water can be as deep as 16 feet (about 5 meters).
Although rainfall can vary, parts of the delta are always wet from flooding. Water lilies and papyrus are abundant.
The delta is home to kingfishers, herons, and water birds such as ducks, geese, and ibises.
When the waters recede, grazing animals arrive. These include antelope, springbok, and lechwe. The lechwe is a semi-aquatic antelope that feeds on grasses in shallow water. It can graze while standing in water up to 20 inches (50 centimeters) deep. Its elongated hooves help it move through the soft mud on the swamp floor.
The Okavango is the only source of permanent surface water for Botswana. This creates industrial and agricultural demands, such as for diamond mining. An area about 695 square miles (1,800 square kilometers) in size has been designated as the Moremi Wildlife Reserve, one of the few protected areas in Africa.
The Pripet Marshes (also spelled Prepay or Pipit) form a very large wetland in Eastern Europe, covering the southern part of Belarus and northern Ukraine. The marshes are located in a forested basin of the Privet River, and the swamp is the largest in Europe.
Location: Southern Belarus and northern Ukraine
Area: Approximately 104,000 square miles (270,000 square kilometers)
Classification: Marsh, bog, and swamp
Formed during the last ice age, which ended about 10,000 years ago, the marshes were filled with sand and gravel left behind as the glaciers melted. The many lakes in the area are in the process of turning into bogs. Sandy lowlands can be found among a maze of rivers, and pine forests and floodplains add to the diversity of the ecosystem. About one-third of the region is forested.
The climate is cool, with winter temperatures ranging from 18° to 25°F (–8° to –4°C). Warmer temperatures are found in and around the marshes. Annual precipitation is 22 to 26 inches (55 to 65 centimeters).
Trees growing here include pine, birch, alder, oak, aspen, white spruce, and hornbeam. Hornbeam is a type of birch that has smooth, gray bark and catkins (drooping scaly flower clusters with no petals).
Many types of birds live in the marsh, including orioles, grouse, woodpeckers, owls, blue tits, and ducks. Mammals include lynxes, wolves, foxes, wild boars, Asian deer, beavers, badgers, and weasels.
Much of the land has been cleared for lumber and agricultural use over the last several hundred years. Large-scale land reclamation (draining swampland to create cropland) in the twentieth century occurred to promote the development of agricultural areas. Crops grown in the area include rye, barley, wheat, flax, potatoes, and vegetables. Grasses used as cattle feed are also grown here.
The Pine Barrens
The Pine Barrens (or Pineland) are located on the outer coastal plain of Long Island and New Jersey, including parts of the Delaware River and the Jersey Shore. Much of the area is open forest broken by marshes, swamps, and bogs. The area was formed during the last Ice Age.
The Pine Barrens
Area: Over 1,000,000 acres (400,000 hectares)
Classification: Bog, swamp, and marsh
The northwest part of the Pine Barrens experiences relatively cold winters, with average January temperatures of less than 28°F (–2°C). The southern area is milder, with average winter temperatures above freezing. Summers are hot, with averages for July ranging from about 70°F (21°C) in the northwest to more than 76°F (24°C) in the southwest. Precipitation (rain, sleet, or snow) is evenly distributed throughout the seasons, averaging between 44 and 48 inches (112 and 122 centimeters) annually.
The Pine Barrens are home to about 100 endangered species of plants. Many rare species include the glade cress, great plains ladies-tresses, grooved yellow flax, and some insectivorous plants. Other plants include wild azaleas, purple cone flowers, Indian grasses, and little bluestems. Rhododendrons, honeysuckles, mountain laurels, wintergreens, and cardinal flowers bring color to the area.
The area is dominated by oak and pine trees, which thrive on the well-drained sites. White cedars grow in the poorly drained bogs. Other trees include buckthorns, dogwoods, sugar maples, hemlocks, birches, ashes, and sweet gums.
The endangered Pine Barrens tree frog makes its home in the park, while bears and wildcats can still be found in some of the woodland areas. Deer, opossums, and raccoons are common.
Commercially, the area is valued for its production of blueberries and cranberries, and for tourism.
Designated by Congress in 1978 as the country’s first National Reserve, the Pine Barrens’ natural and cultural resources are now protected.
On May 1, 2007, a flare from an F-16 plane accidentally dropped into the forest during training, resulting in a fire that burned more than 17,000 acres.
Polar Bear Provincial Park
Polar Bear Provincial Park lies along the southern edge of the Arctic region, on the northwest coast of James Bay and the southern coast of Hudson Bay in Ontario, Canada. A true wilderness, it is accessible only by plane or boat. The dominant type of wetland in the park is peatland. Inland areas of the park contain swamps and marshes, while coastal areas contain saltwater marshes.
Polar Bear Provincial Park
Location: Ontario, Canada
Area: 9,300 square miles (24,087 square kilometers)
Classification: Peatland, swamp, freshwater marsh, and saltwater marsh
Many of the wetlands have formed in kettles (depressions in the ground left behind by retreating glaciers). Rain, melted snow, and overflowing rivers contribute to the water supply. As kettle lakes fill in with vegetation, marshes are formed, and coastal marshes have developed with the movement of the tides. The flat-topped ridges that run along the beach, parallel to the coast, help prevent drainage back into the sea.
Because the park lies along the southern edge of the Arctic region, temperatures are cold. Freezing weather prevails for six to eight months. Summers are short with the average temperature between 60° and 70°F (16° and 25°C). Precipitation is usually less than 21 inches (55 centimeters).
Vegetation varies depending on altitude and wetness. In the higher, cooler regions of the park, plant life includes sedges, goose grasses, and flowering saxifrages. Cotton grasses, sedges, and birches grow in the lower areas. In drier places, blueberries, crowberries, and louseworts are found. Salt-tolerant plants grow in the saltwater marshes, including aquatic grasses, cotton grasses, lungworts, and lyme grasses. Caribou and reindeer lichens grow in wetlands closer to forested areas.
Many waterfowl, such as the lesser snow goose, use the park in spring and fall as they migrate to their Arctic breeding grounds. Thousands of mallard ducks pass through in the fall, and the western and southwestern parts of the park form a migration path for shorebirds, such as the ruddy turnstone, black-bellied plover, and several species of sandpipers. Canada geese nest in the park.
Polar bears spend their summers in the park while breeding. Caribou and moose roam the area, moving north in the warmer weather. Beavers, muskrats, otters, foxes, and wolves are just a few of the many other mammals that make the park their year-round home.
The Cree Indians live along the coastal areas and use the park for hunting, fishing, and trapping. The Cree own two hunting and fishing camps where guests can fish and hunt waterfowl, grouse, and snipe. No other non-native hunting or fishing is permitted.
Since 1970 the area has been protected from development. Commercial or industrial use of natural resources is prohibited. Most of the park is designated as wilderness zones, nature reserves, or historical zones, where wildlife is protected.
The Usumacinta (oo-soo-mah-SEEN-tah) Delta is the most extensive wetland on the Gulf Coast of Mexico. It contains freshwater lagoons, swamps, marshes, and mangrove swamps. Its waters are rich in nutrients and support a major coastal fishery.
Location: Gulf Coast of Mexico
Area: 2,470,000 acres (998,000 hectares)
Classification: Swamp, marsh, and mangrove swamp
Many waterbirds breed and winter in the area. These include herons, egrets, storks, ibises, and spoonbills. Shorebirds that winter in the delta are ducks and coots.
A few manatees from the West Indies can be found here, as well as the endangered Morelet’s crocodile.
Threats to the delta have come from drainage for agriculture and oil spills from a nearby oil field. Also, mangrove trees are being cut for timber.
The marshy area of Caithness and Sutherland countries is known as Flow Country. The name “flow” comes from an old Norse word meaning “marshy ground.” Flow Country is one of the largest blanket bogs in the world, and it is still growing. Some of the peat found here is more than 8,000 years old.
Location: Northeast corner of Scotland
Area: 902,681 square acres (365,310 hectares)
Classification: Blanket bog
Typical plants that grow in Flow Country include sphagnum moss, heather, purple moorgrass, sedges, and rushes. The insect-eating plant, sundew, inhabits the bog.
Many bird species are supported by the bog. Sixty-six percent of the European communities’ greenshanks and the entire population of black-throated divers live there.
The peat that grows in a blanket bog is very valuable as fuel for home heating and industrial use. Peat mining is endangering this ancient ecosystem. In the 1980s, the Scottish government and several private companies began planting pine and fir trees. The trees support the forestry industry, but will eventually take over the wetland. Planting was halted by 1990 and the land was purchased by the Royal Society for the Protection of Birds (RSPB) in 1995 to preserve 14,800 acres (6,000 hectares) of forest.
Batzer, Darold P., and Rebecca R. Sharitz. Ecology of Freshwater and Estuarine Wetlands. Berkeley: University of California Press, 2007.
Cox, Donald D., and Shirley A. Peron. A Naturalist’s Guide to Wetland Plants: An Ecology for Eastern North America. Syracuse, NY: Syracuse University Press, 2002.
Fowler, Theda Braddock. Wetlands: an Introduction to Ecology, the Law, and Permitting. Lanham, MD: Government Institutes, 2007.
Mitsch, William J., and James G. Gosselink. Wetlands. 4th ed. Hoboken, NJ: Wiley: 2007.
Moore, Peter D. Wetlands. New York: Chelsea House, 2006.
Scrace, Carolyn. Life in the Wetlands. New York: Children’s Press, 2005.
Shea, John F., et al. Wetlands, Buffer Zones and Riverfront Areas: Wildlife Habitat and Endangered Species. Boston: MCLE, 2004.
Swarts, Frederick A. The Pantanal: Understanding and Preserving the World’s Largest Wetland. St. Paul, MN: Paragon House Publishers, 2000.
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WHAT ARE WETLANDS?
Wetlands are transition zones between land and aquatic systems where the water table is usually near or at the surface, or the land is covered by shallow water. Wetlands range in size from less than one acre to thousands of acres and can take many forms, some of which are immediately recognizable as "wet." Other wetlands appear more like dry land, and are wet during only certain seasons of the year, or at several year intervals. The U.S. Army Corps of Engineers reports that most U.S. wetlands lack surface water and waterlogged soils during at least part of each growing season.
Some of the more commonly recognized types of wetlands are marshes, bogs, and swamps. Marshes are low-lying wetlands with grassy vegetation. Bogs are wetlands that accumulate wet, spongy, acidic, dead plant material called peat. Shrubs, mosses, and stunted trees may also grow in bogs. Swamps are low-lying wetlands that are seasonally flooded; they have more woody plants than marshes and better drainage than bogs.
According to Thomas E. Dahl, in Status and Trends of Wetlands in the Conterminous United States 1998 to 2004 (2006, http://wetlandsfws.er.usgs.gov/status_trends/national_reports/trends_2005_report.pdf), there were an estimated 107.7 million acres of wetlands in the forty-eight coterminous states in 2004. This constituted about 5.5% of the total land area, whereas deepwater (rivers and lakes) constituted 1% and upland ("dry" land) constituted most of the total land area at 93.5%. (See Figure 7.1.) Of the wetland areas, 95% were freshwater and 5% were estuarine (coastal saltwater). (See Figure 7.2.) Dahl does not include data on Alaska and Hawaii, but the U.S. Environmental Protection Agency (EPA) notes in "Wetlands: Status and Trends" (February 22, 2006, http://www.epa.gov/OWOW/wetlands/vital/status.html) that in the 1980s an estimated 170 to 200 million acres of wetlands existed in Alaska—covering slightly more than half of the state—and Hawaii had 52,000 acres.
Hydrology and Wetland Formation
Wetlands are distributed unevenly, but occur in every state and U.S. territory. (See Table 7.1.) They are found wherever climate and landscape cause groundwater to discharge to the land surface or prevent rapid drainage from the land surface so that soils are saturated for some time.
In wetlands, when the soil is flooded or saturated, the oxygen used by the microbes and other decomposers in the water is slowly replaced by oxygen in the air, because oxygen moves through water about ten thousand times slower than through air. Thus, all wetlands have one common trait: hydric (oxygen-poor) soils. As a result, plants that live in wetlands have genetic adaptations in which they are able to survive temporarily without oxygen in their roots, or they are able to transfer oxygen from the leaves or stem to the roots. This anaerobic (without oxygen) condition causes wetland soils to have the sulfurous odor of rotten eggs.
Local hydrology (the pattern of water flow through an area) is the primary determinant of wetlands. Wetlands can receive groundwater in-flow, recharge ground-water, or experience both inflow and outflow at different locations. Figure 7.3 illustrates water movement in several different wetland situations. Part A in Figure 7.3 shows how wetlands do not always occupy low points and depressions in the landscape. They can occur in flat areas that have complex underground water flow.
Part B in Figure 7.3 shows a fen, which is a type of wetland that accumulates peat deposits like bogs do. Fens, however, are less acidic than bogs and receive most of their water from groundwater rich in calcium and magnesium. As part B shows, fens occur on slopes at groundwater seepage faces and are subject to a continuous supply of the chemicals that are dissolved in the groundwater.
Land along the sides of streams or rivers receives a continuous water supply and is ideal for wetland growth. It may also receive some groundwater discharge, as shown in part C in Figure 7.3. Bogs, shown in part D in Figure 7.3, are wetlands normally found on uplands or extensive flatlands. Most of their water and chemistry comes from precipitation.
Riverine (areas along streams, rivers, and irrigation canals) and coastal area wetlands are highly subject to periodic water level changes. Coastal area wetlands, for example, are affected by predictable tidal cycles. Other coastal and riverine wetlands are highly dependent on flooding and seasonal water level changes. Some examples are the floodplains of the Illinois and Missouri rivers.
TYPES OF WETLANDS
A wide variety of wetlands exist across the United States because of regional and local differences in hydrology, water chemistry, vegetation, soils, topography, and other factors. There are two large groups of wetlands: estuarine (coastal) and freshwater (inland). (See Figure 7.2.) Estuarine wetlands are linked to estuaries and oceans and are places where fresh- and saltwater mix, such as a bay or where a river enters the ocean. In estuaries the environment is one of ever-changing salinity and temperature. The water level fluctuates in response to wind and tide. Examples of estuarine wetlands are saltwater marshes and mangrove swamps.
|Location of various wetland types|
|Wetland type||Primary regions||States|
|Source: "Table 3. Locations of Various Wetland Types in the United States," in Wetlands: Their Use and Regulation, U.S. Congress, Office of Technology Assessment, March 1984, http://govinfo.library.unt.edu/ota/Ota_4/DATA/1984/8433.PDF (accessed January 11, 2007)|
|Inland freshwater marsh||Dakota-Minnesota drift and lake bed; Upper Midwest; and Gulf Coastal Flats||North Dakota, South Dakota, Nebraska, Minnesota, Florida|
|Inland saline marshes||Intermontane; Pacific Mountains||Oregon, Nevada, Utah, California|
|Bogs||Upper Midwest; Gulf-Atlantic Rolling Plain; Gulf Coastal Flat; Atlantic Coastal Flats||Wisconsin, Minnesota, Michigan, Maine, Florida, North Carolina|
|Tundra||Central Highland and Basin; Arctic Lowland; and Pacific Mountains||Alaska|
|Shrub swamps||Upper Midwest; Gulf Coastal Flats||Minnesota, Wisconsin, Michigan, Florida, Georgia, South Carolina, North Carolina, Louisiana|
|Wooded swamps||Upper Midwest; Gulf Coastal Flats; Atlantic Coastal Flats; and Lower Mississippi Alluvial Plain||Minnesota, Wisconsin, Michigan, Florida, Georgia, South Georgia, South Carolina, North Carolina, Louisiana|
|Bottom land hardwood||Lower Mississippi Alluvial Plain; Atlantic Coastal Flats; Gulf-Atlantic Rolling Plain; and Gulf Coastal Flats||Louisiana, Mississippi, Arkansas, Missouri, Tennessee, Alabama, Florida, Georgia, South Carolina, North Carolina, Texas|
|Coastal salt marshes||Atlantic Coastal Zone; Gulf Coastal Zone; Eastern Highlands; Pacific Moutains||All Coastal states, but particularly the Mid- and South Atlantic and Gulf Coast states|
|Mangrove swamps||Gulf Coastal Zone||Florida and Louisiana|
|Tidal freshwater wetlands||Atlantic Coastal Zone and Flats; Gulf Coastal Zone and Flats||Louisiana, Texas, North Carolina, Virginia, Maryland, Delaware, New Jersey, Georgia, South Carolina|
The most common location of freshwater wetlands is the floodplains of rivers and streams, the margins of lakes and ponds, and isolated depressions surrounded by dry land. Some examples of inland wetlands are the Florida Everglades, wet meadows, swamps, fens, bogs, prairie potholes, playa lakes, and wet tundra.
Wetlands are further divided by their vegetation. Emergent wetlands (marshes and wet meadows) are dominated by grasses, sedges, and other herbaceous (non-woody) plants. Emergent wetlands account for 73% of estuarine wetlands, even though they represent only 25.5% of freshwater wetlands. (See Figure 7.2.) Shrub wetlands (including shrub swamps and bogs), which are characterized by low-to-medium-height woody plants, make up 13% of estuarine wetlands and account for 17% of freshwater wetlands. Forested wetlands, mostly wooded swamps and bottomland hardwood forests, are dominated by trees and account for 51% of freshwater wetlands. (Bottomland hardwood forests are generally found along the edges of lakes and rivers and in sinkholes.)
HOW WETLANDS FUNCTION
Wetlands provide essential ecological functions that benefit people and the ecological systems surrounding the wetlands, as well as the wetland itself. The plants, microbes, and animals in wetlands are all key players in the water, nitrogen, carbon, and sulfur cycles.
Wetland functions fit into several broad categories:
- High plant productivity
- Temporary water storage
- Trapping of nutrients and sediments
- Soil anchoring
Not all wetlands perform all functions, nor do they perform all functions equally. The location of the wetland in the watershed and its size determine how it functions. (A watershed is the land area that drains to a stream, river, or lake.) Other factors that affect wetland function are weather conditions, quality and quantity of water entering the wetland, and human alteration of the wetland or the land surrounding it. The values of wetland functions to human communities depend on the complex relationships between the wetland and the other ecosystems in the watershed. An ecosystem consists of all the organisms in a particular area or region and the environment in which they live. The elements of an ecosystem all interact with each other in some way and depend on each other either directly or indirectly. (See Figure 7.4.)
Wetlands—Nursery, Pantry, and Way Station
Wetlands are diverse and rich ecosystems, which provide food and shelter to many different plants and animals. The combination of shallow water, high nutrient levels, and primary productivity (plant growth and reproduction) is perfect for the development of organisms that form the base of the food chain. The water, dense plants, their root mats, and decaying vegetation are food and shelter for the eggs, larvae, and juveniles of many species. Smaller animals avoid predators by hiding among the vegetation while they wait to prey on still smaller organisms. Fish of all sizes seek the warmer, shallow waters to mate and spawn, leaving their young to grow on the rich diet provided by the wetlands. Food and organic material that is flushed out of wetlands and into streams and rivers during periods of high water flow feed downstream aquatic systems, including commercial and sport fisheries.
Estuarine marshes, for example, are among the most productive natural ecosystems in the world. They produce huge amounts of plant leaves and stems that make up the base of the food chain. When the plants die, decomposers such as bacteria in the water break them down to detritus (small particles of organic material). Algae that grow on plants and detritus are the principal foods for shellfish such as oysters and clams, crustaceans such as crabs and shrimp, and small fish. Small fish are the food for larger commercial species such as striped bass and bluefish. (See Figure 7.5.) The EPA states in Wetlands Functions and Values (March 19, 2007, http://www.epa.gov/watertrain/wetlands/module08.htm) that "the fish and shellfish that depend on wetlands for food or habitat constitute more than 75% of the commercial and 90% of the recreational harvest."
Both estuarine and freshwater wetlands also serve as way stations for migrating birds. The Central Flyway extending from south-central Canada through the north-central United States and into Mexico, for example, provides resting places and nourishment for migratory birds (which individually number in the millions) during the migration season. Without this stopover area, the flight to their Arctic breeding grounds would be impossible. Chesapeake Bay with its extensive tidal and freshwater marshes on the East Coast Atlantic Flyway gives winter refuge to thousands of ducks and geese.
Wetlands' Role in Biodiversity
Wetlands are the source of many natural products, including furs, fish and shellfish, timber, wildlife, and wild rice. A wide variety of species of microbes, plants, insects, amphibians, reptiles, fish, birds, and other animals make their homes in or around wetlands because of the availability of water. For others, wetlands provide important temporary seasonal habitats. Physical and chemical features such as landscape shape (topology), climates, and abundance of water help determine which species live in which wetland.
In "Wetlands and People" (February 22, 2006, http://www.epa.gov/owow/wetlands/vital/people.html), the EPA notes that "more than one-third of the United States' threatened and endangered species live only in wetlands." When wetlands are removed from a watershed or are damaged by human activity, the biological health of the watershed declines. Wetland health has a commercial impact as well. Dahl indicates that 75% of the fish and shellfish commercially harvested in the United States and up to 90% of the recreational fish rely directly or indirectly on wetlands for their survival. Dahl also notes that in 2004, 72% of freshwater mussels were imperiled and 39% of native freshwater fish species were at risk of extinction.
Waterfowl are birds such as ducks and geese that spend much of their lives in wetlands, lakes, rivers, and streams. The well-being of waterfowl populations is tied directly to the status and abundance of wetland habitats. According to the U.S. Fish and Wildlife Service's (USFWS) Division of Bird Habitat Conservation (December 12, 2006, http://www.fws.gov/birdhabitat/NAWMP/index.shtm), waterfowl are the most well-known and economically important group of migratory birds in North America. By 1985 (when waterfowl populations had decreased to record lows) approximately 3.2 million people were spending nearly $1 billion annually to hunt waterfowl. In addition, about 18.6 million people spent $2 billion on "waterfowl-watching" activities, such as observing and photographing them.
Measures to preserve and protect the waterfowl population include the North American Waterfowl Management Plan. A joint strategy adopted by the governments of the United States, Canada, and Mexico, the plan established an international committee with six representatives from each of the three countries. Its purpose is to provide a forum for discussion of major, long-term international waterfowl issues and to make recommendations to the directors of the three countries' national wildlife agencies. The Division of Bird Habitat Conservation notes that as of the end of 2006, $4.5 billion had been invested under the plan to protect, restore, and/or enhance 15.7 million acres of waterfowl habitat. North American Waterfowl Management Plan projects also target all wetland-associated species in their conservation efforts.
Wetlands absorb water, much like sponges. By temporarily storing runoff and flood waters, wetlands help protect adjacent and downstream property owners from flood damage. Wetland plants slow the flow of water, which contributes to the wetland's ability to store it. The combined effects of storing and slowing the flow of water permit it to percolate through the soil into groundwater, which recharges aquifers, and to move through the watershed with less speed and force.
Wetlands are particularly valuable in urban areas because paved and other impermeable surfaces shed water, increasing the rate, velocity, and volume of runoff so that the risk of flood damage increases. Loss or degradation of wetlands indirectly intensifies flooding by eliminating absorption of the peak flows and gradual release of floodwaters.
Nutrient and Sediment Control
Figure 7.6 shows how wetlands improve the quality of water. Wetlands act like natural water filters. When water is stored or slowed down in a wetland by the plants and root masses that grow there, sediment settles out and remains in the wetland so that the water leaving the area is much less cloudy than the water that entered. The loss of cloudiness or turbidity has important consequences for both human health and the ecological health of the watershed. Turbidity has been implicated in disease outbreaks in drinking water. Furthermore, turbid water bearing silt has been responsible for smothering plants and animals in rivers, streams, estuaries, and lakes.
Wetlands can also trap nutrients (phosphorous and nitrogen) that are dissolved in the water or attached to the sediment. Nutrients are either stored in the wetland soil or used by the plants to enhance growth. If too much nutrient material reaches rivers, streams, lakes, and reservoirs, it can cause eutrophication, resulting ultimately in the death of many aquatic organisms. (See Figure 6.12 in Chapter 6 and the related discussion.)
Wetlands also play an important role in soil anchoring. The thick mesh of wetland vegetation and roots acts like a net and helps hold soil in place even during periods of relatively high water flow. Removing wetland vegetation the lines a stream or river leads to poorly anchored soil and an increased water flow, which carries away the soil. The result can be severe erosion and changes to the contours of channels, making them deeper and flatter. As a result, aquatic communities at the erosion location are disrupted or eliminated, and downstream aquatic systems are damaged by silt.
Marsh plant fringes in lakes, estuaries, and oceans protect shorelines from erosion in a similar fashion. The plants reduce soil erosion by binding the soil in their root masses. At the same time, the plants and root masses cushion the force of wave action, retarding scouring of shorelines.
ECONOMIC BENEFITS OF WETLANDS
Appreciation of the economic value of wetlands has undergone a dramatic change since the 1970s. Before that time, wetlands were considered useless, good only for taking up space and breeding mosquitoes. The emphasis was on filling and draining wetlands to turn them into productive land for development and agriculture. In the mid-1970s the growing environmental movement with its emphasis on clean water led to a closer examination of wetlands and their role in watersheds and the global ecosystem. Wetlands are now valued not only for their ecological role but also for their contribution to the economy.
Some of the most popular recreational activities, including fishing, hunting, and canoeing, occur in and are dependent on healthy wetlands. The EPA notes in the fact sheet "Economic Benefits of Wetlands" (February 22, 2006, http://www.epa.gov/owow/wetlands/facts/fact4.html) that "more than half of all U.S. adults (98 million people) hunt, fish, birdwatch, or photograph wildlife." In 1991 spending on these activities amounted to $59.5 billion. Figure 7.7 shows that 42% of Americans who observed, fed, or photographed wildlife on trips away from home in 2001 visited wetlands for these activities.
An example of the value of these wetland-related recreational activities can be found in the USFWS's 2001 National Survey of Fishing, Hunting and Wildlife -Associated Recreation (October 2002, http://www.census.gov/prod/2002pubs/FHW01.pdf). The USFWS states that in 2001, 34.1 million people aged sixteen years and older went fishing and spent an average of $1,046 each; 28.4 million anglers went freshwater fishing and 9.1 million went saltwater fishing. Overall, anglers spent $35.6 billion in 2001 on fishing trips, $4.6 billion on equipment, $6 billion on food and lodging, and $3.5 billion on transportation. They spent nearly $5.3 billion on land-use fees, guide fees, equipment rental, boating expenses, and bait. Camping equipment, binoculars, and special fishing clothing accounted for $721 million in expenditures. Equipment such as boats, vans, and cabins cost $11.6 billion. Anglers spent $3.2 billion on land leasing and ownership and $860 million on magazines, books, membership dues and contributions, licenses, stamps, tags, and permits.
Jerry Leonard reports in Fishing and Hunting Recruitment and Retention in the U.S. from 1990 to 2005: Addendum to the 2001 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation (February 2007, http://library.fws.gov/nat_survey2001_recruitment.pdf) that wetland-related activities are also important to children of all ages. In 2005, 64% of all first-time anglers were aged twenty or younger. In addition, 42% of children of any age living at home were exposed to fishing for the first time in 2005—49% of males and 35% of females.
The National Marine Fisheries Service notes in Fisheries of the United States 2005 (February 2007, http://www.st.nmfs.gov/st1/fus/fus05/fus_2005.pdf) that the value of the U.S. commercial fish landings (the part of the fish catch that is put ashore) in 2005 was $3.9 billion. Nearly 30% of the value of U.S. finfish landings was from species that are dependent on near-coastal waters and their wetlands for breeding and spawning. The EPA estimates in the National Coastal Condition Report II (2005) (December 2004, http://www.epa.gov/owow/oceans/nccr/2005/Chapt1_Intro.pdf) that "95% of commercial fish and 85% of sport fish spend a portion of their life cycles in coastal wetland and estuarine habitats. Adult stocks of commercially harvested shrimp, blue crabs, oysters, and other species throughout the United States are directly related to wetland quality and quantity."
Because wetlands function like sponges by absorbing and storing water, they help control flood waters and the resultant loss of life and property. In Economic Benefits of Wetlands (May 2006, http://www.epa.gov/OWOW/wetlands/pdf/EconomicBenefits.pdf), the EPA notes that floods in the United States cost about $2 billion annually. However, depending on their size, wetlands can store millions of gallons of water and then release the water slowly after the flood surge has passed, reducing flood damage. Wetlands can also buffer the effects of coastal tropical storms and hurricanes. The EPA suggests that if the Mississippi-Louisiana coastline had more wetland areas, then the effects of Hurricane Katrina would have been lessened.
HISTORY OF WETLANDS USE
Until well into the twentieth century wetlands were considered nature's failure, a waste in nature's economy. For this reason, people sought to increase the usefulness of wetlands. In the agricultural economy of that time, land unable to produce crops or timber was considered worthless. Many Americans began to think of draining these lands, an undertaking that required government funds and resources.
In the nineteenth century state after state passed laws to facilitate drainage of wetlands by the formation of drainage districts and statutes. When a number of landowners in an area petitioned for a drainage project, a hearing was held. A district encompassing the area affected could be created with the power to issue bonds, drain the area, and bill the landholders—petitioners and opponents alike. Coupled with an agricultural boom and technological improvements, reclamation projects multiplied in the late nineteenth and early twentieth centuries. The farmland under drainage doubled between 1905 and 1910 and again between 1910 and 1920. By 1920 state drainage districts in the United States encompassed an area larger than Missouri.
The earliest effective resistance came from hunters, sportsmen, and naturalist lobbies. Organizations such as the Izaak Walton League, the Audubon Society, and the American Game Protective Association deplored the destruction by drainage of wildlife habitats and began to press for protection of wetlands. These early conservation efforts met chilly receptions both from the public and the courts. A growing number of Americans, however, were beginning to sympathize with conservationists. Drainage projects were often disappointing—soils had proven to be poorer than expected, and the costs were generally greater than expected.
Lower Klamath Lake in Northern California became a striking example of reclamation's potential for creating wastelands far more desolate than those they replaced. The lake, a shallow sheet of water fringed by marshes, had been set aside by Theodore Roosevelt in 1908 as a waterfowl sanctuary. Nonetheless, in 1917 the water inflow was cut off to reclaim the land. The lakebed dried up and became prey to dust storms. The peat in the marsh bottom caught fire. Rather than being a reclaimed area of extraordinary fertility, the former wetlands became an ecological travesty. According to the USFWS's Klamath Basin National Wildlife Refuges (April 7, 2007, http://www.fws.gov/klamathbasinrefuges/history.html), even though time has helped reverse the damage, less than 25% of the historic wetland basin remains. In spite of this, the basin continues to support tremendous bird life on a smaller scale.
Efforts were made to help the Klamath Basin recover. According to the news release "President Bush to Propose Record-Level $3.9 Billion for Conservation Programs" (January 30, 2003, http://www.usda.gov/wps/portal/), the U.S. Department of Agriculture (USDA) reports that in the budget for fiscal year 2004, President George W. Bush proposed setting aside $8 million for water conservation and water quality enhancements in the Klamath Basin. The article "Federal Agencies Issue Final Mandates for Klamath Dams" (California Chronicle, January 30, 2007) notes that the Departments of Interior and Commerce mandated that fishways and fish ladders be operational in the area, making it economically favorable to remove dams that blocked water to the area, rather than relicensing the dams and providing fishways and ladders using alternative methods. This action led the way toward returning the Klamath River to being a productive salmon river.
Similarly, for many years Florida sought to drain the Everglades, a vast wetland region covering much of the southern part of the state. Efforts there resulted in lands prone to flooding and peat fires. Peat fires are particularly dangerous because they burn underground and can flare up without warning long distances from where they were originally ignited. Costs escalated, and the drainage district went broke. Across the nation the gap between the cost and the value of reclaimed land widened even more. The agricultural depression beginning in the 1920s increased the growing skepticism as to the value of reclamation. Nonetheless, during the Great Depression (1929–39), programs such as the Works Progress Administration and the Reconstruction Finance Corporation encouraged wetland conversion as a way to provide work for many unemployed people. By the end of World War II (1939–45) the total area of drained farmland had increased sharply.
Concern over Property Rights
Dispute over wetlands regulation reflects the nation's ambivalence when private property and public rights intersect, especially because three-fourths of the nation's wetlands are owned by private citizens. In recent years many landowners have complained that wetlands regulation devalued their property by blocking its development. They argued that efforts to preserve the wetlands have gone too far, citing instances where a small wetland precludes the use of large tracts of land. Many people believe this constitutes taking without just compensation.
The "takings" clause of the U.S. Constitution provides that when private property is taken for public use, just compensation must be paid to the owner. Wetland owners claim that when the government, through its laws, eliminates some uses for their land, the value is decreased, and they believe they should be paid for the loss.
In the 1970s and 1980s state courts and the lower federal courts frequently handed down contradictory rulings on the issue of compensation for wetland-related takings. In 1992 the U.S. Supreme Court, in Lucas v. South Carolina Coastal Council (505 U.S. 1003), resolved the issue of compensation when land taken for an accepted public good loses significant value.
David Lucas, a homebuilder, bought two residential lots on a South Carolina barrier island in 1986. He planned to build and sell two single-family houses similar to those on nearby lots. At the time he purchased the land, state law allowed house construction on the lots. In 1988 South Carolina passed the Beachfront Management Act to protect the state's beaches from erosion. Lucas's land fell within the area considered in danger of erosion; as a result, Lucas could no longer build the houses.
Lucas went to court, claiming that the Beachfront Management Act had taken his property without just compensation because it no longer had any value if he could not build there. Lucas did not question the right of the state of South Carolina to take his property for the common good. Rather, he claimed the state had to compensate him for the financial loss that resulted from the devaluing of the property.
The Supreme Court said that a state could stop a landowner from building on his or her property only if he or she was using it for a "harmful or noxious" purpose—for example, building a brickyard or a brewery in a residential area. This was not the case. Lucas had planned to build homes, a legitimate purpose that was neither harmful nor noxious. Although it was possible to define the planned buildings as harmful to South Carolina's ecological resources, this would not be consistent with earlier Court interpretations of "harmful." Only by showing that Lucas had intended to do something "harmful or noxious" with the land could the state take his land without compensation. This the state did not do, and, therefore, it owed him the money.
People are not the only ones who have dramatically altered wetlands. Nonnative—also called exotic—species have been as devastating to wetlands as humans by changing the nature of the ecosystem, thereby interfering with its function and the survival of native plants and animals. Plants and animals introduced either accidentally or deliberately can cause unexpected harm by displacing native species from their habitat or by placing stress, such as disease or predation, on a native species.
In 1899 the coypu (Myocastor coypus ) was introduced into California for the fur-farming trade. This animal is a beaverlike aquatic South American rodent that is bred for its fur. This introduction was originally viewed as a way to provide economic benefit. Subsequently, state and federal agencies as well as private interests were responsible for introducing the coypu into the wild in fifteen states to provide a new fur resource. In coastal states such as Maryland and Louisiana, the results have been disastrous.
Coypu live in fresh, intermediate, and brackish marshes and wetlands and feed on the vegetation. They eat all the vegetation in an area, changing a marsh to a barren mudflat. Coypu feed on the base of plant stems and dig for roots and rhizomes in the winter. Their grazing strips large patches of marsh, and their digging turns over the upper peat layer. This conversion of marsh to open water destroys valuable habitat for muskrat, wading birds, amphibians, reptiles, ducks, fish, crabs, and a host of other species, as well as causing erosion and siltation.
Invasive plant species can be as harmful as invasive animal species. Eurasian watermilfoil, phragmites (common reed grass), hydrilla, and purple loosestrife are introduced species that have disrupted wetland systems. Purple loosestrife (Lythrum salicaria ) is a good example. It is a perennial herb with reddish-purple flowers that may reach six feet in height under the right conditions. It was an important medicinal herb and ornamental as early as two hundred years ago on the East Coast and was probably introduced for this reason. It has no known North American predators and has a high reproductive capacity—up to three hundred thousand seeds per stalk. Because it can outcompete most native wetland plants, it can change the character and ecological function of a marsh. This is a serious threat because many wetland and other wildlife species are adapted to and depend on specific plants.
LOSS AND GAIN IN WETLAND ACREAGE
When the first Europeans arrived in North America, Thomas E. Dahl and Gregory J. Allord indicate in History of Wetlands in the Coterminous United States (March 7, 1997, http://water.usgs.gov/nwsum/WSP2425/history.html) that there were an estimated 221 million acres of wetlands in the lower forty-eight states. In his 2006 report, Dahl notes that in 2004 there were an estimated 107.7 million acres. In the intervening years, more than 50% of the wetlands in the lower forty-eight states had been lost. Wetlands had been drained, dredged, filled, leveled, and flooded to meet human needs. Although natural forces such as erosion, sedimentation, and a rise or drop in sea level may erase wetlands over time, most wetland losses have been caused by humans. Many of the nation's older cities, such as New York City, Baltimore, Philadelphia, New Orleans, and Charleston, are built on filled wetlands.
However, Dahl mentions that after decades of wetland losses there was an annual gain of thirty-two thousand acres of wetlands from 1998 to 2004. (See Figure 7.8.) Additionally, the loss of wetland shrank from 458,000 acres in the 1950s and 1970s to 290,000 acres in the 1970s and 1980s, which is a decrease of 37%. By the 1980s and 1990s the annual wetland loss had declined to 58,500 acres, which is a 79% decrease from the 1970s and 1980s.
Dahl details the reasons for wetlands losses during the 1998–2004 period. Figure 7.9 shows that the highest acreage lost annually was because of urban development. Dahl determines that urban and rural development accounted for an estimated 61% of wetland losses. In addition, 70,100 acres of wetlands were estimated to have been lost to deepwater habitats. Deepwater habitats are "environments where surface water is permanent and often deep, so that water, rather than air, is the principal medium in which the dominant organisms live." Some wetlands (18,000 acres) were lost to silviculture, the planting of trees.
Dahl also discusses the reasons for wetland gains. (See Figure 7.9.) More than 70,000 acres of wetlands were gained from wetland restoration and conservation programs converting agricultural land to wetlands, and nearly 350,000 acres were gained from these programs converting other types of land, such as prairie, forest, or scrub land, to wetlands.
WETLAND PROTECTIVE LEGISLATION AND PROGRAMS
Since the early 1970s conservationists have turned to the courts to challenge reclamation projects and protect wetlands. If drainage once seemed to improve the look of the land, beginning in the 1970s it was more likely to be seen as degrading it. Wetlands turned out to be not wastelands, but systems efficient in harnessing the sun's rays to feed the food chain and play an important role in the global cycle of water, nitrogen, carbon, and sulfur.
As the drainage movement once found support in state laws and federal policies, so did the preservation movement. In 1977 President Jimmy Carter issued an executive order instructing federal agencies to minimize damage to wetlands. In 1989 the EPA adopted a goal of "no net loss" of wetlands, meaning that where a wetland is developed for other uses, the developer must create a wetland elsewhere to maintain an overall constant amount of wetland acreage.
Clean Water Act
Section 404 of the Federal Water Pollution Control Act of 1972 is commonly called the Clean Water Act (CWA). The goal of the CWA is to "restore and maintain the chemical, physical, and biological integrity of the nation's water." Wetlands are considered part of the nation's water and are covered by the CWA.
The CWA authorizes the Army Corps of Engineers to be the primary federal authority for the protection of wetlands. The Corps' jurisdiction encompasses all navigable waters of the United States, plus their tributaries and adjacent wetlands, and includes ocean waters within three nautical miles of the coastline and isolated waters where the use, degradation, or destruction of these waters could affect interstate commerce or foreign commerce. The Corps evaluates the impact of proposed projects that involve wetlands by considering comments from the EPA, the USFWS, the National Marine Fisheries Service, and the affected states. Regulations established under the CWA require that any project affecting more than one-third of an acre of wetlands or five hundred linear feet of streams must be approved by the Corps.
CWA JURISDICTION QUESTIONED
Between 2000 and 2002 legal challenges arose over the extent of the Corps' authority under Section 404 of the CWA and the meaning of certain terms used in the act (such as "waters of the United States" and "navigable waters"). In the CWA information brief The Supreme Court's SWANCC Decision (August 2003, http://homer.ornl.gov/nuclearsafety/nsea/oepa/guidance/cwa/swancc_info_brf.pdf), the U.S. Department of Energy details one such challenge.
According to the brief, the Solid Waste Agency of Northern Cook County (SWANCC) wanted to develop a nonhazardous solid waste disposal facility on a site that contained isolated ponds and wetlands. The Corps denied SWANCC a Section 404 permit to fill those wetlands because they were used by migratory birds. Lower courts found in favor of the Corps, and SWANCC appealed the finding to the U.S. Supreme Court.
On January 9, 2001, the Supreme Court issued the decision Solid Waste Agency of Northern Cook County v. United States Army Corps of Engineers (531 U.S. 159). The Court determined that the Corps' authority under the CWA did not extend to isolated wetlands if they were not "adjacent" to navigable waters. It held that the Corps exceeded its statutory authority by asserting CWA jurisdiction over the ponds that SWANCC wanted to fill based solely on the use of those "non-navigable, isolated, intrastate" waters by migratory birds.
PROPOSED CLEAN WATER AUTHORITY RESTORATION ACT
The 2001 SWANCC decision narrowed the scope of wetlands, streams, lakes, and other waters protected under the CWA, which has prompted a move to restore protection. The proposed Clean Water Authority Restoration Act (CWARA) would restore the broad scope of protection to these water bodies and reestablish protections for "isolated" wetlands throughout the United States. The most recent version of the bill was introduced in both the U.S. House of Representatives and the U.S. Senate in May 2005. In early 2007 the bill was in the first stages of the legislative process in both chambers of Congress, having been referred to subcommittees for consideration.
Farm Bill of 1996
The 1996 Farm Bill reauthorized the Conservation Reserve Program and created the Wetlands Reserve Program. The two programs are designed to protect and restore wetlands.
WETLANDS RESERVE PROGRAM
The Wetlands Reserve Program (WRP) is a voluntary USDA program and has been implemented in forty-nine states. The program provides farmers with financial incentives, such as a fair market price for land, to retire marginal farmland and, in many cases, to restore and protect wetlands. In the key points sheet "Farm Bill 2002" (September 2004, http://www.nrcs.usda.gov/programs/farmbill/2002/pdf/WRPKyPts.pdf), the USDA notes that the program had enrolled nearly 1.5 million acres in 2004. Retiring cropland through the WRP has benefited the recovery of threatened or endangered species and has protected wetlands. The WRP was reauthorized under the Farm Bill of 2002 and is to extend through December 31, 2007.
CONSERVATION RESERVE PROGRAM
The Conservation Reserve Program (CRP) was originally authorized in the Farm Bill of 1985 as a soil conservation strategy that included paying farmers to retire marginal cropland from production for ten years. Its political support came from its potential to reduce expensive crop surpluses. The Natural Resources Conservation Service notes in "Conservation Reserve Program" (March 26, 2007, http://www.nrcs.usda.gov/Programs/crp/) that under the CRP the Farm Service Agency pays farmers to plant natural vegetation in their "highly erodible cropland or other environmentally sensitive acreage."
Unlike the WRP, farmers do not have to permanently retire their land under this program, but instead can do so for ten-year intervals. As a wetland protection and restoration strategy, the program has been successful in terms of the thousands of acres of cropland that have been restored to a natural state, which in many cases includes wetlands. The CRP was reauthorized in the Farm Bill of 2002, extending the program through December 31, 2007.
State Wetland Protection Programs
Many states have enacted their own state laws to protect wetlands. These laws may complement or be more stringent than federal regulations. For example, Maryland has had state laws to protect tidal wetlands since the early 1970s. In 1989 Maryland adopted its Nontidal Wetlands Act to provide the same protections to freshwater wetlands.
Besides using their CWA authority, states have included wetland protection in their water quality standards, passed laws protecting ecologically important wetlands such as the Dismal Swamp in Virginia and North Carolina, established mitigation banking, and created public education programs to increase public awareness of the value of wetlands. Several states have set up special funds to buy important wetlands.
As shown in Figure 7.8, wetland gains have been made in recent years. Figure 7.9 shows the reasons for these gains. Many efforts are ongoing at the private, local, state, and federal levels to protect existing wetlands and to create new ones. Wetland losses can be offset by restoring, creating, enhancing, replacing, or reallocating wetlands:
- Wetland restoration—the return of a wetland to a close approximation of its condition before disturbance, including reestablishment of its predisturbance aquatic functions and related physical, chemical, and biological characteristics.
- Creation—the construction of a wetland in an area that was not a wetland within the past one hundred to two hundred years and is isolated from other wetlands.
- Enhancement—the modification of one or more structural features of an existing wetland to increase one or more functions based on management objectives. Enhancement, while causing a positive gain in one function, frequently results in a reduction in another function.
- Replacement or reallocation—activities in which most or all of an existing wetland is converted to a different type of wetland and has the same drawback as enhancement.
Each of these approaches has benefits and drawbacks.
Many of the wetland areas in the United States are privately owned. A number of government programs, both regulatory and voluntary, exist to foster wetland protection, and some foster both restoration and enhancement. Some of the most successful wetland programs and projects are the result of private initiatives. Frequently, private organizations form partnerships with landowners to buy, lease, or create easements paid for with private, or a mix of private and public, funds.
Organizations such as the Nature Conservancy, Ducks Unlimited (DU), the Audubon Society, the Chesapeake Bay Foundation, and hundreds of others are working with private landowners, corporations, local communities, volunteers, and federal and state agencies in innovative projects to protect and restore wetlands. For example, the Nature Conservancy oversees many wetland restoration projects, including two on the Illinois River—Spunky Bottoms (2007, http://www.nature.org/initiatives/freshwater/work/illinoisriver.html) and Emiquon (2007, http://www.nature.org/wherewework/northamerica/states/illinois/preserves/art1112.html)—that aim to return more than eighty-five hundred acres of farmed land to their original wetland state.
In another example, the DU is working with the National Resources Conservation Service to implement the WRP in the Mississippi Alluvial Valley, which according to the DU, in "Mississippi Alluvial Valley" (2007, http://www.ducks.org/conservation/initiative21.aspx), historically comprised 24.7 million acres of hardwood bottom stretching from southern Illinois to Louisiana. In "Conservation in Mississippi" (2007, http://www.ducks.org/Page1666.aspx), the DU reports that it is working to conserve over 250,000 acres of waterfowl habitat throughout Mississippi by restoring hydrology and planting bottomland hardwood seedlings.
Constructed wetlands are marshes that are built to filter contaminated water. They consist of soil and drainage materials (such as gravel), water, plants, and microorganisms. Using constructed wetlands for wastewater treatment is a simple, economical, and environmentally friendly method that is being used more frequently than in the past.
Constructed wetland treatment systems are designed and built to use the natural processes involving wetland soils, vegetation, and their associated microbes to help treat wastewater. They are designed to take advantage of many of the same processes that occur in wetlands but in a more controlled manner. Even though some of these systems are operated solely to treat wastewater, others are designed with the multiple objectives of using treated wastewater as a source of water for the creation or restoration of wetland habitat for wildlife and environmental enhancement. The primary drawback to constructed wetlands for wastewater treatment is that they are land intensive; large land tracts are not always available at affordable prices.
There are two general types of constructed wetland treatments: subsurface flow systems and free water surface systems. Both types are usually built in basins or channels with a natural or human-made subsurface barrier to limit seepage. The subsurface flow systems keep water flowing through soil, sand, gravel, or crushed rock underground to minimize odors and other related problems. (See Figure 7.10.) Subsurface flow systems are also known as rock-reed filters, vegetated submerged bed systems, and root-zone systems. Free water surface systems are designed to simulate natural wetlands, with the water flowing over the soil surface at shallow depths.
The EPA's Office of Water reports in Constructed Treatment Wetlands (August 2004, http://www.epa.gov/owow/wetlands/pdf/ConstructedW.pdf) that approximately five thousand constructed wetland treatment systems have been built in Europe and about one thousand are operating in the United States.
Marsh construction and wetland rehabilitation as a method of disposing of dredged materials are another growing source of wetland construction. The Army Corps of Engineers has been using dredged material to restore or construct marshes since 1969. Dredged material is placed on shallow bay bottoms to build up elevations to an intertidal level, usually by pumping dredged material to the marsh construction site. If the site is exposed to high wind or wave action, protective structures such as rock or concrete breakwaters are built. Vegetation can be planted or the site may be left to develop naturally. Generally, within two to three years, these sites are indistinguishable from natural wetlands in appearance.
Restoration of the Florida Everglades
The Everglades is a premier wetland in the United States. It is designated as an International Biosphere Reserve, a World Heritage Site, and a Wetland of International Importance. According to the World Heritage Committee, the Everglades is the only U.S. site on the List of World Heritage in Danger (April 10, 2007, http://whc.unesco.org/en/danger/). Figure 7.11 shows the location of the Everglades and how it has been reduced to about half its former size.
According to the South Florida Ecosystem Restoration Task Force (April 6, 2007, http://www.sfrestore.org/), the Everglades is part of the South Florida Ecosystem, an eighteen-thousand-square-mile region extending from the Kissimmee River near Orlando to the Florida Keys. Originally a wide expanse of wetland, pine forests, mangroves, coastal islands, and coral reefs, in the twenty-first century it is one of the nation's most highly populated and manipulated regions. Its freshwater supply comes from rainfall in the Kissimmee River Basin and southward, mostly in May through October.
Slow and rain driven, the natural cycle of freshwater circulation feeding the Everglades historically built up in shallow Lake Okeechobee, which averages twelve feet deep and covers about 730 square miles. Thus began the flow of the wide, shallow "river of grass," as it was called by Native Americans. Fifty miles wide in places, one to three feet deep in the slough's center, and only six inches deep elsewhere, it flowed south at a rate of about one hundred feet per day across the saw grass of the Everglades to the mangrove estuaries on the Gulf of Mexico. A six-month dry season followed this flow. During the dry season water levels gradually drop. The plants and animals of the Everglades are adapted to the alternating wet and dry seasons.
During the past one hundred years an elaborate system of dikes, canals, levees, floodgates, and pumps was built to move water to agricultural fields, urban areas, and the Everglades National Park. Water runoff from agriculture and urban development brought excess nutrients into the Everglades, reducing production of beneficial algae and promoting unnatural growth of other vegetation. Ill-timed human manipulation of the water supply interfered with the natural water cycle, ruining critical spawning, feeding, and nesting conditions for many species.
The Florida legislature has enacted a number of laws to combat the growing water shortage in Florida, including the Everglades. The 1981 Save Our Rivers Act and the 1990 Preservation 2000 Fund authorized the water management districts to buy property to protect water sources, groundwater recharge, and other natural resources. The South Florida Water Management District (SFWMD; 2007, http://www.evergladesplan.org/pm/progr_land_aquisition.cfm), an agency that oversees flood protection and water supply, began buying out landowners in the eastern Everglades area in hopes of retaking thousands of acres of agricultural and residential property at an estimated cost of $2.2 billion. The action is aimed at restoring water flow to Everglades National Park.
In 1998 the Army Corps of Engineers and the SFWMD released their plan for improving Florida's ecological and economic health: the Comprehensive Everglades Restoration Plan (CERP). This plan covers the entire region and its water problems and focuses on recovering the major characteristics that defined the "river of grass." Specifically, the plan calls for:
- Reducing the freshwater flows into the Caloosahatchee River and the St. Lucie Canal, thereby restoring to the Everglades water now lost to the tide.
- Returning the water flow in the Kissimmee River to its former floodplain to achieve a more meandering river system.
- Restoring forty thousand acres of marshes for water storage and filtration to remove nutrients before water entering the Everglades.
- Modifying water deliveries through improved timing and distribution to mimic historic water conditions.
- Reestablishing historic flows and water levels to sloughs feeding into Florida Bay to restore natural estuarine salinity.
The Water Resources Development Act of 2000 approved the CERP. The SFWMD (2007, http://www.ever gladesplan.org/about/about_cerp_brief.aspx) states that this plan will take more than thirty years to carry out and will cost an estimated $7.8 billion. The primary goal of the project is to restore critical water flows to the Everglades and ensure adequate water supplies for cities, communities, and farmers in southern Florida well into the future. The cost of the project will be shared equally between the state of Florida and the federal government.
The very word "wetland" indicates that water is the first requirement for wetlands to exist. A wetland can be identified by three basic factors: soil, vegetation, and water regime (hydrology). A wetland generally is described as an area where water is the dominant factor in determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface. Specifically, a wetland is an area that is periodically or permanently saturated or covered by surface water or groundwater , that displays hydric soils (unique soils associated with extended saturation), and that typically supports or is capable of supporting hydrophytic (water-loving) vegetation.
Occurrence and Characteristics
Wetlands form in areas where one or more of the following occur:
- The land is flat and water runs off the surface very slowly;
- Water becomes ponded in land-surface depressions;
- Infiltration of precipitation into the soil is slow;
- Groundwater discharges to the land surface; or
- The water table (the upper surface of the saturated zone of an unconfined groundwater system) is at the land surface.
In the broadest sense, all wetlands fall between two extremes with respect to where they get their water. On the one hand, wetlands may receive most of their water supply from precipitation. On the other hand, they may receive most of their water from groundwater discharge. One type of wetland that receives most of its water from precipitation is a vernal pool. These temporary pools dry up when precipitation is lacking. A different type of wetland, and one that receives most of its water from groundwater discharge, is called a fen. Fens usually occur in low areas, such as at the base of hillsides or in land-surface depressions. Wetlands that are present along streams, called riverine or riparian wetlands, fall between these two extremes because the source of water to a stream depends on precipitation in upstream areas and groundwater inflow to the stream–wetland system.
Plant and Animal Communities.
The type of soil development and the plant and animal communities that are supported depend on the depth of water and the length of time it is available, known as its hydroperiod. Where water is present most of the year, wetlands tend to be dominated by softstemmed herbaceous vegetation and grasses. Where water will be present only for a brief time, and where soil surfaces will dry long enough to allow germination of woody species, brush or trees will be the dominant vegetation. In areas of restricted drainage, the accumulation of partially decomposed sphagnum moss and other acid-loving plants builds up deep peat layers.
Submerged aquatic plants, which are those that grow completely underwater, usually grow in the part of the wetland where the water is deepest. Emergent aquatic plants, which are those that have the lower part of the plant underwater but the upper part above the water, grow where the water is shallower. Some wetland plants near the edge of water do not actually grow in water, but they are considered to be wetland plants because their roots are in the saturated soils directly adjacent to the water.
Wetland plant communities generally have distinctive patterns called zones. For example, in the wetlands that are in land-surface depressions, such as in glacial terrain, the zones generally have a concentric pattern. The open-water zone where the submerged plants grow is in the middle. This is sometimes also called the deep-marsh zone. This zone is surrounded by the shallow-marsh zone where the emergent plants grow. Beyond the water's edge is the wet-meadow zone. Wetlands along streams have similar plant zones, also depending on water depth. Wetlands in flat, coastal areas generally do not have such distinct plant zones because the vast flat areas commonly are covered by only one plant type.
Just as water provides the basic conditions for the distribution of plant zones in wetlands, the plant zones themselves provide habitat for animals. Certain microorganisms and invertebrate animals can be found in some plant zones but not in others. Other animals, usually the more mobile ones, such as waterfowl, use all the plant zones, but for different reasons. For example, some plants provide food for waterfowl, but other plant zones provide shelter and nesting sites.
Wetlands contain some plants and aquatic animals that live only in wetlands and that are different from those living in upland areas. However, some upland animals occasionally use wetlands for food and shelter. For these reasons, wetlands are important ecosystems in their own right, and also are important parts of the larger natural environment.
"Marsh," "swamp," and "bog" are some names commonly used to identify wetlands. Other names for types of wetlands include bottomland, fen, mangrove, mire, moor, muskeg, peatland, playa, pothole, reedswamp, slough, swamp, vernal pool, wet meadow, and wet prairie.
To wetland scientists, these terms can be used to identify specific wetland types. But because of the diversity of wetlands, descriptive schemes based on landscape position have been developed to identify broad wetland systems. Wetlands at the ocean's edge are marine systems, whereas wetlands in estuaries (where rivers meet the ocean) are estuarine systems. Wetlands along the edges of rivers and streams are riverine or riparian systems, and wetlands along the edges of lakes are lacustrine systems. Upland wetlands not connected to rivers or lakes are palustrine wetlands.
Water supply, and consequently, vegetation and soils vary for each of the systems. Marine systems are dominated by tides. Estuarine systems are influenced by the interaction of tides and river flows. Riverine systems reflect the controlling role of flooding from high flows, while the water supply for lacustrine systems depends on the lake level and the water supply to the lake. Palustrine systems usually are dominated by rain and snowfall. As noted previously, groundwater may play an influential role in any of these systems, depending on the local geological situation.
The different types of places where wetlands can be found can be divided into six groupings of terrain: mountains, plateaus and high plains, playas, river valleys, coastal, and glacial and dune.
Mountains have small uplands and lowlands separated by large, steep valley sides. Wetlands in mountains generally form in the narrow flat uplands and in the narrow lowlands between the base of mountain slopes and the streams. Wetlands in the higher areas of mountains are among the best examples of those that are dependent on precipitation for their source of water. Wetlands in mountain valleys receive their water primarily from groundwater discharge at the base of mountain slopes and from nearby streams.
Plateaus and High Plains.
Plateaus and high plains have broad, extensive uplands and relatively small, narrow lowlands in the river valleys. Wetlands in plateau and high plains landscapes generally are restricted to the valley bottoms along streams. The wetlands in the valleys receive water from the stream and from groundwater discharge to the stream valley. If riparian wetlands are dependent primarily on the stream, they are dependent on precipitation in their upstream watershed. If wetlands in river valleys are dependent primarily on groundwater discharge, the size of the groundwater flow system is the primary consideration in determining their source of water.
Playas are extensive, flat lowlands that do not have streams draining them. The source of water to wetlands in playas is largely from stream flow that originates from precipitation in the surrounding uplands. Groundwater and precipitation directly on the wetland generally are much smaller contributors of water.
Large river valleys have relatively wide lowlands. The source of most water to the riparian wetlands along the river is the river itself, but groundwater also discharges to the wetlands along the river as well as to other wetlands across the valley bottom not connected to the river. Floods also cause some types of wetlands to form in river valleys. Even without floods, other types of wetlands form when high river levels cause water to move sideways through the stream banks and fill depressions in the floodplain. For these types of wetlands, changes in the level of the river cause changes in water level in the wetlands.
Many coastal plains have broad, flat areas. Perhaps the main reason why wetlands occur in flat coastal areas is the low slope of the land surface. Broad, flat lowlands commonly have slow runoff and also tend to have shallow water tables. Groundwater discharges to wetlands across the broad flatlands, but probably most groundwater discharges near the edge where the plains meet regional uplands. Wetlands in flat coastal areas are among the most extensive wetland systems in the world.
Glacial and Dune.
Glacial landscapes are parts of the Earth that were covered by glaciers during the last Ice Age. Glacial landscapes have isolated depressions that can have a wide variety of shapes and sizes. Wetlands often form in the depressions in such landscapes if the water table is close to land surface. Most of the depressions do not have streams entering or leaving them; therefore, streamflow generally is not a major source of water to the wetlands. Wetlands in these areas receive their water supply from precipitation and/or groundwater discharge. In glacial terrain, some wetlands have no groundwater input; some receive groundwater inflow through part of their bed and lose water to groundwater through other parts; and some receive groundwater inflow throughout their bed. Wetlands of all three types can be present on regional uplands as well as on regional lowlands.
Conserving and Mitigating Wetlands
Wetland ecosystems play varied but important roles in the landscape. Depending on their type and location, wetlands can moderate and influence the timing of flows (including flood flows) in streams and rivers. Wetlands play important roles in helping to maintain streamflow and groundwater supplies because they hold water that otherwise would run off the land surface and be "lost" to a downstream watershed. The stored water can be slowly released to streams and to underlying groundwater systems. Wetlands can improve water quality by trapping and removing sediments and nutrients; in fact, wetlands are so effective that some natural and artificial wetlands are used to treat wastewater.
Wetlands are critical habitats for a variety of plant and animal species. About one-third of the species federally listed as endangered or threatened in the United States depend on wetlands. Wetlands provide resting and nesting habitat for more than half of the nation's migratory bird species.
Society is beginning to appreciate the ecological values of wetlands in supporting a variety of wildlife species. In addition to the direct economic benefits from flood control and water quality improvement, wetlands offer significant recreational and educational benefits.
Despite these recent realizations, wetlands historically have been viewed as not valuable, and have been drained or filled at an alarming rate, often to allow agricultural development. Over half of the wetlands in the United States's lower 48 states were lost to various land uses between the late 1700s and the mid-1980s. Although the trend has slowed, wetland loss still continues.
Mitigating Wetland Loss.
Despite ongoing losses of wetlands in the United States (and worldwide), many strides have been made in conserving and restoring wetlands both through private efforts and through legislation and government programs. The Swampbuster provision of the 1985 U.S. Farm Bill, the Conservation Reserve Program, the Wetlands Reserve Program, and the North American Wetlands Conservation Act have helped protect and restore hundreds of thousands of wetland acres across the country. Another help in slowing the loss has been the federal Clean Water Act, which requires that permits be obtained from the U.S. Army Corps of Engineers for developments that will significantly affect wetlands. Wetland mitigation guidelines often include replacement specifications that require replacing an acre of wetland lost to development by one or more acres of wetland developed or enhanced in another area.
If a mitigation offset cannot be accomplished as a part of the development, a developer may "buy" wetland acres at a "wetland bank" in or near the same watershed, to offset the loss at the development site. The wetland bank is an area of restored, constructed, or enhanced wetland maintained specifically for such banking purposes. Under exceptional circumstances, acres of an existing wetland that are specifically preserved from development can be used as "bank credit."
Depending on the situation, the replacement may be a direct replacement, or it may be a "paper" replacement. Direct replacement may involve restoring a wetland lost to other uses, or it may involve converting an area lacking significant wetland characteristics to an area capable of playing the role of a wetland in the landscape. A paper replacement might involve an agreement to protect appropriate amounts of wetland acreage in another area, or it might involve the use of appropriate acreage from a wetland bank.
The best solution to conserving wetlands is to reduce or prevent wetland loss in the first place. Educating the public about the value of wetlands is one step in protecting these natural ecosystems. With 75 percent of the nation's wetlands in private ownership, the future of wetland protection will increasingly rely on volunteer involvement. The key to furthering wetland protection is to motivate communities to value the unique environmental, social, and economic values wetlands provide, and to create practical solutions to protect, enhance, or restore those values.
see also Everglades; Fish and Wildlife Issues; Land-Use Planning; Watershed, Restoration of a; Wetlands.
Thomas C. Winter (terrains)
N. Earl Spangenberg (mitigation)
Dahl, T. E., and C. E. Johnson. Wetlands—Status and Trends in the Conterminous United States Mid-1970s to Mid-1980s. Washington, D.C.: U.S. Department of Interior, Fish and Wildlife Service, 1991.
Kauffman, S. C. Water Matters, Vol. 1. Arlington, VA: National Science Teachers Association, 1994.
Mitsch, William J., and James G. Gosselink. Wetlands, 3rd ed. New York: John Wiley & Sons, 2000.
National Academy Press. Compensating for Wetland Losses Under the Clean Water Act. Washington, D.C.: National Academy Press, 2001.
National Geographic Society. Our Disappearing Wetlands. National Geographic Magazine vol. 182, no. 4 (1992):2-45.
National Wetlands Inventory. U.S. Fish and Wildlife Service. <http://wetlands.fws.gov>.
National Wetlands Research Center. U.S. Geological Survey. <http://www.nwrc.usgs.gov>.
ACID BOGS AND ANCIENT CONDITIONS
Bogs are wetlands characterized by the presence of saturated organic soil (peat) and acidic water. The acidity and anoxic (lowoxygen or no-oxygen) conditions of bogs help preserve organic materials (e.g., plants and animals) for hundreds, even thousands of years. Many human artifacts also have been discovered in these wetlands. Human bodies estimated to be 2,000 years old have been found so well preserved that the color of the hair and eyes could be determined, as well as the last meal eaten.
Scientists use anoxic bogs as natural record-keepers that indicate changes in plant communities over time. The sediments can be dated, and preserved pollen and other plant components can be used to examine changes in plant communities and in the overall environment. Data from bogs also are useful to climate modelers interested in reconstructing past climate-change scenarios over thousands of years.
WHAT (AND WHO) DEFINES A WETLAND?
What is legally considered a wetland has particular importance with respect to the requirements for wetland preservation. On the one hand, agricultural interests, developers, and others want more freedom to develop and drain both seasonally wet regions and permanent wetlands; hence, they desire a restrictive definition of wetlands. On the other hand, environmentalists and natural resources managers want a more inclusive definition that affords protection for more lands. As a result of decades of debate, many definitions of wetlands have been developed by scientists and policymakers. The definition used often depends on the requirements of the user.
Wetlands are habitats characterized by saturated (waterlogged) soils for at least part of the year and plants that are adapted to grow under wet conditions. They may be completely covered by water or the water may be just below the ground. There are many different types of wetlands, such as swamps (wetlands dominated by trees), marshes (wetlands dominated by nonwoody plants such as grasses and sedges), wet meadows, bogs, fens, flood-plain forests, lakes, and ponds.
Wetlands are to a large extent the product of the topography of the land. They develop wherever there is a depression in the land that brings the water table (groundwater) close to or even above ground. The type of wetland that will develop in a particular area depends on the rate of water flow, the length of the season of soil saturation, latitude (polar versus temperate versus tropical), proximity to the coast (marine versus freshwater wet-lands), and the surrounding geology.
Plant Adaptations to Wetlands
It is challenging for a plants to grow in constantly damp conditions. The saturated soil contains little or no oxygen compared to upland soil, therefore the roots of wetland plants require special adaptations to enable them to survive. Water lilies have air channels that run from their leaves, which are in constant contact with the air, to their roots under water. Water lilies also have their stomata only on the upper surface of their leaves (most plants have stomata on the lower surface) so that water can not enter when these pores open to allow carbon dioxide in for photosynthesis. Salt marsh grasses (Spartina species) also transport oxygen to their roots, where it may be excreted into the surrounding soil and create a small oxygenated zone around their roots. Plants that grow completely underwater, such as seagrasses and pondweeds, use the oxygen created as a by-product of photosynthesis to aerate their roots. Most wetland plants have also adapted to wet conditions through changes in their metabolism. Non-wetland plants, for example, typically produce an alcohol (ethanol) as a breakdown product of sugar metabolism when the soil is saturated with water. Ethanol is toxic to plants. Wetland plants have different enzymes that prevent the formation of the alcohol.
Although only a limited number of species can thrive in the constantly saturated soils of wetlands, those plants that have adapted are often extremely productive. As anyone who has planted a garden knows, one of the major factors limiting the growth of terrestrial plants is water. Having adapted to life in constantly damp conditions, wetland plants never have to worry about getting water. As a result, their growth rates can be very high.
The Value of Wetlands to Humans
Wetlands are very important features in the landscape and provide humans with some tangible benefits. They act like a sponge helping to reduce the impacts of floods by absorbing water and serving as a reservoir for groundwater. As water flows through a wetland, pollutants such as excess silt and harmful nutrients are trapped; thus, the wetland acts as a filter of pollutants and helps to maintain clean water. Wetlands serve as a vital habitat to many different species of wildlife, including many that are very rare and in danger of extinction.
The value of wetlands has not always been appreciated. A conservative estimate is that over 30 percent of the original wetlands in the United States have been lost forever. These were filled in the past to make way for farms, houses, highways, businesses, and other human activity. Since the early 1970s, the attitude toward wetlands has changed. Not only are there now strong efforts in most states to protect the remaining wetlands, many environmental agencies and land conservation groups are working to restore wetlands damaged by past human activities.
Current Threats to Wetlands
Even with a greater sense of the value of wetlands among much of the public, there are still pressures on these habitats. The ability of wetlands to
|GROWTH HABITS OF WETLAND PLANT||S|
|Completely submerged||Sea grasses, pondweeds, water plantain, water milfoil, elodea|
|Floating plants, unrooted in substrate||Duckweeds, bladderworts, water hyacinth|
|Floating leaves, rooted in substrate||Water lilies, lotus, floating hearts, water chestnut|
|Emergent perennials: roots in substrate under water, leaves and stems above water||Cattails, common reed, purple loosestrife, salt marsh grasses, tule, saw grass, wild rice|
|Emergent shrubs||Buttonbush, alders, leather leaf, sweet gale|
|Trees: constantly submerged||Mangroves, bald cypress, black spruce|
|Trees of floodplains: tolerate periodic flooding||Cottonwood, willow, silver maple, black ash|
absorb pollutants is not unlimited. Excessive amounts of pollution entering a wetland over a long period of time is likely to cause long-term changes in the wetland. One of the world's most famous wetlands, the Everglades of southern Florida, has suffered for years from pollution from fertilizers used by farms upstream from it. The pollution has resulted in some major changes in the plant community and suspected declines in the diversity of animals it supports.
Another major threat to wetlands is changes in hydrology (the flow of water). Water is the lifeblood of wetlands. If too much water is removed for human consumption or to irrigate cropland, the wetland may be degraded into a less-valuable habitat or even disappear completely. The Florida Everglades has to compete with the farms and rapidly growing cities of southern Florida for this precious resource and has suffered as a result. Not only is the quantity of water important to maintaining wetlands, but so is the timing. Many wetlands depend on seasonal flooding followed by a dry period. This type of natural cycle may be altered by dams, which may hold back the water during the wet season.
Direct filling of wetlands, although less common than it was twenty years ago, still occurs, particularly with smaller wetlands that may be perceived as less valuable than larger ones. Some small wetland types contain rare species of animals precisely because they are too small and temporary in existence to support fish predators, pointing out that size is not always a good indicator of value.
Finally, many wetlands throughout the world are threatened by invasions of nonnative plant species. Purple loosestrife, a European garden plant, has taken over many freshwater marshes in the northeastern United States. West Coast salt marshes are threatened with being overrun by tall cord-grass, an East Coast salt marsh species. These are only two examples of a very widespread problem.
see also Aquatic Ecosystems; Aquatic Plants; Carnivorous Plants; Endangered Plants; Invasive Species; Peat Bogs.
Mitsch, William J., and James G. Gosselink. Wetlands, 3rd ed. New York: John Wiley & Sons, 2000.
Niering, William A., and Charles Elliot, eds. Wetlands. National Audubon Society Nature Guides, 1983.
Tiner, Ralph W. In Search of Swampland: A Wetland Sourcebook and Field Guide. New Brunswick, NJ: Rutgers University Press, 1998.
Wetlands are low-lying ecosystems that are saturated with water at or close to the surface. (An ecosystem consists of all the animals, plants, and microorganisms that make up a particular community living in a certain environment.) The most common types of wetlands are swamps, marshes, and bogs. Wetlands provide habitats for an incredibly wide variety of plants and animals. They also are important because they absorb heavy rainfalls and prevent flooding. In addition, wetlands protect the ground water humans depend on for drinking by capturing and neutralizing surface pollutants.
However, wetlands are rapidly disappearing because they are being drained and filled for farming and urban growth. Wetlands also are being destroyed by pollution, especially the runoff of agricultural fertilizers and sewage dumping.
Swamps are shallow bodies of water in a low-lying, poorly drained area. These wetlands support a wide range of plant life, especially trees and high shrubs. In southeastern North America, swamp forests are typically dominated by such tree species as bald cypress, water tupelo, swamp
tupelo, and eastern white cedar. More northern temperate swamps are usually dominated by red maple, silver maple, American elm, and green or swamp ash.
Swamps provide a habitat for numerous species of animals. For example, swamps of bald cypress provide dwelling for the pileated woodpecker, red-shouldered hawk, Carolina wren, and many other small birds. These swamps also provide a nesting habitat for colonies of wading birds such as herons and egrets. Mammals supported by cypress swamps include swamp rabbits, white-tailed deer, and panthers. Many species of amphibians and reptiles—including the American alligator—live in cypress swamps.
Marshes are large wetlands dominated by rushes, sedges, and low-lying grasses. Typical plants of North American marshes include cattails, reeds, bulrushes, and saw-grass. Marshes can support relatively large populations of birds and certain mammals such as muskrats. Relatively small, fringing marshes around lakes and ponds are common in the prairies of North America. The borders of these marshy areas, called potholes, have historically provided major breeding habitats for surface-feeding ducks such as mallards, pintails, and blue-winged teals.
Words to Know
Biodiversity: Existence of a variety of plant and animal species in an ecosystem.
Ecosystem: The collection of plants, animals, and microorganisms in an area considered together with their environment.
Peat: Soil composed chiefly of decaying plant matter.
Primary succession: Natural replacement over time of one plant community with another more complex one.
Bogs are areas of wet spongy ground composed chiefly of peat (soil composed chiefly of decaying plant matter). The water underneath the surface-floating peat contains very little oxygen and other nutrients. It is also very acidic. As a result, bogs are dominated by acid-loving vegetation such as sphagnums (an order of mosses), sedges, and heaths.
Wetlands are dynamic ecosystems that are in transition between land and water habitats. Over time, most wetlands gradually fill in, a natural process known as primary succession. All wetlands were originally lakes or other bodies of water. Tons of plants, animals, and insects grow and die each year. The decaying material from these organisms gradually accumulates in small lakes. After a while, the lake becomes a wetland. The process continues with the wetland filling in more and more. Eventually, the wetland becomes a meadow, which in turn becomes a forest.
Wetlands also are delicate ecosystems. The biodiversity (the existence of a variety of plant and animal species in an ecosystem) of a particular wetland is maintained by the conditions that exist in that wetland. The plants and animals that thrive in a specific wetland have done so by adapting to the soil, water, nutrient supply, and other conditions found there. In general, wetlands that are well supplied with phosphorus (in the form of phosphate) and to a lesser degree nitrogen (as nitrate or ammonium) sustain relatively large populations of plants and animals. This is commonly the case for marshes, which are among the most productive natural ecosystems on Earth. In contrast, wetlands with low supplies of nutrients, such as bogs, sustain only small populations of plants and animals.
All wetlands have great value as natural ecosystems, and they all support species of plants and animals that occur nowhere else. Their usefulness in providing essential habitat for fish, birds, and other wildlife cannot be overstated. Similarly, humans gain from wetlands, which control floods and erosion, cleanse the water that flows through them, and extend supplies of water for drinking or irrigation. In addition, wetlands have an aesthetic (beauty) value that is priceless.
Unfortunately, most of the world's wetlands are being lost rapidly. Land developers drain and fill them in. Since the beginning of European settlement in America, more than 65 million acres have been lost. Often, wetlands are used for the disposal of municipal solid wastes and sewage. Run-offs of chemical pollutants from farmland further pollute wetlands, disturbing their delicate soil-water balance and endangering their many plant and animal species.
[See also Biodiversity; Water ]
WETLANDS are any of an array of habitats—including marshes, bogs, swamps, estuaries, and prairie potholes—in which land is saturated or flooded for some part of the growing season. According to the U.S. Fish and Wildlife Service, wetlands contain water-loving plants (hydrophytes) and hydric soils. They serve many ecological and practical purposes. Wetlands provide habitat and breeding sites for fish, shellfish, birds, and other wildlife; help maintain biological diversity (biodiversity); reduce the effect of floods by diverting and storing floodwaters;
provide protection from storm waves and erosion; recharge ground waters; and improve water quality by filtering out sediments, excess nutrients, and many chemical contaminants. Wetlands provide recreational, research, and aesthetic opportunities such as fishing, boating, hunting, and observing and studying wildlife.
Since 1780 human activity has destroyed more than half the wetlands of the United States, which now make up only 5 percent of the land surface of the contiguous forty-eight states, or 104 million acres. Nevertheless, they are extremely productive, exceeding even the best agricultural lands and rivaling rain forests in quantity and diversity of plant and animal life. More than half of the saltwater fish and shellfish harvested in the United States—and most of the freshwater sport fish—require wetlands for food, reproduction, or both. At least half of the waterfowl that nest in the contiguous states use the midwestern prairie potholes as breeding grounds. Wetland dependent animals include bald eagles, ospreys, beaver, otter, moose, and the Florida panther.
Few people recognized the value of wetlands until the 1970s. Before then, most people considered wetlands to be wastelands. In an effort to make them more productive—primarily through agriculture or development—people destroyed them by draining, ditching, diking, or filling. Early legislation, such as the Swamp Lands acts of 1849, 1850, and 1860, allowed fifteen states on the Mississippi River to "reclaim" wetlands for cultivation. By the mid-twentieth century, accumulating evidence, including U.S. Fish and Wildlife wetlands inventories in 1954 and 1973, made clear that destruction of wetlands was causing declines in fish and waterfowl. Federal, state, and local laws—notably the federal Clean Water Act of 1972 and amendments in 1977—attempted to regulate destruction.
Development, agriculture, and increasing pollution still threaten U.S. wetlands. One-third of wetland losses have occurred in midwestern farmbelt states. All but three states (Alaska, Hawaii, and New Hampshire) have lost more than 20 percent of their wetlands. Biologists and economists agree that preserving wetlands is less expensive than attempting to restore those that have been damaged, and experts still argue whether it is even possible to restore wetlands and how scientists might measure restoration. The economic and biological feasibility of restoration is debated each time a developer seeks permission to build on a wetland, thus destroying it, and offers (or is required) to attempt to rehabilitate a second site in return. Many biologists feel that because damaged sites cannot be returned to their previous states, it may not be acceptable to allow this tradeoff.
Council of Environmental Quality. Environmental Trends. Washington, D.C.: Executive Office of the President, 1989.
National Research Council. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. Washington, D.C.: National Academy Press, 1992.
Susan J.Cooper/c. w.
"Wetlands" is the collective term for habitats that are too wet to be upland and not wet enough to be fully aquatic. They occur in areas of transition between dry upland and open water or in low areas where drainage water collects or the water table is at the ground's surface.
Wetlands are characterized by:
- the presence of surface water, at least part of the year
- unique soils that differ from adjacent uplands (due to the influence of waterlogging)
- plants adapted to wet soil conditions (hydrophytic vegetation)
There are many types of wetlands, differing in water chemistry, hydrology, soils, topography, climate, and vegetation. The broadest categories are coastal and inland wetlands. Coastal wetlands experience periodic flooding by saltwater or brackish water, and include estuaries (tidal marshes), mud flats, and mangrove swamps. They are nurseries for crustaceans, such as shrimp, and many fish species, and are also important habitat for birds and other wildlife. The presence of coastal wetlands can reduce inland erosion and other damage from hurricanes and winter storms.
Inland wetlands are freshwater wetlands and occur throughout the interior of a continent. These wetlands include: cattail marshes and wet meadows dominated by grasses, sedges, and herbs; swamps dominated by woody vegetation such as shrubs and trees; and peatlands (fens and bogs) that contain a buildup of peat, which forms as plants die and fall into the water and are not completely decomposed. The Florida Everglades are a vast inland wetland system.
A key factor determining what kind of soil and plant community develops in a wetland is the depth and duration of waterlogging and its effect on oxygen (O2) in the soil. Soils that are waterlogged for any length of time become depleted of O2 because soil microbes and plant roots use it during cellular respiration. The oxygen is not quickly replaced by O2 from the atmosphere because O2 diffuses very slowly through water. The anoxic (low oxygen) conditions influence soil development. Decomposition of plant litter and other organic matter is slowed in absence of O2 and the wetland soils become high in organic matter. If decomposition is much slower than the production of plant matter, peat will form. Peatlands typically occur in northern climates where low average temperatures further slow decomposition.
Since O2 availability is a limiting factor for plants growing in wetlands, most wetland plants have structural adaptations that increase gas exchange. Some have spongy tissues, called aerenchyma, in their stems and roots that conduct O2 within the plant from the aboveground shoot down to the roots. Others produce adventitious roots above the anoxic zone or have prop roots with pores that let in oxygen from the atmosphere.
In the past, many people viewed wetlands as mosquito-infested wastelands needing to be drained. More than one-half of the original wetlands of the United States have been drained or otherwise altered. Now there is a public consciousness that wetlands are important and valuable natural resources. Wetlands improve water quality by removing and retaining nutrients from surface waters and trapping sediments. They reduce flood and storm damage, and act to control erosion of shorelines. They provide important habitat for fish, crustaceans, and other wildlife and produce natural products such as blueberries, cranberries, rice, mink, and beaver. They support hunting and fishing activities and provide other recreational and educational opportunities.
see also Estuaries; Global Climate Change; Limnologist
Mitsch, William J., and James G. Gosselink. Wetlands. New York: Van Nostrand Reinhold, 1986.
Williams, Michael, ed. "Understanding Wetlands." In Wetlands: A Threatened Landscape. Cambridge, MA: Basil Blackwell, Inc., 1990.