Wetlands are transitional areas between land and water bodies where water periodically floods the land or saturates the soil. The term wetland includes environments such as marshes, swamps, bogs, and estuaries. Wetlands may be covered in shallow water most of the year or be wet only seasonally. Plants and animals found in wetlands are uniquely adapted to these conditions.
Level III ecoregions of Alaska, 2003
Wetlands in the United States are highly diverse because of regional differences in climate, geology, soils, and vegetation. There are approximately 105.5 million acres of wetlands in the country. The majority of this is freshwater wetland (95 percent, or 100.5 million acres). The rest is tidal, or saltwater, wetland and is found along the coasts. Wetlands are found in nearly all states—there are arctic tundra wetlands in Alaska, peat bogs in the Appalachians, and riparian (riverbank) wetlands in the arid west. Table 4.9 lists some of the different types of wetlands and their acreage in the forty-eight contiguous United States, as well as how acreage has changed in the decade from 1986 to 1997.
Level III ecoregions of Alaska, 2003
As of 2004, well over half the original North American wetlands have vanished. A few states have lost nearly all their original wetlands. With the recognition of the importance of wetlands and the institution of protective measures, the pace of wetland loss has slowed in recent decades. About 58,500 wetland acres were lost each year between 1986 and 1997, with forested wetlands suffering the most damage. Although this represents an 80 percent
Level III ecoregions of Alaska, 2003
drop from the previous decade, wetland loss is still significant. (See Figure 4.6.) The new land uses of these converted wetlands are shown in Figure 4.7. Wetlands provide critical habitats for fish and wildlife. They also purify polluted water and check the destructive power of floods and storms. Finally, wetlands provide recreational
opportunities such as fishing, hunting, photography, and wildlife observation.
Endangered Bog Plants
Bogs are non-tidal wetland ecosystems that form where poor drainage and low oxygen levels combine with a low mineral content to retard the decay of organic material. Over time, peat, partially decayed organic substances, begins to solidify, forming layers over the surface of ponds. Migrating birds and amphibians, including some salamanders, are among the animals most commonly found in bog habitats. Bog flora includes coarse, grasslike plants called sedges and unusual carnivorous plants such as sundew and pitcher plants. Carnivorous plants capture and digest small insects in order to obtain nutrients unavailable in their unique environments, most often minerals such as nitrogen and phosphorus. The leaves of the sundew are covered with hundreds of tiny "tentacles" that are used to trap insects. The sundew traps an average of five insects per month. Pitcher plants maintain a pool of acidic fluid at the bottom of their "pitchers." Hairs on the inside of the pitchers point downward, preventing insects from exiting once they enter. Insects are attracted to the pitchers by the enticing red color inside.
Bog plants are threatened primarily by encroaching urbanization. Boggy wetlands are either drained or filled for use as dumping grounds. In addition, the suppression of naturally occurring fires discourages the formation of bog ecosystems. One bog species, the funnel-shaped green pitcher plant, first appeared on the Endangered Species List in 1979. Found in Alabama, North Carolina, and Georgia, it has declined largely due to collection by humans, who find these insect-eating plants both interesting and exotic. The collection of carnivorous plant species has also disrupted bog ecosystems by allowing mosquitoes and flies to proliferate.
The Florida Everglades
The Everglades covers approximately 5,000 square miles of southern Florida. It includes a wide diversity of both temperate and tropical habitat types, including saw-grass prairies, mangrove swamps, pine forests, cypress forests, marshes, and estuaries, and represents one of the wildest and most inaccessible areas in the United States. The area was formed by centuries of water flow from Lake Okeechobee in south-central Florida to Florida Bay, and is often described as a shallow "river of grass." The highest land in the Everglades is a mere seven feet above sea level. Everglades National Park is the largest remaining subtropical wilderness in the United States, and is home to endangered species such as the American crocodile, Florida panther, wood stork, and West Indian manatee. The Everglades became a National Park in 1947, and the region has also been designated an International Biosphere Reserve, a World Heritage Site, and a Wetland of International Importance.
Everglades habitats are now threatened by many factors. First, water control through an extensive system of canals and levees has brought both droughts and floods to Everglades lands. Much of the Everglades' water has traditionally been diverted for irrigation or to supply metropolitan areas. In fact, the portion of the Everglades inundated by water has been reduced drastically over the twentieth century, destroying numerous habitat areas. Occasional releases of large amounts of water, on the other hand, flood habitats, harming species such as alligators, whose nests may be washed away. Pollution is a second factor in Everglades deterioration. Harmful pollutants now found in the Everglades include fertilizers and pesticides from agricultural runoff, as well as mercury. Fertilizers encourage the rampant growth of vegetation that chokes wetlands, while pesticides and mercury poison species. One plant species that is affected is Garber's spurge, a beach herb that thrives in sandy peripheral soil. With its decline, parts of the Everglades have been more prone to soil erosion. Invasive species have also altered Everglades habitats. Alien species such as Brazilian pepper and Australian pine have reduced native plant populations. Finally, fire suppression related to human encroachment has caused habitat alteration. Park officials now adhere to a prescribed burn schedule, setting fires in three-to ten-year intervals as necessary.
Multiple efforts were made in the 1990s and early 2000s to help restore the Everglades. Florida's Everglades Forever Act, passed in 1994, attempted to limit agricultural runoff as well as set water quality standards. The Comprehensive Everglades Restoration Plan, passed by Congress in 2000, is a 38-year project drawn up by the U.S. Army Corps of Engineers. It aims to restore natural water flow patterns in the Everglades and to redirect water to the marshes. In December 2000, President Bill Clinton signed the Water Resources Development Act of 2000, which committed over $4 billion to Everglades restoration.
Tidal Wetlands—The Mangroves
Mangrove forests are among the most biodiverse wetland ecosystems on earth. They are found in tropical coastal waters, often near river mouths. The tree species found in mangrove forests possess special roots that allow them to survive in brackish water. Mangrove forests harbor numerous unique species worldwide, such as crab-eating monkeys, fishing cats, and diverse species of birds and fish. They also provide food and wood for local communities, stabilize coastlines, and provide barriers from the sea during storms. Mangrove forests once lined three-quarters of the world's tropical coasts. Now, according to the World Resources Institute, an environmental advocacy group, less than half these forests remain. Indonesia, a country of more than 13,000 islands, possesses the most mangrove forestland of any country. Brazil and Australia also have extensive mangrove habitats.
Mangroves are disappearing in part because they have traditionally been regarded as sinister, malarial wastelands. In Florida, for example, mangroves were flooded every year to control mosquito populations. Mangrove forests have also been sold to logging companies for paper pulp, pest-proof timber, and chipboard for coastal development. Many mangrove forests have also been replaced with saltwater ponds for commercial shrimp farming. The shrimp industry is perhaps the most immediate threat to mangrove forests today.
During the Vietnam War, herbicides were dumped on an estimated 124,000 hectares (approximately 306,410 acres) of mangrove forests in South Vietnam. These areas remain, for the most part, entirely barren—a true wasteland.