Wetlands
Wetlands
Wetlands are a diverse group of areas in which land is saturated with water for prolonged periods. They are among the most productive environments on earth and support a wide range of plant and animal life. Wetlands can be freshwater, saltwater, or brackish (part fresh and part salt) and are one of the most delicate and complex ecosystems (areas in which living things interact with each other and the environment).
Wetlands are nether totally aquatic (watery) nor terrestrial (dry land), but rather are in the zone between permanently wet and normally dry conditions. Wetlands can be found on every continent, and are often called marshes, swamps, or bogs. Despite their fragility, wetlands perform a variety of important, natural functions. Where the sea meets the land, tidal estuaries or salt marshes form a buffer zone, protecting the mainland from the onrushing sea. Wetlands improve water quality by filtering the water that passes through them. They also remove much of the excess carbon and nitrogen that humans pump into the air. Wetlands contain a great deal of food for sea life and other animals, while providing a safe haven for spawning (egg laying and hatching).
CHARACTERISTICS OF WETLANDS
No matter what wetlands are called, they all have three characteristics. First, they all have waterlogged soil. In such soil, water is at or above the soil surface for a long enough time during a year to influence and determine what grows there. Second, a certain type of plant called a "hydrophyte" grows in wetlands. Although there are as many as 5,000 species of such specialized plants, from mangroves and cattails to bald cypress and rushes, all are hydrophytes because they have in some manner developed their own way of getting a steady supply of air to their submerged roots. Third, the soil found in a typical wetland is mostly poor in oxygen and very acidic. This also determines what can grow there.
Wetlands are usually either freshwater wetlands or saltwater wetlands, although there are some in which the two meet and mingle. Saltwater wetlands naturally occur at the coasts where the sea meets the land. Tidal salt marshes with salt-tolerant plant species can be found along the Arctic and Atlantic seaboards of North America, the Gulf of Mexico, and the European coastline. Mangrove forests whose thick trees are concentrated in the Indian Ocean and West Pacific region, are the subtropical equal of tidal salt marshes. Most of the wetlands in the temperate parts of the world are freshwater marshes. In the continental United States, 90 percent of the wetlands are freshwater marshes. Worldwide, wetlands account for about 6.5 percent of the Earth's total land surface, and the bulk of them are found in the world's tropical zones.
A river like the Mississippi River, which cuts down across the United States from Minnesota to the Gulf of Mexico, is a good example of how such a large moving body of water with seasonal flooding can build wetlands and keep them alive. Each spring, as the gorged river would search for the shortest route to the Gulf of Mexico, it would overflow its banks, depositing rich sediment. The river also pushed most of the saltwater at the Gulf back into the sea. The combination of sediment buildup and freshwater infiltration allowed wetlands to develop. Many plants that were sensitive to salt were able to take hold and grow, keeping the land in place.
Until the eighteenth century, wetlands were considered worthless and places to be avoided, and this annual flooding process was left undisturbed. But with the development of the levee system (a bank of earth along a river to prevent flooding), begun in New Orleans in the early 1700s, the flooding was stopped and the now-dry land became "useable" by people. With the continued development of levees and permanent flood control, the Mississippi River now has no choice but to deposit its wealth of sediment into the Gulf of Mexico. Since then, the wetlands of New Orleans have been disappearing.
PLANT AND ANIMAL LIFE IN WETLANDS
The variety of plant and animal life found in and around wetlands is huge and amazing. They are home to all types of birds, snakes, fishes, turtles, raccoons, beavers, alligators, and shellfish. All these and many more animals depend on wetlands for food and shelter. Wetlands also provide a welcome resting and feeding place for migrating (seasonally moving) birds. Many animals need to be in wetlands in order to reproduce. A great deal of today's commercial fishing industry depends in some way on the fertility of wetlands. Because they are so rich in nutrients and in all manner of interdependent life forms, wetlands are very delicate, intricate, and vulnerable ecosystems. Major changes in wetlands can produce a ripple effect.
HUMAN EFFECTS ON WETLANDS
Despite national laws and international agreements protecting critical wetlands, the impact of human development has had a profoundly negative effect on wetlands. Wetlands are, therefore, among the most threatened of habitats, and hundreds of thousands of acres are disappearing every year in the United States alone. Without the enforcement of laws put in place to protect wetlands, they may be one of the first ecosystems to vanish completely.