Wetlands
What are wetlands?
Wetlands can be thought of as 'biological supermarkets.' They provide great volumes of food that attract many animal species．These animals use wetlands for part of or all of their life-cycle．Dead plant leaves and stems break down in the water to form．small particles of organic material called 'detritus.' This enriched material feeds many small aquatic (水生的) insects, shellfish, and small fish that are food for larger predatory (食肉的) fish, reptiles, amphibians (两栖动物), birds, and mammals.
What are the functions and values of wetlands?
Long regarded as wastelands, wetlands are now recognized as important features in the landscape that provide numerous beneficial services for people and for fish and wildlife．Some of these services, or functions, include water quality improvement, floodwater storage, fish and wildlife habitat, aesthetics, and biological productivity．These beneficial services, considered valuable to societies worldwide, are the result of the inherent and unique natural characteristics of wetlands.
Water storage．Wetlands function like natural tubs or sponges, storing water and slowly releasing it．This process slows the water's momentum and erosive potential, reduces flood heights, and allows for ground water recharge, which contributes to base flow to suce water systems during dry periods．Although a small wetland might not store much water, a network of many small wetlands can store an enormous amount of water．The ability of wetlands to store floodwaters reduces the risk of costly property damage and loss of life--benefits that have economic value to us．For example, the U．S．Army Corps of Engineers found that protecting wetlands along the Charles River in Boston, Massachusetts, saved ＄17 million in potential flood damage.
Water filtration．After being slowed by a wetland, water moves around plants, allowing the suspended sediment to drop out and settle to the wetland floor．Nutrients from fertilizer application, manure, !caking septic tanks, and municipal sewage that are dissolved in the water are often absorbed byplant roots and microorganisms in the soil．Other pollutants stick to soil particles．In many cases, this filtration process removes much of the water's nutrient and pollutant load by the time it leaves a wetland．Some types of wetlands are so good at this filtration function that environmental managers construct similar artificial wetlands to treat storm water and wastewater.
Biological productivity．Wetlands are some of the most biologically productive natural ecosystems in the world, comparable to tropical rain forests and coral reefs in their productivity and the diversity of species they support．Abundant vegetation and shallow water provide diverse habitats for fish and wildlife．Aquatic plant life flourishes in the nutrient-rich environment, and energy converted by the plants is passed up the food chain to fish, waterfowl, and other wildlife and to us as well．This function supports valuable commercial fish and shellfish industries.
Fish and wildlife habitat．More than one-third of the United States' threatened and enered species live only in wetlands, and nearly half use wetlands at some point in their lives．Many other animals and plants depend on wetlands for survival.
For many animals and plants, like wood ducks and swamp rose, inland wetlands are the only places they can live．For others, such as black bear, raccoon (浣熊), and deer, wetlands provide important food, water, or shelter．Many of the U．S．breeding bird populations--including ducks, geese, woodpeckers, hawks, and many song-birds--feed, nest, and raise their young in wetlands．Migratory waterfowl use coastal and inland wetlands as resting, feeding, breeding, or nesting grounds for at least part of the year.
Recreation and aesthet