Wetlands provide many functions that are valued by people. These functions (and their values) include: surface water storage (flood control), shoreline stabilization (wave damage protection/shoreline erosion control), streamflow maintenance (maintaining aquatic habitat and aesthetic appreciation opportunities), groundwater recharge (some types replenish water supplies), sediment removal and nutrient cycling (water quality protection), supporting aquatic productivity (fishing, shellfishing, and waterfowl hunting), production of trees (timber harvest), production of palatable herbaceous growth (livestock grazing and haying), production of peaty soils (peat harvest), and provision of plant and wildlife habitat (hunting, trapping, plant/wildlife/nature photography, nature observation, and aesthetics). Some of the "values" are attained at the expense of natural wetlands, such as peat mining, farming (e.g., cranberry production), and timber harvest, although the latter can return to a more natural state depending on site-specific silvicultural practices.
Figure 16. One of wetlands' most valued functions is flood storage, which also helps improve water quality by permitting water-borne sediments to drop out of suspension.
The location of wetlands (their position on the landscape), their shape (geomorphology), their vegetation, soils, and hydrology all play important roles in determining the functions of individual wetlands. For example, wetlands along rivers and streams are in excellent positions to temporarily store floodwaters and to assist in water quality renovation. Wetlands in headwater locations (source of streams) are groundwater discharge sites important to maintaining streamflow. Marshes along rivers, lakes, and streams are often productive fish, waterfowl (ducks and geese), and waterbird (herons and bitterns) habitats. Basin wetlands store surface water, while slope wetlands do not. Wetlands on sandy soils may be groundwater recharge wetlands linked directly to underground aquifers.
Wetlands provide valuable habitats for many species of animals. Some animals spend their entire lives in wetlands, while others use wetlands for breeding and nursery grounds or for feeding or obtaining drinking water. About two-thirds of the major U.S. commercial fishes depend on estuaries and salt marshes for nursery or spawning grounds, including menhaden, bluefish, fluke, sea trout, spot, mullet, croaker, striped bass, and drum. Coastal wetlands along spawning streams are important for many salmon species on the Pacific Coast. Most freshwater fishes are wetland-dependent and nearly all recreationally important freshwater species spawn in the aquatic portions of wetlands. Northern pike, yellow perch, carp, smallmouth bass, largemouth bass, bluegill, bullhead, and minnows are examples of freshwater fishes that spawn in wetlands. Amphibians (frogs and salamanders) breed in wetlands and many spend their entire lives in wetlands.
Nearly all 190 species of North American amphibians are wetland-dependent. Numbers of amphibians in small wetlands are astonishing (e.g., 1600 salamanders and 3800 frogs in a 100-foot wide gum pond in Georgia). The American alligator, our largest reptile, thrives in southern swamps and marshes. Turtles are among the most frequently observed wetland animals, basking on logs and shorelines in and around wetlands. Waterfowl and waterbirds (e.g., sandpipers, herons, egrets, bitterns, avocets, rails, and oystercatchers) are obviously wetland-dependent, but many songbirds also nest and/or feed in wetlands, such as sparrows (swamp, song, sharp-tailed, and seaside), wrens, blackbirds (yellow-crowned and red-winged), warblers, and kingbirds. Terns, killdeers, hummingbirds, pheasants, turkeys, woodpeckers and several raptors (e.g., marsh hawk, red-shouldered hawk, and barred owl) also frequent wetlands. Mammals common to wetlands include beaver, muskrat, moose, caribou, and white-tail deer. In northern areas, the latter species overwinters in evergreen forested wetlands ("deer-yards") where food, shelter, and less snowpack are found.
Figure 17. The American alligator occurs in wetlands from North Carolina south.
Destruction of wetlands eliminates or severely minimizes their values. Drainage of wetlands prevents surface water storage and reduces their water quality enhancement function, while accelerating the flow of water downstream which may cause increased flood damages. Wetland filling does likewise as well as destroying vital habitats for native fish and wildlife species. The vast majority of wetland benefits accrue to the general public which makes it important to conserve these valuable natural resources.