Often conjuring images of dank, smelly, mosquito-infested wastelands, upon closer look, wetlands are actually biologically diverse and productive ecosystems. Home to a variety of plant life, including floating pond lilies, cattails, cypress, tamarack, and blue spruce, wetlands support diverse communities of invertebrates, which in turn support a wide variety of birds and other vertebrates. Primary consumers from crustaceans, mollusks, and aquatic insect larvae to muskrats, geese, and deer rely on the abundance of algae, plants, and detritus for food. Wetlands also support a variety of carnivores, including dragonflies, otters, alligators, and osprey. Thus, wetlands of the world maintain biologically diverse communities of ecological and economic value.
| Origin | Definition | Citation |
| US Fish and Wildlife Service (USFWS) | . lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Wetlands must have one or more of the following three attributes: 1. at least periodically, the land supports predominately hydrophytes; 2. the substrate is predominately undrained hydric soil; and 3. the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year. | Cowardin et al. 1979 |
| Ramsar Convention on Wetlands | Areas of marsh, fen, peatland, or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish, or salt including areas of marine water, the depth of which at low tide does not exceed 6 meters. | Finlayson & Moser 1991 |
| National Research Council (NRC) | The minimum essential characteristics of a wetland are recurrent, sustained inundation or saturation at or near the surface and the presence of physical, chemical, and biological features reflective of recurrent, sustained inundation or saturation. Common diagnostic features of wetlands are hydric soils and hydrophytic vegetation. | NRC 1995 |
| Table 1: Excerpts from three wetland definitions distinguishing wetland habitats from other ecosystems | ||
What may seem like a relatively straightforward task, developing a precise definition for wetlands presented some difficulty and resulted in many different definitions (Table 1). Part of the difficulty arises from the diversity of wetland types that exist around the world, from salt or brackish water coastal marshes and mangroves to inland freshwater swamps, peatlands, riparian wetlands, and marshes. Furthermore, as transitional areas, wetlands can possess characteristics of both terrestrial and aquatic ecosystems while also possessing characteristics unique unto themselves. Despite the diversity of wetland types, all wetlands share some common features. To be considered a wetland, an area must have:
Many ecologically and economically important species call wetlands home for at least part of their lives. For instance, commercially important fishes and shellfish, including shrimp, blue crab, oysters, salmon, trout, and seatrout rely on, or are associated with, wetlands. Wetlands are also critical habitat for migratory birds and waterfowl, including ducks, egrets, and geese. In fact, more than one-third of the species listed as threatened or endangered in the United States live solely in wetlands and nearly half use wetlands at some point in their lives (USEPA 1995). As such, many wetlands are often recognized as important conservation or restoration targets.
While covering only 6% of the Earth's surface, wetlands provide a disproportionately high number of ecosystem services, in addition to maintaining biodiversity. For instance, wetlands also mitigate floods, protect coastal areas from storms, improve water quality, recharge groundwater aquifers, serve as sinks, sources, or transformers of materials, and produce food and goods for human use. When evaluating the economic value of these various functions, Costanza et al. (1997) concluded that the economic value provided by wetland ecosystems exceeded that provided by lakes, streams, forests, and grasslands and was second only to that provided by coastal estuaries.
Increasing recognition of the value and importance of wetland ecosystems over the last century led to the creation of laws, regulations, and plans to restore and protect wetlands around the world. In the US, wetlands protection largely falls under the Clean Water Act of 1972, which requires permits for dredging and filling activities in most US wetlands and monitors water quality standards. Initiatives such as the "no-net-loss policy," which was recommended by the National Wetlands Policy Forum in 1988, aim to limit further wetland loss in the US, requiring wetland creation, restoration, or mitigation to offset wetland losses due to human activity. With mitigation, wetlands are created, restored, or enhanced to offset or replace wetland loss due to development. The Ramsar Convention, an international treaty aimed at conserving wetlands, requires member countries to develop national wetland policies, to establish wetland reserves, and to designate one or more wetlands as an area of international importance. All these efforts are designed to protect or conserve wetlands and the ecosystem services they provide.
