Wetlands

Wetlands are areas in which shallow standing water or saturated soil occurs for a period long enough or with enough regularity to influence the development of biotic assemblages and/or soil characteristics. Wetlands can be fresh, brackish or saline, can be inland or coastal, can be connected to or isolated from other aquatic systems, and are generally shallow enough to support rooted vegetation that emerges from the water surface, even if that vegetation is not present at all times. Wetlands are locations of focused ecological flows and changes of state. Many inland wetlands, for example, are areas of groundwater discharge or recharge. In recharge wetlands, nearby contaminants may easily enter the groundwater profile; conversely, in discharge wetlands, rare biotic communities may be supported by the outflow of nutrient-rich groundwater. Coastal wetlands are the site of important ecological interactions between marine and terrestrial environments, where the larval and juvenile stages of many marine animals are supported by nutrient fluxes from the nearby landmass.

Wetlands can be classified by hydrology, which is a function of climate and the wetland's position in a landscape. Wetlands perched high in a watershed will tend to be recharge wetlands, where precipitation and surface water become groundwater. They may be ephemeral, rather than permanent. Because precipitation is nutrient-poor, they may be oligotrophic or have low species diversity. Wetlands in the [Page 1946]middle of a watershed will tend to be flow-through systems, experiencing groundwater discharge and recharge, and are more likely to be biotically diverse and permanent. Wetlands low in a watershed are likely to be permanent, experiencing groundwater discharge and/or fringing larger water bodies such as lakes, rivers, and oceans. Fens are wetlands that are largely dependent on groundwater for their hydrology; their ecology is highly dependent on the chemistry of the groundwater, and very sensitive to groundwater fluctuations. Fens in areas of limestone bedrock often receive very calcium-rich water, and are known as calcareous fens or marl flats, hosting a highly specialized flora. Bogs are wetlands that are largely dependent on rainwater for nutrients and hydrology (ombrotrophic), and tend to be low-diversity and nutrient-poor.

Biotic community and habitat can also classify wetlands. The Western folk taxonomy of wetlands relies primarily on vegetative structure, distinguishing “swamps” (forested wetlands) from “marshes” (grassy wetlands). Community composition is often effective shorthand for classifying certain wetland types dominated by characteristic vegetation, as with the cordgrass marshes of the American East Coast, or the mangrove swamps of tropical coasts worldwide. Wetlands serve to store surface water in a landscape, often reducing, delaying, and desynchronizing flood peaks. Coastal wetlands often act to reduce storm surges and coastal erosion; the loss of wetlands in coastal Louisiana was widely cited in 2005 as a culprit in the devastation caused by Hurricane Katrina. Wetlands provide essential habitat for many species, including most game birds and a large number of endangered species. Wetland soils, rich in organic matter, have proven extremely productive under agriculture once the technical challenges to draining were overcome in the early 1900s.

Wetlands have long been seen as waste areas to be reclaimed or ignored, and the many synonyms have also served as metaphors for undesirability or difficulty, such as: Swamped, quagmire, spewy, or bogged down. Few, even among the European and American Romantic tradition in the 1800s, saw transcendent beauty in wetland areas. They have been associated in many cultures with wilderness or the supernatural and nonhuman, and used as burial places or as refuges from colonial incursion and control. Control over wetlands, using large-scale technologies of drainage, is often linked to state expansion and the assertion of control over state territory (for example, in the Florida Everglades, Italy's Pontine Marshes, and the Tigris/Euphrates marshes in Iraq). Only with the 20th-century environmental movement, and the publication of such popularscience books as Bill Niering's Life of the Marsh, have wetlands become the object of societal concern, aesthetic appreciation, and legal protection at the local, national, and international level. They are one of the few ecosystems defined by statute: The U.S. federal government defines them as “those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions” (40 CFR 232.2).

...