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Definitions

What is a wetland? Current definitions include three main components: (1) the presence of water at the surface or within the root zone, (2) unique soil conditions that differ from adjacent uplands, and (3) vegetation adapted to the wet conditions (Mitsch and Gosselink 2000). Precise wetland definitions are needed by wetland managers and regulators as well as wetland scientists (Mitsch and Gosselink 2000). The wetland regulatory definition used to establish Federal jurisdiction for the wetland permitting program under section 404 of the Clean Water Act is:

…those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas [33 CFR 328.3(b); 1984].

This definition of wetlands outlines the three parameters necessary for wetland development, namely hydrology, vegetation, and soils. The site-specific criteria for determining the extent to which these three parameters exist in the field is contained in the 1987 Federal Manual for Determining Wetland Boundaries (U.S. Army Corps of Engineers 1987) which is used to determine the geographic boundaries of wetlands in the United States.

The wetland definition adopted by scientists in the U.S. Fish and Wildlife Service for the purposes of inventorying wetland resources in the United States is:

Wetlands are 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 predominantly hydrophytes, (2) the substrate is predominantly 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 and others 1979).

This definition is the standard for the NWI and is the national standard for wetland mapping, monitoring, and data reporting as determined by the Federal Geographic Data Committee (Dahl 2000).

Once a wetland-upland boundary is defined and delineated, the quality or capability of the wetland to function becomes a concern. There is great diversity in the types of wetlands in the South, the functions they perform, and the goods and services they provide society. To deal with this diversity, wetlands are grouped according to factors that substantially contribute to wetland functioning. Hydrogeomorphic (HGM) classification (Brinson 1993) groups wetlands based upon their landscape position, water source, and hydrodynamics. By grouping or classifying wetlands using the HGM classification, the presumption is that wetlands with similar landscape position, water source, and hydrodynamics will function similarly. In the Southern United States, most forested wetlands are classed as riverine, flat, and depression wetland. Much of the following discussion deals with these three classes.