Swamps, marshes, bogs, fens, sloughs, and bottomlands - we have many names for wetlands, but what makes a wetland a wetland? A single, comprehensive, universally accepted definition does not exist which concisely and accurately defines all wetlands. Because wetlands have diverse mixes of vegetation, from tidal marshes on the Atlantic and Pacific Coasts to bottomland hardwood forests along the Patoka River, varying degrees of water, from cypress swamps in Posey County to wet prairie in Lake County, and exist in many parts of the landscape, such as isolated pothole wetlands in Steuben County to backwater wetlands along the Wabash River, one definition could not possibly fit all wetlands.
Regardless, all wetlands do have some common traits, which help answer the question - what is a wetland. In general, wetlands are areas where water covers the soil, or is present either at or near the surface of the soil for part or all of the year, including the growing season for plants. Wetlands are in-between places, which lie between deep water in lakes and streams and dry land. Wetlands support an array of plants and animals which have adapted to life in saturated or flooded conditions. Wetlands have soils which differ from soils in dry areas, exhibiting characteristics that show the soil developed in saturated conditions. Wetlands can be identified by these basic indicators: vegetation, hydrology and soils. All three characteristics must be present during some portion of the growing season for an area to be a jurisdictional wetland - a wetland protected by the Clean Water Act.
For the purpose of regulation under the Clean Water Act, the U.S. Army Corps of Engineers (Corps) defines wetlands as:
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.
Listed below are descriptions of these indicators, which further explain the definition of wetlands.
In the United States, near 5,000 different plants may live in wetlands. These plants, known as hydrophytic vegetation, are listed in regional publications of the U.S. Fish and Wildlife Service. For example, cattails, bulrushes, sphagnum moss, bald cypress, willows, sedges, rushes, arrowheads and lily pads usually occur in wetlands. Plants which grow in wetlands also exhibit certain physical qualities, such as shallow root systems, swollen trunks, or roots found growing from the plant stem or trunk above the soil surface.
Approximately 2,000 named soils in the United States occur in wetlands. Such soils, called hydric soils, have characteristics that show they developed in conditions where the presence of water has limited soil oxygen for long periods during the growing season. If the Natural Resources Conservation Service (NRCS) has listed the soil in your area as hydric, the area might be a wetland. Hydric soil indicators include:
- Soil consists predominantly of decomposed plant material (peats or mucks).
- Soil has a thick layer of decomposing plant material on the surface.
- Soil has a bluish gray or gray color below the surface, or the major color of the soil at this depth is dark (brownish black or black) and dull.
- Soil has the odor of rotten eggs.
- Soil is sandy and has a layer of decomposing plant material at the soil surface.
- Soil is sandy and has dark stains or dark streaks of organic material in the upper layer below the soil surface.
Some wetlands are hard to recognize because they are dry during part of the year. Wetland hydrology refers to the presence of water at or above the soil surface for a sufficient period of the year to significantly influence the plant types and soils that occur in the area. Although the most reliable evidence of wetland hydrology may be provided by gauging station or groundwater well data, such information is limited for most areas and, when available, requires analysis by trained individuals. Thus, we observe most hydrologic indicators during field inspection. Most do not reveal either the frequency, timing, or duration of flooding or the soils saturation. However, the following indicators provide some evidence of the periodic presence of flooding or soil saturation:
- Standing or flowing water is observed on the area during the growing season.
- Soil is waterlogged during the growing season.
- Water marks are present on trees or other erect objects. Such marks show that water periodically covers the area to the depth shown on the objects.
- Drift lines, which are small piles of debris oriented in the direction of water movement through an area, are present. These often occur along contours and represent the approximate extent of flooding in an area.
- Thin layers of sediments are deposited on leaves or other objects.
There are a myriad of sources of information on wetlands, include scientific explanations, legal explanations, and technical manuals. This short list is meant to provide you with a place to continue your reading on this topic.
- U.S. Army Corps of Engineers: 1987 Wetland Delineation Manual [PDF]
- U.S. Army Corps of Engineers: Technical and Biological Resources
- U.S. EPA: America's Wetlands - Our Vital Link Between Land and Water
- U.S. EPA: Wetland Fact Sheets
- Wisconsin Dept. of Administration: Basic Guide to Wisconsin's Wetlands and Their Boundaries [PDF]