Swamp Wetland
Alacoque Whitchurch
One commonly used classification system for wetlands was developed by Cowardin and is described in Classification of Wetlands and Deepwater Habitats of the United States. The Cowardin system is used by the U.S. Fish and Wildlife Service for the National Wetlands Inventory. In this system, wetlands are classified by landscape position, vegetation cover and hydrologic regime. The Cowardin system includes five major wetland types: marine, estuarine, lacustrine, palustrine and riverine.
Another common wetland classification system, used by the U.S. Army Corps of Engineers, was developed by Brinson and is described in A Hydrogeomorphic Classification for Wetlands. As the title implies, wetlands are classified by their geomorphic setting, dominant water source (e.g. precipitation, groundwater or surface water) and hydrodynamics. The hydrogeomorphic (HGM) includes five major wetland types: riverine, slope depressional, flat and fringe.
Marshes are defined as wetlands frequently or continually inundated with water, characterized by emergent soft-stemmed vegetation adapted to saturated soil conditions. There are many different kinds of marshes, ranging from the prairie potholes to the Everglades, coastal to inland, freshwater to saltwater. All types receive most of their water from surface water, and many marshes are also fed by groundwater. Nutrients are plentiful and the pH is usually neutral leading to an abundance of plant and animal life. We have divided marshes into two primary categories: non-tidal and tidal.
Marshes recharge groundwater supplies and moderate streamflow by providing water to streams. This is an especially important function during periods of drought. The presence of marshes in a watershed helps to reduce damage caused by floods by slowing and storing flood water. As water moves slowly through a marsh, sediment and other pollutants settle to the substrate or floor of the marsh. Marsh vegetation and microorganisms also use excess nutrients for growth that can otherwise pollute surface water such as nitrogen and phosphorus from fertilizer.
Non-tidal marshes are the most prevalent and widely distributed wetlands in North America. They are mostly freshwater marshes, although some are brackish or alkaline. They frequently occur along streams in poorly drained depressions and in the shallow water along the boundaries of lakes, ponds and rivers. Water levels in these wetlands generally vary from a few inches to two or three feet, and some marshes, like prairie potholes, may periodically dry out completely.
Highly organic, mineral rich soils of sand, silt, and clay underlie these wetlands, while lily pads, cattails (see photo), reeds and bulrushes provide excellent habitat for waterfowl and other small mammals, such as Red-winged Blackbirds, Great Blue Herons, otters and muskrats. Examples of non-tidal marshes are: Prairie potholes, playa lakes, vernal pools and wet meadows.
Due to their high levels of nutrients, freshwater marshes are one of the most productive ecosystems on earth. They can sustain a vast array of plant communities that in turn support a wide variety of wildlife within this vital wetland ecosystem. As a result, marshes sustain a diversity of life that is disproportionate with their size. In addition to their considerable habitat value, non-tidal marshes serve to mitigate flood damage and filter excess nutrients from surface runoff.
Unfortunately, like many other wetland ecosystems, freshwater marshes have suffered major acreage losses to human development. Some have been degraded by excessive deposits of nutrients and sediment from construction and farming. Severe flooding and nutrient deposition to downstream waters have often followed marsh destruction and degradation. Such environmental problems prove the vital roles these wetlands play. This realization has spurred enhanced protection and restoration of marsh ecosystems, such as the prairie potholes and the Everglades.
Tidal marshes can be found along protected coastlines in middle and high latitudes worldwide. They are most prevalent in the United States on the eastern coast from Maine to Florida and continuing on to Louisiana and Texas along the Gulf of Mexico. Some are freshwater marshes, others are brackish (somewhat salty), and still others are saline (salty), but they are all influenced by the motion of ocean tides. Tidal marshes are normally categorized into two distinct zones, the lower or intertidal marsh and the upper or high marsh.
In saline tidal marshes, the lower marsh is normally covered and exposed daily by the tide. It is predominantly covered by the tall form of Smooth Cordgrass (Spartina alterniflora). The saline marsh is covered by water only sporadically and is characterized by Short Smooth Cordgrass, Spike Grass and Saltmeadow Rush (Juncus gerardii). Saline marshes support a highly specialized set of life adapted for saline conditions.
Tidal marshes serve many important functions. They buffer stormy seas, slow shoreline erosion and are able to absorb excess nutrients before they reach oceans and estuaries. Tidal marshes also provide vital food and habitat for clams, crabs and juvenile fish, as well as offering shelter and nesting sites for several species of migratory waterfowl.
Pressure to fill in these wetlands for coastal development has led to significant and continuing losses of tidal marshes, especially along the Atlantic coast. Pollution, especially near urban areas, also remains a serious threat to these ecosystems. Fortunately, most states have enacted special laws to protect tidal marshes, but diligence is needed to assure that these protective measures are actively enforced.
A swamp is any wetland dominated by woody plants. There are many different kinds of swamps, ranging from the forested Red Maple, (Acer rubrum), swamps of the Northeast to the extensive bottomland hardwood forests found along the sluggish rivers of the Southeast. Swamps are characterized by saturated soils during the growing season and standing water during certain times of the year. The highly organic soils of swamps form a thick, black, nutrient-rich environment for the growth of water-tolerant trees such as Cypress (Taxodium spp.), Atlantic White Cedar (Chamaecyparis thyoides), and Tupelo (Nyssa aquatica). Some swamps are dominated by shrubs, such as Buttonbush or Smooth Alder. Plants, birds, fish, and invertebrates such as freshwater shrimp, crayfish, and clams require the habitats provided by swamps. Many rare species, such as the endangered American Crocodile, depend on these ecosystems as well. Swamps may be divided into two major classes, depending on the type of vegetation present: shrub swamps and forested swamps.
Swamps serve vital roles in flood protection and nutrient removal. Floodplain forests are especially high in productivity and species diversity because of the rich deposits of alluvial soil from floods. Many upland creatures depend on the abundance of food found in the lowland swamps, and valuable timber can be sustainably harvested to provide building materials for people.
Due to the nutrient-rich soils present in swamps, many of these fertile woodlands have been drained and cleared for agriculture and other development. Historically, swamps have been portrayed as frightening no-man's-lands. This perception led to the vast devastation of immense tracts of swampland over the past 200 years, such as the destruction of more than half of the legendary Great Dismal Swamp of southeastern Virginia.
Forested swamps are found throughout the United States. They are often inundated with floodwater from nearby rivers and streams. Sometimes, they are covered by many feet of very slowly moving or standing water. In very dry years they may represent the only shallow water for miles and their presence is critical to the survival of wetland-dependent species like Wood Ducks (Aix sponsa), River Otters (Lutra canadensis) and Cottonmouth Snakes (Agkistrodon piscivorus). Some of the common species of trees found in these wetlands are Red Maple and Pin Oak (Quercus palustris) in the Northern United States, Overcup Oak (Quercus lyrata) and Cypress in the South, and Willows (Salix spp.) and Western Hemlock (Tsuga sp.) in the Northwest. Bottomland hardwood swamp is a name commonly given to forested swamps in the south central United States.
Shrub swamps are similar to forested swamps except that shrubby vegetation such as Buttonbush, Willow, Dogwood (Cornus sp.) and Swamp Rose (Rosa palustris) predominates. In fact, forested and shrub swamps are often found adjacent to one another. The soil is often water logged for much of the year and covered at times by as much as a few feet of water because this type of swamp is found along slow moving streams and in floodplains. Mangrove swamps are a type of shrub swamp dominated by mangroves that covers vast expanses of southern Florida.
Bogs are one of North America's most distinctive kinds of wetlands. They are characterized by spongy peat deposits, acidic waters and a floor covered by a thick carpet of sphagnum moss. Bogs receive all or most of their water from precipitation rather than from runoff, groundwater or streams. As a result, bogs are low in the nutrients needed for plant growth, a condition that is enhanced by acid forming peat mosses.
There are two primary ways that a bog can develop: bogs can form as sphagnum moss grows over a lake or pond and slowly fills it (terrestrialization), or bogs can form as sphagnum moss blankets dry land and prevents water from leaving the surface (paludification). Over time, many feet of acidic peat deposits build up in bogs of either origin. The unique and demanding physical and chemical characteristics of bogs result in the presence of plant and animal communities that demonstrate many special adaptations to low nutrient levels, waterlogged conditions, and acidic waters, such as carnivorous plants.
Bogs serve an important ecological function in preventing downstream flooding by absorbing precipitation. Bogs support some of the most interesting plants in the United States (like the carnivorous Sundew) and provide habitat to animals threatened by human encroachment.
c80f0f1006