Types of Wetlands

Fresh or salt water? That's one of the first questions to ask when you are trying to determine the type of wetland. On the coast or inland? This is the second question. These answers will guide you to the five categories of wetlands recognized by most scientists and wetlands regulators: Marine (coastal, salt water), Estuarine (coastal, salt/freshwater mix), Riverine (associated with rivers and streams), Lacustrine (associated with lakes), and Palustrine (miscellaneous freshwater wetlands, generally shallow).

It's a good idea to use these terms when discussing wetlands with scientists or regulators; these terms have specific definitions and are not as variable as the common names that vary with region and country. For example, the words fen, bog, mire, peatland, and moor all refer to freshwater wetlands that produce peat. (Peat is the compressed layer of dead plants that resist decay in acidic wetland environments.) Yet these terms are also used colloquially: "...especially that boggy part on the curve." So was this person referring to a real bog or just a wet place? More likely the latter. If, however, you were to say "I have a wet area on my property; is it some kind of palustrine wetland?" This question eliminates saltwater marshes, estuaries, and lakeside wetlands. It will help the expert determine what kinds of plants, soils, and hydrology to look for.

Marine Wetland. Photo: © Carolyn Duckworth Estuarine Wetland. Photo: © U.S. Army Corps of Engineers Riverine Wetland. Photo: © USFWS Lacustrine Wetland. Photo: © Jennifer Whipple Palustrine Wetland. Photo: © U.S. Army Corps of Engineers

Marine Wetlands: Saltwater wetlands along coasts

Water levels rise and fall with the daily tides; they can be subject to the force of waves and storms and to ocean currents. Characteristics of marine wetlands vary with the level of tidal, wave, and current effects. Salt-tolerant plants called halophytes are dominant. Common halophytes include grasses such as Spartina species. Subtidal marine wetlands are submerged continuously; intertidal marine wetlands are periodically exposed.

Estuarine Wetlands: Coastal wetlands within estuaries (zones where fresh and salt water mix)

Estuarine wetlands usually have some access to oceans, with significant inflows of freshwater. Water levels rise and fall with the daily tides and can be subject to the force of waves and storms. Characteristics vary with the level of tides, waves and amount of salinity, which can vary with location and interactions with oceans and freshwater sources. Halophytes are dominant. Subtidal estuarine wetlands are submerged continuously, while intertidal estuarine wetlands are only periodically exposed.

The wetlands of estuaries, such as at the mouth of the Columbia River, also provide essential resting and feeding places for salmon.

Riverine Wetlands: Wetlands in the channels of rivers and streams

Riverine wetlands occur along streams, rivers, and irrigation canals throughout the United States. They are particularly noticeable in western states such as Idaho because they form ribbons of trees and shrubs in an otherwise arid landscape. You may have heard of these inland wetlands by their other name: riparian areas.

Riverine wetlands play an essential role in maintaining healthy streams and rivers. They typically support dense stands of trees such as cottonwood and quaking aspen, shrubs such as mountain maple and red alder, and grasses. These plants help bind the soil of banks, protect the banks from erosion during floods, and trap additional sediment from floodwaters.

The plants also provide habitat for wildlife. For example, birds - from tiny warblers to majestic bald eagles - use riparian areas for cover from the weather and for breeding, resting, and foraging sites. Many species of salmon are dependent on healthy riverine wetlands and riparian areas for survival.

Riparian habitat represents only about one percent of land in the Intermountain West, but scientists estimate that as much as eighty percent of the birds and other animals of the West depend on riparian habitats during all or part of their lives. Like other kinds of wetlands, riverine wetlands have been affected by human disturbance.

Lacustrine Wetlands: Wetlands around lakes and reservoirs

These freshwater wetlands form around the perimeter of lakes and reservoirs. They are larger than twenty acres or contain water depths of six feet. Like marine and estuarine wetlands, lacustrine wetlands are exposed to wave action.

Palustrine Wetlands: Isolated, inland wetlands not associated with lakes or reservoirs

Smaller and shallower than lacustrine wetlands, palustrine wetlands include marshes, wet meadows, bogs, potholes, and playas. Palustrine wetlands may be connected by surface or groundwater to rivers or lakes, or they may be isolated.

Forested palustrine wetlands occur in areas with abundant moisture, such as in the mountains. In the Rockies, look for them on the west side of watershed divides. For example, forest wetlands occur more frequently on the Idaho side of the Bitterroot Mountains, which receive more precipitation than the Montana side.

Forested wetlands are easily missed, but if you walk into a forest wetland, your senses will detect the difference. The air is often cooler, the ground damp if not soggy. Ferns and mosses may be abundant, and other understory plants thicker. Look for tamarack, western red cedar, and western hemlock.

In Idaho, forest wetlands provide habitat for several species of salamanders, toads, and several frogs. The Coeur d'Alene salamander exists only in moist forest areas of northern Idaho where rocky areas meet the wetlands.

More open areas, such as sloughs, feature many kinds of grasslike plants such as sedges, bulrushes, cattails, and reeds.

Other special types of isolated, palustrine wetlands include hot springs and vernal pools.

Hot springs, which are numerous in Idaho, provide warm wetland habitat that supports a variety of rare life. In no other wetlands will you find thermophiles - heat-loving micro-organisms. These warm wetlands also harbor rare plants such as giant helleborine and Jones' primrose. In the winter, hot springs provide food and water for many animals.

Vernal pools, also called ephemeral ponds, typically are wet in the spring after snowmelt or seasonally heavy rains. Their shallow, quickly disappearing waters cannot support fish; thus they provide essentially predator-free breeding areas for amphibians. Some scientists estimate that half of the amphibians in the U.S. breed only in these and other seasonal wetlands.

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