Water Habitats: Wetlands
We've all heard of bogs, swamps, salt marshes, and ponds. You might even be lucky enough to live near one, or have an idea of what they look like. What you may not know is that they are all classified as wetlands. A wetland is any place on land where a large area is saturated with water permanently or seasonally. Mangrove forests, vernal pools, and riparian forests are all examples of different types of wetlands. There are wetlands on every continent except Antarctica, and scientists consider them the most biologically diverse of the ecosystems.
There are three major factors scientists consider when classifying a wetland: the water, the soil, and the plants present in the ecosystem. One of these factors may be enough to determine if an area is a wetland, but usually it is a combination of these factors.
In order to have a wetland there must be water. However, there may be areas that look completely dry that are still considered wetlands. A wetland is any area that is inundated (flooded) or saturated for a certain number of days that add up to 7.5% of the growing season in an area. The growing season begins when the first buds appear on plants and ends with the first frost. For the rest of the year the area could have no water at all.
The water in a wetland is one of three types: saltwater, brackish, or freshwater. Saltwater wetlands are often found along seashores. Their water is salty due to coastal tidewater inundating the area. Brackish wetlands exist in places where inland freshwater mixes with saltwater. Most brackish wetlands are marshes where tidal flood-waters mix with mainland runoffs like rivers and streams. Freshwater wetlands exist inland along streams and ponds, or where freshwater gathers.
The soil in wetlands is called hydric soil. Hydric soils are those that are wet long enough during the growing season that create anaerobic (without oxygen) conditions. This is an important difference from regular soils where oxygen is present. Without oxygen in the soil, a plant's roots are unable to respire. The anaerobic conditions in hydric soil create a place where hydrophytes (water-loving plants) and aquatic organisms thrive.
Wetland soil layers may be either organic or mineral. Organic soils are characterized by a deep layer of decaying plant matter at the soil surface. This organic layer grows thicker as dead plant matter accumulates faster than it can decompose under anaerobic conditions. Mineral soils are made of sand, silt, clay, and elements such as iron and manganese. In hydric soils the surface organic layer may be very thick or thin, depending on if it is being washed away, and the oxidized soil layer is either very thin or missing. The mottled layer may be thick or thin, depending on how often water is present and how much the water table changes. The gleyed layer is often very close to the surface, especially if water is present all the time.
Since there is a lot of water in the soil and very little oxygen, the plants that grow in wetlands are specially adapted to survive in this unique environment. We call these plants hydrophytic plants. Some hydrophytic plants are able to survive when completely submerged, and others float on the water's surface without definite roots. In areas with brackish water, plants have evolved to survive in both fresh and salt water. Some plants have even evolved to eat insects! Common hydrophytic plants that you may already know are water lilies, cattails, and water grasses.
If you would like to learn more about hydrophytic plants, the University of Florida has compiled a list of native and non-native plants that call their wetlands home.
Although scientists don't use animals to determine which areas are wetlands, they are an important part of the wetland ecosystem. Wetlands contain animals of all shapes and sizes, from the gigantic moose to the tiny dragonfly nymph. They are home to hundreds of different species, and are an important stopover for migratory birds. Hundreds of animals you can't see, some so small you'd need a microscope to find them, call wetlands home. Most animals that live in wetlands have adapted to living partially submerged all year.
The University of Vermont has a short list of the animals found in Louisiana's coastal wetlands. There are over 735 different species in the wetlands of this state. Imagine how many live in wetlands around the world!
Do you know the difference between these types of wetlands? Here's a helpful list of the different types of wetlands and how they are defined.
Common Wetland Habitats
Bog - wetland ecosystem that is high acidic and has an accumulation of dead plants known as peat.
Swamp - wetland characterized by trees and shrubs.
Saltwater Marsh - found along the shores of bays and rivers, it is a community of plants living in salty soil that is flooded and exposed by alternating tides.
Freshwater Marsh - community of plants living in freshwater found along ponds, lakes, streams, and some rivers.
Prairie Pothole - wetland found in the grasslands of central North America.
Mangrove Forest - fresh or saltwater wetland found in tropical areas such as Africa, Mexico, coastal Australia, and the southern United States.
Sandy Beach - sandy soil containing vegetation such as beach grasses, often found along the ocean and on bays and some rivers.
Vernal Pools - bodies of water that often exist only during the spring and dry up for the rest of the year.
Interested in learning more about wetlands?
- Wetland Habitats
- What Lives in Wetlands?
- Identification, Delineation, and Mitigation of Hydrophotic Plants
- What are Wetlands?
- Wetlands of the World (PDF)
- Why Restoring Wetlands is More Critical Than Ever
- From Wetland to Wasteland: The Destruction of the Hamoun Oasis
- National Wetlands Inventory
- Biomes: Wetlands
- Wetland Types
- Wetlands Fact Sheet (PDF)
- Recognizing Wetlands (PDF)
- Inland Wetlands (Non-Tidal)
- Wetlands: Wonderlands Not Wastelands
- What is a Wetland?
Written By: Lynn Taylor