One way to learn about the Great Lakes is to start by exploring the region’s coastal wetlands. Scattered throughout the Great Lakes basin, coastal wetlands are among the region’s most ecologically valuable and productive habitats.
Fish and wildlife depend on coastal wetlands for food and shelter. Scientists estimate that two thirds of all Great Lakes fish use coastal wetlands for spawning and reproduction.
Coastal wetlands also play an essential role in maintaining the health of the Great Lakes aquatic ecosystem by providing several important functions. They:
- Improve Great Lakes water quality by filtering pollutants and sediment;
- Store and cycle nutrients and organic material from land into the aquatic food web;
- Reduce flooding and erosion during periods of high water.
There are several different types of coastal wetlands in the Great Lakes basin. They vary in size and structure, but all are connected to the Great Lakes either by surface water or groundwater.
Here are some common types of Great Lakes coastal wetlands.
These bodies of Great Lakes water are partly protected from the full force of the lakes. They may be open embayments, which are protected by the curvature of the Great Lakes shoreline. Or they may be protected embayments, which are carved into the shoreline and protected by features such as sand spits.
The mouth of the St. Clair River is a good example of a river delta. River deltas form when sediments flow downstream and build up near a river’s mouth. This process produces slower currents that allow sediment to accumulate, forming islands and bars. The channeled water produces a branched system of waterways, vegetation, mud flats and pools.
Dune and Swale
These unique habitats feature an alternating pattern of narrow sandy ridges and saturated depressions (or swales) parallel to a lakeshore. This topography formed when glaciers retreated and left behind mounds of sand and sediment in a series of dunes or ridges. A good example of a dune and swale habitat is located near Sturgeon Bay in northwest Michigan. The habitats provide excellent habitat for many migratory bird species.
Drowned River Mouth
These flooded areas are characterized by a permanent channel that meanders through a flood plain. This habitat is partly separated from the Great Lakes by sandy or rocky spits. Marshes often form in the calmer areas behind the spits and provide important spawning and nursery areas for fish and migrating waterfowl. The spits, if forested, often have high concentrations of migrating landbirds.
One habitat closely related to coastal wetlands is called an emergent marsh, which is linked to fluctuating Great Lakes water levels. When water levels fall, for instance, open mudflats are exposed and eventually sprout with vegetation, creating an emergent marsh. These areas are among the most productive of all habitats for waterfowl and other waterbirds. Large marshes or marshes within a wetland complex often support a diverse breeding bird community because of the variety of habitat conditions. The Red-necked Grebe, Least Bittern, Redhead, Ruddy duck, and Marsh wren are among the bird species that nest exclusively in emergent marshes.