Cofrin Center for Biodiversity

Airphotos illustrate effect of water level change in Green Bay on coastal marshes

As the water level of Green Bay (Lake Michigan) rises and falls it has a profound effect on the coastal marshes. Water level on Green Bay regularly rises and falls in a roughly cyclical pattern of about 10 to 20 years that has been observed and recorded since the late 1800's. When the water is high most of the marsh vegetation dies. When the water falls the vegetation recolonizes the exposed area, primarily from seeds residing in the mud. If the water falls far enough the marsh vegetation will be replaced by sedge meadow, willows and alders, or even trees. When the water rises again these plants will also die, and the cycle will repeat.

The plants of the west shore wetlands are adapted to this pattern of rising and falling water levels and indeed the diversity of the plants in the wetlands would be severely reduced if water levels were fixed. In the series of photos below you can see the effects of changing water level on a Green Bay coastal marsh known locally as Peters Marsh. The pictures vary in angle of view.

Year	Comment	click image for enlargement
1974	This was near record high water level (new records were set in 1986). Most of the marsh is submersed and was eventually reduced to a very small area
1976	The water level fell, exposing extensive areas of mud in 1976.
1980	The area of exposed mud in 1976 is now covered by marsh
1985	Rising water level has begun to reduce the area of marsh.
1986	Prolonged high water has flooded the marsh. A new record was set for high water level in Lake Michigan in 1986.
1988	The falling water level is followed by an expansion of the marsh vegetation
1999	Rapidly falling water levels have exposed areas which have not been seen in the last 3 decades. The pale brown/whitish areas are recently exposed sand which has been submersed for over 30 years.

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects