Skip common site navigation and headers
United States Environmental Protection Agency
Great Lakes Ecosystem
Begin Hierarchical Links EPA Home > Great Lakes EcosystemsWetlands > Abiotic & Floristic Characterization: Plate 4
Major Findings: Abiotic Factors
Major Findings: Vegetation Analysis
List of Tables
List of Figures
List of Plates


Great Lakes Coastal Wetlands: Abiotic and Floristic Characterization

Plate 4.  Wetland Site Types of Riverine and Estuarine Systems

Deltas form when stream sediments are deposited and accumulate at the mouth of a river creating multiple shallow channels, low islands, and abandoned meanders that can allow for extensive wetland development. Wetland habitats within the delta range from the generally sandy or gravel substrates and swift current of the main channel, to the more protected secondary channels, where the slow to non-existent current permits thick accumulations of organics. Delta formation is best developed in areas of low gradient flow, where nearshore currents are relatively weak and thus do not rapidly remove deposited material.

Delta of the Sturgeon River in Portage Lake, Upper Peninsula, MichiganPlate 4a. Delta of the Sturgeon River in Portage Lake, Upper Peninsula, MI. The Sturgeon River drops its sediment load as it enters Portage Lake, creating a well-developed delta. Several old meanders and oxbow ponds are clearly visible within the delta. (1978 color infra-red photography, Michigan Department of Natural Resources).

Lacustrine or freshwater estuaries, formed where some tributary rivers enter the lakes, represent a zone of transition from stream to lake within which water level, sedimentation, erosion, and biological processes are controlled by fluctuations in lake level. Most Great Lakes estuaries were formed as buried river mouths, when stream channels cut during an earlier time were drowned or buried by the subsequent rise in the Great Lakes to present water levels. Fairly steep upland slopes help shield the estuary, while reduced water velocities lead to deep accumulations of organics; the result is a protected, fertile (but topographically circumscribed) wetland. Longshore transport and infilling may modify the submerged river mouth, leading to distinct estuarine forms with different wetland characteristics.

Open Estuary at Sand River, Bayfield County, WisconsinPlate 4b. Open Estuary at Sand River, Bayfield County, WI. Estuaries that are open to the lake typically display a branching inlet pattern that clearly reveals their origin as a drowned river mouth. Sand bars have formed at the mouth of this estuary, but do not appear to seriously impede water flow. (Photo by Eric Epstein, 1996).


Barred Estuary at Salmon River, New YorkPlate 4c. Barred Estuary at Salmon River, NY. Longshore transport has nearly barred this estuary by depositing a barrier dune across its mouth, slowing river discharge into Lake Ontario and forcing the river to meander broadly. The opening at the river mouth is now maintained by jetties. (Photo by John Griebsch 1990).

Begin Site Footer

EPA Home | Privacy and Security Notice | Contact Us