Ecological Restoration of Grassy Island and the Wyandotte National Wildlife Refuge in the Detroit River

Bruce A. Manny, U.S. Geological Survey
Biological Resources Division, Great Lakes Science Center

Introduction and History

Grassy Island appears on maps of the Detroit River dating back to 1796 as a marshy area about 2.4 ha (6 acres) in size west of Fighting Island and north of Grosse Ile. Then, the river bottom around the island sloped gradually off on all sides into deeper channels. This area was first called "Ile Marecageuse" on a map compiled in 1796 and "Grassy Island" on later maps. An 1873 fisheries report contains a line drawing of the "Grassy Island Pond Fishery" for spawning whitefish that shows a large seine being drawn in by two horse-drawn windlasses inside two of several sheds constructed on the island (Milner 1873). This enterprise employed 30 men, working night and day, September to November and produced 45,000 adult whitefish per spawning season. Thereafter, the U.S. Coast Guard installed three navigation lights near the island for ships down bound in the Fighting Island Channel. In 1959, the island area began to be used by the Army Corps of Engineers (ACOE) as a Confined Disposal Facility (CDF) for polluted dredge spoils.

In 1955, Grassy Island was under the jurisdiction of the U.S. Treasury Department, which had reserved it for installation of navigation aids by the U.S. Coast Guard (Larson 1981). In September 1959, the ACOE began diking a proposed 121 ha (300 acre) area around Grassy Island for disposal of dredge spoils from the Rouge River. In October 1959, at a meeting between the ACOE, the U.S. Bureau of Sport Fisheries and Wildlife, and the Michigan Department of Conservation, Congressman John D. Dingell negotiated an agreement that the ACOE could continue construction of the Grassy Island CDF. In January 1960, Mr. Dingell introduced federal legislation to designate Grassy Island and surrounding shoals as a National Wildlife Refuge because wild celery (Vallisneria americana) is abundant and widely distributed near Grassy Island and is the preferred food of diving ducks, such as canvasbacks, redheads, and scaup. The area attracts thousands of diving ducks during their fall and spring migration when these ducks consume large numbers of wild celery tubers (Manny et al. 1988). In July 1960, the Department of Interior agreed that at such time as the Interior Department received jurisdiction over the Grassy Island area, it would not object to continued use by the ACOE of the a 29 ha (72 acre) CDF for dredge spoils from the Rouge River (Larson 1981). An act to create the Wyandotte National Wildlife Refuge, including Grassy Island and surrounding shoals out to a water depth of 2 m (6 ft) and an area of about 121 ha (300 acres extending downstream to the Mamajuda Light near Point Hennepin), became law on August 3, 1961 (Larson 1981). Grassy Island is presently administered as a satellite under the Shiawassee National Wildlife Refuge of the Fish and Wildlife Service near Saginaw, Michigan.

Grassy Island was originally a marshy, low-lying area of emergent and submersed vegetation that might be classified today as a Great Lakes coastal marsh. On an 1815 map, such marshes are contiguous along both sides of the entire 51 km (32 mile) length of the Detroit River. However by 1982, such habitat had been reduced by shoreline development to less than 3% of its original area in Michigan waters. Today, only remnants of that marsh, such as Humbug Marsh and portions of Stony Island and Gilbraltar Bay at the southern end of Grosse Ile, remain in Michigan waters of the river. These remnants contain stands of bottom-land hardwoods, glacial lakeplain prairie, coastal plain pond communities, and a variety of wetland types. Such coastal marshes are used as spawning, nursery, feeding, migration, overwintering, and refuge habitat by many of the 47 species of fish that spawn in the lower Detroit River, including northern pike, muskellunge, largemouth and smallmouth bass, walleye, and possibly lake sturgeon, and as feeding and resting habitat by more than 17 species of birds of prey (raptors), including eagles, hawks, falcons, and kestrels, and 48 species of non-raptors, including loons, herons, neotropical songbirds, cranes, and cattle egrets, that migrate through the Detroit River area each year.

Comparison of Detroit River maps drawn in 1815 and 1982 reveals that: over 97% of wetlands in Michigan waters have disappeared under shoreline modifications; 90% of the remnant wetlands in the Detroit River are found downstream of Grassy Island; and about 40% of these remnant wetlands are in Humbug Marsh and on small, undeveloped islands forming the "Conservation Crescent" around the southern tip of Grosse Ile (Jones 1997). Because wetland habitats are essential to a high diversity of fish and wildlife species at various stages of their life cycle, such Great Lakes coastal marshes have been classified as globally unique and significant in biological diversity by The Nature Conservancy (1994).


In 1994, Grassy Island on the Wyandotte refuge was selected by the U.S. Department of Interior as a demonstration site for hazardous materials management. The goal of the initiative is to demonstrate the ability of Interior bureaus to work together to develop remedial action plans and field test innovative technologies for cleanup of Interior lands. The objectives are to address concerns about land use requirements, trust responsibilities, environmental protection, and natural resource management, while achieving cleanup goals more rapidly and at less cost than current methods. In 1997, the U.S. Geological Survey's Biological Resources Division investigated contamination of surficial soils on Grassy Island and of wild celery tubers growing on shoals surrounding the island. Then also, the Survey's Water Resources Division investigated groundwater movements around the island and contaminants in subterranean soils and water.


At least 20 species of submersed aquatic macrophytes occur in the Detroit River: wild celery (Vallisneria americana), water stargrass (Heteranthera dubia), waterweed (Elodea canadensis), Eurasian watermilfoil (Myriophyllum spicatum), bushy pondweed (Najas flexilis) and redhead grass (Potamogeton richardsonii) predominate in the vicinity of Grassy Island (Schloesser and Manny 1986). Shallow water habitat, gradually sloping off into deeper waters, exists only on the west side of Grassy Island in a small 9.1 ha (20 acre), unnamed embayment. Wild celery is abundant and widely distributed near Grassy Island. Because it is the preferred food of canvasbacks, redheads, and scaup, the refuge attracts and holds thousands of diving ducks during their fall and spring migrations. Because of its strategic location, its continued supply of food resources, and secure resting space it provides in an area heavily impacted by human activities, the Wyandotte National Wildlife Refuge and Detroit River are mentioned as essential waterfowl habitat in the North American Waterfowl Management Plan.

Terrestrial plants on Grassy Island include giant reed grass (Phragmites communis), cattails (Typha spp.), as well as aspen, cottonwood, willow, wild cherry and box elder trees that provide little suitable habitat for animals. Wildlife use of small ponds on Grassy Island has not been fully characterized.

Lake sturgeon once spawned on the rocky bottom in swift currents just northeast of Grassy Island, one of seven historic spawning areas in the Detroit River (Goodyear et al. 1982). This fish is listed as "threatened" by 19 of the 20 states in its original range, and by seven of the eight Great Lakes states, including Michigan. Recent, incidental catches of genetically unique, juvenile lake sturgeon in Lake Erie near the Detroit River suggest that sturgeon are reproducing again in the Detroit River. More than 10 million walleye, white bass, steelhead, and salmon migrate through the Detroit River each year and attract many sport fishers to the refuge.

Bald eagles, a federally endangered species, have nested recently near Grassy Island and tens of thousands of canvasback and redhead ducks winter on the refuge. Pheasant, swallow, red-wing blackbird, gulls, terns, Canada geese, woodcock, wood duck, loon, kingfisher, and many species of shore birds inhabit the refuge.

Coyote, gray fox, whitetail deer, raccoon, woodchuck, spotted turtle, and muskrat have either been seen or identified by signs they left on Grassy Island. Two years ago, a family of river otter were seen near the lower Detroit River, beaver have recently returned to nearby Livingston, Oakland, and Washtenaw Counties, and in 1998 a wild black bear wandered down the I-75 right-of-way into suburban Detroit. This was the first sighting of a wild black bear in Oakland County since the early 1800s. In time, some of these animals may recolonize the Wyandotte refuge.

Effectiveness and Further Steps

The Grassy Island CDF contains no impermeable liner or cap and ponds on it are above river level. Therefore, the potential for leakage of contaminants from the Grassy Island CDF is being evaluated. Pathways for contaminant movement include leakage under the dike and exposure to dredge spoils at the island's surface. The risk to biological resources posed by exposure to contaminants in the river and on the island needs to be assessed.

The quality of existing habitats for production of fish and wildlife is low on Grassy Island, due to the monotypic dominance of giant reed grass and exposure to dredged sediments, and medium on shoals surrounding Grassy Island, due to contamination of river bottom sediments. The condition of historic fish spawning grounds on the refuge is unknown. The amount of marsh vegetation on the Wyandotte refuge is limited.

Questions which the U.S. Geological Survey's Biological Resources Division may address in the future include:

The little remaining riverside marsh and shallow-water habitat on gradually sloping, undeveloped shorelines in the Detroit River now limits the production of many resident fish and wildlife species there. The Wyandotte National Wildlife Refuge has potential for restoration of diverse habitats that would sustain unique and globally significant, resident and migratory, fish and wildlife.

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