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The two areas selected for study, the north coast of the Keweenaw Peninsula and the western embayment of Lake Superior near Duluth-Superior, differ greatly in their mixing and dispersal characteristics. Nearshore turbidity along the Keweenaw Peninsula contrasts to relatively large turbid eddies off of Duluth-Superior. Turbidity along the north coast of the Keweenaw Peninsula is frequently confined to an even narrower coastal area later in the summer which is under the influence of the strong, well-defined coastal current. Flowing northeast along the north shore of the Keweenaw Peninsula during the summer months, the Keweenaw current follows the coast at speeds ranging from 40 to 90 cm/sec. (Yeske, 1973). Although sometimes narrower, the Keweenaw current normally ranges in width from five to ten kilometers. The surface thermal structure of this current indicates the presence of eddies, meanders, and counter-currents (Ragotzkie, 1966; Smith, 1972). Other studies of the Keweenaw Current structure include Ragotzkie and Bratnik (1965), Smith and Ragotzkie (1970) and Yeske, et. al. (1972).
This report is a sedimentation study, forming part of an assessment of environmental impacts associated with in-lake disposal of dredge spoil on Lake Superior. This assessment was requested by the St. Paul District Office of the US Corps of Engineers and funded under contract number DACW37-74-C-0013 to the University of Wisconsin-Madison in August, 1973. Field and laboratory studies focused on two locations where a substantial amount of dredging is done annually: Duluth-Superior and the Keweenaw Waterway.
This project was funded by the Corps of Engineers to study effects of in-lake dredge spoil disposal on toxicity and availability of heavy metals to the biota of Lake Superior. Attention was focused on the benthic organisms in direct contact with the sediment. In the laboratory sublethal bioassays were used to examine effects of mercury and zinc contaminated sediments on the burrowing scud, Pontoporeia affinis. This amphipod is the predominant benthic invertebrate in Lake Superior and a major food base for Lake Superior fishes. Changes were observed in locomotor activity of Pontoporeia as a measure of their health on sediments with and without added mercury and zinc, and whole body concentrations of these metals were measured in Pontoporeia after exposure to the enriched sediments for periods of two days to two weeks. The benthic communities near Duluth-Superior were surveyed and maps showing distribution and abundance of organisms were prepared. Samples were collected for background levels of various elements in sediments, invertebrates, and fish in Lake Superior. Shorebird populations were surveyed at Duluth-Superior and the Keweenaw Peninsula. The authors also worked with scientists at Michigan Technological University to obtain similar information for the Corps of Engineers at the Keweenaw Waterway and adjacent Lake Superior.