Sampling sites in the western tip of Lake Superior and the Duluth-Superior harbor. (A) Locations of the DBC, LRII, and BBL sites. (B) DBC is located within the Duluth-Superior harbor (46°46.16′N, 092°05.40′W). (C) LRII is located along the north shore of Lake Superior at the outer urban limits of Duluth (46°50.23′N, 092°00.15′W). (D) BBL is located along the north shore of Lake Superior about 25 km from downtown Duluth (46°55.06′N, 091°51.15′W).