A SURVEY OF SAGINAW RIVER AND SAGINAW BAY, LAKE HURON, SEDIMENTS USING 2 BIOASSAYS WITH THE AMPHIPOD DIPOREIA SPP

The Saginaw River and Saginaw Bay ecosystem is identified as an Area of Concern by the International Joint Commission for recognized anthropogenic contamination, which includes sediments. The potential impact of sediment-associated contamination of Saginaw Bay and Saginaw River was evaluated by employing two solid phase bioassays with the amphipod Diporeia spp. (formerly named Pontoporeia hoyi). Two effects examined in the bioassays were mortality after 28 d and avoidance/preference for the sediments after 5 d. Saginaw Bay Station S-61, located off the coast of Tawas Bay, was the only location where bay sediment elicited significant mortality. Although sediment preference tended to increase from the inner bay to the outer bay with S-61 the most preferred, there were no statistical differences among stations. River sediments from all stations collected in December 1989 produced significant mortality, with sediments from Station SR-106, just below the Bay City Waste Water Treatment Plant out-fall, producing the greatest response. Sediments from SR-106 were also the most avoided of the river sediments from this first collection. A subsequent collection of sediments in June 1990 from the Saginaw River produced no mortality and no significant avoidance of the sediments. The results from these two bioassay methods suggest the presence of potential contaminant problems in both the bay and river, and indicate that both lethal and sublethal effects may occur.