SEDIMENTATION IN WESTERN LAKE SUPERIOR

The single largest source of sediment to Lake Superior is the eroding red clay bluffs of the Wisconsin shoreline between the Apostle Islands and Duluth. One contributing source from the red clay bluff area is the Nemadji River. This project’s objective is to determine the extent of the Nemadji River plume in Lake Superior. Based on the bathymetry and echo sounder profiles, 63 sediment grab samples were taken and described. Samples were analyzed for water content, organic carbon, and grain size. For most of the lake, storm wave activity prevents the accumulation of fine-grained sediments in water depths of less than 100 meters; however, preliminary results indicate deposition of silt/clay size particles in water depths as shallow as 20 meters near the Nemadji River mouth. We have mapped the south/southeastern boundary of the footprint, and we are in the process of delineating the northern and western boundaries of the footprint. This footprint of plume sedimentation is important in determining the fate and dispersal of sediment from the Nemadji River.