THE EFFECTS OF RED CLAY TURBIDITY AND SEDIMENTATION ON AQUATIC LIFE IN THE NEMADJI RIVER SYSTEM

Red clay erosion in southwestern Lake Superior has been a natural process along shorelines and in tributary streams and rivers since decline of lake levels following the Pleistocene period. Exposure of the unconsolidated glacial lake deposits resulted in fairly high and constant rates of erosion long before man began to alter the landscape. Rates of erosion along the Lake Superior shoreline have averaged up to 3.1 meters/year since 1938 (1) with contributions of 2· x. 106 metric tons of red clay soils annually ( 2). An additional 5.6 x 105 metric tons are added by stream erosion (3). There is evidence that rates of erosion were accelerated by logging operations during the late 1800's, but this increase probably did not add significantly to the impact of the red clays on the Lake Superior ecosystem.EP