A paleolimnological assessment of human impacts on Lake Superior

Abstract

To understand environmental conditions in Lake Superior over the last two centuries, we conducted a paleolimnological study on two sediment cores collected in the eastern and western regions of the lake. We examined the diatom fossil assemblages, sedimentation rates, organic and trace metal accumulation rates, and GIS-reconstructed human land use stressors in order to evaluate lake history and the impacts of human activities. There is evidence that the diatom community reorganized due to nutrient enrichment beginning around the time of European settlement and significant agricultural development. Trace metal profiles tracked a period of mining and ore processing which temporarily increased trace metal loads to the lake in the mid- to late-20th century. In recent decades, more oligotrophic diatom species were favored, suggesting nutrient decreases associated with remedial activities. The diatom community is now dominated by the Cyclotella comensis complex, suggesting changes in the lake's physical and chemical processes associated with climate change. Similar long-term environmental trends were observed in both core locations, but the timing of some events differed, indicating localized effects such as nutrient enrichment. An understanding of Lake Superior's past responses to human activities can inform management decisions that account for influences within and outside the lake's catchment.