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.
Bibliographical noteFunding Information:
Thanks go to: Lisa Allinger and Kitty Kennedy for field and laboratory assistance; the Guildford/Hecky Laboratory (Large Lakes Observatory) for providing microscope use; Robert Hecky and Mark Edlund for providing guidance and feedback during development of the manuscript; LacCore (Jessica Heck and others) for pollen preparation; Rick Knurr (University of Minnesota Analytical Geochemistry Laboratory) for trace metal analyses; Sergei Katsev for core location expertise and sharing R/V Blue Heron ship time as well as Tom Johnson, Stephanie Guildford, Steven Colman and other members of the Large Lakes Observatory for providing valuable guidance; the crews of the EPA R/V Lake Guardian and the R/V Blue Heron for assistance with sample collection; Brian Bandli and the Scanning Electron Microscope Laboratory at UMD for SEM diatom images. This work is the result of research sponsored by the Minnesota Sea Grant College Program supported by the NOAA office of Sea Grant, United States Department of Commerce, under grant No. R/CC-01-10 . The U.S. Government is authorized to reproduce and distribute reprints for government purposes, notwithstanding any copyright notation that may appear hereon. This paper is journal reprint No. JR 610 of the Minnesota Sea Grant College Program. Training set data were provided through a grant to E. Reavie from the U.S. Environmental Protection Agency under Cooperative Agreement GL-00E23101-2.
- Lake Superior
- Nutrient enrichment
- Water quality