The recent diatom-based paleolimnology of Lake Michigan

Quantitative analysis of siliceous microfossils in a dated sediment core from Lake Michigan reveals the anthropogenic history of pelagic conditions from the last ~ 160 years. Sediments deposited before the twentieth century contained low diatom abundances comprising species associated with oligotrophic conditions. Diatom-assemblage reorganization in the early to mid-twentieth century resulted in an increase in diatom-model-inferred water-column-phosphorus concentrations associated with cultural eutrophication. In recent decades, better nutrient management and water-quality recovery drove a decline of high-nutrient indicating diatom taxa. The most recent two decades manifest the effects of the extensive dreissenid invasion (a continued reduction in diatom-accumulation rate) and likely atmospheric warming (the rise in summer-diatom taxa representing a longer summer stratification and ice-free period). Like many areas of the Great Lakes basin, Lake Michigan's paleolimnological sequence reflects the widespread eutrophication of the twentieth century, followed by remediation and a modern condition affected by multiple stressors.