Diatom and geochemical paleolimnology reveals a history of multiple stressors and recovery on Lake Ontario

Abstract Among the Laurentian Great Lakes, Lake Ontario is the farthest downstream and has the longest history of environmental stress from human activities. Two sediment cores, spanning the last 300 years, from Lake Ontario were analyzed for diatom composition and geochemistry and compared with anthropogenic activities in the surrounding watershed. Despite some regional variation a clear, lake-wide record of cultural eutrophication and recovery is presented in three phases: (1) a largely pre-impact phase (1700s through ~ 1920) dominated by oligotrophic/mesotrophic diatoms and more inorganic sediment accumulation; (2) an accelerated eutrophication phase (1920s to 1980s) reflecting human population growth, watershed modifications and rapid industrial expansion as indicated by increases in nutrient-tolerant diatom taxa and sediment contaminants; and (3) a recovery phase (1980s to present) when diatom-inferred nutrient concentrations trended back to pre-impact levels in response to pollution abatement measures and novel stressors such as dreissenid invaders and climate change. Based on our long-term record, Lake Ontario’s ecosystem continues to evolve in response to contemporary stressors.