A crisis of lake hypoxia in the Anthropocene: The long-term effects of climate and nutrients

Climate change is altering thermal stratification in lakes worldwide. Reduction in winter mixing lead to prolonged oxygen depletion, lasting for years to centuries, potentially becoming permanent. Although there is convincing evidence of lake deoxygenation globally, its duration, timing, and impacts over decadal to centennial timescales remain uncertain. Here, we introduce a novel model-data assimilation approach using 150 years of limnological and paleolimnological data to evaluate the anthropogenic impact and future of deep dissolved oxygen in Lake Geneva. We find that climate change has influenced winter mixing, with divergent effects on bottom oxygen concentrations before and after eutrophication. Over centennial timescales, eutrophication, not climate warming, triggered unprecedented bottom-water hypoxia. However, by 2100, climate change will be the main driver of hypoxia in Lake Geneva and similar lakes, even with reduced phosphorus concentrations. With climate change locking in the effects of phosphorus loading on hypoxia, the significance of reducing loading remains intact.