Unraveling Lake Geneva's hypoxia crisis in the Anthropocene

Despite global evidence of lake deoxygenation, its duration, timing, and impacts over decadal to centennial timescales remain uncertain. This study introduces a novel model approach using 150 yr of limnological and paleolimnological data to evaluate the anthropogenic impacts on deep oxygen in Lake Geneva. Results highlight an increase in oxygen consumption rates due to cultural eutrophication, initially triggering historical hypoxia, subsequently exacerbated by reduced winter mixing induced by climate change. Simulations of pre-eutrophication conditions and future climate scenarios define safe operating spaces for the lake to thrive without severe hypoxia risk. Complete winter mixing and O2 recharge once every 3 yr can compensate the oxygen demand in Lake Geneva, even when exceeding 1.5 g O2 m−2 d−1. However, when complete winter mixing becomes less frequent, even consumption rates similar to those observed before eutrophication can cause persistent hypoxia, posing a significant threat to the survival of hypolimnetic aquatic life.