A simple model for predicting oxygen depletion of lakes under climate change

The advent of climate change has placed lakes at risk of facing potential declines in water quality and aquatic ecosystems. This includes the increase in lakes experiencing substantial dissolved oxygen (O₂) depletion. Through its influence on the thermal structure of lakes, via elevated water temperatures and alterations in stratification phenology, climate change intensifies detrimental biogeochemical and ecological processes involved in O₂ consumption rates, giving rise to conditions like hypoxia/anoxia. However, predicting O₂ dynamics is difficult, with in-situ O₂ depletion rates showing considerable lake-dependent variability, underpinned by distinct underlying mechanisms. Our study attempts to overcome these lake-specific features and targets distilling key components of O₂ depletion into a simple and transferable conceptual model applicable across a diverse array of lakes and at large scales. Using O₂ depletion rates from literature reflecting variability in trophic state, we quantified the typical O₂ depletion rate ranges for oligotrophic, mesotrophic, and eutrophic lakes and assessed their temperature sensitivity for a broader climate-impact assessment. Our model gave reasonable estimates for O₂ depletion and risks of anoxia through three explanatory variables: trophic state, stratification duration, and hypolimnion temperature. We validated our model predictions using data from five German lakes and assessed the relative importance of the three influencing factors. This easy-to-use approach holds potential value for lake management in attaining fast assessments of potential future problems with O₂ dynamics in a given lake even in the absence of in-situ data. Moreover, it allows scaling of O₂ dynamics continentally/globally without lake-specific hydrological or morphological details.