A framework for stabilizing deep-water oxygen under future climate change

The deoxygenation of deep-water during summer stratification presents a significant challenge for lake ecosystems, further exacerbated by climate change. To better understand future oxygen dynamics and evaluate mitigation strategies, we developed a simple 1-D model that incorporates water-column and sediment oxygen consumption, as well as vertical mixing. This model estimates deep-water oxygen profiles during summer stratification based on temperature profiles, bathymetry and oxygen depletion parameters. We apply the model to Lake Erken in Sweden, achieving an RMSE of less than 1 mg L^-1 and an average oxygen demand of 0.55 mg L^-1 d^-1. Projected water temperature and diffusivity from a hydrodynamic model were used to drive the oxygen model under different Representative Concentration Pathways (RCPs). Climate projections indicate from 2020 to 2099, the deep-water annual anoxic (<0.5 mg L^-1) period will increase by 21 days under RCP 6.0 and 32 days under RCP 8.5. Extended stratification periods, ranging from 1 to 5 days per decade, emerge as the key driver of future deoxygenation. To maintain current oxygen levels by the end of this century, oxygen consumption rates would need to be reduced by approximately 20% under RCP 6.0 and 30% under RCP 8.5. Ensuring oxygen stability is crucial for preventing further water quality degradation and protecting fish habitats. Our approach offers a transferable, data-efficient framework for climate-adaptive eutrophication management.