Simulating the effect of nutrient reduction on hypoxia in a large lake (Lake Erie, USA-Canada) with a three-dimensional lake model

Hypoxia, or low dissolved oxygen (DO) concentrations, in lakes is commonly linked to eutrophication caused by excessive nutrient loadings. While nutrient-driven eutrophication creates a potential for hypoxia, the full realization of this potential, as well as its location, ultimate size, and duration, is to a large degree dependent on the lake's physics. Herein, we employed a three-dimensional coupled hydrodynamic and ecological model of Lake Erie to explore the potential for spatial and temporal developments of hypoxia and its response to nutrient load reductions. Reducing loads by 40 to 50% relative to the 2008 load will result in significant reductions (~ 50%) of hypoxia in terms of its maximum and mean areal extents and duration, as well as providing significant improvements in mean hypolimnetic DO. We also explored the impact of different DO threshold concentrations to characterize hypoxia, and found that responses at lower thresholds are most sensitive to variation in nutrient loads.