High Sensitivity of Lake Hypoxia to Air Temperatures, Winds, and Nutrient Loading: Insights From a 3-D Lake Model

A three-dimensional hydrodynamic-ecological model is applied to Lake Erie to predict the response of dissolved oxygen (DO) to independent changes in air temperature, wind speeds and total phosphorus (TP) loading. Warmer temperatures and lower wind speeds increased the size and duration of hypoxic and anoxic regions by lengthening the stratified period. Decreased wind speed increased hypolimnion thickness while decreasing its temperature and DO consumption rate. Decreased TP loading improved DO conditions with a reduction of 75% effectively abolishing hypoxia. Anoxia was more sensitive to air temperature, wind, and nutrient changes than was hypoxia. New metrics that capture the spatial and temporal dimensions of low DO conditions were more sensitive than the commonly cited maximum areas of hypoxia or anoxia. Over most of the relevant range of forcing factors, the simple and first-order effect of a 1 degrees C temperature change was equivalent to a 10-14% change in TP loads, while a 1% change in wind speed was equivalent to a 2-3% change in TP loads. Reduced ice cover in warmer climates will likely increase air temperature effects even further.