Meteorological drivers of oxygen depletion in Lake Mendota

Physical, chemical and biological lake processes are sensitive to climate. Global circulation models generally predict future increases in air temperature, but are more uncertain in predictions of other meteorological driver variables, such as wind. Understanding how important biogeochemical lake processes, such as hypolimnetic anoxia, may respond across a gradient of climate scenarios requires a process-based, numerical, aquatic ecosystem model. Past studies using these models to predict future changes in lakes have primarily focused on the response of lake thermal structure to rising air temperature. Less work has been done investigating the impacts of other meteorological driver variables, especially on biogeochemical processes. This study provides an analysis of the effect of changes in three important meteorological driver variables (air temperature, wind speed and relative humidity) on hypolimnetic anoxia in a eutrophic, north temperate lake using the anoxic factor, an index that captures the temporal and spatial extent of anoxia. Air temperature and relative humidity were found to have a positive correlation with anoxic factor, while wind speed had a negative correlation. Given climate projections for the region of interest, air temperature was found to have the greatest potential impact on the anoxic factor, followed by wind speed and then relative humidity. Across the scenarios, variation in the simulated anoxic factor was primarily due to changes in the timing of onset and decay of stratification. Air temperature and wind speed exhibited significant diurnally asymmetric effects, with daytime air temperature and nighttime wind speed having a greater impact on the anoxic factor. While the differences in effect magnitude from day to night were relatively minor, the discrepancy could be important for predicting future changes in lakes for regions that are expected to experience strong diurnally asymmetric changes in climate