Climate change is shifting the hydrodynamics and temperature of both the Great Lakes and their tributary rivers. Both hydrology and temperature may play potent roles in mediating the magnitude of watershed nutrient load and their fate upon reaching the lake. Tributary hydrology reflects the source of water (groundwater vs surface runoff) and seasonal timing of discharge, while tributary temperature determines the density difference between river and lake water. Similarly, mixing patterns in these massive lakes strongly influence whether tributary loads remain near the shore or become diluted in the open water, while the thermal profile determines whether inflowing river water is trapped at the surface, sinks to the bottom, or stays at an intermediate depth. These physical interactions are critical for understanding the ecological impact of tributary loads, and how it is mediated by climate change. We are merging watershed nutrient load studies with a 3-dimensional hydrodynamic model of Lake Michigan to assess how the location of a tributary interacts with its seasonal patterns of temperature, discharge, and nutrient concentrations to determine impact on the coastal environment.
Mooney (fellow): UW Center for Limnology weekly seminar, April 19, 2017