Divergence from expected warming effects: Thermal stratification patterns in northern Lake of the Woods

Lake of the Woods (LotW) is a large, temperate lake that has been extensively studied due to eutrophication and cyanobacterial harmful algal bloom (cHAB) issues. Several mechanistic models have been developed for the lake to inform adaptive management plans for nutrients in the system. While these modeling exercises were an essential step in managing eutrophication and cHABs, issues persistent in LotW, climate change is confounding our understanding of the system. Here, we present a description of qualitative field observations to demonstrate stratification and persistence in LotW is highly variable among different regions. We observed stratification patterns in the northern embayments to be highly variable, with indications of mixed water columns in basins that were previously thought to be persistently stratified during the summer as specified in ecosystem models. We propose that the complicated bathymetry and hydrology of northern LotW creates a suite of complex interactions with the competing influences of thermal stratification, and decomposition of stratification through wind and current mixing associated with extreme weather events. Proper representation and improved understanding of the patterns and impacts of varying stratification is crucial for the sustainable management of LotW, particularly in the context of climate change impacts and expected intensification of stratification in other temperate systems.