Out of sight out of mind? Implications of winter vs. summer conditions for lakes on the northern Great Plains.

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Lakes across the Canadian prairies are excellent model systems to advance our understanding of climate effects on lake food-webs. Together, regional geomorphology and climate result in a tremendous diversity in morphological, physical and chemical lake characteristics on a small spatial scale. As a result, taxonomic richness, food-web complexity and species assemblages vary dramatically among lakes. Additionally, recently intensified land-use can have detrimental impacts on lakes, including toxic algal blooms in the summer and fish kills in the winter. A unique and rapidly developing theory is that the state of lakes in the winter is critically important in determining the dynamics of food webs in the summer ("winter control"). The first goal of this project is to quantify the impacts of winter conditions on food-web structure in these lakes and develop novel quantitative models to predict the risk of winterkill. Second, we will continue our long-term lake surveys to contrast the importance of summer vs. winter conditions for current climate regimes, and experimentally test their respective impacts on zooplankton assemblages. Third, we will evaluate long-term changes by comparing reconstructed productivity and food-web patterns over the past 100 yrs with simultaneous changes in climate and land-use. Ultimately, based on the here established associations of food-web composition with climate and land-use, we will use existing climate change scenarios to predict future conditions in these lakes. The results of this study will be instrumental in improving and adapting management approaches for these lakes, such as water-quality protection and fisheries. Furthermore, this study will also generate important new insights into the functioning of freshwater lakes and their vulnerability to climate change. While prairie lakes can be extreme in respect to environmental conditions and are more sensitive to climate change, the biota in freshwater lakes should respond similarly to changes in hydrology and water chemistry, particularly as there are broad taxonomic similarities to boreal lakes.