The lake ice continuum concept: Influence of winter conditions on ecosystem dynamics

Emily Cavaliere, Global Institute of Water Security, University of Saskatchewan, Saskatoon, SK, Canada, Isabelle B. Fournier, Département de Biologie, Université Laval, Laval, QC, Canada, Václava Hazuková, Climate Change Institute, School of Biology and Ecology, University of Maine, Orono, ME, Garrett P. Rue, Institute for Arctic and Antarctic Research, University of Colorado - Boulder, Boulder, CO, Steven Sadro, Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, Stella A. Berger, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany, James B. Cotner, Ecology, Evolution and Behavior, University of Minnesota - Twin Cities, St. Paul, MN, Hilary Dugan, Center for Limnology, University of Wisconsin, Madison, WI, Stephanie E. Hampton, Center for Environmental Research, Education, and Outreach, Washington State University, Pullman, WA, Noah R. Lottig, Center for Limnology, University of Wisconsin, Boulder Junction, WI, Bailey C. McMeans, Biology, University of Toronto Mississauga, Mississauga, ON, Canada, Tedy Ozersky, University of Minnesota - Duluth, Duluth, MN, Stephen M. Powers, Biology, Baylor University, Waco, TX, Milla Rautio, Département de Sciences Fondamentales, Université de Québec à Chicoutimi, Saguenay, QC, Canada and Catherine M. O'Reilly, Department of Geography, Geology and the Environment, Illinois State University, Normal, IL

Background/Question/Methods
Millions of lakes worldwide are distributed at latitudes or elevations resulting in the winter formation of lake-ice. However, many lakes with extended records of ice history show declines in ice duration over the last century—a trend that is expected to continue with climate warming with some lakes already becoming intermittently ice-covered or ice-free. The formation of lake-ice mutes linkages with the watershed and atmosphere, constraining transfer of energy, heat, light, and material—ultimately, creating an aquatic environment that strongly contrasts with open-water conditions. Therefore, reductions in duration of ice cover can substantially alter winter energetic regime within lakes. Although ongoing changes in ice conditions may have a myriad of cascading effects on lakes, we lack a conceptual framework to understand and predict the effect of such changes on ecosystem structure and function. We present the Lake Ice Continuum Concept (LICC) that explores how lake ice duration, its thickness, snow depth, and energy inputs affect physical, chemical, and biological structure of lakes. In support, we offer three case study examples to demonstrate key processes and patterns relevant to the conceptual model and associated hypotheses in a changing world.
Results/Conclusions
Lakes without winter ice or lakes that experience intermittent winter ice cover have the potential for higher energetic fluxes through wind exposure, and higher input rates of allochthonous material when precipitation falls as rain. As a result of the increased connectivity to the atmosphere and landscape, lakes that lose ice cover will respond more directly to variation in winter or early spring weather patterns, leading to profound differences in the early spring lake condition. By regulating energetic fluxes, lake ice determines the dominant physical mixing regimes within lakes, influences time scales of mixing, controls the distribution of matter and energy throughout the water column, and establishes the template for biological structure and ecosystem function. Differences in phytoplankton biomass and rates of primary productivity along the continuum of light availability in ice covered lakes will drive differences in the oxycline and variation in redox potential with depth. Such vertical gradients will in turn affect biochemical reactions and, together with differences in rates of biological uptake, the distribution of nutrients. Developing such a general limnological framework is imperative for understanding how winter lake dynamics change latitudinally with climate and how the structure and function of lakes may shift under climate scenarios.