| Summary: | We attempted to experimentally warm an arctic whole lake to mimic the effects of on-going climate warming on food web and whole lake ecosystem process and function. The goals were to increase water temperature by up to 4°C (celsius), deepen epilimnion (warmer surface water layer) by up 2 meters (m), and delay ice-on by up to 2 weeks. Logistically this proved very challenging, and took a year or so to figure out the mechanics. By 2018, we had successfully warmed lake Fog 1, with 44 days of heating, a 3°C warmer, deeper epilimnion that mixed 15 days later. We were able to use our lake temperature and warming data to improve upon our ability to simulate lake mixing processes, and were able to predict the lake thermal response to the lake warming manipulation. Those results provide a more complete understanding of lake thermal processes in arctic freshwater lake systems and how they will respond to predicted future warming. For fish growth, one of our primary response variables, we detected an interaction in that growth decreased with increasing temperatures, but only when food availability was low. In addition, our bioenergetic simulations supported our experimental results and suggested that the benefits related to thermoregulation will be highest when food availability is low. In terms of other measured lake factors (e.g., zooplankton, macroinvertebrates) which may have been affected by lake warming, we observed that inter-annual differences among lakes in food web composition and temperature regime tended to overwhelm any potential lake warming responses. In addition, the long, cold winters appear to reset the lakes after warming, with no carryover effects. However, by 2020, the project was largely shut down by the Covid pandemic, and in 2021-2022, by the Covid-based regulations put in place at the field camp. In sum, based on our limited time series of experimental lake warming, these Arctic lakes appear to be somewhat robust to the direct effects of small levels of climatic warming; however, the indirect effects of climate warming and variability (e.g., thermokarst failure [tundra melt and slough]) may be more profound and are under exploration.
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