Six doctoral students were supported on National Science Foundation (NSF) IGERT grant DGE-0966346 “I-WATER: Integrated Water, Atmosphere, Ecosystems Education and Research Program,” for which we are grateful (IAO, WB, RWL, CS, KC, CW). We acknowledge the Niwot Ridge Long Term Ecological Research Network site (LTER) (NSF grant DEB-1637686) and Loch Vale Watershed Long-Term Monitoring and Research Programs for use of the lake monitoring data. We are additionally grateful to the field and laboratory technicians for their tireless work collecting and analyzing samples from lakes within RockyMountain National Park (ROMO) as a part of the 2016 field season, and for ROMO park staff who were instrumental in facilitating a successful research season (permit ROMO-2016-SCI-0014)
Phytoplankton -- Colorado, Aquatic organisms -- Effect of climatic changes on, Lake ecology, Cryosphere, Atmospheric deposition -- Colorado, Mountain ecology
Climate change is altering biogeochemical, metabolic, and ecological functions in lakes across the globe. Historically, mountain lakes in temperate regions have been unproductive because of brief ice-free seasons, a snowmelt-driven hydrograph, cold temperatures, and steep topography with low vegetation and soil cover. We tested the relative importance of winter and summer weather, watershed characteristics, and water chemistry as drivers of phytoplankton dynamics. Using boosted regression tree models for 28 mountain lakes in Colorado, we examined regional, intraseasonal, and interannual drivers of variability in chlorophyll a as a proxy for lake phytoplankton. Phytoplankton biomass was inversely related to the maximum snow water equivalent (SWE) of the previous winter, as others have found. However, even in years with average SWE, summer precipitation extremes and warming enhanced phytoplankton biomass. Peak seasonal phytoplankton biomass coincided with the warmest water temperatures and lowest nitrogen-to-phosphorus ratios. Although links between snowpack, lake temperature, nutrients, and organic-matter dynamics are increasingly recognized as critical drivers of change in high-elevation lakes, our results highlight the additional influence of summer conditions on lake productivity in response to ongoing changes in climate. Continued changes in the timing, type, and magnitude of precipitation in combination with other globalchange drivers (e.g., nutrient deposition) will affect production in mountain lakes, potentially shifting these historically oligotrophic lakes toward new ecosystem states. Ultimately, a deeper understanding of these drivers and pattern at multiple scales will allow us to anticipate ecological consequences of global change better.
© 2020 The Authors. Ecology published by Wiley Periodicals LLC on behalf of Ecological Society of America. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Oleksy, I. A., W. S. Beck, R. W. Lammers, C. E. Steger, C. Wilson, K. Christianson, K. Vincent, G. Johnson, P. T. J. Johnson, and J. S. Baron. 2020. The role of warm, dry summers and variation in snowpack on phytoplankton dynamics in mountain lakes. Ecology 101(10):e03125. 10.1002/ecy.3132