Thursday, October 04, 2018, 12:30PM - 1:30PM
Winter limnology in Rocky Mountain National Park: Understanding evolving physical and biogeochemical controls on aquatic ecosystem structure under ice cover
In mountainous regions such as Colorado's Front Range, changes in hydroclimatology and enhanced exogenous input of nitrogen from atmospheric deposition are driving changes in lake ecosystems. While summer is an important period when primary production dominates lake ecosystem structure and function, less is known about how these trophodynamics change during the longer period of winter ice cover. Ongoing research of Bear Lake, located in the sub-alpine transition zone of Rocky Mountain National Park, Colorado, USA has shown that depth profiles of dissolved oxygen change in the lake due to variation of snow cover on the ice. Preferential deposition of snow on the east side of the lake driven by wind creates a shallower depth to the oxycline by limiting light penetration through the snow and ice to support photoautotrophs compared to the snow-free west side of the lake. However, concentrations of dissolved organic carbon (DOC) appear consistent across these surface cover conditions and increase slightly by depth. Under the competing role of snow cover influencing primary production near the surface in producing oxygen against heterotrophic processes consuming it at depth, we hypothesize that the developing strata create a redox gradient where dissolved organic matter (DOM) accumulates in a reduced state below the oxycline to essentially act as a battery to store chemical energy. Favoring heterotrophic activity, this further promotes the assimilation of nitrogen into the DOM pool and an evolving reservoir of labile carbon to prime the aquatic ecosystem during lake turnover in the spring. For this seminar I will present data collected from Bear Lake throughout the winter of 2018, to better elucidate these shifts in aquatic ecosystem function against physical and chemical gradients. This both advances our understanding of oligotrophic, mountain lake sensitivity to change and predicting response to future pressure, also identifying key biogeochemical processes that may seasonally control microbial and planktonic foodweb structure.