SG: RUI: Resilience of mountain lakes across a gradient of glacial retreat and vegetation advance

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Mountain landscapes worldwide, long considered sentinels of environmental change, are changing rapidly as glaciers retreat and vegetation advances upslope. Pristine lakes within those landscapes, especially lakes whose iconic beauty has led to their designation as World Heritage sites, have strong tourist appeal. Yet that beauty is threatened by changes to the clarity of the lake waters. Conservation efforts for these potentially fragile ecosystems would benefit from a predictive understanding of lake responses to global climate change. This research explores the consequences of these landscape-level changes for lake ecosystems. Rather than study a single system over a long time, these researchers will substitute a comparison of lake ecosystems that currently differ in the extent of glacial and vegetation coverage in the catchment. The primary aim of the research is to compare lake responses to rain and snowmelt-driven inputs of materials such as glacial flour, the finely ground rock from glaciers, and dissolved products of organic matter decomposition. Both of these materials have strong effects on the clarity of the water or water transparency, which in turn influences many aspects of lake ecosystem function. Lake responses will be examined using two complementary measurements of ecological resilience: resistance, the magnitude of change in the system following rain or snowmelt events; and recovery, the rate of return to previous conditions. Project findings will deepen the basic scientific understanding of the effects of changing landscapes on lake ecosystems in the Rocky Mountains. Undergraduate students will be engaged in all stages of the research, including planning, data collection, analysis, and publication. Targeted efforts will be made to attract students from diverse backgrounds and experiences. Because water transparency of mountain lakes is a powerful case study through which to communicate ecosystem-level effects of environmental change to a broader audience, a short film describing the research will be produced and distributed.The proposed research will test the overarching hypothesis that changes in the resilience of water transparency occur systematically as lake catchments shift from glaciated to rocky to vegetated states. Specifically, resistance of water transparency is predicted to increase with glacial loss and decrease with vegetation advance. Additionally, recovery rates of water transparency are predicted to increase as the regulator of transparency shifts from suspended rock flour in glacial catchment lakes to dissolved organic matter (DOM) in vegetated catchment lakes. To test these hypotheses, high frequency monitoring buoys equipped with sensors that measure turbidity and the fluorescent component of DOM will be deployed in five lakes that vary across a gradient of glacial and vegetation coverage. Concurrent hydrological data will be used to better understand dynamics of material inputs and their relationships to meteorological data recorded at nearby weather stations. More generally, the research probes the relationship between the two components of resilience by testing whether resistance and recovery change independently as glaciers retreat and vegetation advances. The potential for uncoupled changes in the two components of resilience is a unique and transformative aspect of the research program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.