MOUNTAIN LAKE ECOLOGY IN THE AGE OF RAPID GLOBAL CHANGE

​Despite seeming remote and pristine, mountain lakes in Rocky Mountain National Park have been subjected to elevated nitrogen (N) deposition for over 50 years because of atmospherically-transported regional pollution originating from industrial and agricultural activities. However, recently we have observed increases in filamentous green algae on the lake shores of The Loch and Sky Pond, two lakes in the Loch Vale Watershed, Rocky Mountain National Park. We collected sediment cores from these two lakes and conducted geochemical and pigment analyses to ask (1) whether contemporary assemblages of phototrophic microbes are different now than in the past, (2) if there has been an increase in primary production, and (3) if the changes are similar between two lakes in the same watershed.  We found that chlorophytes have increased by 200-300% in both lakes in recent decades while diatom taxa have shifted from the benthos to planktonic habitats, with decreases in overall diversity. In recent decades, warming trends have accelerated with implications for seasonal snowpacks, lake ice duration, and lake thermal structure. Combined with chronic N deposition, these factors appear to have moved these historically ultra-oligotrophic systems into a new ecosystem state, possibly unique in the context of the Anthropocene.