Nutrients and warming alter mountain lake benthic algal structure and function

Sky Pond is one of three alpine lakes in the Loch Vale Watershed. Like many alpine lakes in RMNP, Sky Pond was categorized historically as an oligotrophic lake. Oligotrophic lakes are oxygen-rich, nutrient-poor, with very low algal productivity that coincide with clear water and minimal aquatic vegetation. Crystal clear oligotrophic lakes provide habitat for species, such as trout, and serve as sources of high-quality drinking water for downstream communities.
Footprints at the bottom of lake filled with green algae
Human footprints in Sky Pond filled with green algae.

NPS Photo/I. Oleksy

In 2010, researchers began to observe luxuriant mats of green algae growing on the bottom of The Loch and Sky Pond along the shoreline. They later found it was widely distributed in both lakes, and not just along the shore. To better understand the specific drivers of this ecological shift and its influence on productivity levels, researchers from USGS and CSU analyzed lake sediment cores and performed field and laboratory experiments to find out what could be causing the new algal growth. By reconstructing a timeline of algal species changes they learned that benthic green algae are more abundant now than any other time in the last 200 years. In field experiments, researchers found that enrichment of fertilizers (nitrogen and phosphorus) from atmospheric deposition favored green algae with the highest overall algal biomass. From laboratory experiments, however, they found that temperature was also important in algal growth and ecosystem processes.

These findings suggest that ecological communities and processes in alpine lakes are shifting in response to climate-driven warming and nutrient increases; overtime, this could lead to larger algal blooms, reduced lake clarity, and changes in water quality.

This project is funded in part by Rocky Mountain Conservancy as part of the Bailey Research Fellowship Program.

Meet the Scientists

Isabella Oleksy is an ecosystem ecologist who studies the movement and
transformation of nutrients through watersheds and into lakes. She currently works as a postdoctoral researcher at the University of Wyoming and lives in Fort Collins, Colorado.

"Long-term datasets allow us to tease apart the natural variability of ecosystem processes from that caused by human disturbances, like regional air pollution and global climate change. The beauty of these datasets is that they only become more valuable as time goes on. The insights scientists gain from long-term datasets ultimately deepen our understanding of the causes underpinning ecological change everywhere."
Jill Baron
Jill Baron began her career as a researcher for the National Park Service in 1976 and since 1994 has been a research ecologist with the U.S. Geological Survey. As an ecosystem ecologist, she studies the effects of global change (atmospheric deposition and climate change) on the soils, vegetation, and lakes of mountain ecosystems.

"Our public lands are precious for the environments they preserve and the spiritual renewal they provide to those who venture into them, and even for those who can’t visit but simply know they are there. Resource management that builds from a foundation of scientific knowledge, including patient long-term observations of natural change, is essential to helping our beloved mountains adapt to rapidly changing conditions."

Rocky Mountain National Park

Last updated: November 7, 2022