Ground-Truthing “Greenness” in Arctic Lakes

Ground-Truthing “Greenness” in Arctic Lakes

By Catherine Kuhn, PhD Student, University of Washington School of Environmental and Forest Sciences

Imagine a vast flatness stretching in all directions. Now fill that space with bird songs, the rustling of bull rushes, and the drone of a float plane vanishing into the distance. In July 2018, I found myself perched on the edge of a lake in the Yukon Flats Wildlife Refuge with a pile of gear at my feet, watching the tiny dot of the plane disappear south into the foothills of the Crazy Mountains.

Our group had come to the Yukon Flats Wildlife Refuge as part of NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE), a 10-year field experiment to understand the fate of permafrost release in a warming world. David Butman (UW), two USGS collaborators, and I were dropped by floatplane at a remote cabin in the middle of the Flats to investigate the role arctic lakes play in biogeochemical feedbacks in this changing landscape.

Between 1,400 to 1,850 billion metric tons of carbon (1) are locked up in the soils of the circumpolar North, which is almost twice the amount of carbon in the atmosphere (2). At the project’s start, the prevailing understanding was that lakes acted as reactors, processing and releasing previously frozen carbon from permafrost soils into the atmosphere as greenhouse gases. As the Arctic continues to warm at a rate double the global average, this creates a positive feedback loop that accelerates climate change (3).

However, new research published by our group and others this year in Nature Climate Change (4,5), suggests the majority of these lakes are cycling mostly modern carbon. My work explores how spatially synchronous lakes are across the landscape by linking field measurements of productivity to satellite remote sensing.

Catherine Kuhn in the Field

Regardless of carbon source, arctic lakes experience seasonal boom-and-bust cycles of productivity.  Preliminary research from our group shows a strong link between rates of gross primary productivity and satellite observations of lake color. Every summer, lakes change color as they warm and fill up with life. Flying over the lakes, the colors are striking and can provide clues into ecological conditions. One lake might be pea-soup green from cyanobacteria while its neighbor is yellow-brown from mats of submerged aquatic plants.

The lakes are remote; summer access is by float plane only. At each site, we collected water samples and deployed sensors off the pontoon of the plane to measure lake optics. One lake was too small for a normal take-off; our pilot Jim Webster demonstrated his experience and skill by instead slingshotting along the edge of the lake to get up to speed. Each day we would return to the cabin, which was studded with nails to keep the bears out, to filter samples and charge up equipment for the next day.

A float plane waits to take off

Our measurements would provide a ground truth for an airborne hyperspectral sensor called AVIRIS-NG, which collects images of the earth from an aircraft and was coordinated by NASA to fly over the lakes during our trip. Airborne remote sensing observations are crucial for mapping this remote landscape. The research flights would give us a birds-eye view of the thousands of lakes dotting the landscape.

At the cabin, filtering water samples into the broad sunlight of the late evening gave me time to ponder the scale of the surrounding landscape. As one human, it is hard to comprehend the sheer size of this carbon pool, just as it is hard to understand the size of the problem of climate change. Each lake filter I collected was just one tiny clue in this bigger puzzle. Accumulating and interpreting these clues is the work of science. NASA’s ABoVE campaign can amplify the work of scientists from many disciplines by bringing us to work side-by-side in our efforts to understand this rapidly changing landscape.

Keywords: Arctic, carbon, green, airborne, ABoVE, organic carbon, terrestrial, climate change, terrestrial ecology, NASA, productivity

Acknowledgements: This research was made possible by funding from the NASA ABoVE program and an NASA NESSF graduate research fellowship. Special thanks to our field team, including my advisor Dr. David Butman, our pilot Jim Webster and our USGS collaborators.

Literature Cited:

  1. Tarnocai, Charles, et al. “Soil organic carbon pools in the northern circumpolar permafrost region.” Global biogeochemical cycles 23.2 (2009).
  2. Schuur, Edward AG, et al. “Vulnerability of permafrost carbon to climate change: Implications for the global carbon cycle.” AIBS Bulletin 58.8 (2008): 701-714.
  3. J. Richter-Menge, J. E. Overland, J. T. Mathis, and E. Osborne, Eds., 2017: Arctic Report Card 2017, http://www.arctic.noaa.gov/Report-Card.
  4. Elder, Clayton D., et al. “Greenhouse gas emissions from diverse Arctic Alaskan lakes are dominated by young carbon.” Nature Climate Change 8.2 (2018): 166.
  5. Bogard, Matthew J., and David E. Butman. “No blast from the past.” Nature Climate Change 8.2 (2018): 99.