Troubled Waters

Last updated: February 7, 2023

Understanding what’s happening to Arctic lakes may help us save them

By Ignacio Lobos

Not long ago, on a cool September day deep in Alaska’s Yukon Flats National Wildlife Refuge, a floatplane dropped Catherine Kuhn and a team of scientists near a cabin studded with nails to keep curious grizzly and black bears at bay.

But hungry bears and blood-sucking mosquitoes were not her concern as Kuhn set out to collect water samples and tally other field measurements on the shores of a large shallow lake.

For Kuhn, a Ph.D. candidate in the UW’s School of Environmental and Forest Sciences, the primary focus was on the lake’s color. As a member of Associate Professor David Butman’s Ecosystem Biogeochemistry Group, she was seeking to discover what the shallow waters in front of her, and the millions like it in the Arctic Circle region, might reveal about carbon cycling and climate change.

“Many studies have suggested that the color of water can give us a clue as to what lakes might be doing at any given time, and how they’re responding to environmental change,” Kuhn said.

Lake color may tell us how fast climate change is occurring and how far reaching it is.

But it’s one thing to study lake color to determine the exchange of greenhouse gases in a single lake — or as many as can be reached by hiking through mosquito-infested terrain or by floatplane during a short and expensive scientific mission. It is quite another to tackle the problem at a global scale, where millions of bodies of water are involved.

To make the job more feasible, Kuhn and Butman rely on the power of cloud computing, developing new methods to analyze and determine lake color with the help of Big Data. They glean that data by poring over decades-worth of satellite images, interpreting low-flying aircraft photos and conducting key field work to determine how climate change is affecting nearly 500,000 lakes in Alaska and Northern Canada.

So far, their work has shown that lake color is an important attribute that can help scientists more accurately track climate change. How lakes change in color in one of the most remote areas of the world may just turn out to be the proverbial canary in a coal mine. What happens here has the power to affect everything and everyone thousands of miles away.

When color tells a story

The color of a lake has many stories to tell — its hue intrinsically connected to key ecological processes and the presence of multiple chemical and biological compounds. Lakes can act like furnaces, with the potential to release large amounts of carbon dioxide (CO2) and methane into the atmosphere, or to take some back through photosynthesis.

“A lake green in color during the short Arctic growing season could indicate it’s alive with aquatic plants and phytoplankton,” Kuhn said, processing greenhouse gases through photosynthesis and converting that energy into biomass much like a growing tree. A lake brown in color could indicate less biomass and decreased photosynthesis, potentially releasing more carbon into the air.

In other words, a green lake is generally speaking a healthier lake, pulling off greenhouse gases from the air and feeding flora and fauna alike, while a brown lake generally speaking could be a dying lake, potentially releasing more gases and contributing to climate change.

So, as the climate changes, are these lakes in the Arctic region getting greener or browner? That’s the question Kuhn and colleagues are seeking to answer.

To get a better picture of what is going on in the Arctic Circle, Kuhn and Butman are among more than 200 scientists taking part in an ambitious 10-year NASA field experiment — the Arctic-Boreal Vulnerability Experiment (ABoVE) — that in part seeks to quantify the ecological impacts of a rapidly changing climate. They are studying permafrost, forests, bodies of water, other rich ecosystems and human communities.

For their part of the work, Kuhn and Butman have partnered with the United States Geological Survey to research whether there’s a correlation between rates of gross primary productivity (the amount of carbon fixed during photosynthesis by all producers in the ecosystem) and satellite observations of lake color.

“Understanding and quantifying climate change is a major challenge,” Kuhn said. “We hope what we learn from lake color will be a valuable addition to research.”

From teaching high school in Oakland to working in an Arctic lake

Being dropped off the grid into the middle of a vast 11-million-acre wildlife refuge is a humbling experience, Kuhn said. The refuge is Alaska’s largest boreal wetland basin, home to about 39 mammal species, 18 fish species and 147 bird species. When the refuge’s 30,000 lakes and ponds thaw out after a long winter, millions of birds come to feed and lay eggs. Come fall, they branch out all over the continent via the four North American flyways.

“It’s an incredible place,” said Kuhn, who up to a few years ago was teaching environmental science to high school students in Oakland, Calif. But Kuhn became captivated by the stories of scientists she brought into her classroom. After six years of teaching, she went back to school, first to Yale and now at the UW, where in 2019 she was named a Husky 100 for her outstanding efforts as a student.

During her time here, Kuhn has developed new methods that combine satellite data, field surveys and big data analysis to understand how inland waters are responding to human activities and how they’re behaving under the stresses of climate change.

And while she still loves field work, she has come to rely on cloud computing to do the bulk of her research — an adjustment made easier by a thriving science community at the UW that wants her to succeed.

Data-driven science and cloud computing propels Kuhn’s research

To get started, Kuhn sought the help of the eScience Institute, which trains researchers to leverage data science tools, methods and best practices. The institute also partners with Research Computing, a unit in UW Information Technology (UW-IT) that designs cloud-based solutions appropriate to data-driven science, and works with cloud providers such Amazon, Google and Microsoft to bring educational resources and design solutions for cloud deployment to the UW.

“It has been fantastic to have all of their combined expertise,” Kuhn said. “My work would not have been possible without their training and guidance. It certainly accelerated my research.”

Seeing the results of Kuhn’s work has been especially thrilling to Rob Fatland, UW-IT’s Director of Cloud and Data Solutions.

“This is what we want to see, researchers who are not mystified by cloud computing and are relying on its power to make great advances in their work,” Fatland said. “When you couple cloud computing to the kind of solution-focused expertise at the eScience Institute, there’s not much we can’t tackle.”

Kuhn was indeed facing a big job, said Amanda Tan, a data scientist with the eScience Institute and an earth systems modeling expert who helps UW researchers migrate their work to the cloud. Kuhn needed to sample the color of 584,769 lakes during the growing season from satellite images taken between 1984 and 2019 to see if they were getting greener or browner — 54 million observations of lake color in all.

For her computations in the cloud, Tan worked with Kuhn to build scalable workflows for spectral analysis of the lakes and to go “back in time” to measure color changes for each lake over three decades.

The data, she said, is showing widespread decline in lake greenness, with 26 percent of the lakes under study showing significant change. Certain hot spots showed 2.5 times greater decline in greenness during the June/July growing season.

The greatest decline is being seen in warmer and wetter basins, she said, making the ecological implications clearer. Warmer water temperatures, oxygen depletion and shading out of primary producers by highly-absorbing organic carbon may be shifting green lakes to brown, she said.

“What we are seeing is consistent with model projections of accelerated browning in a wetter climate in Finland,” Kuhn said. Such a decline could have a profound and immediate effect on the flora and fauna that depend on these life-giving waters.

Lake color is but one piece of the puzzle as scientists seek to understand the scope and speed of climate change, Kuhn said.

“For many people, it would be hard to comprehend why we are interested in lakes thousands of miles from their homes,” Kuhn said. “But the world is deeply interconnected in ways that we’re just beginning to understand. What is happening in the Arctic may just end up affecting us all.”