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Graduate student Reid Milstead takes samples from a lake
November 30, 2022

Shining light on the sun’s role in lake carbon cycling

Written By: Alex Holloway

Lakes are home to reservoirs of organic matter that may ultimately move into the soil or the atmosphere.

Christy Remucal, an associate professor of civil and environmental engineering at UW-Madison, is leading a research project to understand how sunlight plays into this process, which is called the carbon cycle.

The carbon cycle details how carbon in the atmosphere, soil or water moves among those different reservoirs—and maintaining the right balance is key to the future of our climate. Too little carbon dioxide in the atmosphere and our planet freezes; too much and we roast.

In lakes, says Remucal, dissolved organic matter is a “soup” of organic chemicals introduced through nearby plants or bacteria that live in the water. Sometimes this matter is visible in satellite images as splotches of murky brown where inland water flows into the ocean.

“If you’ve ever seen, in wetlands, that tea-colored stuff in the water, that’s organic matter,” she says. “It’s important for carbon cycling because it’s made up of organic carbon and if it gets mineralized, it makes carbon dioxide, which is a greenhouse gas.”

Remucal’s research group is using advanced mass spectrometry techniques to understand what happens when sunlight interacts with organic matter in lakes. The researchers are studying waters that are part of the National Science Foundation’s North Temperate Lakes Long Term Ecological Research Program (LTER). Organic matter can vary from lake to lake—Lake Mendota’s will be different from what’s found in a bog in northern Wisconsin, for example—so working with the LTER program allows Remucal’s group to compare samples from well-studied aquatic systems from across the state.

A lot of research has focused on bacteria’s role in creating carbon dioxide in lakes. They consume the dissolved organic matter in water and produce carbon dioxide as a byproduct, in the same way we produce carbon dioxide through respiration. Remucal’s photochemistry research looks at the phenomenon from a new angle.

“Lake models don’t really consider sunlight at all,” she says. “We’re looking at that process, which has been understudied and neglected, but we think could be really important in some lakes.”

Carbon dioxide is the most prevalent greenhouse gas on earth, and studying how it proliferates through natural processes will help us understand the factors that contribute to our changing climate. “Because lakes are so influential in how much carbon dioxide gets released into the atmosphere, it’s very important to understand how this process happens,” Remucal says. “This can help make better forecasts for carbon behavior, which is really important for our understanding of climate change.”

Featured photo caption: Graduate student Reid Milstead takes samples from a Wisconsin lake. Milstead is working with Associate Professor Christy Remucal to study how sunlight affects the carbon cycle in lakes.