Up In the Air: Understanding Lake Mendota’s Climate Contributions

An unusual scene at Picnic Point – Ankur Desai’s lab prepares to install an anemometer and gas analyzer on the UW Safety tower. Photo: A. Hinterthuer

On a hot, windy morning in late June, Ankur Desai and other members of his lab took their first steps to bridging a big gap in data between the aquatic and atmospheric sciences, as they set out in a cherry picker for a leisurely ride down the Lakeshore Path. Jonathan Thom and David Reed, two research associates in Desai’s lab, led the slow-rolling charge toward the UW-Madison’s safety pole stationed at Picnic Point.
While we often tout Lake Mendota as “the most studied lake in the world,” when it comes to how the lake interacts with the atmosphere around it, says Desai, “we’ve really just been scratching the surface.”
Ankur Desai and Jonathan Thom strategize how to mount their scientific instruments to the tower. Photo: G. Golub
Ankur Desai and Jonathan Thom strategize how to mount their scientific instruments to the tower. Photo: G. Golub

This lack of data on Lake Mendota’s climate contributions isn’t unusual. Desai, a professor of atmospheric and oceanic sciences here at the UW-Madison, has spent the last several years trying to understand how ecosystems interact with the atmosphere and how they exchange gases like carbon dioxide. Lakes, he says, “are a particularly understudied system.” This is a problem, he says, because research indicates that lakes and streams play a significant role in the global carbon cycle and suggests that their contributions have been underestimated.
Those studies are what led Desai to the Picnic Point safety pole. The pole currently exists as away to warn boaters about inclement conditions – acting as an unmanned lighthouse of sorts to let folks know when they might need to come in off Lake Mendota. Now, though, it will do double duty. Thom and Reed strap themselves into the basket of the cherry picker and head to a point high up on the pole, where they mount a boom as far out over Lake Mendota as possible. On the boom, they place a sonic anemometer, which can measure both horizontal and verticlal wind speeds and directions, and an infrarad gas analyzer that will measure the carbon dioxide and water vapor coming off of the lake.
This new array of atmospheric instruments will keep tabs on Lake Mendota’s evaporation and emissions. Photo: Desai Lab

“One of the technologies we use in my lab a lot is eddy covariance,” Desai explains. “So if we can measure atmospheric turbulence, we can accurately infer how much carbon dioxide or evaporation or anything else is occurring between the lake and the atmosphere.”
Paul Schramm looks on as David Reed and Jonathan Thom raise the cherry picker to the tower. Photo: A. Hinterthuer

The instrumentation is a “carbon copy” he says of what is already on the roof of Hasler Lab along the UW-Madison’s Lakeshore Path. But that location isn’t ideal, as the instruments are limited to only registering northerly flow and the building itself disrupts wind patterns.
Desai says the current project will yield better results and is a perfect example of an “experiment of opportunity.” He was able to borrow the instruments needed from a group in Wyoming, UW Safety just so happened to have a tower in a perfect location, and groups like the Center for Limnology, the Long-Term Ecological Research project and others were more than willing to help.
Now Desai has an “eye in the sky” that will monitor how emissions and evaporation in Lake Mendota change as our climate warms, ice cover shrinks, invasive species move in and more – making Lake Mendota’s claim of ‘the most studied lake in the world” ring a little more true.