Lake Mendota teems with teaching and research efforts – and algae

Top: Aboard the boat, students and researchers roam in search of signs of how development has affected the ecology of Madison’s Lake Mendota. Mendota is a trademark urban lake, but it could be any lake, anywhere in Wisconsin, says limnologist Steve Carpenter. “I see this lake as a symbol of our ability to manage the other 15,000 lakes in this state,” Carpenter says. Middle: Students aboard the university’s Limnos research boat listen as limnologist John Magnuson explains the day’s projects. Bottom: Students in John Magnuson’s Limnology class lab sift through a tub of Lake Mendota sediment samples collected from aboard the Limnos research boat. Photos: Jeff Miller

At nearly 10,000 acres wide and 80 feet deep, with waters draining a constantly changing landscape, it’s doubtful scientists will crack every mystery about Lake Mendota.

But they’re trying.

During any given semester, Lake Mendota lives up to its billing as the most studied lake in North America, with a popular undergraduate course taught on its waters and numerous research projects analyzing it inside-out. No university in the world is more versed in limnology, or the science of what makes a lake tick.

On weekday afternoons, the 26-foot research trawler “Limnos” veers out toward University Bay with about a dozen students on board. The 33-year-old vessel, built especially for Lake Mendota research by a Two Rivers marina, stands out among the sailboats and recreational cruisers – especially with its line of tattered flags and bright red “Badger tracks” painted on the flat aluminum bed.

There’s a tremendous amount of information to be gleaned below the glassy surface. Students send bright black-and-white secchi disks into the blue-green water to measure water clarity; they measure temperature, dissolved oxygen, nitrogen and phosphorus levels; they survey plankton from top to bottom; they inventory aquatic life dredged from the muck.

This is the lab portion of Zoology 315, a class that serves up the rare opportunity to do field research in the university’s own backyard. The course attracts about 150 students each semester, but only about one-third of those students opt for the two-credit lab section on Lake Mendota and the Limnology Lab’s northern outpost, Trout Lake Station.

“The best part of this course is it’s the ultimate hands-on experience,” says Karen Wilson, a teaching assistant who runs labs aboard Limnos. “We get samples out here and can analyze them in the same afternoon in the laboratory.”

“I also don’t have to worry about keeping my students’ attention,” she adds. “We’re out in the middle of the lake – what better way to spend an afternoon?”

The biggest surprises come when the class steers out to Mendota’s deepest hole, and students contrast surface waters with frigid depths. At about 10 meters, temperatures drop off radically and dissolved oxygen almost vanishes – a symptom of what ails this highly eutrophic, or overly enriched, lake.

Mendota’s deep hole gets the most attention, Wilson says, since it reveals the lake’s thermal stratification. It’s so well-studied that the bottom has collected more than its share of research equipment lost overboard. “I’d hate to speculate how much limno-trash is out there in that deep hole,” she says.

Zoology professor John Magnuson, director of the Limnology Lab who has taught the course since 1967, says the course dates back to 1907, and is the first such course taught in North America. It connects today’s students with past generations of limnologists, such as E.A. Birge, Chauncey Juday and Arthur Hasler, whose research put Mendota on the science world’s map.

“Being a limnologist is like being in a blimp and trying to examine the city of Madison on a foggy day,” says Magnuson. “The waters are opaque and we can’t see into them, so limnologists continually try new methods to remotely sense or sample what’s happening below the surface.”

To that end, several new efforts are in the works. Limnologist Paul Hanson is developing new radio buoys for Mendota that will continually monitor the environment, from surface to bottom, and radio the information back to limnology computers. Magnuson says the project will provide the fine-detail analysis of lake changes that can’t be collected now.

They are also adding a genetic component to lake research with a new “microbial observatory” developed by agronomist Eric Triplett. The goal is to define the diversity and roles of the thousands of strains of microbes that exist in lakes.

These projects build on the lab’s Long-Term Ecological Research (LTER) project, which examines how massive forces like climate change, agriculture, deforestation and urban development affect the ecology of lakes in southern and northern Wisconsin.

There are more urgent issues for Mendota. Limnologist Steve Carpenter studies eutrophication, which is the constant overloading of nutrients like phosphorus from agricultural and urban runoff, causing huge blooms of scummy blue-green algae. Beyond being an eyesore, eutrophication can permanently damage water quality.

A new study by Carpenter and economics professor W.A. Brock used computer models to define a “cliff edge” for Mendota, a point at which the damage from eutrophication becomes irreversible. “We are certain the cliff exists. The good news is we’re not there yet,” Carpenter says.

“Lake Mendota is extremely fragile, and we could make some very expensive mistakes here,” he says. “A problem that costs $10 million to fix now could easily grow to a $100 million problem if left unchecked.”

Carpenter notes that the state Department of Natural Resources has a major watershed management program at work on Mendota now, helping change land-use practices that impact the lake. UW–Madison limnologists are measuring the effects of that project.

Mendota is a trademark urban lake, but it’s amazing how perspectives can change on the water. Cruising between Picnic and Frautschi points, for example, one becomes isolated from development, and the forested shores are lined with limestone bluffs, their crevices home to scores of swallows. It could be any lake, anywhere in Wisconsin.

“I see this lake as a symbol of our ability to manage the other 15,000 lakes in this state,” Carpenter says.