The North Temperate Lakes Long Term Ecological Research project monitors our lakes all year long, and has noticed shrinking ice seasons.

The North Temperate Lakes Long Term Ecological Research project monitors our lakes all year long, and has noticed shrinking ice seasons.

NTL LTER website

Timing is Everything, Especially to The Team of Researchers Studying our Changing Northwoods Lakes

by Adam Hinterthuer

Ray Allen, a new postdoctoral researcher at TLS, spent his winter converting a cinder block room not much larger than a storage closet into a fish hatchery. He arranged aquariums onto shelves, ordered equipment like “egg tumblers” online and worried about the timing of the annual thawing of the Northwoods’ ice-covered lakes.

“All winter and spring I’ve been asking ‘When’s it going to happen and am I going to be prepared?’” Allen says, “Because around this time last year the lakes had already opened up.”

Allen’s concern about timing is more than appropriate, considering that he is part of a large team of researchers studying how the timing of annual events like “ice off” affects the organisms that call our rapidly changing lakes home.

Humans have long kept tabs on seasonal changes in nature – taking note of the timing of everything from flowering plants, to migrating birds, to spawning fish. These observations have helped indigenous peoples hunt, fish and gather foods and medicines for thousands of years and were a hallmark of famed Wisconsin naturalist Aldo Leopold’s writings on conservation.

The practice of making these kinds of observations is called phenology and, this spring and summer, a team of University of Wisconsin-Madison and Wisconsin Department of Natural Resources (WDNR) researchers is launching a project focused on the phenology of northern Wisconsin lakes.

The origins of the project, says TLS director, Gretchen Gerrish, stem from the fact that the timing of important seasonal events is changing. The North Temperate Lakes Long Term Ecological Research project, which is based out of TLS, has monitored seven Vilas County lakes since the early 1980s. And that monitoring has tracked not only shorter winter ice seasons on the lakes, but increasingly extreme variability in the dates when lakes freeze and thaw.

“This really started when we were thinking about long-term data and the ice record showing this increased variability where we’ve had five times the variability in the last ten years than we’ve seen in the last hundred,” Gerrish explains. For example, in 2013, Trout Lake thawed in late May, a full 50 days later than the 2012 ice-off event.

Zach Feiner, a scientist at the University of Wisconsin-Madison’s Center for Limnology, calls this “phenological whiplash.”

“One year, like last year, you’ll have a really early ice off and spring and then this year is a really late year,” he explains, “So you have back-to-back extremes in opposite directions, so what does that mean for the lake and everything in it?”

Feiner says ice off is like a “light switch” that triggers a lot of activity in our lakes, from the spawning of fish like walleye and muskellunge, to large blooms of the tiny plant life called phytoplankton that form the base of a lake’s food web. When that switch is flipped at increasingly variable times, it can have all sorts of impacts – like larval fish missing the plankton blooms that normally sustain them, or plankton adapted for early spring conditions suddenly forced into action in late May.

Through a combination of being out on the lakes monitoring conditions, conducting experiments in the lab and running ecosystem models through computers, Feiner says, the team can start to piece together how all of these changes are impacting organisms at both an ecological and evolutionary level.

Trout Lake Station postdoc Ray Allen spent his winter building a "fish hatchery" in the Station basement. Photo: Amber Mrnak
Trout Lake Station postdoc Ray Allen spent his winter building a “fish hatchery” in the Station basement. Photo: Amber Mrnak

Of course, like all science, getting to those answers will only happen piece by piece, which brings us back to Ray Allen and TLS’s new “fish hatchery.”

Allen’s role in the project is to focus “on spring spawning fish, like walleye and musky and doing some experiments to see how water temperature may be affecting their survival and development in these changing conditions,” he says.

Luckily for Allen, this year saw a late “ice off” of our lakes, which meant that he was ready to go and as lakes thawed this spring, he was out with colleagues collecting fish embryos, which he brought back to raise in his experimental aquariums.

Those aquariums all hold water that Allen keeps at different temperatures to mimic the variability we are seeing in our Northwoods lakes. He’ll be monitoring how different temperatures impact things like egg viability, larval fish survival and even how extreme temperatures can impact whether a fish develops into a male or female.

What Allen finds might be only one piece of a much larger puzzle of how our changing climate is changing our lakes and, in turn, the organisms living in them. But it’s okay, he says, if that takes some time. “This is very much a short-term component of a larger issue, but it will lead to better knowledge of the long-term.”