A study spanning more than ten years across three lakes has found that heatwaves have a dramatic impact on algae blooms.
Algal growth in one lake increased, on average, by 57 percent in the days following a heatwave – and that was the least impacted lake in the study. A second lake saw that number more than double, with a mean increase of 127 percent, while algal production in the most-impacted of the three lakes increased by 183 percent after heatwaves, nearly triple its normal conditions. The report was published May 1 in the journal Limnology and Oceanography Letters.
Heatwaves seem to “magnify what’s going on in the lake,” says the study’s lead author, Danny Szydlowski.
For example, a heatwave that occurs during the first algae bloom of the season or right after a large dose of nutrients have entered a lake sets conditions on a course toward explosive algal growth. In times of fewer disturbances, “you still see a bump [in algal productivity],” he says, but “it is just not as dramatic.”
Szydlowski, who is a graduate student at the University of Wisconsin-Madison’s Center for Limnology, says his research does more than show a conclusive connection between heatwaves and algal growth in lakes, it points to important management considerations.
“We can’t control the weather, but we can focus on things we can control like nutrient inputs, or invasive species that might come in and lead to food web disturbances,” he says, noting that any management actions that create more stability in a lake can help minimize the severity of impacts when a heatwave occurs.
His study also underscores the importance of long-term research, Szydlowski says.
“By definition heatwaves are these rare, extreme temperature events, so in a given summer you might have only one or two of them,” he says. “Unless you’re sampling every single day of the summer, you’re not going to capture their effects on lakes.”
Luckily, sampling lakes every day of the summer is exactly what Szydlowski’s been doing the past few years. He has helped monitor Peter, Paul and Tuesday Lakes, which all sit within the boundaries of the University of Notre Dame’s Ecological Research Center, perched on the border of Wisconsin and Michigan’s Upper Peninsula.
The lakes have a storied history in freshwater research and have been the site of numerous foundational experiments. They have also, for the past decade, been the subject of daily scientific monitoring from May through August each summer – rain or shine, teams of researchers and their undergraduate field technicians have taken their boats out onto the lakes to collect water samples and analyze them for, among other things, chlorophyll concentrations, which are an indicator of algae growth.
Without that daily sampling, Szydlowski says, it would have been impossible to follow the lakes’ response to heatwaves. Over those ten summers, 29 different heatwaves occurred. And 24 of those heatwaves triggered increased algal growth – a powerful indicator of how they impact lakes.
“The fact that we were able to see an increase [in algae] following that many events is really unique,” Szydlowski says. “In ecology you rarely see something that is so consistent.”
Except, of course, for the summer crews of researchers heading out to collect data on Peter, Paul and Tuesday Lakes – day after day, year after year.
Full report available here: https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lol2.70024
Media Contact: dszydlowski@wisc.edu or hinterthuer@wisc.edu, 608-630-5737