A Tale of Three Lakes | Ohio Sea Grant

[ ☰ ] Ohio State University

The Ohio State University

Ohio Sea Grant


A Tale of Three Lakes

12:00 pm, Sun April 28, 2024 – Great Lakes Sea Grant researchers are examining how different nutrients and temperature influence harmful algal blooms and their associated toxins

In the first highly integrated experimental study of cyanobacterial harmful algal blooms across diverse Great Lakes environments, researchers are examining three of the Great Lakes to determine how different nutrients and temperature influence bloom growth and resulting toxins.

The results are illuminating the similarities and differences in how blooms start, persist and produce toxins in these diverse environments and will inform more specific bloom management strategies.

close-up of algal bloom with a bridge in the background

A large bloom of Microcystis cyanobacteria near the mouth of the Fox River looking south toward the Leo Frigo Memorial Bridge in Green Bay, WI.

“We’re dealing with lakes with different histories, geochemistries and blooms, and we can’t put all cyanobacteria into one box and find one single solution,” said George Bullerjahn, Distinguished Professor Emeritus of biology at Bowling Green State University. “This research will target each lake and identify potential management strategies special to those environments. It would be great if we could say every bloom is the same, but that’s clearly not the case.”

For the Ohio Sea Grant-funded research, Bullerjahn is focused on studying Lake Erie, specifically in the central basin and Sandusky Bay. Meanwhile, Todd R. Miller, associate professor in the Joseph J. Zilber College of Public Health at the University of Wisconsin Milwaukee, is examining waters from Green Bay in Lake Michigan, and Robert W. Sterner, director of the Large Lakes Observatory and professor of biology at the University of Minnesota Duluth, is conducting research on waters from western Lake Superior. Both are receiving funding from their respective Great Lakes Sea Grant programs.

Cyanobacterial harmful algal blooms have increased in frequency and toxicity over the past few decades driven by a warming climate and nutrient loading, which occurs when excess phosphorus and nitrogen from fertilizers and sewage treatment plant discharges run off into the surrounding water. These increasing blooms have public health ramifications on drinking water, recreational activities and food production and come with economic costs, such as resulting decreases in tourism and fishing.

Dr. Todd Miller and Ph.D. student Anjana Adhikari talk about their Sea Grant-funded research looking at the causes of cyanobacterial harmful algal blooms.

To date, these blooms in the Great Lakes have been investigated lake-by-lake or even river-by-river, with studies in each location tuned to local perspectives and framed with different research questions, making it difficult to generalize findings and determine how results from one location can be applied elsewhere.

a person on a boat using a hose to fill up a jug

Through the project, researchers collected water samples from the three Great Lakes and then amended them with nitrogen and phosphorus.

In this new Sea Grant project, the researchers standardized an experimental approach to compare how patterns of nitrogen and phosphorus affect algal blooms and vary across Lakes Superior, Michigan and Erie and how those are influenced by temperature and climate change. Through short (48 hours) and long (28 days) bioassays — biochemical tests — they’re examining the factors that cause a bloom as well as those that influence the bloom and its toxicity over time.

“If people wanted to do similar kinds of assays in other lake systems, this would be a good template to use,” Bullerjahn said. “If someone wants to look at bloom drivers, say, in Lake Balaton in Hungary, they could do it like this. If anybody across the world did it this way, it might be a nice comparison to what we see in the Great Lakes.”

Using the single experimental design over a period of two years, the researchers conducted short experiments to determine what nutrients — nitrogen, phosphorus, or a combination of both — drive the blooms and cause them to expand. They are also examining the influence of temperature by running experiments at ambient temperatures and with an increase to reflect a modest amount of climate change. This will allow researchers to see how current biological communities differ in growth in a warmer world.

“A little bit of warming, even just 3 degrees, gives us measurably higher biomass and therefore faster growth,” Sterner said, noting that the change occurred in the absence of any added nutrients. “Given a 9-day window, twice as much algae is produced under warming conditions than under ambient conditions.”

Through longer experiments, the researchers examined how blooms change and what resulting toxins win out in the long run.

Lake Superior

Lake Superior is an oligotrophic lake, meaning it has low nutrients, algae, and zooplankton. Sterner said blooms in oligotrophic lakes aren’t very well studied.

“Cyanobacterial blooms on Lake Superior were unheard of prior to 2012. We see them now especially in warm years, and the largest blooms have happened in years of very large rainstorms,” Sterner said.

large bottles filled with liquids sit on racks

Researchers conducted biochemical experiments called assays to study the factors affecting bloom growth and toxicity. Here, large bottles are bubbled with air in a “long” assay.

In this three-state study, regarding bloom growth responses, Lake Superior had the most consistent growth response to phosphorus, especially when combined with elevated temperatures. Sterner also documented the surprising appearance of blooms caused by a cyanobacteria organism called Dolichospemrum.

“I sometimes think of short bioassays as telling us about what steers the community during its seasonal progression,” Sterner said. “Knowing whether the journey turned left or right helps us understand the pathway that was taken. The results of our work are most directly applicable to questions of whether nitrogen, phosphorus or both should be controlled.”

“Analysis is still underway in our long assay study, but my graduate student Reane Loiselle is seeing taxonomic differences in algal response to nutrients that will help us understand what factors promote different algae when they compete with each other for nutrients,” Sterner said.

Lake Erie

“In Lake Erie it’s a little more complicated, but really nitrogen is the bigger player here,” Bullerjahn said. “Early on in the spring, phosphorus appears to play a more important role, but further in summer and fall nitrogen takes over as the dominant nutrient.”

“The messaging here is we need to limit phosphorus to starve out the bloom. It looks to me that might help, but we need to keep eye on nitrogen, because nitrogen additions later in summer increase the bloom. We see that both at ambient and elevated temperatures,” Bullerjahn said. “This problem isn’t going to go away and will probably get worse with higher temperatures.”

Lake Erie algal blooms show mixed communities of cyanobacteria organisms that include Dolichospemrum as well as Microcystis and Planktothrix. In Sandusky Bay, an ecosystem in transition, Planktothrix blooms were common for most of the past two decades. But such a bloom did not occur in the 2022, the first year of the project. Instead, an Aphanizomenon cyanobacterial harmful algal bloom occurred in June, potentially producing a novel suite of cyanotoxins that could be harmful to human and animal health. This work may help determine the conditions that may favor the historical Planktothrix cyanobacterial harmful algal blooms over the current Aphanizomenon bloom, and vice versa.

2014 Frank Lichtkoppler Retirement

A “short” bioassay setup used by researchers at the University of Minnesota Duluth to study how nitrogen and phosphorus drive blooms over a 48-hour timespan.

Lake Michigan

Miller’s team in Wisconsin is studying the blooms in Green Bay and the Fox River at Lake Michigan.

Green Bay is impacted by heavy nutrient loading, Miller said, and most of these nutrients are introduced through a single major river, the Fox River, which drains an agriculturally intensive Fox-Wolf watershed.

“This is similar to the western basin of Lake Erie and Maumee River basin. The type of species causing blooms is also similar between the two systems. Microcystis is the dominant species in both systems. However, Green Bay also frequently has blooms of other species, particularly nitrogen fixing Aphanizomenon and Dolichospermum, and in late fall the blooms tend to be mixed with eukaryotic species.”

“Both short and long bioassays show that Green Bay phytoplankton, particularly cyanobacteria, grow mainly in response to nitrogen additions relative to phosphorus and mixed responses to increases in temperature,” Miller said. “Toxin production also increased in response to nitrogen additions. Whether toxins increased due to growth or increases in production per cell is still being teased apart.”

What’s next for this research?

Now, the researchers want to break their results down to a molecular level and determine the genetic diversity of the blooms and what toxins they make, which will take the rest of 2024 to conclude. Having a better understanding of what conditions cause certain cyanobacteria to make a certain compound will help the researchers advise water treatment experts about detailed management strategies.

“When you look at a bloom, it looks like green paint cast on water. It might be Microcystis, but it’s not a monoculture. There are genetic variations within that bloom,” Bullerjahn said. “Some are toxic genotypes, some are nontoxic. Some form large colonies, some form small colonies. It’s a much more complicated system in terms of the diversity of the cyanobacteria than what’s apparent to the naked eye.”

“The messaging here is we need to limit phosphorus to starve out the bloom. … This problem isn’t going to go away and will probably get worse with higher temperatures.”
Dr. George Bullerjahn

The researchers will make their data available to the public later this year and publish their research findings in 2025.

“We can make recommendations or summarize what we’re seeing in light of management decisions,” Bullerjahn said, “but it’s up to the water managers to make those decisions.”

For more about this multi-Sea Grant-funded project, watch the latest Freshwater Science webinar, featuring the three researchers.

Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.

ARTICLE TITLE: A Tale of Three Lakes PUBLISHED: 12:00 pm, Sun April 28, 2024 | MODIFIED: 1:24 pm, Mon April 29, 2024
Share Streams Print
Joan Slattery Wall
Authored By: Joan Slattery Wall
Writer/Editor, Ohio State University - John Glenn College of Public Affairs  FIND MORE TAGGED as HARMFUL ALGAL BLOOMS, RESEARCH