By Georgia Hill

Rising temperatures and changing environmental conditions in the Great Lakes contribute to harmful algal blooms. New research suggests that the nearshore regions of Lake Superior could indicate climate change’s effects on the region’s ecosystem. 

Cyanobacteria, also known as blue-green algae, are a type of bacteria found in freshwater that can grow rapidly and produce toxins that cause harm to animals and humans.

Cyanobacteria blooms are often associated with warm, nutrient-rich lakes. But some recently have been showing up in cold, low-nutrient lakes such as Superior, according to a study recently published in the Journal of Great Lakes Research.

The study cited reports of four cyanobacteria blooms along the north shore of Lake Superior since 2019. But monitoring information about these blooms – and potentially, future blooms – is limited, according to the authors from York University and the Ontario Ministry of the Environment.

The researchers wanted to get a better idea of which cyanobacteria species were growing in northern nearshore areas of Lake Superior, and which environmental conditions contributed to algae growth.

They collected samples from ten nearshore stations along the Canadian shoreline throughout spring, summer, and fall over the course of one year.

Across all seasons and sampling locations, the researchers identified 23 cyanobacterial species. They found the most cyanobacteria growing in embayments and bays. Growth was also linked to higher nutrient levels and stormy conditions.

Cyanobacteria blooms are not yet a widespread concern on Lake Superior, and these species make up a small fraction of the algae in the lake, according to the study. But excessive growth of this bacteria can lead to blooms that impede recreation and deplete the oxygen in the water, said Kirill Shchapov, lead researcher on the study and freshwater ecologist now at the Cawthron Institute in New Zealand. This is especially true in cold, low-nutrient lakes like Superior. 

“Lake Superior is warming much faster than the other Great Lakes,” said Shchapov. “But it is also in an area far from large human populations.”

The north shore of Lake Superior is a pristine area with a majority of untouched land, which made the discovery of this bacteria all the more interesting, said Schapov. 

However, agricultural runoff, less ice cover in the wintertime, and strong storms that deposit nutrients all make the lake more hospitable for these species. 

Cyanobacterial blooms in Lake Erie and Lake Michigan are more common due to warmer waters and a larger human population around nearshore locations. Because Lake Superior is a cold, low-nutrient lake with less land development, finding cyanobacterial blooms in nearshore locations tells us how quickly climate change is impacting the lake. 

Evidence of climate change in areas like this highlights the extent of its impact on the environment, said Sapna Sharma, a professor of biology at York University who supervised the funding and execution of the study. 

“I think about climate change a lot in this situation because this is a colder area where there aren’t that many people,” said Sharma. “It speaks to the fact that more nutrients are getting into the lake, but also Lake Superior in particular is warming.”

Sharma said that increases in cyanobacterial blooms, especially in pristine areas in the middle of nowhere, warrant more intense and frequent monitoring in areas with closer human populations. 

According to the U.S. Environmental Protection Agency, cyanobacterial blooms can deplete the oxygen in water, making it unsustainable for fish populations. The blooms can also produce toxic byproducts known as cyanotoxins. 

When these toxins are ingested by humans and animals, they can cause health effects ranging from headaches and skin irritation to liver or kidney damage. 

While these blooms have adverse effects on the environment and the health of populations around the lakes, Shchapov said that frequent monitoring and research of algal blooms can help to predict the frequency of these blooms and help prevent them from harming the environment and the people who live around the Great Lakes.