About ten years ago, a bloom of cyanobacteria appeared in Lake Superior. Since that time, scientists have searched for answers as to why this problem occurs in this specific lake.
Lake Superior—bordered by Canada, Minnesota, Wisconsin, and Michigan—holds one-tenth of our planet’s surface freshwater. The largest of the Great Lakes of North America, Lake Superior is also the world's largest freshwater lake by surface area and third largest by volume.
Cyanobacteria, also known as Cyanophyta, are blue-green algae that can use up oxygen and block light, harming organisms trapped underwater. Due to their short life, however, the few blooms that do occur in Lake Superior are typically small. Samples and good data are limited.
Besides harming other species in the lake, these organisms can threaten the health of fish, dogs, and humans through the toxins they create—which can make their way into water intakes.
Things that propel algae blooms tend to be temperature, sunlight, water conditions, and nutrients—such as phosphorus, which can wash into lakes from farm fertilizer and manure. But unlike Lake Erie and Lake Michigan’s Green Bay—which are warmer, shallower, and are surrounded by sources of agricultural runoff—Lake Superior is cold, deep, and without many nutrients.
Since the first bloom was reported in Lake Superior in 2012, no major levels of toxins had been confirmed. Then, in September of 2021, a bloom was spotted near the port city of Superior, Wisconsin. Not only was a beach’s water left streaky green, but a toxin stronger than cyanide—a rapidly acting, potentially deadly chemical—was also detected. This measurement was made just above a level the United States Environmental Protection Agency has set for safe swimming.
Algae blooms in northern Canadian waters of Lake Superior, for example, have appeared in areas that are primarily forest and woody wetlands. These areas show only small amounts of agricultural and urban residue in the water, which leads scientists to wonder what causes blooms in this lake.
“The data have convinced me that the changing climate system has pushed Lake Superior into a new state, one where we get these blue-green blooms,” said Robert Sterner, director of the Large Lakes Observatory at University of Minnesota-Duluth. “One of the things that’s driving our work is if, in fact, we’re in the beginning of something that’s getting worse, we really owe it to the world to try to understand this circumstance as best we can.”
Throughout the summer of 2021, scientists from local universities and state and federal agencies spent time collecting, filtering, and testing water from Lake Superior. They’re hoping to learn more and help the lake and other lakes that struggle with algae blooms.
In general, the Great Lakes region has seen an increase of about 10% in annual precipitation during the past century. Temperatures are also expected to increase. A recent climate assessment funded by the EPA said, “by the end of the century, annual average air temperatures near Lake Superior could increase by as much as eight degrees.”
Dave Zweifel called attention to the issue in a column for The Capital Times. “Yet another warning that climate change is causing problems not just for those who live in lowlands, in fire-prone forests or depend on water sources that are rapidly drying up,” Zweifel wrote. “It's becoming a problem for us all.”
[Sources: Chicago Tribune; The Capital Times]