News Feature | November 28, 2013

Research: Lack Of Nitrogen Turns Some Algae Toxic

Sara Jerome

By Sara Jerome


Researchers are getting closer to understanding what causes blue-green algae—a nuisance keeping swimmers out of lakes across the country—to grow, thrive, and become toxic.

It was already known that phosphorus promotes algae growth. "But why some blue-green algae would turn toxic remained a mystery" until researchers studied algae on Lake Mendota in Madison, WI, Capital Newspapers recently reported

They found that blue-green algae turns toxic due to a lack of nitrogen, the report said, citing researchers at the UW-Madison Sea Grant Institute.

“Under certain circumstances, it’s the nitrogen levels that fuel the production of toxins in blue-green algae,” said Katherine McMahon, a professor with the Department of Civil and Environmental Engineering at the University of Wisconsin-Madison, in an announcement from the Institute. “Phosphorus is important, but you need to have that critical component of nitrogen stress to trigger toxin production.”

The findings are published in PLOS ONE. The unpredictability of algae made it fertile ground for research.

"Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales," the abstract explained.

The study explored algae patterns dating back centuries. Lucas Beversdorf, one of the researchers, pored over records from Lake Mendota dating back to the late 1800s. He discovered that the shift in these blooms "happened every year at the same time. This could help researchers and public health officials predict the likelihood of harmful algal blooms occurring in the lake," the announcement said. 

Why do algae follow this pattern? "We suspect it’s some sort of survival mechanism,” Beversdorf said. “The cells are just trying to maintain their homeostasis until there’s enough nitrogen for them to get back to their normal growth patterns.”

As it turns out, the blooms come in peace. 

“The algae aren’t making the toxin to hurt anybody,” McMahon said. “One theory is that they’re making it to store nitrogen and by accident, it happens to be toxic to humans, dogs and cows, etc...”

Blue-green algae can cause liver damage in people and kill animals, Water Online previously reported. 

Image credit: "Flood Fight Shots - KC 056," © 2010 Kansas City District, used under an Attribution 2.0 Generic license:

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