Connection found between nitrogen levels in water and toxic algae production

Scientists have long known that phosphorus fuels growth of algae in lakes and streams. Wisconsin Sea Grant researchers have found that nitrogen levels are a factor in whether or not these algae - specifically, blue-green algae -produce toxins. The findings, published inPLOS ONEhave parts of the scientific community buzzing."Under certain circumstances, it's thenitrogenlevels 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. "Phosphorus is important, but you need to have that critical component of nitrogen stress to trigger toxin production."

The study, conducted on Lake Mendota in 2010-2011, involved multiple measurements each week during the summer for the presence of blue-green algae along with nitrogen and phosphorus levels. The first year of testing, researchers noticed a distinct change in the blue-green algae population. "There was a massive bloom of nontoxic blue-green algae in the lake in late June," said Lucas Beversdorf, who was McMahon's Ph.D. student at the time. "The algae used up all the nitrogen in the water, and then the bloom disappeared. After that, we started to see the production of toxic blue-green algae."

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Taxonomy

• Water Quality
• Toxins
• Aquatic Ecologist