People who spend time on Lake Champlain and other Vermont lakes are probably aware that beaches close regularly during warmer months due to an increased presence of cyanobacteria, often called blue-green algae.
Traditionally, scientists have considered excess phosphorus to be the culprit of cyanobacteria blooms, which can cut off sunlight and oxygen from marine life and cause other harm to humans and the environment. But a recent University of Vermont study finds nitrogen could also play a role in fueling them.
To conduct the study, which was published last month in the Journal of Limnology and Oceanography, researchers collected weekly water samples in St. Albans Bay and Missisquoi Bay to test for phytoplankton, cyanotoxins and nutrient loads.
“We wanted to know what mechanisms were driving the differences in bloom behaviors,” said Kate Warner, who led the study while earning her doctoral degree at UVM’s Rubenstein School of Environment and Natural Resources. “And we found out through taking these samples that it was likely nitrogen that was leading to some of these large scale differences.”
The bays, which are both extensions of Lake Champlain, are shallow and connect to two different watersheds, which allowed the scientists to analyze how different dynamics affect bloom development. They didn’t find the blooms were particularly toxic, but did see differences in size that Warner suspects were caused by nitrogen in Missisquoi Bay.
Researchers discovered that cyanobacteria populations in Missisquoi Bay had double the nitrogen concentration of those in St. Albans Bay, Warner said. “And that could lead to this strong difference in bloom biomass, potentially because they have those extra nutrients to grow.”
The research can provide more insight, data and information into how nitrogen influences the toxicity of blooms, said Mindy Morales, an associate professor at the Rubenstein School of Environment and Natural Resources and co-author of the paper.
“Long term, it’ll inform watershed management specifically around nitrogen,” she said. “Because typically, we’ve really focused primarily on phosphorus in the basin.”
Warner and Morales plan to continue their research next year by collecting and analyzing samples from four sites along Lake Champlain to further understand how nitrogen affects the size and toxicity of blooms.
“My hope is to really understand how different environmental factors can potentially lead to the selection of these non-toxic and toxic strains of cyanobacteria.”
