Toxic cells survive winter and trigger algal blooms in Lake Eerie

Lake Erie is the 4th largest of the Great Lakes and is surrounded by both the United States and Canada. The lake supplies drinking water to 11 million people and it is a crucial natural resource.

Unfortunately, Lake Erie is also prone to harmful algal blooms during the summer months, sometimes growing so large as to make drinking water unsafe.

These algal blooms are driven by nutrient runoff from agricultural operations, but other factors can contribute to the blooms such as water temperature and precipitation.

A new study conducted by researchers from the University of Michigan has discovered that the blooms are triggered by specific cyanobacteria cells that lay dormant over the winter in sediment at the bottom of the lake.

Algal blooms are made of Microcystis, a type of cyanobacteria, and in the spring, the overwintering cells emerge from the bottom.

The study, published in the journal PLOS ONE, helps explain why algal blooms are so prevalent in the beginning summer months.

“The study suggests that the initial buildup of blooms can happen at a much higher rate and over a larger spatial extent than would otherwise be possible, due to the broad presence of viable cells in sediments throughout the lake,” said Christine Kitchens, a lead author of the study. “These overwintering cells can quickly be entrained within the water column–particularly after a storm event–and start actively growing.”

Previous studies have shown that overwintering Microcystis cells can survive harsh conditions as well as “seed” seasonal algal blooms, but it was not known if the cells were behind blooms in the Great Lakes, including Lake Erie.

To find out, the researchers collected sediment-core samples at 16 sites across 145 square miles of Lake Erie over a two year period.

After the samples were collected, the researchers conducted a series of lab tests to see if Microcystis cells can survive over winter and how many of the cells produce toxic bacteria.

The researchers found that the cells could still grow after spending a winter in the water and toxic strains of the bacteria grew faster than non-toxic strains.

The study explains why the percentage of toxic cells is higher in the early summer months, which is something the National Oceanic and Atmospheric Administration’s Lake Erie monitoring program first observed.

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By Kay Vandette, Earth.com Staff Writer