A Long and Strange Bloom: The algae in Lake Erie have been behaving in a very unusual way this year

TOLEDO, OH – Lake Erie was green with toxic algae in 2022, but that’s hardly a surprise.

What’s surprising is what kind it was and how long the little green buggers have been hanging around this year — about a month beyond what’s typical for the annual sticky scum season on the lake.

Like an uninvited guest who won’t go away, the Lake Erie algae bloom lingered into November, increasing in size after Halloween during a final gasp that had researchers scratching their heads and revising their prediction models.

“This has been a long time coming,” said Rick Stumpf, an oceanographer at the National Oceanic and Atmospheric Administration (NOAA) who leads Lake Erie seaweed forecasts. “It definitely dragged on for another month over some of the last few years.”

Forecasters called this year’s bloom “moderately severe,” a 6.8 on a 10-point scale, far worse than the June forecast. In the last 20 years of data collection, it is the sixth worst record and the only time a bloom has lasted into November.

Flowering began in mid-July and, as usual, reached its peak in August, covering an area of ​​380 square miles. Most years, strong September winds and cooler temperatures interrupt flowering and by early October it has disappeared.

This year the algae stuck around. On October 31, the bloom spread over 140 square miles, stretching along the coast between Monroe and Oak Harbor. A week later, on November 8, a day before the bloom abruptly burst, its size had doubled to 260 square miles, much of it covered in thick foam.

Why the algae persisted for so long isn’t yet known for certain, but Stumpf said the bloom did another unusual thing in October.

It has changed species.

The algae of Lake Erie are typically dominated by a cyanobacterium called microcystis. In early October, a new strain of bacteria called dolichospermum, or “Dolly,” took over.

“Dolly” is not new to Lake Erie. It’s common and sometimes causes blooms in the central lake basin, Stumpf said. But it’s usually in July and lasts a couple of weeks.

“In the Western Basin, it’s usually there. A few years it was enough for it to be noticeable, but it doesn’t dominate flowering,” she said. “It was really rare.”

To the uninitiated, the difference would not have been apparent. Dolly produces a harmful green foam like microcystis, which creates a liver toxin that can make humans and animals sick. Thankfully, toxin levels were very low this fall, but Stumpf could be due to the season being delayed. Levels of bloom toxins typically taper off in the fall.

He theorized that the nitrogen in the atmosphere may have helped the bloom last through November because Dolly can absorb nutrients from the air.

It can also tolerate colder water than microcystis.

The impact of weather conditions on the severity of flowering this year is being studied. The warm water temperature combined with nutrients, mainly phosphorus, fuel algae growth. However, Stumpf said the water was no warmer than usual in October. It also wasn’t rainier than normal, which would have helped bring more nutrient runoff to the lake.

The amount of rain each spring is a huge factor in the severity of flowering and can vary significantly each year. Over time, Stumpf said spring runoff appears to increase and bring more nutrients to the lake in early summer when temperatures rise.

The Maumee River watershed, which accounts for about 90 percent of the total phosphorus that enters the lake’s western basin, primarily through farms and livestock feeding operations that produce liquid manure, received additional rainfall and runoff in July as bacteria they started to grow.

“If this is a cycle that we could break out of, or if this is a reflection of some climate change, we will have to watch,” Stumpf said.

Bloom prediction models are also taking another look.

On Nov. 16, NOAA issued a final bloom assessment that addressed the discrepancy between predicted bloom severity (3.5) and actual severity (6.8). The difference suggests that current forecasting models “lack a component of flowering dynamics.”

Meteorologists use several models from NOAA and a couple from Stanford and the University of Michigan. University models were more accurate this year, said Don Scavia, an aquatic ecologist at UofM and a member of the forecasting team.

The difference, Scavia said, is that university models take more account of the amount of phosphorus already in the lake from previous years. These nutrients are deposited in the sediment and can be resuspended and available to feed the growth of bacteria.

“Our models account for this and their (NOAA) models don’t, and that could be one of the differences in this year’s predictions,” Scavia said. “NOAA uses the ensemble — all models — which is the right thing to do, but then you end up with sort of an average forecast rather than the extremes.”

“I think the difference is worth looking at.”

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