A long, strange bloom: Lake Erie algae acted very unusual this year

TOLEDO, OH — Lake Erie was green with toxic algae in 2022, but that is certainly no surprise.

What is a surprise is what kind it was and how long the little green buggers hung around this year — about a month beyond what’s typical for the annual goopy scum season on the lake.

Like an unwanted guest who won’t leave, Lake Erie’s algae bloom loitered well into November — increasing in size after Halloween during a final gasp that has researchers scratching their heads and reviewing their forecast models.

“This was long,” said Rick Stumpf, an oceanographer at the National Oceanic and Atmospheric Administration (NOAA) who leads Lake Erie algae forecasting. “It definitely dragged on for another month beyond some of the recent years.”

Forecasters called this year’s bloom “moderately severe,” a 6.8 on a 10-point scale — much worse than June predictions. In the past 20 years of data-gathering, it’s the sixth worst on record and the only time a bloom lasted into November.

The bloom began in mid-July and, per usual, hit its peak in August, topping out at 380-square miles in size. Most years, strong September winds and cooling temperatures disrupt the bloom and it’s gone by early October.

This year, the algae hung around. On Oct. 31, the bloom spread across 140 square miles, stretching along the coast between Monroe and Oak Harbor. A week later, on Nov. 8, a day before the bloom abruptly sputtered out, its size had doubled to 260 square-miles, many of them covered by dense scums.

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

It changed species.

Lake Erie’s algae is typically dominated by a cyanobacteria called microcystis. In early October, a new strain of bacteria named dolichospermum, or “Dolly,” took over.

“Dolly” isn’t new to Lake Erie. It’s common and sometimes causes blooming in the lake’s central basin, said Stumpf. But that’s usually in July and lasts a couple of weeks.

“In the western basin, it’s usually present. Some years it’s been enough to be noticeable, but it doesn’t dominate the bloom,” he said. “That’s been really rare.”

To the layperson, the difference wouldn’t have been noticeable. Dolly produces green scum that’s harmful like microcystis, which creates a liver toxin that can sicken humans and animals. Thankfully, the toxin levels were very low this fall, but Stumpf said that could have been due to the lateness of the season. Bloom toxin levels typically taper in autumn.

He theorized that nitrogen in the atmosphere may have helped the bloom hang-on into November because Dolly can absorb the nutrients from the air.

It can also tolerate cooler water than microcystis.

The impact of weather conditions on the bloom severity this year is being studied. Warm water temperature coupled with nutrients, primarily phosphorus, fuel algae growth. However, Stumpf said the water was not 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 bloom severity and that can vary significantly each year. Over time, Stumpf said spring runoff appears to be increasing and bringing more nutrients to the lake into early summer when temperatures are increasing.

The Maumee River watershed — which accounts for roughly 90 percent of the total phosphorus entering the lake’s western basin, primarily through farms and livestock feeding operations producing liquid manure — received additional rain and runoff in July as bacteria were starting to grow.

“Whether that’s a cycle that we may come out of, or whether this is a reflection of some climate change, we’re going to have to be looking at,” Stumpf said.

Bloom forecast models are also getting another look.

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

Forecasters use several models from NOAA as well as a couple from Stanford and the University of Michigan. The university models were more accurate this year, said Don Scavia, a UofM aquatic ecologist and forecast team member.

The difference, Scavia said, is that the university models take into greater account the amount of phosphorus already existing in the lake from previous years. Those nutrients settle into sediments and can become re-suspended and available to feed bacteria growth.

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

“I think the difference is worth looking at.”

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