Algal bloom this year was bigger than expected

PORT CLINTON — The 2023 harmful algal bloom in Lake Erie was more severe than expected. And it's possible that climate change could be the reason, as the blooms are getting started earlier, a federal scientist says. Dr. Richard Stumpf, a National Oceanic and Atmospheric Administration oceanographer who has been studying Lake Erie's harmful algal bloom for years, discussed this year's bloom after a federal agency issued a final report. On June 29, Stumpf and other scientists gathered at Stone Laboratory at Put-in-Bay to issue the algal bloom forecast for this year. It's an annual event that's been taking place for years. Stumpf and his colleagues predicted an algal bloom that would measure as a 3 in severity, on a scale of 1 to 10, with a potential range in severity from 2.5 to 4. Instead, a "seasonal assessment" issued on Nov. 2 by the National Centers for Coastal Ocean Science reported that the bloom this year actually had a severity index of 5.3, defined as moderately severe. That's still less than the 6.8 measured for the 2022 bloom, but larger than scientists had expected. Severity is defined as the estimated biomass of the bloom and the area it covers, as shown in satellite photos. The 2023 bloom covered 312 square miles versus 416 square miles last year. It peaked in mid-August and largely hugged the U.S. coast, stretching from Monroe, Michigan, to Port Clinton in Ohio. The bloom started on July 4, the second-earliest start since 2002. Only the 2018 bloom started earlier. Stumpf cited the early start of the bloom as one factor explaining why it was bigger than expected this year. "More severe is a combination of factors," he explained in an email to the Register. "The biggest factor is that the blooms are starting earlier now, in July, this year at the very beginning of July," Stumpf wrote. "The bloom starting earlier may allow it to more effectively use more of the phosphorus. Smaller blooms tend to not use all the phosphorus the Maumee River provides. "An additional one is timing of the peak bloom resulting from the early start. Our 2015 paper showed blooms tending to peak about Labor Day in the data to that time. However, now they more often peak in August," Stumpf wrote. "This gives the bloom more time to sit at the peak biomass, causing what I call a 'plateau', rather than a 'peak.'" The Register asked Stumpf if climate change is warming the lake's water and causing the bloom to start earlier. "We are working on the question. Climate change is likely. We are now looking at whether water temperature in late spring is a factor," Stumpf said. "We have evidence of a link to winter temperature. There is less ice on the lake in more recent years. This may alter the ecosystem in a number of ways," he wrote. "We are looking at timing of spring bloom — of diatoms and such, the 'good' algae — to see if that has changed because they do compete." Stumpf noted that, in August, a revised forecast had been issued that was closer to the mark. "Forecasting duration is a challenge, but we will be looking into it," he wrote. "This year, our update on Aug. 1 picked this up pretty well. The goal is to bring this into the initial seasonal forecast of about June 30."