This year's algal bloom was smaller than usual

SANDUSKY — This year's harmful algal bloom in Lake Erie was smaller than usual, and also was smaller than what scientists forecast on July 9. A "seasonal assessment" issued Thursday by scientists at NOAA, the National Oceanic and Atmospheric Administration, reports this year's bloom had a severity index of just 3, much smaller than the 7.3 bloom recorded last year. The Register reported on July 9 that scientists were predicting a mild algal bloom, with a severity of 4.5 So the forecast of a mild bloom turned out to be correct, although the bloom was even smaller than scientists predicted. In Thursday's report, the NOAA scientists say their July forecast was "a small overestimate." By comparison, Lake Erie's largest algal bloom so far, in 2015, had a severity of 10.5, while the large bloom in 2011 was rated a 10. This year's bloom was the smallest since 2012, which was just below 3. All of those numbers refer to how big an algal bloom is during the peak 30 days of the bloom. Algal bloom sizes have fluctuated widely in recent years — the 2020 bloom is very similar in size to the 2018 and the 2016 bloom — so it's apparently too soon to conclude that efforts by state officials to reduce the size of the bloom are already working. "This year had about the same amount of water and phosphorus flowing out of the Maumee River as 2016 or 2018 (all relatively low flow years)," said NOAA scientist Richard Stumpf, the lead author of Thursday's report, in a Friday email to the Register. "When we start to see lower phosphorus concentrations for the same discharge, then we know we are succeeding in phosphorus management. The same amount of water will carry a smaller load of phosphorus," he said. "In that case, with lower phosphorous concentrations, a bigger flow year could still produce only a small bloom." Stumpf was the lead forecaster in July. He created the NOAA email newsletter, which tracks the algal bloom every year. As in the past, forecasters will spend the winter tinkering with their work and studying how they can make their predictions even better in the coming years. "This forecast uses an ensemble of different models, which consider phosphorus loading into the lake during the spring and early summer," Stumpf and his co-authors wrote Thursday. "One of the models correctly forecast the severity, other models over-estimated the severity by different amounts. We will be examining these differences in comparison with forecasts for previous years to evaluate the models," the scientists wrote. The annual forecast relies largely on the amount of phosphorus put into the lake by the Maumee River. That's measured by Heidelberg University's National Center for Water Quality research, which is run by Laura Johnson, a Heidelberg biology professor who also participates in the annual forecast. The Heidelberg lab's measurements show that this year, the Maumee River put less than half as much phosphorus into Lake Erie as in 2015, when the lake had its biggest harmful algal bloom so far. Thursday's report says this year's algal bloom might have been bigger, but that weather intervened. "The winds may have shorted the duration of the bloom. If the peak of the end of August had lasted into mid-September, the severity could have been as high as 3.4, as observed in 2018," it says.