OHIO — The annual Harmful Algal Bloom (HAB) forecast for Lake Erie was hosted last Thursday, July 9, by the Stone Laboratory, Ohio Sea Grant, and The Ohio State University. Projections for 2020 indicate that this year’s bloom is likely to be smaller than the previous year. Researchers provided a potential range in severity of between 4 and 5.5 on a scale of 1-10, using 2008 as a baseline. Within that range, this year’s forecast HAB severity is projected to be a 4.5, according to Dr. Rick Stumpf, Oceanographer with NOAA’s National Center for Coastal Ocean Sciences. The HAB severity for 2019 reached 7.3, a near match to the forecasted 7.5 for that year.

In addition to NOAA, the forecast is developed in partnership with Heidelberg University, Ohio Sea Grant, Ohio State University Stone Lab, University of Michigan, Stanford University, Carnegie Institute for Science, and North Carolina State University. The researchers make use of a “sample of models” to develop the forecast, according to Dr. Stumpf. Different teams develop their own models using varying inputs and assumptions, the results are then merged to create the annual HAB forecast.

“It was quite a wet spring [last year],” noted Dr. Strumpf. “The total phosphorus and the discharge were actually equal to the severity of 2011 and 2015. The total bioavailable phosphorus, however, was much lower, and [last year’s] bloom was consistent with that.”

“So, last year nature actually handed us an experiment to confirm that bioavailable phosphorus is the key factor on this, as compared to the total phosphorus.”

As explained earlier by Dr. Laura Johnson of Heidelberg University, bioavailable phosphorus is the measurement of total available dissolved phosphorus, and 8% of particulate phosphorus (typically found as phosphorus attached to soil). For spring 2020, Dr. Johnson’s research found that particulate phosphorus was exceptionally high, perhaps due to excessive runoff from unplanted fields from last year, though that is uncertain. Dissolved phosphorus remained relatively low, though not below the targets necessary to meet the commitments made in the The Great Lakes Water Quality Agreement, according to Dr. Stumpf.

“The target for phosphorus would lead to a severity of 3,” Dr. Stumpf said. “And so, while we are definitely better than last year, we are forecasting that we will be above the target. That means there will be some noticeable bloom out on Lake Erie.” For water entering the lake from the Maumee River, phosphorus levels are measured by Heidelberg University at a station in Waterville. This station is one of 29 stations throughout the watershed where sampling occurs in collaboration with multiple agencies. And, the Waterville station is also one of 24 stations located across Ohio and Michigan that are collectively part of the Heidelberg Tributary Loading Program. Heidelberg University has conducted water sampling in the watershed since 1975 - 45 years. Each station collects water between one to three water samples per day, all year-round, which are retrieved weekly for lab analysis.

In addition to monitoring waterways throughout the Maumee region, Dr. Johnson briefly mentioned the results of soil sampling conducted within the watershed during the presentation’s question and answer session.

“The things that would be affecting something like a dissolved phosphorus runoff in agriculture areas, or, honestly, even golf courses and residential areas, usually the first thing, is over-application of phosphorus,” she said. “So, if you have a lot of soil phosphorus in a field, it tends to just leach dissolved phosphorus.” However, Dr. Johnson immediately noted that soil sample data does not indicate that this is occurring in the watershed. “Now, we don’t see, in any data that we have, that soil test phosphorus in this region is exceedingly high,” she said, “There are very small hot spots, here and there, but it’s not something that is very common for the Maumee River Watershed.”

In response to an earlier question, Dr. Johnson also noted that, “One of the things that we’ve learned is that the ways in which farmers apply fertilizer or manure can have up to, potentially, a 30% reduction or effect on dissolved or reactive phosphorus.”

“But remember to flip that around.”

“That means an awful lot of that load that comes out, that 70%, is reflecting some number of past years.”