A look at farm phosphorus in the Lake Erie Harmful Algal Bloom Forecast for 2024

By Dusty Sonnenberg, CCA, Field Leader, a project of the Ohio Soybean Council and Soybean Check-off (Adapted from NCCOS, Richard Stumpf)

For the last decade, each spring the attention of residents along the coast of the Western Lake Erie Basin, and other lake stakeholders curiously await the prediction of the Lake Erie Harmful Algal Bloom Forecast. The Western Lake Erie Harmful Algal Bloom Early Season Prediction was released in early May. The projection is a joint effort of the National Oceanic and Atmospheric Administrations (NOAA) along with the National Center for Water Quality Research at Heidelberg University.

What is the initial projection?

In the summer of 2024, Western Lake Erie is projected to experience a moderate harmful algal bloom (HAB), according to the first 2024 Lake Erie Harmful Algal Bloom Early Season Projection issued by NOAA’s National Centers for Coastal Ocean Science (NCCOS).

Models from this spring indicate a likely bloom severity between 4.5 and 7.5 (a moderate bloom is closer to a severity of 5). To date, precipitation and total bioavailable phosphorus (TBP) loads from the Maumee River in April were well above average, with the second highest April TBP loads since 2000. If precipitation for the rest of the spring remains near or below average, a moderate bloom is likely. If precipitation continues to be above average, a bloom with a severity closer to 7 is expected. The uncertainty for this forecast will continue to narrow as additional rain and river discharge data is collected over the next few weeks.

How is the forecast determined?

The severity of the western Lake Erie cyanobacterial bloom depends on input of total bioavailable phosphorus (TBP) from the Maumee River during the loading season of March 1 – July 31. The NOAA forecast gives an estimate of potential bloom severity based on a combination of TBP measurements to date collected by Heidelberg University and forecasts of river discharge (by NOAA’s Ohio River Forecast Center) and phosphorus loads from now into July.

Projections of the bloom’s severity will be issued weekly through late June. On June 27, NOAA will issue the official Lake Erie HAB Seasonal Forecast in coordination with Ohio Sea Grant. Any bloom that develops will change with time and move with the wind, and NOAA will provide information on the presence and location of any bloom throughout the summer.

Projections of the bloom’s severity will be issued weekly through late June. On June 27, NOAA will issue the official Lake Erie HAB Seasonal Forecast in coordination with Ohio Sea Grant. Any bloom that develops will change with time and move with the wind, and NOAA will provide information on the presence and location of any bloom throughout the summer.

How does agriculture factor into forecast?

Along with the phosphorus from agricultural fields found in the river from the spring rains, another form of P load comes from what has been referred to as legacy phosphorus.

“This is the phosphorus that was already found in the lake or is held in the soils that have high phosphorus levels. This is phosphorus available to the algal bloom every year,” said Chris Winslow, director of the Ohio Sea Grant College Program.

Ohio’s farmers, along with other commodity groups and agricultural organizations in the state, have invested millions of dollars in research aimed at determining the cause of the algal bloom, and finding potential management practices to functionally mitigate the problem. Farmers are working closely with universities, government agencies, and environmental groups to make changes to protect the water. Practices like cover crops, nutrient management plans, soil sampling and more are increasing every year, and farmers are applying less fertilizer than ever before.

What trends have been seen with regard to on-farm phosphorus use?

Greg LaBarge, CPAg/CCA, Ohio State University Extension Field Specialist, Agronomic Crops, provided the following update over the winter regarding trends in P use in Ohio, which can have negative impacts on water quality resulting in algal blooms. Fertilizer P can increase crop yields. Yet, excessive P can have negative impacts on water quality, resulting in toxic algal blooms. To properly calibrate the use of P for maximum crop yield efficiency and environmental safety, it is important to monitor P use trends, understand the changes to P recommendations from 1995 to today, review changes in soil test phosphorus (STP), and identify the sources of P used. Two recent factsheets examine P nutrient use at two scales: statewide and regional. The regional results were summarized by Crop Reporting Districts (CRD). The two publications and their links are Phosphorus (P) Nutrient Use in Ohio ANR-0143, found at https://go.osu.edu/ohiop, and Ohio Phosphorus (P) Use by Crop Reporting District ANR-0144, found at https://go.osu.edu/ohiocrdp.

These two reviews of P use reveal several trends impacting agronomic management and environmental outcomes: Ohio purchased P fertilizer use is trending downward. During the highest use period (1993–1997), 206,000 tons of P2O5 were applied annually. In the most recent period (2018–2022), annual applications averaged 137,000 tons. Agriculture reduced the average yearly P2O5 application by 33% between the two periods.

All nine Ohio crop reporting districts (CRDs) show a declining trend in P2O5 usage from 1994 to 2022. The reduction rate ranges from 50 to 868 tons annually. Seven of nine Ohio CRDs show increased availability of P2O5 sourced from manure. CRD 30 and 80 show a decline. The 2017–2022 average annual increase in manure P2O5 is 28 to 355 tons for the seven districts with an increase.