By Richard Stumpf, NOAA
Lake Erie has experienced late summer cyanobacteria blooms routinely since 2003. Research into the blooms points to phosphorus inputs from local rivers, especially the Maumee, as the prime factor controlling the blooms. To help with management and understanding, the National Ocean Service began an annual forecast of bloom severity in 2012.
By 2014, a numerical severity index ranging from 1 to 10 was developed, making it easier to communicate interannual variations in bloom intensity. The scale was calibrated with the intense 2011 bloom being assigned a 10, with 1 representing little or no bloom biomass over the bloom season from July to October. Overall cyanobacterial biomass was determined using data collected by satellite every one-two days.
The current iteration of the forecast is based on the amount of phosphorus entering the lake in the spring from the Maumee River, which provides the largest single source of phosphorus into any of the Great Lakes and carries a high concentration of bioavailable phosphorus, the form most suitable for supporting algal growth and bloom formation. This phosphorous comes mostly from agricultural runoff into the Maumee River from March to July. Despite these high phosphorous levels, however, intense blooms of cyanobacterial only form from July to September when water temperatures rise sufficiently to allow rapid cyanobacterial growth.
By early May, there is sufficient information from water samples and models to begin to project the size of the bloom. Phosphorus is monitored by Heidelberg University with daily samples analyzed each week. Weather models now allow the National Weather Service to forecast river discharge in Ohio from 45-60 days out, based on models using precipitation and temperature. Combining the measurements and models, NOAA has enough information to cover March to July, and issues a projection of the potential bloom size in early May. This projection is updated each week as more phosphorus measurements are collected. In early July, most of the phosphorus has been delivered, and the formal seasonal forecast is issued.
This year, the annual prediction of bloom severity will be made on July 12 at Ohio State University’s Stone Laboratory. The event is organized with the Ohio Sea Grant program and will include information on other aspects of the bloom and management strategies.
Richard Stumpf is an oceanographer with the National Centers for Coastal Ocean Science, an arm of the US National Oceanic and Atmospheric Administration (NOAA).