HI there! I was just told that it is excess potassium causing blue algae...

Asked August 15, 2019, 1:54 PM EDT

HI there! I was just told that it is excess potassium causing blue algae blooms. Is there any truth to this as I thought nitrogen and phosphorous were the main culprits.

Franklin County Ohio

1 Response

Potassium is an essential nutrient, including for blue-green algae (technically called cyanobacteria). However, I think branding potassium as a "cause" of blue-green algal blooms may be overstatement.

Yes, potassium is necessary to all living things. However, phosphorus is usually described as the most likely limiting nutrient in fresh waters. When professionals discuss causes of blue-green algal blooms, they almost always discuss (1) phosphorus concentrations/loads or (2) the nitrogen:phosphorus ratio (ordinarily as a 16:1 molar ratio which converts to 7.2:1 μg/L). Excessive phosphorus prompts blooms and skews the N:P ratio below these thresholds. However, nitrogen will also need to be present to facilitate the generation of toxins.

An example: the National Oceanic and Atmospheric Administration, Heidelberg University (Tiffin, OH), the University of Toledo, and OSU's Stone Laboratory (Put-in-Bay, OH) collaborate to issue a prediction of how bad the blue-green algae bloom on Lake Erie is likely to be each year. As the season progresses, the bloom almost always falls solidly within the range predicted early in the season. That prediction is based on how much phosphorus is loaded to the lake's western basin by spring rains (note https://www.glerl.noaa.gov/res/HABs_and_Hypoxia/lakeErieHABArchive/projection_2019_07.pdf). It's the amount of phosphorus measured that allows for this remarkably accurate annual prediction.