Factsheet – Nutrient stoichiometry and cyanobacterial blooms in the Ohio River

In recent years, cyanobacterial blooms have been observed throughout the Ohio River, and during these blooms cyanotoxin concentrations often exceed the WHO moderate-risk recreation threshold of 10-20 µg/L, and occasionally exceed 5,000 µg/L (Ohio River Valley Sanitary Commission [ORSANCO] online data). Despite the tremendous threat posed by cyanobacterial blooms, predicting the onset, severity, and duration of cyano-HABs remains a major challenge, particularly in rivers. Additionally, depletion of DSi is a potential trigger for a cyano-HAB, but testing this hypothesis requires concurrent data on DSi, and such data are rare, particularly in rivers. The project used a combination of historical data analysis and original data collection, coupled with a stoichiometric index, to gain insights into cyano-HAB formation in the Ohio River. We found that silicon can play a strong role in determining which types of algae are dominant in the Ohio River at different times of the year and that silicon is likely to play a role in the occurrence of algal blooms in the Ohio River.