Search

Cyanobacteria harmful algal blooms (cHABs) are increasing in frequency and extent globally and their growth is known to be driven by eutrophication. Lake Victoria has year-round blooms of the cosmopolitan cyanobacteria Microcystis aeruginosa, which can produce microcystins that are dangerous at µg/L concentrations and endanger fisheries by bloom decomposition inducing hypolimnion anoxia. Lake Victoria is shared by Kenya, Tanzania, and Uganda and supports the livelihood of more than 73 million people. Using bottle incubations, we assessed the effects of nutrient type (nitrogen (N), phosphorus (P), micronutrients) and form (urea, nitrate, ammonium; phosphate, G6P) on phytoplankton growth and microcystin production across four sites in the Nyanza Gulf of Lake Victoria during June-July 2022. Results suggest primary N limitation followed by serial P and micronutrient colimitation across the gulf. Nitrate addition induced 2-3 times more growth than other N forms at one site, while urea, ammonium and nitrate had a similar positive effect on growth at the remaining three sites. Micronutrient and P effects were spatially variable, but increased growth under micronutrient enrichment suggest that organic nutrient recycling may be limited by micronutrients in parts of the gulf. Though blooms of Microcystis aeruginosa were common, microcystin was only detected (>2 ug/L) at one site (Homa Bay). Our findings will inform best management practices for nutrient management in Lake Victoria's watershed to reduce cHABs in this highly relied upon natural resource. [ABSTRACT FROM AUTHOR]