What’s really ‘fueling’ harmful algae in Lake Okeechobee?

Lake Okeechobee is the largest lake in Florida and the second largest in the Southeastern United States. Over the past two decades, blooms of blue-green algae (Microcystis) have emerged in the lake and have been flushed into nearby urban estuaries, causing serious environmental and public health issues.

Excess nutrients from industries, agriculture and urban development—particularly nitrogen and phosphorus—are well-known causes of harmful algal blooms worldwide. Historically, Lake Okeechobee has only been considered to be impaired for phosphorus, leading to targeted efforts aimed at reducing phosphorus runoff from agricultural sources in the watershed.

Now, new research marks a groundbreaking step in understanding and preserving this crucial ecosystem. Researchers from Florida Atlantic University's Harbor Branch Oceanographic Institute have conducted the first comprehensive sampling across the Lake Okeechobee Waterway in South Florida, which extends from the St. Lucie Estuary on the east coast to the Caloosahatchee River Estuary on the west coast.

To determine what's causing recent cyanobacterial blooms, researchers conducted two research cruises across the Lake Okeechobee Waterway and three sampling events of these blooms. They measured nitrogen isotopes in phytoplankton to see if human waste or fertilizers were involved.

Results of the study, published in the journal Harmful Algae, reveal that combating harmful algal blooms in Lake Okeechobee requires managing both phosphorus and nitrogen, and that human waste played a role in influencing these Microcystis blooms. Findings also underscore the importance of rainfall and extreme rainfall events in driving these big blooms.