Florida Tech Study Links Low Oxygen to Algal Blooms

Florida Tech researchers have linked low oxygen levels in the Banana River to the release of nutrients that feed harmful algal blooms, according to a study published in August in Frontiers in Marine Science.

Scientists tested oxygen levels at 80 locations across the Banana River, part of the Indian River Lagoon system that stretches from near Kennedy Space Center southward. They found dissolved oxygen at the river floor was 10 to 15 percent lower than at the surface, threatening bottom-dwelling organisms like clams, shrimp and worms even when fish in upper layers face no immediate threat.

"If you're a fish swimming in the water above the bottom, you may not even notice that there's an oxygen problem," said Austin Fox, an assistant professor of marine sciences at Florida Tech and the study's lead author. "What does notice are all the clams and the shrimp and the worms and all the things that dig around in the sediment."

Researchers also identified "muck," a fine-grained organic sediment on the riverbed, as a contributor to low oxygen in areas up to 500 meters away. When organisms that keep sediment oxygenated die off, phosphorus trapped beneath the muck re-enters the water, triggering algal blooms that worsen oxygen depletion—a cycle researchers call internal nutrient loading.

Hypoxic conditions occurred 90 percent of the time at one or more sensor locations. Fox's team is now quantifying the full impact of low oxygen in the Indian River Lagoon and its tributaries to identify nutrient sources and develop solutions.