Understanding the Effect of Salinity Tolerance on Cyanobacteria Associated with a Harmful Algal Bloom in Lake Okeechobee, Florida

USGS takes a deep dive into red tide and examines the relationship between USACE water management decisions on Lake Okeechobee, nutrient loading, and coastal red tide blooms. The paper also examines other factors impacting certain red tide species such as salinity. Great read on the science of red tide. (Scientific Investigations Report 2018–5092, U.S. Department of the Interior, U.S. Geological Survey)

Lake Okeechobee (located at 27o north latitude and 81o west longitude) is a large shallow lake (1,900 square kilometers [km2]) that receives inflow from the Kissimmee River and other smaller tributaries (fig. 1). The bloommaterial for this study came from Eagle Bay on the north side of the lake. An earthen dike that surrounds the lake wasconstructed to control adjacent flooding. When lake stage threatens the integrity of the dike, water is released to the Atlantic Ocean through the St. Lucie Canal and to the Gulf of Mexico through the Caloosahatchee River. Releases follow the Lake Okeechobee Regulation Schedule, developed and implemented by the U.S. Army Corps of Engineers and theSouth Florida Water Management District (SFWMD), toensure the lake is at a low enough stage to accommodate summer season runoff and rainfall (U.S. Army Corps of Engineers, 2008).

Lake Okeechobee is classified as a moderately eutrophic (Brezonik and Engstrom, 1998) shallow waterbody that hasundergone ecological changes because of external nutrient loading from agriculture (Havens and others, 1996) and, more recently, by internal loading of phosphorus from lakebed sediments (Pollman and James, 2011). Ample phosphorus and other nutrients create the ideal conditions for cyanobacterial blooms and have been documented in the lake since 1970 bythe SFWMD (1989). The first large-scale bloom occurred in1986, was dominated by Dolichospermum circinale (formerlyAnabaena circinalis), and covered approximately 310 km2.

Some of the conditions that lead to cyanobacterial blooms are warm temperatures, sunlight, water-columnstability, and sufficiently high concentrations of nitrogen and (or) phosphorus. While all cyanobacteria need amplephosphorus to thrive, inorganic nitrogen limitation allows a subset of cyanobacteria, those capable of using atmospheric nitrogen, to be more successful. Dolichospermum (formerlyAnabaena) has the ability to fix nitrogen (Rosen and others,2017), compared to Microcystis, a nonnitrogen fixing genus,that needs to acquire nitrogen from inorganic sources.

During the summer of 2016, regulatory discharges from Lake Okeechobee into the Caloosahatchee River and the St. Lucie Canal and Estuary occurred during an extensive cyanobacterial bloom (National Aeronautics andSpace Administration, 2016).

Read the full paper . . .