Will sending water from the Big O south save Florida Bay’s sensitive ecosystem and the coral reefs of the Florida Keys … or destroy them?
Proponents of the push to send more water from Lake Okeechobee south to Florida Bay were celebrating earlier this month, with the announcement of more federal and state funding to raise portions of the Tamiami Trail. A series of bridges will allow more freshwater to flow under the Tampa-to-Miami roadway that has acted as a dam transecting the Everglades since 1928.
The plan calls for using canals to move water from Lake Okeechobee to a reservoir and stormwater treatment area (STA) in the southern Everglades Agricultural Area (EAA). The lake water will be stored, cleaned in the STA and sent south, as needed, to Everglades National Park and Florida Bay.
One researcher, who has spent three decades studying Florida Bay and the Florida Keys, fears that instead of restoring Florida Bay’s sea grass, an infusion of freshwater from the big lake could result in massive algal blooms and the loss of even more of the Florida Keys’ precious coral reefs.
He voiced those concerns in January in a hearing of the Florida Senate Subcommittee on Agriculture, Environment and General Government.
The reason for his concern: While state and federal agencies have done much to send more water south to Everglades National Park since 1982, the increased flows have triggered bigger algal blooms in Florida Bay and accelerated the decline of coral reefs in the Florida Keys.
For more than 30 years, Dr. Brian Lapointe, who makes his home on Big Pine Key, has taken water samples and tracked the nutrients and algae at Looe Key Reef. Dr. Lapointe has used stable nitrogen isotopes to “fingerprint” nitrogen sources. His research was central to efforts to stop the use of septic tanks in the Keys, and converting to central sewer systems and advanced wastewater treatment that includes nitrogen removal.
Dr. Lapointe explained that he has been measuring concentrations of ammonium, nitrate and phosphate in the water, and nitrogen and phosphorus contents of seaweeds on the reef since 1984 as part of his long-term study of coral reefs.
“In the 1980s, water quality in the Keys was relatively good,” he said, although some algal blooms were observed flowing out of Florida Bay. In the 1990s, the Florida Keys National Marine Sanctuary Advisory Council (SAC) became convinced the water quality problems were due to a lack of freshwater flow to Florida Bay.
George Barley, one of the original founders of the Everglades Foundation and chairman of the SAC, convinced everyone the key was to send water south. Dr. Lapointe said in a recent interview. “Between 1991 and 1995, they ramped up the freshwater flows to Shark River Slough and Taylor Slough. It resulted in some of the largest cyanobacterial (aka blue-green algae) blooms in Florida and extended from Florida Bay to the offshore reefs.
“As they began to move more water south, they did not consider the downstream effects of nitrogen,” he said. Nitrogen is the limiting factor to algal blooms in central and western Florida Bay and a key stressor to coral at parts per billion concentrations. Coral and the beneficial algae that live symbiotically with the coral are very sensitive to the ratio of nitrogen to phosphorus in the water, he explained. When the ratio of nitrogen to phosphorus increases, the coral becomes starved for phosphorus. A healthy ratio of nitrogen to phosphorus for the coral is about 10 to 1 or less, he said. His 30-year study found nitrogen-to-phosphorus levels have risen to 70 to 1 at Loee Key, and high ratios in the Everglades runoff are a major contributor to the problem.
“When you give them high nitrogen and low phosphate, it makes them more vulnerable to high temperature and bleaching as well as coral disease,” he explained. Between 1996 and 2000, the Florida Keys lost 40 percent of living coral, Dr. Lapointe said. “It was obvious to me and to everyone in the Keys that this plan had backfired, these increased flows were damaging the coral reef ecosystems.”
The political movement to send freshwater from Lake Okeechobee south ignores the details of the global problem that coral reefs are facing, said Dr. Lapointe. The coral reefs have a very low threshold of damage from excess nitrogen and phosphorus starvation, which make them more susceptible to increasing sea surface temperatures.
In addition to contributing to blooms of cyanobacteria and harming the coral, increased nitrogen in the water also feeds the sargassum (a brown seaweed). In 2018 and again this year, massive amounts of sargassum washed up on shore throughout the Florida Keys and along east coast beaches to Cape Canaveral. While in the ocean sargassum provides beneficial habitat to marine animals, too much of it can be harmful as it depletes the oxygen in the water and results in fish kills.
Dr. Lapointe is not alone in his concerns about the nitrogen levels in the water that flows south from Orlando through Lake Okeechobee and to the Everglades. Research conducted by the late Dr. Karl Havens, former director of Florida Sea Grant, found algal blooms in Lake Okeechobee were nitrogen-limited. The lake now has so much phosphorus available in the water year round that the availability of nitrogen in the water has become the key ingredient to algal blooms.
In the 1980s, when algal blooms first became a noticeable problem on the big lake, the predominant species of blue green algae were those capable of “fixing” nitrogen from the air, such as Anabeana. In more recent years, the dominant cyanobacteria in Lake Okeechobee blooms have been Microcystis aeruginosa, which is not a nitrogen “fixer.”
In the summer of 2018, when a massive Microcystis aeruginosa bloom occurred on Lake Okeechobee, Dr. Havens predicted the bloom would “flip” when it ran out of available nitrogen, and that after the Microcystis aeruginosa died off, another bloom of Anabaena could thrive. Dr. Havens was proven correct when the first bloom shrank dramatically, and a second bloom of Anabaena took its place. At the same time in the coastal waterways, the Microcystis aeruginosa concentrations continued to increase, indicating those waterways still had sufficient nitrogen in the water to feed that blue-green algae.
According to the Environmental Protection Agency’s website, “coral reefs are adapted to low nutrient levels; so an excess of nutrients can lead to the growth of algae that blocks sunlight and consumes oxygen corals need for respiration. This often results in an imbalance affecting the entire ecosystem. Excess nutrients can also support growth of microorganisms, like bacteria and fungi, that can be pathogenic to corals.”
A 2012 study by researchers from the United Kingdom’s University of Southampton Institute for Life Sciences and the Coral Reef Laboratory in the National Oceanography Centre, Southampton, published in the journal “Nature Climate Change,” found that excess dissolved inorganic nitrogen starves the beneficial algae that symbiotically live in the coral. Corals are made up of many polyps that jointly form a layer of living tissue covering the calcareous skeletons. They depend on single-celled algae called zooxanthellae, which live within the coral polyps, the study explains. The coral animal and the associated marine algae depend on each other for survival in a symbiotic relationship, where the coral supplies the algae with nutrients and a place to live. In turn, the algae offer the coral some products of their photosynthesis, providing them with an important energy source. Large nitrogen concentrations block their ability to absorb phosphate necessary for their lifecycles. The Southhampton study found the symbiotic algae are important to maintain the living coral’s immunity from diseases. If the symbiotic algae are not healthy, the coral reef becomes more vulnerable to disease, according to the study.
At the same time, the nutrient loads feed other algae. Surface algal blooms block sunlight from reaching the coral; when the algae dies, it also pulls the oxygen from the water, creating a “dead zone.”
Dr. Lapointe made a presentation to the Florida Senate Subcommittee on Agriculture, Environment and General Government on Jan. 9, 2019. It is available online on the Florida Channel at https://thefloridachannel.org/videos/1-9-19-senate-appropriations-subcommittee-on-agriculture-environment-and-general-government/.