'Perfect storm' caused lagoon superbloom
STORY
The 2011 algae superbloom, which smothered much of the Indian River Lagoon and started a drastic decline in estuary health that continued in 2012, was caused by “a perfect storm of coincidental factors,” according to Joel Steward of St. Johns River Water Management District.
Steward, the keynote speaker at last week’s Indian River Lagoon Symposium at Harbor Branch Oceanographic Institute, said two exceptionally cold winters, hypersalinity caused by a drought, and the mysterious die-off of drift algae set the stage for the ecological disaster.
A pulse of nutrients, including fertilizer runoff, that washed into the lagoon during two March downpours helped trigger the collapse.
“The superbloom was unprecedented in terms of magnitude and duration,” Steward said. “It began in March 2011 and continued until October and killed 44 percent of seagrass, lagoon-wide.”
The day-long symposium included 60 scientific presentations about the health and ecology of the lagoon.
Other speakers reported that chlorophyll, a marker of lagoon distress that indicates excess nutrients, increased 10-tenfold in some places during the bloom and that more than 2,000 metric tons of sea grass have been lost in the past two years.
“We have had the greatest loss of biomass ever, and we are not seeing recovery,” said Robert Chamberlain, a St. Johns River Water Management District scientist.
Lori Morris, another St. Johns scientist, said seagrass loss continued in 2012, with a massive brown algae bloom clouding the water in the northern lagoon and a mysterious die-off north of Vero Beach.
“In total we have lost two-thirds of the seagrass between Vero Beach and the northern end of the Indian River Lagoon,” Morris said. “For some reason, Indian River County was the hardest hit area.”
The 2011 superbloom came as a shock to the scientific and policymaking communities.
For a number of years leading up to 2011, conditions in the lagoon improved steadily with lower nutrient levels, increased water clarity and greater seagrass coverage than in the 1940s.
Then, within an eight-month period, decades of progress were suddenly reversed.
All of the factors cited by Stewart combined to increase nutrients in the lagoon that fed the overgrowth of algae, cutting off sunlight and killing seagrass.
The cold may have contributed to the bloom, according to Steward.
“It probably killed some of the tropical clams that had been filtering the water and some of the tropical grazers,” small organisms that dine on algae and keep its levels down.
“All the different parts of the system fit together like cogwheels,” Steward said. “If you pull out a couple of the wheels, the system breaks down and the algae get out of control.”
The cold snaps may also have helped kill the drift algae, a sort of underwater tumbleweed that is beneficial to the lagoon, though Steward stressed that the cause of the drift algae collapse is still under investigation, with laboratory experiments planned to try and solve the mystery.
What’s clear about the loss of the drift algae is that when it all died for whatever reason, its organic material contributed to the excess of nutrients in the lagoon feeding the bad algae, tiny phytoplankton that consume oxygen and make the water murky.
Scientists held out hope for the lagoon, despite the extent of recent catastrophes. “Nature will restore itself if conditions are right,” said symposium manager and Harbor Branch scientist Dennis Hanisak.
Steward said people cannot control many of the factors needed to restore the lagoon's health and preserve its unique ecology, but that there are three things that can be done. “We can limit the external nutrient loading,” he said. “We know with a high degree of certainty that can do a lot for the system.”
Limiting external nutrient loading is the aim of the fertilizer regulations passed by Vero Beach, Sebastian and Indian River Shores in the past year or two, and of projects like the county’s Egret and Spoonbill marshes that filter water headed for the lagoon, removing nitrogen and phosphorus, the two main chemicals algae feeds on.
Steward said dredging muck that completely covers the bottom of the lagoon in some places is a second thing government agencies can do. The muck contains large quantities of nutrients that are released under certain conditions, and removing the muck would help restore water clarity and natural ecology.
“Flushing is another possibility,” Steward said, “but we need to evaluate that one very carefully.”
According to symposium scientists, storm surges caused by the 2004 hurricanes may have flushed out much of the stagnant pollution in the lagoon, contributing to the success of seagrass in following years, and there has been discussion in the county about creating an opening between the lagoon and the Atlantic at Bethel Creek to accomplish a similar effect on a smaller scale.
Steward says that could conceivably help conditions in the lagoon but that any plan would have to be studied in great detail to make sure there would not be unintended consequences.
