Barnes Sound, south of the Card Sound Bridge, has been hammered numerous times over the years — especially when water managers opened the flood gates of the C-111 canal, which drains the farms and nurseries of South Miami-Dade. In 2006, a massive long-lasting bloom crept from Northeast Florida Bay into Barnes Sound and reached the southern reaches of Biscayne Bay — a milky cloud scientists blamed on some combination of hurricanes, polluted farm runoff from the C-111 and a $270 million project to widen the 18-Mile Stretch between Florida City and Key Largo.
But that bloom never moved north of Turkey Point into the open bay, where a strong tidal flush tends to limit algae development and helps maintain water clarity — a selling point fishing guide Branham highlights on his website: “We have no algae problems, no jet skis, and plenty of bonefish, permit and tarpon.”
But this one appears to have staying power, with the first anecdotal reports from county water sampling crews and anglers coming in mid-June.
“When I first heard about it, my initial reaction was that it would probably dissipate quickly,’’ said Chris Kelble, a research oceanographer at NOAA’s Atlantic Oceanographic and Meteorological Laboratory on Virginia Key. “I’m frankly surprised and concerned that it hasn’t happened with this one.’’
It’s the same period when much of South Florida has been drenched by tropical deluges. Since July 1, the southeast coast has received more than double the typical rainfall for the month, according the South Florida Water Management District. Since June, water managers also have lowered Miami-Dade’s canals twice in anticipation of storms and are also releasing water into Miami-Dade’s canal system from swollen Everglades marshes north of Tamiami Trail.
Over the last month, district spokesman Randy Smith said the three major flood gates north of Homestead’s Bayfront Park have been dumping an average of 673,200 gallons a minute into the bay — enough to fill 45 backyard swimming pools. There have been no releases from the C-111 canal further south, he said.
It adds up to a huge shift in water chemistry for the bay — steady daily slugs of fresh but turbid water, carrying all sorts of stuff, from decaying bits of plants to sand, soil and various pollutants, including nitrogen and phosphorus from farm and yard fertilizer.
“We can’t rule out the discharges may be having some sort of impact on the bloom, but we’re still waiting for the scientists to come up with some sort of determination,” said Smith.
That could be difficult, said Markley. Water samples don’t show unusually high nutrient levels, she said, but the blooms may have already absorbed much of it. There are other questions as well. The weakest blooms are around the mouths of the drainage canals and though it’s a high volume of runoff, similar amounts have been released in the past without triggering blooms. The bloom also appears to have started before the recent big rains
“We really don’t know exactly what is different this year,’’ Markley said. Salinity levels, water temperatures and a host of other factors all can play a role in fueling algae explosions.
Unlike red tide and other types of toxic algae, which can paralyze and kill fish, manatees and other sea life and cause respiratory problems for people, these blooms don’t pose a health risk to the public, said Christopher Sinigalliano, an environmental microbiologist at NOAA’s Virginia Key lab.
The blooms are primarily diatoms, which he described as tiny glass-like shells. The normally benign microscopic marine plants are commonly found in bay waters but at much lower concentrations. Why the blooms smell so fetid also isn’t exactly clear, but it could be the smell of all the dense “biomass” decaying, not unlike a pile of rotting yard clippings.
Aside from the odor, the most immediate concern is for the marine environment. Lengthy blooms can block light vital to seagrass and other bottom plants and animals that provide food and shelter for everything from baby lobsters to bonefish. Dense concentrations also can choke sponges, filter-feeders that help keep water clear, with the sticky algae filling their internal canals with a mucous-like ooze.
The encouraging news so far, said Sinigalliano, is “we don’t seem to be seeing a lot of ecological damage.’’
But historically, blooms also can go through troubling transformations, with one variety giving way to other potentially toxic strains.
“It’s not uncommon for blooms to progress and change over time in their composition,’’ said Steve Blair, a senior biologist for Miami-Dade’s environmental agency. “It’s fine now. There doesn’t seem to be any human health concerns, but we have to keep watching it.’’