Nearly two years after the ‘guacamole’ algae bloom that blanketed the Treasure Coast in the summer of 2016, there are plenty of theories, but we don’t “know” the cause.
The prevailing theory was that algae in the freshwater released from Lake Okeechobee through the C-44 canal seeded the bloom, which grew to thick mats when it was fed by the nutrient-rich local basin runoff.
That’s the theory — but we don’t know, and can’t know for sure that the algae came from the lake, because the algae was not examined on the microscopic level at the time, according to UF algae expert Dr. H. Dail Laughinghouse IV. It was not examined in 2016, and it’s too late to examine it now. Without that data, we can’t be sure where the algae and/or cyanobacteria that made up the ‘guacamole’ algal bloom originated.
Dr. Laughinghouse said researchers believe that, wherever it came from, something in the basin runoff that feeds into the St. Lucie estuary caused the algal bloom to grow rapidly into thick mats and release toxins.
The algae didn’t grow into thick mats in the lake, he noted. If the algae that covered Treasure Coast waterways came from the lake, whatever caused it to grow into the ‘guacamole’ mats was apparently not in the lake.
Theories on what caused the bloom to explode include discharges from leaking septic tanks, sewage spills and runoff from Treasure Coast farms and urban areas.
Research conducted since the 2016 bloom has found that the phosphorus levels in the C-44 canal are significantly higher than the phosphorus level in the water in Lake Okeechobee. Nitrogen levels in local runoff are also significantly higher than nitrogen levels in the lake water.
According to South Florida Water Management District data, water in the C-44 is around 300 parts per billion phosphorus. The phosphorus levels in water in Lake Okeechobee vary according to the lake depth, and amount of turbidity, but in general it averages around 120-130 ppb. Water entering the lake from the north averages around 140 ppb. The Florida Department of Environment Protection goal for Lake Okeechobee is 40 ppb phosphorus.
The 2017 study, “Septic systems contribute to nutrient pollution and harmful algal blooms in the St. Lucie Estuary, Southeast Florida, USA,” by Dr. Brian E. Lapointe, Laura W. Herren and Armelle L. Paule, of the Harbor Brand Oceanographic Institute at Florida Atlantic University, Marine Ecosystem Health Program, found the local basin runoff contributed 70 percent of the nutrients that fed the algal blooms.
The researchers also noted that excessive releases of freshwater from Lake Okeechobee disrupt the salinity levels in the estuaries and are harmful to that ecosystem even if there is not an algal bloom.
According to Dr. Laughinghouse, algae needs both phosphorus and nitrogen to grow, and limiting phosphorus can control algae blooms. Controlling nitrogen is a little trickier, according to the Florida Department of Environmental Protection, because if nitrogen is not readily available, some algae can “fix” nitrogen from the air.
So what do we know?
• Algae is everywhere there is moisture — lakes, rivers, canals, ponds and the ocean. It’s part of the natural ecosystem, and the base of the food chain.
• Cyanobacteria (blue-green algae) is not new. In fact, it the oldest life form on the planet. It’s been here an estimated 3.8 billion years.
• Excess nutrient loads in the water can cause the algae to grow rapidly. This is called a “bloom.”
• Some forms of cyanobacteria sometimes (not always) release toxins that can be dangerous to fish, wildlife and humans.
• Thirty years ago, DEP set the target maximum phosphorus loading into Lake Okeechobee at 105 metric tons annually, with a goal for the lake water to be no more than 40 parts per billion phosphorus. That goal has never been met. The phosphorus load from the north has averaged three to four times the DEP maximum. South Florida Water Management District data shows the water flowing into the lake averages around 140 ppb phosphorus.
• The high levels of phosphorus flowing into Lake Okeechobee are harmful to the lake’s ecology, and contribute to the growth of invasive plants.
• While the phosphorus levels in the water in Lake Okeechobee are much too high for its ecological balance, the levels in runoff in the St. Lucie basin are even higher. Phosphorus levels in basin runoff along the C-44 canal average 300 ppb phosphorus, per SFWMD data.
• Releasing excess freshwater to the St. Lucie would be harmful even if the phosphorus levels were less than 40 ppb, because the freshwater releases disrupt the salinity levels in the estuary.
• Releasing freshwater from the lake to the Caloosahatchee River is necessary to prevent saltwater intrusion. Due to man-made changes, the river basin drains more quickly than nature intended and as a result, the river depends on lake releases for much of its water supply during the dry season.
• HABs can and do occur in salt water. HABs called “brown tide” and “red tide” are examples. According to the National Oceanic and Atmospheric Administration (NOAA) “Harmful algal blooms, or HABs, occur when colonies of algae — simple photosynthetic organisms that live in the sea and freshwater — grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds. The human illnesses caused by HABs, though rare, can be debilitating or even fatal. HABs have been reported in every U.S. coastal state, and their occurrence may be on the rise. HABs are a national concern because they affect not only the health of people and marine ecosystems, but also the ‘health’ of local and regional economies.”
• Algal blooms are not always harmful. According to NOAA, “Not all algal blooms are harmful. Most blooms, in fact, are beneficial because the tiny plants are food for animals in the ocean. In fact, they are the major source of energy that fuels the ocean food web. A small percentage of algae, however, produce powerful toxins that can kill fish, shellfish, mammals, and birds, and may directly or indirectly cause illness in people. HABs also include blooms of non-toxic species that have harmful effects on marine ecosystems. For example, when masses of algae die and decompose, the decaying process can deplete oxygen in the water, causing the water to become so low in oxygen that animals either leave the area or die.”
• Even when the salinity levels are normal, the excess nutrients in runoff in the St. Lucie estuary and along the Treasure Coast are harmful to the environment. According to the 2015 Martin County Watershed to Reef study, nutrient pollution from coastal runoff has been linked to reef damage.