Innovative technologies used to treat harmful algal blooms

Posted 10/1/21

The SFWMD Water Resources Accountability and Collaboration group reviewed innovative technologies used to control …

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Innovative technologies used to treat harmful algal blooms

In April SFWMD used innovative technologies to deal with a harmful algal bloom at the Pahokee Marina
In April SFWMD used innovative technologies to deal with a harmful algal bloom at the Pahokee Marina

WEST PALM BEACH — The South Florida Water Management District (SFWMD) Water Resources Accountability and Collaboration group reviewed innovative technologies used to control Harmful Algae Blooms (HABs) at their Sept. 30 meeting.

“We are heavily, heavily focused on reducing pollution, which fuels algal blooms,” said SFWMD Executive Director Drew Bartlett. “This summer we started using some new technology to try to figure out how to address them when they show up, but our mission is improving water quality to prevent HABs.”

He said over the past several years, the state has dedicated $1.2 billion to SFWMD in this effort to improve water quality. He said while hundreds of thousands of dollars have been spent to treat HABs, 99.9% of the focus is on controlling pollution.

Dr. Anna Wachnicka, lead scientist in the SFWMD Applied Sciences Bureau, explained that cyanobacteria are an ancient group of autotrophic microscopic bacteria.

“You can find them in almost all aquatic systems, including fresh water, brackish water and marine,” she said. They can form large colonies consisting of hundreds of thousands of cells. Those colonies are easily spotted from the air.

Reproduction of cyanobacteria is influenced by many factors, Wachnicka explained. “They love stagnant, warm, nutrient-rich water. When conditions are right, they can reproduce really quickly and create those large-scale blooms on lakes, including Lake Okeechobee.

Blue-green algae also play an important role in the nitrogen cycling on the lake. Some of the species can fix nitrogen from the air and those species are called diazotrophs, she continued. They also have specialized gas vesicles which allow them to move up and down in the water column, which allows them to find the nutrients and light they need.

Cyanobacteria can survive extreme environmental conditions, she said. “You can find them in hot springs.” Several species can produce cynaotoxins, but not all of them. “So, not all blooms that show up on the lake are toxic,” Wachnicka continued.

Cyanobacteria and algae are extremely important components of all aquatic systems. They are a very important food source in the ecosystem.

“We need algae and we need cyanobacteria in aquatic systems,” she continued. Blooms are a natural occurring phenomena. Usually in the summer when the weather gets warmer, cyanobacteria and algae start blooming,” she said. “However when they start growing out of control – and that is usually what happens in unbalanced systems – that is when they become problematic.

Not all blooms have to be toxic to be harmful, she added.

Nutrient over-enrichment is associated with urban and agricultural development, she said. Increasing global temperatures will likely contribute to increasing HABs in the future.

Very typical for Lake Okeechobee are blooms formed by microcystins aregonosa, said Wachnicka.

When a layer of algae forms on the water, that decreases the amount of sunlight that penetrates the water, which can cause other algae and aquatic plants to die, fall to the bottom of the lake and decompose. “During the decomposition process, we end up with very low oxygen levels in the water which can affect other organisms in the lake,” she said. If fish are trapped in a confined area during an algal bloom, this can result in a fish kill.

Satellites are useful tools, but should not be used as a replacement for water quality testing. Satellites cannot detect what species of algal is present or if there are any toxins in the water. The satellite images can be used to find the areas that should be monitored for testing.

Wachnicka said algal blooms can be broken up by rain or wind.

SFWMD has 32 monitoring stations on Lake Okeechobee that collect data on physical, chemical and biological water quality. The sampling is done at all 32 locations, bi-weekly during the wet season (May - October) and monthly from nine locations during the dry season (November - April).

Wachnicka said water quality varies in different areas of the lake.

Data shows since May, the northern part of the lake had higher number of bloom events than the central part of the lake, she said. In part, this could be due to turbidity in the central part of the lake which blocks sunlight. This lower light condition inhibits growth of algae and cyanobacteria, she said.

In the past wet season, the bloom conditions were more favorable early in the season. The percentage of bloom events decreased over time. She said approximately 24% of the samples out of 288 samples collected this summer had bloom conditions. Concentrations of toxins were higher in samples collected early in the wet season.

Microcsytis aeruginosa, which is not a nitrogen-fixer, was the dominant taxon most frequently recorded in the center of the lake. The samples in the south area of the lake more often had mixed algae or algae that can fix atmospheric nitrogen, she continued.

The concentration of nutrients in the water decrease over time because the algae uses the nutrients in the water. At the end of the wet season, as nitrogen levels in the water decrease, conditions are more favorable for algae that can fix nitrogen from the air. Testing found levels of Microcsytis aeruginosa was highest in May and decreased later in the wet season.

SFWMD is using science-based strategies to treat HABs, explained Rory Feeney, SFWMD Land Resources Bureau Chief.

Working with Florida Department of Environmental Protection (FDEP), Feeney said they used the same strategy they developed to control invasive exotic plants.

The plan included:
• Enhanced monitoring;
• Mechanical removal;
• Pumps to increase circulation;
• Hydrogen peroxide to break down cyanobacteria; and,

• New innovations.

These response plans do not reduce the need to control nutrients entering the water, he explained. He said they are not trying to treat all cyanobacteria. Cyanobacteria and algae are part of the eocsystem.

When a HAB took over the Pahokee marina in April, SFWMD quickly mobilized their tools. The first step was to mechanically remove the top layer of the algal bloom scum. An aquatic weed harvester with a vacuum pump was utilized. Working section by section, the contractor was able to remove a considerable amount of the biomass. The solids were separated out. The water was processed and treated with ozone (which clarifies the water and also eliminates microcystin). The remaining solids were transported to a site away from waterways to be broken down by sunlight. To prevent a rebound of the blue-green algae at the marina, the area was treated with algaecide, and retreated in a week. Inhouse drone pilots surveyed the marina to verify the treatment.

“We know that stagnant waters help stimulate algal growth,” Feeney continued. To eliminate those problems at the marina the West Palm Beach field station deployed a portable pump to move water through the marina’s most stagnant areas. They also worked with DPI to pilot a new technology using ultrasonic sound waves just under the water surface. This technology is believed to disrupt the algae cells. These tranducers have a radius of about 500 feet.

Sections of sheet wall were removed from the marina to improve water circulation.

The pump was a temporary fix. SFWMD has deployed water circulators throughout the marina (originally developed to prevent water from icing over), to improve water circulation in and out of the marina.

“We believe the totality of our efforts really helped,” he said. Microcystin levels at the marina dropped to below detectable levels.

In May, SFWMD and FDEP hired BlueGreen Water Technologies to treat an algal bloom in the Caloosahatchee River using an algaecide called Lake Guard Oxy, a formulation of sodium carbonate that turns into hydrogen peroxide in water. The hydrogen peroxide reacts with the cyanobacteria in the upper layer of the water due to a special coating that allows the product to float for a few hours. This formulation may reduce the amount of active ingredient used on a per acre basis.

The contract performed 112 treatment and re-treatment applications in 56 residential areas along 48 miles of the Caloosahatchee River. The treatment eliminated the algal blooms within 24 hours. The best results were in stagnant water such as dead-end canals and marinas.

Spot treatment was performed at the Franklin Lock, where before treatment, microcystin levels were at 8.2 micrograms per liter. The World Health Organization considers levels above 8 micrograms per liter to be unsafe for human recreational contact (such as swimming). Testing showed a sharp decline in microcystin, with a slight rebound on the fourth day, suggesting re-treatment would be necessary.

Also in May, blue-green algae was observed along the L10 and L12 canals in western Palm Beach County. SFWMD tested a different algaecide, also hydrogen peroxide based, called Pack 27. The contractor treated about 10 miles of canals. Water quality was tested before, during and after treatment. As expected, microcystin levels dropped.

SFWMD also worked on HAB’s at Port Mayaca. At the end of June, blue-green algae blooms began to take over the lock structure at the head of the C-44 (St. Lucie) canal. “We deployed our contractor to treat the area with Lakeguard Oxy,” said Feeney. About 25 acres were treated, “and Mother Nature cooperated with a series of cloudy days and favorable winds,” he said.

“Winds play an important role in how or if we respond. Depending on the winds, what can be there on Monday, might not be there the very next day,” he explained.

An ultrasonic transducer was also installed in the C-44 canal, just east of Conners Highway. “We found the chlorophyll A has remained low in the area,” he said. Recently a second transducer was deployed west of Conners Highway.

algal bloom, blue-green algae, SFWMD, Pahokee