Algae bloom on Lake Okeechobee has decreased to about 30 percent of the lake

OKEECHOBEE — The National Oceanic and Atmospheric Administration Friday reported that the algal bloom on Lake Okeechobee has decreased to about 30 percent of the lake. In addition, about half of the bloom has decreased significantly in concentration. At its peak on July 2, the bloom was in about 90 percent of the lake, according to NOAA data.

The image acquired by NOAA on July 18 shows that the bloom area has decreased to about 30 percent (184 square miles) of lake area, down from about 60 percent on July 17. The concentration in the bloom has also decreased. About half (54 percent) of the bloom area on the July 18 image has cyanobacteria concentration of less than 100,000 cells per milliliter (cells/ml). Concentrations in the “red” areas are more than 1 million cells per milliliter.

“The massive algae bloom that covered nearly all of Lake Okeechobee a week ago appears to be undergoing a change based on satellite images from July 17 and 18. Those successive images suggest a progressive decline in the spatial extent of the bloom. At this time it is unclear what is happening due to a lack of data,” stated Karl Havens, director, Florida Sea Grant.

“Based on research conducted in other lakes, there are a couple of reasons why the bloom may be shrinking. First, the Microcystis bloom in Lake Okeechobee might have used up all of the dissolved inorganic nitrogen in the water and now it is figuratively starving. Second, and somewhat related, it might be that the bloom is going through a replacement cycle, where Microcystis will be replaced by a different kind of algae that can get its nitrogen from the atmosphere, such as Anabaena. That species of blue-green algae has formed large blooms in Okeechobee in past years.

This image from NOAA was recorded on July 17, 2018, where algae on Lake Okeechobee is significantly decreased from the July 14 images.

“Because the state of Florida does not have a systematic and comprehensive algae bloom monitoring program in the lake, with sampling frequent enough to determine what is happening, we may never know the cause of the observed changes.”

This July 18, 2018, image from NOAA shows another sharp decrease of algae in Lake Okeechobee from just the day before.

The satellite images are only available at set intervals. Due to cloud cover, no usable images were available July 6-13.

The July 14 image showed algae in about 80 percent of the lake, and also that the concentration was decreasing. July 17 imagery showed the bloom continue to decrease, as did the July 18 imagery.

The NOAA imagery does not indicate what kind of cyanobacteria is present. There are thousands of types of cyanobacteria, although only about a dozen have been documented in Lake Okeechobee. Some — not all — of the types of cyanobacteria known to live in the lake can produce toxins under certain conditions. However, even cyanobacteria that can produce toxins does not always do so.

According to Dr. Edward Phlips, a professor with the University of Florida’s Department of Fisheries and Aquatic Sciences, algal blooms can be in the water column and the casual observer may not even notice it.

The NOAA computer imagery uses scans in a spectrum of light the human eye cannot detect.

Cyanobacteria also have gas vesicles which act as buoyancy control devices. The vesicles can be expanded and filled with gas, causing the cyanobacteria to float on the surface, or deflated, which causes the cyanobacteria to descend into the water column.

The NOAA image does not show what the human eye sees. It’s computer-generated imagery using data the satellite collects to locate concentrations of cyanobacteria in the water. Different colors on the imagery show areas of varying cyanobacteria concentration.

The NOAA image does not show how many different types of cyanobacteria are present, or which types of cyanobacteria are present. It does not show whether or not toxins are present.

According to oceanographer Michelle Tomlinson of the NOAA National Ocean Service, NOAA does similar studies of other lakes in the United States. The algorithm we developed for the imagery separates out the cyanobacteria from any other background algae in the lake, she explained. There may be some non-harmful phytoplankton mixed in there, she added.

Oceanographer Rick Stumpf with the NOAA National Centers for Coastal Ocean Science explained: “The satellite is seeing the concentration up to 1-2 feet deep into the water. So even when the water will not show the scum everyone notices, the satellite can see how much bloom there is at that level. He said the areas that show as “red” on the imagery are higher concentrations and those are the areas people are more likely to actually see scum on the water surface.

“Also, each satellite pixel covers the area of a stadium. In contrast, someone on the field can only make out maybe 30 yards across,” he added. Mr. Stumpf explained that NOAA also uses different wavelengths of light, including red and near-infrared, that the satellite detects that can’t be seen with the human eye.

According to Dr, Havens, algae blooms could be controlled by cleaning the water before it enters the lake and other waterways.

“The solution to the algal bloom problem is to clean up the nutrient sources north of Lake Okeechobee and in the land around the two estuaries,” he explained in a July 20 commentary on the Florida Sea Grant website. “Control of dispersed sources of nutrients in those watersheds will be a huge challenge and while projects are underway by the state to accomplish them, it could take decades before substantive results are seen.

 

Cyanobacterial blooms monitored by satellites — Q & A

Rick Stumpf and Shelly Tomlinson of the National Oceangraphic and Atomspheric Administration answer frequently asked questions about the way NOAA uses satellite imagery to monitor cyanobacteria, commonly called “blue green algae.”

What satellite are we using?
Sentinel-3a, part of the European Union’s Copernicus program, built by the European Space Agency (ESA) and operated by EUMETSAT (EU Meteorological Satellite office). It was launched in 2016, data became available in 2017. A matching satellite Sentinel-3b was launched in April, and should start providing routine data in 2019.

What does the satellite see?
The satellite looks at the amount of light in many wavelengths. To detect cyanobacteria we use several wavelengths of red and near-infrared light (this infrared detects brightness, not temperature). For water, only the light from the upper 1-3 feet is measured. Differences between these bands detect pigments that are characteristic to cyanobacteria.

What do the colors in the bloom images mean?
Red means high concentration, followed by orange, yellow, green, then blue. Black is “not detectable”, concentrations too low to see or be a risk. Green and above have concentrations that the World Health Organization has found could causes a risk to human health from direct exposure. Blue colors indicate some risk is possible. Areas with “green” colored concentrations have potential for small patchy scums. Areas with “red” concentrations (1 million cells/mL) will have large scum areas.

Why does a satellite see a bloom, when I can’t see one from an airplane or a boat?
From airplane, we have only our eye, and we can really only see “scum” patterns. The satellite can see details we cannot see, so can see high concentrations even when there is not a scum. If there is a bit of wind (above 5 knots or so), the scum doesn’t form, but the bloom is still there.

From a boat, we can only see about 20 yards around, while the satellite pixel covers the area of a football stadium. If you look closely at the water from your boat you might see flecks of what looks like green sawdust in the water.

Does the amount of scum change through the day?
Yes, if the winds change through the day, the amount of scum will change. Also, the cyanobacteria tend to float up in the morning, and sink in the late afternoon.

Why does the bloom concentration change from day to day?
The cyanobacteria in Lake Okeechobee tends to float up in early day, and sink in late day. If winds are light or calm, it will form a scum. As wind picks up it prevents scum formation, and strong winds can mix the bloom down into the water, so it is less visible.

The July 14, 2018, imagery from NOAA shows the cyanobacteria is still in about 80 percent of Lake Okeechobee, but the concentrations have lessened since July 2 as indicated by the reduction in the red and orange areas.

Image captured by NOAA satellite shows widespread algal bloom on Lake Okeechobee on July 2, 2018. The July 2 imagery created by NOAA shows cyanobacteria in 90 percent of Lake Okeechobee. The red and orange colors indicate the highest concentrations.

Editor Katrina Elsken can be reached at kelsken@newszap.com

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