By Karl Havens, director, Florida Sea Grant
Editor’s note: A previous version of this story stated that the photo of the Lake Okeechobee algae bloom was taken on July 9, 2017. The photo was actually taken on July 9, 2018. The photo caption as been corrected.
Update August 16, 2018 –
NOAA satellite images from August 14 indicate that the blue-green algae bloom now covers 50 percent of the surface of Lake Okeechobee. This is interesting because a strong line of thunderstorms crossed the lake late on Friday, which could have disrupted the bloom by mixing mud into the water column, starving the algae of light. However, this was not the case and instead the bloom still seems very robust. It is hard to predict when it will decline. Blue-green algae blooms like warm water, and they outcompete other kinds of algae when the water is very warm. Therefore, unless a tropical storm or hurricane halts the bloom, it might take the onset of colder water in the late fall or winter to end it.
Update August 10, 2018 –
The most recent August 9 satellite image from NOAA indicates that the resurging blue-green algae bloom is continuing to expand in its coverage and intensity on Lake Okeechobee. It is estimated that the bloom now covers 45 percent of the lake. We use the word resurging because two weeks ago the bloom appeared to be dissipating – perhaps due to weather conditions or because the algae ran out of dissolved nitrogen in the lake water. We speculated that the bloom might reemerge and be dominated by a species, like Anabaena, that could obtain the nitrogen it needs to grow from the atmosphere. The last update confirmed that this predicted change in the kind of algae did happen, and this latest image indicates that the bloom is steadily growing in size.
Update August 9, 2018 –
On August 7, Dail Laughinghouse, an assistant professor of applied phycology at the UF/IFAS Fort Lauderdale Research and Education Center, collected water samples from Lake Okeechobee. He found the samples of blue-green algae included: three species of Microcystis, which dominated the bloom that started in June and six species of Anabaena.
As noted earlier, it is impossible to say how long the bloom will persist, because it is controlled in part by wind, rain and cloud cover, which are unpredictable. However, the bloom now includes Anabaena, a species that can obtain, or fix, the nitrogen it needs from the atmosphere. With continued sunny days, warm water, abundant phosphorus from the lake sediments and an unlimited source of nitrogen from the atmosphere, this bloom has the ingredients it needs to grow. This is different from the original bloom of Microcystis, which needed nitrogen from the lake water. Our original post below explains the various sources of both nitrogen and phosphorus in the lake.
Update August 1, 2018 –
A recent analysis of water samples from Lake Okeechobee by the South Florida Water Management District indicates that the algae bloom on the lake is dominated by Microcystis and also by Anabaena, a cyanobacteria that is able to obtain nitrogen from the atmosphere. Appearance of Anabaena is consistent with the hypothesis that the bloom is going through a replacement cycle, where Microcystis has used up the nitrogen in the lake water and is being replaced by a different kind of algae that can get its nitrogen from the atmosphere, like Anabaena. Given the scarcity of data, it is unlikely that a rigorous test of this hypothesis ever will be possible.
Update July 30, 2018 –
NOAA satellite images from July 29 indicate that the algae bloom in Lake Okeechobee is growing. On July 26, the bloom covered about 30 percent the lake. On July 29, the bloom covered 220 square miles or approximately 40 percent of the lake.
Update, July 27, 2018 –
NOAA satellite images from July 22, 25 and 26 indicate a progressive expansion of the bloom on Lake Okeechobee from 10 to 20 to 30 percent coverage of the lake. We do not know whether or not this indicates a recovery of the bloom, a second phase where another species of cyanobacteria is forming a new bloom, or just natural variability over a few days.
Update, July 20, 2018 – 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.
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.
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.
Original post starts here:
Since early June, massive blooms of blue-green algae, or cyanobacteria, have formed at the surface and in the water column of Lake Okeechobee, and the St. Lucie and Caloosahatchee rivers and estuaries.
These ecosystems are connected by a series of canals, and when water in the lake rises to a high level, it is discharged to the estuaries.
As noted in an earlier Florida Sea Grant article, large amounts of rainfall from Hurricane Irma, and an abnormally wet spring in 2018 have likely moved high concentrations of water and algae-fueling nitrogen and phosphorus into those ecosystems.
The watersheds of all three ecosystems contain large sources of nutrients due to historical and current land uses, including agriculture and septic systems. When runoff does happen, water from all three places has the potential to fuel blooms.
In Lake Okeechobee, Hurricane Irma may have also stirred up lake-bottom sediments, introducing even more phosphorus into the water. Once the long, sunny days of summer began, the water heated up, allowing blooms to form on a large scale.
As of July 14, blooms covered nearly all of Lake Okeechobee, and were either on the water surface or just below the surface. This widespread coverage, which can be seen in satellite imagery produced by Richard Stumpf of the NOAA National Ocean Service, has persisted since late June, and does not appear to be abating.
Scientists are not certain when the blooms will end. Since sunlight is an essential ingredient for blooms of this scale, the bloom can be long-lasting unless disrupted by multiple days of cloudy weather, a tropical storm, or colder weather in the late fall.
We will continue to provide updated maps showing bloom coverage of Lake Okeechobee based on NOAA satellite imagery, and report on any substantive changes.
Blooms have also been reported in multiple locations in the St. Lucie and Caloosahatchee rivers and estuaries, raising concerns about negative impacts to the regional water-dependent economies, as well as human health effects of contact with the water.
The composition of the blooms has not been documented at every location. According to Barry Rosen, a biologist with the United States Geological Survey, the toxin-producing species Microcystis aeruginosa and Microcystis viridis are dominant at some locations in the lake and also at a location where a sample was taken from the Caloosahatchee River. Both of the Microcystis species have the potential to form blooms.
Are water discharges from Lake Okeechobee to blame for the blooms in the rivers and estuaries?
Finding the same kind of blue-green algae dominating the blooms in the lake and in one of the estuaries neither confirms nor negates a physical connection. Microcystis is a common bloom-former in lakes across the United States, Europe and Asia. Therefore, based on this data alone, we cannot say that the lake seeded the estuaries with a bloom.
On average, 60 percent of the total fresh water going into both the St. Lucie and Caloosahatchee estuaries originates from the local watersheds, and 40 percent originates from Lake Okeechobee. The long-term average percentages for nutrient inputs are about the same.
The percentages at any given time can, of course, differ. For example if lake water is discharged during a time when there is no local watershed runoff, the lake contribution of fresh water and nutrients will be much higher than those of the local watersheds.
Normally, a drop in estuary salinity shortly after lake discharges begin is a sign that Lake Okeechobee is affecting the estuaries. In 2018, the relationship is more complicated, and the lake discharges may not be definitively connected to blooms, particularly in the St. Lucie Estuary. When heavy rainfall fell over the St. Lucie watershed, the salinity dropped to zero before discharges of water from the lake began. On the other hand, lake discharges may have contributed substantially to a drop in salinity and nutrient inputs to the Caloosahatchee.
Actually since the rivers and estuaries are nutrient-rich, and low salinity is needed to allow blooms of the aforementioned species of blue-green algae, conditions supportive of blooms existed in both estuaries before lake discharges began.
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. 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.
Karl Havens has 35 years’ experience in aquatic research, education and outreach, and has worked with Florida aquatic ecosystems and the use of objective science in their management for the past 23 years. His area of research specialty is the response of aquatic ecosystems to natural and human-caused stressors, including hurricanes, drought, climate change, eutrophication, invasive species and toxic materials. He is a recipient of the Edward Deevey, Jr. Award from the Florida Lake Management Society for his research dealing with Florida lake ecosystems.