Lake Okeechobee in Florida is Home to harmful algae due to human waste and other factors
The largest lake in Florida and the second largest in the Southeastern region of the US is Lake Okeechobee. Blue-green algae (Microcystis) blooms have been occurring in the lake for the past 20 years, and they have caused major environmental and public health problems by spreading into adjacent urban estuaries.
Harmful algal blooms are known to occur worldwide as a result of excess nutrients from industries, agriculture, and urban growth, notably nitrogen and phosphorus. Only phosphorus has historically been seen to be a problem for Lake Okeechobee, which has prompted focused attempts to lower phosphorus runoff from agricultural sources in the watershed.
Recent findings represent a significant advancement in our knowledge of and efforts to protect this important ecosystem. The first thorough sampling across the Lake Okeechobee Waterway in South Florida, which runs from the St. Lucie Estuary on the east coast to the Caloosahatchee River Estuary on the west coast, has been carried out by researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute.
Researchers carried out three bloom sampling activities and two study cruises throughout the Lake Okeechobee Waterway to ascertain the cause of the recent cyanobacterial blooms. They examined the nitrogen isotope content of phytoplankton to determine whether fertilizers or human waste were a factor.
The study’s findings, which were published in the journal Harmful Algae, show that controlling phosphate and nitrogen levels is necessary to prevent harmful algal blooms in Lake Okeechobee and that human waste may have had an impact on these Microcystis blooms. The importance of rainfall, especially intense rainfall episodes, in causing these large blooms is further highlighted by the findings.
Urbanized estuaries and the Kissimmee River, which drains into Lake Okeechobee and travels north through the Kissimmee Chain of Lakes to the larger Orlando area, were found to have higher levels of inorganic nitrogen. Moreover, it was determined that one of the factors influencing the growing frequency of these blooms in Lake Okeechobee is Orlando’s growing urbanization.
“Strategies that solely target phosphorus reduction are insufficient, given the results of our study,” senior author and research professor at FAU Harbor Branch Brian Lapointe, Ph.D., stated. Reducing both nitrogen and phosphorus is necessary to combat hazardous cyanobacterial blooms. Because of their combined effect, which frequently results in more severe and enduring toxic algal blooms, controlling both nutrients is essential. Human waste is a key source of these nutrients in metropolitan areas such as the watersheds of the Caloosahatchee and St. Lucie rivers.
Results indicate significant alterations in Lake Okeechobee’s algae conditions throughout time. The lake’s microcystin levels, nitrogen-to-phosphorus ratios, and Microcystis cell populations have all increased from earlier decades. By the late 1990s, phosphorus levels had risen from 50 micrograms per liter in the mid-1970s to above 100 micrograms per liter. Because of the increased phosphorus, dangerous cyanobacteria like Dolichospermum started to outcompete other algae.
The trips happened between 2019 and 2020, and the sampling took place between 2018 and 2021. As opposed to isolated or sporadic sampling, this method offered a comprehensive, cohesive view of conditions throughout the whole canal at a single moment in time or over a specified period of time.
The warm, rainy season from May to October saw a rise in the prevalence of harmful Microcystis in the lake following the 2004–05 hurricanes, which caused considerable losses in fish and aquatic plants. There were comparable large blooms in 2013, 2016, and 2018. There were no significant Microcystis blooms in the St. Lucie or Caloosahatchee estuaries that the researchers could find because the research cruises took place in the comparatively dry years of 2019 and 2020.
According to Lapointe, “major nitrogen loading occurs during these rainfall events, which we now realize happened in 2013, 2016, and 2018.” “The lake and estuaries experienced large blooms after these intense rain events.”
Results also indicate that bloom production was accelerated in the urbanized Caloosahatchee River Estuary and St. Lucie Estuary due to greater nitrogen levels. Because the nutrients—phosphate, ammonium, and nitrate—are so reactive, the researchers saw thick “scum” on the top of the water in those estuaries.
“The growth response is like ‘Miracle Grow,’ when water and Microcystis are released into the estuaries from Lake Okeechobee,” Lapointe explained. The estuaries had the highest levels of phosphate, nitrate, and ammonium that we could find. Human waste is frequently linked to these nutrients. In particular, we found higher nitrogen isotope concentrations, suggesting that a substantial source of this nitrogen is human waste.
Significant differences in the water quality between sites were also discovered by the researchers, and these differences had an impact on the growth and severity of algal blooms. The areas most affected by human waste, Pahokee Marina and Cape Coral, saw the largest blooms.
According to Lapointe, “data from the Florida Keys demonstrates comparable patterns of nitrogen enrichment, and our research suggests that such changes may be occurring throughout the entire watershed.”
The Everglades used to naturally flow southward with water from the Lake Okeechobee watershed. The Lake Okeechobee Waterway, which was established as a result of modifications to the water management system, periodically reroutes lake water. The C-44 canal channels it eastward into the St. Lucie Estuary, while the C-43 canal channels it westward into the Caloosahatchee River and the Estuary.
Nitrogen levels affect microcystis blooms and their toxicity in Lake Okeechobee and the St. Lucie Estuary, and our research indicates that nitrogen enrichment is rising. Reduced nitrogen is essential to prevent dangerous algal blooms in the estuaries downstream and along the lake’s canal, according to co-author and assistant research professor Rachel Brewton, Ph.D., of FAU Harbor Branch. Reduce these inputs as soon as possible, as the Upper Kissimmee River has a significant nitrogen burden. While the St. Lucie and Caloosahatchee estuaries have defined Total Maximum Daily Loads for phosphorus and nitrogen, respectively, Lake Okeechobee does not, and new plans for the lake’s tributaries are aimed at addressing nitrogen reductions.
The size of the watersheds and the unique characteristics of the receiving waters, such as their chemistry and hydrology, determine how these blooms affect different areas of the ecosystem.
Malcolm McFarland, Ph.D., co-author and associate research professor at FAU Harbor Branch, explained, “In the lab, we measured chlorophyll a, microcystins, and amounts of Microcystis and other phytoplankton by analyzing their cell concentrations and pigments in water samples.” The study vessels’ water samples were subjected to flow cytometry in order to analyze live algae cells and prevent losses resulting from preservation and storage.
These blooms are affecting large lakes, rivers, estuaries, and coastal areas more frequently, which raises concerns that in the future, drinking water supplies, recreational opportunities, tourism, and fisheries may be further threatened by the poisons these blooms and their accompanying activities carry.
According to Lapointe, “these blooms have national implications for public health, environmental quality, and economic well-being in addition to impacting Florida’s vital water resources.” “Knowing these changes enables us to tackle the difficulties in protecting our waters and guarantees clean, safe water for communities throughout the nation.”
The South Florida Water Management District’s Lake Okeechobee Component A Reservoir project and the Lake Okeechobee Watershed Restoration Project, as well as better wastewater treatment and water storage north of Lake Okeechobee, are being driven by the findings of this research.
Nicole Stockley, a former research engineer at FAU Harbor Branch, is a co-author of the study.
The US National Aeronautics and Space Administration (NASA) Water Resources Program (80NSSC19K1200) provided funding for this study. The Florida Center for Coastal and Human Health, which was established with funding from the Harbor Branch Oceanographic Institute Foundation, gave further assistance for this study.
