Lake Okeechobee, the largest freshwater lake in Florida, has long been a cornerstone of the state’s ecological framework and water management strategy. Covering an expansive area of approximately 730 square miles but maintaining a relatively shallow average depth of 9 feet, the lake plays a critical role in supporting agricultural demands and mitigating flood risks. Its interconnection with the Everglades through a complex network of canals further underscores its environmental importance. Beyond these functional roles, the lake is celebrated for its recreational opportunities, including fishing, boating, and birdwatching, drawing numerous visitors each year to appreciate its natural beauty.
In recent years, Lake Okeechobee has experienced a troubling rise in harmful algal blooms, predominantly caused by cyanobacteria species such as Microcystis aeruginosa. This particular species is notorious for producing toxins that jeopardize both aquatic life and human health. These microscopic algae flourish in warm, nutrient-laden waters, frequently culminating in dense blooms that compromise water quality and ecosystem stability. The phenomenon of diel vertical migration — the cyclical daily movement of cyanobacteria between the water surface and deeper layers — adds a complex layer to understanding these blooms, as it affects their resilience, spatial distribution, and growth dynamics in turbid environments like Lake Okeechobee.
While diel vertical migration has been observed and documented extensively in various aquatic systems, its precise influence on bloom intensity and water quality remains insufficiently elucidated. This gap in knowledge poses a significant challenge for environmental managers and scientists aiming to predict and mitigate harmful algal incidents. Addressing this, a team of researchers devised an innovative physical-biogeochemical model that simulates the intricate interactions between water movement and cyanobacterial behavior, offering unprecedented insight into the daily vertical cycling of these organisms within the lake.
Collaborating researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute and the University of South Florida’s College of Marine Science conducted an in-depth investigation during the summer months when blooms are typically most pronounced. Previous modeling efforts in Lake Okeechobee have accounted for physical and biological factors independently, yet none have simultaneously captured the dynamic diel migration of cyanobacteria with the precision required to understand bloom development at the diurnal scale. This sophisticated model integrates physical processes, such as wind-driven currents and vertical mixing, with biological processes including growth rates and movement behaviors, producing a holistic representation of bloom dynamics.
Vertical mixing, driven by wind stress and variations in water temperature, is a fundamental force influencing nutrient and oxygen transport within the water column. In Lake Okeechobee, this mixing facilitates nutrient replenishment near the surface where photosynthesis occurs, but also redistributes biomass throughout the water body. The model demonstrated that cyanobacteria migrate upward in the early morning to optimize light exposure, thereby enhancing their photosynthetic capacity and cellular proliferation. Concurrently, prevailing winds predominantly originating from southern and southeastern directions push these buoyant cyanobacteria toward northern and northwestern shorelines, resulting in geographically distinct accumulation patterns.
As darkness envelops the lake in the evening hours, cooler temperatures combined with wind-induced turbulence foster vertical redistribution of cyanobacteria, diffusing cells more evenly throughout the water column. This interplay between biological migration and physical transport culminates in a diurnal rhythm wherein cyanobacterial surface concentrations peak late in the morning to midday, then decline sharply by afternoon. Notably, wind-driven lake currents induce near-daily lateral displacement of blooms, often manifesting as narrow, elongated bands of algae less than two kilometers wide tracing along the northern lakeshore — a phenomenon detectable via satellite imagery and in situ observations.
These findings underscore the dominant influence of vertical migration and mixing over horizontal advection in shaping surface bloom intensity and distribution within Lake Okeechobee. Seasonal shifts in bloom severity were also linked to temperature and wind fluctuations. Warmer temperatures enhance cyanobacterial metabolic and growth rates, while stronger wind conditions intensify mixing that submerges organisms below optimal light zones, suppressing bloom formation. This delicate balance highlights the sensitivity of bloom dynamics to climate-driven variations in meteorological factors.
To authenticate the model’s predictive accuracy, the research team employed a multipronged data collection approach. Surface and bottom water samples from diverse sampling sites provided empirical measures of cyanobacteria abundance. Real-time sensor deployments tracked temporal fluctuations in algal concentrations within the lake’s central basin, while sequential satellite remote sensing furnished spatially comprehensive evidence of bloom distribution and migration. The convergence of these datasets validated the diel vertical migration patterns incorporated in the model and confirmed the spatial bloom heterogeneity projected by simulations.
Lead author Dr. Mingshun Jiang, an associate research professor at FAU Harbor Branch, emphasized the critical role of vertical processes in bloom formation, stating that “the daily rise and fall of cyanobacteria, governed by diel vertical migration and mixing, sets the stage for bloom development each day.” He further noted that while horizontal transport influenced bloom spread over longer periods, it was the vertical cycling and rapid surface growth that predominantly dictated bloom intensification and surface visibility. These insights offer a predictive framework that could revolutionize bloom monitoring and early warning systems in Lake Okeechobee and similar ecosystems.
Despite the progress, the study acknowledges unresolved complexities surrounding cyanobacterial biology that warrant further investigation. For instance, the mechanisms underpinning colony aggregation and senescence in Microcystis aeruginosa remain poorly quantified, presenting an impediment to fully characterizing bloom lifecycle dynamics. Enhanced field studies are essential to refine estimates of migration speeds, timing precision, and morphological traits of these colonies, enabling more accurate incorporation into predictive models.
Lake Okeechobee’s hydrology, influenced by inflows from the Kissimmee River watershed and outflow discharges toward the Everglades and regional estuaries like the St. Lucie and Caloosahatchee Rivers, creates a highly interconnected aquatic network. This connectivity means that bloom occurrences in the lake potentially cascade impacts downstream, affecting water quality and phytoplankton communities in sensitive estuarine environments. Understanding bloom dynamics within the lake is therefore pivotal for regional water resource management and ecological conservation strategies.
The comprehensive approach employed in this study—melding hydrodynamic modeling with biological behavior simulations—represents a transformative advance in limnological research. It not only elucidates the physical-biological interplay shaping harmful algal blooms but also establishes a platform for future enhancements incorporating detailed ecological variables. The ability to predict bloom timing, location, and intensity with greater confidence holds promise for informing mitigation actions, safeguarding public health, and preserving the integrity of freshwater ecosystems.
As climate patterns continue to shift, exacerbating the conditions conducive to harmful cyanobacterial blooms, models such as this will be increasingly vital. They enable scientists and policymakers to anticipate changes, adapt management practices, and safeguard critical water resources. The collaboration between academic institutions and funding agencies such as NASA and the Florida Department of Environmental Protection highlights the interdisciplinary and interagency efforts necessary to tackle these complex environmental challenges.
Subject of Research: Cells
Article Title: Modeling water quality and cyanobacteria blooms in Lake Okeechobee: II. Dynamics of diurnal cycles and impacts of cyanobacteria diel vertical migration
News Publication Date: 9-Apr-2025
Web References:
https://www.fau.edu/hboi/
https://usf.edu/
https://www.sciencedirect.com/science/article/pii/S0304380025000018
References:
Mingshun Jiang et al., “Modeling water quality and cyanobacteria blooms in Lake Okeechobee: II. Dynamics of diurnal cycles and impacts of cyanobacteria diel vertical migration,” Ecological Modelling, April 2025. DOI: 10.1016/j.ecolmodel.2025.111107
Image Credits: Brian Lapointe and Brian Cousin, FAU Harbor Branch
Keywords
Aquatic ecosystems, Ocean pH, Cyanobacteria, Surface water acidification, Water, Ecological modeling, Lakes, Wind speed, Pattern formation, Red tides, Ecological processes, Cell growth
Tags: cyanobacteria species impactdiel vertical migration in algaeecological effects of algal bloomsenvironmental importance of EvergladesFlorida water quality issuesfreshwater lake managementharmful algal blooms researchLake Okeechobee ecologyMicrocystis aeruginosa toxinspatterns of toxic algae bloomsrecreational activities in Lake Okeechobeewater management strategies in Florida
