Abstract
Harmful algal blooms (HABs), in particular those consisting of the
cyanobacteria \textit{Microcystis}, are becoming
increasingly more common across the globe. Despite the growing body of
evidence that suggests vertical heterogeneity of
\textit{Microcystis} can be a precursor to HAB
formation, the abiotic drivers of vertical distribution of
\textit{Microcystis} are poorly understood in the field
environment. The prediction of subsurface cyanobacteria is also
pertinent because subsurface concentrations are not easily recognizable
to the public or lake system managers, creating an unnoticed safety
hazard. High-frequency temporal and vertical data were collected from an
Eulerian research station anchored in a stratified and eutrophic lake
for five months. Data show that the magnitude of the subsurface
\textit{Microcystis} concentration peak and the center
of gravity of the deep cyanobacteria layer are statistically
significantly mediated by the thermal structure of the lake. The peak
subsurface cyanobacteria biovolume scales linearly with the thermocline
depth and temperature, whereas the center of gravity of the subsurface
cyanobacteria biovolume scales linearly with the mixed layer depth and
temperature. Furthermore, our data suggest there is a seasonal evolution
of the subsurface cyanobacteria center of gravity that could potentially
indicate timing of HAB onset. Based on easily measured parameters
associated with the vertical lake temperature profile and meteorological
conditions, we provide evidence of predictable trends in subsurface
cyanobacteria variables.