Abiotic drivers of a deep cyanobacteria layer in a stratified and eutrophic lake

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.

A theoretical modeling framework for motile and colonial harmful algae

“…Using a Bayesian biophysical model with a high‐frequency dataset, Del Giudice et al ( 2021 ) were able to quantitatively show that quiescent conditions are not enough: High surface water temperatures and high irradiation are also necessary for bloom formation. Recently, it has been suggested that vertical heterogeneity (i.e., subsurface peaks) of M. aeruginosa concentration is an important precursor to Microcystis surface bloom formation (Seegers et al, 2015 ; Xiao et al, 2018 ; Wilkinson et al, 2019 ; Taylor et al, 2021 ). Therefore, it is reasonable to assume improving models for the drivers of M. aeruginosa vertical distributions will likely lead to improved predictions of HAB timing.…”

“…In a previous field study, statistical methods were used to elucidate the reliance of Microcystis ‐dominated algal vertical distributions on lake thermal stratification variables (Taylor et al, 2021 ). Following the protocol discussed in Vinatier et al ( 2011 ), which suggests using statistical and mechanistic models in an iterative manner to uncover forcings of spatial heterogeneity, we propose a mechanistic model to analyze the effects of hydrodynamic and biological processes underlying the spatial patterns observed in the previous field study.…”

“…In a previous field study, statistical methods were used to elucidate the reliance of Microcystis-dominated algal vertical distributions on lake thermal stratification variables (Taylor et al, 2021).…”