Abiotic Drivers of a Deep Cyanobacteria Layer in a Stratified and Eutrophic Lake

Abstract

Harmful algal blooms are one of the most imminent threats to freshwater quality across the globe (Huisman et al., 2018;O'Neil et al., 2012). Of the HAB-forming cyanobacteria species, Microcystis are of particular concern due to their ubiquity and their production of Microcystin toxins. There are numerous evolutionary advantages that allow Microcystis to thrive across the globe, and one such advantage in stratified lakes is the ability of vertical motility. Cell buoyancy is modulated by adjusting ballast weight through production or metabolism of dense carbohydrates to offset low density intracellular gas vesicles, allowing Microcystis to move up or down the water column (Reynolds et al., 1987). The speed of unicellular vertical motility can be greatly enhanced by forming colonies, which is a typical occurrence in natural environments (Xiao et al., 2018).Traditionally, Microcystis vertical migration in natural environments has been hypothesized to be nutrient-driven chemotaxis (Fogg & Walsby, 1971;Ganf & Oliver, 1982). However, as lakes become more eutrophic and nutrients become a less limiting substrate, abiotic factors tend to dominate Microcystis vertical motility (Xiao et al., 2018). Most of the work on physical drivers has focused on light, wind, and temperature. Walsby (1985, 1986) demonstrated experimentally that Microcystis cells will increase in density under high irradiance conditions to sink to a preferred low light intensity, but their ability to regain buoyancy was dependent on water temperature. In laboratory experiments, You et al. (2018) demonstrated that Microcystis vertical buoyant velocities were consistently and significantly faster at higher temperatures. Cao et al. (2006) suggested vertical distributions of different phytoplankton species, especially Microcystis, were largely correlated with wind events (and had no correlation with nutrients) in a field study of Lake Taihu, China. As a result, it has been suggested the relationship between Microcystis vertical motility and timing of HAB onset should be explored more in depth (

A three-part coupled statistical and physical model to monitor water quality parameters governing disinfection byproduct risk at an urban drinking water intake

“…The algorithm terminates splitting when the child nodes are pure, meaning it contains only elements from one predictor (Brieman et al, 1984). The machine learning framework is implemented in MATLAB using the TreeBagger function (Taylor et al, 2021;Mathworks, 2022). A number of regression modeling frameworks were tested as part of this study, and the TreeBagger function was selected with an optimal number of trees that minimize model error.…”

Modeling Physical and Physiological Processes Reveals the Role of Turbulence in the Prerequisites for Microcystis Blooms

“…The formation of Microcystis blooms is considered to be a large number of Microcystis colonies gathered on the surface of some areas of lakes or reservoirs, especially, downwind bay or reservoir backwater areas in summer, via migrating in the vertical and horizontal directions (Feng et al., 2018; Ndong et al., 2017). Meteorological conditions, especially turbulence caused by wind and waves, are considered to be the main factors affecting the spatial migration and accumulation of Microcystis colonies (Taylor et al., 2021; H. Wang et al., 2016). When the turbulence is small, the buoyant Microcystis colonies can float to the water surface and gather in the downwind area.…”