Investigating Abiotic Drivers for Vertical and Temporal Heterogeneities of Cyanobacteria Concentrations in Lakes Using a Seasonal In Situ Monitoring Station

Abstract

Harmful algal blooms (HAB) are ubiquitous ecological and public health hazards because they are composed of potentially toxic freshwater microorganisms called cyanobacteria. The abiotic drivers for toxic HAB are investigated using a research station deployed in a eutrophic lake in Minnesota in 2016. This research station provides full-depth water quality (hourly) and meteorological conditions monitoring (5 min) at the sampling site. Water quality monitoring provides chemical, physical, and biological measurements, that is, phycocyanin concentration, a photosynthetic pigment distinct to cyanobacteria. The high cyanobacteria biovolume (BV) in the epilimnion observed in mid-July persisted until late September when it was distributed uniformly throughout the water column. A scaling relationship was developed among BV heterogeneity, thermal stratification stability, and surface water temperature. This relationship was verified in a dimictic lake the following year. The proposed scaling relationship is relevant to sampling protocols of HAB as it informs if the sample depth is representative of the entire water column. During the strongly stratified period, BV accumulated above the thermocline and in the photic zone, with distinct peaks forming occasionally both near the water surface and at locations with photosynthetically active radiation approximately equal to 10 μE/m 2 s. Our observations suggest that the temporal/vertical variability of cyanobacteria BV is strongly influenced by lake dynamics, thermal structure, seasonal temperature variation, and light availability. These observations demonstrate that cyanobacteria tend to move and accumulate in specific warm water layers, confined by the thermocline and determined by well-defined light conditions.

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.…”

Development of a Risk Characterization Tool for Harmful Cyanobacteria Blooms on the Ohio River

“…Third, we considered the in situ sensing of chlorophyll and phycocyanin pigments as more direct and time relevant indicators of cyanobacteria biomass [ 59 ]. Indeed, fixed location phytoplankton pigment sensing has been used with some success for signaling and forecasting risk related to cyanoHABs [ 59 – 64 ]. This strategy can work well when there are specific points of public health concerns such as drinking water intakes or swimming beaches.…”

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

“…This process must depend on the relationship between turbulent strength and the floating ability of Microcystis . In addition, turbulence can directly affect the growth of Microcystis (Arnott et al., 2021; Wilkinson et al., 2019). If the cell density in the water column is very high, even though Microcystis colonies are evenly distributed vertically in the mixed layer, the cell density at the water surface is still very high, then blooms will still occur.…”