Summer heatwaves promote blooms of harmful cyanobacteria

Abstract

Dense surface blooms of toxic cyanobacteria in eutrophic lakes may lead to mass mortalities of fish and birds, and provide a serious health threat for cattle, pets, and humans. It has been argued that global warming may increase the incidence of harmful algal blooms. Here, we report on a lake experiment where intermittent artificial mixing failed to control blooms of the harmful cyanobacterium Microcystis during the summer of 2003, one of the hottest summers ever recorded in Europe. To understand this failure, we develop a coupled biological-physical model investigating how competition for light between buoyant cyanobacteria, diatoms, and green algae in eutrophic lakes is affected by the meteorological conditions of this extreme summer heatwave. The model consists of a phytoplankton competition model coupled to a one-dimensional hydrodynamic model, driven by meteorological data. The model predicts that high temperatures favour cyanobacteria directly, through increased growth rates. Moreover, high temperatures also increase the stability of the water column, thereby reducing vertical turbulent mixing, which shifts the competitive balance in favour of buoyant cyanobacteria. Through these direct and indirect temperature effects, in combination with reduced wind speed and reduced cloudiness, summer heatwaves boost the development of harmful cyanobacterial blooms. These findings warn that climate change is likely to yield an increased threat of harmful cyanobacteria in eutrophic freshwater ecosystems.

Global warming as a driving factor for cyanobacterial blooms in Lake Karaoun, Lebanon

“…The increase in surface water temperatures and the length of thermal stratification as a direct response to increased water temperatures coincided with higher abundance of cyanobacterial bloom in Lake Karaoun (Figure 4). This is in agreement with other studies those reported that climate warming may favour the growth and abundance of cyanobacterial species which are well adapted to higher temperatures and stratified conditions as well [21][22] . Moreover, the stratification period was coincided with low epilimnion nutrient concentrations in the lake.…”

“…Changes in plankton community as a result of global warming are a growing concern in ecological studies, as those properties substantially contribute to ecosystem functioning [21][22][23]. According to Paerl et al [24], climate change can result in modified patterns, intensities and duration of precipitation and droughts.…”

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

“…Direct effects, such as rising temperatures, and indirect effects, such as intensified stratification, favor cyanobacterial blooms. Increased water temperature is expected to give cyanobacteria a selective advantage over competing phytoplankton because of the high optimal growth temperature of cyanobacterial species (Elliott et al, 2006;Jöhnk et al, 2008). Laboratory studies on Microcystis aeruginosa have demonstrated increasing growth rates with increasing temperatures from 20 to 32 C (van der Westhuizen and Eloff, 1985;Watanabe and Oishi, 1985;Imai et al, 2009).…”

Existing and emerging cyanocidal compounds: new perspectives for cyanobacterial bloom mitigation

“…Eutrophication and climate change cause massive growth of cyanobacteria in water bodies across the world (Jöhnk et al 2008;Paerl and Huisman 2008). Several publications presented in this special issue of Aquatic Ecology entitled ''Cyanobacterial bloom.…”