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Griffith-led research has revealed that both the decrease in wind and increase in temperature accompanying climate change can cause bigger algal blooms in the future. Published in Water Research, the study found that a 20% decrease in wind speed will result in algal blooms of the freshwater cyanobacteria Microcystis that are almost one and a half times bigger.
“This decrease in wind will have a more than six-fold larger impact on algal blooms than a 2°C increase in air temperature associated with climate change,” said lead author Mohammad Hassan Ranjbar, a PhD candidate at the Australian Rivers Institute.
“Harmful algal blooms of the freshwater cyanobacteria Microcystis are a global problem and are expected to intensify with climate change, however, to date the impact of atmospheric stilling, the decrease in near-surface wind speed, has not been considered.
“Our research is the first to demonstrate that atmospheric stilling along with increasing air temperature can favour blooms of these buoyant, colony-forming cyanobacteria.” Co-author Professor David Hamilton, Acting Director of the Australian Rivers Institute, said that the results of this research show that “wind speed needs to be included in any projections looking at changes in the frequency, distribution and magnitude of algal blooms under climate change.”
“Decreases in wind speed have been forecast to occur in several regions across the globe with climate warming, which reduces the mixing of the water column. The reduced turbulence in the water column allows buoyant cyanobacteria to float to the surface and form blooms.”
To test if wind stilling affected the distribution and biomass of cyanobacteria in the water column the researchers applied a novel individual-based model which they combined with a hydrodynamic model to simulate the movement of water in the lake.
“For the first time the model was able to show the algal colony size change dramatically in response to the turbulence, light, temperature, and nutrients in the water column of a shallow urban lake,” Mr Mohammad Hassan said.
“Using this model, it was clearly evident that the formation of algal blooms was far more sensitive to the atmospheric slowing of wind speed associated with climate change than it was to warming temperatures.”
The authors stress that this atmospheric stilling should be included in predictions of algal blooms under climate change.