Less wind from climate change may mean larger algal blooms, new research shows

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In simulations at Australia’s Griffith University, less wind speed increased simulated mean algal colony sizes by 38%. Photo credit: Juli, stock.adobe.com

A new study out of Australia’s Griffith University has found that a 20% decrease in wind speed from climate change could result in algal blooms almost one-and-a-half times their current size.

Using a 3D hydrodynamic model to simulate the movement of water in a lake, researchers were able to determine that less wind reduces mixing in the water column in lakes and other bodies of water, allowing buoyant cyanobacteria to float to the surface and form blooms.

Lead author Mohammad Hassan Ranjbar, a PhD candidate at the Australian Rivers Institute, said that the impact of less wind on algal blooms is more than six times that of a 2°C increase in air temperature associated with climate change. While a 2°C increase in air temperature increased simulated mean colony size by 5%, the study found in simulations that less wind speed increased simulated mean colony size by 38%.

“Our research is the first to demonstrate that atmospheric stilling along with increasing air temperature can favour blooms of these buoyant, colony-forming cyanobacteria,” Ranjbar said in an announcement from Griffith University.

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Atmospheric stilling is the decrease in near-surface wind speed.

Co-author Professor David Hamilton, acting director of the Australian Rivers Institute, said the research shows 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.”

Turbulence, light, temperature, and nutrients in the water column of a shallow urban lake can also impact the size of algal blooms, the study states.

“Trends in observed terrestrial near-surface wind speed show that atmospheric stilling is widespread worldwide,” the study’s conclusion states. “If this trend continues, especially in combination with rising temperatures and increasing loads of nutrients, there may be a substantial increase in the frequency and extent of cyanobacteria blooms globally, suggesting that water resource managers should consider the increased risk of cyanobacterial blooms under a warmer and calmer future climate.”

The individually-based model for the simulation consisted of three sub-models that included rate of colony size change, growth in relation to light, nutrients, and temperature, and buoyancy for size-dependent vertical movement.

The researchers chose a decrease of wind speed of up to 20% of the measured wind speed in January and February 2020, the period when the model was applied to Australia’s Forest Lake.

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