Whether controlling hydrodynamic conditions is an effective solution to alleviate cyanobacterial blooms

Abstract

The main purpose of this study was to determine the threshold and mechanism of the fluid field affecting cyanobacterial blooms based on monitoring of Taihu Lake fluid field data combined with artificial simulation experiments. The increase of carbon dioxide (CO₂) content in L-wave (wind speed of 3 m s⁻¹, wave height of 0.03 m) under simulated low wind waves promoted the peak of cell density, chlorophyll-a and optimal/maximal quantum yield of PSII (Fv/fm). At the same time, the water flow of 0.004–0.008 m s⁻¹ increased the collision frequency between cyanobacteria cells and activated the activity of antioxidant enzymes, so that cyanobacteria in the L-wave secreted more extracellular polymers (EPS) and α-d-glucopyranose, thereby enhancing cell adhesion. The maximum cell size of cyanobacteria was observed under the condition of L-wave strongly indicated that the low wind and wave environment promoted the formation of cyanobacterial blooms. However, the fluid field intensity was further enhanced to simulate the high-wave (H-wave, i.e., wind speed 3 m s⁻¹ and wave height 0.1 m). The excessive shear stress (4.54 × 10⁻² Pa) under H-wave produced a large amount of reactive oxygen species (ROS), which caused oxidative stress damage to cyanobacteria. The expression of peroxiredoxin (prx) increased by 1.57 times, which fully confirmed the imbalance of ROS scavenging system in cyanobacteria cells in H-wave, thereby inhibiting the formation of cyanobacterial blooms. By combining the monitoring and simulation experiments of Taihu Lake and using the structural equation model, it was found that adjusting the intensity of fluid field, colony formation and biomass were effective strategies to alleviate the outbreak of cyanobacterial blooms.

Novelty and relevance statement

The optimal fluid field thresholds and mechanism for bloom formation were determined through a combination of field monitoring and artificial simulation. However, exceeding this threshold (wind speed 3 m s⁻¹ and wave height 0.03 m) inhibited the formation of cyanobacterial blooms. This study will provide new insights and guidance for bloom control.