Modeling the response of Microcystis aeruginosa blooms to wind-induced turbulence in a stratified reservoir: Biomass and vertical distribution perspectives

• M. aeruginosa dynamics is regulated by hydrodynamics and thermodynamics. • Critical turbulence increases with stratification and decreases with mixed layer. • Thermal dynamics’ impact on algal biomass depends on initial biomass. • Stronger stratification and shallower mixed layer lead to higher algal aggregation. Harmful algal blooms caused by Microcystis are a global ecological challenge. While wind-induced turbulence is a primary driver of algal spatial migration and biomass accumulation, existing studies on blooms in thermally stratified waters have predominantly focused on relationships between stratification indices and bloom dynamics, neglecting the pivotal role of turbulence in these processes. The spatiotemporal scale mismatch between turbulence and thermal stratification poses new challenges for investigating their synergistic effects on algae. This study focused on Microcystis aeruginosa (Kutzing) Kutzing ( M. aeruginosa ), the dominant species in algal blooms of the Daheiting Reservoir. It employed a cyanobacterial bloom model coupling turbulence-driven physical and physiological processes to investigate the spatiotemporal dynamics of M. aeruginosa biomass and vertical distribution in stratified waters, examining their responses to initial biomass, stratification intensity, mixed layer depth, and wind events. The results showed that turbulence nonlinearly affected the biomass of M. aeruginosa , with a maximum biomass increment occurring at a turbulent dissipation rate of 2.69 × 10 −4 m 2 /s 3 . The critical turbulent dissipation rate for uniform distribution (Morisita’s index < 1) was positively correlated with stratification intensity, but negatively correlated with mixed layer depth. Additionally, the critical turbulent dissipation rate increases with biomass, and when biomass exceeded 2.5 × 10 5 cells/mL, M. aeruginosa consistently exhibited aggregated vertical distribution. The impacts of stratification intensity and mixed layer depth on biomass were contingent upon the initial biomass: stronger stratification and shallower mixed layers promoted biomass accumulation under low initial biomass, whereas the opposite held under high initial biomass. This study elucidates the synergistic mechanisms through which thermal stratification and wind-induced turbulence drive M. aeruginosa blooms, providing novel insights for harmful algal bloom control in stratified waters.