Sediment Suspension Induced by Fluid Field Promotes Cyanobacterial Colony Aggregation and Bloom Formation in Shallow Lakes

Cyanobacterial bloom is one of the most prominent ecological challenges worldwide. As the key process of cyanobacterial bloom, colony formation is influenced by interactions between hydrodynamic processes and sedimentary nutrient cycling in shallow lakes. However, the specific mechanisms of cyanobacterial growth and aggregation through these interactions remain insufficiently understood. In this study, a laboratory-scale simulation was conducted to replicate the characteristic fluid fields of a real shallow lake and examine their combined effects with sediments on cyanobacterial colony formation. Results showed that sediment disturbance under a suitable fluid field significantly enhanced nitrogen and phosphorus release, leading to a 2.35-fold increase in cell density and a 1.9-fold rise in chlorophyll-a concentration. The fluid field further promoted the secretion of bound extracellular polymeric substances and microcystin-LR, reducing cell surface charge and facilitating cell adhesion with sediments. Gene expression analysis revealed that ntcA and pstA were upregulated, enhancing nutrient assimilation, while the increased expression of MAE-415 and rfbB accelerating EPS synthesis. Structural equation modeling showed that the fluid field and nutrient concentration were the primary factors driving colony formation. These findings provide new insights into the coupled physical–biological processes that promote colony formation and suggest strategies for cyanobacterial bloom control in eutrophic shallow lakes.