Diurnal variations in light intensity and different temperatures play an important role in controlling cyanobacterial blooms

Abstract

Abstract Temperature and light intensity have a significant impact on cyanobacteria. This study conducted laboratory experiments to evaluate the combined effect of different temperatures and diurnal light intensities on cyanobacteria. The sufficient Microcystis aeruginosa and Phormidium ambiguum cells were transferred into three incubators at 30°C, 20°C, and 10°C temperatures for 23 days to acclimatize. After 23 days of incubation, the light intensities were changed diurnally hourly by 100 µmol m-2 s-1 starting from 6:00 to 18:00, where maximum light intensity reached 600 µmol m-2 s-1 at 11:00 to 13:00 and then decreased parallel till 18:00. The samples were collected at three-hour intervals — 6:00, 9:00, 12:00, 15:00, 18:00, and 21:00 — to analyze hydrogen peroxide (H2O2) concentration, protein concentration, chlorophyll-a (Chl-a) content, and catalase (CAT) activity. M. aeruginosa and P. ambiguum showed an increasing trend of H2O2, Chl-a, and CAT for 30°C, 20°C, and 10°C until 15:00, and after that, it decreased with decreasing PAR variations. There was a significant positive effect of temperature in M. aeruginosa and P. ambiguum on H2O2 concentration (30°C to 10°C, p< 0.001 and p<0.01 respectively), protein concentration (30°C to 10°C, p< 0.001 in both species), and Chl-a content (30°C to 10°C, p< 0.001 in both species). CAT activity was directly proportional to H2O2 concentration at each temperature. Chl-a/protein content in lowering temperatures (30°C to 10°C) harms both species' growth conditions. These findings would provide the necessary tools for treating cyanobacterial blooms.