Effects of light and water disturbance on the growth of Microcystis aeruginosa and the release of algal toxins.

Eutrophication of water constitutes a serious threat to global water quality. Light intensity and water disturbance are important factors affecting the growth of algae and the release of algal toxins. In this study, algal growth indicators, algal enzyme systems, and algal toxin release in Microcystis aeruginosa under different light intensities and water disturbances were determined. The results showed that 2500 lx and 120 rpm were the optimal conditions for the growth of M. aeruginosa. The growth of algal cells was inhibited by high light intensity and high water disturbance. However, the optimal conditions for algal growth were not favorable conditions for the release of algal toxin. The highest concentration of microcystin-LR (MC-LR), observed at 4500 lx and 80 rpm, was 198.1 μg/L, whereas the highest single cell toxin production reached up to 10.49 × 10  μg/cell at 7000 lx and 120 rpm. Redundancy analysis results showed that the concentration of MC-LR was positively correlated with algal cell density and antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase, and malondialdehyde [MDA]) and negatively correlated with the total nitrogen and total phosphorus consumption rates and MDA. Single cell toxin production was negatively correlated with algal cell density and antioxidant enzyme activity but positively correlated with MDA content. PRACTITIONER POINTS: There was an optimal water disturbance condition for algae growth affected by the light intensity. Optimal conditions for algae cell growth are not necessarily the optimal conditions for algal toxin release. Enzyme indicators have correlation with the release of algae toxins and the growth of algae cells.