Quantitative study on the survivability of <italic>Microcystis</italic> colonies in lake sediments.

<italic>Microcystis</italic> colonies can overwinter in sediment and may inoculate the water column through recruitment, promoting the annual recurrence of <italic>Microcystis</italic> blooms. Through microcosm experiments, the survivability of benthic <italic>Microcystis</italic> was quantitatively investigated by elucidating the dynamics of its cell numbers, photosynthetic activity, and toxin content under various sediment conditions. The abundance of <italic>Microcystis</italic> colonies in the sediment samples did not decrease significantly over the 22-week experiment at 5 °C, whereas more than 90% of the benthic population died within 3 months at 25 °C. The survivability of the <italic>Microcystis</italic> colonies under the aerobic conditions of surface sediments was significantly lower than under the anaerobic conditions of deep sediments. Toxic <italic>M. aeruginosa</italic> and non-toxic <italic>M. wesenbergii</italic> exhibited similar survivability, although the final survival efficiency of <italic>M. aeruginosa</italic> was higher than that of <italic>M. wesenbergii</italic> at 15 and 25 °C. Microcystin quotas remained stable at 5 and 15 °C but decreased significantly at 25 °C. The photosynthetic activity of the benthic <italic>Microcystis</italic> colonies decreased gradually, with a larger decline rate at higher temperatures. Our study suggests that most benthic <italic>Microcystis</italic> colonies can overwinter successfully, with microcystins preserved and photosynthetic activity maintained, significantly increasing the risk of bloom formation. However, they were unable to accumulate in the sediments of subtropical shallow lakes over a period of years. [ABSTRACT FROM AUTHOR]