秋冬季温度降低对微囊藻衰亡和沉降的作用机制

Mechanism of temperature reduction in autumn and winter on decline and sedimentation of Microcystis

为明确温度降低对微囊藻衰亡和沉降的影响,对贡湖微囊藻水华的消退过程进行了监测,同时开展了室内低温培养试验。结果表明:室内试验模拟结果与野外秋冬季的现象基本吻合,微囊藻一般在温度低于15℃时衰亡,低于12.5℃大量沉降;温度降低造成群体粒径显著减小,与群体内死亡的藻细胞数量有关,当死亡率达到25%~45%时,大群体普遍开始解体并分散成小群体;微囊藻在低温下重力密度持续增长,最终失去自主上浮能力;秋冬季降温初期微囊藻沉降主要由群体小型化和松散化导致,重力密度增大很可能是降温后期微囊藻沉降的主要原因。

In order to clarifying the impact of temperature reduction on the decline and sedimentation of Microcystis,the decline process of Microcystis bloom in Gonghu Lake was monitored and low temperature culture experiments were conducted.The results show that the laboratory simulation results are basically consistent with the phenomenon in the field in autumn and winter.Microcystis generally declines at temperature below 15℃and sinks in large numbers below 12.5℃.The temperature reduction leads to a significant decrease in the size of the Microcystis colonies,which is related to the number of dead algal cells within the colony.When the mortality rate reaches 25%~45%,the large colonies will generally begin to disintegrate and disperse into small colonies.Gravity density of Microcystis continues to increase at low temperatures,and it eventually loses its ability to autonomously float to the surface.The initial decline in sedimentation of Microcystis in autumn and winter is mainly caused by colonies miniaturization and loosening,and the increase of gravity density is likely to be the main cause of Microcystis sedimentation in the later stages of temperature reduction.