State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, Jiangsu, 210008, China,
Environ Sci Pollut Res Int. 2013 Dec;20(12):8546-56. doi: 10.1007/s11356-013-1812-9. Epub 2013 May 16.
Short-term hydrodynamic fluctuations caused by extreme weather events are expected to increase worldwide because of global climate change, and such fluctuations can strongly influence cyanobacterial blooms. In this study, the cyanobacterial bloom disappearance and reappearance in Lake Taihu, China, in response to short-term hydrodynamic fluctuations, was investigated by field sampling, long-term ecological records, high-frequency sensors and MODIS satellite images. The horizontal drift caused by the dominant easterly wind during the phytoplankton growth season was mainly responsible for cyanobacterial biomass accumulation in the western and northern regions of the lake and subsequent bloom formation over relatively long time scales. The cyanobacterial bloom changed slowly under calm or gentle wind conditions. In contrast, the short-term bloom events within a day were mainly caused by entrainment and disentrainment of cyanobacterial colonies by wind-induced hydrodynamics. Observation of a westerly event in Lake Taihu revealed that when the 30 min mean wind speed (flow speed) exceeded the threshold value of 6 m/s (5.7 cm/s), cyanobacteria in colonies were entrained by the wind-induced hydrodynamics. Subsequently, the vertical migration of cyanobacterial colonies was controlled by hydrodynamics, resulting in thorough mixing of algal biomass throughout the water depth and the eventual disappearance of surface blooms. Moreover, the intense mixing can also increase the chance for forming larger and more cyanobacterial colonies, namely, aggregation. Subsequently, when the hydrodynamics became weak, the cyanobacterial colonies continuously float upward without effective buoyancy regulation, and cause cyanobacterial bloom explosive expansion after the westerly. Furthermore, the results of this study indicate that the strong wind happening frequently during April and October can be an important cause of the formation and expansion of cyanobacterial blooms in Lake Taihu.
短期水动力波动预计会因全球气候变化而在全球范围内增加，这种波动会强烈影响蓝藻水华。本研究通过野外采样、长期生态记录、高频传感器和 MODIS 卫星图像，调查了中国太湖蓝藻水华对短期水动力波动的消失和重现。在浮游植物生长季节，主导东风引起的水平漂移主要导致蓝藻生物量在湖泊西部和北部积累，并在较长时间尺度上形成后续水华。在平静或微风条件下，蓝藻水华变化缓慢。相比之下，一天内的短期水华事件主要是由风引起的水动力引起的蓝藻群体的夹带和脱夹带引起的。对太湖西风事件的观测表明，当 30 分钟平均风速（流速）超过 6 m/s（5.7 cm/s）的阈值时，风致水动力会夹带蓝藻群体。随后，蓝藻群体的垂直迁移受水动力控制，导致藻类生物量在整个水深范围内彻底混合，最终表面水华消失。此外，强烈的混合还可以增加形成更大和更多蓝藻群体的机会，即聚集。随后，当水动力变弱时，蓝藻群体不断向上漂浮而没有有效的浮力调节，西风过后导致蓝藻水华的爆发性扩张。此外，本研究结果表明，4 月和 10 月频繁发生的强风可能是太湖蓝藻水华形成和扩张的重要原因。
