基于高频高光谱近感观测量化风对蓝藻水华的影响

Quantifying the effect of wind on cyanobacteria blooms based on high frequency hyperspectral proximity observations

全球气候变化显著影响湖泊理化环境和生态系统演化,对生态系统服务造成负面影响甚至引发生态系统灾变,其中风速下降可能促使富营养化湖泊蓝藻水华的暴发和水面漂浮集聚。以往由于较低的观测频次,往往很难精细量化风对蓝藻水华的影响。利用陆基高光谱近感观测技术,基于分钟小时尺度开展周年高频观测,通过对6—10月蓝藻生长期太湖表层水体叶绿素a浓度统计分析,量化蓝藻水华高频动态变化特征,确定蓝藻水华漂浮集聚的风速阈值。研究发现,随着风速的下降,水体表层叶绿素a浓度随之增加,蓝藻水华出现概率也随之增加。概率分析显示,当近地面风速小于2.5 m/s时,湖泊表层比较容易形成明显肉眼可见的蓝藻水华,藻华发生概率为55.1%。长时间持续的低风速容易诱发蓝藻水华形成和漂浮集聚,强风浪事件后低风速出现1~2天叶绿素a往往就能恢复以往较高水平,这为管理者有效防控蓝藻水华提供了新视角。长期气象观测显示,气候变化影响下太湖地区风速呈现显著下降趋势,增加了蓝藻竞争优势和发生概率,有助于其在表面漂浮集聚。在未来的气候变化情景下,如果风速继续呈现下降趋势,在营养盐条件不变情况下湖泊表层蓝藻水华发生概率可能还会上升,增加蓝藻水华防控难度,也对流域和湖体营养盐管控来缓解蓝藻水华提出更高要求。

Global climate change has a significant impact on the evolution of lake environments and ecosystems,with negative consequences for ecosystem services.The decrease in wind speed may promote the outbreak and floating accumulation of cyanobacterial blooms in eutrophic lakes.In previous studies,it was often difficult to accurately quantify the effect of wind on cyanobacterial blooms due to the low observation frequency of real-time synchronous monitoring of wind speed and chlorophyll-a concentration.Based on ground-based hyperspectral proximal sensing technology,high-frequency observation of real-time synchronous monitoring of wind speed and chlorophyll-a concentration was carried out at minute and hourly scales.Through statistical analysis of the chlorophyll-a concentration in the surface water of Lake Taihu during the cyanobacterial growth period from June to October,the high-frequency dynamic change characteristics of cyanobacterial blooms were quantified,and the wind speed threshold of floating aggregation of cyanobacterial blooms was determined.It was found that as the wind speed decreased,the concentration of chlorophyll-a in the surface water increased and so did the probability of cyanobacterial blooms.The probability analysis showed that when the near-surface wind speed was less than 2.5 m/s,the obvious cyanobacterial bloom was easily formed on the lake surface,with the occurrence probability of cyanobacterial bloom greater than 55.1%.Low wind speed for a long time is easy to induce cyanobacteria bloom formation and floating aggregation,and chlorophyll-a usually recovers to a higher level within 1-2 days after strong wind and wave events,which provides a new perspective for managers to effectively prevent and control cyanobacteria bloom.Under the influence of climate change,the wind speed in the Lake Taihu area showed a significant decreasing trend,which increased the competitive advantages and the occurrence probability of cyanobacteria bloom.In the future climate change scenario,if the wind speed continues to decrease,the occurrence probability of cyanobacteria bloom on the lake surface may increase under the same nutrient conditions,which increases the difficulty of cyanobacteria bloom prevention and control.Therefore,higher requirements for nutrient control in the watershed and lake body are needed to mitigate cyanobacteria blooms.