Extreme Weather Event Triggers Cascade Towards Extreme Turbidity in a Clear-water Lake
Extreme Weather Event Triggers Cascade Towards Extreme Turbidity in a Clear-water Lake
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DOI：
10.1007/s10021-017-0121-4
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发表时间：
2017-12-01
期刊：
影响因子：
3.7
通讯作者：
Engelhardt, Christof
中科院分区：
文献类型：
--
作者：
Kasprzak, Peter;Shatwell, Tom;Engelhardt, Christof
气候预报预测全球极端天气事件将增加，但有关生态系统后果的信息却很少。对湖泊特别重要的是严重的风暴，它可以通过破坏分层期间的垂直热结构来影响生态地球化学过程和生物群落。2011年7月经过德国北方的一场异常风暴提供了一个机会，可以评估这种极端事件对一个营养贫乏的深湖的物理和生态特征之间相互作用的后果和潜在机制。风速是有记录以来最极端的。在整个事件中测量的一系列变量一致表明，一系列过程将清澈的湖泊推向异常浑浊的状态。具体而言，温跃层加深风暴夹带的蓝藻的深叶绿素最大值位于约8米深的表面混合层。从光限制释放，强烈的光合作用的蓝藻促进初级生产，增加藻类生物量，提高pH值，从而导致大量的方解石沉淀的水平从来没有观察到在三十年的湖泊监测。结果，水的透明度从6.5 m下降到2.1 m，为40年来的最低记录，透光层在几周内缩小了约8 m。这些结果表明，蓝藻水华不仅受到气候变暖的促进，而且也可能由极端风暴引发。如果这种事件变得更加强烈或频繁，那么形成深度叶绿素最大值的清水湖泊在未来似乎特别危险。
Climate forecasts project a global increase in extreme weather events, but information on the consequences for ecosystems is scarce. Of particular significance for lakes are severe storms that can influence biogeochemical processes and biological communities by disrupting the vertical thermal structure during periods of stratification. An exceptional storm passing over northern Germany in July 2011 provided an opportunity to assess the consequences and underlying mechanisms of such extreme events on the interplay between the physics and ecological characteristics of a deep, nutrient-poor lake. Wind speeds were among the most extreme on record. A suite of variables measured throughout the event consistently indicates that a cascade of processes pushed the clear-water lake into an exceptionally turbid state. Specifically, thermocline deepening by the storm-entrained cyanobacteria of a deep chlorophyll maximum located at about 8 m depth into the surface mixed layer. Released from light limitation, intense photosynthesis of the cyanobacteria boosted primary production, increased algal biomass, raised the pH and thus induced massive calcite precipitation to a level never observed within three decades of lake monitoring. As a consequence, water transparency dropped from 6.5 to 2.1 m, the minimum on record for 40 years, and the euphotic zone shrank by about 8 m for several weeks. These results show that cyanobacterial blooms not only are promoted by climate warming, but can also be triggered by extreme storms. Clear-water lakes developing a deep chlorophyll maximum appear to be particularly at risk in the future, if such events become more intense or frequent.