Drought and heatwave mesocosm experiment on Canadian Rocky mountain periphyton communities from alpine ponds.

The accelerating rate of global climate change at higher elevations and latitudes is increasing the potential for extreme climatic events. Here, a knowledge gap exists in how the order of exposure to and duration of droughts and heatwaves affect their cumulative impact on aquatic communities. We tested experimentally for the effects of simultaneous versus sequential exposures to drought and heatwave on sediment-dwelling algal communities (epipelon) from small fishless alpine lakes. In both simultaneous and sequential exposure treatments involving drought followed by a heatwave the negative effect of drought offset the negative effect of warming on chlorophyll-inferred algal biomass and taxonomic composition. Reversal of order of exposure (i.e., heatwave followed by drought) lowered their cumulative effect on community structure. These findings highlight the potential for drought events to dominate over heatwaves in altering shallow littoral ecosystems at high elevations under a rapidly warming climate.

全球气候变化在高海拔与高纬度地区的发展速率持续加快，极端气候事件的发生风险也随之提升。当前学界在干旱与热浪的暴露顺序及持续时长如何共同影响二者对水生生物群落的累积效应这一问题上，仍存在研究空白。本研究针对小型无鱼高山湖泊的沉积物附着藻类（epipelon）群落，通过实验探究了干旱与热浪同时暴露、先后暴露两种情境下的效应差异。在同时暴露处理，以及先干旱后热浪的先后暴露处理中，干旱所带来的负面效应抵消了升温对基于叶绿素推定的藻类生物量及类群组成的负面影响。若将暴露顺序反转（即先热浪后干旱），则会降低二者对群落结构的累积效应强度。本研究结果表明，在气候快速变暖的背景下，相较于热浪，干旱事件更可能主导高海拔地区浅水底栖沿岸生态系统的变化过程。