Long-term perspectives on aquatic ecosystem change with thawing permafrost

全球大约25%的湖泊位于永久冻土区，这些湖泊最容易受到气候变暖的影响，因为永久冻土区融化速度加快。要了解湖泊生态系统如何对永久冻土退化作出反应，需要从长远的角度来看待最近的变化，以便将其置于自然生态系统变异性的背景下。我的研究将使用湖泊沉积物岩心来重建湖泊历史（百年到千年的时间尺度），以解决我们对湖泊生态系统对由于永久冻土融化而发生的变革性景观变化的反应的理解中的关键知识差距。我将探讨在加拿大西北地区永久冻土融化的两种不同情景下，水生生态系统的长期变化。第一种情景集中在永久冻土带南部边界的湖泊（靠近Hay河），那里的永久冻土带融化导致森林永久冻土带支持的泥炭高原转变为湿地。这些景观变化改变了陆地碳向湖泊的径流，这对碳和污染物循环以及水生生物群之间的生态相互作用具有影响。第二种情景考察了永久冻土退化的一种壮观形式，即在地面冰含量高的地区（如北北省因努维克附近）的湖泊海岸线上形成的退行性融化滑坡。融化滑坡的发展向湖泊释放了大量无机物质（如粘土颗粒），这些物质从水柱中清除了有机碳和营养物质，并增加了水的清晰度。解冻滑坡后水体清晰度的增加可能会增加水生生物对有害紫外线辐射的暴露，这是受滑坡影响的湖泊的潜在压力源，但尚未得到彻底的研究。在千年时间尺度上对湖泊历史的研究，在两种永久冻土融化情景下，将使我能够重建过去温暖时期的生态系统条件，作为评估最近人类引起的气候变暖下的当前条件的参考框架。北方拥有丰富的淡水资源，永久冻土融化将继续加剧，成为这些生态系统的压力源。通过研究湖泊在不同时间和空间尺度上对这种压力源的反应，我的研究将为未来气候变暖下水生食物网的命运提供见解，有助于保护加拿大北部健康和多样化的水生生态系统。

Approximately 25% of all lakes globally are located in permafrost regions, and these lakes are among the most vulnerable to climate warming through accelerated rates of permafrost thaw. A long-term perspective is needed to understand how lake ecosystems are responding to permafrost degradation, in order to place recent changes in the context of natural ecosystem variability. My research will use lake sediment cores to reconstruct lake histories (centennial to millennial timescales), in order to address key knowledge gaps in our understanding of the responses of lake ecosystems to the transformative landscape changes occurring as a result of permafrost thaw. I will explore long-term aquatic ecosystem changes under two contrasting scenarios of thawing permafrost in Canada's Northwest Territories. The first scenario focuses on lakes at the southern limit of permafrost (near Hay River), where thawing permafrost leads to the conversion of forested permafrost-supported peat plateaus into wetlands. These landscape changes alter terrestrial carbon run-off to lakes, which has implications for carbon and contaminant cycling, and ecological interactions among aquatic biota. The second scenario examines a spectacular form of permafrost degradation, retrogressive thaw slumps that form on the shorelines of lakes in areas of high ground-ice content, such as near Inuvik, NT. Thaw slump development releases large amounts of inorganic material (such as clay particles) to lakes, which scavenges organic carbon and nutrients out of the water column, and increases water clarity. The increase in water clarity following thaw slumping may increase the exposure of aquatic biota to harmful UV radiation, a potential stressor in slump-impacted lakes that has yet to be thoroughly investigated. The study of lake histories on millennial timescales, under both permafrost thaw scenarios, will allow me to reconstruct ecosystem conditions during past warm periods as a frame of reference from which to evaluate current conditions under recent human-induced climate warming. The north hosts an abundance of freshwater resources, and permafrost thaw will continue to intensify as a stressor on these ecosystems. By examining lake responses to this stressor over varying temporal and spatial scales, my research will provide insights into the fate of aquatic food webs under future climate warming, contributing to the protection of healthy and diverse aquatic ecosystems in northern Canada.