Revealing the dark side of the lake: How winter dynamics control summer conditions in northern prairie lakes

加拿大大草原的硬水湖泊水化学和食物网结构的高度可变性及其对气候条件的强烈依赖性使这些湖泊成为评估气候变化如何影响湖泊生态系统的理想系统。全球环流模型预测，冬季气温上升幅度最大，这将缩短冰层覆盖的时间，改变融雪的时间和数量（这些湖泊的主要水源）。然而，大多数关于温带湖泊的研究都是在无冰季节进行的，而冬季被认为是休眠期。因此，我们对湖泊动力学及其控制的了解主要来自夏季条件。近年来，人们认识到，冰下生态地球化学过程不仅具有高度的动态性，而且对夏季的生物、物理和化学过程具有重要的影响。以气候为主要变量，必须仔细描述当前冬季动态，以确定未来暖冬的直接和间接影响的重要性，特别是在硬水湖泊中。我以前的工作表明，冬季氧动力学控制冰下呼吸，无论是在硬水和北方湖泊。与此相反，控制碳和氮的循环与北方湖泊有很大不同，水文，物理和化学因素更具影响力。因此，我的建议的重点将是划分代谢（呼吸，初级生产）与物理（扩散），化学（硝化，C沉淀）和水文（例如，地下水输入，雪融化）的过程中，在秋季-冬季-春季过渡的草原湖泊，使用实验室实验和实地观察相结合。* 拟议的工作将首次不仅评估冰下地球化学过程的相互作用，而且还确定代谢、化学和物理对C、O和N动态的贡献的相对重要性。这项工作对于预测湖泊对鱼类和无脊椎动物群落的可居住性，以及更好地了解草原湖泊在全球碳循环中的作用具有重要意义。随后，它将使我们能够预测未来气候变化如何影响这些过程中的任何一个或所有过程：具体来说，夏季气温升高（热应力，富营养化，水位下降）和冬季气温升高（冬季死亡风险降低，碳捕获增加）的影响是协同的，主要的还是独立的？在全球范围内，硬水湖泊（如加拿大大草原上的湖泊）占所有内陆沃茨的近50%。因此，这项工作也将在全球范围内高度相关，以了解硬水湖泊生态系统的结构和功能，并预测气候变化，人口增长和农业发展的未来影响。

The high variability of water chemistry and food-web structure in hardwater lakes across the Canadian prairies and their strong dependencies on climate conditions make these lakes ideal systems to evaluate how climate change will impact lake ecosystems. Global circulation models project that temperature increases will be highest in winter, which will shorten the duration of ice cover and change timing and amount of snowmelt (the major supply of water to these lakes). Yet, most research on temperate lakes has been conducted during the ice-free season while winter was considered a dormant period. Hence, our knowledge of lake dynamics and their controls is largely derived from summer conditions. Recently, it has been recognized that under-ice biogeochemical processes can not only be highly dynamic but also significantly influence biological, physical and chemical processes in summer. With climate as a master variable, it will be crucial to carefully characterize current winter dynamics to determine the importance of direct and indirect effects of future milder winters, particularly in hardwater lakes. My previous work indicated that winter oxygen dynamics are controlled by under-ice respiration, both in hardwater and boreal lakes. In contrast, controls of carbon and nitrogen cycles differ strongly from boreal lakes with hydrologic, physical and chemical factors being more influential. Hence, the focus of my proposal will be to partition the importance of metabolic (respiration, primary production) vs. physical (diffusion), chemical (nitrification, C precipitation) and hydrological (e.g., groundwater inputs, snow melt) processes during the fall-winter-spring transitions in prairie lakes, using a combination of laboratory experiments and field observations. ***The proposed work will, for the first time, not only assess the interactions of biogeochemical processes under ice, but also determine the relative importance of metabolic, chemical and physical contributions to C, O and N dynamics. This work will be important for predicting inhabitability of lakes for fishes and invertebrate communities, and better understanding the role of prairie lakes in the global carbon cycle. Subsequently, it will enable us to forecast how future climate change may influence any or all of these processes: Specifically, will the effects of warmer summer temperatures (thermal stress, eutrophication, reduced water levels) and milder winters (lower winterkill risk, increased carbon capture) be synergistic, protagonistic or independent? On a global scale, hardwater lakes (such as those across the Canadian prairies) represent almost 50% of all inland waters. Hence this work will also be highly relevant globally to understand structure and functioning of hardwater lake ecosystems and anticipate future impacts of climate change, population growth and agricultural development.