Air-water exchange and energy flux paths in small lakes

风致水体运动是湖泊的一项重要物理特征，在湖泊生态和生物地球化学中起着至关重要的作用。作用在水面上的风应力产生湍流混合层、表面波、大尺度流动结构以及内波，这些可以将能量传递到更深的地方。表面动量输送和相应的边界层湍流强度也影响着湖面与大气之间的热量和溶解气体的交换以及蒸发速率。控制空气-水交换的过程主要是在海洋和高风速下进行的研究。人们对小湖泊中的动量转移速率及其与其他转移系数的相互关系知之甚少，因为那里的风速和取水长度通常都很小。在这个项目中，我们汇编了最近对10个不同的小湖泊进行的动量、热量、水汽和气体通量的大气涡动协方差(EC)测量。这一独特的数据集将被用来分析从风到水的动量传输与风速和取水长度的关系，并推导出不同传输系数之间的机理关系。将通过对三个湖泊中的波浪、水流和湍流的广泛测量来补充正在进行的大气EC测量，从而研究湖泊内的能量通量路径。我们将分析动能在不同类型的流动中的分配及其随风速、湖泊大小和垂直密度层结的函数而从产生到消散的命运。因此，我们对小湖泊中与大气强迫有关的能量通量路径提供了一个全面的机制理解。该项目的发现将提高目前模拟和预测湖泊-大气相互作用的能力，并将有助于生物地球化学和淡水生态学中的一些最新研究问题。

Wind-induced water motions are an important physical characteristics of lakes and play a vital role in their ecology and biogeochemistry. Wind stress acting at the water surface generates a turbulent mixing layer, surface waves, large-scale flow structures as well as internal waves, which can convey energy to greater depths. The surface momentum transfer and the corresponding intensity of boundary-layer turbulence also affects the exchange of heat and dissolved gases between the lake surface and the atmosphere as well as the rate of evaporation. The processes which control air-water exchange have mainly been studied in the ocean and at high wind speeds. Not much is known about the rate of momentum transfer and its interrelation to other transfer coefficients in small lakes, where the wind speed and fetch length are typically small. In this project, we compile recently conducted atmospheric eddy-covariance (EC) measurements of momentum, heat, water vapor and gas fluxes over 10 different small lakes. This unique data set will be used to analyze the dependence of the momentum transfer from wind to water on wind speed and fetch length and to derive mechanistic relationships between the different transfer coefficients. The energy flux paths within lakes will be studied by complementing ongoing atmospheric EC measurements with extensive measurements of waves, currents and turbulence in three lakes. We will analyze the partitioning of kinetic energy into different types of flows and its fate from generation to dissipation as a function of wind speed, lake size and vertical density stratification. As a result, we provide a comprehensive mechanistic understanding of energy flux paths in small lakes in relation to atmospheric forcing. The project findings will improve current capabilities for modelling and predicting lake-atmosphere interactions and will contribute to a number of up-to-date research questions in biogeochemistry and freshwater ecology.