Methane emissions from small lakes: Dynamics and distribution patterns (MethDyn)

小型湖泊已被确定为全球甲烷预算中甲烷的重要来源。这些湖泊单位面积的甲烷通量高于大型湖泊，占全球湖泊甲烷排放量的主要部分。然而，湖泊范围内的甲烷排放量的估计存在很大的不确定性，因为测量和模型方法，占湖泊中甲烷的时间和空间变异性是罕见的。该项目的目的是调查小型湖泊中的甲烷动态和分布模式以及小型湖泊的甲烷排放量，并确定湖泊特性和量化决定小型湖泊全湖甲烷排放量的过程。因此，重点将是甲烷，秋季翻转，以及不同的通量路径每年，全湖甲烷排放的空间梯度的相对重要性和时间变异性。将进行密集的实地实验，测量溶解甲烷和甲烷排放的内部动态、空间异质性、全湖分布和时间变异性，以具有不同性质的六湖为例，说明主要排放途径以及非生物条件。现有技术的测量技术（例如，涡动协方差系统、单波束和多波束回声测深仪、甲烷和二氧化碳探测器、自动沸腾通量漏斗和扩散通量室、超便携式温室气体分析仪、氧气和二氧化碳光电管）将与密集的水采样和水样本分析相结合（溶解甲烷，甲烷同位素组成，氧化速率，和其他水成分），以满足足够的时间和空间分辨率以及关于所有非生物参数，特别是溶解甲烷浓度的可靠绝对数据的要求。这些现场实验将通过使用3D甲烷模型进行的甲烷动力学数值模拟来补充。数值方法的目的是模拟溶解甲烷的水平输送、交换和分布动力学，以及在小湖泊中变化的边界条件下甲烷向大气的全湖扩散通量，并研究气候变化和不同的风强迫如何影响翻转期间甲烷向大气的扩散通量，以及它们对年、全湖排放。

Small lakes have been identified as a significant source of methane in the global methane budget. These lakes have higher methane fluxes per unit area than large lakes and contribute a major fraction of global methane emissions from lakes. However, the estimation of lake-wide methane emissions underlies large uncertainties, because measurements and model approaches that account for the temporal and spatial variability of methane in lakes are rare. The aims of the project are to investigate methane dynamics and distribution patterns in and methane emissions from small lakes as well as to characterize lake properties and to quantify processes that determine the lake-wide methane emissions from small lakes. Thereby, the focus will be on the relative importance and temporal variability of spatial gradients in methane, autumn overturn, and the different flux paths for annual, lake-wide methane emissions. Intensive field experiments will be conducted measuring the internal dynamics, spatial heterogeneity, lake-wide distribution, and temporal variability of dissolved methane and methane emissions that account for the main emission pathways together with abiotic conditions on the example of six lakes having different properties. State of the art measuring techniques (e.g., an eddy-covariance system, single- and multi-beam echosounder, methane and carbon dioxide probes, automated ebullition flux funnels and diffusive flux chambers, an ultraportable greenhouse gas analyzer, oxygen and carbon dioxide optodes) will be combined with intensive water sampling and water sample analysis (dissolved methane, methane isotopic composition, oxidation rates, and other water constituents) to meet the requirements of sufficient temporal and spatial resolution and reliable absolute data on all abiotic parameters and in specific on the dissolved methane concentration. These field experiments will be complemented by numerical simulations of the methane dynamics conducted with a 3D Methane Model. The purpose of the numerical approaches is to simulate horizontal transport, exchange and distribution dynamics of dissolved methane, and the lake-wide diffusive flux of methane to the atmosphere under changing boundary conditions in small lakes as well as to investigate how climate change and different wind forcing affect the diffusive flux of methane to the atmosphere during overturn periods and their relative contribution to the annual, lake-wide emissions.