The role of littoral zones as source of methane in lakes: Dynamics, distribution patterns, and emissions

在全球甲烷收支中，小湖泊（<1 km2）已被确定为一个重要的甲烷来源。这些湖泊在全球范围内的自然内陆水体中占主导地位，单位面积的甲烷通量高于大型湖泊。然而，对全湖甲烷排放量的估计存在很大的不确定性，因为考虑湖泊内和湖泊之间甲烷的时空变化的测量很少。该项目的目的是在区域和区域间范围内调查小湖泊的甲烷动态和分布模式以及甲烷排放。因此，重点将放在确定溶解甲烷浓度和甲烷排放的系统模式和代用物上，从而使从选定数量的湖泊获得的结果能够普遍化并在空间上扩大尺度。主要假设是：(1)由于湖泊性质的不同，不同湖泊的溶解甲烷浓度和甲烷排放量存在较大差异；(2)在区域乃至更大的空间尺度上，湖泊和流域性质以及非生物参数可以作为溶解甲烷浓度和甲烷排放量的代用指标；(3)在翻转期（即秋季和破冰后），缺氧低磷离子的形成和程度与混合动力学相结合，决定了小湖泊的年弥漫性甲烷排放；(4)除湖泊特征和非生物条件外，湖泊间微生物群落（产甲烷菌和氧化菌）组成的差异可能解释了湖泊甲烷排放的差异。这些假设将通过密集的实地实验进行验证，测量内部动态、空间异质性、全湖分布、溶解甲烷和甲烷排放的季节变化，以及小斯瓦本和巴伐利亚湖泊及其之间的非生物条件。最先进的原位测量技术（例如，涡流共变系统，单波束和多波束回声测深仪，甲烷探针，自动扩散通量室和烟囱，氧气和二氧化碳光电，CTD和热敏电阻）将与密集的水样采样和水样分析(溶解甲烷，甲烷同位素组成，微生物群落组成，和其他水成分)，以满足足够的时间分辨率和所有非生物参数，特别是溶解甲烷浓度的可靠绝对数据的要求。

Small lakes (<1 km2) have been identified as a significant source of methane in the global methane budget. These lakes dominate in area the global extent of natural, inland water bodies and have higher methane fluxes per unit area than large lakes. However, the estimation of lake-wide methane emissions underlies large uncertainties, because measurements that account for the temporal and spatial variability of methane in and between lakes are rare. The aim of the project is to investigate methane dynamics and distribution patterns in and methane emissions from small lakes on a regional and inter-regional scale. Thereby, the focus will be on the identification of systematic patterns and proxies for the dissolved methane concentration and methane emissions that allow the generalization and spatial up-scaling of the results obtained from a selected number of lakes. The main hypothesis are that (1) the dissolved methane concentration and methane emissions differ substantially between lakes due to their different lake properties; (2) lake and catchment properties as well as abiotic parameters may serve as proxies for the dissolved methane concentration and methane emissions on a regional or even larger spatial scale; (3) the formation and extent of an anoxic hypolimnion in combination with mixing dynamics during overturn periods (i.e., in autumn and after ice break-up) determine the annual, diffusive methane emissions from small lakes; (4) apart from lake characteristics and abiotic conditions, differences in the composition of the microbial community (methane producing and oxidizing bacteria) between lakes may explain differences in the lake-wide methane emissions from lakes. These hypotheses will be tested by intensive field experiments measuring the internal dynamics, spatial heterogeneity, lake-wide distribution, and seasonal variability of dissolved methane and methane emissions together with abiotic conditions in and between small Swabian and Bavarian lakes. State of the art in-situ measuring techniques (e.g., an eddy-covariance system, single- and multi-beam echosounders, methane probes, automated diffusive flux chambers and funnels, oxygen- and carbon dioxide-optodes, CTD, and thermistors), will be combined with intensive water sampling and water sample analysis (dissolved methane, methane isotopic composition, composition of the microbial community, and other water constituents) to meet the requirements of sufficient temporal resolution and reliable absolute data on all abiotic parameters and in specific on the dissolved methane concentration.