The effect of flow velocity on methane production and oxidation in aquatic sediments.

内陆水域是全球碳循环的重要组成部分。内陆水体温室气体甲烷(CH4)的排放因其对气候变化的影响而日益受到全球关注。最近的研究努力旨在改善对内陆水域甲烷排放的时空动态的基于过程的理解。尚未解决的研究问题包括：CH4排放动态的驱动因素是什么？它们如何受到全球变化和水系人为变化(如河流筑坝或水库建设)的影响？目前被认为影响水生沉积物甲烷产生、氧化和排放速率的许多因素都与流速直接或间接相关。然而，要素和潜在过程的流动依赖性并没有被明确考虑。在这个项目中，我们将使用新的实验介孔系统在一系列有针对性的实验室实验中研究这些过程的流动依赖性。该实验装置模拟了水生沉积物暴露在从快速(浅水)到静水(静水)生态系统的水力梯度中的环境条件。例如，作为筑坝的结果，这种转变发生在河流蓄水的纵向坡度上。这些实验的目的是将流速的影响从影响沉积物和沉积物-水界面总甲烷收支的过程中分离出来。结果将被落实到基于流程的模型中。除了相关的生物地球化学参数外，流速(近床面湍流)也将被考虑作为模型的显式边界条件。虽然该模型将使用从实验室实验获得的数据进行验证，但将使用系统分析方法分析流速影响不同类型水生生态系统甲烷排放的概念框架。

Inland waters are important components of the global carbon cycle. Emissions of the greenhouse gas methane (CH4) from inland water bodies are of growing global concern, because of their impact on climate change. Recent research efforts aim at improving the process-based understanding of the spatial and temporal dynamics of CH4 emissions from inland waters. Among the open research questions are: What are the driving factors of CH4 emission dynamics and how are they influenced by global change and anthropogenic alterations of aquatic systems, like river damming or reservoir construction? Many of the factors that are currently considered to affect the rates of methane production, oxidation and emission from aquatic sediments are directly or indirectly related to flow velocity. The flow-dependence of the factors and underlying processes, however, has not been considered explicitly. In this project we will use novel experimental mesocosm systems to study the flow-dependence of these processes in a series of targeted laboratory experiments. The experimental setup simulates the environmental conditions to which aquatic sediments are exposed in a hydraulic gradient from fast-flowing (lotic) to still water (lentic) ecosystems. Such transitions occur, for example, along longitudinal gradients in river impoundments as a consequence of damming. The experiments aim to detangle the effects of flow velocity from the processes that contribute to the overall methane budget in the sediment and the sediment-water interface. The results will be implemented into a process-based model. Besides relevant biogeochemical parameters, also flow velocity (near-bed turbulence) will be considered as an explicit boundary condition of the model. While the model will be validated using the data obtained from laboratory experiments, the conceptual framework by which flow velocity affects methane emissions from different types of aquatic ecosystems will be analyzed with a system-analytical approach.