Collaborative Research: Characterization and mechanistic modeling of methane production, flow and ebullition from fine-grained sediments in a temperate lake

甲烷是一种强有力的温室气体，但它对地球的影响？中国的气候仍然没有受到很好的约束，部分原因是全球甲烷排放到大气中的不确定性。大气甲烷的一个重要来源是在地表水体（包括湖泊、湿地和海洋）下富含有机物的沉积物中产生的甲烷。从沉积物中释放的甲烷绕过溶解在水柱中，并到达大气中的部分可能会显着地促进全球变暖，这部分关键取决于模式和时空特征的自由气体从底层沉积物排放。了解甲烷沸腾的进展，需要更好的机制模型的沉积物中的水文过程，更好地了解控制气体生产和积累，气泡生长，导管的演变和持久性，排气孔间距，沸腾率，和发作，频率和持续时间的排气事件的参数和驱动力。该项目的目标是建立细粒沉积物中甲烷产生、迁移和释放的定量模型。数学和计算模型将受到全面的实地和实验室实验的约束和检验，这些实验将描述甲烷排放的速率、持续时间和频率，气泡上升和甲烷在水柱中的溶解，沉积物中气体排放管道的形态和间距，气体在浅层沉积物中相对于其可能的生产地点的分布，以及沉积物中甲烷生成代谢途径和速率。为数值模型提供信息的实地数据将从马萨诸塞州波士顿附近的上神秘湖中心盆地的细粒沉积物中已知甲烷排放的区域获得。甲烷是一种重要的温室气体，名义上比二氧化碳强20倍。目前，科学界正在集中精力更好地限制甲烷通量，并提高我们对甲烷来源和气候变化之间反馈的理解。在许多情况下，甲烷不是直接释放到大气中，而是从底层沉积物释放到水体中，其中甲烷是由生物活动产生的，或者是从更深的生热源输送而来。控制沉积物甲烷排放的机制还不清楚。在这个项目中，我们寻求推进目前的理解甲烷运输和释放细粒沉积物。如果成功，我们的研究结果将为综合建模奠定基础，以限制全球湖泊，湿地，河口和浅大陆边缘的甲烷释放。

Methane is a potent greenhouse gas, but its effects on Earth?s climate remain poorly constrained, in part due to uncertainties in global methane fluxes to the atmosphere. An important source of atmospheric methane is the methane generated in organic-rich sediments underlying surface water bodies, including lakes, wetlands, and the ocean. The fraction of the methane released from the sediments that bypasses dissolution in the water column and reaches the atmosphere may contribute significantly to global warming, and this fraction depends critically on the mode and spatiotemporal characteristics of free-gas venting from the underlying sediments. Advances in understanding methane ebullition require better mechanistic models of the hydrologic processes in the sediments, better understanding of the parameters and driving forces controlling gas production and accumulation, bubble growth, conduit evolution and persistence, vent spacing, ebullition rates, and the episodicity, frequency, and duration of venting events. The goal of this project is to develop quantitative models of methane production, migration and release of methane from fine-grained sediments. The mathematical and computational models will be constrained by and tested against comprehensive field and laboratory experiments that will characterize the rate, duration, and frequency of methane venting, bubble rise and dissolution of methane in the water column, the morphology and spacing of gas vent conduits in sediments, the distribution of gas in shallow sediments relative to its likely locus of production, and methane production metabolic pathways and rates in the sediments. Field data to inform the numerical models will be acquired from an area of known methane venting from fine-grained sediments in the central basin of Upper Mystic Lake, a dimictic kettle lake near Boston, Massachusetts.Methane is an important greenhouse gas, nominally 20 times more potent than carbon dioxide. There is currently a focused effort from the scientific community to better constrain methane fluxes and improve our understanding of the feedbacks between methane sources and climate change. In many settings, methane is released not directly to the atmosphere, but to bodies of water from underlying sediments where the methane is generated by biological activity, or transported from deeper sources of thermogenic origin. The mechanisms controlling methane venting from sediments are not well understood. In this project, we seek to advance current understanding of methane transport and release from fine-grained sediments. If successful, our findings will lay the groundwork for integrated modeling to constrain the global methane release from lakes, wetlands, estuaries and shallow continental margins.