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，但它对地球气候的影响仍然很差？S，部分原因是全球甲烷进入大气的通量存在不确定性。大气甲烷的一个重要来源是富含有机物质的沉积物中产生的甲烷，这些沉积物位于地表水体之下，包括湖泊、湿地和海洋。从沉积物中释放的甲烷绕过水柱中的溶解并到达大气中的比例可能对全球变暖起到重要作用，而这一比例关键取决于从底层沉积物中释放的自由气体的模式和时空特征。要想更好地理解甲烷沸腾，需要更好地模拟沉积物中的水文过程，更好地了解控制天然气生产和聚集、气泡生长、管道演化和持续时间、喷口间距、沸腾速率以及喷口事件的偶然性、频率和持续时间的参数和驱动力。该项目的目标是开发甲烷从细粒沉积物中产生、迁移和释放的定量模型。数学和计算模型将受到综合野外和实验室实验的约束和检验，这些实验将表征甲烷排放的速率、持续时间和频率、甲烷在水柱中的气泡上升和溶解、沉积物中气体排放管道的形态和间距、浅层沉积物中气体相对于其可能的生产地点的分布，以及甲烷在沉积物中的生产代谢途径和速率。为数值模型提供依据的现场数据将从马萨诸塞州波士顿附近的上神秘湖中央盆地的细粒沉积物中已知的甲烷喷发区域获得。甲烷是一种重要的温室气体，名义上是二氧化碳的20倍。目前，科学界正在集中力量更好地限制甲烷通量，并提高我们对甲烷来源与气候变化之间反馈关系的理解。在许多环境中，甲烷不是直接释放到大气中，而是从底层沉积物中释放到水体中，在那里甲烷是由生物活动产生的，或者是从更深层次的热源输送来的。控制甲烷从沉积物中排出的机制还不是很清楚。在这个项目中，我们试图推进当前对甲烷从细粒沉积物中迁移和释放的理解。如果成功，我们的发现将为综合建模奠定基础，以限制全球从湖泊、湿地、河口和浅海大陆边缘释放甲烷。

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.