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.
