Sediments

The dynamics of methane transport in lake sediments control the release of methane into the water column above, and the portion that reaches the atmosphere may con-tribute significantly to the greenhouse effect. The observed dynamics are poorly understood. In particular, variations in the hydrostatic load on the sediments, from both water level and barometric pressure, appear to trigger free gas bubbling (ebulli-tion). We develop a model of methane bubble flow through the sediments, forced by changes in hydrostatic load. The mechanistic, numerical model is tuned to and com-pared against ebullition data from Upper Mystic Lake, MA, and the predictions match the daily temporal character of the observed gas releases. We conclude that the com-bination of plastic gas cavity deformation and flow through “breathing ” gas conduits explains methane venting from lake sediments. This research lays the groundwork for integrated modeling of methane transport in the sediment and water column t