Methane in the Columbia River Plume

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Near shore and continental shelf areas are significantly more supersaturated with CH4 than are the open oceans, yet global CH4 budgets ignore this fact because of the paucity of data. Investigations of the near shore regions of Washington and Oregon, particularly those areas influenced by the Columbia River plume and evaluations of the impact of this plume on the rate of CH4 evasion to the atmosphere will help to construct accurate CH4 budgets. The lower Columbia River is, on average, supersaturaterd with methane by a factor of 120. There is also an active population of methane oxidizing bacteria within the river with an average consumption rate of 20 nM methane per day. Preliminary evidence indicates that within the estuary, as the salinity increases above about 5 parts per thousand, this microbial activity ceases. This study will determine whether a marine population of methane oxidizing organisms becomes established as the Columbia River plume moves downstream and consumes the residual methane or if the riverine supply of methane is completely evaded to the atmosphere. Ths study is relevant to all river systems and is of significance to current attempts to develop a methane budget for the oceans.