Abstract
The concentrations of methane (CH4) were measured in several Pacific Northwest rivers and flux rates of CH4 to the atmosphere were estimated. These rivers were supersaturated almost everywhere, with typical CH4 concentrations in the surface waters between 10 and 500 nM. Even though stream variability was very high, CH4 concentrations tended to increase significantly in deeper, slower moving sections of the rivers. In more turbulent sections of the rivers, the accumulated CH4 was rapidly evaded to the atmosphere resulting in high flux rates. Fluxes were estimated with two models (eddy cell and large eddy) and by direct measurement of CH4 loss within specific river reaches. The flux rates encountered during this study ranged from 0 to 317 mg CH4 m−2 d−1. Microbial CH4 oxidation accounted for about 25% of the total CH4 lost from the Columbia River but was insignificant in the more turbulent Wenatchee River.