Waterfalls enhance regional methane emissions by enabling dissolved methane to bypass microbial oxidation

River waters are significant sources of atmospheric methane whose local emissions increase with river slope and turbulence. However, when integrated regionally, the amount of dissolved methane released to the atmosphere is uninfluenced by local changes in turbulence when no additional loss mechanisms are present. Here we tested the hypothesis that waterfalls enhance both local and regional atmospheric methane emissions if microbial methane oxidation is significant in river waters. Rates of net atmospheric emission and net aerobic methane oxidation were measured in river waters containing waterfalls across western New York revealing that methane oxidation can diminish atmospheric emissions when turbulence is less. However, at waterfalls, 88 ± 1% of the dissolved methane supersaturation was released to the atmosphere, increasing net methane emission rates substantially beyond oxidation (0.1–16.2 × 106 nM d-1 for waterfall emission; 10–39 nM d-1 for oxidation), and ultimately enhancing regional methane emissions by enabling dissolved methane to bypass an oxidative sink. Waterfalls can substantially increase methane emissions from rivers with high microbial oxidation rates, because turbulence allows methane to bypass oxidation, according to in-situ measurements and water sampling of rivers in New York State