Oxygen Ebullition From Lakes

The exchange of oxygen between lakes and the atmosphere is assumed to be driven by diffusion. Here we show that lakes can emit significant amounts of O 2 by emerging gas bubbles—a process called ebullition. We found very high proportions of 17 ± 10% O 2 (maximum 34%) in emerging gas bubbles in two shallow eutrophic reservoirs. In the studied reservoirs, O 2 emission by ebullition was of similar magnitude as diffusive O 2 fluxes. By reanalyzing previous studies, we show that the process is ubiquitous and probably quantitatively relevant in many places. We present evidence that O 2 in bubbles originates both from photosynthetic oxygen production and hence bubble formation in the oxic water and from stripping by emerging methane bubbles. Ebullition can turn lakes undersaturated in respect to the atmosphere into a net O 2 source. Neglecting O 2 ebullition leads to an overestimation of lake internal respiration.