Pulse emission of H₂ from the source at 30-m depth. A. Snapshots of an H₂ gas pulse propagation in time. B. [H₂%] distribution along a vertical line passing through the source point (see white line on the t = 0 snapshot of Fig. 4A). Note that the [H₂] measured at a given depth will strongly vary over the pulse propagation cycle. C. [H₂] distribution at 80-cm depth as a function of time. Reference case: no active bacteria, K = 10 Da, surplus in gas pressure at source is 2 bar, Depth of source = 30 m.