Effects on the benthic diffusive boundary layer imposed by microelectrodes

Oxygen microgradients and fluxes were studied in a 0.3–0.6‐mm‐thick diffusive boundary layer (DBL) of aquatic sediments by the use of O 2 microelectrodes with sensing tips of 5 µ m. One microelectrode was introduced vertically from above while another was introduced along the same vertical axis from below, thus penetrating up through the sediment. Microelectrodes introduced from below did not alter the DBL, but those introduced from above reduced its thickness by 25–45%. The effect was detected even when the microsensor tip was situated >1 mm above the sediment surface. The reduction of the DBL resulted in steepening the O 2 gradient. In typical coastal sediments, the microelectrode thereby increased the diffusive O 2 flux by 8%; in a highly sulfidic sediment the increase was 59%.