EFFECTS ON THE BENTHIC DIFFUSIVE BOUNDARY-LAYER IMPOSED BY MICROELECTRODES

Oxygen microgradients and fluxes were studied in a 0.3-0.6-mm-thick di ffusive boundary layer (DBL) of aquatic sediments by the use of O2 mic roelectrodes with sensing tips of 5 mum. One microelectrode was introd uced vertically from above while another was introduced along the same vertical axis from below, thus penetrating up through the sediment. M icroelectrodes 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 s ediment surface. The reduction of the DBL resulted in steepening the O 2 gradient. In typical coastal sediments, the microelectrode thereby i ncreased the diffusive O2 flux by 8%; in a highly sulfidic sediment th e increase was 59%.