Oxygen uptake kinetics in the benthic boundary layer

Abstract

A simple, one‐dimensional, transport‐reaction model of oxygen uptake by sediments during incubation experiments assumes zero‐order reaction kinetics for oxygen removal in the pore water of sediments and takes the apparent diffusive limitation posed by the benthic boundary layer into account. Model calculations are in excellent agreement with experimental data obtained during in situ benthic flux chamber experiments in Gullmarsfjorden, Sweden, during fall (water temp, 10°C) and winter (−1°C). The boundary layer “resistance,” represented by a mean diffusive sublayer thickness, was estimated with a series of radioactive tracers. The oxygen uptake curve was initially approximately linear but became exponential below ~100 µM oxygen. The half‐removal time of oxygen below 100 µM corresponds to a boundary layer resistance similar to that obtained with the radiotracers. The nearly constant rate of decrease of oxygen during the initial phase of the incubations suggests that incubation techniques can be used to obtain an approximate measure of the oxygen uptake rate of sediments as long as the concentration remains above the transition where the curve changes from approximately linear to exponential. This procedure, however, underestimates the oxygen uptake rate by 28–34% compared to model results. Model calculations also suggest that oxygen uptake rates can differ substantially between chamber and outside sediments, especially when hydrodynamic conditions influencing the apparent boundary layer resistance are different within and outside chambers.