High temporal resolution oxygen imaging in bioirrigated sediments

A technique is presented for temporal characterization of the bioirrigation activity of benthic macrofauna and for quantitative estimation of its effects on the oxygen exchange between the sediment and the overlying water. The technique is based on high temporal resolution (15-30 s) oxygen imaging aided by a planar oxygen optode and can be applied under laboratory and field conditions, both freshwater and marine. It allows direct observation of the complex 2D oxygen dynamics in the sediment around the burrow while the animal dwells undisturbed in its natural environment. The conditions to which the animal is exposed can easily be controlled or manipulated. Chironomus plumosus, widely distributed freshwater insect larvae, were used in a case study. Their bioirrigation activity was divided into a random succession of pumping intervals (duration 5.4 ± 1.7 min) and rest periods (duration 9.2 ± 5.8 min). The burrow ventilation resulted in a highly variable volume of the oxygenated sediment surrounding the burrow and the associated sedimentary oxygen uptake rate through the burrow wall (OUB), both changing dramatically within minutes. Their variability was higher in a burrow under construction than around a stationary burrow. The average OUB rate (∼0.15 μmol O₂ h^-1), when translated into a time-averaged O₂ flux across the burrow wall, constituted approximately 64% of the stationary diffusive oxygen flux measured at the sediment-water interface (∼0.9 mmol O ₂ m^-2 h^-1).