The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns: the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment-water interface.

No abstract

International audienceThe heterogeneity of oxygen distribution in a Hediste diversicolor burrow environment was investigated in a laboratory experiment using a 6-mm thick tank equipped with oxygen planar optodes. The twodimensional oxygen distribution in a complete burrow was monitored every 2 min for 4 h. Oxygen concentrations fluctuated over a scale of minutes in the burrow lumen and wall (up to 2 mm) reflecting the balance between worm ventilation activity and oxygen consumption. The magnitude of the three surrounding micro-horizons (oxic, oscillating and anoxic) induced by the intermittent worm ventilation was spatially and temporally variable within the structure. Oxygen variations appeared to be controlled by distance from the sediment–water interface and the direction of water circulation. Moreover, there was an apparent ‘buffer effect’, induced by the proximity to the overlyingwater, which reduced the variations of lumen and wall oxygen in the upper part of the structure. These results highlight the heterogeneous distribution and dynamics of oxygen associated with H. diversicolor burrows and ventilation activity. They also highlight the necessity of integrating this complexity into the current burrow-base models in order to estimate the ecological importance of burrowing species in coastal ecosystems