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Total Oxygen Uptake and Bioirrigation Activity in Coastal Sediments

University of Bordeaux (France)

Involved scientists: B. Deflandre & O. Maire

Robust oxygen optodes (OXROB10) connected to a FireStingO2 oxygen meter (FSO2-4, 4 oxygen channels) were used to measure the sediment oxygen uptake in four undisturbed sediment cores from Aquitaine coastal sediments. Depending on study sites location, sediment cores were collected with a multiple-corer or by scuba divers and then kept at in situ conditions in a thermo-regulated incubator on shipboard, or in a thermo-regulated room at the Marine Station of Arcachon (France). Once calibrated, each oxygen optode was cautiously inserted through a cap (Fig.1) used to hermetically close the sediment cores at the beginning of the incubations. This procedure allows for continuous measurement of the oxygen concentration in the overlying water of sediment enclosures. The oxygen (OXROB10) and temperature (TSUB21) sensors were connected via the FireStingO2 oxygen meter to a laptop (Fig.2). Examples of temporal changes in dissolved O2 concentrations are shown in Figure 3 for the four core incubations. Taking into account both the sediment surface and the volume of the overlying water, the slope of the O2 evolution was used to calculate the sediment oxygen uptake.

The fast response time of the sensors and its versatility facilitates continuous assessment of short-time changes in O2 concentration. It also represents a very interesting tool to investigate the influence of bioirrigation activity of infauna in the ecological and biogeochemical functioning of coastal ecosystems. For instance, simultaneous measurements of O2 dynamic and bio-irrigation processes (using a fluorescent dissolved tracer) are currently developed by our team within the EPOC laboratory (University of Bordeaux) to investigate the role of the Thalassinid shrimp Upogebia pusilla in remineralization processes of sediment organic matter. Variation of O2 concentration linked to burrow ventilation by the shrimp is shown in Figure 4.

For further information, please contact Bruno Deflandre: b.deflandreepoc.u-bordeaux1.fr

Fig. 1: The sediment cores in a thermo-regulated incubator with inserted oxygen sensors.

Fig. 2: Complete setup with the oxygen meter FireStingO2 and Laptop on top of the incubator.

Fig. 3: Temporal changes of O2 in closed sediment cores without the Thalassinid shrimp Upogebia pusilla.

Fig. 4: Temporal changes of O2 concentration in a closed sediment core with a Thalassinid shrimp Upogebia pusilla.