MEPS 140:217-226 (1996)  -  doi:10.3354/meps140217

A new tool ('planar optrodes') for measuring fine scale 2-dimensional O₂ distributions in benthic communities is presented and discussed. The sensor consists of an O₂-quenchable fluorophore cast onto a 25 x 55 mm, 175 µm thick transparent PVC sheet, which can be introduced into sediments and microbial mats. The O₂ sensitive fluorescence emitted by the planar optrode was measured with a high resolution CCD camera. A 3-point calibration was performed for each pixel in the acquired images to calculate the 2-dimensional oxygen distribution with high accuracy. Calibrated images covered an area of 13 x 17 mm and the set-up allowed the 2-dimensional distribution of O₂ to be resolved with a spatial resolution of 26 µm. The sensitivity of the sensor had excellent long-term stability. The planar optrode was used to record the oxygen equilibration between small gas bubbles and surrounding water with a temporal resolution of 20 s. The sensor was also used to measure the vertical and horizontal O₂ distribution in an intertidal sediment. The obtained distribution correlated well with O₂ concentration microprofiles measured with an O₂ microelectrode. The data showed pronounced differences in the O₂ penetration depths due to patchy distribution of highly labile organic carbon and showed differences in thickness of the diffusive boundary layer due to small topographic structures on the sediment surface. Potential applications of the planar optrode are presented and discussed.

O₂-microprofiles · Optrodes · Two-dimensional O₂ distribution · Sediments · Respiration