PLANAR OPTRODES - A NEW TOOL FOR FINE-SCALE MEASUREMENTS OF 2-DIMENSIONAL O-2 DISTRIBUTION IN BENTHIC COMMUNITIES

A new tool ('planar optrodes') for measuring fine scale 2-dimensional O-2 distributions in benthic communities is presented and discussed. T he sensor consists of an O-2-quenchable fluorophore cast onto a 25 x 5 5 mm, 175 mu m thick transparent PVC sheet, which can be introduced in to sediments and microbial mats. The O-2 sensitive fluorescence emitte d by the planar optrode was measured with a high resolution CCD camera . A 3-point calibration was performed for each pixel in the acquired i mages to calculate the 2-dimensional oxygen distribution with high acc uracy. Calibrated images covered an area of 13 x 17 mm and the set-up allowed the 2-dimensional distribution of O-2 to be resolved with a sp atial resolution of 26 mu m. The sensitivity of the sensor had excelle nt long-term stability. The planar optrode was used to record the oxyg en 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 O-2 distribution in an intertidal sediment. T he obtained distribution correlated well with O-2 concentration microp rofiles measured with an O-2 microelectrode. The data showed pronounce d differences in the O-2 penetration depths due to patchy distribution of highly labile organic carbon and showed differences in thickness o f the diffusive boundary layer due to small topographic structures on the sediment surface. Potential applications of the planar optrode are presented and discussed.