A method to improve the spatial resolution of photosynthetic rates obtained by oxygen microsensors

To determine gross photosynthesis in benthic microalgal communities, oxygen microelectrodes were used to measure the rate of decrease within the first 4 s after extinction of light. Photosynthetic rates calculated from third-order polynomial fits to the curve of decreasing O-2 concentration were compared to the rates obtained by the traditional method, where rates were estimated from linear regression. When photosynthesis was calculated for the fitted initial rates of O-2 decrease, maximum rates in microbial mats were up to 32% higher, and the depth-integrated gross photosynthesis was 5%-10% higher than the rates determined by the traditional method. The determinations from fitted initial rates also resulted in a more detailed profile of phytosynthetic rate than that normally obtained. Computer simulation based on diffusion models, where the estimated initial rates of O-2 decrease were assumed to represent actual photosynthesis rates, verified the validity of the curve-fitting procedure for obtaining high-resolution photosynthesis profiles.