Oxygenation of intertidal estuarine sediments by benthic microalgal photosynthesis

A mathematical model was used to define the relative importance of microalgal photosynthesis and physical processes in the formation and maintenance of the oxygenated zone on the surface of intertidal estuarine sediments. Manometric measurements of sediment uptake and release showed that gross oxygen production usually exceeded aerobic community respiration. Polarometric microprobes measured vertical oxygen distributions in the sediment. Surface levels of oxygen ranged from 200% saturation in summer to 70% in winter. Profiles and flux measurements allowed calculation of sediment diffusion coefficients. Empirical evaluation of the terms of the model showed that epipelic diatom photosynthesis as a source of oxygen at low tide may exceed atmospheric diffusion by an order of magnitude. On a diurnal and seasonal basis, however, the diatoms may be less important to the oxygenation process than the physical forces of the tide.