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Marine Ecology Progress Series

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MEPS 119:237-241 (1995)  -  doi:10.3354/meps119237

Impact of microsensor-caused changes in diffusive boundary layer thickness on O2 profiles and photosynthetic rates in benthic communities of microorganisms

Lorenzen, J., Glud, R. N., Revsbech, N. P.

Although O2 microsensors used for study of benthic photosynthesis have tip diameters of less than 10 um and stem diameters of about 150 um at a distance of 0.5 cm from the tip, they do change the local flow pattern in the overlying water and thereby reduce the thickness of the diffusive boundary layer (DBL). The reduced DBL resulted in a lower diffusional resistance towards export of O2 from communities with a net production of O2, and insertion of a microsensor in such a community therefore resulted in lowered O2 concentrations. The total diffusion flux out of the photosynthetic layer was not significantly affected by the presence of the microsensor. The higher upward flux into the water phase was counterbalanced by a reduced downward flux into the sediment. The O2 profiles and diffusion fluxes were only affected when the surface was smooth, while the effect of microsensor insertion was undetectable when the surface was made irregular by small tufts, bubbles, etc. In the investigated cyanobacteria-dominated mats, the gross photosynthetic rates as measured by the light/dark shift technique were unaffected by the presence of a microsensor.

Microelectrodes . Oxygen . Diffusive boundary layer . Benthic photosynthesis

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