Oxygen Distribution Heterogeneity Related to Bioturbation Quantified by Planar Optode Imaging

Abstract

Oxygen plays a key role in benthic microbial ecology. Until recently, oxygen concentration in sediments was measured with oxygen microsensors along a vertical profile (one dimension) from the surface until a few centimeters into the sediment. With this approach, however, it is a tedious job to describe or overcome the heterogeneity of oxygen distribution in environments such as bioturbated environments. Recently, a new technique has been introduced that allows the investigation of two-dimensional oxygen distribution and dynamics at a high resolution in the upper sediment column. This non-destructive technique takes advantage of an oxygen-quenchable fluorophore, which is cast into a thin sheet, the planar optode. The latter may be introduced in sediments and is used in situ or in laboratory experimentation, coupled with an optical system allowing the oxygen quantification. Oxygen optodes were used in experimentation dedicated to the study of oxygen heterogeneity induced by macrofaunal bioturbation. Oxygen images of sediments inhabited by a biodiffusor, the gastropod Cyclope neritea, and two gallery diffusors, the annelids Nereis virens and Nereis diversicolor, were used to compare the impact of these organisms on oxygen distribution in sediments. Diffusive oxygen flux and a heterogeneity index were quantified based on oxygen images. Results showed that all species increased oxygen distribution heterogeneity, and that this heterogeneity increased with increasing total diffusive fluxes.