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Measuring the flux of oxygen to a muddy sediment with a cylindrical microcosm
Booij, K.; Sundby, B.; Helder, W. (1994). Measuring the flux of oxygen to a muddy sediment with a cylindrical microcosm. Neth. J. Sea Res. 32(1): 1-11
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, meer
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  • Booij, K.
  • Sundby, B.
  • Helder, W.
Abstract
    We have examined the effects of changing the flow velocity and the oxygen concentration in the water overlying a muddy sediment on the flux of oxygen across the sediment-water interface and on the distribution of oxygen within the pore water. The experiment was carried out on an intertidal sediment from the western Wadden Sea, using a cylindrical microcosm with a calibrated flow regime. Steady-state and transient-state models were used to estimate the values of the effective diffusion coefficient for oxygen in the pore water. Increasing the flow velocity caused a significant though small increase in the oxygen concentration in the pore water, but had little effect on the concentration gradient at the sediment-water interface. The concentration gradient in the boundary layer was too small at any of the flow velocities to account for the oxygen flux into the sediment via molecular diffusion. This is ascribed to a pressure gradient which exists in rotating flows, disrupting the diffusive boundary layer and augmenting the flux via advection. Model calculations indicate that about 25% of the flux can be attributed to irrigation by burrowing organisms, but in contrast to previous results with sandy sediments, irrigation of the pore water caused by the radial pressure gradient can be considered to be negligible. The effective diffusion coefficient ranged from 4·10-9m²·s-1 at a depth of 1 mm below the sediment-water interface to 1·10-9 m²·s-1 deeper in the sediment. These estimates are within a factor of 1 to 3 of the molecular diffusion coefficient for oxygen, which is surprisingly close in view of the high numerical densities of meiofauna and macrofauna in this sediment.
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