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Rapid redistribution of oxygen in a sandy sediment induced by changes in the flow velocity of the overlying water
Booij, K.; Helder, W.; Sundby, B. (1991). Rapid redistribution of oxygen in a sandy sediment induced by changes in the flow velocity of the overlying water. Neth. J. Sea Res. 28(3): 149-165
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579, more
Peer reviewed article  

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  • Booij, K.
  • Helder, W.
  • Sundby, B.

    The response of the oxygen distribution in a sandy sediment to changes in the flow velocity of the overlying water was studied in a cylindrical benthic chamber with a homogeneous friction velocity field at the sediment-water interface. The oxygen penetration depth in the sediment increased more than threefold when the friction velocity was increased from 0 to 0.95 cm·s-1, corresponding to a free-flow velocity increase of 0 to 15 cm·s-1. The oxygen flux to the sediment also increased. The oxygen profiles in the sediment responded within seconds to minutes to a change in the friction velocity. Two possible mechanisms of oxygen transport were identified and modelled. First, it was assumed that the steady-state flux is controlled by a diffusion-like process, with a diffusion coefficient that increases with increasing friction velocity. Zero-order reaction kinetics was also assumed. Transient states were modelled by assuming that the diffusion in the pore water would respond instantaneously to the change in friction velocity. Most model estimates of the diffusion coefficient were between 2.10-9 and 2.10-8 m²·s -1. However, estimates of the diffusion coefficient at various depths showed a pronounced maximum at 2 mm, which indicates that the diffusion model is not valid. The second mechanism of oxygen transport was identified by evaluating the radial pressure gradient existing in the chamber. This pressure gradient, which is created by the rotating flow, may advect water vertically into the sediment. An order-of-magnitude calculation indicates that this advection may account for 10 to 80% of the measured fluxes, depending on the magnitude of the friction velocity. This phenomenon arises when solute fluxes between coarse-grained sediments and water are studied in benthic chambers with a rotating water column. Caution is necessary when interpreting results obtained with such devices.

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