Estimation of a characteristic friction velocity in stirred benthic chambers

Abstract

The ecology of water bodies can be greatly affected by the flux of solutes across the sediment-water interface. This solute flux is frequently measured using either benthic chambers in the field or incubated sediment cores, where in both cases the sediment is removed from the influence of the natural hydrodynamics. To compensate, the overlying water is usually stirred in some manner, e.g. with a rotating impeller, in an attempt to reproduce the natural field conditions. The hydrodynamics affect the diffusive-boundary-layer thickness, which can be one of the major controls on solute flux magnitude. Thus, a quantitative understanding of the effects of chamber stirring is vital. In this paper a characteristic friction velocity is presented as a function of a given stirrer configuration and stirring rate. The developed scaling relationship correlates well (R2 ≈ 0.9) with previously reported friction velocities in benthic chambers, over a range of chamber configurations and sizes. It is now possible, using this equation for characteristic friction velocities, to ensure that benthic chambers experience similar turbulence intensities to natural environments, without elaborate turbulence measurements.