SS3.15 Physical Forcing and Pelagic-Benthic Interactions in Aquatic Systems
Date: Thursday, June 13, 2002
Time: 4:45:00 PM
Location: Oak Bay
van DurenLA, NIOO-CEMO, Yerseke, Netherlands,
Hendriks, I, E, NIOO-CEMO, Yerseke, Netherlands,
Petersen, J, K, NERI, Roskilde, Denmark,
Larsen, J,  , NERI, Roskilde, Denmark,
van Sikkelerus, B, P, NIOO-CEMO, Yerseke, Netherlands, 
Herman, P, M, NIOO-CEMO, Yerseke, Netherlands,
Heip, C, H, NIOO-CEMO, Yerseke, Netherlands,
Combined flume and field experiments on boundary layer hydrodynamics over mussel beds
The effects of mussel beds on boundary layer hydrodynamics have been investigated in a large laboratory flume, using an Acoustic Doppler Velocimeter (ADV). Water samples were taken at different heights above the mussels to assess chlorophyll profiles above the mussels. Mussel beds have a distinct influence on the hydrodynamic regime due to the combined effects of increased roughness and the effect of the exhalent jets produced by the filtering activity of the mussels. The reduced Reynolds stress at low velocities leads to reduced exchange of particulate material over the mussels, and increased depletion of lower water layers over the mussel bed. In flume tanks, levels of turbulence are generally artificially reduced by turning vanes and laminizers, in order to produce a nicely predictable boundary layer. In the field, wave action and other sources of turbulence are not dampened and the situation is much less predictable. Very few field measurements of turbulence levels in the benthic boundary layer are available. We measured flow profiles in the boundary layer of a sheltered wind-driven estuary over mussels and over patches of bare sand, using an array of ADVs under both calm and windy conditions. Flow velocities, turbulence intensities, and Reynolds stress were compared to the flume experiments and the effect of wave action on these parameters was assessed. Subsequently the field and flume studies were compared to assess the relevance of flume experiments for ecosystem studies.