The quest for sustainable fisheries has been accompanied by a rapid expansion
of the aquaculture industry worldwide. In order to investigate the effects of
commercial mussel beds on the surrounding environment it is necessary to understand the coupling of the benthic mussels to the overlying water column. Vertical transport of plankton, nutrients and oxygen to benthic mussels is usually dominated by turbulent processes. This thesis investigates vertical mixing at 2 field sites which were used in the European Union framework 5 project MaBenE (Management of Benthic Ecosystems in relation to physical forcing and environmental constraints).
The first site is the Limfjorden in Denmark, where vertical mixing is driven by
meteorological forcing. Because the turbulence levels were generally too low for the ADCP techniques to provide meaningful turbulence data, a water column potential energy model is developed. The model incorporates surface heat exchange, wind mixing and wave mixing. It is found that the significant wave height is the most appropriate parameter to represent the meteorological forcing of turbulence.
The second site is the Oosterschelde in The Netherlands. The strong tides in
this embayment produce relatively high levels of turbulence, which can be detected using the ADCP techniques. Analysis of the turbulence generated over a mussel bed and a sand site allow the comparison of bottom drag coefficients which were 0.0032 over mussels and 0.0026 over sand.
An overview of turbulence in the bottom boundary layer is presented, along
with a description of the ADCP techniques employed and developed during these
studies. A description of the field sites is followed by results from the observational campaigns. The thesis finishes with a discussion of the results, comparing the two different study sites and the differences in turbulence over mussel beds and sand.