shellfish hydrodynamics

Observations are used to consider the influences of turbulent flow through a suspended shellfish canopy in the microtidal Danish Limfjorden.  The influence is two-way in that the turbulence is affected by the farm and the farm is affected by the turbulence.  Observations include current meter/profiler moorings and turbulence microstructure profiling.  The canopy reduces the flow speeds within the canopy interior and that this slow-down is sufficient to reduce levels of turbulent kinetic energy.  Rates of turbulent kinetic energy dissipation e were between 10-8 and 5x10-6 m2s-3.  It was difficult to link the farm effect to changes in stratification.  This was partly due a high degree of natural variability and also that the farm doesn’t actually do that much mixing relative to background variability.   Vertical diffusivities enable estimates of the role of mixing on depletion and suggest that in the present situation it is secondary in term of contribution but that it could dominate in certains situations.  The work suggests several avenues for enhanced sustainable shellfish production.  Canopy flushing can be enhanced with suitable arrangement of crop within a farmed area but that vertical flux estimates suggest it can not be explained entirely through one dimensional arguments.  Stratification persists within the farm and so exposure to nutrient-deplete water can be minimized through staggered crop heights.  However, in order to benefit from this knowledge it requires improved understanding of long term variability in the background environment.

The project is called Mumihus.