Grid-generated
turbulence in a mesocosm experiment
S. Nerheim, J.E. Stiansen, H. Svendsen-2002
Hydrobiologia, 484(1-3): 61-73
Abstract:
In two mesocosm experiments designed to study the
effect of nutrients and turbulence on trophic levels below fish larvae in
the ecosystem, turbulence was created by oscillating grids. Utilizing two
different frequencies, two levels of turbulence (`high' and `low') were
generated in a total of eight mesocosms in both experiments. In each
mesocosm a two-layer density structure was created. We succeeded in
generating turbulence that mimics turbulence found in natural ecosystems,
with turbulent eddies on larger scales than those relevant for organism
interactions. Energy dissipation rates (ε)
were calculated from the frequency spectrums of the measured turbulent
velocities. In the second experiment the average energy dissipation rates in
the upper layer were 1.9×10-7 W
kg-1 and 5.5×10-8 W kg-1
in the `high' and `low' enclosures, respectively. Finding `background'
turbulence levels between 5.3×10-9
and 3×10 -8 W kg-1, we
suggest that future experiments consider turbulent measurements as a
standard variable.
(Department of Oceanography, Göteborg
University, Box 460, SE 405 30 Göteborg,
Sweden, e-mail of S. Nerheim: sine@oce.gu.se ,
e-mail of J.E. Stiansen: jan.erik.stiansen@imr.no ,
e-mail of H. Svendsen: harald.svendsen@gfi.uib.no)