Grid-generated turbulence in a mesocosm experiment

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 (epsilon) 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 1.9x10(-7) W kg(-1) and 5.5x10(-8) W kg(-1) in the 'high' and 'low' enclosures, respectively. Finding 'background' turbulence levels between 5.3x10(-9) and 3x10(-8) W kg(-1), we suggest that future experiments consider turbulent measurements as a standard variable.