EFFECT OF WIND ON THE DISTRIBUTION OF PHYTOPLANKTON CELLS IN LAKES REVISITED

Experimental evidence suggests that winds having speeds >2-3 m s-1 are required to mix floating phytoplankton cells (or colonies) away from the water surface. We consider theoretical, steady state distributions of phytoplankton in a lake caused by turbulence and circulation patterns induced by winds having speeds above this critical level. The model incorporates an eddy diffusivity which varies with position in the water column. It predicts concentration variations in the downwind direction which are more in accord with experiment than a previously presented model having an eddy diffusivity uniform in the vertical. If the windspeed is less than the critical value, then a floating phytoplankton scum is expected to remain on the surface. The horizontal distribution of a phytoplankton population will be very different depending on whether the windspeed is greater or less than the critical speed.