Effect of wind on the distribution of phytoplankton cells

Experimental evidence suggests that winds having speeds>2-3 m s-l 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 expcrimcnt than a previously presented model having an eddy diffusivity uniform in the vertical. If the windspccd 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. Webster (1990) presented a theory which shows how the circulation and mixing induced by a steady wind blowing above a lake should lead to horizontal heterogeneity in the distri-bution of a nonneutrally buoyant phytoplank-ton population in the lake. The theory predicts that a buoyant population should be more strongly concentrated toward the downwind end of the lake. This prediction is in accord with the measured distributions of blue-green