MODELING PHYTOPLANKTON PATCHINESS UNDER THE INFLUENCE OF WIND-DRIVEN CURRENTS IN LAKES

A model has been developed that describes phytoplankton patchiness under the influence of wind-induced circulation in lakes. It is shown that especially in large lakes the adjustment of the horizontal phytoplankton distribution to a change in windspeed (in the lower windspeed region) can take several weeks, but the vertical patchiness response is much faster, usually within 1 d. In the model presented here, the phytoplankton cells are allowed to disperse in the horizontal direction by introducing a dispersion coefficient in the wind direction that takes into account some of the effects of mixing by large-scale currents in the horizontal plane. The model shows that horizontal and vertical patchiness increases with the flotation velocity of the phytoplankton, decreases with windspeed, and decreases with the strength of the horizontal wind-induced circulation currents compared to the circulation strength in the vertical plane. Model results are in agreement with observations reported in the literature. With the help of the model results, simulations of surface chlorophyll patterns in lakes can give important information about the general pattern of horizontal wind-driven circulation.