On the distribution of blue}green algae in lakes: wind-tunnel tank experiments

In this study, we demonstrate in the laboratory that the distribution of weakly floating algae in wind-driven, steady state, two-dimensional flow in a water body is in accord with theoretical predictions. We confirm the theoretical results that the concentrations of algal colonies of uniform flotation speed should increase exponentially in the downwind direction and that the length scale of this concentration variation should be inversely proportional to the colony flotation speed. We observed accumulation of a surface film at the downwind shore of our tank. This film dampens surface waves, inhibits surface mixing, modifies the nearshore water circulation, traps the algae, and allows the algae to accumulate into mats. In a recent paper, Webster (1990) presented a theory to explain how wind-induced flows and turbulence combine to determine the hor-izontal and vertical distributions of a weakly floating (or weakly sinking) phytoplankton population in a lake. He assumed that the dis-tribution of phytoplankton under steady stat