THE RADIATIVELY DRIVEN NATURAL-CONVECTION BENEATH A FLOATING PLANT LAYER

If part of a water body is shaded while an adjacent part is warmed by direct sunlight, contrasting thermal gradients develop. This different ial heating generates a surface flow from the illuminated into the sha ded portion of the water body. One example of this situation is macrop hytes floating on the surface of a small lake. The macrophytes shade t he underlying water, and if there is open water adjacent to this shade d region, then differential heating may be expected. We show that the presence of the roots of small floating plants displaces the intrusion downward but does not prevent its formation. Further, we show that re lations describing the differential absorption mechanism in the absenc e of macrophyte roots remain valid with roots present. Using these rel ationships, we calculate that an intrusion generated by differential h eating may contribute significantly to replacement of nutrients taken up by the macrophytes.