LIGHT ADAPTATION OF OSCILLATORIA-AGARDHII AT DIFFERENT TIME SCALES

The Markermeer is a eutrophic shallow wind exposed lake. In contrast t o other eutrophic lakes in the area persistent blooms of the cyanobact erium Oscillatoria agardhii do not occur. The severe variations in the available light energy, caused by an excessive resuspension of sedime nt, are held responsible for this absence. Field experiments were cond ucted in the Markermeer, to investigate the relations between O. agard hii and the specific Light climate in the Markermeer, emphasizing the adaptation rate and extent to light energy level variations. In experi ments with traditional light and dark bottles, and bottles moving up a nd down the water column it was observed that vertical mixing tended t o increase the net production of oxygen, as the exposure time near the water surface is too short to cause light inhibition. From experiment s with a vertical perspex tube it was concluded that during days with maximum hourly light energy levels above 200 mu E . m(-2). s(-1), the light utilization efficiency was much higher in the morning hours than during the afternoon. This phenomenon did usually not occur at days w ith lower mean irradiance levels. After prolonged periods of low energ y levels (below 50 mu E . m(-2). s(-1)), the light utilization efficie ncy increases significantly but the maximum production level does not increase.