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FIGURE 5-6. Planktonic primary productivity in Pond B 

 on 24 July 1972. 



also followed procedures of Rogers (1969) except that the slides were 

 soaked only 5 min in 20% glycerol. Finally, the preparations were mounted 

 in Farrant's medium (Meynell and Meynell 1965) and dried for several 

 days before viewing. Only tracks with at least four exposed grains were 

 counted. Tests with three species of flagellates in culture showed that no 

 significant amounts of '"C were lost by the preservation with Lugol's. 

 Also, there was a linear increase in tracks per cell as the exposure time of 

 the emulsion increased. The maximum exposure for the planktonic algae, 

 13 hours, gave about three tracks per Rhodomonas cell and about one 

 track per cell of Mallomonas. This is within the limits for the method 

 suggested by Knoechel and Kalff (1976a, 1976b). 



The track autoradiography (Figure 5-7) shows the strong dominance 

 of the 3 Mm flagellate group during the afternoon. Their biomass (Figure 5- 

 3) was also high at this time but the productivity of this group is obviously 

 higher per individual than that of the other groups. When the data are 

 expressed as production per unit of biomass (Figure 5-8), the Rhodomonas 

 and 6^lm. flagellates have a photosynthesis peak in the early afternoon, the 

 3Mm organisms peak in late afternoon, and the Chromulina peaks in the 

 early evening. This is one of the ways that the algae share the resources, 

 here the light, in the pond. 



Given the changing relationships between light, photosynthesis, and 

 algal biomass, it is difficult to translate from an hourly photosynthesis rate 

 measured in the morning to a value for an entire day. If indeed a 

 significant fraction of the algae are moving back and forth from the 

 benthic to the planktonic systems, then an individual alga cell in situ may 

 not be exposed to inhibiting light levels for as long a period as a cell held in 

 a sample bottle for 3 or more hours. The situation is similar to that of 

 algae in the epilimnion of a lake where m situ organisms are circulated 

 through a variety of light levels while algae in incubation bottles are held 

 at a constant (and often inhibiting) level of light. In both these situations, it 

 is difficult to estimate the true daily productivity either from a 3-, 1 2- or 24- 



