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V. Alexander et al. 



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FIGURE 5-10. Productivity and biomass of the 

 epipelic algae in Pond J, 1971, productivity in ponds 

 B, C and E, 1972, and Pond A, 1973. 



Productivity 



Several summer-long epipelic productivity studies were carried out in 

 the ponds between 1971 and 1973 with weekly sampling beginning as soon 

 as the ice disappeared in late June and continuing into late August. A 

 modified carbon- 14 technique was used for these measurements. Details 

 are given in Stanley (1976a). Four randomly chosen cores were taken from 

 the sediments and the top centimeter of each core was mixed into a 

 combined sample. Four subsamples were then settled onto the bottom of 

 400-ml chambers made by gluing together the bottoms of acrylic Petri 

 dishes. The amount of sediment in each chamber was less than 1.0 g dry 

 weight to avoid CO2 depletion. We found that up to 0.5 g of sediment 

 could be used without a decline in the rate of photosynthesis per gram of 

 sediment due to shading. Isotope was injected through a serum stopper 

 and the chamber incubated in the pond (2 to 4 hours). After filtration of 

 the algae and sediment at the end of the experiment, the samples were 

 combusted by wet oxidation and the liberated CO 2 trapped and counted in 

 a liquid scintillation cocktail. 



