Primary Producers 207 



1.0 



0.8 h 



C\J 



'E 



o 



o- 0.6 



i 0.4 



Q. 

 u 



I 0.2 



c 

 o 



"1 1 r 



-1 1 1 1 



- 8.0 ~ 



20 



Jun 



_] I I I L 



10 20 



Jul 



I I I I 



10 20 



Aug 



10.0 



6.0 



C7> 



4.0 ^e 



2.0 .9- 

 a. 



FIGURE 5-18. Pf„ax of planktonic and epipelic algae in tun- 

 dra ponds at 8°C, 1973. (After Stanley 1974.) 



Gargas (1971) gave the same interpretation to a similar decrease in /o.s of 

 estuarine epipelic algae in a Danish mudflat. Note, however, that we 

 attribute the very rapid short-term decline in phytoplankton /o.s in early 

 July to nutrient effects (see below). 



The low productivity of the Barrow ponds is not due to low activities 

 per unit of cell mass. Unfortunately, our evidence is not perfect as we have 

 had to use the biomass data for 1971 (Figure 5-2, 5-10) with the P max data 

 for 1973 (Figure 5-18). An additional assumption that had to be made was 

 that the photosynthetically active epipelic algae were one-sixth of the total 

 biomass {B). Stanley (1976b) has predicted this based on models. The Pmax 

 B~^ ratios, (mg C)(mg algal C)"' day"' range from 0.2 to 3.0 for 

 phytoplankton and 0.4 to 1.0 for the epipelic algae. These values are as 

 high as or even higher than the highest values tabulated by Berman and 

 PoUingher (1974, their Table 6) from a variety of other studies. One reason 

 for this high ratio in the plankton might be the high grazing rate. Usually, 

 phytoplankton consist of a number of subpopulations, some of which are 

 senescent, some actively dividing, and some growing slowly in an almost 

 steady-state condition. Here, only the actively dividing subpopulation 

 would survive. 



The photosynthetic capacity of the phytoplankton, measured as P^ax 

 B~\ varies somewhat over the season but in 9 out of 12 measurements it 

 was between 0.4 and 1.0 (Figure 5-19) during 1971. This is expected from 

 the close correspondence between the Pmax m ' (Figure 5-18) and the 

 biomass for other years. The three excursions from the range given above 

 occurred at the beginning of the first bloom, at the peak of the first bloom, 

 and at the peak of the second bloom. 



PmaxB~^ ratios for the epipelic algae are more difficult to estimate 

 than for the phytoplankton because of methodological difficulties, but 

 they too probably change little over the season. The total epipelic biomass 

 in the top 5 cm of the sediment increases continuously over the summer 



