Heferokonfo ^ Cyonophyta 



Diofom Q] Chrysophyfo 



Primary Producers 195 



Chlorophyfo 



100 



B B-l B-7 B-4 B-8 E 



B-IO B-12 B-ll B-5 B-9 



Plastic Enclosed Subponds within Pond B 



FIGURE 5-9. Proportional distribution ofepipelic algal 

 groups in tundra subponds within Pond B, July 1972. 



There is neither a uniform distribution of epipelic algae in the top 5 

 cm of sediment nor an algal mat at the surface. Instead, the cell density is 

 highest near the surface, with a steady downward decline (Table 5-5). In 

 1971, about half the biomass was in the upper 1 cm, and nearly 80% in the 

 top 2 cm. This was determined from both chlorophyll a and photosynthesis 

 measurements on 1-cm-thick sediment core sections (Figure 5-11). In 

 1973, Fenchel (1975) determined that 64% of the total number of algae was 

 in the top 2 cm and the remainder was in the 2 to 4 cm layer. Others (e.g., 

 Round 1964, Gruendling 1971, Fenchel and Straarup 1971) have found 

 similar vertical distributions of algae in temperate lake and estuarine 

 sediments. For these photosynthetic organisms, this means that only a 

 small fraction of the total can be producing at any one time since the great 

 majority are buried below the 1% level of light extinction, estimated to be 

 only about 2 mm in the tundra pond sediments. Yet these cells are 

 certainly alive, as evidenced by their appearance under the microscope and 

 their ability to photosynthesize as soon as they are placed in sunlight 

 (Figure 5-11). Algae can survive for months in the dark (Bunt and Lee 

 1972) and here it appears that cells produced at the surface are 

 continuously being mixed into the deeper sediments by a number of 

 mechanisms. Hence, it is not surprising that the seasonal patterns of total 

 biomass and productivity are very dissimilar (Figure 5-10). 



