244 V. Alexander et al. 



Detailed studies of the algal biomass every 3 hours for an entire day 

 revealed that the total biomass changed as much as 3-fold in a few hours. 

 The most likely explanation is that small flagellates (3 nm and 6 ^m in 

 length) moved down into the upper layers of the sediment during the low- 

 light periods and moved back into the water column for the afternoon. 

 Larger forms typical of plankton, such as Rhodomonas minuta and 

 Chromulina, stayed in the water continually. Sediment algae were 60 

 times more abundant per milliliter than the plankton algae so there was an 

 adequate reservoir of cells. 



Phytoplankton primary productivity, measured by light and dark 

 bottle uptake of H^COa, paralleled the curves for chlorophyll and 

 biomass. There was a peak in early July, a mid-summer low, and another 

 peak at the end of August. The rates were reasonably high per unit of 

 volume: 8 /ig C liter"' hr "' in the early peak, 1 ^g C liter ' hr ' in mid- 

 summer, and up to 17 Mg C liter ' hr " ' at the end of August. However, 

 the total volume of the system is so low that production was only about 1 g 

 C m " yr*', one of the lowest ever measured. Detailed studies of 

 productivity every 3 hours showed that the maximum occurred from early 

 afternoon (1400) until mid-evening (2000). This coincided with the 

 appearance of the 3 nm flagellates in the water column. On one day, the 

 specific growth rate(^g C (^g C) ' hr ') of the 3 ^xm flagellates peaked at 

 0.04 hr ' at 2000, the rate of the 6 ^m flagellates and of Rhodomonas 

 peaked at 0.03 hr"' at 1400, and that of the Chromulina peaked at 0.02 

 hr"' at 2300. 



Epipelic Algae 



In the sediments, the majority of the algae are attached to particles. 

 Some 50% of the total biomass was chlorophytes (green algae) and 

 42% was cyanophytes (blue-green algae). Common algae were 

 Chlamydomonas, Closterium, and Aphanizomenon (blue-green). Diatoms 

 were also present. The cells are small, usually less than 10 ^m in length; 

 numbers ranged from 2 to 4 x 10'" m ' (0.5 to 1.0 g C m ■^). Throughout 

 the year, there was a gradual increase in biomass. Within the sediment, 

 50% of the biomass was in the top 1 cm; another 30% was at the 1-2 cm 

 depth. Perhaps because of the animal activity which continually mixed the 

 sediment, the algae did not form a mat at the surface. 



Primary productivity was estimated with a '^C technique in which a 

 maximum potential photosynthesis rate was measured with a diluted 

 sample and then an in situ rate calculated from the light-depth 

 relationship. The depth of the 1% light level was only 2 mm but algae from 

 greater depths were always able to photosynthesize when placed in light. 

 The productivity began as soon as the ice melted and rose steadily from 2 

 mg C m " hr"' on 21 June to 16 mg C m ' hr"' in mid-July. After this 

 peak, the productivity steadily declined throughout the rest of the summer. 



