Primary Producers 199 



> " 1 



10 July 1973 

 Pond A 

 Temp. = 8°C 



1.0 



a. 

 Q 



c 

 a> 

 E 

 ■o 



0) 

 CO 



2.0 



25 50 75 100 



Percent of Light Saturated Photosynthesis 



FIGURE 5-12. Percentage of light- 

 saturated photosynthesis at various depths 

 in the sediment of a pond. The line also 

 represents the relative light intensity at 

 various depths; the shaded area represents 

 estimated true productivity. 



mid-day photosynthesis rates were extrapolated to daily rates, based on 

 measurements of the diurnal pattern of photosynthesis of these algae 

 (Figure 5-13), and the daily rates summed (15 June to 1 September) for an 

 estimate of annual production. These values ranged from 10.1 to 4.1 g C 

 m'" in Pond J, 1971 and in Pond A, 1973, respectively and are about 10 

 times greater than the plankton production of 0.6 to 0.9 g C m ^ 



The sediment algae are not so important in deeper arctic lakes. For 

 example, in 1971 at nearby Ikroavik Lake (2.2 m deep) the total net 

 epipelic fixation was only 2.3 g C m ~\ primarily because of the shorter ice- 

 free period, lower water temperatures, and lower light intensity at the 

 sediment surface. The plankton algae productivity was only slightly lower, 

 about 2.2 g C m~". In still deeper Alaskan lakes, like Lake Schrader 

 (average depth 30 meters), epipelic photosynthesis is probably 

 insignificant because of the turbid water (Hobbie, personal 

 communication). This was not the case in Char Lake in the Canadian 

 Arctic which is both deep and very clear. Here, Kalff and Welch (1974) 

 estimated a plankton production of 4.2 and a benthic microalgae 

 production of 8.9 g C m ^ This lake, however, has a moss-covered 

 bottom (production of 8.4 g C). 



