200 



V. Alexander et al. 



— ^ Photosynthesis 



Light 



I Range of four samples 



1200 



1800 



2400 

 Time, hr 



0600 



1200 



FIGURE 5-13. Hourly epipelic photosynthesis 

 rates and insolation, Pond B, taken on three days 

 in 1972. 



In temperate regions only the shallow lakes have significant benthic 

 photosynthesis. However, the combined total algal production is almost 

 always greater than in the arctic ponds. In Marion Lake, British 

 Columbia, epipelic algae contributed about 40 g C m~^ yr Mo a total 

 primary production of 66 g C m " yr~' (Hargrave 1969). As another 

 example, about 70% of the total primary production measured by Wetzel 

 (1964) in Borax Lake was by benthic microalgae. Finally, in Lake Fureso, 

 the production was 143 g C m^^ yr^^ for the epipelic algae but only 50 gC 

 m "" yr ' ' for the plankton (Hunding 1971). All of these lakes are shallow, 

 so significant amounts of light penetrate to the bottom. Thus, morphology 

 seems to play an indirect role in determining the relative proportions of 

 planktonic and benthic algal photosynthesis. Other, more direct 

 controlling forces will be discussed in detail later. 



