Primary Producers 193 



growing season. Char Lake (Kalff and Welch 1974) and lakes Peters and 

 Schrader (Hobbie 1964) have 8- or 9- month growing seasons and most of 

 their primary production actually occurs beneath the ice cover. Meretta 

 Lake, which receives sewage, indicates that the potential production of 

 arctic lakes can be quite high. 



EPIPELIC ALGAE* 



Biomass of Algae 



Epipelic microalgae, mostly greens and blue-greens, are abundant in 

 the pond surface sediments. Some forms are motile, but the majority are 

 attached to sediment and detritus particles. For this reason, direct cell 

 counts were made in 1971 by dilution of a mixed sediment sample (to 5 

 cm), filtration onto a 0.45-Mm black Millipore filter, and counting with an 

 epi-illuminated fluorescence microscope. This was rather a crude method 

 as only the red fluorescence of the chloroplasts could be seen and separate 

 species could not be identified. On the other hand, the fluorescence made it 

 easy to count all of the algae on the surface of the sediment particles. The 

 numbers were converted to biomass from estimations of the volumes of the 

 dominant algae (a specific gravity of 1 .0 was assumed). This technique was 

 used on weekly samples from Pond J collected at the same time and place 

 as the productivity samples (Stanley 1976a). A slightly different technique, 

 a direct count without the filtration step, was used by Fenchel (1975) in 

 Pond A in 1973 (7 weeks). The results agreed quite well. The algal species 

 were identified and their relative abundance determined by C. Coulon on 

 several occasions during 1972 by using diluted samples and a conventional 

 light microscope. 



Chlorophyll a concentrations, another indicator of algal biomass, 

 were measured in 1972 in Pond B. The upper 5 cm of a sediment core was 

 sectioned at 1 cm intervals and extracted, with frequent shaking, for 12 

 hours with 90% acetone. After centrifugation, the optical density of the 

 sample was read at 665 nm. Turbidity, phaeophytin corrections, and 

 calculations were according to Lorenzen (1967). 



The Pond B epipelic assemblage was dominated by Chlorophyta and 

 Cyanophyta. These two groups made up 50% and 40%, respectively, of the 

 total biomass. Some of the most common blue-green forms are 

 Microcystis, Gomphonema, and Aphanozomenon, while the common 

 green algae are Chlamydomonas , Closterium, and Ankistrodesmus (Table 

 5-4). However, as Figure 5-9 illustrates, the composition can vary 

 considerably from one pond to another. Obviously the dominant benthic 



* D.Stanley 



