Primary Producers 



V. Alexander. D. W. Stanley, R. J. Daley, and C. P. McRoy 



PHYTOPLANKTON* 



Populations 



Seasonal variations in algal species and biomass were measured 

 weekly from 1970 to 1973 in four or five IBP study ponds. In addition, 

 species distribution in a larger number of ponds was investigated on two 

 occasions. Dr. Staffan Holmgren, then at the Institute of Limnology, 

 Uppsala University, provided taxonomic help with the nannoplankton 

 during 1971. 



A settling chamber technique, based on the technique of Utermohl 

 (1958), was used throughout the study to count phytoplankton. In 1970, 

 the technique was used with an inverted microscope. Later, the technique 

 was modified (Coulon and Alexander 1972) so that a permanent slide was 

 produced that could be examined with a conventional phase-contrast 

 microscope. With this technique, even the most delicate flagellates such as 

 Rhodomonas minuta and various species of Chromulina showed no 

 change in appearance. Cell biomass estimates were obtained from 

 Nauwerck (1963) and from calculations involving the measured average 

 lengths and widths of each species and the volumes of geometric figures. 

 These volume estimates (in nva^) were changed to wet weight values by 

 assuming a density of 1.0 (thus, 10^jum^=l mg). 



Chlorophyll measurements provided another estimate of 

 phytoplankton biomass. The technique was basically that described by 

 Strickland and Parsons (1965). Glass fiber filters (Gelman A) were used 

 for concentrating the algae and the chlorophyll was extracted in 90% 

 acetone at 5°C for 24 hours. After centrifugation, the absorption of light 

 was measured in a scanning spectrophotometer. 



The chlorophyll content of the ponds invariably showed a rapid rise 

 after the spring melt (Figure 5-1). Next, the concentrations fell to very low 

 values in mid-July followed by a rise in August. In some years, a year-end 

 peak was measured. Unfortunately, there are only a few samples from 

 September so the constancy of the late summer peaks is not known. 

 Overall, the very low levels indicate extremely small quantities of algae 



*V. Alexander 



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