600 



CAMPBELL 



BELEWS CREEK 

 STEAM STATION 



1000 2000 



I  I 



SCALE, m 



Fig. 1 Belews Lake sampling stations. 



drying, and the phytoplankton in the preparation were enumerated 

 in two transects of the cover slip at 450x magnification with a standard 

 Ught microscope. Analyses revealed counts that approximated a 

 Poisson distribution. Counts of at least 100 cells or units were made 

 and were found to have a counting error not greater than ±20%. The 

 entire cover-slip area was scanned for presence of scarcer taxa. 

 Because oil-immersion objectives can be used in identifying taxa, this 

 simple method of live phytoplankton analysis has the advantage over 

 use of a hemocytometer, Sedgewick— Rafter, or Palmer— Maloney 

 counting chamber. Further description and discussion of this 

 technique are presented by Campbell (1973) and Weiss et al. (1974; 

 1975; 1978a). All taxa were identified by species where possible. 

 Phytoplankton abundance was measured by density (number of cells 

 or units/ml) and biovolume (mm^/m^). Biovolumes were calculated 

 with a volume factor for each taxon determined by water displace- 

 ment of plasticine clay models constructed to scale from observa- 

 tions and average measurements. For colonial or filamentous forms, 

 the average number of cells per unit was taken into account. For 

 diatoms, which have large central vacuoles, only the percentage of 

 the total cell volume representing the plasma volume (Strathmann, 

 1967) was used. The enrichment index used is modified from Palmer 

 (1969) to account for density. The points Palmer assigned to each of 

 the pollution-tolerant species in a sample were multiplied by the 

 number of units per milliliter for that species, and the accumulative 



