Biological Survey — Oswego Watershed 145 



Oneida lakes; charts 6-8 show the same data for the protozoa, 

 algae and diatoms in the nannoplankton. The genera of which 

 representatives were found are listed under the explanation o£ 

 the chart showing the distribution of the group to which they 

 belong. Thus the letters C, S. or following a genus indicate 

 that it was observed in Cayuga, Seneca or Oneida lake respec- 

 tively. Genera not followed by any letter were observed in all 

 three lakes. The value assigned to the vertical rectangles in the 

 figures varies from 150 to 50,000 depending upon the group of 

 organisms. Each rectangle is provided with a scale of ten equal 

 spaces in the lower left rectangle. The value of one of these spaces, 

 which varies in the different figures, is indicated in the legend. 

 In chart 5, the data for Oneida lake are not to the same scale as 

 the others, and must be multiplied by ten for comparison with 

 Cayuga and Seneca lakes. The various plankton organisms were 

 determined to the genus whenever possible. The number of indi- 

 viduals, or colonies in the case of some of the Cyanophyceae, 

 diatoms, etc., of each genus identified were computed for each 

 sample. 



The results of the plankton studies conducted during the sum- 

 mer of 1927 and shown graphically in the charts indicate that 

 Cayuga and Seneca lakes were relatively poor in plankton or- 

 ganisms. Oneida lake was very rich in plankton organisms at all 

 depths during the entire period covered by the observations. 



Methods: Samples of net plankton were obtained by drawing a closing net 

 of number 20 silk bolting cloth with bucket, through a vertical distance of 

 5 or 10 meters of water. These samples were placed in vials or small bottles 

 and enough 95 per cent alcohol was added to make approximately a 70 per 

 cent solution. Later these samples were made up to a, uniform volume of 20 cc . 

 For making counts of the smaller organisms, such as algae, diatoms and pro- 

 tozoa, one cc. of the sample was transferred with a volumetric pipette to a 

 >Sedgwick-Kafter cell. The counts were made by enumerating under a com- 

 pound microscope, the organisms present in ten squares taken at random 

 from the cell. For the enumeration of the larger organisms, such as Crustacea 

 and rotifers, a two cc. portion of the sample was placed in a Watch glass and 

 all the organisms therein counted. The results were reduced to the number 

 of organisms per liter of water. For this purpose the net was considered 

 80 per cent efficient, that is, it was assumed that it strained the organisms 

 from 80 per cent of the water through which it was drawn. A check on the 

 efficiency of the net was made by determining the organisms in a sample 

 obtained by straining a known volume of water and also in a similar sample 

 obtained by drawing the net slowly through a certain vertical distance of 

 water. The results were approximately equal, indicating that the efficiency 

 of the net approximates 80 per cent. 



The samples of nannoplankton were obtained by taking water samples at 

 various depths with a water sampler. The water was strained through the 

 plankton net and one liter samples were centrifuged with a "Foerst number 

 14 centrifuge" and reduced to a small volume which was placed in a vial and 

 enough distilled water and formaldehyde added to make 10 cc. of suspension 

 in 4 per cent formalin. In a few cases when the water samples could not be 

 centrifuged on the same day that they were collected, liter quantities of water 

 were measured and enough formalin added to preserve them for a day or two 

 when the whole sample was centrifuged and made up in the usual manner. 

 The enumerations of nannoplankton were also reduced to the number of or- 

 ganisms per liter of lake water. 



