Biological Survey — Oswego Watershed 155 



red heat for 20 minutes and then kept at a cherry red heat for 45 

 minutes. 



It is obvious that this method gives but a rough approximation 

 of the actual weights of dry matter, organic matter and ash in the 

 water of each lake. The data are based upon the solid matter 

 (living organisms, remains of organisms and suspended inorganic 

 particles) that were removed by the centrifuge. Some of the very 

 fine particles as well as inorganic matter and salts in solution, 

 would not be removed from the water by the centrifuge so that the 

 figures for dry weight represent the weight of all solid particles 

 that were so removed. The weight of organic matter represents 

 materials lost upon ignition after the water was removed. The ash 

 represents the residue after the dry matter was ignited. One 

 source of error is the small quantities of water samples employed. 

 However, duplicate samples were analyzed in most cases, and these 

 usually checked closely. The final data in chart 9 represents the 

 averages of analyses of 16 or 24 separate samples of water from 

 each lake and illustrates graphically the differences in the three 

 lakes in quantities of dry matter and organic matter. 



The data in Table 2 from which chart 9 is derived show that the 

 organic matter in Cayuga and Seneca lakes in general is greatest 

 between the surface and 20 meter depths and in Oneida lake be- 

 tween the surface and 3 meter depths, The total dry weights show 

 no striking or consistent differences with vertical distribution in 

 any of the three lakes. This is apparently due to the relatively 

 greater ash content in the deeper water. In Cayuga and Seneca 

 lakes the water samples taken in late June and July contain a 

 rather uniformly lower amount of organic matter and usually also 

 less dry matter than the water samples taken later in the season 

 (August). One of the factors responsible for the increase in or- 

 ganic matter appears to be the rise in the temperature, especially 

 in the surface water of these deep lakes. Oneida lake, which is 

 shallow, warms up much earlier in the summer, shows but very 

 little difference in temperature between the surface and the bottom 

 water.* No striking seasonal variation in organic matter was ob- 

 tained between June and August. 



The weights of dry matter and organic matter were computed 

 for each lake by taking the average of the weights obtained from 

 duplicate samples, taken at two depths, surface and ten meters, at 

 two different times at two different stations located near the north 

 and the south end of Cayuga and Seneca lakes. The values for 

 Oneida lake were derived by taking the average weights for dupli- 

 cate samples taken at five depths, surface to 12 meters, taken four 

 different times. The weights of organic matter and dry matter 

 were computed in pounds per acre of lake water for the upper 10 

 meters in order to allow a direct comparison of the three lakes. 

 Chart 9 shows that Cayuga and Seneca lakes are relatively low in 

 organic matter, 107 pounds and 124 pounds per acre respectively, 



See tables of chemical analyses, Series 111, p. 128. 



