130 PLANKTON OF WISCONSIN LAKES 



Nannoplankton 



Four samples of centrifuge material were obtained from Lake Wau- 

 besa in 1915 and a dozen samples in 1916. In the former year the 

 catches were made between August 11 and October 23, inclusive, but 

 in the latter year samples were taken about every two weeks from May 

 24 to October 30. The amount of water eentrifuged in 1915 was 5,732 

 liters and 11,641 liters in 1916, making a total of 17,373 liters for the 

 two years. (Table 2.) 



Organic Matter. The results obtained for the organic matter in the 

 sixteen samples of nannoplankton are summarized in table 29, p. 198, 

 and the analyses are given in detail in table 48, p. 214. In 1915 the 

 minimum quantity of dry organic matter was 2,871.2 milligrams per 

 cubic meter of water and the maximum was 6,143.2 milligrams, the 

 latter being more than twice as large as the former ; the mean quantity 

 for the four catches of this year was 4,260.2 milligrams. In 1916 the 

 amount was much smaller, the minimum falling to 801.0 milligrams 

 and the maximum reaching only 4,830.0 milligrams, a sixfold difference. 

 The mean for 1916 was also much smaller than that of 1915, being only 

 2,977.5 milligrams. In both years, however, the amount of organic 

 matter in the nannoplankton of Lake Waubesa was larger than in Lake 

 Mendota or in Lake Monona. 



The curve marked B in figure 39 gives the story of the organic mat- 

 ter in the nannoplankton of Lake Waubesa in 1916. There was a de- 

 cline in the amount in late May and early June reaching a summer 

 minimum on June 15. This period was succeeded by one in which there 

 was a regular increase lasting from early July to September 7, the 

 highest point in the curve being attained on the latter date. A period 

 of decrease was noted for the rest of September, but there was a mod- 

 erate increase during the first half of October followed by a further 

 decline during the remainder of this month. 



A comparison of this curve with the one marked C in figure 37 shows 

 that the story of the nannoplankton of Lake Waubesa in 1916 was sub- 

 stantially the same as that of the nannoplankton of Lake Monona in 

 this year. There are slight differences, however ; the rise in Lake Wau- 

 besa was more rapid in the earlier stages and the decline more gradual 

 so that the autumn peak of the curve has a broader aspect than that of 

 Lake Monona. Another difference is that the small secondary peak in 

 October shown in the curve for Lake Waubesa is not represented in 

 the curve for Lake Monona. In general, though, the curves for the 

 organic matter of the nannoplankton of these two lakes are very similar 

 in outline and they both differ markedly from that of Lake Mendota for 

 this year as shown in curve A, figure 31. 



