104 PLANKTON OF WISCONSIN LAKES 



CHAPTER V 

 THE PLANKTON OF LAKE MONONA 



Samples of net plankton were obtained from Lake Monona each year 

 from 1911 to 1916, inclusive, with the exception of 1914. This ma- 

 terial was secured chiefly for the purpose of making qualitative and 

 quantitative comparisons with the results obtained on Lake Mendota. 

 No winter observations were made on Lake Monona and it was not 

 practicable to begin the work very promptly in the spring nor to con- 

 tinue it very late in the autumn, so that the catches cover only the 

 period from late May to late October or early November. 



The area, volume, and mean depth of Lake Monona are much smaller 

 than those of Lake Mendota, but the maximum depth of the former 

 is only about three meters less than that of the latter. (Table 1, p. 181). 

 Lake Monona receives the water from the outlet of Lake Mendota as 

 well as that from two other streams. The water of Lake Monona is 

 subject to considerable pollution, which is a matter of much impor- 

 tance both from a biological and from a chemical standpoint. It re- 

 ceives (a) the effluent of the sewage disposal plant of Madison, (b) 

 the greater part of the storm water drainage of this city, (c) the 

 effluent from a small private sewage disposal plant at South Madison, 

 and (d) some trade wastes consisting principafly of the effluent from 

 a large beet sugar factory. Just what effect this pollution has upon 

 the plankton crop of the lake is not definitely known, but these polluted 

 waters carry an abundance of material which may be utilized by vari- 

 ous plankton organisms. 



The Net Plankton 



Table 2 (p. 181) shows the number of samples of net plankton pro- 

 cured each year, as well as the volume of water strained and the total 

 quantity of dry plankton. Only four samples were taken in 1911 

 and but six in 1912. In 1913 and in 1916 catches were obtained at 

 more frequent intervals so that the data are sufficient to construct 

 curves for the results of these two years. In general the net plankton 

 of Lake Monona contained a larger proportion of algal material than 

 that of Lake Mendota. 



Organic matter. The organic matter constituted from 68.9 per cent 

 to 97.7 per cent of the total dry weight of the net plankton, with an 



