144 PLANKTON OF WISCONSIN LAKES 



tions in the average for the complete series of net catches range from a 

 minimum of 23 kilograms to a maximum of 695 kilograms per hectare 

 (20 pounds to 620 pounds per acre) for the deep part of the lake. 



When the area and the volume of the entire lake are taken into ac- 

 count, the amount of dry organic matter in the 47 net samples from 

 Lake Monona varies from a minimum of 9 kilograms to a maximum 

 of 278 kilograms per hectare of surface (8 pounds to 248 pounds per 

 acre), with an average of about 72 kilograms per hectare (65 pounds 

 per acre). For the whole lake the average standing crop of net plank- 

 ton yields 101 metric tons of dry organic matter. The mean quantity 

 of organic matter in the 21 samples of net plankton corresponding to 

 the nannoplankton catches is a little less than 69 kilograms per hectare 

 (61 pounds per acre). 



Lake Waubesa. The 18 samples of net plankton from Lake Waubesa 

 yielded an average of 1,665 milligrams of dry organic matter per cubic 

 meter of water, or almost twice as much as the average for Lake Monona 

 and five times as much as the mean of Lake Mendota. (Table 25.) The 

 nitrogen constituted an average of 7.54 per cent of the dry organic mat- 

 ter, the ether extract 4.64 per cent, the pentosans 5.90 per cent, and the 

 crude fiber 4.70 per cent. The percentages of nitrogen and of ether 

 extract are appreciably below those of the net plankton from Lakes 

 Monona and Mendota, but the percentage of the pentosans is higher. 

 The percentage of crude fiber is higher than that noted in the material 

 from Lake Monona, but lower than that of Lake Mendota. The average 

 percentages of crude protein, ether extract, pentosans, and crude fiber 

 account for 62.36 per cent of the organic matter, leaving 37.64 per cent 

 of undetermined nitrogen free extract. In the net material from Lake 

 Mendota the nitrogen free extract constituted an average of only 26.49 

 per cent of the organic matter and in that from Lake Monona only 26.13 

 per cent. 



The quantity of dry organic matter in the complete series of net 

 catches from Lake Waubesa varied from a minimum of 471 milligrams 

 to a maximum of 4,232 milligrams per cubic meter of water. In that 

 part of the lake having a depth of 10 meters or more (p. 139) the 

 amount varied from about 48 kilograms to 427 kilograms per hectare 

 (42 pounds to 381 pounds per acre). The average standing crop of dry 

 organic matter in this region of the lake was 170 kilograms per hectare 

 (151 pounds per acre). For the 16 samples of net plankton correspond- 

 ing to the same number of nannoplankton catches, the average is some- 

 what smaller, namely, 1,639 milligrams per cubic meter of water, or 

 167 kilograms per hectare (149 pounds per acre) for the deep part of 

 the lake. 



