In Table 10, data are presented for samples taken from 8 

 lakes during the late July period of maximum stress on 

 nutrient supplies. Analyses are reported only for the 

 four elements which critical concentration comparisons 

 indicated might limit plant growth. When the Jarrell- 

 Ash data were verified by standard quantitative procedures, 

 data obtained by both types of analyses are presented. 



Comparisons with analyses of samples from other lakes 

 emphasize that the phosphorus concentration in plants from 

 Salsich Lake (0.18%) was relatively low. Whitney Lake 

 also seems close to phosphorus deficiency for Elodea 

 growth, as indicated by the 0.17% value for the index 

 segment. The data on Clear Lake are of interest because 

 the phosphorus concentration was relatively high at 

 0.24% but the nitrogen concentration of 1.94% in the second 

 one-inch was the lowest of any sample, and only slightly 

 above the 1.60% critical value. The 2.70% and 0.29% 

 concentrations of nitrogen and phosphorus, respectively, 

 in the Erickson Lake samples were high, but the 0.28% 

 calcium concentration in the terminal one-inch index 

 segment was at the critical level. It is not surprising 

 that calcium might be a limiting factor in soft water 

 lakes and that species with a higher requirement for 

 calcium than Elodea , or less capacity to absorb calcium 

 from the environment, might be eliminated from soft water 

 lakes such as Erickson. 



Probably the most consistently low values in Table 10 are 

 to be observed in the copper data. In Elodea from 5 of 

 the 8 lakes copper concentrations were low enough to 

 suggest a growth-limiting role of that element. 



In contrast to the other 6 lakes, Allequash and Little 

 Spider Lakes seem relatively well supplied with all the 

 essential nutrient elements. 



The data in Table 11 are from analyses of Ceratophyllum 

 demur sum index segments from Lake Mendota at Madison, 

 Wisconsin. Mendota is an extremely fertile, hard-water 

 lake which has extensive beds of macrophytes and trouble- 

 some algae blooms. The unusual fertility of Lake Mendota 

 is reflected in the very high concentrations of nutrient 

 elements in the samples. For example, the average con- 

 centration of nitrogen in the second one-inch segment was 

 3.75%; the phosphorus concentration was 0.65%. These 

 values are well above comparable values in plants from the 

 northern Wisconsin lakes and are approximately 3x and 6x 



31 



