Table 5. The total phosphorus content of various segments 

 of Elodea occidentalis harvested when phosphorus 



* Insufficient tissue for analysis 



Critical Concentrations of Additional Elements 



The results of experiments to establish the critical 

 concentrations of elements other than nitrogen and phos- 

 phorus in index segments of Elodea are summarized in 

 Table 6. As anticipated, the critical concentrations for 

 the trace elements were much lower than for the major 

 essential elements. Values ranged from 8 ppm for zinc 

 to only 0.15 ppm for molybdenum. The total range of 

 concentration of each element also is indicated in Table 

 6. It is apparent that the concentrations of the essential 

 elements in Elodea are not fixed values but vary over a 

 considerable range. 



Critical concentrations were not established for the trace 

 elements chlorine and copper. Because of the low plant 

 requirements for chlorine and the large quantities in 

 rainfall as a result of atmospheric contamination, it is 

 unlikely chlorine would be a limiting factor in macro- 

 phyte growth under field conditions. This is not true of 

 copper. As established in Section V of this report, 

 there is a strong possibility that copper supply is 

 growth limiting in some northern Wisconsin lakes. 

 Unfortunately, in spite of elaborate purification efforts, 

 several experiments to establish a critical copper con- 

 centration in Elodea were unsuccessful. 



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