EXPERIMENTAL PROCEDURES 



The general culture conditions and harvesting procedures 

 employed were described in Section IV. 



Several chelates of iron were compared as an iron source, 



primarily. EDTA (ethylenedinitrilo)-tetraacetic acid and 



EDDHA ethylenediamine di- (o-hydroxyphenylacetate) 



The EDDHA was obtained from Geigy Chemical Co. as an 86.3 



percent pure salt. Iron chelates were prepared as a 



0.01 M stock solution of FeEDTA (2.78 g FeSCV7H 2 and 3.72 



g Na 2 EDTA) and as a 0.01 M stock solution of FeEDDHA (140 



mg KOH, 278 mg FeSCK • 7H 2 0, and 424 mg EDDHA). 



RESULTS 



The composition of the macrophyte culture medium developed 

 on this project is presented in Table 13. 



Concentrations of Elements 



The initial step in formulating the macrophyte medium was 

 to determine from the critical concentration experiments 

 in Section IV the minimum concentration of each essential 

 element which was just adequate to produce maximum growth 

 of Elodea in a 4-week period in two liters of solution. 

 These values were compared with the amounts of the elements 

 necessary to maintain the critical concentration in 5.0 g 

 of oven-dry growth of Elodea and Ceratophyllum . From these 

 comparisons some upward adjustments in element concentra- 

 tions seemed necessary, particularly in the three major 

 element cations, calcium, magnesium, and potassium. As 

 a result, the concentrations of the essential elements 

 in the solution of Table 13 are approximately double the 

 minimum concentrations for maximum yield derived from 

 critical concentration experiments. 



Providing each element at the lowest but adequate con- 

 centration was considered desirable to reduce the 

 possibility of adverse effects on growth due to high salt 

 concentrations and toxic trace element concentrations. 

 Minimum deviation from the low concentrations characteristic 

 of lakes and streams also seemed desirable. 



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