SECTION IV 



DEVELOPMENT OF PLANT ANALYSIS AS AN ASSAY OF 



NUTRIENT SUPPLIES FOR THE GROWTH OF NUISANCE MACROPHYTES 



Development of plant analysis for nutrient assay in lakes 

 and streams required that the critical concentrations of 

 all of the essential elements likely to limit plant growth 

 would be established in laboratory experiments for the 

 macrophytes on which the assay was to be based. Elodea 

 occidentalis and Ceratophyllum demursum were selected as 

 the primary test organisms. Both species are abundant 

 and troublesome in Wisconsin lakes. There is a marked 

 morphological difference in the two organisms in that 

 Elodea produces abundant roots while Ceratophyllum 

 does not. In the time available, critical concentrations 

 for all the essential elements except chlorine and copper 

 were established in Elodea occidentalis and for a number 

 of the elements in Ceratophyllum demursum . 



EXPERIMENTAL PROCEDURES 



The composition of the nutrient medium used in the critical 

 concentration experiments is indicated in Table 1. This 

 is the same culture medium employed in earlier studies 

 (Gerloff and Krombholtz, 1966) except that iron (0.56 ppm) 

 was provided as a chelate of EDDHA (ethylenediamine di- (a- 

 hydroxyphenylacetate) rather than as FeEDTA. Algae-free 

 cultures were essential. Otherwise, the abundant algae 

 growth which developed made it impossible to interpret the 

 results in terms of the nutritional requirements of the macro- 

 phytes. The procedure for obtaining algae-free macrophytes 

 also was described earlier (Gerloff and Krombholtz, 1966). 



The most convenient culture vessels were three-liter Florence 

 flasks containing two liters of nutrient medium. The flasks 

 were stoppered and closed except for aeration and exhaust 

 tubes provided with cotton filters in glass-tubing that 

 passed through the stoppers. Each complete assembly was 

 sterilized by autoclaving. The cultures were bubbled con- 

 tinuously with air filtered through cotton and activated 

 charcoal and then enriched to 1% C0 2 . All cultures were 

 kept in a constant environment room or growth chambers 

 maintained at approximately 23°C and provided with artificial 

 light of 800-1700 foot candle intensity. The cultures in a 



