ABSTRACT 



Plant analysis was developed as a relatively simple 

 procedure for evaluating nutrient supplies and growth- 

 limiting nutrients for nuisance macrophytes in lakes and 

 streams. Plant analysis requires establishing in index 

 segments of the macrophytes the critical concentration 

 (minimum plant concentration for maximum yield) of each 

 essential nutrient likely to limit growth. Critical 

 concentrations for nitrogen, phosphorus, sulfur, calcium, 

 magnesium, potassium, iron, manganese, zinc, boron, and 

 molyldenum were established in appropriate index segments 

 of Elodea occidentalis . The copper critical concentration 

 was estimated. Critical concentrations for nitrogen, 

 phosphorus, and several other elements were established in 

 Ceratophyllum demursum . 



To evaluate plant analysis, samples of Elodea and Cerato- 

 phyllum were routinely collected from Wisconsin lakes, 

 analyzed for essential nutrients, and the analyses were 

 compared with the critical concentrations for indications 

 of nutrient deficiency. A growth-limiting role of an 

 element in a lake was indicated by plant concentrations 

 below the critical level. Nitrogen, phosphorus, calcium, 

 and copper were at or close to critical levels in one or 

 more lakes. Neither phosphorus nor nitrogen seemed to be 

 a general growth-limiting nutrient in the lakes sampled. 

 The most unexpected result was an indication of copper 

 deficiency in several lakes. 



From the extensive nutritional experiments to establish 

 critical element concentrations, a synthetic nutrient 

 medium for general macrophyte culture was developed. 



This report was submitted in fulfillment of Project No. 

 18040 DGI under the sponsorship of the Water Quality 

 Office, Environmental Protection Agency. 



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