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Plant analysis was developed as a relatively simple procedure for evaluating nutrient supplies and growthlimiting 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 Ceratophyllum 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.

Plant analysis for nutrient assay of natural waters, by Gerald C. Gerloff. Project officer, Gary Glass.