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Two different methods of evaluating nutrient limitations of periphyton bioassays,using water from the River Rhine and eight of its tributaries
Authors:Ferdinand Schanz  Heinz Juon
Institution:1. Hydrobiologisch-limnologische Station der Universit?t Zürich, Seestrasse 187, CH-8802, Kilchberg, Switzerland
Abstract:An investigation was untertaken to evaluate the nutrient status of the River Rhine (two stations) and eight of its tributaries (total of ten samplings). Determinations of the following inorganic substances were made: PO4 ?3-P; NO3 ?-N; NO2 ?-N; NH4 + -N and Cl?. In addition, pH and carbonate alkalinity were measured. Bioassays to obtain the algal growth potential (AGP) were carried out using periphyton from the River Rhine. A linear relationship could be established between NO3 ?-N and the AGP, while the AGP showed a non-linear dependence on the PO4 3?-P concentration. The critical N/P ratio for N or P limitation of the algal growth in bioassays was evaluated graphically and by calculation. The results of the two methods are in good agreement: N is the limiting factor at NO3 ?N/PO4 3?-P ratios less than 10, while P is limiting at ratios greater than 20. At values between 10 and 20 neither N nor P can be supposed with certainty to be limiting.
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