The use of TN:TP and DIN:TP ratios as indicators for phytoplankton nutrient limitation in oligotrophic lakes affected by N deposition |
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| Authors: | Ann-Kristin Bergström |
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| Institution: | 1. Department of Ecology and Environmental Science, Ume? University, 901 87, Ume?, Sweden
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| Abstract: | The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and
DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate
whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton.
Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes)
and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the
study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios
was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate
addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton.
Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating
P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes
with high to very high amounts of N deposition. |
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