Isotopic variations of the nitrogen in Lake Superior |
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| Authors: | Patrick C Pang Jerome O Nriagu |
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| Institution: | Canada Centre for Inland Waters, Burlington, Ontario, Canada L7R 4A6 |
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| Abstract: | The isotopic compositions of nitrogen in lake water, plankton samples and the organic-N fractions extracted from sediments at selected stations in Lake Superior are presented. The δ15N values of the Kjeldahl total-N and acid hydrolyzable-N in the lake sediments are similar (range, +4.7–+6.7; mean, +5.5 %.). The δ15N data for the various extracts are independent of the age and concentration of nitrogen in the sediments. On the other hand, the δ15N values of lake water (+ 0.6‰), phytoplankton (+ 1.6 %.) and Zooplankton (+ 5.0‰) in the water column suggest significant discrimination against the heavier nitrogen isotope in the food chain of the lacustrine environment. The data emphasize the need for a better understanding of the autogenous isotopic fractionation before the isotopic method can be used to fingerprint the sources of nitrogen in a limnetic ecosystem. |
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