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| Titel |
Quantifying nitrate dynamics in an oligotrophic lake using Δ¹⁷O |
| VerfasserIn |
U. Tsunogai, S. Daita, D. D. Komatsu, F. Nakagawa, A. Tanaka |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 3 ; Nr. 8, no. 3 (2011-03-17), S.687-702 |
| Datensatznummer |
250005571
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| Publikation (Nr.) |
 copernicus.org/bg-8-687-2011.pdf |
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| Zusammenfassung |
| The stable isotopic compositions of nitrate, including the 17O
anomalies (Δ17O), were determined twice in 1 yr (June and August 2007)
in the oligotrophic water column of Lake Mashu, Japan. These data were then
used to quantify the geochemical dynamics of nitrate in the lake, by using
the deposition rate of the atmospheric nitrate onto the entire catchment area
of the lake. The total amount of nitrate in the lake water decreased from 4.2
to 2.1 Mmol during the period between the observations, while the average
Δ17O values remained uniform at +2.5‰. The Δ17O values corresponded
to an small and uniform mixing ratio of atmospheric nitrate to total nitrate
of 9.7 ± 0.8%. These results indicate that 0.52 ± 0.34 Mmol of
the remineralized nitrate was fed into the water column through
nitrification, while 2.6 ± 0.4 Mmol of nitrate was simultaneously
removed from the water column by assimilation, during the period between the
observations. The lake water dissolved nitrate was characterized by rapid
removal through assimilation during summer until it was almost completely
removed from the euphotic layer, as well as continuous feeding into the lake
through nitrification (3.2 ± 0.3 Mmol a−1)
and deposition (0.35 ± 0.2 Mmol a−1), regardless of the seasons. The 15N-depleted
nitrogen isotopic compositions of nitrate were as low as −6.5‰ in
June, which also indicates that in-lake nitrification is the major source of
nitrate in the lake and suggests that there is low potential for
denitrification in and around the lake. Atmospheric nitrate deposited into
the lake will be assimilated quickly, having a mean residence time of 1.2 ± 0.1 yr.
In addition, more than 90% of the assimilated nitrate
will be remineralized to nitrate and re-assimilated via active nitrogen
cycling in the lake. |
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