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| Titel |
Semi-annual carbon and nitrogen isotope variations in the water column of Lake Bled, NW Slovenia |
| VerfasserIn |
A. Bratkič, M. Sturm, J. Faganeli, N. Ogrinc |
| 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 ; 9, no. 1 ; Nr. 9, no. 1 (2012-01-03), S.1-11 |
| Datensatznummer |
250006646
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| Publikation (Nr.) |
 copernicus.org/bg-9-1-2012.pdf |
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| Zusammenfassung |
| The variability in the stable isotope signature of carbon and nitrogen in
particulate organic matter and dissolved species in the water column of the
mesotrophic subalpine Lake Bled in NW Slovenia has been determined. After
the algae bloom from August to December in 2008, samples were taken from the
deepest part of the lake which develops an anoxic hypolimnion for most of
the year. C/N molar ratios and δ13CPOC and δ15NPN values suggest an autochthonous source for particulate
organic matter (POM). According to the isotope model, autochthonous carbon
accounted for a major part of the particulate organic carbon (POC), ranging
from 86% to 96% in September and October, while in December the
proportion of allochthonous carbon was more pronounced, ranging from 57%
to 59%. Low δ13CPOC and δ15NPN values
(from −36 to −33‰ and from 0.8 to 1.8‰), observed below 24 m in August and
September, indicate the bacterial origin of POM, mainly from methanotrophic
bacteria. δ15NNO3 and δ15NPN values decreased with depth. The relations between δ15NPN and NO3- and NH4+ concentrations
suggest that NH4+ is the main assimilation species for nitrogen in
POM. Nitrification was active between 12 and 18 m deep in September and
October, indicated by increased NO3- concentrations and decreased
δ15NNO3 values. The correlation between nitrate
concentrations and δ15NNO3 values suggests active water
column denitrification in October 2008. The decrease in δ15NNO3 values observed in December could be explained by
degradation of organic matter, followed by nitrification of the degradation
products. During our sampling period, there was no evident influence of
sewage, agriculture, or atmospheric deposition on the nitrogen balance in
the lake. |
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