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| Titel |
Technical Note: Comparison between a direct and the standard, indirect method for dissolved organic nitrogen determination in freshwater environments with high dissolved inorganic nitrogen concentrations |
| VerfasserIn |
D. Graeber, J. Gelbrecht, Brian Kronvang, B. Gücker, M. T. Pusch, E. Zwirnmann |
| 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. 11 ; Nr. 9, no. 11 (2012-11-28), S.4873-4884 |
| Datensatznummer |
250007419
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| Publikation (Nr.) |
 copernicus.org/bg-9-4873-2012.pdf |
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| Zusammenfassung |
| Research on dissolved organic nitrogen (DON) in aquatic systems with high
dissolved inorganic nitrogen (DIN, the sum of NO3–, NO2– and
NH4+) concentrations is often hampered by high uncertainties
regarding the determined DON concentration. The reason is that DON is
determined indirectly as the difference between total dissolved nitrogen
(TDN) and DIN. In this standard approach to determine DON concentrations,
even small relative measurement errors of the DIN and TDN concentrations
propagate into high absolute errors of DON concentrations at high DIN : TDN
ratios. To improve the DON measurement accuracy at high DIN : TDN ratios,
we investigated the DON measurement accuracy of this standard approach according to
the DIN : TDN ratio and compared it to the direct measurement
of DON by size-exclusion chromatography (SEC) for freshwater systems. For
this, we used standard compounds and natural samples with and without DIN
enrichment. We show that for the standard approach, large errors of the
determined DON concentrations at DIN : TDN ratios >0.6 occur for both
standard compounds and natural samples. In contrast, measurements of DON by
SEC always gave low errors at high DIN : TDN ratios due to the successful
separation of DON from DIN. For SEC, DON recovery rates were 91–108% for
five pure standard compounds and 89–103% for two standard compounds,
enriched with DIN. Moreover, SEC resulted in 93–108% recovery rates for
DON concentrations of natural samples at a DIN : TDN ratio of 0.8 and the
technique was successfully applied to a range of samples from waste water
treatment plants to forest and agricultural streams. With 2.5 h of measurement
time per sample, SEC is slower, but more accurate than the standard approach
for determination of DON concentrations in freshwaters with DIN : TDN
ratios >0.6. To sum up, the direct DON measurement by SEC enables better
understanding of the nitrogen cycle of urban and agricultural freshwater
systems. |
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