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| Titel |
Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer |
| VerfasserIn |
J. B. Heffernan, A. R. Albertin, M. L. Fork, B. G. Katz, M. J. Cohen |
| 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. 5 ; Nr. 9, no. 5 (2012-05-11), S.1671-1690 |
| Datensatznummer |
250007023
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| Publikation (Nr.) |
 copernicus.org/bg-9-1671-2012.pdf |
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| Zusammenfassung |
| Aquifer denitrification is among the most poorly constrained fluxes in
global and regional nitrogen budgets. The few direct measurements of
denitrification in groundwaters provide limited information about its
spatial and temporal variability, particularly at the scale of whole
aquifers. Uncertainty in estimates of denitrification may also lead to
underestimates of its effect on isotopic signatures of inorganic N, and
thereby confound the inference of N source from these data. In this study,
our objectives are to quantify the magnitude and variability of
denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect
on N isotopic signatures at the regional scale. Using dual noble gas tracers
(Ne, Ar) to generate physical predictions of N2 gas concentrations for
112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely
correlated with dissolved oxygen (O2). Negative relationships between
O2 and δ15NNO3 across a larger dataset of 113
springs, well-constrained isotopic fractionation coefficients, and strong
15N:18O covariation further support inferences of denitrification
in this uniquely organic-matter-poor system. Despite relatively low average
rates, denitrification accounted for 32 % of estimated aquifer N inputs
across all sampled UFA springs. Back-calculations of source δ15NNO3 based on denitrification progression suggest that
isotopically-enriched nitrate (NO3–) in many springs of the UFA
reflects groundwater denitrification rather than urban- or animal-derived
inputs. |
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