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| Titel |
¹⁷O excess traces atmospheric nitrate in paleo-groundwater of the Saharan desert |
| VerfasserIn |
M. Dietzel, A. Leis, R. Abdalla, J. Savarino, S. Morin, M. E. Böttcher, S. Köhler |
| 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 ; 11, no. 12 ; Nr. 11, no. 12 (2014-06-17), S.3149-3161 |
| Datensatznummer |
250117466
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| Publikation (Nr.) |
 copernicus.org/bg-11-3149-2014.pdf |
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| Zusammenfassung |
| Saharan paleo-groundwater
from the Hasouna area of Libya contains up to 1.8 mM of nitrate, which
exceeds the World Health Organization limit for drinking water, but the
origin is still disputed. Herein we show that a positive 17O excess in
NO3− (Δ17ONO3 =
Δ17ONO3 − 0.52 δ18ONO3) is
preserved in the paleo-groundwater. The 17O excess provides an excellent
tracer of atmospheric NO3−, which is caused by the interaction of
ozone with NOx via photochemical reactions, coupled with a
non-mass-dependent isotope fractionation. Our
Δ17ONO3 data from 0.4 to 5.0 ‰ (n = 28)
indicate that up to 20 mol % of total dissolved NO3- originated
from the Earth's atmosphere (x[NO3−]atm), where the
remaining NO3− refers to microbially induced nitrification in soils.
High Δ17ONO3 values correspond to soils that are
barren in dry periods, while low Δ17ONO3 values
correspond to more fertile soils. Coupled high
Δ17ONO3 and high x[NO3−]atm
values are caused by a sudden wash-out of accumulated disposition of
atmospheric NO3− on plants, soil surfaces and in vadose zones within
humid–wet cycles. The individual isotope and chemical composition of the
Hasouna groundwater can be followed by a binary mixing approach using the
lowest and highest mineralised groundwater as end members without considering
evaporation. Using the δ34SSO4 and δ18OSO4 isotope signature of dissolved SO42−, no
indication is found for a superimposition by denitrification, e.g. involving
pyrite minerals within the aquifers. It is suggested that dissolved
SO42− originates from the dissolution of CaSO4 minerals during
groundwater evolution. |
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