 |
| Titel |
Limitations of the isotopic composition of nitrates as a tracer of their origin |
| VerfasserIn |
Wolfram Kloppmann, Bernhard Mayer, Neus Otero, Mathieu Sebilo, Daren Gooddy, Dan Lapworth, Ben Surridge, Emmanuelle Petelet Giraud, Christine Flehoc, Nicole Baran |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145825
|
| Publikation (Nr.) |
 EGU/EGU2017-9797.pdf |
|
|
|
|
|
| Zusammenfassung |
| Nitrogen and oxygen isotopes are traditionally considered and frequently used as tracers of
nitrate sources in watersheds used for drinking water production. The enrichment of synthetic
nitrate-containing fertilizers in 18O due to the contribution of atmospheric oxygen in the
production process confers a specific isotopic fingerprint to mineral fertilizers. In spite of the
still widespread use on nitrate-containing synthetic fertilizers, their characteristic N and
O isotope signatures are rarely unambiguously observed in nitrate-contaminated
groundwater. We postulate, in line with Mengis et al. (2001), that fertilizer-derived nitrate
is not directly and rapidly transferred to groundwater but rather retained in the
soil-plant system as organic N and then mineralized and re-oxidized (termed the
mineralization-immobilization turnover, MIT) thereby re-setting the oxygen isotope
composition of nitrate and also changing its N isotope ratios. We show examples from
watersheds on diverse alluvial/clastic and carbonate aquifers in eastern and northern France
where, in spite of the use of mineral fertilizers, evidenced also through other isotopic
tracers (boron isotopes), both N and O-isotope ratios are very homogeneous and
compatible with nitrification of ammonium where 2/3 of oxygen is derived from soil
water and 1/3 from atmospheric O2. These field data are corroborated by lysimeter
data from Canada. Even if in areas where ammonium is derived from chemical
fertilizers, N values still tend to be lower than in areas where ammonium is derived
from manure/sewage, this is clearly a limitation to the dual isotope method (N, O)
for nitrate source identification, but has important implications for the nitrogen
mobility and residence time in soils amended with synthetic fertilizers (Sebilo et al.,
2013).
Mengis M., Walther U., Bernasconi S. M., Wehrli B. (2001) Limitations of Using δ18O
for the Source Identification of Nitrate in Agricultural Soils. Environmental Science &
Technology, 35, 1840-1844.
Sebilo M., Mayer B., Nicolardot B., Pinay G., Mariotti A. (2013) Long-term fate of
nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences of the
United States of America, 110, 18185-18189. |
|
|
|
|
|
|