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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Denitrification rate (¹⁵N isotope pairing) |- | '''Approach:''' ¹⁵N-nitrate addition; ¹⁵N₂ and ¹⁵N₂O production measured by MIMS/GC-IR..."

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Created page with "{{BreadcrumbsNutrients}} * Page authors: PRIMO * Responsible curator: Hagen Buck-Wiese ---- __TOC__ <div class="model-box"> {| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Denitrification rate (15N isotope pairing) |- | '''Approach:''' 15N-nitrate addition; 15N2 and 15N2O production measured by MIMS/GC-IR..."

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* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Denitrification rate (15N isotope pairing)
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| '''Approach:''' 15N-nitrate addition; 15N2 and 15N2O production measured by MIMS/GC-IRMS
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| '''Context:''' incubation, lab
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| '''Spatial scale:''' point sample
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| '''Temporal scale:''' hours
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| '''Units:''' µmol N m-2 d-1; nmol N L-1 d-1
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| '''Community captured:''' bulk
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| '''Co-measurements:''' nitrate and nitrite concentrations, N2 and N2O concentrations
|}
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== Method Overview ==

The 15N isotope pairing technique (IPT) measures denitrification directly by tracking the production of 15N-labelled dinitrogen gas. 15N-nitrate (K15NO3) is added to anoxic or suboxic incubations, and denitrifiers reduce the labelled nitrate to N2 and N2O. Because both 14NO3- and 15NO3- are present, the N2 produced contains three isotopologue combinations: 14N14N (from two unlabelled nitrate), 14N15N (from one of each), and 15N15N (from two labelled nitrate). The ratio of these isotopologues, measured by MIMS (membrane inlet mass spectrometry) or GC-IRMS, allows total denitrification to be calculated from the labelled fraction alone<ref name="Steingruber2001">Steingruber, S. M., Friedrich, J., Gächter, R., & Wehrli, B. (2001). Measurement of denitrification in sediments with the 15N isotope pairing technique. ''Applied and Environmental Microbiology'', 67(9), 3771–3778. https://doi.org/10.1128/AEM.67.9.3771-3778.2001</ref>. This approach provides direct, unambiguous measurement of N2 production without relying on proxy gases or inhibitors.

=== Scale of measurement ===

Point sample; short incubations (hours) under suboxic or anoxic conditions. The method can be applied to water column samples or sediment slurries.

=== Data generated ===

Denitrification rates in nmol N2-N L-1 d-1 or µmol N m-2 d-1 (for sediment measurements). The 15N2O fraction provides a simultaneous estimate of incomplete denitrification to N2O.

=== Units & currency ===

Units are nmol N2-N L-1 d-1 or µmol N m-2 d-1. The currency is nitrogen.

=== Sample size ===

Typical samples are 250 mL to 1 L in volume.

=== Repositories & databases ===

== Limitations ==

The method assumes that isotope pairing patterns follow a binomial distribution, which requires complete mixing of labelled and unlabelled nitrate and uniform access by denitrifying organisms to both substrate pools. Anammox organisms also produce 15N-labelled N2 from the added 15NO3-/15NO2-, which can overestimate denitrification rates if not corrected for. Isotope dilution from unlabelled nitrate regeneration during the incubation reduces sensitivity.

== Example Applications & Protocols ==

=== Classic examples ===
* Steingruber et al. (2001) ''Measurement of denitrification in sediments with the 15N isotope pairing technique'' <ref name="Steingruber2001" />

=== Recent applications ===
* Bourbonnais et al. (2024) ''Denitrification in oxygen minimum zones'' <ref name="Bourbonnais2024">Bourbonnais, A., Reistetter, E., Bange, H. W., Duhamel, S., Fripiat, F., Granger, J., Loick-Wilde, N., Marconi, D., Somes, C., Tuerena, R. E., & Altabet, M. A. (2024). Advances in understanding the marine nitrogen cycle in the GEOTRACES era. ''Oceanography'', 37(2). https://doi.org/10.5670/oceanog.2024.406</ref>

=== Common calculations/conversions ===
* Total denitrification rate Dtotal = D14 + D15; where D15 = (14N15N + 2 × 15N15N) / 2 × atom% 15N enrichment.

== References ==

[[Category:Main Pages|Model types]]

15N tracer-based method - Revision history