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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Denitrification isotope fingerprint (δ¹⁵N, δ¹⁸O-NO₃) |- | '''Approach:''' natural abundance IRMS of δ¹⁵N and δ¹⁸O in nitrate |- | '''Context:..."

2026-05-12T23:09:36Z

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 isotope fingerprint (δ15N, δ18O-NO3) |- | '''Approach:''' natural abundance IRMS of δ15N and δ18O in nitrate |- | '''Context:..."

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{{BreadcrumbsNutrients}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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<div class="model-box">
{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Denitrification isotope fingerprint (δ15N, δ18O-NO3)
|-
| '''Approach:''' natural abundance IRMS of δ15N and δ18O in nitrate
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| '''Context:''' ''in situ''
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| '''Spatial scale:''' point sample
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| '''Temporal scale:''' days to weeks (integrative)
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| '''Units:''' ‰ (per mil) δ15N-NO3- and δ18O-NO3-
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| '''Community captured:''' bulk
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| '''Co-measurements:''' nitrate concentrations
|}
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== Method Overview ==

The dual isotopic composition of dissolved nitrate — δ15N-NO3- and δ18O-NO3- — is measured in water samples collected in situ. During denitrification, both 14N and 16O are preferentially consumed, enriching the residual nitrate pool in both 15N and 18O in a near-1:1 molar ratio. Nitrification, by contrast, produces new NO3- with low δ15N and δ18O, diluting isotopic signatures. The divergence or convergence of δ15N and δ18O in nitrate therefore serves as a qualitative and semi-quantitative indicator of active denitrification versus nitrification. Isotope ratio mass spectrometry (IRMS) is performed after conversion of NO3- to N2O by bacterial denitrifiers (denitrifier method).

=== Scale of measurement ===

Point sample. The isotopic signal integrates over the timescale at which the nitrate pool turns over through biological activity, typically days to weeks in the euphotic zone and much longer in the deep ocean.

=== Data generated ===

δ15N-NO3- and δ18O-NO3- values (‰ vs. air N2 and VSMOW). The slope of the δ15N vs. δ18O relationship (ideally 1:1 for denitrification) and deviations from it constrain the relative roles of denitrification and nitrification.

=== Units & currency ===

Units are ‰ (per mil). The currency is nitrogen.

=== Sample size ===

Typical samples are 20–100 mL in volume (frozen immediately after collection for later analysis).

=== Repositories & databases ===

== Limitations ==

The isotopic signatures of denitrification can be driven by multiple simultaneous nitrate sources and sinks with overlapping signatures, making unique attribution difficult without additional data. Isotope exchange between δ18O-NO3- and ambient water can complicate the δ18O signal. Quantitative interpretation requires isotope mass-balance or inverse models. The method cannot distinguish between different denitrifying organisms or environments (water column vs. sediment) from water column measurements alone.

== Example Applications & Protocols ==

=== Classic examples ===
*

=== Recent applications ===
* Bourbonnais et al. (2024) ''Advances in understanding the marine nitrogen cycle in the GEOTRACES era'' <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 ===
* Isotopic enrichment factor ε (‰) = 1000 × (α − 1), where α = klight/kheavy; for denitrification ε15N ≈ −15 to −30‰.

== References ==

[[Category:Main Pages|Model types]]

Natural Abundances of 15N and 18O - Revision history