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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! N assimilation rate (Chl-normalised) |- | '''Approach:''' ¹⁵N tracer incubation, EA-IRMS, chlorophyll normalisation |- | '''Context:''' incubation, simulated ''in situ'' |- | '''Spatial sca..."

2026-05-12T17:44:17Z

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;" ! N assimilation rate (Chl-normalised) |- | '''Approach:''' 15N tracer incubation, EA-IRMS, chlorophyll normalisation |- | '''Context:''' incubation, simulated ''in situ'' |- | '''Spatial sca..."

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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;"
! N assimilation rate (Chl-normalised)
|-
| '''Approach:''' 15N tracer incubation, EA-IRMS, chlorophyll normalisation
|-
| '''Context:''' incubation, simulated ''in situ''
|-
| '''Spatial scale:''' point sample
|-
| '''Temporal scale:''' 12–24 h
|-
| '''Units:''' (x)mol N µg Chl-1 d-1
|-
| '''Community captured:''' all (usually > 0.2 µm)
|-
| '''Co-measurements:''' background δ15N (PON), ambient [NO3-], temperature, PAR, Chl, initial blank
|}
</div>
<div style="clear:both"></div>

== Method Overview ==

This is a normalised variant of the 15N-nitrate uptake method. The incubation and EA-IRMS measurement proceed identically to the bulk nitrate uptake method: 15N-labelled nitrate is added at tracer concentrations, samples are incubated under simulated ''in situ'' conditions, and the particulate fraction is filtered onto GFF filters for 15N enrichment analysis. The uptake rate is then normalised to the chlorophyll-a concentration measured in the same sample<ref name="Dugdale1986">Dugdale, R. C., & Wilkerson, F. P. (1986). The use of 15N to measure nitrogen uptake in eutrophic oceans; experimental considerations. ''Limnology and Oceanography'', 31(4), 673–689. https://doi.org/10.4319/lo.1986.31.4.0673</ref>. Chlorophyll normalisation removes the effect of varying biomass concentrations across samples, providing the chlorophyll-specific nitrogen assimilation rate (VNO3), which is directly comparable across environments and seasons without biomass correction.

=== Scale of measurement ===

Each incubation provides a point measurement. Incubation durations of 12–24 h yield daily-integrated rates. Chlorophyll normalisation does not change the temporal or spatial scale but improves ecological interpretability by removing biomass variability.

=== Data generated ===

Chlorophyll-specific nitrate uptake rate (VNO3, (x)mol N µg Chl-1 d-1). This rate reflects the physiological nitrogen acquisition capacity of the phytoplankton community per unit biomass and is used to compare nutrient acquisition across contrasting environments.

=== Units & currency ===

Units are (x)mol N µg Chl-1 d-1. The currency is nitrogen.

=== Sample size ===

Typical samples are 0.5–2 L in volume.

=== Repositories & databases ===

== Limitations ==

In addition to the standard assumptions of the 15N tracer method (steady-state system, negligible nitrification), the chlorophyll normalisation assumes that chlorophyll-a is an accurate and consistent proxy for phytoplankton biomass. This assumption is violated when chlorophyll:carbon ratios vary substantially due to photoacclimation, nutrient stress, or taxonomic shifts. Chl-specific rates cannot be directly converted to volumetric or areal uptake without a separate biomass estimate.

== Example Applications & Protocols ==

=== Classic examples ===
* Dugdale & Goering (1967) ''Uptake of new and regenerated forms of nitrogen in primary productivity'' <ref name="Dugdale1967">Dugdale, R. C., & Goering, J. J. (1967). Uptake of new and regenerated forms of nitrogen in primary productivity. ''Limnology and Oceanography'', 12(2), 196–206. https://doi.org/10.4319/lo.1967.12.2.0196</ref>
* Dugdale & Wilkerson (1986) ''The use of 15N to measure nitrogen uptake in eutrophic oceans'' <ref name="Dugdale1986" />

=== Recent applications ===
* Kafrissen et al. (2022) ''An 8-year record of phytoplankton productivity and nutrient distributions from surface waters of Saanich Inlet'' <ref name="Kafrissen2022">Kafrissen, M. E., Giesbrecht, K. E., Cronin, K., Strang, J., Quiring, W., & Varela, D. E. (2022). An 8-year record of phytoplankton productivity and nutrient distributions from surface waters of Saanich Inlet. ''Scientific Data'', 9, 434. https://doi.org/10.1038/s41597-022-01434-y</ref>

=== Common calculations/conversions ===
* VNO3 ((x)mol N µg Chl-1 d-1) = ρNO3- / [Chl].
* To recover volumetric rate: ρNO3- = VNO3 × [Chl].

== References ==

[[Category:Main Pages|Model types]]

15N-ρNO3/chl a (N assimilation rate) - Revision history