View source for Δ15N

{{Short description|Measure of the ratio of stable isotopes nitrogen-15 and nitrogen-14}}
{{DISPLAYTITLE:''δ''<sup>15</sup>N}}
In  [[geochemistry]], [[hydrology]], [[paleoclimatology]] and [[paleoceanography]], '''''δ''<sup>15</sup>N'''  (pronounced "delta fifteen n") or '''delta-N-15''' is a measure of the ratio of the two [[stable isotope]]s of [[nitrogen]], [[Nitrogen-15|<sup>15</sup>N]]:[[Nitrogen-14|<sup>14</sup>N]].<ref>{{cite book | last=Katzenberg | first=MA | title=Biological Anthropology of the Human Skeleton | chapter=Chapter 13: Stable Isotope Analysis: A Tool for Studying Past Diet, Demography, and Life History | year=2008 | publisher=Wiley | edition=2nd | isbn=978-0-471-79372-4 }}</ref>

==Formulas==

Two very similar expressions for {{delta|15|N}} are in wide use in [[hydrology]].<ref name="hed">{{cite journal|last=Bedard-Haughn|first=A.|title=Tracing {{delta|15|N}} through landscapes: potential uses and precautions|journal=Journal of Hydrology|volume=272|pages=175–190|year=2003|issue=1–4|bibcode=2003JHyd..272..175B|doi=10.1016/S0022-1694(02)00263-9}}</ref>  Both have the form <math>1000\cdot\frac{s-a}a</math> ‰ (‰ = permil or parts per thousand) where ''s'' and ''a'' are the relative abundances of <sup>15</sup>N in respectively the sample and the atmosphere.  The difference is whether the relative abundance is with respect to all the nitrogen, i.e. <sup>14</sup>N plus <sup>15</sup>N, or just to <sup>14</sup>N.  Since the atmosphere is 99.6337% <sup>14</sup>N and 0.3663% <sup>15</sup>N, ''a'' is 0.003663 in the former case and 0.003663/0.996337 = 0.003676 in the latter.  However ''s'' varies similarly; for example if in the sample <sup>15</sup>N is 0.385% and <sup>14</sup>N is 99.615%, ''s'' is 0.003850 in the former case and 0.00385/0.99615 = 0.003865 in the latter.  The value of <math>1000\cdot\frac{s-a}a</math> is then 51.05‰ in the former case and 51.38‰ in the latter, an insignificant difference in practice given the typical range of {{val|-20 |to| 80}} for {{delta|15|N}}.

==Applications==
The ratio of <sup>15</sup>N to <sup>14</sup>N is of relevance because in most biological contexts, <sup>14</sup>N is preferentially uptaken as the lighter isotope. As a result, samples enriched in <sup>15</sup>N can often be introduced through a non-biological context.

One use of <sup>15</sup>N is as a tracer to determine the path taken by fertilizers applied to anything from pots to landscapes.<ref name="hed" />  Fertilizer enriched in <sup>15</sup>N to an extent significantly different from that prevailing in the soil (which may be different from the atmospheric standard ''a'') is applied at a point and other points are then monitored for variations in {{delta|15|N}}.<ref>{{Cite journal |last1=Janovský |first1=Martin P. |last2=Ferenczi |first2=Laszlo |last3=Trubač |first3=Jakub |last4=Klír |first4=Tomáš |date=2024-06-26 |title=Stable isotope analysis in soil prospection reveals the type of historic land-use under contemporary temperate forests in Europe |journal=Scientific Reports |language=en |volume=14 |issue=1 |pages=14746 |doi=10.1038/s41598-024-63563-1 |issn=2045-2322 |pmc=11208554 |pmid=38926400}}</ref>

Another application is the assessment of human waste water discharge into bodies of water.<ref>{{Cite web | url=http://longislandsoundstudy.net/2010/07/sediment-delta-15/ |title = Sediment Delta 15N|date = 23 July 2010}}</ref>  The abundance of <sup>15</sup>N  is greater in human waste water than in natural water sources.  Hence {{delta|15|N}} in [[Benthic zone|benthic]] sediment gives an indication of the contribution of human waste to the total nitrogen in the sediment.  Sediment cores analyzed for {{delta|15|N}} yield an historical record of such waste, with older samples at greater depths.

{{delta|15|N}} is also used to measure food chain length and the trophic level of a given organism; high {{delta|15|N}} values are positively correlated with higher trophic levels; likewise, organisms low on the food chain generally exhibit lower {{delta|15|N}} values. Higher {{delta|15|N}} values in [[apex predator]]s generally indicate longer food chains.<ref>{{cite journal |last1=Perkins |first1=Matthew J. |last2=McDonald |first2=Robbie A. |last3=Van Veen |first3=F. J. Frank |last4=Kelly |first4=Simon D. |last5=Rees |first5=Gareth |last6=Bearhop |first6=Stuart |date=27 March 2014 |title=Application of Nitrogen and Carbon Stable Isotopes (δ15N and δ13C) to Quantify Food Chain Length and Trophic Structure |journal=[[PLOS One]] |volume=9 |issue=3 |pages=e93281 |doi=10.1371/journal.pone.0093281 |pmid=24676331 |pmc=3968125 |bibcode=2014PLoSO...993281P |doi-access=free }}</ref>

== References ==

<references/>

== See also ==
* {{delta|13|C|link}}
* {{delta|18|O|link}}
* {{delta|34|S|link}}
* [[Isotopic signature]]
* [[Isotope analysis]]
* [[Isotope geochemistry]]

{{DEFAULTSORT:Delta15N}}
[[Category:Bioindicators]]
[[Category:Nitrogen]]
[[Category:Isotopes of nitrogen]]
[[Category:Environmental isotopes]]
[[Category:Geochemistry]]


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