In geochemistry, hydrology, paleoclimatology and paleoceanography δ15N (pronounced "delta fifteen n") or delta-N-15 is a measure of the ratio of stable isotopes 15N:14N.
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Formulas
Two very similar expressions for δ15N are in wide use in hydrology. Both have the form
Applications
One use of 15N is as a tracer to determine the path taken by fertilizers applied to anything from pots to landscapes. Fertilizer enriched in 15N 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 δ15N.
Another application is to assessment of human waste water discharge into bodies of water. The abundance of 15N is greater in human waste water than in natural water sources. Hence δ15N in benthic sediment gives an indication of the contribution of human waste to the total nitrogen in the sediment. Sediment cores analyzed for δ15N yield an historical record of such waste, with older samples at greater depths.