text: The ratio of N to N is of relevance because in most biological contexts, N is preferentially uptaken as the lighter isotope. As a result, samples enriched in N can often be introduced through a non-biological context.
  One use of N is as a tracer to determine the path taken by fertilizers applied to anything from pots to landscapes.  Fertilizer enriched in 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 .
  Another application is the assessment of human waste water discharge into bodies of water.  The abundance of N  is greater in human waste water than in natural water sources.  Hence  in benthic sediment gives an indication of the contribution of human waste to the total nitrogen in the sediment.  Sediment cores analyzed for  yield an historical record of such waste, with older samples at greater depths.
   is also used to measure food chain length and the trophic level of a given organism; high  values are positively correlated with higher trophic levels; likewise, organisms low on the food chain generally exhibit lower  values. Higher  values in apex predators generally indicate longer food chains.