(Solved): For nitrogen isotope analysis, atmospheric nitrogen is the standard for comparison comparing 15N ...

For nitrogen isotope analysis, atmospheric nitrogen is the standard for comparison comparing ${}^{15}\mathrm{N}$ to ${}^{14}\mathrm{N}$ abundance. The standard ratio for the two isotopes $=3.613\times 10^{?3}$. There is interest in quantifying the sources of nitrate in the Ohio river watershed. In addition to sampling point sources, stable isotope analysis has reported the following abundance of ${}^{15}\mathrm{N}$ to ${}^{14}\mathrm{N}$ in a subwatershed. An ${}^{18}\mathrm{O}/{}^{16}\mathrm{O}$ measurement has also been reported with a $?$ value of 5.5 . Estimate the likely source of nitrogen based on the figure below and isotope composition of $\mathrm{N}$ and $\mathrm{O}$.