Routine measurement of dissolved inorganic N-15 in precipitation and streamwater

The difficulty of measuring N-15 in dilute solutions has limited the potent ial of ecosystem labeling experiments and model comparisons. By concentrati ng the N from large (up to 20 L) water samples on ion-exchange resin column s we obtained enough N for accurate and reproducible N-15 measurement using the Teflon tape diffusion method Analysis of standards demonstrated >95% r ecovery of inorganic N from samples, and delta(15)N values comparable to th ose obtained using standard distillation methods. The value of the blank at our laboratory was 0.16 mu moles N. Analytical precision was within 2 part s per thousand delta(15)N when samples of streamwater from the Bear Brook w atersheds (1800 eq.ha(-1).yr(-1) N addition at 192 parts per thousand delta (15)N) were kept frozen until analysis. The analytical process is lengthy, but once set up can easily be performed for large numbers of samples.