Use of mixed ion exchange resin and the denitrifier method to determine isotopic values of nitrate in atmospheric deposition and canopy throughfall

The objective of this study was to test a technique that utilizes mixed bed resins and the denitrifier method to determine δ15N and δ18O of nitrate inputs under varying conditions found in the field. Temperature increases and greater loading of nitrogen led to significant increases in δ18O values and longer incubation times led to significant increases in δ15N values, but the changes were relatively small. Results of our study confirm that mixed ion exchange resin can be used to accurately measure natural abundance isotopic values of nitrate in samples of atmospheric deposition and throughfall. However, we also conclude that caution should be applied when using these mixed bed resins in the field if they will be exposed to high temperatures (e.g., >40 °C). This method can increase the feasibility of conducting high density sampling of stable isotopes in atmospheric deposition and canopy throughfall samples with the goal of identifying sources of nitrate, and thus represents an important methodological advance for ecosystem science.