ARTICLE pubs.acs.org/est
Isotopic Character of Nitrous Oxide Emitted from Streams Helen M. Baulch*,† Environmental and Life Sciences Graduate Program, Trent University, 1600 West Bank Drive, Peterborough ON K9J 7B8 Canada
Sherry L. Schiff and Simon J. Thuss‡ Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo ON N2L 3G1
Peter J. Dillon Department of Environmental and Resource Studies, Trent University, 1600 West Bank Drive, Peterborough ON K9J 7B8 Canada
bS Supporting Information ABSTRACT: Global models have indicated agriculturally impacted rivers and streams may be important sources of the greenhouse gas nitrous oxide (N2O). However, there is significant uncertainty in N2O budgets. Isotopic characterization can be used to help constrain N2O budgets. We present the first published measurements of the isotopic character of N2O emitted from low (24) order streams. Isotopic character of N2O varied seasonally, among streams, and over diel periods. On an annual basis, δ18O of emitted N2O (þ47.4 to þ51.4%; relative to VSMOW) was higher than previously reported for larger rivers, but δ15N of emitted N2O (16.2 to þ2.4% among streams; relative to atmospheric N2) was similar to that of past studies. On an annual basis, all streams emitted N2O with lower δ15N than tropospheric N2O. Given these streams have elevated nitrate concentrations which are associated with enhanced N2O fluxes, this supports the hypothesis that streams are contributing to the accumulation of 15N-depleted N2O in the troposphere.
’ INTRODUCTION Concentrations of the biogenic greenhouse gas nitrous oxide (N2O) are increasing in the atmosphere. Agricultural nitrogen (N) fertilization is the dominant cause of anthropogenic N2O emissions. The contribution of N2O to warming is modest in global terms (
