Isotopic signals of summer denitrification in a northern hardwood forested catchment

Sarah K Wexler (Lead Author), Christine L Goodale, Kevin J McGuire, Scott W Bailey, Peter M Groffman

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)


Despite decades of measurements, the nitrogen balance of temperate forest catchments remains poorly understood. Atmospheric nitrogen deposition often greatly exceeds streamwater nitrogen losses; the fate of the remaining nitrogen is highly uncertain. Gaseous losses of nitrogen to denitrification are especially poorly documented and are often ignored. Here, we provide isotopic evidence (δ15NNO3 and δ18ONO3) from shallow groundwater at the Hubbard Brook Experimental Forest indicating extensive denitrification during midsummer, when transient, perched patches of saturation developed in hillslopes, with poor hydrological connectivity to the stream, while streamwater showed no isotopic evidence of denitrification. During small rain events, precipitation directly contributed up to 34% of streamwater nitrate, which was otherwise produced by nitrification. Together, these measurements reveal the importance of denitrification in hydrologically disconnected patches of shallow groundwater during midsummer as largely overlooked control points for nitrogen loss from temperate forest catchments.
Original languageEnglish
Pages (from-to)16413-16418
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America (PNAS)
Issue number6
Early online date3 Nov 2014
Publication statusPublished - 18 Nov 2014


  • nitrogen cycle
  • denitrification
  • stable isotopes
  • forested watershed
  • streamwater chemistry

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