Isotopic signals of summer denitrification in a northern hardwood forested catchment

TitleIsotopic signals of summer denitrification in a northern hardwood forested catchment
Publication TypeJournal Article
Year of Publication2014
AuthorsWexler, SK, Goodale, CL, McGuire, KJ, Bailey, SW, Groffman, PM
JournalProceedings of the National Academy of Sciences
Pagination16413 - 16418
Date Published2014/11/18/
ISBN Number0027-8424, 1091-6490
KeywordsDenitrification, forested watershed, Nitrogen Cycle, Stable isotopes, streamwater chemistry

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.

Short TitlePNAS