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Isotopic signals of summer denitrification in a northern hardwood forested catchment.

Authors
  • Wexler, Sarah K1
  • Goodale, Christine L2
  • McGuire, Kevin J3
  • Bailey, Scott W4
  • Groffman, Peter M5
  • 1 Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853; School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom; [email protected] [email protected] , (United Kingdom)
  • 2 Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853; [email protected] [email protected]
  • 3 Department of Forest Resources and Environmental Conservation, Virginia Water Resources Research Center, Virginia Tech, Blacksburg, VA 24061;
  • 4 US Forest Service, Northern Research Station, North Woodstock, NH 03262; and.
  • 5 Cary Institute of Ecosystem Studies, Millbrook, NY 12545.
Type
Published Article
Journal
Proceedings of the National Academy of Sciences
Publisher
Proceedings of the National Academy of Sciences
Publication Date
Nov 18, 2014
Volume
111
Issue
46
Pages
16413–16418
Identifiers
DOI: 10.1073/pnas.1404321111
PMID: 25368188
Source
Medline
Keywords
License
Unknown

Abstract

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 (δ(15)NNO3 and δ(18)ONO3) 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.

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