Premium
Isotopic identification of soil and permafrost nitrate sources in an Arctic tundra ecosystem
Author(s) -
Heikoop Jeffrey M.,
Throckmorton Heather M.,
Newman Brent D.,
Perkins George B.,
Iversen Colleen M.,
Roy Chowdhury Taniya,
Romanovsky Vladimir,
Graham David E.,
Norby Richard J.,
Wilson Cathy J.,
Wullschleger Stan D.
Publication year - 2015
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2014jg002883
Subject(s) - permafrost , tundra , snowmelt , arctic , environmental science , nitrification , isotopic signature , environmental chemistry , nitrate , snow , nitrogen , atmospheric sciences , geology , ecology , geomorphology , stable isotope ratio , chemistry , oceanography , physics , organic chemistry , quantum mechanics , biology
The nitrate (NO 3 − ) dual isotope approach was applied to snowmelt, tundra active layer pore waters, and underlying permafrost in Barrow, Alaska, USA, to distinguish between NO 3 − derived from atmospheric deposition versus that derived from microbial nitrification. Snowmelt had an atmospheric NO 3 − signal with δ 15 N averaging −4.8 ± 1.0‰ (standard error of the mean) and δ 18 O averaging 70.2 ± 1.7‰. In active layer pore waters, NO 3 − primarily occurred at concentrations suitable for isotopic analysis in the relatively dry and oxic centers of high‐centered polygons. The average δ 15 N and δ 18 O of NO 3 − from high‐centered polygons were 0.5 ± 1.1‰ and −4.1 ± 0.6‰, respectively. When compared to the δ 15 N of reduced nitrogen (N) sources, and the δ 18 O of soil pore waters, it was evident that NO 3 − in high‐centered polygons was primarily from microbial nitrification. Permafrost NO 3 − had δ 15 N ranging from approximately −6‰ to 10‰, similar to atmospheric and microbial NO 3 − , and highly variable δ 18 O ranging from approximately −2‰ to 38‰. Permafrost ice wedges contained a significant atmospheric component of NO 3 − , while permafrost textural ice contained a greater proportion of microbially derived NO 3 − . Large‐scale permafrost thaw in this environment would release NO 3 − with a δ 18 O signature intermediate to that of atmospheric and microbial NO 3 . Consequently, while atmospheric and microbial sources can be readily distinguished by the NO 3 − dual isotope technique in tundra environments, attribution of NO 3 − from thawing permafrost will not be straightforward. The NO 3 − isotopic signature, however, appears useful in identifying NO 3 − sources in extant permafrost ice.