Publication Date:
2015-05-14
Description:
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.
Print ISSN:
0148-0227
Topics:
Biology
,
Geosciences
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