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Mobility of Nitrogen‐15‐Labeled Nitrate and Sulfur‐34‐Labeled Sulfate during Snowmelt
Author(s) -
Campbell John L.,
Mitchell Myron J.,
Mayer Bernhard,
Groffman Peter M.,
Christenson Lynn M.
Publication year - 2007
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2006.0283
Subject(s) - snowmelt , forest floor , throughfall , environmental chemistry , snow , lysimeter , tracer , sulfate , snowpack , nitrate , chemistry , leaching (pedology) , meltwater , mineralization (soil science) , nitrogen , leachate , environmental science , hydrology (agriculture) , soil water , geology , soil science , physics , geotechnical engineering , organic chemistry , geomorphology , nuclear physics
The objective of this study was to investigate the winter dynamics of SO 4 2− and NO 3 − in a forested soil to better understand controls on these acidifying anions during snowmelt. In February 2004, a stable isotopic tracer solution with 93 atom% 34 S as H 2 34 SO 4 and 99 atom% 15 N as NH 4 15 NO 3 was applied to the snowpack at the Hubbard Brook Experimental Forest in New Hampshire. The chemical and isotopic compositions of throughfall, snow, snowmelt, and forest floor leachates were monitored for 10 mo following the addition of the tracers. The 34 SO 4 2− and 15 NO 3 − tracer amounts in forest floor leachates were highest in the first fractions of meltwater and declined exponentially until returning to ambient levels in mid‐May. Isotopic mass balances indicated that SO 4 2− and NO 3 − were conservative in the snowpack, with tracer recoveries near 100%. In contrast, only 54 to 62% of the 34 SO 4 2− and 49 to 58% of the 15 NO 3 − were recovered in forest floor leachates, suggesting that much of the SO 4 2− and NO 3 − that infiltrated the forest floor during snowmelt was retained or transformed. Microbial biomass δ 15 N values in the forest floor remained low during snowmelt and the natural abundance values of δ 18 O–NO 3 − in forest floor leachates were indicative of an atmospheric rather than a microbial source. These results suggest that, in this study, microbial immobilization and subsequent mineralization and nitrification of snowpack NO 3 − was insignificant in the forest floor during snowmelt.