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This article in SSSAJ

  1. Vol. 71 No. 6, p. 1934-1944
     
    Received: Aug 14, 2006


    * Corresponding author(s): jlcampbell@fs.fed.us
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doi:10.2136/sssaj2006.0283

Mobility of Nitrogen-15-Labeled Nitrate and Sulfur-34-Labeled Sulfate during Snowmelt

  1. John L. Campbell *a,
  2. Myron J. Mitchellb,
  3. Bernhard Mayerc,
  4. Peter M. Groffmand and
  5. Lynn M. Christensond
  1. a U.S. Forest Service, PO Box 640, Durham, NH 03824
    b State Univ. of New York, College of Environmental Science and Forestry, 1 Forestry Dr. Syracuse, NY 13210
    c Univ. of Calgary, 2500 University Dr. NW, Calgary, AB, Canada T2N 1N4
    d Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545-0129

Abstract

The objective of this study was to investigate the winter dynamics of SO4 2− and NO3 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% 34S as H2 34SO4 and 99 atom% 15N as NH4 15NO3 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 34SO4 2− and 15NO3 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 SO4 2− and NO3 were conservative in the snowpack, with tracer recoveries near 100%. In contrast, only 54 to 62% of the 34SO4 2− and 49 to 58% of the 15NO3 were recovered in forest floor leachates, suggesting that much of the SO4 2− and NO3 that infiltrated the forest floor during snowmelt was retained or transformed. Microbial biomass δ15N values in the forest floor remained low during snowmelt and the natural abundance values of δ18O–NO3 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 NO3 was insignificant in the forest floor during snowmelt.

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