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

^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

View larger version (17K): [in this window] [in a new window]   Fig. 1. Schematic diagram of snowmelt and forest floor lysimeters.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Daily cumulative precipitation, snowmelt, forest floor (FF) leachate and weekly snowpack water equivalent (SWE) (± standard error) for the period from when the chemical and isotopic tracers were applied (18 Feb. 2004) to the end of the snowmelt (22 Mar. 2004). Vertical bars indicate the daily quantity of precipitation (snow, rain, or snow–rain mix) at the study site with the scale shown on the secondary y axis.

View larger version (16K): [in this window] [in a new window]   Fig. 3. Fluxes of SO42––S, NH4+–N, and NO3––N in throughfall, snowmelt, and forest floor (FF) leachates for the snow-covered period (6 Dec. 2003–22 Mar. 2004). For each ion, different lowercase letters indicate significant differences among throughfall, snowmelt, and forest floor leachate fluxes ( = 0.05). Error bars indicate the standard error of the group means.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Mean daily soil temperature (primary y axis) at six depths (1, 3, 7, 15, 30, and 50 cm) and soil frost depth (secondary y axis) measured from January to April 2004. Error bars for soil frost indicate standard errors of the means.

View larger version (11K): [in this window] [in a new window]   Fig. 5. Isotopic [(a) 34S–SO42–, (b) 15N–NO3–, (c) 15N–NH4+, and (e) 18O–NO3–] and (d) Br– values measured in throughfall, snowpack, snowmelt, and forest floor (FF) leachates from 31 Dec. 2003 to 8 June 2004. The dashed line indicates the date of the tracer application (18 Feb. 2004), which consisted of enriched 34S–SO42–, 15N–NO3–, and Br–.

View larger version (16K): [in this window] [in a new window]   Fig. 6. Potassium chloride-extractable and microbial biomass 15N values measured before the isotopic tracer addition (18 Feb. 2004), during snowmelt (4 Mar. 2004), and in midsummer (12 July 2004). Different lowercase letters indicate significant differences in KCl-extractable 15N and microbial biomass 15N among the three sampling dates ( = 0.05). Error bars indicate the standard error of the group means.