HR: 0830h
AN: B21D-0746    [PDF]
TI: Differentiating atmospheric and mineral sources of sulfur during snowmelt using $\delta^{34}$S, $^{35}$S activity, and $\delta^{18}$O of sulfate and water as tracers
AU: * Shanley, J B
EM: jshanley@usgs.gov
AF: U.S. Geological Survey, Box 628, Montpelier, VT 05601 United States
AU: Mayer, B
EM: bernhard@geo.ucalgary.ca
AF: University of Calgary, 2500 University Drive NW, Calgary, AB T2N IN4 Canada
AU: Mitchell, M J
EM: mitchell@syr.edu
AF: SUNY - Envi. Sci. and Forestry, One Forestry Drive, Syracuse, NY 13210 United States
AU: Michel, R L
EM: rlmichel@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 434, Menlo Park, CA 94025 United States
AU: Bailey, S
EM: Scott.Bailey@unh.edu
AF: U. S. Forest Service, Hubbard Brook Experimental Forest R.R.#1, Box 779, Campton, NH 03223 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 434, Menlo Park, CA 94025 United States
AB: The biogeochemical cycling of sulfur was studied during the 2000 snowmelt at Sleepers River Research Watershed in northeastern Vermont, USA using a combination of isotopic, chemical, and hydrometric measurements. The snowpack and 10 streams of varying size and land use were sampled for sulfate concentrations and isotopic analyses of $^{35}$S, $\delta^{34}$S, and $\delta^{18}$O of sulfate. Values of $\delta^{18}$O of water were measured at one of the streams. Apportionment of atmospheric and mineral S sources based on $\delta^{34}$S was possible at 7 of the 10 streams. Weathering of S-containing minerals was a major contributor to sulfate flux in streamwater, but atmospheric contributions exceeded 50% in several of the streams at peak snowmelt and averaged 41% overall. In contrast, $\delta^{18}$O$_{sulfate}$ values of streamwater remained significantly lower than those of atmospheric sulfate throughout the melt period, indicating that atmospheric sulfate undergoes microbial redox reactions in the soil that replace the oxygen of atmospheric sulfate with isotopically lighter oxygen from soil water. Streamwater $^{35}$S activities were low relative to those of the snowpack; the youngest $^{35}$S-ages of the atmospheric S component in each of the 7 streams ranged from 184 to 320 days. Atmospheric S contributions to streamwater, as determined by $\delta^{34}$S values, co-varied both with $^{35}$S activity and new water contributions as determined by $\delta^{18}$O$_{water}$. However, the $\delta^{18}$O$_{sulfate}$ and $^{35}$S ages clearly show that this new water carries very little of the atmospheric sulfate entering with the current snowmelt to the stream. Most incoming atmospheric sulfate first cycles through the organic soil S pool and ultimately reaches the stream as pedogenic sulfate.
DE: 0317 Chemical kinetic and photochemical properties
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 1806 Chemistry of fresh water
SC: Biogeosciences [B]
MN: 2003 Fall Meeting