Bernhard Mayer Myron J. Mitchell Scott W. Bailey James B. Shanley 2008 <p><span>Stable sulfur (S) isotope ratios can be used to identify the sources of sulfate contributing to streamwater. We collected weekly and high-flow stream samples for S isotopic analysis of sulfate through the entire water year 2003 plus the snowmelt period of 2004. The study area was the 41-ha forested W-9 catchment at Sleepers River Research Watershed, Vermont, a site known to produce sulfate from weathering of sulfide minerals in the bedrock. The&nbsp;</span><i>&delta;</i>³⁴<span>S values of streamwater sulfate followed an annual sinusoidal pattern ranging from about 6.5&permil; in early spring to about 10&permil; in early fall. During high-flow events,&nbsp;</span><i>&delta;</i>³⁴<span>S values typically decreased by 1 to 3&permil; from the prevailing seasonal value. The isotopic evidence suggests that stream sulfate concentrations are controlled by: (1) an overall dominance of bedrock-derived sulfate (</span><i>&delta;</i>³⁴<span>S ~&nbsp;6&ndash;14&permil;); (2) contributions of pedogenic sulfate (</span><i>&delta;</i>³⁴<span>S ~&nbsp;5&ndash;6&permil;) during snowmelt and storms with progressively diminishing contributions during base flow recession; and (3) minor effects of dissimilatory bacterial sulfate reduction and subsequent reoxidation of sulfides. Bedrock should not be overlooked as a source of S in catchment sulfate budgets.</span></p> application/pdf 10.1016/j.scitotenv.2008.03.020 en Elsevier Seasonal and event variations in δ³⁴S values of stream sulfate in a Vermont forested catchment: Implications for sulfur sources and cycling article