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Isotopic Evidence for Determining the Sources of Dissolved Organic Sulfur in a Forested Catchment

Kang, Phil-Goo, Mitchell, Myron J., Mayer, Bernhard, Campbell, John L.
Environmental Science & Technology 2014 v.48 no.19 pp. 11259-11267
acidification, aluminum, biogeochemistry, forested watersheds, groundwater, methylmercury compounds, solutes, stable isotopes, streams, sulfur, surface water, toxicity, Adirondacks, New York
Understanding sulfur (S) biogeochemistry, especially in those watersheds subject to elevated levels of atmospheric S inputs, is needed for determining the factors that contribute to acidification, nutrient losses and the mobilization of toxic solutes (e.g., monomeric aluminum and methylmercury). S is found in a variety of both organic and inorganic forms undergoing a range of biotic and abiotic transformations. In watersheds with decreasing atmospheric S inputs, internal cycling is becoming dominant in affecting whether there is net loss or retention of S. Little attention has been given to the role of dissolved organic S (DOS) in affecting S biogeochemistry. DOS originates from assimilatory and bacterial dissimilatory S reduction (BDSR), the latter of which produces ³⁴S-depleted S. Within groundwater of the Archer Creek Catchment in the Adirondack Mountains (New York) there was reoxidation of reduced S, which was an important source of SO₄²–. DOS in surface waters had a higher variation of δ³⁴S–DOS values (−6.0 to +8.4‰) than inorganic S with δ³⁴S–SO₄²– values ranging from +1.0 to +5.8‰. Inverse correlations between δ³⁴S values of SO₄²– and DOS suggested that BDSR played an important role in producing DOS.