Abiotic Addition of Sulfide to Dissolved Organic Matter

Brett A. Poulin1,2, Joseph Nolte Ryan2, Kathryn Nagy3, Aron Stubbins4, Thorsten Dittmar5 and George Aiken1, (1)United States Geological Survey, Boulder, CO, United States, (2)University of Colorado Boulder, Environmental Engineering, Boulder, CO, United States, (3)Univ Illinois at Chicago, Chicago, IL, United States, (4)Skidaway Institute of Oceanography, University of Georgia, Savannah, GA, United States, (5)University of Oldenburg, Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Oldenburg, Germany
Abstract:
Sulfur-containing functional groups in dissolved organic matter (DOM) play important roles in controlling the chemical speciation and geochemistry of trace metals in surface waters, wetland soils, and pore waters. The abiotic addition of sulfide to DOM is recognized as an important mechanism responsible for the elevated concentration of sulfur and high relative abundance of reduced sulfur groups in DOM. Despite these observations, there is little experimental information on the organic molecules that sulfur incorporates into and the speciation of the incorporated sulfur. We present results from laboratory and field efforts that characterize changes in organic sulfur chemistry under sulfidic conditions. In the laboratory, Suwannee River hydrophobic organic acid (HPOA) was reacted with sulfide at an environmentally relevant sulfide-to-DOM concentration ratio (0.06 mol S2-(mol C)-1). Elemental composition and sulfur K-edge X-ray absorption near-edge structure (XANES) spectra of Suwannee River samples show a 55% molar increase in reduced sulfur accompanied by a shift in reduced sulfur speciation from primarily heterocyclic (75% of reduced S) to predominantly exocyclic (90% of reduced S) following sulfide exposure. An analysis of samples by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) reveals an increase in molecular formula assignments with sulfur heteroatoms (e.g., CHOS, CHONS) likely due to reactions with sulfide. For the field component, the HPOA fraction of DOM was isolated from surface and pore water samples collected from four locations across a sulfate gradient in the Florida Everglades. Elemental composition and FTICR-MS spectra of DOM samples show that the (1) organic sulfur content and (2) percentage of molecular formula assignments containing sulfur heteroatoms correspond with the aqueous sulfide concentration. The results provide insight into the alteration of DOM in sulfidic environments and its implications for sulfur cycling.
Back to: The Biogeochemistry of Dissolved Organic Matter (DOM) III