Microscale Characterization of Sulfur Speciation in Lake Sediments

• Published in: Environmental science & technology Vol. 47; no. 3; pp. 1287 - 1296
• Main Authors: Zeng, Teng, Arnold, William A, Toner, Brandy M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05.02.2013
• Subjects: Carbon - analysis; Earth sciences; Earth, ocean, space; Ecosystem; Engineering and environment geology. Geothermics; Exact sciences and technology; Fluorescence; Geochemistry; Geologic Sediments - chemistry; Hydrogen-Ion Concentration; Iron - chemistry; Lakes; Lakes - chemistry; Marine and continental quaternary; Mineralogy; Oxidation-Reduction; Pollution, environment geology; Porosity; Seasons; Sediments; Silicates; Sulfates - analysis; Sulfides - analysis; Sulfides - chemistry; Sulfur; Sulfur - analysis; Surface Properties; Surficial geology; Thermodynamics; United States; Water geochemistry; Wetlands; X-Ray Absorption Spectroscopy; North America; lake sediments; X-ray fluorescence; solid phase; pore water; sulfur; X-ray spectra; sulfates; North America; seasonal variations; dissolved organic carbon; speciation
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es303914q

Prairie pothole lakes (PPLs) are naturally sulfur-enriched wetlands in the glaciated prairie region of North America. High sulfate levels and dynamic hydrogeochemistry in combination render PPLs a unique environment to explore the speciation of sedimentary sulfur (S). The goals of this research were to define and quantify the solid-phase S pools in PPL sediments and track seasonal dynamics of S speciation. A quantitative X-ray microprobe method was developed based on S 1s X-ray absorption near-edge structure (XANES) spectroscopy and multienergy X-ray fluorescence mapping. Three S pools–pyritic S, reduced organic S (organic mono- and disulfide), and oxidized S (inorganic sulfate, ester sulfate, and sulfonate)–were identified in PPL sediments. No significant seasonal variation was evident for total S, but S speciation showed a seasonal response. During the spring–summer transition, the reduced organic S decreased from 55 to 15 mol %, with a concomitant rise in the oxidized S. During the summer–fall transition, the trend reversed and the reduced organic S grew to 75 mol % at the expense of the oxidized S. The pyritic S, on the other hand, remained relatively constant (∼22 mol %) over time. The seasonal changes in S speciation have strong potential to force the cycling of elements such as mercury in prairie wetlands.