Materials and MethodsSurface water samples were collected in pre-combusted (450 °C, 6 hr) glass jars, filtered through pre-combusted (550 °C, 5.5 hr) glass fiber filters (0.7 m, Millipore) on site, and stored on ice for transport. Upon arrival in the laboratory, the samples were 0.22 m filtered (mixed cellulose esters, Millipore) and stored at 4 °C. The porewaters were collected by centrifugation 1 and were then 0.2 m filtered (PTFE, Pall Life Sciences). Sulfate and other anions were measured via ion chromatography (Dionex ICS 2000 with an AS19 4 mm column).Liquid state 1 H NMR spectra were obtained on a 400 MHz Bruker Biospin Avance III NMR equipped with a broadband inverse probe using a water suppression pulse program (optimized WATERGATE pulse sequence from Lam and Simpson 2 ) with a 2 sec recycle delay, a time domain of 16k, and 2000 co-added scans (approximately 3 hour run time). This sequence
Electron donating capacity (EDC) values were determined for a set of pore water samples collected from the sediments of four separate wetlands in the Cottonwood Lakes Study Area in Jamestown, ND by mediated electrochemical analysis, reaction with substituted nitro(so)benzenes, and calculation based on measured organic carbon and sulfide concentrations. The samples were taken from four hydrologically connected and increasingly sulfidic wetlands within the study site. Parallel trends in EDC values related to hydrologic conditions and to in situ reduced sulfur content were observed by all three methodologies. In particular, it was found that sulfide and dissolved organic matter (DOM) are the primary and secondary reductants, respectively, in these systems. The efficacy of these reductants in transforming organic contaminants, however, is largely driven by native pore water reduced sulfur content. Manipulation of the systems demonstrate that while DOM is capable of reducing highly oxidized contaminants or reactive intermediates, this likely only occurs once the reducing capacity of the sulfide is exhausted. Sulfide therefore was the dominant electron donor in the pore water samples.
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