Seasonal Sulfur Redox Cycling in Two Constructed Wetlands with Insight on How They Age.

Long-term metal remediation in wetland treatment systems (WTSs) involves facilitating dissimilatory sulfate reduction to produce sulfide and mineralize metals in deep sediments. We evaluated seasonal sulfur cycling in two constructed wetlands (Maintained WTS constructed in 2007, and the Unmaintained WTS constructed in 2000) on the Savannah River Site in Aiken, South Carolina, USA. Significant interactions in sulfide concentration were observed between sediment depth, season, and wetland (F = 4.64, df = 11, P = 3.28 × 10 - 5). In the Maintained WTS, dissimilatory sulfate reduction dominated the surface sediments during the warm season (0-2 cm depth, t=-2.66, P = 9.70 × 10 - 3), unlike the Unmaintained system. Sulfate concentrations in pore waters increased in the warm season (F = 7.84, df = 1, P = 6.50 × 10 - 3), contrary to expectations. Sulfur limitation in the Unmaintained WTS during the warm season correlated with increased sulfur assimilation in giant bulrush. Lower sulfide concentrations in surface sediments of the Unmaintained WTS illustrated aging effects. The Maintained WTS shows potential for managing erosion, pH reduction, and sulfur limitation observed in the older Unmaintained WTS.