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

Area of Science:

• Environmental Science
• Geochemistry
• Ecology

Background:

• Long-term metal remediation in wetland treatment systems (WTSs) relies on dissimilatory sulfate reduction in sediments.
• Understanding seasonal sulfur cycling is crucial for optimizing WTS performance and longevity.

Purpose of the Study:

• To evaluate and compare seasonal sulfur cycling in a maintained WTS and an unmaintained WTS.
• To assess the impact of wetland age and maintenance on dissimilatory sulfate reduction and metal remediation.

Main Methods:

• Field study comparing two constructed wetlands (Maintained WTS, est. 2007; Unmaintained WTS, est. 2000) on the Savannah River Site.
• Analysis of seasonal sulfide and sulfate concentrations in sediment and pore water at varying depths.
• Correlation of sulfur cycling with plant sulfur assimilation (giant bulrush).

Main Results:

• Significant interactions between sediment depth, season, and wetland type influenced sulfide concentrations.
• Dissimilatory sulfate reduction was dominant in the surface sediments of the Maintained WTS during the warm season.
• Contrary to expectations, sulfate concentrations in pore waters increased in the warm season, and sulfur limitation was observed in the Unmaintained WTS, linked to plant assimilation.

Conclusions:

• The Maintained WTS demonstrates effective sulfur cycling and potential for metal remediation, contrasting with aging effects in the Unmaintained WTS.
• Wetland maintenance is critical for sustaining dissimilatory sulfate reduction and preventing sulfur limitation.
• The Maintained WTS offers a model for managing erosion, pH, and sulfur dynamics in constructed wetlands.