Metal-sulfide dynamics in a constructed wetland in the southeastern United States
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The DOE-NNSA Tritium Processing Facility at the Savannah River Site (SRS) releases effluent averaging 31.0 and 20.5 ppb Cu and Zn, respectively, to H-02 constructed wetland for remediation before release to Upper Three Runs Creek to meet compliance with state and federal water quality regulations. Comparison of acid-volatile sulfide (AVS) to organic carbon normalized simultaneously extracted metals (SEM) and SEM to total metals concentrations indicates some Cu and Pb and most Zn accumulating in surface sediments is sequestered in AVS and SEM extractable phases including metal-sulfides and organic carbon complexes. Although biogeochemical changes resulting from batch simulated sediment resuspension triggered release of enough total metals to exceed NPDES permit limits, DGT-bioavailable metals and BLM-generated inorganic dissolved metals data suggest a negligible increase in bioavailable metals, likely due to scavenging of released metals by particulate Fe(OH)3. Better understanding site-specific metal sequestration and (re)mobilization processes can lead to wetland design improvement.