Spatiotemporal Changes in Trace Metal Bioavailability in The Sediment Porewater of a Constructed Wetland Using Passive Porewater Samplers.

Sediments in aquatic systems often act as a major sink for contaminants. Diffusive gradient in thin films (DGTs) and in situ equilibrium dialysis samplers (peepers) are two major in situ porewater sampling devices that overcome the problems associated with conventional porewater sampling methods. In this study, DGTs and peepers were used to study the spatial and seasonal effects (cool months: October-February, warm months: May-September) on metal bioavailability in the H-02 constructed wetland, and the sink vs. source role of the sediments by calculating the metal resupply capacity (R). Data showed similar seasonal trends in metal concentrations using both passive samplers, peepers and DGTs. Pooled Cu and Zn concentrations measured using DGTs were lower in warm months (1.67 ± 1.50 and 2.62 ± 0.68 μg.L -1 , respectively, p < 0.001) vs. (2.12 ± 0.65 and 5.58 ± 1.33 μg.L -1 , respectively, p < 0.001) in cool months (mean ± 95% Confidence Intervals). Sulfate (SO 4 2- ) concentrations were significantly (p = 0.0139) lower in warm months (averaged at 0.22 ± 0.05 mg.L -1 ) compared to (0.16 ± 0.05 mg.L -1 ) in cool months. The increase in SO 4 2- concentration is an indicator of the lower activity of sulfate reducing bacteria (SRB) which need SO 4 2- during the anaerobic respiration, in which SO 4 2- is reduced to sulfide (S 2- ) which forms insoluble salts with Cu and Zn, which could partially explain higher bioavailability of these metals in the cool season. Metal resupply capacity of the sediments was mostly < 0.2 for Cu and Zn. Taken together, the H0-2 wetland sediments mostly acted as a sink to both Cu and Zn over the course of this study.