Title: Metal fluxes at the sediment–water interface in a free water surface constructed wetland

Abstract

Metal biogeochemistry in the sediment, water, and the sediment–water interface (SWI) was studied in a free water surface constructed wetland. Concentrations of labile copper (Cu), zinc (Zn), sulfate, chloride, and dissolved organic carbon (DOC) were measured with the diffusive gradients in thin film (DGT) and peeper. A good agreement between peeper- and DGT-measured metals was observed for Cu (regression r² = 0.3, 95% CI of the slopes > 0), but not for Zn (95% CI of the slopes overlapped with 0), which was attributed to the different complexed compounds between Cu and Zn in porewater. The depth profile of labile metals in sediment porewater varied with time and was consistent with the solid-phase metal deposition, showing higher concentrations in the surface layer (3 to –3 cm) than in the bottom layer (–4 to –13 cm). The depth-averaged labile Cu and Zn concentrations measured by DGT were 1.0 and 3.1 µg/L, and labile sulfate, chloride, and DOC concentrations measured by peeper were 1.8, 3.6, and 2.1 mg/L, respectively. A sharp decrease in sulfate occurred in September when sulfate concentrations became the lowest among sampling months. This was caused by the seasonal sulfur cycles in the wetland, where the dominant sulfur reactionmore » is sulfate reduction in warm seasons and sulfide oxidation in cold seasons. Different metal-removal mechanisms were observed in the two wetland cells; sulfur dynamics controlled the removal processes in the cell without frequent disturbance but failed to influence metal removal in the cell with frequent disturbance due to the interruption of anoxic layers. The flux ratios that compare labile element concentrations between the water column and the SWI (R-Cu, R-Zn, R-DOC, R-sulfate, and R-chloride) were generated to determine metal diffusive fluxes at the interface. Labile Zn was mostly transported from the water to the SWI during all seasons (R-Zn < 1 for all months except January). Labile Cu moved from the SWI to the water during the warm months (R-Cu < 1), which was explained by the bioturbation-induced transport of organic matter based on the positive correlations between R-Cu and R-DOC. In general, sediment can serve either as a sink or a source depending on the environmental conditions, metal speciation, and presence of living organisms. Here, metal flux at the SWI is a key component in the biogeochemical cycling of a constructed wetland.« less

Authors:

Xu, Xiaoyu  ^[1];

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Baddar, Zeinah Elhaj ^[1]

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1. Univ. of Georgia, Aiken, SC (United States)

Publication Date:

Thu Jul 07 00:00:00 EDT 2022

Research Org.:

Savannah River Ecology Laboratory (SREL), Aiken, SC (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1893101

Grant/Contract Number:  

EM0005228

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Monitoring and Assessment

Additional Journal Information:

Journal Volume: 194; Journal Issue: 8; Journal ID: ISSN 0167-6369

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; constructed wetlands; diffusive gradients in thin films; metal biogeochemistry; metal flux; peeper; sediment-water interface