Hydrological and Biogeochemical Controls Governing the Speciation and Accumulation of Selenium in a Wetland Influenced by Mine Drainage

Abstract

Controls governing the speciation and accumulation of Se in a 3.7 ha marsh influenced by mine drainage were assessed through examination of water balance, water quality, sediment, and plant tissue components. Over the eight month study period, mean monthly flows ranged from 1,600 to 2,300 m³•d⁻¹ (hydraulic retention time of 1 to 3 days). Total Se concentrations in the marsh outflow were lower than the inflow by 0.4 to 6.2 µg•L⁻¹ (mean difference = 3.3 µg•L⁻¹), illustrating Se removal. Se accumulation pathways are illustrated by elevated concentrations of Se in sediments (3 to 35 mg•kg⁻¹dw) as well as in below ground (2 to 41 mg•kg⁻¹ dw; mean = 10 mg•kg⁻¹ dw) and above ground (0.8 to 6.3 mg•kg⁻¹ dw; mean = 2 mg•kg⁻¹ dw) emergent plant tissues. Redox stratification in the shallow water column has a marked effect on Se speciation and behaviour, illustrating bottom water removal of dissolved selenate in suboxic horizons and increased mobility of dissolved organo-Se. Mass balance data yield inflow and outflow loading rates for Se of 27 g•d⁻¹ and 23 g•d⁻¹, respectively (net accumulation rate of 4 g•d⁻¹ or 0.11 mg• m² •d⁻¹). The rate of accumulation as calculated from the mass balance agrees with independently measured rates of Se accumulation in sediments for the site (3.6 to 8.1 g•d⁻¹ or 0.10 to 0.22 mg•m⁻² d⁻¹). This article is protected by copyright. All rights reserved

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