The effects of cattails (Typha latifolia L.) on concentrations and partitioning of metals in surficial sediments of surface-flow constructed wetlands

The concentration and partitioning of metals in vegetated and unvegetated s urface sediments were compared among four wetlands designed for wastewater treatment. In wetlands with a significant depth gradient, the highest conce ntrations of metals were found in deeper unvegetated sediments. When the ef fect of depth was removed, surface sediments with and without cattails (Typ ha latifolia L.) had similar concentrations of total metals (Fe, Mn, Zn and Cu). However, vegetated sediments of all four wetlands had higher organic content (p<0.01). Furthermore, the redox potential was significantly lower (p<0.01) in vegetated sediments for 3 out of 4 wetlands. Vegetated and unve getated sediments were also compared based on geochemical fractions (reacti ve, silicate, persistent organic and pyritic). Generally, half of the total metal concentration in sediments was associated with the reactive fraction (metal oxides, monosulfides and adsorbed onto organic matter). Zn was an e xception as half of the total Zn was associated with the persistent organic fraction. The partitioning of metals in shallow vegetated sediments differ ed from deep unvegetated sediments at the Monahan and Falconbridge wetlands . In contrast, there was no significant difference in the partitioning of m etals in surface sediments with or without cattails at the Panel and Riverw alk wetlands. This study suggests that the effect of cattails on the bulk c oncentration and partitioning of metals may be minimal in surface-flow cons tructed wetlands.