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 vegetatedand unvegetated surface sediments were compared among fourwetlands designed for wastewater treatment. In wetlands witha significant depth gradient, the highest concentrations ofmetals were found in deeper unvegetated sediments. When theeffect of depth was removed, surface sediments with andwithout cattails (Typha latifolia L.) had similarconcentrations of total metals (Fe, Mn, Zn and Cu). However,vegetated sediments of all four wetlands had higher organiccontent (p < 0.01). Furthermore, the redox potential wassignificantly lower (p < 0.01) in vegetated sediments for 3out of 4 wetlands. Vegetated and unvegetated sediments werealso compared based on geochemical fractions (reactive,silicate, persistent organic and pyritic). Generally, halfof the total metal concentration in sediments was associatedwith the reactive fraction (metal oxides, monosulfides andadsorbed onto organic matter). Zn was an exception as halfof the total Zn was associated with the persistent organicfraction. The partitioning of metals in shallow vegetatedsediments differed from deep unvegetated sediments at theMonahan and Falconbridge wetlands. In contrast, there was nosignificant difference in the partitioning of metals insurface sediments with or without cattails at the Panel andRiverwalk wetlands. This study suggests that the effect ofcattails on the bulk concentration and partitioning ofmetals may be minimal in surface-flow constructed wetlands.