Role of plants in metal cycling in a tidal wetland: Implications for phytoremidiation

Accumulation of 8 metals and the semimetal As in 29 plant species was quantified in a restored tidal wetland on a contaminated site. Transfer coefficients between sediment and aboveground plant tissues were lower than in many other systems; from 0.013 (Pb) to 0.189 (Mn). A minor fraction of the sediment metal pool cycled through the aboveground vegetation (≤ 0.02%). However, during the four years of this study, species composition changed, and plant biomass as well as the metal pool in the vegetation increased (≤ 0.12%). Succession to either a willow dominated brushwood or a monospecific reed stand can further enlarge this pool (2.5%). Since the amount of trace metals in the wetland soil or in suspended solids deposited during tidal flooding is some orders of magnitude larger than the vegetation pool, phytoextraction is not applicable. The growth of plant species with low accumulation in aboveground tissues, e.g. Scirpus maritimus or Typha latifolia, may be preferred since this might result in lower toxic metal distribution to the wider environment.

► Wetland plants colonized the metal contaminated site following restoration.
► Low metal pool in the aboveground vegetation makes phytoextraction inapplicable.
► High Cd and Zn accumulation in willow trees may be of concern.
► Metal accumulation was lowest in aboveground tissues of large emergent macrophytes.
► Management which promotes macrophytes may reduce food chain contamination.