The influence of plants on concentration and fractionation of Zn, Pb, and Cu in salt marsh sediments (Tagus Estuary, Portugal)

Abstract

Sediment cores were collected from two sites of the Tagus estuary salt marshes which differed in degree of metal contamination. At each site, six 60-cm-long cores were taken, three from a non-vegetated intertidal zone, and one from each of areas colonized by salt marsh plants, Spartina maritima, Halimione portulacoides and Arthrocnemum fruticosum, respectively. Total concentrations and concentrations in sequential extractions of Zn, Pb, and Cu were determined in several sediment layers. Sediment slices containing most of the roots (5–15-cm depth) were enriched in metals in comparison with other depths in the core and with non-vegetated cores. Additionally, metals in sediment slices with roots were preferentially linked to the residual fraction. These results are evidence that aquatic plant roots can have a strong influence on metal concentration and speciation in sediments. Since metals become immobilized in vegetated sediments, the preservation of salt marshes or the creation of artificial wetlands could be considered as an efficient natural means for maintaining ecosystem health or restoring ecosystem quality.