Distribution of metals and stable Pb isotopes in salt marsh sediments

Bioturbation by the plants Sarcocornia fruticosa and Spartina maritima and by the polychaetes Nereis diversicolor was study in sediments of Rosário saltmarsh (Tagus, Portugal). Sediment cores colonized and non-vegetated were collected and depth variation of Zn, Cu, Cd and Pb contents were determined. Stable Pb isotopes ratios were also assessed. These parameters were also quantified in the roots and aboveground plant parts. The metal contents in roots were 1-3 orders of magnitude higher than in aboveground plant parts indicating a weak upward translocation. Colonized sediments have higher levels of Zn, Cu, Cd and Pb when compared with non-vegetated ones. Depth profiles of 206Pb/207Pb and 206Pb/208Pb in sediments and roots showed a decrease towards the surface as a result of a higher proportion of anthropogenic Pb components. Enrichment factors varying with depth, suggesting the presence of preferential layers of metal accumulation in roots. N. diversicolor also changed the vertical distribution of metals and Pb isotope ratios in sediments being classified as upward conveyors. These results suggested that Pb isotopic ratios are tracers of particle movements within the sediment.