Soils and porewater of the rhizosphere of mangrove trees, Rhizophora mangle L. and Avicennia schaueria Leech., of the salt marsh grass Spartina alterniflora Loisel, and of unvegetated mud flats, were analyzed salinity, platinum electrode redox potential, organic matter content, sulfide concentrations, and the total changeable concentrations of trace metals (Fe, Zn, Cu, Pb and Cd). The study was conducted in a fringe m forest in Sepetiba Bay, Rio de Janeiro, Brazil. The rhizospheres differed in their biogeochemistry. Mud f Rhizophora soils were very reducing, with highest concentrations of sulfide. Avicennia soils showed t variability of the variables measured, with the rhizosphere changing from oxic to anoxic conditions. Spa on the other hand, were generally oxic, with very low sulfide concentration.The distribution of trace metals in these soils varied with the major physical and chemical characteris flat soils presented the highest total trace metal concentrations followed by mangrove soils and Spartina soils. exchangeable trace metals were similar among the different soils with the exception of Avicennia soils, wh their characteristic instability of redox conditions, presented much higher exchangeable trace metals conc RESUMO Solos e aguas intersticiais sob a influencia da rizosfera de arvores de mangue (Rhizophora mangle L. e Avicennia schaueriana Stapf & Leech.), de graminea de marisma Spartina alterniflora Loisel, e de areas sem vegetacao em planicies de lama, foram analizados em relacao ao pH, potencial redox, salinidade, teor de materia organica e concentraSao de sulfetos, e das concentraoces totais e trocaveis de metais traco (Fe, Zn, Cu, Pb e Cd), em uma floresta de mangue de franja na Baia de Sepetiba, Rio de Janeiro. Os resultados mostraram que a rizosfera das diferentes plantas mostraram diferenSas significativas em sua biogeoquimica. Os solos de planicie de mare e sob Rhizophora apresentaram-se mais redutores e com altas concentrac6es de sulfetos. Os solos sob Avicennia mostraram as maiores variaSoes dos parametros medidos, alternado condioces 6xicas e an6xicas. Por outro lado, os solos sob Spartina apresentaram-se geralmente 6xicos, com baixas concentra,ces de sulfetos.As concentraoces de metais traco tambem foram diferentes entre os diferentes solos, variando de acordo com as principais caracteristicas fisico-quimicas. Os solos de planicie de mare apresentaram as maiores concentraoces de metais totais, seguindo-se os solos de mangue e por ultimo os solos sob Spartina. Entretanto, as concentraoces trocaveis de metais traSo foram semelhantes para todos os solos, menos aqueles sob Avicennia, que devido a sua tipica instabilidade de potencial redox, apresentou a maiores concentrazces de metais trocaveis.

The distribution and bioavailability of trace metals in two contrasting tropical coastal lagoons were studied. The concentration of trace metals in aquatic macrophytes was compared with those found in sediments under weakly and strongly bound forms. The results showed that total metal concentrations in sediments did not explain the concentration found in plants. The highest concentrations in macrophytes were observed in the lagoon which had a higher fraction of metals weakly bound to sediments, but presented the lower total metal content. Low redox potential was the major variable keeping metals in non-bioavailable forms, possibly as refractory sulfides and metal-organic complexes. Among the macrophytes, rooted species showed lower concentrations of metals as compared to algae.