Biogeoquimica do Enxofre em Sedimentos de Sapais. Efeitos na Quimica do Ferro e do Manganes

The objective of this work was to improve our understanding of the sulphur cycling in coastal areas. The work was done in inter tidal sediments and included the study of the influence of Spartina maritima roots on the reactivity of sulphur, iron and manganese. The field work was carried out in Tagus salt marshes, in a vegetated site and in a near by non-vegetated sediment, and in the intertidal area of Ria Formosa. The study was complemented with laboratory experiments. Sediment cores were sampled and the concentrations of dissolved and solid sulphides, thiosulphate, sulphite, sulphate, total dissolved iron, total dissolved manganese and dissolved Fe(II) were measured. Other interpretive parameters were also determined. On the basis of chemical equilibria, calculations were made to obtain theoretical thermodynamic data. The results pointed out that: i) Spartina maritima influences the chemical reactions in the Tagus salt-marsh sediments. Vegetated sediments are enriched in oxidised sulphur species while sediments without the presence of roots have higher concentrations of sulphides. ii) Dissolved Fe(II) concentration ii) Dissolved Fe(II) concentration is controlled by the presence of sulphides. iii) Calculations based on chemical equilibria suggest that iron monosulphides control the concentration of Fe(II) in interstitial waters of non-vegetated sediments. Carbonates control dissolved Mn(II)Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga