Manganese behavior at the sediment-water interface in a mangrove dominated area in Sepetiba Bay, Se Brazil

Abstract

We investigated the behavior of Mn in intertidal environments in a mangrove dominated area in Sepetiba Bay, southeast Brazil, to characterize the contribution of diagenetic remobilization to the Mn cycling and bioavailability near the sediment-water interface. Sediment cores and pore water were collected in a mixed mangrove forest and in adjacent unvegetated mud and sand flats, during the rain season (November 1995) and the dry season (June 1996). Redox conditions control the distribution of solid-phase Mn in sediment, associated with diffusional and non-diffusional dissolved Mn transport in pore water. Diverse conditions observed in the studied environments (e.g. mangrove forest rhizosphere and high permeability of sand flat sediments), may remarkably affect the Mn vertical distribution within sediments, and contribute to its seasonal variability. Solid-phase Mn variability was strongly associated with weakly- bound (0.5 M HCl-extractable) phases, which composed most of solid-phase Mn in surface Mn-enriched sediment layers and nearly half of solid-phase Mn in sub-surface Mn-depleted layers, in all environments. The dynamic nature of Mn in this study, particularly in muddy sediments, suggests that: (i) Mn transference from sediments to overlying waters and its transport to adjacent environments occurs, (ii) Mn is present as bioavailable forms within the sediments, and (iii) Mn may potentially have a strong influence on the behavior of other elements (e.g. metal pollutants) within intertidal sediments