Mercury and flooding cycles in the Tapajós river basin, Brazilian Amazon: The role of periphyton of a floating macrophyte (Paspalum repens)

► During rainy season mercury (Hg2+) is carried out from terrestrial to aquatic systems by runoff. ► Macrophyte roots accumulates Hg2+ from suspended particulate matter (SPM). ► Hg methylation increases during the wet season. ► Flooded forest is a source of labile organic carbon and bioavailable Hg. ► Macrophytes decompose during the dry season and made up terrestrial soil.