Dissolved gaseous mercury (DGM) formation/consumption was measured during several scientific excursions in the Negro River basin, Amazon, Brazil. Measurements were carried out following diel patterns in both white and black water bodies. In white waters, with pH values around 7 and low dissolved organic carbon (DOC) concentration, mercury saturation prevails during the sunlit period, similar to behavior observed elsewhere. This was attributed to DGM generated by a photoinduced mechanism of Hg2+ reduction. On the other hand, in black waters, with pH around 5 and high DOC values (up to 20 mg L-1), DGM concentration stays below the detection limit during sunlit periods, which was associated to photoinduced Hgº oxidation. Photochemical experiments carried out in situ corroborate the influence of sunlight on DGM formation/consumption. A comparison of diel DGM saturation is presented for both black and white water bodies.
dissolved gaseous mercury (DGM); dissolved organic carbon (DOC); black water; photolysis
