Maurice Bourgoin Laurence auteur aut IRD Quemerais B. auteur aut IRD Guyot Jean-Loup auteur aut IRD Laraque Alain auteur aut IRD Seyler Patrick auteur aut IRD text conferencePaper eng text/pdf reformatted digital access This study describes the transport and speciation of mercury and the associated role of organic matter in these processes at the confluence of the Negro ('black waters') and Solimoes ('white waters') rivers which form the Amazon river. The Negro presents the highest total Hg content (11,6 to 18,2 ng 1-1) due to the extreme particulate Hg concentration which reaches values (2074 ng g-1 at the surface) 10 to 20 times higher than these measured in other Amazon tributaries. The total organic carbon analysed in the Negro consists primarily of particulate carbon (54.8%), while the dissolved organic carbon is composed mainly of humic compounds (50%), carriers for most of the metal ions transported in both rivers. At the confluence of the Negro and Solimoes Rivers, we observe an abrupt decrease of the Hg content. Isotopic mass balance showed that the mixing of waters was achieves 25 km downstream the confluence. Sixty km downstream, the flux of Hg decreases to 73 kg d-1, which represents a net loss of 5 kg dissolved Hg d-1 and 15 kg particulate Hg d-1, assuming that the discharge was constant during the sampling survey and without significant input from other tributaries. However, the observed losses can be correlated to the distribution of the total suspended matter which is not conservative throughout the mixing zone and with the particulate and colloidal organic carbon; net loss of POC is also observed. We suggest that these particulate losses occur during the flocculation of organic matter within the zone of rapidly changing physical and chemical conditions downstream of the confluence, and the deposition of these particles along the mixing zone favoured by a decreasing river discharge during the sampling survey. (Résumé d'auteur) specialized MERCURE COURS D'EAU TRANSPORT SOLIDE CONTAMINATION POLLUTION DES EAUX CONTINENTALES MATIERE EN SUSPENSION GEOCHIMIE EXPLOITATION DU SOUS SOL AMAZONIE 038POLCON Manaus'99 - Hydrological and Geochemical Processes in Large Scale River Basins, Manaus (BRA), 1999/11/16-19 8 multigr. Guyot Jean-Loup ed. edt IRD s.l. s.n. 1999 https://www.documentation.ird.fr/hor/fdi:010025636 [F B010025636] https://www.documentation.ird.fr/hor/fdi:010025636 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010025636.pdf IRD - Base Horizon / Pleins textes 2001-07-31 2021-05-20 fdi:010025636 fre