Transport and behaviour of total mercury in the Amazon river at the confluence of black and white waters

1999

Colloque

Maurice Bourgoin Laurence, Quemerais B., Guyot Jean-Loup, Laraque Alain, Seyler Patrick

Guyot Jean-Loup (ed.), Manaus'99 : hydrological and geochemical processes in large scale river

s.l. : s.n., 1999, 8 p. multigr.

Manaus'99 - Hydrological and Geochemical Processes in Large Scale River Basins, Manaus (BRA), 1999/11/16-19

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)

Pollution continentale [038POLCON]

MERCURE ; COURS D'EAU ; TRANSPORT SOLIDE ; CONTAMINATION ; POLLUTION DES EAUX CONTINENTALES ; MATIERE EN SUSPENSION ; GEOCHIMIE ; EXPLOITATION DU SOUS SOL

AMAZONIE

Fonds IRD [F B010025636] ; La Paz

fdi:010025636