Moreira Turcq Patricia auteur aut IRD Seyler Patrick auteur aut IRD Guyot Jean-Loup auteur aut IRD Etcheber H. auteur aut IRD text journalArticle eng text/pdf born digital access The nature and distribution of organic matter in the mixing zone of black (Rio Negro) and white (Rio Solimoes) waters in the Amazon River was studied to understand the processes responsible for its transport and distribution. Water samples from 13 stations, including Rio Negro, Rio Solimoes and Rio Madeira and ten stations downstream of the confluence with the Amazon, were collected during a low-water period. Particulate organic matter (POM; >0.7 mum) and dissolved organic matter (DOM; <0.7 mum) were quantified by analysing elemental carbon and nitrogen and by high-temperature catalytic oxidation, and characterized by infrared spectrometry and fluorescence microscopy. We also performed adsorption experiments with DOM and alumina particles to determine the adsorption abilities and the nature of the most reactive DOM. Adsorption was estimated by measuring the amount of dissolved organic carbon (DOC) lost during the experiments. We found a significant difference between the measured and theoretical fluxes of the two end members in DOC (-52%), particulate organic carbon (-32%), and particulate organic nitrogen (-59%). This suggests that organic matter is not conservative at the confluence of the two rivers. Among processes affecting POM and DOM during the mixing of the two rivers, adsorption may be one of the principal mechanisms by which the dissolved fraction is removed. Adsorption experiments showed that up to ca 40% of DOC can be removed by adsorption reactions. Furthermore, dissolved organic nitrogen was preferentially adsorbed onto alumina surfaces, which may be important for the fractionation of organic matter in the Amazon river system and seems to be related to the origin and freshness of the DOM. specialized COURS D'EAU MATIERE ORGANIQUE DISSOUTE MATIERE ORGANIQUE PARTICULEE TRANSPORT SOLIDE DISTRIBUTION SPATIALE CARBONE ORGANIQUE AZOTE RAPPORT C/N ANALYSE CHIMIQUE PH CONDUCTIVITE ADSORPTION GEOCHIMIE CHIMIE DE L'EAU AMAZONIE 062MECEAU04 17 7 1393-1404 2003 0885-6087 International Symposium on Hydrological and Geochemical Processes in Large Scale River Basins, Manaus (BRA), 1999/11/16-19 https://www.documentation.ird.fr/hor/fdi:010031306 0885-6087 [F B010031306] https://www.documentation.ird.fr/hor/fdi:010031306 https://www.documentation.ird.fr/intranet/publi/depot/2015-09-11/010031306.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2003-09-25 2015-11-09 fdi:010031306 fre