Particulate organic carbon, sterols, fatty acids and pigments in theAmazon River system

Water samples were collected from the Amazon River system during a high flood period, in June 1989, and lipids associated with particles retained on GF/F filters were examined. Particles showed a highly variable organic carbon content (1.8-29.0%). Corresponding organic carbon concentrations varied from 0.36 to 1.13 mg/l. The flood conditions encountered during the sampling period may feed exceptional inputs ofsoil organic matter into the tributaries and the Amazon River. Composition and concentration of sterols, fatty acids and pigments were determined to estimate the relative portion of terrigenous and autochthonous fraction of this complex organic matter. Sterol distribution patterns were similar to other equatorial rivers, in the Orinoco (Venezuela) and Solo (Indonesia). In comparison with the dominant profile of the Amazon system, distinct patterns were found in the Trombetas River (29 delta^5,22 ? 27 delta^5 ? 29 delta^5 ≫ 28 delta^5, 28 delta^5,22) and in the Tapajos River (27 delta^5,22 > 27 delta^5 ≫ 29 delta^5, 28 delta^5, 28 delta^5,22). These fingerprints reflect different vegetation types of drainage basins and distinct planktonic pools. The distribution of even-carbon numbered saturated fatty acids in the carbon range of 24-36 revealed low inputs of constituents associated with cuticular waxes of vascular plants in Black waters and in the Tapajos River (?200 ng/l), higher in White waters (328-483 ng/l) and highest in the Trombetas River (704 ng/l) and in stagnant waters ofa small lake close to the Amazon (1088 ng/l). Pigment concentrationsshowed that in the main river and most tributaries vegetal carbon did not represent more than 2%, except for the Tapajos River (6.2%) andin relatively stagnant waters sampled along the main river (9.2%). Based on relative abundance of Chl b, Chl c, fucoxanthin, peridinin, alloxanthin, and zeaxanthin, various phytoplanktonic assemblages were evidenced in the Amazon River system. Branched fatty acids in the carbon [ABSTRACT FROM AUTHOR]