ORIGINS AND PROCESSING OF ORGANIC-MATTER IN THE AMAZON RIVER AS INDICATED BY CARBOHYDRATES AND AMINO-ACIDS

Aldose, amino acid, and elemental compositions were determined for flu x-weighted samples of coarse (>63 mum) and fine (<63 mum) particulate organic material and ultrafiltered (>1,000 Daltons) dissolved organic matter collected at three sites along the Brazilian Amazon River and s ix of its major tributaries. Concentrations of total organic C (TOC) w ere relatively uniform (550 +/- 100 muM) at all sites, with DOC compri sing the major (50-100%) component. An average of 77% of the total DOC was isolated by ultrafiltration. The greatest compositional differenc es observed in the Amazon River system were among the coarse, fine, an d dissolved organic fractions. All coarse particulate fractions were n itrogen-poor (atomic C:N = 21) and exhibited stable carbon isotope, al dose, and amino acid compositions similar to those of angiosperm tree leaves. Coarse particulate organic materials, although the least degra ded of the three fractions, had lost appreciable carbohydrate and had immobilized excess nitrogen of apparent bacterial origin. Fine particu late materials were more nitrogen-rich (C:N = 9) than coarse counterpa rts and had lower total aldose yields and glucose percentages. Fine pa rticles gave greater total yields of amino acids, characterized by hig h ratios of basic vs. acidic components. Coexisting dissolved organic materials recovered by ultrafiltration were nitrogen-poor (C:N = 27-52 ) and yielded the lowest amounts of aldoses, among which deoxy sugars were concentrated. Dissolved fractions gave extremely low yields of am ino acids in mixtures that were enriched in nonprotein components and in acidic vs. basic molecules. These yield and composition patterns ar e consistent with a ''regional chromatography'' model in which highly degraded leaf material is solubilized and then partitioned between soi l minerals and water during transport to the river, resulting in suspe nded fine particulate organic materials of soil origin that are nitrog en-rich and coexisting dissolved organic substances that are nitrogen- poor.