Origins and processing of organic matter in the Amazon River as indicated by carbohydrates and amino acids

Abstract

Aldose, amino acid, and elemental compositions were determined for flux-weighted samples of coarse (> 63 pm) and fine (< 63 pm) particulate organic material and ultrafiltered (> 1,000 Daltons) dissolved organic matter collected at three sites along the Brazilian Amazon River and six of its major tributaries. Concentrations of total organic C (TOC) were relatively uniform (55Ok 100 PM) at all sites, with DOC comprising the major (50-100%) component. An average of 77% of the total DOC was isolated by ultrafiltration.The greatest compositional differences observed in the Amazon River system were among the coarse, fine, and dissolved organic fractions. All coarse particulate fractions were nitrogen-poor (atomic C : N = 21) and exhibited stable carbon isotope, aldose, and amino acid compositions similar to those of angiosperm tree leaves. Coarse particulate organic materials, although the least degraded of the three fractions, had lost appreciable carbohydrate and had immobilized excess nitrogen of apparent bacterial origin. Fine particulate materials were more nitrogen-rich (C : N = 9) than coarse counterparts and had lower total aldose yields and glucose percentages. Fine particles gave greater total yields of amino acids, characterized by high 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 amino acids in mixtures that were enriched in nonprotein components and in acidic vs. basic molecules. These yield and composition patterns are consistent with a "regional chromatography" model in which highly degraded leaf material is solubilized and then partitioned between soil minerals and water during transport to the river, resulting in suspended fine particulate organic materials of soil origin that are nitrogen-rich and coexisting dissolved organic substances that are nitrogen-poor. manuscript.

Evidence for terrigenous dissolved organic nitrogen in the Arctic deep sea

“…1 (see Table 2). The amino acid signature of the Amazon River, its tributaries (Hedges et al 2000), and the Lena River (Lara et al 1998) resulted in PCA factor 1 values consistently Ͼ1.4 (Fig. 3).…”

Endoparasite fauna of Brycon amazonicus and B. melanopterus(Characidae, Bryconinae) from Negro and Solimões rivers, Amazon, Brazil

“…Many studies have described that the characteristics of the Solimões River are favorable for aquatic fauna and flora, such as high suspended sediment, salt and organic matter load (Leenheer and Santos 1980;Hedges et al 1994), while the Negro River presents a general depletion of the species, which is associated to the low concentration of dissolved salts and absence of suspended matter, low pH and the high concentrations of humic compounds (Leon et al 2006). These abiotic advantages that support a higher diversity on the Solimões River may have influenced the parasite fauna of B. amazonicus on the present study, as the Brillouin diversity index established that the parasite fauna was more diverse in the hosts of this local.…”

Enzymatic analysis of riverine bacterioplankton production

“…Christine Foreman and William Sobczak assisted with the enzyme and productivity assays. been applied to DOC (Thurman 1986;Hedges et al 1994;Moran and Hodson 1994) to trace its origin, composition, and fate, but connections to bacterial productivity have been difficult to demonstrate. Direct studies of bacterial productivity in relation to DOC have involved productivity assays in conjunction with analyses for specific labile DOC components, such as amino acids and sugars.…”