Biogeochemical characteristics of organic matter in the particulate and colloidal fractions downstream of the rio Negro and Solimoes rivers confluence

Abstract

-The analysis of organic matter in the rio Negro, rio Solimões and rio Amazonas focused on total organic carbon (TOC), as determined at two main sizes, the particulate form (> 0.2 µm) and the colloidal form (0.2 µm to 5000 dalton). These fractions were obtained by tangential ultrafiltration carried out on 50 l water samples. The total polysaccharide contents were determined by a colorimetric method, the main classes of organic compounds by pyrolysis and gas chromatography coupled with mass spectrometry (Py-GC-MS), and the lignin or non-lignin phenols by cupric oxide alkaline oxidation and high performance liquid chromatography (HPLC) with photodiode array spectrophotometer detection. Upstream of the confluence of the rio Negro and rio Solimões, the rivers show characteristic differences. The rio Negro has low discharge, high levels of TOC% for the two fractions, high levels of polysaccharides, low levels of lignin phenols and high levels of hydroxybenzyl non-lignin phenols. The main classes of organic compounds also give a distribution different for the particulate (phenols associated to aromatic compounds) and the colloidal (aromatic compounds and sugars). For the rio Solimões, the compositional features are generally reversed. Downstream of the confluence, the colloidal fraction showed noteworthy levels of lignin-derived compounds associated with increasing levels of polysaccharides correlated to the distance from the confluence. biogeochemistry / organic matter / Py-GC-MS / HPLC / phenols / lignin / particulate / colloidalRésumé -Caractères biogéochimiques de la matière organique particulaire et colloïdale en aval de la confluence des rios Negro et Solimões. L'analyse de la matière organique dans les eaux du rio Negro, du rio Solimões et du rio Amazonas a porté sur la charge totale en suspension (TSM) ainsi que sur les fractions particulaire (> 0.2 µm) et colloï-dale (0.2 µm à 5000 dalton). Ces fractions ont été obtenues par ultrafiltration tangentielle exécutée sur des échantillons

Characterization and Copper Binding of Humic and Nonhumic Organic Matter Isolated from the South Platte River: Evidence for the Presence of Nitrogenous Binding Site

“…Our modeling results combined with the structural data offer new evidence that nitrogen group might play an important role for metal binding at very low metal concentrations that are relevant for natural systems. Preferential binding with nitrogen groups might have a significant implication on the behavior of metal species in the aquatic environment because DOM components enriched in nitrogen are known to exert a strong affinity for particles ( , ). Consequently, modifications of the physical chemical characteristics of the river (e.g., runoff events, mixing of rivers) can remove metal ions bound to DOM from solution via preferential sorption of Me-DOM to sediment.…”

Revealing forms of iron in river-borne material from major tropical rivers of the Amazon Basin (Brazil)

“…The organic matter content was estimated by a conversion factor of 2, corresponding to the average mass-ratio of C in humic substances (Swift, 1996). A a matter of fact, according to Gadel et al (2000), the polysaccharide content in our samples was assumed to be minor.…”

“…Carbon is significant as colloidal matter in the Rio Negro (30 to 40% of TOC) whereas it is dominantly present in the dissolved (Ͻ5 kD) fraction in the Amazon River Mounier et al, 2002). The composition of organic matter was studied on various samples from the Rio Negro, Rio Solimoes, and Amazon by Gadel et al (2000). These authors showed that the average …”

“…The colloidal fraction is likely to be composed of more "mature" organic material while the particulate fraction is made of less reactive, "younger" organic debris and decayed parts of organisms (Gadel et al, 2000). Differences could also result from in situ production of organic matter with chemical characteristics different from the soil derived organic matter (Degens et al, 1991).…”

Pyrolysis‐Gas Chromatography/Mass Spectrometry Characterization of Humic Acids in Coastal Spodosols from Southeastern Brazil

“…Phenol (Phi) and 3/4-mcrhylphenol (Ph4) plot at the far lefi:, with low loadings on F2, These compounds are frequently associated with DOC, and Buurman er al, (2005) mentioned phenols, merhylphenols, guaiacols, and various polysaccharide producrs as pyrolytic compounds of DOC in incipient and well-developed podzols. Other Py-GC/MS analyses of DOC have been reported by, e,g,, Frimmel (2000) and Gadel er al, (2000), Gadel et al, (2000) described particulate and dissolved SOM of rhe Rio Negro, Brazil, Because the Rio Negro drains tropical podzols and peat, its D O C is directly related to our present work, Rio Negro DOC contained 32% aromarics, 37% N compounds, 11% sugars, 19% phenols, and 1,3% amino sugars, Frimmel (2000) mentioned rhe presence of C^ to Cg alkenes and alkadienes, alkylbenzenes and dihydroxybenzenes, alkylphenols, guaiacols, and syringols as pyrolysis producrs of DOC, Two samples from black (peat) warer from central Kalimantan, Indonesia (Buurman et al,, 2012), contained 25% aromatic compounds, 10% lignin, 25% phenols, and 25% polysaccharide producrs. The latter consisred mainly of acetic acid and furans.…”