Organic matter in Bolivian tributaries of the Amazon River: A comparison to the lower mainstream

Abstract

We determined the concentrations and compositions of coarse particulate (Ͼ63 m), fine particulate (0.1-63 m), and dissolved (0.001-0.1 m) organic matter collected along a river reach extending from a first-order stream in the Bolivian Andes, through the Beni River system, to the lower Madeira and Amazon Rivers. Dissolved organic carbon (DOC) concentrations increased down the total reach from ϳ80 to 350 M. The percentage of total DOC with a molecular weight greater than ϳ1,000 atomic mass units that could be isolated by ultrafiltration also increased downstream from 40 to 80%. Weight percentages of organic carbon in the ultrafiltered isolates also grew downstream from 5% at the uppermost station to 37% in the Amazon mainstem. Organic carbon composed only 0.4-1.2 weight percentage of the total mass of the fine particulate fraction, which accounted for 70-80% of the total organic carbon (TOC) in transport through the highly turbid (ϳ600-2000 mg L Ϫ1 ) Beni sequence. Observed compositional differences were related primarily to the size fractions in which the organic matter occurred. On average, coarse particulate organic material exhibited an atomic C : N of 24, whereas ultrafiltered DOM was nitrogen poor, (C : N)a ϭ 34, and fine particulate material was nitrogen rich, (C : N)a ϭ 15. The lignin and stable-carbon isotopic compositions of these fractions indicate tree leaves and other nonwoody tissues from C3 land plants as predominant sources. Three molecular parameters demonstrate that the coarse, fine, and dissolved fractions of individual water samples are increasingly degraded downstream. Elemental nitrogen, amino acids, and basic amino acids are all preferentially associated with fine minerals. Observed geographical patterns included more positive ␦ 13 C values in particulate organic matter from high altitude sites and an increase in the abundance and degradation of ultrafiltered dissolved organic matter down the drainage system. Many of these compositional patterns are imprinted within materials carried by low-order, high-altitude tributaries and appear to reflect processes occurring on the landscape.

Transport and diagenesis of dissolved and particulate terrigenous organic matter in the North Pacific Ocean

“…This is 1-2 orders of magnitude greater than L 6 in the dissolved phase. In fact, POM L 6 is 10-40% of L 6 values measured in fine particulate material in the mainstem Amazon River (1240 mg 100 mg OC À1 ; Hedges et al, 2000), 12-52% of Mississippi suspended particulate values (B900 mg 100 mg OC À1 ; Onstad et al, 2000), and >100% of suspended particulate values in some Russian rivers (140-870 mg 100 mg OC À1 ; Lobbes et al, 2000). Aerosols from the combustion of woody plants include a variety of lignin-derived constituents (Simoneit et al, 1993;Rogge et al, 1998), but carbon-normalized lignin values for aerosols are unavailable for comparison.…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…It is highly resistant to microbial degradation (Kawakami, 1989) and its association with cellulose and hemicellulose polysaccharides imparts degradation resistance to these polymers as well (Crawford, 1981). Hence, lignin is widely distributed in depositional environments such as soils and peats (Hedges and Oades, 1997;Miyajima et al, 1997;Tsutsuki et al, 1994;Yavitt et al, 1997), riverine sediments (Hedges et al, 1986(Hedges et al, , 2000Meyers et al, 1995), and coastal marine sediments (Dittmar and Lara, 2001;Gough et al, 1993;Miltner and Emeis, 2001). Lignin's aromatic character makes it the major source of naturally occurring aromatic compounds.…”

The influence of seasonalness on the structural characteristics of aquatic humic substances extracted from Negro River (Amazon State) waters: interactions with Hg(II)

“…The 13 C NMR results indicated significant differences in the content of functional groups present in the samples 41 nd -not detected, AHS -aquatic humic substance, HA -humic acid, FA -fulvic acid, DOM -dissolved organic matter, OM -organic matter. 4,2007 of AHS (Table 4).…”

“…Comparing the C/N atomic ratios with those found in literature (Table 3), there is an inference of a lesser degree of humification of the AHS samples utilized in this study, but also comparable to values obtained for OM extracted from samples taken from the Amazon River having particle sizes between 0.1 and 63 μm. 41 The C/O atomic ratio is related to the carbohydrate content of the HS. Elevated values of this ratio indicate a greater degree of humification due to the diminishing of carbohydrate content.…”