Dissolved humic substances of the Amazon River system1
Open accessAbstract
Aquatic humic and fulvic acids from nine mainstem and seven major tributary sites in the Amazon River Basin are characterized by their elemental and lignin phenol compositions. Combined humic substances represent 60% of the riverine dissolved organic carbon (DOC), with fulvic to humic acid (FA : HA) ratios in the mainstem averaging 4.7±1.0. All dissolved humic and fulvic acids have clearly recognizable lignin components at levels (8 and 3% of the carbon) suggesting a predominantly allochthonous source. Lignin compositional characteristics are dominated by diagenetic transformations, which include preferential loss of methoxylated structural units and oxidative degradation of lignin side chains. Fulvic acids have consistently lower lignin levels, lower lignin phenol methoxylation, higher acid : aldehyde ratios, and higher C: N ratios than coexisting humic acids, all indicative of greater aerobic degradation of the fulvic acid fraction. An extreme example of lignin degradation is seen in the Rio Negro humic and fulvic acids, which differ significantly in lignin and elemental compositions from other blackwater tributary and mainstem samples. Over most of the mainstem humic and fulvic acids behave conservatively. However, downstream of the Rio Negro confluence, humic acids appear to be selectively adsorbed onto fine suspended particles. Approximately 25 and 40% of the total fluxes of lignin and of carbon are represented in the dissolved humic substances. The annual flux of dissolved, chemically recognizable lignin in the Amazon River at Obidos is calculated to be 1.2 × 10 11 g yr−1.
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In forested Amazonian floodplain lakes, local allochthonous inputs are high, comprising most of the suspended organic matter and nutrient inputs.
“In forested Amazonian floodplain lakes, local allochthonous inputs are high, comprising most of the suspended organic matter and nutrient inputs (Ertel et al., 1986; Hedges et al., 1986; Sobrinho et al., 2016).”
From Threshold responses of floating meadow fish communities to floodplain forest cover in the lower Amazon River (2025) · cites this paper as Ertel et al., 1986
The Discussion (page not provided) says suspended particulate organic matter in the Amazon system is essentially all derived from soil or vascular plants, supporting its allochthonous origin. The paper does not establish that local inputs supply most suspended organic matter or nutrients to forested floodplain lakes; its measurements concern riverine dissolved humic substances. (LLM, conf=0.84)
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Cites
Importance of heavy metal-organic matter interactions in natural waters
Reuter, J. H., & Perdue, E. M. (1977) · Geochimica et Cosmochimica Acta · doi:10.1016/0016-7037(77)90240-x · Cited by 432 · see citing works
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Grinstead, S., Arantes, C. C., Winemiller, K. O., Kelso‐Winemiller, L. C., de Oliveira, J. A., Petrere, M., & Freitas, C. E. C. (2025) · Conservation Biology · doi:10.1111/cobi.70110
- Authors
- Ertel, J. R., Hedges, J. I., Devol, A. H., Richey, J. E., & Ribeiro, M. D. N. G.
- Affiliations
- University of Washington (US)
- Instituto Nacional de Pesquisas da Amazônia (BR)
- Corresponding author
- Ertel, John R.
- Venue
- Limnology and Oceanography
- Publisher
- Wiley
- Published
- 1986-07
- Volume
- 31
- Issue
- 4
- Pages
- 739-754
- ISSN
- 0024-3590 (ISSN-L)
- 1939-5590
- OpenAlex
- W2120891916
- Cited by
- 445
- References
- 1
- Citations by year
- 2026: 3 · 2025: 6 · 2024: 7 · 2023: 4 · 2022: 5 · 2021: 11 · 2020: 6 · 2019: 15 · 2018: 57 · 2017: 13 · 2016: 18 · 2015: 10 · 2014: 18 · 2013: 13 · 2012: 10
- FWCI
- 11.71
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Limnology and Oceanography (publishedVersion)
- Funders
- National Science Foundation
- University of Washington
- Topics
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
- Physical Sciences › Environmental Science › Ecology › Peatlands and Wetlands Ecology
- Life Sciences › Agricultural and Biological Sciences › Soil Science › Soil Carbon and Nitrogen Dynamics
- Keywords
- dissolved humic substances, fulvic acid, humic acid, Amazon River, dissolved organic carbon, lignin phenols, lignin degradation, allochthonous organic matter, Rio Negro, organic carbon flux, diagenesis
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