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Volume 13, issue 14
Biogeosciences, 13, 4279–4290, 2016
https://doi.org/10.5194/bg-13-4279-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 4279–4290, 2016
https://doi.org/10.5194/bg-13-4279-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 29 Jul 2016

Research article | 29 Jul 2016

Chemodiversity of dissolved organic matter in the Amazon Basin

Michael Gonsior1, Juliana Valle2,3, Philippe Schmitt-Kopplin3,4, Norbert Hertkorn3, David Bastviken5, Jenna Luek1, Mourad Harir3, Wanderley Bastos6, and Alex Enrich-Prast2,5 Michael Gonsior et al.
  • 1Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD 20688, USA
  • 2Departamento de Ecologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21941-901, Brazil
  • 3Research Unit Analytical BioGeoChemistry, Helmholtz Zentrum München, 85764 Neuherberg, Germany
  • 4Analytical Food Chemistry, Technische Universität München, 85354 Freising-Weihenstephan, Germany
  • 5Department of Thematic Studies – Environmental Change, Linköping University, 58183 Linköping, Sweden
  • 6Laboratory of Environmental Biogeochemistry, Universidade Federal do Rondônia, Rodovia, 76801-974, Brazil

Abstract. Regions in the Amazon Basin have been associated with specific biogeochemical processes, but a detailed chemical classification of the abundant and ubiquitous dissolved organic matter (DOM), beyond specific indicator compounds and bulk measurements, has not yet been established. We sampled water from different locations in the Negro, Madeira/Jamari and Tapajós River areas to characterize the molecular DOM composition and distribution. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with excitation emission matrix (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC) revealed a large proportion of ubiquitous DOM but also unique area-specific molecular signatures. Unique to the DOM of the Rio Negro area was the large abundance of high molecular weight, diverse hydrogen-deficient and highly oxidized molecular ions deviating from known lignin or tannin compositions, indicating substantial oxidative processing of these ultimately plant-derived polyphenols indicative of these black waters. In contrast, unique signatures in the Madeira/Jamari area were defined by presumably labile sulfur- and nitrogen-containing molecules in this white water river system. Waters from the Tapajós main stem did not show any substantial unique molecular signatures relative to those present in the Rio Madeira and Rio Negro, which implied a lower organic molecular complexity in this clear water tributary, even after mixing with the main stem of the Amazon River. Beside ubiquitous DOM at average H ∕ C and O ∕ C elemental ratios, a distinct and significant unique DOM pool prevailed in the black, white and clear water areas that were also highly correlated with EEM-PARAFAC components and define the frameworks for primary production and other aspects of aquatic life.

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We present in this study a highly diverse and complex chemodiversity of dissolved organic matter (DOM) in the Amazon Basin analyzed by modern ultrahigh-resolution mass spectrometry and optical property analyses. DOM within the Rio Madeira (white water), Rio Negro (black water) and Rio Tapajós (clear water) area showed a large overlap of thousands of molecular formulae, but also unique signatures were apparent for each region, with significant correlations to colored DOM.
We present in this study a highly diverse and complex chemodiversity of dissolved organic matter...
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