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Biogeochemistry

, Volume 131, Issue 3, pp 281–302 | Cite as

Seasonal and spatial variability of dissolved organic matter composition in the lower Amazon River

  • Michael Seidel
  • Thorsten Dittmar
  • Nicholas D. Ward
  • Alex V. Krusche
  • Jeffrey E. Richey
  • Patricia L. Yager
  • Patricia M. MedeirosEmail author
Article

Abstract

We analyzed the molecular composition of dissolved organic matter (DOM) in the lower Amazon River (ca. 850 km from Óbidos to the mouth) using ultrahigh-resolution mass spectrometry and geochemical tracers. Changes in DOM composition along this lower reach suggest a transition from higher plant-derived DOM to more algal/microbial-derived DOM. This result was likely due to a combination of autochthonous production, alteration of terrigenous DOM as it transits down the river, and increased algal inputs from floodplain lakes and clearwater tributaries during high discharge conditions. Spatial gradients in dissolved organic carbon (DOC) concentrations varied with discharge. Maximal DOC concentrations were observed near the mouth during high water, highlighting the importance of lateral inputs of DOM along the lower river. The majority of DOM molecular formulae did not change within the time it takes the water in the mainstem to be transported through the lower reach. This is indicative of molecules representing a mixture of compounds that are resistant to rapid alteration and reactive compounds that are continuously replenished by the lateral input of terrestrial organic matter from the landscape, tributaries, and floodplains. River water incubations revealed that photo- and bio-transformation alter at most 30% of the DOM molecular formulae. River discharge at the mouth differed from the sum of discharge measurements made at Óbidos and the main gauged tributaries in the lower Amazon. This indicates that changes in hydrology and associated variations in the source waters along the lower reach affected the molecular composition of the DOM that is being transported from the Amazon River to the coastal ocean.

Keywords

Amazon River Ultra-high resolution mass spectrometry Dissolved organic matter 

Notes

Acknowledgements

We thank Katrin Klaproth (University of Oldenburg, Germany) for technical assistance. We gratefully acknowledge funding provided by the Gordon and Betty Moore Foundation (ROCA, GBMF-MMI-2293 and 2928) and FAPESP (#08/58089-9). We are also very thankful to the associate editor and the three anonymous reviewers for their detailed and thoughtful comments that greatly improved an earlier version of this manuscript. We further thank the Brazilian government for the opportunity to sample in the Amazon River.

Supplementary material

10533_2016_279_MOESM1_ESM.docx (887 kb)
Supplementary material 1 (DOCX 887 kb)

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Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  • Michael Seidel
    • 1
    • 2
  • Thorsten Dittmar
    • 2
  • Nicholas D. Ward
    • 3
    • 5
  • Alex V. Krusche
    • 4
  • Jeffrey E. Richey
    • 3
  • Patricia L. Yager
    • 1
  • Patricia M. Medeiros
    • 1
    Email author
  1. 1.Department of Marine SciencesUniversity of GeorgiaAthensUSA
  2. 2.Research Group for Marine Geochemistry (ICBM-MPI Bridging Group), Institute for Chemistry and Biology of the Marine Environment (ICBM)Carl von Ossietzky University of OldenburgOldenburgGermany
  3. 3.School of OceanographyUniversity of WashingtonSeattleUSA
  4. 4.Centro de Energia Nuclear na AgriculturaUniversidade de São PauloPiracicabaBrazil
  5. 5.Department of Geological SciencesUniversity of FloridaGainesvilleUSA

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