Articles | Volume 13, issue 2
Biogeosciences, 13, 467–482, 2016
Biogeosciences, 13, 467–482, 2016

Research article 22 Jan 2016

Research article | 22 Jan 2016

Spatial and seasonal contrasts of sedimentary organic matter in floodplain lakes of the central Amazon basin

R. L. Sobrinho1,2, M. C. Bernardes1, G. Abril1,3, J.-H. Kim2,4, C. I Zell2, J.-M. Mortillaro5, T. Meziane5, P. Moreira-Turcq6, and J. S. Sinninghe Damsté2,7 R. L. Sobrinho et al.
  • 1Universidade Federal Fluminense, Department of Geochemistry, 24020-141, Niteroi, Rio de Janeiro, Brazil
  • 2NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, 1790 AB Den Burg, Texel, the Netherlands
  • 3Laboratoire EPOC, Université Bordeaux 1, CNRS UMR-5805, Avenue des Facultés, 33405 Talence, France
  • 4Department of Marine Science and Convergence Technology, Hanyang University ERICA campus, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan-si, Gyeonggi-do 426-791, South Korea
  • 5UMR-CNRS-IRD-UPMC 7208, BOREA, Département Milieux et Peuplements Aquatiques, MNHN, CP 53, 61 rue Buffon, 75231 Paris CEDEX 05, France
  • 6IRD (Institut de Recherche pour le Développement) GET (Géosciences Environnement Toulouse), Casilla 18-1209, Lima 18, Peru
  • 7Utrecht University, Faculty of Geosciences, P.O. Box 80.021, 3508 TA Utrecht, the Netherlands

Abstract. In this study, we investigated the seasonal and spatial pattern of sedimentary organic matter (SOM) in five floodplain lakes of the central Amazon basin (Cabaliana, Janauaca, Canaçari, Mirituba and Curuai) which have different morphologies, hydrodynamics and vegetation coverages. Surface sediments were collected in four hydrological seasons: low water (LW), rising water (RW), high water (HW) and falling water (FW) in 2009 and 2010. We investigated commonly used bulk geochemical tracers such as the C : N ratio and the stable isotopic composition of organic carbon (δ13Corg). These results were compared with lignin phenol parameters as an indicator of vascular plant detritus and branched glycerol dialkyl glycerol tetraethers (brGDGTs) to trace the input of soil organic matter (OM) from land to the aquatic settings. We also applied the crenarchaeol as an indicator of aquatic (rivers and lakes) OM. Our data showed that during the RW and FW seasons, the surface sediments were enriched in lignin and brGDGTs in comparison to other seasons. Our study also indicated that floodplain lake sediments primarily consisted of allochthonous, C3 plant-derived OM. However, a downstream increase in C4 macrophyte-derived OM contribution was observed along the gradient of increasing open waters – i.e., from upstream to downstream. Accordingly, we attribute the temporal and spatial difference in SOM composition to the hydrological dynamics between the floodplain lakes and the surrounding flooded forests.

Short summary
The principal objective of the present work is to quantify the fractions of the principal sources of sedimentary organic matter (SOM) in floodplain lakes of the central Amazon basin. The results indicate that the main source of SOM is not the riverine particulate material, as postulated by the literature, but the macrophytes and the forests.
Final-revised paper