Alberic P., Perez M. A. P., Moreira Turcq Patricia, Benedetti M. F., Bouillon S., Abril Gwenaël. (2018). Variation of the isotopic composition of dissolved organic carbon during the runoff cycle in the Amazon River and the floodplains. Comptes Rendus Geoscience, 350 (1-2), p. 65-75. ISSN 1631-0713.
Titre du document
Variation of the isotopic composition of dissolved organic carbon during the runoff cycle in the Amazon River and the floodplains
Alberic P., Perez M. A. P., Moreira Turcq Patricia, Benedetti M. F., Bouillon S., Abril Gwenaël
Source
Comptes Rendus Geoscience, 2018,
350 (1-2), p. 65-75 ISSN 1631-0713
Given the relative scarcity of stable isotope data on dissolved organic carbon (DOC) in the Amazon Basin, we hypothesized that the variability in DOC sources may be underestimated in such major river basins. To explore the links between the mainstem and tributaries and the floodplain, particular efforts were made during five distinct cruises at different stages of the hydrograph between October 2008 and January 2011, to document the spatial and temporal variation of DOC concentrations and delta C-13-DOC in the central Amazon River system (Brazil). Based on more than 200 data, the spatial and temporal variability of delta C-13-DOC values was found to be larger than previously reported in the same area. Although a small range of variation was observed throughout the hydrological cycle in the upper reach of the studied section (-29.2 to -29.5 parts per thousand in the Rio Negro and -28.7 to -29.0 parts per thousand in the Rio Solimoes), a much larger one (-28.0 to -34.6 parts per thousand) was found in the lower reach of the river, as the proportion of open lakes increased downstream in the floodplains. The low variability in the upper reaches suggests constant and homogeneous DOC sources from upland soils and flooded forest, while lower delta C-13-DOC values recorded in the lower reach mainstem at high and falling waters can be attributed to a greater export of plankton-derived C-13-depleted DOC from flooded lakes. Noteworthy are the higher delta C-13-DOC values measured in the Rio Madeira and the associated flooded lakes (-26.5 to -28.8 parts per thousand, which may reflect the imprint from upland headwaters and a weaker density of flooded forest in the watershed. The higher delta C-13-DOC values observed in the lower reach during low waters are still not fully understood. Floating meadows principally consisting of C-4 macrophytes were found to increase delta C-13-DOC values by similar to 1.5 parts per thousand in their vicinity, but this impact was no longer noticeable at distances of similar to 10 m from the plant rafts. This rather modest C-13-enrichment suggests rapid decomposition and/or dilution of this wetland-derived DOC.
Plan de classement
Hydrologie [062]
;
Géologie et formations superficielles [064]
