Modelling the genesis of equatorial podzols: age and implications on carbon fluxes

Other literature type English OPEN
Doupoux, Cédric ; Merdy, Patricia ; Montes, Célia Régina ; Nunan, Naoise ; Melfi, Adolpho José ; Pereira, Osvaldo José Ribeiro ; Lucas, Yves (2017)

Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon river. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and <sup>14</sup>C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retro calculations to take in account the bomb carbon in the young topsoil horizons (<sup>14</sup>C age from 62 to 109&thinsp;y). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (<sup>14</sup>C age 6.8&thinsp;&times;&thinsp;10<sup>3</sup> and 8.4&thinsp;&times;&thinsp;10<sup>3</sup>&thinsp;y) and two profiles with a very old Bh (<sup>14</sup>C age 23.2&thinsp;&times;&thinsp;10<sup>3</sup> and 25.1&thinsp;&times;&thinsp;10<sup>3</sup>&thinsp;y). The calculated fluxes from the topsoil to the perched water-table indicates that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15&thinsp;&times;&thinsp;10<sup>3</sup> and 130&thinsp;&times;&thinsp;10<sup>3</sup>&thinsp;y for the two younger and the two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15&thinsp;&times;&thinsp;10<sup>3</sup>&ndash;25&thinsp;&times;&thinsp;10<sup>3</sup> and 150&thinsp;&times;&thinsp;10<sup>3</sup>&ndash;250&thinsp;&times;&thinsp;10<sup>3</sup>&thinsp;y, respectively.
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