Denitrification, carbon and nitrogen emissions over the Amazonian wetlands

Abstract. In this paper, we quantify CO2 and N2O emissions from denitrification over the Amazonian wetlands. The study concerns the entire Amazonian wetland ecosystem with a specific focus on three focal locations: the Branco Floodplain, the Madeira Floodplain and the floodplains alongside the Amazon River. We adapted a simple denitrification model to the case of tropical wetlands and forced it by open water surface extent products from the Soil Moisture and Ocean Salinity (SMOS) satellite. A priori model parameters were provided by in situ observations and gauging stations from the HyBAm observatory. Our results show that the denitrification and emissions present a strong cyclic pattern linked to the inundation processes that can be divided into three distinct phases: activation – stabilization – deactivation. We quantify the average yearly denitrification and associated emissions of CO2 and N2O over the entire watershed at 17.8 kgN/ha/yr, 0.37 gC/m2/yr and 0.18 gN/m2/yr respectively. When compared to local observations, it was found that the CO2 emissions accounted for 0.01 % of the integrated ecosystem, which emphasis the fact that minor changes to the land cover may induce strong impacts to the Amazonian carbon budget. Our results are quite consistent with the state of the art global nitrogen models with a positive bias of 28 %. When compared to other wetlands in different pedo-climatic environments we found that the Amazonian wetlands have close emissions of N2O to the tropical Congo wetlands and lower emissions than the tropical and temperate anthropogenic wetlands of the Garonne river, the Rhine river, and south-eastern Asia rice paddies. In summary our paper shows that a data driven approach can be successfully applied to quantify N2O and CO2 fluxes associated with denitrification over the Amazon basin. In the future, the use of higher resolution remote sensing product from sensor fusion or new sensors like the SWOT mission will permit the transposition to other large scale watersheds in tropical environment.