Denitrification and associated nitrous oxide and carbon dioxide emissions from the Amazonian wetlands

Jérémy Guilhen (1, 2) , Al Bitar Ahmad (1) , Sabine Sauvage (3) , Marie Parrens (1, 4) , Jean-Michel Martinez (5) , Gwenaël Abril (6) , Patricia Moreira-Turcq (7) , Jose-Miguel Sanchez-Perez (3)

1 CESBIO - Centre d'études spatiales de la biosphère
2 INP - PURPAN - Ecole d'Ingénieurs de Purpan
3 CNRS - Centre National de la Recherche Scientifique
4 DYNAFOR - Dynamiques et écologie des paysages agriforestiers
5 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
6 BOREA - Biologie des Organismes et Ecosystèmes Aquatiques
7 GET - Géosciences Environnement Toulouse

In this paper, we quantify the CO 2 and N 2 O emissions from denitrification over the Amazonian wetlands. The study concerns the entire Amazonian wetland ecosystem with a specific focus on three floodplain (FP) locations: the Branco FP, the Madeira FP and the FP 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 HY-BAM Observatory. Our results show that the denitrification and the trace gas emissions present a strong cyclic pattern linked to the inundation processes that can be divided into three distinct phases: activation, stabilization and deactiva-tion. We quantify the average yearly denitrification and associated emissions of CO 2 and N 2 O over the entire watershed at 17.8 kgN ha −1 yr −1 , 0.37 gC-CO 2 m −2 yr −1 and 0.18 gN-N 2 O m −2 yr −1 respectively for the period 2011-2015. When compared to local observations, it was found that the CO 2 emissions accounted for 0.01 % of the integrated ecosystem, which emphasizes the fact that minor changes to the land cover may induce strong impacts on the Amazonian carbon budget. Our results are consistent with the state of the art of global nitrogen models with a positive bias of 28 %. When compared to other wetlands in different pedoclimatic environments we found that the Amazonian wetlands have similar emissions of N 2 O with the Congo tropical wetlands and lower emissions than the temperate and tropical anthro-pogenic wetlands of the Garonne (France), the Rhine (Eu-rope) and southeastern Asia rice paddies. In summary our paper shows that a data-model-based approach can be successfully applied to quantify N 2 O and CO 2 fluxes associated with denitrification over the Amazon basin. In the future, the use of higher-resolution remote sensing products from sensor fusion or new sensors like the Surface Water and Ocean Topography (SWOT) mission will permit the transposition of the approach to other large-scale watersheds in tropical environments .

Domaines: Interfaces continentales, environnement

Jérémy Guilhen, Al Bitar Ahmad, Sabine Sauvage, Marie Parrens, Jean-Michel Martinez, et al.. Denitrification and associated nitrous oxide and carbon dioxide emissions from the Amazonian wetlands. Biogeosciences, 2020, 17 (16), pp.4297-4311. ⟨10.5194/bg-17-4297-2020⟩. ⟨hal-02931529⟩