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

• Main Authors: J. Guilhen, A. Al Bitar, S. Sauvage, M. Parrens, J.-M. Martinez, G. Abril, P. Moreira-Turcq, J.-M. Sánchez-Pérez
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-08-01
• Series: Biogeosciences
• Online Access: https://bg.copernicus.org/articles/17/4297/2020/bg-17-4297-2020.pdf
• ISSN: 1726-4170; 1726-4189

<p>In this paper, we quantify the <span class="inline-formula">CO₂</span> and <span class="inline-formula">N₂O</span> 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 HYBAM 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 deactivation. We quantify the average yearly denitrification and associated emissions of <span class="inline-formula">CO₂</span> and <span class="inline-formula">N₂O</span> over the entire watershed at 17.8&thinsp;kgN&thinsp;ha<span class="inline-formula">⁻¹</span>&thinsp;yr<span class="inline-formula">⁻¹</span>, 0.37&thinsp;gC-<span class="inline-formula">CO₂</span>&thinsp;m<span class="inline-formula">⁻²</span>&thinsp;yr<span class="inline-formula">⁻¹</span> and 0.18&thinsp;gN-<span class="inline-formula">N₂O</span>&thinsp;m<span class="inline-formula">⁻²</span>&thinsp;yr<span class="inline-formula">⁻¹</span> respectively for the period 2011–2015. When compared to local observations, it was found that the <span class="inline-formula">CO₂</span> emissions accounted for 0.01&thinsp;% 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&thinsp;%. When compared to other wetlands in different pedoclimatic environments we found that the Amazonian wetlands have similar emissions of <span class="inline-formula">N₂O</span> with the Congo tropical wetlands and lower emissions than the temperate and tropical anthropogenic wetlands of the Garonne (France), the Rhine (Europe) and south-eastern Asia rice paddies. In summary our paper shows that a data-model-based approach can be successfully applied to quantify <span class="inline-formula">N₂O</span> and <span class="inline-formula">CO₂</span> 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.</p>