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

Abstract

Abstract. In this paper, we quantify the CO2 and N2O 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 CO2 and N2O over the entire watershed at 17.8 kgN ha−1 yr−1, 0.37 gC-CO2 m−2 yr−1 and 0.18 gN-N2O m−2 yr−1 respectively for the period 2011–2015. When compared to local observations, it was found that the CO2 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 N2O 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 N2O and CO2 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.

High greenhouse gas fluxes from peatlands under various disturbances in the Peruvian Amazon

“…Our measured emissions were relatively high compared to the average 31 ± 22 µg N2O-N m -2 h -1 (average ± standard deviation across studies) from the 410 ± 120 mg dry kg -1 soil NH4 + -N in Southeast Asian wetland forests (van Lent et al, 2015). Our measured fluxes were higher than model-predicted emissions of 21 µg N m -2 h -1 for the Amazon Basin (Guilhen et al, 2020) https://doi.org/10.5194/bg-2021-46 Preprint. Discussion started: 3 March 2021 c Author(s) 2021.…”

“…The 5.4 million km 2 Amazon rainforest is the biggest hotspot of N2O in the world (Figure 1; Ricaud et al, 2009) emitting 1,300 Gg N2O-N yr -1 (Melillo et al, 2001). The contribution of swamp forests to the hotspot is poorly known (van Lent et al, 2015;Guilhen et al, 2020) but a Peruvian palm peat swamp emitted 0.5 to 2.6 kg N2O-N ha -1 yr -1 (van Lent et al, 2015). This was similar to swamp forests of Southeast Asia that emit 2.7 ± 1.7 kg N2O-N ha -1 yr -1 (average ± standard deviation; van Lent et al, 2015).…”

Comment on bg-2021-46

“…Our measured emissions were relatively high compared to the average 31 ± 22 µg N2O-N m -2 h -1 (average ± standard deviation across studies) from the 410 ± 120 mg dry kg -1 soil NH4 + -N in Southeast Asian wetland forests (van Lent et al, 2015). Our measured fluxes were higher than model-predicted emissions of 21 µg N m -2 h -1 for the Amazon Basin (Guilhen et al, 2020) but agreed with huge N2O emissions from floodplains soils of the Brazilian Amazon by Figueiredo et al (2019). Soil NO3content was below the detection limit in most of the anaerobic peat samples.…”

“…The 5.4 million km 2 Amazon rainforest is the biggest hotspot of N2O in the world (Figure 1; Ricaud et al, 2009) emitting 1,300 Gg N2O-N yr -1 (Melillo et al, 2001). The contribution of swamp forests to the hotspot is poorly known (van Lent et al, 2015;Guilhen et al, 2020) but a Peruvian palm peat swamp emitted 0.5 to 2.6 kg N2O-N ha -1 yr -1 (van Lent et al, 2015). This was similar to swamp forests of Southeast Asia that emit 2.7 ± 1.7 kg N2O-N ha -1 yr -1 (average ± standard deviation; van Lent et al, 2015).…”

Amazon Hydrology From Space: Scientific Advances and Future Challenges

“…Guilhen et al. (2020) estimated N 2 O emissions from denitrification in Amazonian wetlands by adapting a simple denitrification model forced by open water surface extent from the Soil Moisture and Ocean Salinity (SMOS) satellite and reported a pattern in denitrification linked to inundation.…”