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The Amazon River basin and its main tributaries mapped over the SRTM (Shuttle Radar Topography Mission -500 m) digital elevation model.
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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 tropi...
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... Amazon basin (Fig. 1) is the world's largest drainage basin with an area of 5.50 × 10 6 km 2 and an average water discharge of 208 000 m 3 s −1 (Callode et al., 2010) representing 20 % of all surface fresh water transported to the ocean. The watershed spans Bolivia, Colombia, Ecuador, French Guiana, Peru, Suriname and Guyana, and 68 % of the basin pertains ...
Context 2
... Amazon basin (Fig. 1) is the world's largest drainage basin with an area of 5.50 × 10 6 km 2 and an average water discharge of 208 000 m 3 s −1 (Callode et al., 2010) representing 20 % of all surface fresh water transported to the ocean. The watershed spans Bolivia, Colombia, Ecuador, French Guiana, Peru, Suriname and Guyana, and 68 % of the basin pertains ...
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Citations
... Under a full irrigation regime, the oxygen content of the soil decreases, which accelerates the processes of denitrification and the emission of N 2 O [121,122]. Additionally, more studies have reported a positive relationship between N 2 O and CO 2 emissions [123][124][125]. These previous works explain the significant positive interaction between nitrifying bacteria and the GHG emissions observed under the full irrigation regime in this study. ...
The soil microbial community is critically important in plant nutrition and health. However, this community is extremely sensitive to various environmental conditions. A pot experiment was conducted during the wheat seedling stage to better understand the influences of the coupled application of nitrogen (N) and microbial decomposing inoculants (MDI) on the soil bacteria community under different water regimes. There were two levels of water and six levels of fertilization. The results reveal that water stress increased the relative abundance of Acidobacteria and decreased that of Firmicutes and Proteobacteria. The application of 250 kg N ha−1 altered the diversity of the bacterial community but increased the relative abundance of nitrifying bacteria. Nitrous oxide (N2O) and carbon dioxide (CO2) emissions were negatively correlated with Myxococcota and Methylomirabilota while positively correlated with Patescibacteria. These two gases were also positively correlated with nitrifying bacteria, and the correlation was more significant under the full irrigation regime. These findings indicate that MDI does not substantially influence the soil bacterial community and its relationship with greenhouse gas emission at the wheat seedling stage and that the abundance of the soil bacterial community would mainly depend on the rational control of the amount of N and water applied.
... Brazil is a major contributor to the global increase in N 2 O emissions, owing to the increase in nitrogen (N) fertilisation (Thompson et al. 2019). Contribution of swamp forests to the Amazonian N 2 O emissions is poorly known (van Lent et al. 2015;Guilhen et al. 2020). A Peruvian palm peat swamp emitted 0.5 to 2.6 kg N 2 O-N ha -1 yr -1 (van Lent et al. 2015) and similar swamp forests in Southeast Asia emitted 2.7 ± 1.7 kg N 2 O-N ha -1 yr -1 (average ± standard deviation; van Lent et al. 2015). ...
... Asterisks directly above box without brackets denote significant difference from all other sites in the plot N 2 O-N m -2 h -1 (average ± standard deviation across studies) from the 410 ± 120 mg dry kg -1 soil NH 4 + -N in Southeast Asian wetland forests (van Lent et al. 2015), despite using an analogous measurement protocol (Hutchinson and Livingston 1993). Our measured fluxes were higher than model-predicted emissions of 21 µg N 2 O-N m -2 h -1 for the Amazon Basin (Guilhen et al. 2020) but agreed with huge N 2 O emissions from floodplains soils of the Brazilian Amazon by Figueiredo et al. (2019). ...
Amazonian swamp forests remove large amounts of carbon dioxide (CO 2 ) but produce methane (CH 4 ). Both are important greenhouse gases (GHG). Drought and cultivation cut the CH 4 emissions but may release CO 2 . Varying oxygen content in nitrogen-rich soil produces nitrous oxide (N 2 O), which is the third most important GHG. Despite the potentially tremendous changes, GHG emissions from wetland soils under different land uses and environmental conditions have rarely been compared in the Amazon. We measured environmental characteristics, and CO 2 , CH 4 and N 2 O emissions from the soil surface with manual opaque chambers in three sites near Iquitos, Peru from September 2019 to March 2020: a pristine peat swamp forest, a young forest and a slash-and-burn manioc field. The manioc field showed moderate soil respiration and N 2 O emission. The peat swamp forests under slight water table drawdown emitted large amounts of CO 2 and CH 4 . A heavy post-drought shower created a hot moment of N 2 O in the pristine swamp forest, likely produced by nitrifiers. All in all, even small changes in soil moisture can create hot moments of GHG emissions from Amazonian wetland soils, and should therefore be carefully monitored.
... The freshwater systems of the Amazon basin, including a massive network of rivers and wetlands, play an important role in Earth's hydrological and biogeochemical cycles (Salati and Marques 1984;Guilhen et al. 2020;Fassoni-Andrade et al. 2021;Fleischmann et al. 2022). Many species in the region are adapted to and thus depend on wetlands (Melack and Coe 2021;Junk 1997). ...
Extreme droughts and floods in the Amazon have great implications for ecosystems and societies. Over the last decade, the region has undergone major extreme events with no equivalent in the previous 100 years. Wetlands have been greatly impacted by these events. This study aims at presenting new indicators for wetlands based on Water Surface Extent (WSE): duration of the flooded and non-flooded season, number of days of extreme events, delay of the start of the flooded season, and severity for each season. These indicators are more adapted for monitoring of wetlands than those based on precipitation, discharge or groundwater information. They are computed for seven major Amazon sub-basins for flooded and non-flooded seasons. These indicators improve our knowledge of the temporal behavior of water surface during different extreme events, such as the 2015/2016 drought and the 2014 flood occurred in the Madeira basin. For the Negro basin and from the point of view of wetlands, the 2015 non-flooded season was 55% more severe than the average of the non-flooded season during the 2011-2018 period. For the Paru, Trombetas, Negro and Solimões basins, we found that a delay in the arrival of the flooded season led to a weak flood season in terms of severity. No correlation between the onset of the flooded season and its severity was found for the Madeira, Xingu and Tapajós basins. Future hydrometeorological monitoring systems would benefit from including, in addition to variables such as river discharge and water elevation, precipitation and vegetation dynamics, a severity index based on water surfaces as proposed in this study.
... The extent of inundated land (also called flooded land or surface water extent), and its temporal variation, are core variables to understand wetland processes and are of interest for multiple scientific disciplines, including ecology Hawes et al., 2012;Luize et al., 2015), land-atmosphere interactions (Prigent et al., 2011;;Taylor et al., 2018), carbon cycling and greenhouse gas emissions (Guilhen et al., 2020;Melack et al., 2004;Richey et al., 2002), and natural hazard management (Restrepo et al., 2020;Trigg et al., 2016). The Amazon basin has been a focus for remote sensing developments and applications in hydrology (Fassoni-Andrade et al., 2021), especially for inundation estimation, given the basin's large scale and global environmental relevance, relatively pristine landscape, and technical challenges posed by persistent cloud cover (Asner, 2001) and dense vegetation. ...
... First, different datasets have been used to quantify the role of Amazon wetlands in the carbon cycle (Guilhen et al., 2020;Melack et al., 2004;Richey et al., 2002;Saunois et al., 2020). An intercomparison assessment of global models forced with different inundation datasets for the Amazon could provide insights into their sensitivity to the estimated inundation. ...
The Amazon River basin harbors some of the world's largest wetland complexes, which are of major importance for biodiversity, the water cycle and climate, and human activities. Accurate estimates of inundation extent and its variations across spatial and temporal scales are therefore fundamental to understand and manage the basin's resources. More than fifty inundation estimates have been generated for this region, yet major differences exist among the datasets, and a comprehensive assessment of them is lacking. Here we present an intercomparison of 29 inundation datasets for the Amazon basin, based on remote sensing only, hydrological modeling, or multi-source datasets, with 18 covering the lowland Amazon basin (elevation <500 m, which includes most Amazon wetlands), and 11 covering individual wetland complexes (subregional datasets). Spatial resolutions range from 12.5 m to 25 km, and temporal resolution from static to monthly, spanning up to a few decades. Overall, 31% of the lowland basin is estimated as subject to inundation by at least one dataset. The long-term maximum inundated area across the lowland basin is estimated at 599,700 ± 81,800 km² if considering the three higher quality SAR-based datasets, and 490,300 ± 204,800 km² if considering all 18 datasets. However, even the highest resolution SAR-based dataset underestimates the maximum values for individual wetland complexes, suggesting a basin-scale underestimation of ~10%. The minimum inundation extent shows greater disagreements among datasets than the maximum extent: 139,300 ± 127,800 km² for SAR-based ones and 112,392 ± 79,300 km² for all datasets. Discrepancies arise from differences among sensors, time periods, dates of acquisition, spatial resolution, and data processing algorithms. The median total area subject to inundation in medium to large river floodplains (drainage area > 1000 km²) is 323,700 km². The highest spatial agreement is observed for floodplains dominated by open water such as along the lower Amazon River, whereas intermediate agreement is found along major vegetated floodplains fringing larger rivers (e.g., Amazon mainstem floodplain). Especially large disagreements exist among estimates for interfluvial wetlands (Llanos de Moxos, Pacaya-Samiria, Negro, Roraima), where inundation tends to be shallower and more variable in time. Our data intercomparison helps identify the current major knowledge gaps regarding inundation mapping in the Amazon and their implications for multiple applications. In the context of forthcoming hydrology-oriented satellite missions, we make recommendations for future developments of inundation estimates in the Amazon and present a WebGIS application (https://amazon-inundation.herokuapp.com/) we developed to provide user-friendly visualization and data acquisition of current Amazon inundation datasets.
... Average N 2 O soil fluxes measured in our study were 2.5-7 times higher than model-predicted emissions of 21 µg N m −2 h −1 for the Amazon Basin (Guilhen et al., 2020) during the dryer period just after the heavy rainfall could indicate the presence of nitrate or other denitrification product in these soils and the effect of pulsing water level (Pärn et al., 2018). ...
Tree stems in tropical peat swamp forests are known as considerable methane (CH4) emitters; however, little is known about their carbon dioxide (CO2) and nitrous oxide (N2O) exchange. Differences between species, especially the role of palm stems in the exchange of greenhouse gasses, have remained largely unknown. We measured stem CO2, CH4, and N2O fluxes from the different heights of widely spread aguaje palms (Mauritia flexuosa) and boarwoods (Symphonia globulifera) and the soil beneath the same trees in a Peruvian Amazon palm swamp using a static closed chamber technique from September 2019 to March 2020. The tree stems were the net emitters of CO2 and CH4 but occasionally showed low N2O uptake. We found the highest stem CH4 emissions (average ± SE) from palm stems of the height of 80 cm (1,601 ± 165.9 μg C m–2 h–1), which are more than 300 times greater compared to the highest fluxes from boarwood stems, at the height of 30 cm (5.12 ± 1.27 μg C m–2 h–1). The average soil CH4 flux was 3,618 ± 465 μg C m–2 h–1. Whereas N2O fluxes from the stems were negligible, the average N2O fluxes from soils beneath the same trees were relatively high, ranging from 53.75 ± 24.04 (close to boarwood trees) to 143.4 ± 68.43 (close to palms) μg N m–2 h–1. While roughly upscaling tree-level fluxes to the stand level of 27,732 km2 of palm swamp in the Pastaza-Marañon foreland basin, these forests are net annual emitters of CH4 and N2O (897 Gg C y–1 and 24 Gg N y–1, respectively). These results highlight the necessity to study this kind of ecosystem more intensely.
... The high rates of precipitation, evapotranspiration and large variations in freshwater storage and river discharge make the Amazon basin a key player in the global climate system, with large contributions to the water, energy, and carbon cycles (Gash et al., 2013;Gatti et al., 2021;Nagy et al., 2016). Amazon surface waters, for instance, are a major source and sink of carbon dioxide (Abril et al., 2014;Amaral et al., 2020;Guilhen et al., 2020;Raymond et al., 2013;Richey et al., 2002) and the largest natural geographic source of methane in the tropics (Kirschke et al., 2013;Melack et al., 2004;Pangala et al., 2017;Pison et al., 2013). Seasonal variations in the water contribute to the formation of tropical forests (Leite et al., 2012), maintain high aquatic productivity (Melack & Forsberg, 2001) and biodiversity (Junk, 1997;Junk et al., 2010), and influence fish distributions and fisheries yield (Junk et al., 2010;Lobón-Cerviá et al., 2015; Figure 1). ...
... The move to hyper-resolution models has been promoted at a global scale due to the development of new numerical techniques, equation sets, and software engineering, as well as increased computing power (Bates et al., 2018). Such modeling systems could then be coupled to models of other processes, as recently done by researchers aiming at understanding flooding impacts on photosynthesis and biosphere in general (Aderson de Castro et al., 2018), feedbacks between surface waters and atmosphere , sediment exports and floodplain trapping (Fagundes et al., 2021;Rudorff et al., 2018), carbon storage and emissions through wetlands and uplands (Hastie et al., 2019;Lauerwald et al., 2020), and dynamics of biogeochemistry cycles at the basin scale or over wetlands (Guilhen et al., 2020). All these efforts will require additional RS data and will move forward our predictability of the effects of ongoing environmental changes in the Amazon basin. ...
... Richey et al. (2002) and Melack (2016) also used estimates of surface water extent to calculate carbon dioxide fluxes. Guilhen et al. (2020) Seminal approaches with RS data were used to delineate inundated area and extent of flooded forests, open water, and herbaceous plants (e.g., Hamilton et al., 2002;Hess et al., 1995Hess et al., , 2003Hess et al., , 2015; Section 4.2) and used to improve estimates of seasonal and interannual variations in methane fluxes. As described in Section 4.2, new satellite-borne sensors and remote-sensing products can now be used to update such approaches (e.g., Parrens et al., 2019;Prigent et al., 2020). ...
Satellite observations offer invaluable insights into hydrological processes and environmental change in the Amazon.
The Amazon Basin is the largest river basin in the world. It covers roughly six million square kilometers, which is about one third of South America. While the sheer scale and difficulty of access makes field observations challenging, remote sensing can provide rich insights. An article recently published in Reviews of Geophysics explores the strengths and limitations of satellite observations of the Amazon basin and makes recommendations for improving these observational systems.
... The extent of inundated land (also called flooded land or surface water extent), and its temporal variation, are core variables to understand wetland processes and are of interest for multiple scientific disciplines, including ecology Hawes et al., 2012;Luize et al. 2015), land-atmosphere interactions (Prigent et al., 2011;Santos et al., 2019;Taylor et al., 2018), carbon cycling and greenhouse gas emissions (Guilhen et al., 2020;Melack et al., 2004;Richey et al., 2002), and natural hazard management (Restrepo et al., 2020;Trigg et al., 2016). The Amazon Basin has been a focus for remote sensing developments and applications in hydrology (Fassoni-Andrade et al., 2021), especially for inundation estimation, given the basin's large scale and global environmental relevance, relatively pristine landscape, and technical challenges posed by persistent cloud cover (Asner, 2001) and dense vegetation. ...
... First, different products have been used to quantify the role of Amazon wetlands in the carbon cycle (Guilhen et al., 2020;Melack et al., 2004;Richey et al., 2002;Saunois et al., 2020). An intercomparison assessment of global models forced with different inundation datasets for the Amazon could provide insights into their sensitivity to the estimated inundation. ...
... Such modeling systems could then be coupled to models of other processes, as recently done by researchers aiming at understanding flooding impacts on photosynthesis and biosphere in general (Castro et al., 2018), feedbacks between surface waters and atmosphere (M. J. Santos et al., 2019), sediment exports and floodplain trapping (Fagundes et al., 2021;Rudorff et al., 2018), carbon storage and emissions through wetlands and uplands (Hastie et al., 2019;Lauerwald et al., 2020), and dynamics of biogeochemistry cycles at the basin scale or over wetlands (Guilhen et al., 2020). All these efforts will require additional RS data, and will move forward our predictability of the effects of ongoing environmental changes in the Amazon basin. ...
... Richey et al. (2002) and Melack (2016) also used estimates of surface water extent to calculate carbon dioxide fluxes. Guilhen et al. (2020) estimated N2O 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. ...
As the largest river basin on Earth, the Amazon is of major importance to the world's climate and water resources. Over the past decades, advances in satellite‐based remote sensing (RS) have brought our understanding of its terrestrial water cycle and the associated hydrological processes to a new era. Here, we review major studies and the various techniques using satellite RS in the Amazon. We show how RS played a major role in supporting new research and key findings regarding the Amazon water cycle, and how the region became a laboratory for groundbreaking investigations of new satellite retrievals and analyses. At the basin‐scale, the understanding of several hydrological processes was only possible with the advent of RS observations, such as the characterization of "rainfall hotspots" in the Andes‐Amazon transition, evapotranspiration rates, and variations of surface waters and groundwater storage. These results strongly contribute to the recent advances of hydrological models and to our new understanding of the Amazon water budget and aquatic environments. In the context of upcoming hydrology‐oriented satellite missions, which will offer the opportunity for new synergies and new observations with finer space‐time resolution, this review aims to guide future research agenda toward integrated monitoring and understanding of the Amazon water from space. Integrated multidisciplinary studies, fostered by international collaborations, set up future directions to tackle the great challenges the Amazon is currently facing, from climate change to increased anthropogenic pressure.
