Contribution of regional sources to atmospheric methane over the Amazon Basin in 2010 and 2011

Abstract

We present an assessment of methane (CH 4 ) atmospheric concentrations over the Amazon Basin for 2010 and 2011 using a 3-D atmospheric chemical transport model, two wetland emission models, and new observations made during biweekly flights made over four locations within the basin. We attempt to constrain basin-wide CH 4 emissions using the observations, and since 2010 was an unusually dry year, we assess the effect of this drought on Amazonian methane emissions. We find that South American emissions contribute up to 150 ppb to concentrations at the sites, mainly originating from within the basin. Our atmospheric model simulations agree reasonably well with measurements at three of the locations (0.28 ≤ r 2 ≤ 0.63, mean bias ≤ 9.5 ppb). Attempts to improve the simulated background CH 4 concentration through analysis of simulated and observed sulphur hexafluoride concentrations do not improve the model performance, however. Through minimisation of seasonal biases between the simulated and observed atmospheric concentrations, we scale our prior emission inventories to derive total basin-wide methane emissions of 36.5-41.1 Tg(CH 4 )/yr in 2010 and 31.6-38.8 Tg(CH 4 )/yr in 2011. These totals suggest that the Amazon contributes significantly (up to 7%) to global CH 4 emissions. Our analysis indicates that factors other than precipitation, such as temperature variations or tree mortality, may have affected microbial emission rates. However, given the uncertainty of our emission estimates, we cannot say definitively whether the noncombustion emissions from the region were different in 2010 and 2011, despite contrasting meteorological conditions between the two years.

Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

“…Moreover, these data also emphasize the need for more spatially extensive sampling across both the Pastaza-Marañón foreland basin and the wider Amazon region as a whole in order to establish if these asynchronous seasonal emission patterns are commonplace or specific to peatlands in the PMFB region. If CH 4 emission patterns for different peatlands in the Amazon are in fact asynchronous and decoupled from rainfall seasonality, then this may partially explain some of the heterogeneity in CH 4 sources and sinks observed at the basin-wide scale (Wilson et al, 2016).…”

“…Recent basin-wide studies suggest that the Amazon as a whole accounts for approximately 7 % of global atmospheric CH 4 emissions (Wilson et al, 2016). N 2 O emissions are of a similar magnitude, with emissions ranging from 2 to 3 Tg N 2 O-N yr −1 (or approximately 12-18 % of global atmospheric emissions) (Huang et al, 2008;Saikawa et al, 2013Saikawa et al, , 2014.…”

“…While we have a relatively strong understanding of the role that the Amazon plays in regional and global atmospheric budgets of these gases, one of the key gaps in knowledge is the contribution of specific ecosystem types to regional fluxes of GHGs (Huang et al, 2008;Saikawa et al, 2013Saikawa et al, , 2014. In particular, our understanding of the contribution of Amazonian wetlands to regional C and GHG budgets is weak, as the majority of past ecosystem-scale studies have focused on terra firme forests and savannas (D'Amelio et al, 2009;Saikawa et al, 2013;Wilson et al, 2016;Kirschke et al, 2013;Nisbet et al, 2014). Empirical studies of GHG fluxes from Amazonian wetlands are more limited in geographic scope and have focused on three major areas: wetlands in the state of Amazonas near the city of Manaus (Devol et al, 1990;Bartlett et al, 1988Bartlett et al, , 1990Keller et al, 1986), the Pantanal region (Melack et al, 2004;Marani and Alvalá, 2007;Liengaard et al, 2013), and the Orinoco River basin (Smith et al, 2000;Lavelle et al, 2014).…”

“…Peatlands are one of the major wetland habitats absent from current bottom-up GHG inventories for the Amazon basin and are often grouped together with non-peat-forming wetlands in regional atmospheric budgets (Wilson et al, 2016). Unlike their Southeast Asian counterparts, most peatlands in the Amazon basin are unaffected by human activity at the current time (Lahteenoja et al, 2009a, b;Lahteenoja and Page, 2011), except for ecosystems in the Madre de Dios region in southeastern Peru, which are impacted by gold mining (Householder et al, 2012).…”

What are the greenhouse gas observing system requirements for reducing fundamental biogeochemical process uncertainty? Amazon wetland CH<sub>4</sub> emissions as a case study

“…The expansion of surface and aircraft observing networks has increased our understanding of the carbon cycle and is essential for precise quantification of trace-gas concentrations (Andrews et al, 2014;Sweeney et al, 2015;Wilson et al, 2016). Surface networks are intrinsically limited in their density, by cost, access to remote terrestrial and marine environments, environmental conditions and other logistical constraints (Schimel et al, 2015b).…”