Large Methane Emission Fluxes Observed From Tropical Wetlands in Zambia

Abstract

Methane (CH4) is a potent greenhouse gas with a warming potential 84 times that of carbon dioxide (CO2) over a 20‐year period. Atmospheric CH4 concentrations have been rising since the nineteenth century but the cause of large increases post‐2007 is disputed. Tropical wetlands are thought to account for ∼20% of global CH4 emissions, but African tropical wetlands are understudied and their contribution is uncertain. In this work, we use the first airborne measurements of CH4 sampled over three wetland areas in Zambia to derive emission fluxes. Three independent approaches to flux quantification from airborne measurements were used: Airborne mass balance, airborne eddy‐covariance, and an atmospheric inversion. Measured emissions (ranging from 5 to 28 mg m−2 hr−1) were found to be an order of magnitude greater than those simulated by land surface models (ranging from 0.6 to 3.9 mg m−2 hr−1), suggesting much greater emissions from tropical wetlands than currently accounted for. The prevalence of such underestimated CH4 sources may necessitate additional reductions in anthropogenic greenhouse gas emissions to keep global warming below a threshold of 2°C above preindustrial levels.

Bottom‐Up Evaluation of the Methane Budget in Asia and Its Subregions

“…The spread of ±10 Tg CH 4 yr −1 implies that the estimates for the wetland sector by wetland models, which differ in model structure, environmental response functions, and parameter values, include considerable uncertainty. The inter‐model difference in South Asian emissions, which ranges from 1.6 to 13.5 Tg CH 4 yr −1 , is remarkable and implies a serious inconsistency in model performance in this subregion (e.g., Ganesan et al., 2018; Shaw et al., 2022).…”

“…CH 4 emissions from natural wetlands have been recognized as one of the major sources of CH 4 . However, simulating the flux with existing wetland models is still difficult because of spatiotemporal heterogeneity and the complexity of the factors that regulate the biogeochemical processes, as revealed by observational validation and model intercomparison studies (e.g., France et al., 2022; Shaw et al., 2022). In the present study, we used a well‐examined model, the Vegetation Integrative SImulator for Trace gases (VISIT: Ito, 2019; Ito & Inatomi, 2012), to simulate F wtl .…”

Satellite data reveal how Sudd wetland dynamics are linked with globally-significant methane emissions

“…The Sudd wetland is fed by seasonal rainfall, particularly in the second half of the calendar year, and by inflow from the White Nile (Bahr el Jebel) (Rebelo et al 2012). Variation in the flood pulse has led to significant changes in the coverage of inundated vegetation, which is now recognized as a key factor behind the magnitude and spatial distribution of methane emissions from natural wetlands (Helfter et al 2022, Shaw et al 2022.…”

“…phragmites, papyrus, rice), sediment ebullition, and diffusive fluxes at the water-atmosphere interface, although further work is needed to understand their relative importance on a regional scale. Analysis of field studies suggest that plant-mediated emissions of methane play a key role over tropical wetlands (Helfter et al 2022, Shaw et al 2022.…”

“…This represents an important shortcoming for mapping wetlands over the tropics where a significant fraction of surface water has emergent or floating vegetation (Hardy et al 2019). Atmospheric measurements have shown that elevated methane emissions from tropical wetlands are highly correlated with these vegetation types (Helfter et al 2022, Shaw et al 2022.…”