Wetlands are important sources of methane (CH4) and sinks of carbon dioxide (CO2). However, little is known about CH4and CO2fluxes and dynamics of seasonally flooded tropical forests of South America in relation to local carbon (C) balances and atmospheric exchange. We measured net ecosystem fluxes of CH4and CO2in the Pantanal over 2014–2017 using tower‐based eddy covariance along with C measurements in soil, biomass and water. Our data indicate that seasonally flooded tropical forests are potentially large sinks for CO2but strong sources of CH4, particularly during inundation when reducing conditions in soils increase CH4production and limit CO2release. During inundation when soils were anaerobic, the flooded forest emitted 0.11 ± 0.002 g CH4‐C m−2 d−1and absorbed 1.6 ± 0.2 g CO2‐C m−2 d−1(mean ± 95% confidence interval for the entire study period). Following the recession of floodwaters, soils rapidly became aerobic and CH4emissions decreased significantly (0.002 ± 0.001 g CH4‐C m−2 d−1) but remained a net source, while the net CO2flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH4fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO2and CH4were similar in all years for each season, but annual net fluxes varied primarily in relation to flood duration. While the ecosystem was a net C sink on an annual basis (absorbing 218 g C m−2(as CH4‐C + CO2‐C) in anaerobic phases and emitting 76 g C m−2in aerobic phases), high CH4effluxes during the anaerobic flooded phase and modest CH4effluxes during the aerobic phase indicate that seasonally flooded tropical forests can be a net source of radiative forcings on an annual basis, thus acting as an amplifying feedback on global warming.
Limited information on greenhouse gas emissions from tropical dry forest soils still hinders the assessment of the sources/sinks from this ecosystem and their contribution at global scales. Particularly, rewetting events after the dry season can have a significant effect on soil biogeochemical processes and associated exchange of greenhouse gases. This study evaluated the temporal variation and annual fluxes of CO2, N2O, and CH4from soils in a tropical dry forest successional gradient. After a prolonged drought of 5 months, large emissions pulses of CO2and N2O were observed at all sites following first rain events, caused by the “Birch effect,” with a significant effect on the net ecosystem exchange and the annual emissions budget. Annual CO2emissions were greatest for the young forest (8,556 kg C ha−1yr−1) followed by the older forest (7,420 kg C ha−1yr−1) and the abandoned pasture (7,224 kg C ha−1yr−1). Annual emissions of N2O were greatest for the forest sites (0.39 and 0.43 kg N ha−1yr−1) and least in the abandoned pasture (0.09 kg N ha−1yr−1). CH4uptake was greatest in the older forest (−2.61 kg C ha−1yr−1) followed by the abandoned pasture (−0.69 kg C ha−1yr−1) and the young forest (−0.58 kg C ha−1yr−1). Fluxes were mainly influenced by soil moisture, microbial biomass, and soil nitrate and ammonium concentrations. Annual CO2and N2O soil fluxes of tropical dry forests in this study and others from the literature were much lower than the annual fluxes in wetter tropical forests. Conversely, tropical dry forests and abandoned pastures are on average stronger sinks for CH4than wetter tropical forests.more » « less
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- DOI PREFIX: 10.1029
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- Journal of Geophysical Research: Biogeosciences
- Medium: X
- Sponsoring Org:
- National Science Foundation
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