Radiative forcing of methane fluxes offsets net carbon dioxide uptake for a tropical flooded forest

Abstract

Wetlands are important sources of methane (CH4) and sinks of carbon dioxide (CO2). However, little is known about CH4 and CO2 fluxes 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 CH4 and CO2 in 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 CO2 but strong sources of CH4, particularly during inundation when reducing conditions in soils increase CH4 production and limit CO2 release. During inundation when soils were anaerobic, the flooded forest emitted 0.11 ± 0.002 g CH4‐C m−2 d−1 and 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 CH4 emissions decreased significantly (0.002 ± 0.001 g CH4‐C m−2 d−1) but remained a net source, while the net CO2 flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH4 fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO2 and CH4 were 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 CH4 effluxes during the anaerobic flooded phase and modest CH4 effluxes 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.

Impact of forest plantation on methane emissions from tropical peatland

“…This difference could be attributable to vegetation‐mediated transport, which was not captured by most of the studies used to derive the IPCC CH 4 emission factor (Blain et al, ). Our annual NEE‐CH 4 over the natural forest are nevertheless lower than those reported from Amazonian peatlands (Teh et al, ) and floodplain wetlands (Dalmagro et al, ; Pangala et al, ). In Amazonian peatlands, CH 4 production is greater owing to high nutrient status and soil pH, and low recalcitrant carbon (Wassmann et al, ).…”

“…We applied two gap-filling approaches (a) mean diurnal course (MDC; Dengel, Levy, Grace, Jones, & Skiba, 2011;Sakabe et al, 2018;Wong et al, 2018) and (b) marginal distribution sampling (MDS; Alberto et al, 2014;Dalmagro et al, 2019;Tang et al, 2018) using the REddyProc package (Wutzler et al, 2018). The MDC is a simple interpolation technique where the missing value is replaced with the averaged value of the adjacent days at exactly that time of day (Falge et al, 2001).…”

Spatial and Temporal Variations in Aboveground Woody Carbon Storage for Cerrado Forests and Woodlands of Mato Grosso, Brazil

“…Drought that normally occurs during the dry season in the southern Amazon Basin causes limitations to leaf photosynthesis (Dalmagro et al, ; Dalmolin et al, ) and net CO 2 exchange (Vourlitis et al, ; Zanella De Arruda et al, ), but during El Niño, drought stress becomes more intense and/or prolonged (Panisset et al, ). The 2015–16 El Niño also caused a decline in net CO 2 uptake for a hyperseasonal forest in the PAN (Dalmagro et al, ) and a decline in gross primary production for woodlands in the southern Amazon Basin (Zhu et al, ). Together, these studies indicate that the decline in Δ C w observed for our study sites may have been widespread across the southern Amazon Basin.…”

Gap‐filling approaches for eddy covariance methane fluxes: A comparison of three machine learning algorithms and a traditional method with principal component analysis

“…WET.PT is thus a seasonal wetland with the WTH near or above the ground level only during wet season. CH 4 emissions occur almost exclusively during the wet season, with inundation acting like a switch (Dalmagro et al, ). In this site, soil respiration and FCH 4 are largely controlled by WTH and soil water content from hourly to weekly timescales (e.g., Johnson et al, ).…”