Seasonal variability of tree methane emissions in the Central Amazon floodplain
Abstract
Saturated soils are a prerequisite for the production of methane (CH4), an important greenhouse gas. As such, models of wetland CH4 emission from floodplains tend to require inundated soils and sediments in order for CH4 to be produced and emitted. However, recent findings have identified trees as the dominant egress pathway for soil-produced CH4 which, in the Amazon floodplain are thought to be responsible for the emission of ~20 Tg CH4 annually to the atmosphere (Pangala et al 2017). That wetland-adapted trees are playing such a large role in emission of soil-produced methane raises the possibility that methane produced deep within the soil column may be accessed and vented to the atmosphere via deep rooting systems thus negating the need for water table to be at the surface for emissions to take place. To test this idea we repeatedly measured CH4 fluxes from the same trees experiencing a dynamic seasonal water table fluctuation across 3 locations in the Amazon River floodplain; the Rios Negro, Solimoes and Tapajos. We used tethered floats as tree tags to facilitate return visits to individual trees that experienced many metres of water table variability and inundation. We took flux measurements at 4 hydrologically distinct time points (rising, peak, declining and low water) from April 2017 to January 2018. Emissions were highest during rising and peak inundation declining rapidly with subsequent campaigns. Peak fluxes were consistent with previous measurements from trees in the Amazon floodplain i.e. up to ~200 mg CH4 m-2 hr-1 during the highest inundation. We identify a strong relationship between inundation, water table and methane emissions within a certain water table range that demonstrates that trees are able to emit methane produced in the soil when the water table is as low as 5m below the forest floor. This capacity for wetland-adapted trees to emit CH4 that was produced deep below the soil surface ultimately does away with the need for water-table to be at the surface for emissions to take place thereby extending the effective methane emitting surface area of forests to areas beyond those experiencing flooding at the time. We present results demonstrating that this increase in the effective CH4 emitting surface area of the Amazon forest constitutes an additional significant contribution to the regional methane budget.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B24B..02G
- Keywords:
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- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0490 Trace gases;
- BIOGEOSCIENCES;
- 0497 Wetlands;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE