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Abstract Tropical floodplains are an important source of methane (CH4) to the atmosphere, and ebullitive fluxes are likely to be important. We report direct measurements of CH4ebullition in common habitats on the Amazon floodplain over two years based on floating chambers that allowed detection of bubbles, and submerged bubble traps. Ebullition was highly variable in space and time. Of the 840 floating chamber measurements (equivalent to 8,690 min of 10‐min deployments), 22% captured bubbles. Ebullitive CH4fluxes, measured using bubble traps deployed for a total of approximately 230 days, ranged from 0 to 109 mmol CH4m−2 d−1, with a mean of 4.4 mmol CH4m−2 d−1. During falling water, a hydroacoustic echosounder detected bubbles in 24% of the 70‐m segments over 34 km. Ebullitive flux increased as the water level fell faster during falling water periods. In flooded forests, highest ebullitive fluxes occurred during falling water, while in open water and herbaceous plant habitats, higher ebullitive fluxes were measured during low water periods. The contribution of diffusive plus ebullitive CH4flux represented by ebullition varied from 1% (high and rising water in open water of the lake) to 93% (falling water in flooded forests) based on bubble traps. Combining ebullitive and diffusive fluxes among habitats in relation to variations in water depth and areal coverage of aquatic habitats provides the basis for improved floodplain‐wide estimates of CH4evasion.
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This content will become publicly available on October 1, 2026
Bald Cypress ( Taxodium distichum ) Knees Are Methane Sources Controlled by Geomorphology, Climate, and Hydrologic Extremes
Abstract While woody root structures, such as bald cypress (Taxodium distichum) “knees,” can act as conduits of methane (CH4), little has been done to explain variation from this flux pathway. We captured spatial (i.e., across knee surface, within sites, between sites) and temporal dynamics of CH4from knees, and built empirical models to predict the contribution of knees to net CH4fluxes. Knee and soil CH4fluxes were measured across seasons within the lower Mississippi Alluvial Valley in a main channel (semi‐permanently flooded), side channel (seasonally flooded), and a reservoir edge (artificially flooded). Knees were a net source of CH4across all seasons, even during periods of soil CH4uptake. During periods of high knee CH4efflux, fluxes varied across the knee surface, decreasing with height from the ground. Knee CH4fluxes at the main and side channels decreased during a severe drought and increased ∼ ten‐fold in summer and two‐fold in winter following flooding events. At the reservoir edge, knee fluxes differed between the controlled draw up and draw down at the same water level, likely due to differences in temperature and oxygen availability. Knee CH4fluxes were positively correlated with water level (measured from subsurface wells, above ∼−70 cm in the soil profile) and subsurface temperature, but the strength of the relationships differed across geomorphic positions. Cypress knees appear to be an important contributor to wetland CH4efflux and accounting for the density of knees is needed to upscale their fluxes and better understand their ecosystem contribution.
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- Award ID(s):
- 2327374
- PAR ID:
- 10648733
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 130
- Issue:
- 10
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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