Dataset Information

Sediment fluxes rather than oxic methanogenesis explain diffusive CH₄ emissions from lakes and reservoirs.

ABSTRACT: Methane emissions from lakes and reservoirs are a major natural source in the global budget of atmospheric CH₄. A large fraction of these emissions are due to diffusive transport of CH₄ from surface waters to the atmosphere. It was suggested recently that CH₄ production in the oxic surface waters is required to compensate for diffusive CH₄ emissions from lakes. In contrast, we demonstrate here that typical diffusive CH₄-fluxes from sediments in shallow water zones, F_sed,S, suffice to explain CH₄ emissions to the atmosphere. Our analysis is based on the combination of an exceptional data set on surface concentrations of CH₄ with a mass balance model of CH₄ that is focused on the surface mixed layer and considers CH₄-fluxes from sediments, lateral transport, gas exchange with the atmosphere, and includes temperature dependencies of sediment fluxes and gas exchange. F_sed,S not only explains observed surface CH₄ concentrations but also concentration differences between shallow and open water zones, and the seasonal variability of emissions and lateral concentration distributions. Hence, our results support the hypothesis that diffusive fluxes from shallow sediments and not oxic methanogenesis are the main source of the CH₄ in the surface waters and the CH₄ emitted from lakes and reservoirs.

SUBMITTER: Peeters F

PROVIDER: S-EPMC6338738 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Sediment fluxes rather than oxic methanogenesis explain diffusive CH4 emissions from lakes and reservoirs.

Peeters Frank F Encinas Fernandez Jorge J Hofmann Hilmar H

Scientific reports 20190118 1

Methane emissions from lakes and reservoirs are a major natural source in the global budget of atmospheric CH4. A large fraction of these emissions are due to diffusive transport of CH4 from surface waters to the atmosphere. It was suggested recently that CH4 production in the oxic surface waters is required to compensate for diffusive CH4 emissions from lakes. In contrast, we demonstrate here that typical diffusive CH4-fluxes from sediments ...[more]

PMID: 30659224

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Project description:Mauritia flexuosa palm swamp, the prevailing Peruvian Amazon peatland ecosystem, is extensively threatened by degradation. The unsustainable practice of cutting whole palms for fruit extraction modifies forest's structure and composition and eventually alters peat-derived greenhouse gas (GHG) emissions. We evaluated the spatiotemporal variability of soil N2 O and CH4 fluxes and environmental controls along a palm swamp degradation gradient formed by one undegraded site (Intact), one moderately degraded site (mDeg) and one heavily degraded site (hDeg). Microscale variability differentiated hummocks supporting live or cut palms from surrounding hollows. Macroscale analysis considered structural changes in vegetation and soil microtopography as impacted by degradation. Variables were monitored monthly over 3 years to evaluate intra- and inter-annual variability. Degradation induced microscale changes in N2 O and CH4 emission trends and controls. Site-scale average annual CH4 emissions were similar along the degradation gradient (225.6 ± 50.7, 160.5 ± 65.9 and 169.4 ± 20.7 kg C ha-1 year-1 at the Intact, mDeg and hDeg sites, respectively). Site-scale average annual N2 O emissions (kg N ha-1 year-1 ) were lower at the mDeg site (0.5 ± 0.1) than at the Intact (1.3 ± 0.6) and hDeg sites (1.1 ± 0.4), but the difference seemed linked to heterogeneous fluctuations in soil water-filled pore space (WFPS) along the forest complex rather than to degradation. Monthly and annual emissions were mainly controlled by variations in WFPS, water table level (WT) and net nitrification for N2 O; WT, air temperature and net nitrification for CH4 . Site-scale N2 O emissions remained steady over years, whereas CH4 emissions rose exponentially with increased precipitation. While the minor impact of degradation on palm swamp peatland N2 O and CH4 fluxes should be tested elsewhere, the evidenced large and variable CH4 emissions and significant N2 O emissions call for improved modeling of GHG dynamics in tropical peatlands to test their response to climate changes.

Dataset Information

Sediment fluxes rather than oxic methanogenesis explain diffusive CH₄ emissions from lakes and reservoirs.

Publications

Sediment fluxes rather than oxic methanogenesis explain diffusive CH<sub>4</sub> emissions from lakes and reservoirs.

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