High peatland methane emissions following permafrost thaw : enhanced acetoclastic methanogenesis during early successional stages

Permafrost thaw in northern peatlands often leads to increased methane (CH4) emissions, but the underlying controls responsible for increased emissions and the duration for which they persist have yet to be fully elucidated. We assessed how shifting environmental conditions affect microbial communities and the magnitude and stable isotopic signature (delta C-13) of CH4 emissions along a thermokarst bog transect in boreal western Canada. Thermokarst bogs develop following permafrost thaw when dry, elevated peat plateaus collapse and become saturated and dominated by Sphagnum mosses. We differentiated between a young and a mature thermokarst bog stage (similar to 30 and similar to 200 years since thaw, respectively). The young bog located along the thermokarst edge was wetter, warmer, and dominated by hydrophilic vegetation compared to the mature bog. Using high-throughput 16S rRNA gene sequencing, we show that microbial communities were distinct near the surface and converged with depth, but fewer differences remained down to the lowest depth (160 cm). Microbial community analysis and delta C-13 data from CH4 surface emissions and dissolved gas depth profiles show that hydrogenotrophic methanogenesis was the dominant pathway at both sites. However, mean delta C-13-CH4 signatures of both dissolved gas profiles and surface CH4 emissions were found to be iso-topically heavier in the young bog (-63 parts per thousand and -65 parts per thousand, respectively) compared to the mature bog (-69 parts per thousand and -75 parts per thousand, respectively), suggesting that acetoclastic methano-genesis was relatively more enhanced throughout the young bog peat profile. Furthermore, mean young bog CH4 emissions of 82 mg CH4 m(-2) d(-1) were similar to 3 times greater than the 32 mg CH4 m(-2) d(-1) observed in the mature bog. Our study suggests that interactions between the methano-genic community, hydrophilic vegetation, warmer temperatures, and saturated surface conditions enhance CH4 emissions in young thermokarst bogs but that these favourable conditions only persist for the initial decades after permafrost thaw

Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils

PublishedIncreasing temperatures in northern high latitudes are causing permafrost to thaw1, making large amounts of previously frozen organic matter vulnerable to microbial decomposition2. Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions3, 4 that determine the amount and form (carbon dioxide (CO2), or methane (CH4)) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear5, 6. We quantified the effect of increasing temperature and changes from aerobic to anaerobic soil conditions using 25 soil incubation studies from the permafrost zone. Here we show, using two separate meta-analyses, that a 10 °C increase in incubation temperature increased C release by a factor of 2.0 (95% confidence interval (CI), 1.8 to 2.2). Under aerobic incubation conditions, soils released 3.4 (95% CI, 2.2 to 5.2) times more C than under anaerobic conditions. Even when accounting for the higher heat trapping capacity of CH4, soils released 2.3 (95% CI, 1.5 to 3.4) times more C under aerobic conditions. These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO2 will strengthen the permafrost C feedback more than waterlogged systems releasing CO2 and CH4 for a given amount of C.Financial support was provided by the National Science Foundation Vulnerability of Permafrost Carbon Research Coordination Network Grant no. 955713 with continued support from the National Science Foundation Research Synthesis, and Knowledge Transfer in a Changing Arctic: Science Support for the Study of Environmental Arctic Change Grant no. 1331083. Author contributions were also supported by grants to individuals: Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program (DE-SC0006982) to E.A.G.S.; UK Natural Environment Research Council funding to I.P.H. and C.E.-A. (NE/K000179/1); German Research Foundation (DFG, Excellence cluster CliSAP) to C.K.; Department of Ecosystem Biology, Grant agency of South Bohemian University, GAJU project no. 146/2013/P and GAJU project no. 146/2013/D to H.S.; National Science Foundation Office of Polar Programs (1312402) to S.M.N.; National Science Foundation Division of Environmental Biology (0423385) and National Science Foundation Division of Environmental Biology (1026843), both to the Marine Biological Laboratory, Woods Hole, Massachusetts; additionally, the Next-Generation Ecosystem Experiments in the Arctic (NGEE Arctic) project is supported by the Biological and Environmental Research programme in the US Department of Energy (DOE) Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the DOE under Contract no. DE-AC05-00OR22725. Support for C.B. came from European Union (FP-7-ENV-2011, project PAGE21, contract no. 282700), Academy of Finland (project CryoN, decision no. 132 045), Academy of Finland (project COUP, decision no. 291691; part of the European Union Joint Programming Initiative, JPI Climate), strategic funding of the University of Eastern Finland (project FiWER) and Maj and Tor Nessling Foundation and for P.J.M. from Nordic Center of Excellence (project DeFROST)

Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils

© 2016 Macmillan Publishers Limited, part of Springer Nature. Increasing temperatures in northern high latitudes are causing permafrost to thaw, making large amounts of previously frozen organic matter vulnerable to microbial decomposition. Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions that determine the amount and form (carbon dioxide (CO2), or methane (CH 4)) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear. We quantified the effect of increasing temperature and changes from aerobic to anaerobic soil conditions using 25 soil incubation studies from the permafrost zone. Here we show, using two separate meta-analyses, that a 10 °C increase in incubation temperature increased C release by a factor of 2.0 (95% confidence interval (CI), 1.8 to 2.2). Under aerobic incubation conditions, soils released 3.4 (95% CI, 2.2 to 5.2) times more C than under anaerobic conditions. Even when accounting for the higher heat trapping capacity of CH 4, soils released 2.3 (95% CI, 1.5 to 3.4) times more C under aerobic conditions. These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO2 will strengthen the permafrost C feedback more than waterlogged systems releasing CO2 and CH 4 for a given amount of C

Methane emissions and production potentials of forest swamp wetlands in the eastern Great Xing'An Mountains, Northeast China

Measurements of methane flux at a few inundated sites in China have been extrapolated to obtain estimates on a national scale. To enable those national estimates to be refined and to compare flux from geographically separated sites comprising the same wetland types, we used a closed chamber method to measure methane flux in uninundated Betula platyphylla-and Larix gmelinii-dominated peatlands in the Northeast China. Our measurements were taken from both vegetated and bare soil surfaces, and we compared flux with environmental measures including vegetation biomass, soil temperature and soil characteristics. We found that methane flux was low, and that there were no significant differences between wetland types, indicating that environmental influences were dominant. We found that flux was positively correlated to temperature in the surface layers of the soil, the above-ground biomass of the shrub and herb layers, total soil carbon and total soil nitrogen; and we suggest that emissions may be due to anaerobic microcosms in the surface layers. The methane production potentials of the soils were low and similar between both sites but inconsistent with the differences between fluxes, and inconsistent with production potentials and fluxes reported from the same wetland types elsewhere, indicating that there were subtle environmental differences between wetlands classed as being of the same type. Differences between fluxes in vegetated chambers with bare soil chambers were insignificant, indicating that no methane emission through aerenchyma occurred at our sites. We concluded that wetland type was not an accurate predictor of methane flux.Bing Yu, Philip Stott, Hongxian Yu, Xiaoyu L