Growing season methane emission from a boreal peatland in the continuous permafrost zone of Northeast China: effects of active layer depth and vegetation

Y Miao,H Meng,R Mao,C Song,L Sun,X Wang

doi:10.5194/bg-9-4455-2012

Abstract

Abstract. Boreal peatlands are significant natural sources of methane and especially vulnerable to abrupt climate change. However, the controlling factors of CH4 emission in boreal peatlands are still unclear. In this study, we investigated CH4 fluxes and abiotic factors (temperature, water table depth, active layer depth, and dissolved CH4 concentrations in pore water) during the growing seasons in 2010 and 2011 in both shrub-sphagnum- and sedge-dominated plant communities in the continuous permafrost zone of Northeast China. The objective of our study was to examine the effects of vegetation types and abiotic factors on CH4 fluxes from a boreal peatland. In an Eriophorum-dominated community, mean CH4 emissions were 1.02 and 0.80 mg m−2 h−1 in 2010 and 2011, respectively. CH4 fluxes (0.38 mg m−2 h−1) released from the shrub-mosses-dominated community were lower than that from Eriophorum-dominated community. Moreover, in the Eriophorum-dominated community, CH4 fluxes showed a significant temporal pattern with a peak value in late August in both 2010 and 2011. However, no distinct seasonal variation was observed in the CH4 flux in the shrub-mosses-dominated community. Interestingly, in both Eriophorum- and shrub-sphagnum-dominated communities, CH4 fluxes did not show close correlation with air or soil temperature and water table depth, whereas CH4 emissions correlated well to active layer depth and CH4 concentration in soil pore water, especially in the Eriophorum-dominated community. Our results suggest that CH4 released from the thawed CH4-rich permafrost layer may be a key factor controlling CH4 emissions in boreal peatlands, and highlight that CH4 fluxes vary with vegetation type in boreal peatlands. With increasing temperature in future climate patterns, increasing active layer depth and shifting plant functional groups in this region may have a significant effect on CH4 emission.

Highlights

Methane (CH4), as one of the most important greenhouse gases, is 25 times more effective in absorbing heat in the atmosphere than carbon dioxide (CO2) on a 100-yr time horizon (IPCC, 2007)
Unlike other previous studies that reported no seasonal variation of CH4 fluxes from peatlands, we found a distinct temporal variation in methane emissions where CH4 fluxes peaked in late summer when the active layer reached the gas-contained layer, and which was consistent with peak pore water CH4 concentration
Our results showed that environmental factors such as temperature and water table level were not responsible for regulating temporal variations of methane emission

Summary

Introduction

Methane (CH4), as one of the most important greenhouse gases, is 25 times more effective in absorbing heat in the atmosphere than carbon dioxide (CO2) on a 100-yr time horizon (IPCC, 2007). The atmospheric CH4 abundance increased from 715 ppb in pre-industrial age to 1774 ppb in 2005. Increases in atmospheric CH4 concentrations (148 %) are greater than the other two greenhouse gases (CO2 35 % and N2O 18 %) over the same time period. Denman et al (2007) estimated that more than 580 Tg yr−1 of CH4 are emitted to the atmosphere, with 33 % originating from natural ecosystem sources. The contribution of different CH4 sources and sinks is still highly uncertain due to the sparseness of in situ observations

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