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• CH 4 and CO 2 fluxes from two wetlands in northeast China are presented. • Most variations of CH 4 were distributed at time scales of several days to some months. • Soil temperature and thaw depth imposed alternated influences on CH 4 at the peatland. • Soil temperature and plant productivity influenced CH 4 emissions at the marsh. • Both wetlands were carbon sinks while the marsh had a net positive radiative forcing. Quantifying net CO 2 exchange (NEE) and CH 4 emissions of northern wetlands and their responses to biophysical controls are central to understanding the role of wetlands in global climate change. This study presents two growing seasons of observations of CO 2 and CH 4 fluxes by eddy covariance technique from a permafrost peatland and an inundated marsh in northeast China. Wavelet analysis was used to explore the temporal multi-scale variations of NEE and CH 4 fluxes and their biophysical controls. NEE showed prominent variations at the diel and the seasonal scales. However, most CH 4 variance was distributed at time scales longer than one day. At the permafrost peatland wavelet analysis revealed strong spectral coherency and alternating coherence between soil temperature and CH 4 fluxes during the spring and summer seasons and between thaw depth and CH 4 fluxes in the late growing season, with the suggestion of an as yet unknown coherence at longer timescales than could be resolved with just growing season records. At the marsh, soil temperature and CH 4 flux showed strong spectral coherency throughout the growing seasons and gross ecosystem production (GEP) additionally imposed its influence on CH 4 mainly during the most active part of the growing season. The growing season average CH 4 emission from the peatland (0.7 g C CH 4 m−2) was quite small and was negligible compared to its growing season NEE (−74.2 g C CO 2). In contrast, the growing season CH 4 emission from the marsh (average 31.1 g C CH 4 m−2) was considerably higher and accounted for about 16.2 % of its NEE (−191.7 g C CO 2 m−2). Although the two wetlands were net carbon sinks during the growing seasons and the permafrost peatland had a negative radiative forcing (i.e., cooling effect), the high CH 4 emissions from the marsh resulted in a net positive radiative forcing (i.e., warming effect). To understand the function of northern wetlands in the global carbon cycle, continuous field observations of these greenhouse gases are vital. [ABSTRACT FROM AUTHOR]

The mid-high latitude permafrost peatlands in the Northern Hemisphere is a major natural source of methane (CH 4 ) to the atmosphere. Ecosystem scale CH 4 emissions from a typical permafrost peatland in the Great Hing'an Mountains were observed during the growing season of 2014 and 2015 using the open-path eddy covariance method. Relevant environmental factors such as temperature and precipitation were also collected. There was a clear diurnal variation in methane emissions in the second half of each growing season, with significantly higher emission rates in the wet sector of study area. The daily CH 4 exchange ranged from 1.8 mg CH 4 m −2 d −1 to 40.2 mg CH 4 m −2 d −1 in 2014 and ranged from −3.9 to 15.0 mg CH 4 m −2 d −1 in 2015. There were no peaks of CH 4 fluxes during the spring thawing period. However, large peaks of CH 4 emission were found in the second half of both growing seasons. The CH 4 emission after Jul 25th accounted for 77.9% of total growing season emission in 2014 and 85.9% in 2015. The total CH 4 emission during the growing season of 2014 and 2015 was approximately 1.52 g CH 4 m −2 and 0.71 g CH 4 m −2 , respectively. CH 4 fluxes during the growing seasons were significantly correlated with thawing depth ( R 2 = 0.71, P < 0.01) and soil temperatures ( R 2 = 0.75, P < 0.01) at 40 cm depth. An empirical equation using these two major variables was modified to estimate growing season CH 4 emissions in permafrost peatlands. Our multiyear observations indicate that the time-lagged volume of precipitation during the growing season is a key factor in interpreting locally inter-annual variations in CH 4 emissions. Our results suggested that the low temperature in the deep soil layers effectively restricts methane production and emission rates; these conditions may create significant positive feedback under global climate change. [ABSTRACT FROM AUTHOR]

• Growing season carbon budget from the peatland was estimated to be 71–95 g C m−2. • Photosynthetically active radiation is a good indicator in estimating photoinhibition. • Soil respiration and plant respiration respond to environmental changes differently. • Detailed utilization and analyses of the eddy covariance data are important. Eddy covariance (EC) technique is a widely used method to quantify the net exchange of CO 2 between ecosystems and the atmosphere. The quality control and data analysis of calculated fluxes are essential to ensure accurate budget estimates. Ecosystem scale CO 2 exchange between a typical permafrost peatland of the Great Hing'an Mountains and the atmosphere was measured during the growing season of 2014 and 2015 using the open-path eddy covariance technique. Footprint analysis and turbulence stationary test were applied to the calculated fluxes to improve the data accuracy. High quality data were then screened to study emission patterns. Combining widely used models with the observed data, an empirical model derived by photosynthetically active radiation was developed to fit daily photosynthesis reduction. Seasonal variation of apparent quantum yield (α , mol CO 2 mol−1 photon), maximum photosynthesis rate (P max , µmol CO 2 m−2 s−1) and temperature sensitivity for respiration (E 0 , K) were found to follow a unimodal distribution and could be simulated by a Gaussian based equation. The use of EC data and the potential issues, especially the bias on respiration estimation, were discussed. Detailed utilization and analyses of the EC data are helpful in revealing the CO 2 exchange patterns on different time scales, and also contribute to reducing the result differences between EC and other measurement techniques. [ABSTRACT FROM AUTHOR]