China contains a considerable amount of wetlands, representing about 4% of China’s surface area. Yet, only a few whole ecosystem studies of wetland methane flux have taken place in China. To understand the impact of climate change on greenhouse gas emission of wetlands is of critical concern for regional and national assessments.

Recently, a research group from Northeast Institute of Geography and Agroecology, CAS, conducted continuous field observations on ecosystem CH₄ emission from a permafrost peatland located in the Da Xing’anling Mountains and a non-permafrost, freshwater marsh on the Sanjiang Plain using the eddy covariance technique. These wetlands are the two most dominant natural wetland types in northeast China. The research aims to understand the differences in the magnitude and seasonal pattern of CH₄ fluxes and dominant drivers of CH₄ exchange from these two wetlands.

Researchers found large differences in seasonal pattern and magnitude of CH₄ exchange for these two wetlands. CH₄ exchange did not show an obvious diurnal cycle, except for weak diurnal variation at the marsh site during the peak growing season of 2013. Peak CH₄ emissions at the peatland occurred in the late growing season and was more than two months later than those of the marsh. Total seasonal CH₄ emission from the peatland, 0.38 to 1.27 g C-CH₄ m^-2, was one order of magnitude smaller than those at the marsh, 19.71 to 21.8 g C-CH₄ m^-2. For the peatland average soil temperature between 10 cm to 60 cm depths was most strongly correlated with seasonal CH₄ variability, but thaw depth was also important during the late growing season. At the marsh soil temperature at 10 cm depth and net ecosystem CO₂ exchange were the main factors related to CH₄ flux.

This study presents the first detailed comparison of ecosystem-scale CH₄ exchange in two principal typical wetland ecosystems of northeast China. The results suggested that the differences in magnitude and responses of CH₄ flux to changes in environmental and biophysical conditions of these different wetland types should be considered when estimating the regional and national carbon budgets and response to future disturbance from land cover change and climate warming.

Fig.1.Path diagrams for the peatland illustrating the effects of environmental parameters on CH₄ flux during the growing seasons.

Fig.2.Path diagrams for the marsh illustrating the effects of environmental parameters on CH₄ flux during the growing seasons.

The research paper by Li Sun and Changchun Song et al. was published in the Journal of Agricultural and Forest Meteorology.