Wetland-atmosphere methane exchange in Northeast China: A comparison of permafrost peatland and freshwater wetlands

Abstract

Northeast China contains a large concentration of wetlands, primarily in two prominent types, freshwater marshes on the lowlands plains to the northeast and mountain permafrost peatlands in the north. Both wetlands types are threatened by disturbance, the marshes from agricultural conversion and the peatlands due to climate warming and loss of permafrost. Here we compare two seasons of ecosystem-scale CH4 fluxes measured via eddy covariance for a permafrost peatland in the Da Xing’anling Mountains and a freshwater marsh on the Sanjiang Plain. The objectives were to quantify CH4 fluxes, compare seasonal trends in the flux and determine the dominant environmental and biophysical drivers of the CH4 flux for these two distinct wetland types.CH4 fluxes at the marsh had a strong seasonal trend peaking in mid-summer, while the pattern for the peatland was muted. Maximum instantaneous fluxes were 1.34μg CH4 m−2s−1 and 9.5μg CH4 m−2s−1 at the peatland and marsh, respectively. Total seasonal CH4 emissions for the peatland, 0.38–1.27g C-CH4 m−2, were an order of magnitude smaller than those at the marsh, 19.71–21.8g C-CH4 m−2. Differences between years were small for both wetlands. We used path analysis to examine environmental and biophysical drivers of the flux and found that soil temperature (average soil temperature between 10cm to 60cm depths for the peatland and 10cm depth for the marsh) was most strongly correlated with seasonal CH4 variability for both wetlands. Secondary influences were thaw depth for the peatland and net ecosystem CO2 exchange for the marsh.Given the temperature sensitivity of CH4 flux for both of these wetlands, future climate warming will likely increase CH4 emissions in northeast China, as well, the continued loss of permafrost in the mountain peatlands will likely further contribute to enhanced CH4 emissions.