Responses of peatland development and carbon accumulation to climate change over the past 2500 years in the Arxan region, Northeast China

As one of the soil types, peat is an important soil carbon storage and archive of past environmental changes. Here we used multi-core and multi-proxy records from a peatland near Da’erbin Lake in the Arxan region of Northeast China to reconstruct peatland development and carbon accumulation history and to understand their responses to past climate changes during the last 2500 years. Our macrofossil results show that the peatland was characterized by a sedge-dominated fen from 490 BCE to 1450 CE, changed to a Sphagnum-dominated poor fen or bog with abundant shrubs (mostly Ericaceae) during the period of 1450–1960 CE, and finally became predominated by Sphagnum after 1960 CE. The time-weighted mean apparent carbon accumulation rate (aCAR) from three cores range from 19.5 to 53.0 g C m^-2 yr^-1 with a mean value of 32.4 g C m^-2 yr^-1, but increase rapidly to 139.2 g C m^-2 yr^-1 during last several decades. During the early stage of the past 2500 years, three coring sites that are only 50 m apart were all in the fen phase but they had highly variable peat properties. The fen-bog transition occurred at different times at these sites due to local influences of autogenic process, permafrost dynamics, or fire disturbance. These observations suggest that fens are highly heterogeneous, not only in peat properties but also in ecosystem dynamics. The dramatic increase in aCAR during the late stage of bog phase after 1960 CE cannot be explained entirely by limited decomposition of recently-accumulated peat. Instead, this was likely due to increasing Sphagnum dominance and resultant low decomposition of Sphagnum-derived organic matter, suggesting the important role of vegetation change in controlling carbon accumulation rates. Around the 1990s CE, an increase in allogenic CAR—after removing the age-related long-term autogenic effect—seems to correspond with a period of increase in regional summer precipitation, revealing a sensitive response of ombrotrophic bog ecosystem to climate change at decadal timescale.