Divergent responses of peatland development and carbon accumulation to volcanic eruptions on the Changbai Mountain, Northeast China

Peatlands are an important carbon reservoir of terrestrial ecosystems and play a key role in the global carbon cycle. Many peatlands exist in volcanic terrains, but we still lack a systematic understanding of the effects of volcanic ash deposition on peatland development and carbon dynamics. Here we used multi-proxy records from multiple cores at a high-elevation (1570 m a.s.l.) peatland complex on the southern slope of the Changbai Mountain-only 13 km from the crater lake Tianchi-to understand the peatland initiation and carbon accumulation processes under the influence of volcanic eruption. We quantified volcanic glass shards abundance in the peat core under a microscope to show the 5-cm-thick major Millennium Eruption (ME) in 946 CE, along with multiple cryptotephra layers identifiable above a constant background of low abundant shards. Plant macrofossil data show that the major ME volcanic ash deposition caused a large decrease in plant taxon richness, while three out of eight cryptotephra layers induced a brief increase in Sphagnum abundance after each ash deposition but had little impact on plant taxon richness. The divergence in response of species composition to different magnitudes of volcanic ash depositions indicates both beneficial and detrimental effects, perhaps depending on the degree of modifying the nutrient or hydrological status of the peatland. Our results also show that the 5-cm thick ME volcanic ash layer acted as an impermeable layer, increasing surface moisture conditions and promoting the formation of new peatlands on the landscape. Moreover, the ME ash deposition caused a significant decrease in the carbon accumulation rate that lasted for >200 years. Our study indicates that volcanic ash depositions have very different impacts on peatlands by promoting new peatland initiation but impeding carbon accumulation of existing peatlands, implying that the balance of these processes would determine the carbon sink capacity of peatlands in a region as a whole.