Effects of volcanic ash deposition on peatland development and carbon accumulation on the southern slope of the Changbai Mountains, Northeast China

Abstract:Peatlands play a key role in the global carbon cycle as an important carbon reservoir in terrestrial ecosystems. Many peatlands exist in volcanic terrains, but we still have limited understanding of the effects of volcanic ash deposition on peatland development and carbon dynamics. There are abundant peatlands in Northeast China, and the Changbai Mountains—a volcanic mountain range with a crater lake at 2189 m a.s.l.—experienced multiple eruptions during the Holocene, including a major eruption in 946 CE (Millennium Eruption: ME).  Here we used multi-proxy records from 10 cores at a high-elevation (1570 m a.s.l.) peatland complex on the southern slope—13 km from the crater lake Tianchi—to understand the peatland initiation and carbon accumulation processes under the influence of volcanic eruption. Volcanic glass abundance in peat core shows multiple ash-rich layers, with the ME being the largest one, visible to the naked eyes. Plant macrofossil data show that the peatland has been a rich fen dominated by sedges (Carex and Eriophorum) and rush (Scheuchzeria palustris) during the last 4000 years, transitioning to a Sphagnum-dominated poor fen only in recent decades. The major ME volcanic ash deposition caused a large decrease in species richness and led to a persistent shift in the peatland species composition from overwhelming dominance of Carex to an increase from <10% to about 40% of Eriophorum. Three out of four other minor volcanic ash layers induced a brief increase in Sphagnum after each ash deposition, but had little impact on species richness. The divergence in response of species composition to different sizes of volcanic ash depositions indicates both beneficial and detrimental impacts, perhaps depending on modifying nutrient or hydrological status of the peatland. Our results also show that the volcanic ash layer from the 5-cm thick ME acted as an impermeable layer, increasing surface moisture conditions and promoting the formation of new peatlands on the landscape. Moreover, the ash deposition caused a significant decrease in the carbon accumulation rate, lasting for >200 years. Our study indicates that volcanic eruption may 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 as a whole.