Peat initiation, soil carbon accumulation, fire, and vegetation changes in north-central Canadian arctic lowland forest peatlands during the Holocene

Abstract:

Peat-forming regions are significant components of the earth system in terms of carbon exchange between the atmosphere and biosphere. While attention has been given to processes controlling carbon accumulation in major peatland/lowland regions at high latitudes, less is known about the processes controlling soil carbon accumulation rates in other globally abundant peat-forming ecosystems, such as lowland arctic forests. These systems are potentially important for two reasons: (1) Many lowland forest peatlands exist at the interface between uplands and aquatic systems; the onset and rate of peat accumulation, as well as the composition of peat mosses, may therefore alter the biogeochemical properties of lakes and streams; (2) soil carbon accumulation might differ from rates observed from the larger open peatlands, offering additional insights to the vulnerability of high-latitude peat to climatic change. We collected and dated 25 peat cores from eight lake sites in an 18,000-km² low-arctic region of Manitoba Canada and measured areal carbon accumulation rates, charcoal concentration (as a proxy for fire severity), and plant macrofossils (as a proxy for vegetation change). The distribution of basal radiocarbon dates indicates that the oldest peat initiation occurred 7,000-8,000 B.P. in post-glacial landscapes, but peak peat formation occurred < 3,000 B.P., presumably as landscape paludification rose with increased net moisture during Neoglacial cooling. In locations where peat initiation occurred before 6,000 B.P., the initial communities were variable (bog-poor fen-moderate rich fen), whereas most sites initiating after 6,000 B.P. formed (and remained) as bogs, suggesting increasing dominance of Sphagnum peatmosses as paludification progressed. Carbon accumulation rates were consistently low (10-30 gm^-2y^-1), with no clear correlation to fire. Also absent was rapid accumulation early in the peatland development characteristic of early successional fens. These results indicate that peat formation and accumulation in lowland forests may respond differently to internal and exogenous drivers compared to larger peatland landscapes and that widespread Sphagnum initiation after 6,000 B.P. may have the potential to alter aquatic biogeochemistry since the mid Holocene.