The Effects of Climate and Fire on Peatland Carbon Dynamics in Central and Eastern Canada

Abstract:

Carbon fluxes in subarctic peatlands could change significantly in response to high-latitude warming. To examine the sensitivity of peatland carbon storage to changes in regional climate, moisture, and disturbance, we measured carbon accumulation and peat characteristics in cores through the transition from the Holocene Thermal Maximum (HTM, ~6-4 ka cal. yr. BP) to the Neoglacial cooling (NGC, ~4-0 ka) as possible analogs to future climate change. We sampled six cores from northern Manitoba and seven cores across southeast Labrador, Canada. These regional contrasts permitted analysis of net moisture regimes on carbon accumulation. We used calibrated ¹⁴C dates, percent carbon, and bulk density measurements to determine long-term carbon accumulation rates for the Holocene. Areal charcoal concentrations were measured as a proxy for historic fire severity, which may mediate the climate-carbon accumulation relationship. Carbon accumulation rates in Labrador showed a clear increase of 29.6 ± 2.4 g C m^-2 yr^-1 during the local HTM and a subsequent decrease of 15.9 ± 2.9 g C m^-2 yr^-1 during the NGC indicating possible influence of regional temperature on carbon dynamics in eastern Canada. In contrast, the Manitoba peatlands did not show a clear relationship between climate and carbon accumulation. Fires were common and severe in Manitoba and often slowed sedimentation rate and C storage, but were rarely present in Labrador. Local variables, including peatland development and fire, may therefore play a larger role in controlling carbon accumulation in the continental interior. The results from these two subaratic regions complicate general hypotheses that high latitude peatlands will be either carbon sinks or sources in the upcoming decades.