Investigating the Effects of Climatic Change and Fire Dynamics on Peatland C Accumulation in Coastal Labrador, Canada

Abstract:

High-latitude Canadian peatlands store a significant stock of soil carbon that has the potential to become mobilized to the atmosphere if climate warming leads to changes in the net balance of plant productivity and decomposition. We completed a detailed study of C accumulation rates from the sediment record in coastal eastern Canada to help to determine the relative impacts of regional climate vs. local processes, such as hydrology and fire disturbance, on rates of C storage. Seven cores from subarctic peatlands in Labrador were analyzed to determine the influence of fires on carbon storage over the past 8,000 years, specifically over known warm periods. Calibrated radiocarbon dates, bulk density, and percent carbon were used to calculate carbon accumulation rates. Areal charcoal concentration was used as a proxy for fire severity. Carbon accumulation rates appear to be most strongly controlled by changing regional climatic regimes. From 8,000 cal yr BP to the present, rates of accumulation averaged 23.1 ± 6.7 gC m^-2 yr^-1. C accumulation rates were highest during the Holocene Thermal Maximum (HTM, 6,000 – 4,000 cal yr BP), averaging 29.6 ± 2.4 g C m^-2 yr^-1 compared to 22.7 ± 3.7 and 15.9 ± 2.9 g C m^-2 yr^-1 before and after the HTM, respectively. Samples containing macroscopic charcoal had an average concentration of 0.62 mm² cm^-3 with a maximum concentration found of 3.51 mm² cm^-3. Consistently low charcoal concentrations indicate that fire was neither common nor severe in these wetter peatlands, implying that fires have historically not been a significant control on C accumulation in Labrador, likely due to the high net moisture of the region. Our work supports a growing body of evidence from high latitude peatlands suggesting that future warming conditions, in the absence of shifts in disturbance regimes, could lead to greater soil C sequestration.