B028-06
Estimating the Magnitude of Long-Term Net C Loss due to Permafrost Thaw in Boreal Peatlands
Tuesday, 8 December 2020: 19:20
Virtual
Lorna I Harris, University of Alberta, Edmonton, AB, Canada, David Olefeldt, University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada, Nicolas Pelletier, University of Montreal, Montreal, QC, Canada; Carleton University, Ottawa, ON, Canada, Christian Blodau, University of Münster, Münster, Germany, Klaus-Holger Knorr, University of Muenster, Muenster, Germany, Julie Talbot, University of Montreal, Département de géographie & Geotop, Montreal, QC, Canada and Merritt R Turetsky, University of Guelph, Guelph, ON, Canada; Institute of Arctic and Alpine Research, Boulder, United States
Abstract:
Boreal peatlands in the discontinuous permafrost zone store a large portion of the global soil carbon (C). Permafrost thaw in peatlands not only exposes old C to microbial decomposition (C loss), but also causes land to subside, with the altered hydrological setting promoting the rapid growth of
Sphagnum moss and thus new peat accumulation at the surface. Some studies suggest this C gained at the surface may offset large C losses from deep peat. However, it is not certain how this potential offset may impact the magnitude of C loss for peatlands in different ecohydrological and climate settings, and with different development histories (e.g. timing of permafrost formation).
Here, we determine the net effect of permafrost thaw on C storage in a peatland complex in the Northwest Territories of Canada. We assessed C storage in 15 peat cores taken from transects along a chronosequence of time since thaw, using the White River Ash tephra layer (~1250 cal. yr BP) as a clearly identifiable chronostratigraphic marker. We also examined peat quality of samples from a subset of cores and completed a one-year aerobic incubation to determine potential decomposability of peat samples from the same transects.
Our results suggest net C loss following permafrost thaw, with average total C stocks decreasing by ~52 ±10 kg C m-2 over 600 years. The post-thaw accumulation of ~22 ± 4 kg C m-2 at the surface over the same period was not sufficient to offset the large C loss. Our data also suggest increased humification of deep peat post-thaw.
