Spatially-integrated estimates of net ecosystem exchange and methane fluxes from Canadian peatlands

K. L. Webster, J. S. Bhatti, D. K. Thompson, S. A. Nelson, C. H. Shaw, K. A. Bona, S. L. Hayne, W. A. Kurz

Peatlands are an important component of Canada's landscape, however there is little information on their national-scale net emissions of carbon dioxide [Net Ecosystem Exchange (NEE)] and methane (CH4). This study compiled results for peatland NEE and CH4 emissions from chamber and eddy covariance studies across Canada. The data were summarized by bog, poor fen and rich-intermediate fen categories for the seven major peatland containing terrestrial ecozones (Atlantic Maritime, Mixedwood Plains, Boreal Shield, Boreal Plains, Hudson Plains, Taiga Shield, Taiga Plains) that comprise > 96% of all peatlands nationally. Reports of multiple years of data from a single site were averaged and different microforms (e.g., hummock or hollow) within these peatland types were kept separate. A new peatlands map was created from forest composition and structure information that distinguishes bog from rich and poor fen. National Forest Inventory k-NN forest structure maps, bioclimatic variables (mean diurnal range and seasonality of temperatures) and ground surface slope were used to construct the new map. The Earth Observation for Sustainable Development map of wetlands was used to identify open peatlands with minor tree cover. The new map was combined with averages of observed NEE and CH4 emissions to estimate a growing season integrated NEE (± SE) at - 108.8 (± 41.3) Mt CO2 season-1 and CH4 emission at 4.1 (± 1.5) Mt CH4 season-1 for the seven ecozones. Converting CH4 to CO2 equivalent (CO2e; Global Warming Potential of 25 over 100 years) resulted in a total net sink of - 7.0 (± 77.6) Mt CO2e season-1 for Canada. Boreal Plains peatlands contributed most to the NEE sink due to high CO2 uptake rates and large peatland areas, while Boreal Shield peatlands contributed most to CH4 emissions due to moderate emission rates and large peatland areas. Assuming a winter CO2 emission of 0.9 g CO2 m-2 day-1 creates an annual CO2 source (24.2 Mt CO2 year-1) and assuming a winter CH4 emission of 7 mg CH4 m-2 day-1 inflates the total net source to 151.8 Mt CO2e year-1. This analysis improves upon previous basic, aspatial estimates and discusses the potential sources of the high uncertainty in spatially integrated fluxes, indicating a need for continued monitoring and refined maps of peatland distribution for national carbon and greenhouse gas flux estimation.