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

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

doi:10.1186/s13021-018-0105-5

Abstract

BackgroundPeatlands 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.ResultsThe 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.ConclusionsThis 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.

Highlights

Peatlands are an important component of Canada’s landscape, there is little information on their national-scale net emissions of carbon dioxide [Net Ecosystem Exchange (NEE)] and methane (CH4)
The purpose of this study is to: (1) synthesize available estimates of NEE and C H4 for bogs, poor fens, and rich-intermediate fens for each of seven major peatland containing ecozones in Canada, (2) create a new 250 m resolution, raster-based peatland map synthesized from existing national landcover and forest structure maps and compare it to the polygon-based Peatlands of Canada Map (PCM) [13], (3) provide new national estimates of C H4 and NEE emissions and the net greenhouse gas balance using the synthesized data combined with the new map, and for comparison combined with the PCM and, (4) investigate potential bioclimatic drivers of emissions of CH4 and NEE
NEE and CH4 emissions Summarizing the studies examined, most of the NEE measurements were from bogs and the least from poor fens (Table 3)

Summary

Introduction

Peatlands are an important component of Canada’s landscape, there is little information on their national-scale net emissions of carbon dioxide [Net Ecosystem Exchange (NEE)] and methane (CH4). The importance of peatlands in the C balance of Canada and the globe has been recognized for decades [8] but we still have a limited understanding of the spatial distribution of peatlands relative to forest ecosystems and their net greenhouse gas (GHG) balance at a national scale, despite a relatively sophisticated understanding and modelling capacity at the plot level (e.g., [9]) This knowledge gap in the national peatland GHG balance must be addressed to satisfy growing international pressure for better GHG estimation and reporting of organic soils on managed lands [e.g., Intergovernmental Panel on Climate Change (IPCC) Supplement to the 2006 Guidelines for National Greenhouse Gas Inventories: Wetlands (Wetlands Supplement—IPCC [10]). Roulet [6] arrived at a similar Canada-wide estimate for a net C sink of 91.6–135.6 Mt CO2 year−1, but a higher estimate of CH4 release of 2–5 Mt CH4 year−1 [6, 18]

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Conclusion