Daytime-only measurements underestimate CH₄ emissions from a restored bog

Gemma P Dooling,Pippa J Chapman,Andy J Baird,Matthew J Shepherd,Tim Kohler

doi:10.1080/11956860.2018.1449442

Gemma P Dooling, Pippa J Chapman + Show 3 more

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https://doi.org/10.1080/11956860.2018.1449442

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Journal: Écoscience	Publication Date: May 20, 2018
Citations: 5	License type: open-access

Affiliation: University of Leeds, Natural England

Abstract

ABSTRACTAccurate estimates of methane (CH4) fluxes from restored peatlands are needed to inform emission factor estimations and reporting. Flux measurements are usually taken during the daytime but such measurements may provide biased estimates of overall CH4 emissions if night-time fluxes differ from daytime fluxes. Diurnal variations in CH4 fluxes have been reported for a range of peatland types, but not for restored raised bogs which are important carbon stores in some countries. To help fill this knowledge gap, we investigated diurnal variations in CH4 emissions from a restored raised bog. CH4 fluxes from a restored raised bog were measured in two 24-hr field campaigns using flux chambers. Carbon dioxide (CO2) fluxes were also monitored, as were a suite of complementary environmental variables. Night-time CH4 fluxes were significantly greater than daytime fluxes during both campaigns, by 10.4% and 36.1%, respectively. In Campaign 1 air temperature was the best predictor of CH4 fluxes, whereas in Campaign 2 net ecosystem exchange (NEE) values were the best predictor. This study shows that diurnal variations in CH4 fluxes exist in a restored peatland and that current approaches biased to daytime measurements will underestimate CH4 emissions from restored peatlands to the atmosphere.

Highlights

Peatlands that have been previously drained, but are rewetted can be significant sources of atmospheric CH4 (Lai 2009)
This study has shown that CH4 fluxes from a restored lowland raised bog dominated by Eriophorum spp. are significantly larger during the night than the day
Of previous studies into diurnal CH4 fluxes where Eriophorum spp. were an important component of the vegetation, some found that daytime CH4 fluxes exceed

Summary

Introduction

Peatlands that have been previously drained, but are rewetted can be significant sources of atmospheric CH4 (Lai 2009). The United Nations Framework Convention on Climate Change and the Kyoto Protocol require signatories to report greenhouse gas (GHG) emissions annually. Guidance from the Intergovernmental Panel on Climate Change (IPCC) on emissions factors specific to CH4 fluxes from rewetted organic soils is only recent (IPCC 2014). Rewetted peatlands are in the category of Agriculture, Forestry and Other Land Use, and this category produced 24% of the global anthropogenic GHG emissions between 2000 and 2009 (IPCC 2013; Wilson et al 2015). The Tier 1 default CH4 emission factor for temperate nutrient-poor rewetted organic soils, based on data from 42 studies, is 33.6 mg CH4 m−2 day−1, with a large variance of 1.1–162.5 mg CH4 m−2 day−1 (IPCC 2014). To help reduce the uncertainty in this estimate, countries are advised to develop more locally representative emissions factors so that differences between study sites, such as time since

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