Multi‐year net ecosystem carbon balance of a restored peatland reveals a return to carbon sink

Abstract

Peatlands after drainage and extraction are large sources of carbon (C) to the atmosphere. Restoration, through re-wetting and revegetation, aims to return the C sink function by re-establishing conditions similar to that of an undrained peatland. However, the time needed to re-establish C sequestration is not well constrained due to the lack of multi-year measurements. We measured over 3 years the net ecosystem exchange of CO (NEE), methane ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>F</mml:mi> <mml:msub><mml:mi>CH</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:msub> </mml:math> ), and dissolved organic carbon (DOC) at a restored post-extraction peatland (RES) in southeast Canada (restored 14 years prior to the start of the study) and compared our observations to the C balance of an intact reference peatland (REF) that has a long-term continuous flux record and is in the same climate zone. Small but significant differences in winter respiration driven by temperature were mainly responsible for differences in cumulative NEE between years. Low growing season inter-annual variability was linked to constancy of the initial spring water table position, controlled by the blocked drainage ditches and the presence of water storage structures (bunds and pools). Half-hour <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>F</mml:mi> <mml:msub><mml:mi>CH</mml:mi> <mml:mn>4</mml:mn></mml:msub> </mml:msub> </mml:math> at RES was small except when Typha latifolia-invaded drainage ditches were in the tower footprint; this effect at the ecosystem level was small as ditches represent a minor fraction of RES. The restored peatland was an annual sink for CO (-90 ± 18 g C m year ), a source of CH (4.4 ± 0.2 g C m year ), and a source of DOC (6.9 ± 2.2 g C m year ), resulting in mean net ecosystem uptake of 78 ± 17 g C m year . Annual NEE at RES was most similar to wetter, more productive years at REF. Integrating structures to increase water retention, alongside re-establishing key species, have been effective at re-establishing the net C sink rate to that of an intact peatland.

Prompt active restoration of peatlands substantially reduces climate impact

“…This study is based on net ecosystem flux measurements of CO 2 (NEE), CH 4 and dissolved organic carbon (DOC) from horticulture-extracted peatlands. The study sites were part of a paired unrestored/ restored eddy covariance tower project in eastern (Québec) and western (Alberta) Canada that took place between July 2013 and November 2016 (Nugent et al 2018, Rankin et al 2018. The active restoration approach, known as the moss layer transfer technique, applied at the study sites incorporates site re-grading, rewetting (ditch blocking and/or infilling), revegetating with material from donor peatlands, protection with straw mulch, and phosphate fertilization where required (see Graf and Rochefort, 2016 for more details).…”

“…The eastern restored site, Bois-des-Bel, has undergone periodic flux monitoring since being restored in the autumn of 1999 (e.g. Petrone et al 2003, Waddington and Day 2007, Waddington et al 2008, Waddington et al 2010, Strack and Zuback 2013, Nugent et al 2018. The well-studied Mer Bleue bog (1998 to present eddy covariance record; Roulet et al 2007) located near Ottawa, ON, Canada was used as a representative undisturbed peatland.…”

“…Mer Bleue is currently the best record to use as the endpoint of the restoration trajectory, as its long-term record captures the wide range in variability when estimating a mean flux. Greenhouse gas flux monitoring occurred continuously over the growing season/year at the eastern and western Canadian paired unrestored/restored sites and undrained peatland, and a standard data post-processing methodology was used (Nugent et al 2018). Main site characteristics of the study sites are presented in table S1.1 (available online at stacks.iop.org/ERL/14/ 124030/mmedia), site-specific measurement techniques and instrumentation in table S1.2, site-specific gap-filling methods for CO 2 and CH 4 in table S1.3 and annual CO 2 , CH 4 and DOC fluxes (mean±95%CI) in g C m −2 yr −1 in table S1.4.…”

“…At the older restored site (RES-15 year), CO 2 uptake similar to that of REF was observed after 14 years (Nugent et al 2018, figure 1). The CO 2 sink was linked to a sufficiently shallow water table, attributed to effective water retention by berms put in place during the restoration process (Nugent et al 2018).…”

“…The Canadian horticultural peat moss industry employs an active restoration strategy that incorporates the moss layer transfer technique (Graf and Rochefort 2016) in addition to rewetting. A multiyear continuous measurement study of ecosystemscale active restoration of a post-extraction peatland showed annual net CO 2 sequestration within 14 years (Nugent et al 2018). To quantify the efficiency of peatland restoration actions, however, the time spent in an unrestored state needs to be accounted for.…”