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 ( F CH 4 ), 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 F CH 4 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.

Restoration of peatlands after peat extraction could be a benefit to the climate system. However a multi-year ecosystem-scale assessment of net carbon (C) sequestration is needed. We investigate the climate impact of active peatland restoration (rewetting and revegetating) using a chronosequence of C gas exchange measurements across post-extraction Canadian peatlands. An atmospheric perturbation model computed the instantaneous change in radiative forcing of CO 2 and CH 4 emissions/ uptake over 500 years. We found that using emission factors specific to an active restoration technique resulted in a radiative forcing reduction of 89% within 20 years compared to IPCC Tier 1 emission factors based on a wide range of rewetting activities. Immediate active restoration achieved a neutral climate impact (excluding C losses in the removed peat) about 155 years earlier than did a 20 year delay in restoration. A management plan that includes prompt active restoration is key to utilizing peatland restoration as a climate change mitigation strategy.

Freshwater marshes have been shown to be strong sinks for carbon dioxide (CO 2 ) on an annual basis relative to other wetland types; however it is likely that these ecosystems are also strong emitters of methane (CH 4 ), reducing their carbon (C) sequestration potential. Multiyear C balances in these ecosystems are necessary therefore to determine their contribution to the global C cycle. Despite this, the number of multiyear studies in marshes is few, with, to the best of our knowledge, only one other Northern marsh C balance reported. This study presents five years of eddy covariance flux measurements of CO 2 , and four years of warm-season chamber measurements of CH 4 at a cooltemperate Typha angustifolia marsh. Annual average cumulative net ecosystem exchange of CO 2 (NEE) at the marsh was −224 ± 54 g C m −2 yr −1 (±SD) over the five-year period, ranging from −126 to −284 g C m −2 yr −1 . Enhancement of the ecosystem respiration during warmer spring, autumn and winter periods appeared the strongest determinant of annual NEE totals. Warm season fluxes of CH 4 from the Typha vegetation (avg. 1.0 ± 1.2 g C m −2 d −1 ) were significantly higher than fluxes from the water surface (0.5 ± 0.4 g C m −2 d −1 ) and unvegetated mats (0.2 ± 0.2 g C m −2 d −1 ). Air temperature was a primary driver of all CH 4 fluxes, while water table was not a significant correlate as water levels were always at or above the vegetative mat surfaces. Weighting by the surface cover proportion of water and vegetation yielded a net ecosystem CH 4 emission of 127 ± 19 g C m −2 yr −1 . Combining CO 2 and CH 4 , the annual C sink at the Mer Bleue marsh was reduced to −97 ± 57 g C m −2 yr −1 , illustrating the importance of accounting for CH 4 when generating marsh C budgets.

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Identifying the drivers of changing continental runoff is key to understanding current and predicting future hydrological responses to climate change. Potential drivers of runoff change include changes in precipitation and evaporation caused by climate warming, physiological responses of vegetation to elevated atmospheric CO 2 concentrations, increases in lower-atmosphere aerosols and anthropogenic land-cover change. In this study, we present a series of simulations using an intermediate-complexity climate and carbon cycle model to assess the contribution of each of these drivers to historical and future continental runoff changes. We present results for global runoff, in addition to northern latitude runoff that discharges into the Arctic and North Atlantic oceans, to identify any potential contribution of increased continental freshwater discharge to changes in North Atlantic deep-water formation. Between 1800 and 2100, the model simulated a 26% increase in global runoff and a 32% runoff increase in the northern latitude region. This increase was driven by a combination of increased precipitation from climate warming and decreased evapotranspiration caused by the physiological response of vegetation to elevated CO 2 . When isolated, climate warming (and associated changes in precipitation) increased runoff by 16% globally and by 27% at northern latitudes. Vegetation responses to elevated CO 2 led to a 13% increase in global runoff and a 12% increase in the northern latitude region. These changes in runoff, however, did not affect the strength of the Atlantic Meridional Overturning Circulation, which was affected by surface ocean warming rather than by runoff-induced salinity changes. This study indicates that physiological responses of vegetation to elevated CO 2 may contribute to changes in continental runoff at a level similar to that of the direct effect of climate warming. RÉSUMÉ [Traduit par la rédaction] Il est primordial de déterminer les causes premières des changements dans le ruissellement continental afin de comprendre les réactions hydrologiques par rapport aux changements climatiques à l'heure actuelle et de les prédire. Voici des facteurs éventuellement responsables : les changements dans les précipitations et l'évaporation causés par le réchauffement climatique, la réaction physiologique des plantes à l'augmentation des concentrations de CO 2 dans l'atmosphère, l'augmentation de la concentration d'aérosols dans la basse atmosphère et les changements dans la couverture terrestre, qui découlent des activités humaines. Dans notre étude, nous présentons une série de simulations fondées sur un modèle du climat et du cycle du carbone de complexité intermédiaire afin d'évaluer le rôle de chacun de ces facteurs dans les changements du ruissellement continental dans le passé et à l'avenir. Nous présentons des résultats pour le ruissellement dans le monde, en plus du ruissellement sous les latitudes nordiques qui se déversent dans les océans Arctique et Atlantique Nord, afin d'établir la contribution évent...