Towards accurate greenhouse gas accounting in Canada: The impact of peat extraction management practices on land use emissions

Peatlands are a type of wetland ecosystem characterized by water-saturated soil conditions that enable the accumulation of peat-a carbon-rich, soil-like substance consisting of partially decomposed biomass, providing long-term carbon storage.However, some peatlands undergo land-use change for peat extraction, which can transform them from net carbon sinks into carbon sources.My study examines the impacts of different management practices associated with peat extraction on greenhouse gas (GHG) emissions.Fieldwork was conducted at two actively harvested peatland sites in Rivière-du-Loup, Quebec, from May to November 2022, each employing distinct management strategies.I assessed the effects of heavy machinery on the uppermost peat layer when preparing the fields for extraction and quantified emissions from stockpiles of harvested peat stored on-site, comparing those covered with an impermeable reflective tarp to those left uncovered.Using a closed chamber and trace gas analyzer, we measured carbon dioxide (CO₂) and methane (CH₄) fluxes across four extraction phases: harrowed, drying, conditioned, and vacuum-harvested.My results show that CO₂ emission rates did not differ significantly between phases.CH₄ emissions, while lower overall than those from undisturbed peatlands, were notably increased during the harrowed, conditioned, and vacuumharvested phases compared to the drying phase.The increase in CH₄ was attributed to a disturbance effect caused by heavy machinery, regardless of varying surface peat conditions, with CH₄ peaking immediately post-disturbance before stabilizing over time.For both covered and uncovered stockpiles, surface flux measurements were taken at various positions, while gas samples from within the piles were analyzed using gas chromatography.Uncovered stockpiles exhibited low CH₄ emissions but had above average CO₂ emissions compared to extracted peat fields, with a mean emission rate of approximately 5 g CO₂-C m -2 day -1 .Uncovered stockpile fluxes varied seasonally, and were significantly higher at the top of stockpiles than at the bottom.Conversely, CO₂ emissions through the tarp of covered stockpiles were ten times lower than those from uncovered iii piles.However, more CH₄ (0.6 g CH₄-C m -3 ) and CO₂ (61.1 g CO₂-C m -3 ) were stored within covered stockpiles, compared to uncovered ones (CH₄ < 0.005 g CH₄-C m -3 ; CO₂: 6.7 g CO₂-C m -3 ).Since fluxes measured over holes in the tarp indicated the release of stored CO2, I assumed-though I could not measure it-that the stored gases would be released as the cover was removed and the peat was taken away for processing.Although stockpiles represented less than 1% of the total study area, they accounted for 1-2% of overall site emissions when including surface fluxes and emissions released during stockpile removal.My findings contribute to a more comprehensive understanding of land-use-related GHG emissions in Canada, offering insights for improved GHG accounting and guiding the peat industry toward best management practices.v Des mesures de flux sur la surface ont été effectuées à divers emplacements aux piles de stockage couvertes et non couvertes, de manière égale des échantillons de gaz prélevés à profondeurs des empilements ont été analysés par chromatographie en phase gazeuse afin d'évaluer le stockage de GES.Les effets des piles de stockage non couvertes présentaient de faibles émissions de CH₄, toutefois des émissions de CO₂ étaient supérieures à la moyenne comparativement aux champs d'extrait de tourbe, avec un taux d'émission moyen d'environ 5 g CO₂-C m -2 par jour.Les émissions des piles de stockage non couvertes étaient variables selon les saisons, et significativement plus élevées au sommet des empilements par rapport à leur base.Inversement, les émissions de CO₂ à travers la bâche des piles de stockage couvertes étaient dix fois plus faibles que celles des piles non couvertes.Cependant, les piles couvertes emmagasinaient plus de CH₄ (0.6 g CH₄-C m -3 ) et de CO₂ (61.1 g CO₂-C m -3 ) que les stocks non couverts (<0.005 g CH₄-C m -3 ; 6.7 g CO₂-C m -3 ).Comme les flux mesurés au-dessus des trous dans la bâche indiquaient la libération du CO2 stocké, j'ai supposé, sans avoir pu prendre des mesures spécifiques, que les gaz stockés seraient libérés lorsque la bâche serait retirée et que la tourbe serait transportée afin d'être traitée.Bien que les stocks représentent moins de 1% de la zone totale de l'étude, ils sont à l'origine de 1 à 2 % des émissions totales du site incluant les flux de surface et les émissions libérées lors du retrait des piles.Mes résultats contribuent à une compréhension plus complète des émissions de GES liées à l'utilisation des terres au Canada, offrant des perspectives pour améliorer la comptabilisation des GES et orienter l'industrie de la tourbe vers de meilleures pratiques de gestion.vi

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