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Peat accumulation in high latitude wetlands represents a natural long-term carbon sink, resulting from the cumulative excess of growing season net ecosystem production over non-growing season (NGS) net mineralization in soils. With high latitudes experiencing warming at a faster pace than the global average, especially during the NGS, a major concern is that enhanced mineralization of soil organic carbon will steadily increase CO 2 emissions from northern peatlands. In this study, we conducted laboratory incubations with soils from boreal and temperate peatlands across Canada. Peat soils were pretreated for different soil moisture levels, and CO 2 production rates were measured at 12 sequential temperatures, covering a range from − 10 to + 35 °C including one freeze–thaw event. On average, the CO 2 production rates in the boreal peat samples increased more sharply with temperature than in the temperate peat samples. For same temperature, optimum soil moisture levels for CO 2 production were higher in the peat samples from more flooded sites. However, standard reaction kinetics (e.g., Q 10 temperature coefficient and Arrhenius equation) failed to account for the apparent lack of temperature dependence of CO 2 production rates measured below 0 °C, and a sudden increase after a freezing event. Thus, we caution against using the simple kinetic expressions to represent the CO 2 emissions from northern peatlands, especially regarding the long NGS period with multiple soil freeze and thaw events.

Physical and chemical, and pore-scale to field-scale properties of peat soil affect the migration of non-aqueous phase liquids (NAPLs) and dissolved-phase solutes in contaminated peatlands in a way not anticipated based on the current understanding derived from their behavior in mineral soil systems. Peat pore surface wettability, which is determined by pore surface chemistry, has strong hysteresis and shows hydrophilic and hydrophobic behaviors during water drainage from and water imbibition into pore spaces. This leads to high residual NAPL saturation in pore spaces. Systematic reduction of pore radius size with depth associated with greater peat decomposition in a typical peat profile leads to an increase in NAPL-entry capillary pressure and a reduction in peat permeability with increasing depth. The former leads to stronger capillarity in deeper peat horizons, causing resistance to NAPL percolation compared to that in shallow ones; along with decreased permeability with depth, this results in higher NAPL mobility in shallower peat. The cumulative effect is preferential horizontal migration of NAPL in shallow less decomposed peat horizons. Occupation of peat macro-pores by NAPL dramatically decreases the effective water permeability and leads to lower rates of water infiltration and groundwater discharge in the contaminated area. With respect to dissolved-phase hydrocarbons, the dual porosity structure of peat soil, which exhibits larger pores and higher effective porosity near the surface, also favours preferential transport in the surface peat layer, and leads to increasing solute retardation with depth. In addition, adsorption of hydrocarbon solutes onto natural dissolved organic carbon present in peat pore water influences the effective adsorption of hydrocarbon solutes onto peat by reducing the apparent adsorption partitioning coefficient. The concepts and evidence presented in this manuscript suggest both free-phase and dissolved-phase hydrocarbon have restricted mobility in peatlands. On this basis, in large peatlands where ecological function is not notably impacted, a case can be made for allowing natural processes to degrade the hydrocarbon, rather than the common response of digging up and disposing of contaminated soils, which destroys the ecosystem function. Les propriétés physiques et chimiques, et celles à échelle des pores et à échelle réelle des terres tourbeuses influent sur la migration des liquides de phase non aqueuse (« NAPL ») et de solutés de phase dissoute dans les tourbières contaminées, et ce, d’une façon non prévue selon la compréhension actuelle fondée sur le comportement de ces liquides et solutés dans les systèmes de sols minéraux. La mouillabilité de surface des pores de tourbe, qui est déterminée par la chimie de surface des pores, a une forte hystérèse et montre des comportements hydrophile et hydrophobe au cours du drainage d’eau des espaces interstitiels et d’imbibition d’eau dans ces espaces poraux. Ceci donne lieu à une haute saturation résiduelle en NAPL dans les espaces interstitiels. La réduction systématique de la dimension des pores avec la profondeur, liée à une décomposition plus importante dans un profil de tourbe typique, mène à une augmentation de la pression capillaire d’entrée des NAPL et à une réduction de perméabilité de la tourbe avec l’augmentation de profondeur. Le premier cas mène à une capillarité plus forte dans des horizons de tourbe plus profonds, y causant une résistance à la percolation des NAPL comparativement à des horizons peu profonds ainsi qu’à une perméabilité diminuée avec la profondeur, engendrant une plus grande mobilité des NAPL dans la tourbe moins profonde. L’effet cumulatif se traduit par une migration horizontale préférentielle des NAPL dans des horizons peu profonds de tourbe moins décomposée. L’occupation de macro pores de tourbe par des NAPL diminue dramatiquement la perméabilité à l’eau efficace et mène à des taux inférieurs d’infiltration d’eau et de décharge d’eau souterraine dans la zone contaminée. En ce qui concerne les hydrocarbures de phase dissoute, la structure de double porosité du sol tourbeux, présentant de plus grands espaces poraux et une porosité efficace plus élevée près de la surface, favorise aussi le transport préférentiel dans la couche de tourbe superficielle et mène au retardement de soluté croissant avec la profondeur. De plus, l’adsorption de solutés d’hydrocarbures sur le carbone organique dissous naturellement présent dans l’eau interstitielle de tourbe a une incidence sur l’adsorption efficace de solutés d’hydrocarbures sur la tourbe en réduisant le rapport de distribution d’adsorption apparente. Les concepts et la constatation présentés dans ce manuscrit suggèrent qu’autant l’hydrocarbure en phase libre que l’hydrocarbure dissous ont une mobilité limitée dans les tourbières. À cet égard, dans de grandes tourbières où la fonction écologique n’est pas particulièrement touchée, on peut justifier de permettre aux processus naturels de dégrader l’hydrocarbure, plutôt que de choisir l’intervention courante de déterrement et de disposition de sols contaminés, ce qui détruit la fonction écosystémique.

Peatlands support vital ecosystem services such as water regulation, specific habitat provisions and carbon storage. In Canada, anthropogenic disturbance from energy exploration has undermined the capacity of peatlands to support these vital ecosystem services, and thus presents the need for their reclamation to a functional ecosystem. As attempts are now being made to implement reclamation plans on post-mining oil sands landscapes, a major challenge remains in the absence of a standard framework for evaluating the functional state of a constructed peatland. To address this challenge, we present a functional-based approach that can guide the evaluation of constructed peatlands in the Alberta oil sands region. We achieved this by conducting a brief review, which synthesized the dominant processes of peatland functional development in natural analogues. Through the synthesis, we identified the interaction and feedback processes that underline various peatland ecosystem functions and their quantifiable variables. By exploring the mechanism of key ecosystem interactions, we highlighted the sensitivity of microbially mediated biogeochemical processes to a range of variability in other ecosystem functions, and thus the appropriateness of using them as functional indicators of ecosystem condition. Following the verification of this concept through current pilot fen reclamation projects, we advocate the need for further research towards modification to a more cost-efficient approach that can be applicable to large-scale fen reclamation projects in this region.

Saline springs can provide clues as to the nature of groundwater flow, including how it relates to subsurface wastewater storage and the distribution of solutes in the landscape. A saline-spring peatland neighboring a proposed in-situ oil facility was examined near Fort McMurray, Alberta (Canada). The study area is situated just north of a saline groundwater discharge zone, which coincides with the erosional edge of the Cretaceous Grand Rapids Formation. Na⁺ (mean 6,949 mg L⁻¹) and Cl⁻ (mean 13,776 mg L⁻¹) were the dominant salts within the peatland, which increased by an order of magnitude in the opposite direction to that of the local groundwater flow. Rivers and freshwater wetlands within the study area had anomalously high salinities, in some cases exceeding 10,000 mg L⁻¹ total dissolved solids within deeper sediments. Saline-spring features were observed as far as 5 km from the study area. A low-permeability mineral layer underlying the peatland restricted vertical groundwater exchange (estimated to be less than several mm over the 4-month study period). Sand and gravel lenses underlying the fen’s high-salinity zone may function as areas of enhanced discharge. High Cl/Br ratios point to halite as a potential source of salinity, while δ¹⁸O and δ²H signatures in groundwater were lower than modern-day precipitation or Quaternary aquifers. The complex connectivity of saline-spring wetlands within the landscape has implications for industry and land-use managers, and justifies incorporating them into monitoring networks to better gauge the magnitude and flow history of natural saline discharge in the oil sands region.

We studied from 1998 to 2003 the fine-scale vegetation dynamics of an abandoned vacuum-mined bog located in southern Québec in which cotton-grass (Eriophorum vaginatum) has become dominant. A water table no deeper than 30–40 cm below the soil surface combined with a volumetric peat water content >70% in the surface peat layer favored the increase in cotton-grass cover in abandoned peat fields. In one of the two peat fields that was monitored, the density of living tussocks was 30,750/ha in 1998. The density decreased constantly to reach 25,900/ha in 2002, a 16% decrease. The expansion of cotton-grass cover was mainly the result of the growth of established tussocks following a rise of the water table. The strong relationship between cotton-grass cover and water table suggests that the latter could be used as a predictor for cotton-grass cover change in mined bogs. The present study does not provide evidence that cotton-grass facilitates the establishment of moss species. At the study site, moss establishment was more highly associated with particular hydrologic characteristics (volumetric peat water content ≥85%) than with the presence of a dense cotton-grass cover. The use of cotton-grass to facilitate the establishment of Sphagnum colonies in mined peatlands is questionable, particularly where other efficient restoration techniques are available.