Vue d'ensemble de la session
|Wednesday, April 06|
Peat extraction activities: Does the extraction phase influence the export of major chemical water quality indicators?
* Mika Little-Devito, University of Alberta, Canada
Kevin Devito, University of Alberta, Canada
William Shotyk, University of Alberta, Canada
Horticultural peat extraction is an expanding industry in Canada with the potential to negatively impact downstream water quality. Previous studies have reported increases in dissolved organic carbon (DOC) and nutrients in outflow water leaving extraction locations. Peat extraction is a multi-year process and the water quality associated with each extraction phase has yet to be quantified in Canada. Changes to the in situ physicochemical processes occurring in the peat at each phase can potentially impact the availability of nutrients, DOC, and major ions. Further, extraction occurs across different biogeoclimatic settings within Canada. This is not accounted for in current management practices, and may influence the chemical composition of outflow water. The objective of this study was to determine the effect of peat extraction activities on the availability and mobility of nutrients, DOC, and major ions in different extraction phases within two biogeoclimatic settings. Undisturbed, restored, and extracted sites were selected in Alberta and New Brunswick. Electrical conductivity (EC), pH, water level, and volumetric flow rate were assessed at surface pools, shallow wells, drainage ditches, and site outflow locations, along with chemical analyses of nitrogen, phosphorus, and DOC. The in situ ion availability was measured in shallow surface peat, alongside measures of peat physicochemical conditions: surface and below ground temperature, soil moisture, and peat aeration. Preliminary results suggest that in situ physicochemical conditions are variable, but extraction activities do not appear to affect surface temperature, soil moisture, or aeration in the surface peat, despite lowered water tables. Recovering sites showed elevated EC and pH values compared to extracted and undisturbed locations. Extracted sites had elevated ammonium and nitrate availability, but newly extracted fields had less available nitrogen compared to mature fields. When ditches were incised into underlying mineral sediments, water quality differed from bog waters. Specifically, EC and pH values were similar to regional surface waters, suggesting that drainage ditch substrate must be considered in impact assessments, especially in terrains containing carbonate minerals. The findings from this study suggest that sites undergoing extraction are at elevated risk of nitrate leaching, but ditch substrate may determine downstream water quality.
Essais de restauration de routes minérales compactées dans des tourbières post-production
* Laurent Daou, Valorès, Canada
Marion Tétégan Simon, Valorès, Canada
Background. Les activités opérationnelles pour la production de la tourbe nécessitent l’aménagement de chemins d’accès de nature minérale. Ces derniers se trouvent impactés par la compaction cumulée au fil des années et relative à la machinerie lourde. La nature non tourbeuse de ces chemins requiert la mise en place de méthodes spécifiques de restauration qui leur sont adaptées. Objectif. Ce projet vise à évaluer le succès d’essais de restauration de sections de chemins dans 3 tourbières situées au Nouveau-Brunswick Méthode. L’effet de la décompaction, d’un ajout de fertilisant et d’un amendement en tourbe ou en sphaigne sur le taux de survie de Larix laricina, Pinus bankskiana et Picea mariana a été mesuré en utilisant une anova multifacteur suivie d’un test post hoc de comparaison HSD de Tukey. L’effet de la décompaction sur la densité apparente du sol, la porosité, l’eau totale, l’eau facilement disponible, la rétention en eau et la conductivité hydraulique à saturation a été mesuré en utilisant des modèles de régression linéaire généralisés. Résultats. Les résultats montrent qu’aucune interaction n’a d’effet sur le taux de survie. En revanche, excepté pour l’ajout de fertilisant (p = 0.39), tous les autres traitements ont, indépendamment l’un de l’autre, un effet positif significatif sur le taux de survie. De plus, Pinus bankskiana et Larix laricina ont des taux de survie significativement supérieurs à ceux de Picea mariana. Les résultats montrent également que la décompaction n’a pas d’effet significatif sur les propriétés hydriques du sol à l’exception de la porosité d’air qui passe de 2.88 % à 5.4 % lorsque le sol est décompacté. Discussion. Ces résultats sont en accord avec la littérature où il est attendu que la décompaction ou les amendements en tourbe ou en sphaigne vont améliorer les taux de survie des arbres en facilitant respectivement la pénétration des racines ou la rétention d’eau du sol. Conclusion. Suivant ces résultats, utiliser des pins gris et des mélèzes en combinaison avec la décompaction et un amendement en tourbe ou en sphaigne apparait comme étant la méthode la plus efficace pour restaurer des routes minérales compactées en utilisant des arbres.
Hydrologic controls on peatland vegetation initiation on a remnant mineral substrate resulting from partial removal of a well pad
* Murdoch McKinnon, University of Waterloo, Canada
Felix Nwaishi, Mount Royal University, Canada
Bin Xu, NAIT Centre for Boreal Research, Canada
Richard Petrone, University of Waterloo, Canada
The partial removal of oil and gas well pads constructed in peatlands followed by introduction of a fen peatland community onto the resulting remnant mineral substrate has been proposed as a possible means of returning these features to pre-disturbance conditions. This technique has been shown to be effective at the partial well pad scale, but it has never been tested on a full well pad. It has therefore remained unclear whether partial removal would result in optimization of soil moisture conditions when implemented at scale. Accordingly, our objectives were to determine whether soil moisture conditions would be consistently optimized for moss initiation across an entire partially removed pad, and to assess the roles of precipitation and hydrologic connectivity in controlling soil moisture. Work was undertaken at a partially removed well pad near Slave Lake, Alberta in 2020 and 2021. Soil moisture (water content and matric potential) was assessed spatially across the pad and half-hourly at four locations. Soil moisture data were compared to established moss water availability thresholds to identify times and locations exhibiting water stress. The degree of hydrologic connectivity between portions of the site was assessed through calculation of lateral hydraulic gradients, quantification of lateral groundwater fluxes, and mapping of water table elevation. Results indicate a high degree of connectivity between the adjacent peatland and the upgradient edge of the pad, as indicated by low hydraulic gradients across this edge. Accordingly, near-saturated moisture conditions and consistent moss water availability were maintained along this edge independent of precipitation. The low hydraulic conductivity of the remnant fill, however, resulted in hydrologic isolation of the centre and downgradient portions of the pad, where soil moisture dynamics were controlled by the magnitude and duration of precipitation events. Given the high water requirements of fen mosses, our results indicate reclamation outcomes following implementation of the technique at scale may be negatively impacted by isolation of inner and downgradient areas if the maximization of water inputs and minimization of losses are not considered in reclamation designs. Accordingly, closure of the site water balance and detailed assessment of the efficiency of mulching treatments is recommended.
Effects of peat harvesting on concentration and downstream fate of organic carbon and nutrients during contrasting wet and dry years
* Rebecca Frei, University of Alberta, Canada
Renae Shewan, University of Alberta, Canada
Ming Cao, University of Alberta, Canada
Benjamin Abbott, Brigham Young University, United States
David Olefeldt, University of Alberta, Canada
The fate of carbon and nutrients mobilized due to land use and climate change is a critical concern for drinking water quality and aquatic habitat. However, the effect of certain land uses, such as peat harvesting for horticulture, has been under-studied in western Canada. Previous research has shown that peat harvesting may increase dissolved organic carbon (DOC) and inorganic nutrient (e.g., nitrogen and phosphorous) concentration and export, but it is unclear how the impacts of peat harvesting compare to other land uses (e.g., agriculture, forests, intact peatlands, urban areas). Furthermore, precipitation is expected to become more variable and intense in western Canada, changing the timing and magnitude of solute export. Because solute export covaries by land use and climate, it is uncertain how peat harvesting will affect downstream water quality. In this study we use a novel analytical framework to analyze solute attenuation and production through the stream network of two ~150 km2 watersheds in central Alberta during contrasting wet and dry years. In subwatersheds substantially impacted by peat harvesting, DOC concentrations increased 2-fold and nitrogen as ammonium (NH4+) increased 10-fold compared to other subwatersheds. Peat harvesting had little effect, however, on phosphorous concentration, which was not predictable by land use in general. During wet conditions, DOC concentration increased while nutrient concentrations decreased or remained static. Stream network analysis revealed that DOC had a neutral mass-balance, indicating little in-stream processing or production. Nutrients, however, were strongly attenuated, such that fewer inorganic nutrients were exported at the watershed outlet than would be expected assuming conservative mixing. Stream network analysis also showed differences in DOC and nutrient attenuation between wet and dry years. Wet conditions generally flushed DOC and nutrients from watersheds and transported more solutes downstream, while dry conditions increased solute attenuation and reduced watershed export. In short, peat harvesting increased DOC and nitrogen concentrations relative to other land uses, and precipitation modulated the distance that peat-derived DOC and nitrogen cascaded downstream to other aquatic ecosystems.
Des indicateurs écologiques simples pour évaluer le succès de la restauration des tourbières au Canada
* Gwendal Breton, GRET/PERG Université Laval, Canada
Line Rochefort, GRET/PERG Université Laval, Canada
L'objectif de cette étude est de construire des critères simples pour évaluer le succès de la restauration des tourbières horticoles canadiennes tout en conservant l’expression de leur complexité écologique.
Rebuild bogs better for birds: what we have learned after 28 years
* André Desrochers, Université Laval, Canada
Line Rochefort, Université Laval, Canada
Over the last several decades, peat has been extracted from bogs of temperate, populated regions of Eastern Canada, leaving large areas devoid of vegetation if unrestored. We tested whether vegetation structure and bird species assemblages 10 to 20 y post extraction differ among natural, unrestored and restored bogs at the scales of individual sites and entire bogs. We conducted bird counts and vegetation surveys between 1993 and 2019, using both point counts (309 sites) and Autonomous Recording Units (80 sites). According to our vegetation surveys, restoration of sites that were previously used for peat harvesting accelerated the establishment of Sphagnum and herbaceous strata, but ericaceous and tree strata were unaffected over 17 y. None of the bird species with large home ranges were associated to natural, unrestored, or restored areas at the bog level. Bird species diversity was similar in restored and natural sites, but lower in unrestored sites. Alder Flycatcher and American Goldfinch occupied restored and unrestored sites more frequently than natural sites, independent of the number of years post extraction. Occupancy of restored sites by Palm and Yellow-rumped Warblers increased over the years, reaching levels similar to those in natural sites 20 years after restoration was implemented. Occupancy of restored sites by Song and Savannah Sparrows increased from 1993-2019 and diverged from their declining occupancy of natural sites. Species assemblages of restored and unrestored sites differed significantly from those of natural sites soon after peat extraction ceased or post restoration. But assemblages from restored and unrestored sites became progressively similar to those of natural sites during the first 20 years, especially in restored sites. We conclude that bird species assemblages of restored bog sites are converging toward those of natural sites, and that restored, and sometimes unrestored, sites provide novel habitats for regionally declining species.