The Canadian Forest Fire Danger Rating System (CFFDRS), and in particular the Fire Weather Index System (FWI), are tools used widely across Canada and globally for assessing wildfire potential and predicting wildfire behaviour. While the FWI system has been readily utilized across a number of different forest stand types, the use of the FWI system to represent wildfire potential or behaviour in peatlands has been shown to be less effective, especially in the case of smouldering (flameless) peat fires. This is, in part, due to the wide variation in peat properties and hydrological responses to meteorological forcings between different peatland types and hydrogeological settings within the same region. To begin to address this issue the next generation CFFDRS has incorporated a Peat Moisture Code (PMC) that better represents the ecohydrological feedbacks controlling peatland water table and near-surface moisture responses to fire weather. This new code, however, will still require interpretation based on peatland characteristics to best understand the potential for peatland smouldering fires to initiate and propagate. Here we utilized Hydrus 1-D to model the hydrological response to a drying period across a large range of hypothetical peat property profiles to quantify peat smouldering thresholds and to test the robustness of the PMC. Using the same fire weather inputs used in Hydrus, we determined the daily PMC (and Drought Code) value throughout the drying period. Using the soil water tension and moisture content output by Hydrus and the bulk density with depth input into our Peat Smouldering and Ignition (PSI) model, which uses a thermodynamic approach to predict smouldering propagation, we determined the PMC values that corresponded to varying levels of peat smouldering potential (i.e., surface ignition, moderate smouldering depth, and extreme smouldering depth) across the range of peat profile types. Finally, we mapped typical peatland types onto the “phase space” of peat properties to develop a tool for fire management agencies to best interpret PMC values and the smouldering potential they represent in the various peatlands within their management areas.

The Hudson Bay Lowlands (HBL) of northern Ontario, a globally significant carbon store, are characterized by expansive peatland complexes of patterned bogs and fens, which play a vital role in regional water regulation. These peatlands are threatened by disturbance from large-scale resource extraction and projected climate change, both of which have the potential to compromise their ecohydrological function. Field measurements and numerical modeling were used to investigate the hydrological responses of peatlands and downgradient streamflow as a consequence of disturbance from mining and shifts in climate, individually and in combination. Mine dewatering reduced groundwater storage by as much as 150 mm, equivalent to a water table lowering of 75 cm, thereby decreasing annual streamflow by 66% in impacted tributaries. Although the projected increases to precipitation and evapotranspiration due to climate change were approximately balanced, resulting in minor changes to storage, there were pronounced shifts in the temporal patterns of streamflow, with a diminished snowmelt and spring freshet occurring a month earlier. When considering the cumulative impacts of climate change coupled with mining, a potential shift in peatland ecohydrology toward new equilibria is plausible, implying altered water movement across the landscape and compromised ecosystem function. This study emphasizes the critical need for further monitoring and modeling efforts to characterize the thresholds and mechanisms driving these ecohydrological changes. This research will guide future investigations on the implications of disturbance on local and regional hydrologic connectivity and facilitate the protection of peatland ecosystems in the HBL and other northern peatland-dominated landscapes.

Metal mining and smelting activities are one of the largest anthropogenic sources of arsenic pollution to the environment, with pervasive consequences to human and environmental health. Several decades of metal processing activities near Yellowknife, NT, Canada have resulted in widespread accumulation of arsenic in biomass, soils, and sediments, exceeding environmental and human health limits. The landscape surrounding Yellowknife is frequently disturbed by wildfire, most recently in 2023, when 2500 km2 burned. While wildfire-mediated release of stored arsenic around Yellowknife likely represents an incipient threat to human and ecosystem health, a quantification of the potential magnitude of arsenic remobilization from wildfires is absent. Here we combine publicly available soil and biomass arsenic concentrations and land cover datasets with the current best estimates of pyrogenic arsenic speciation and release in upland and wetland ecosystems to estimate the potential range of arsenic remobilization due to wildfires in the region surrounding Yellowknife from 1972 to 2023. Since 1972, wildfires have potentially led to the release of 141-562 Mg of arsenic, with 61-381 Mg emitted to the atmosphere and 39-109 Mg mobilized as water-soluble species. The large range in potential atmospheric emissions was due to the range in peat emission efficiency (5%-84%) that resulted in more arsenic being released from wetlands than the uplands. In 2023 alone, our estimated atmospheric release from just four wildfires was between 15%-59% of global annual arsenic wildfire emissions and likely represented between 2 and 9% of total global arsenic emissions from all natural sources. Given that climate change has and will continue to increase both annual area burned and soil burn severity, we emphasize that future increased wildfire activity closer to Yellowknife will place legacy soil arsenic stores at risk of an even larger catastrophic and unprecedented release, especially as wetlands become drier.

Patterned bog and fen peatlands of the Hudson Bay Lowlands, which form one of the largest continuous peatland complexes in the world, are globally significant stores of carbon and important water conveyance and storage features on the landscape. However, expansion of resource exploration and extraction combined with warmer temperatures associated with climate change may result in reduced water availability to these peatland complexes, potentially disrupting peatland hydrological connectivity and hydrogeochemical cycling. A case study on the effects of reduced water availability on peatland hydrological and geochemical function was conducted near the De Beers Victor Diamond Mine, located 90 km west of Attawapiskat. Active dewatering occurred here over a 12-year period (2007-2019) during which a 1.5 km transect was monitored within the mine impacted radius. Hydrological (streamflow and groundwater levels) and chemical (porewater and surface water samples) parameters were collected at the impacted transect and two nearby unimpacted reference sites. Results demon-strated that impacted peatlands had depleted water storage and spent an average of 50 % less time hydrologically connected than unimpacted peatlands. By the end of the study period, increasingly depleted water storage within the dewatering radius resulted in disproportionately lower flowrates in two tributaries downgradient of the mine-impacted peatlands when compared with the reference sites. Moreover, diminished water storage allowed solute-depleted precipitation to reach greater depths within the peat profile, while stronger downwards gradients suppressed upwards flow into fens, limiting the amount of solute-enriched water reaching the surface. The recovery of fen solute concentrations will be a prolonged process (i.e., decades to centuries) due to the slow rate of upwards diffusion, which may result in the transition of these systems towards ombrotrophic bogs. Further studies should focus on the susceptibility of these impacted systems to further reductions in water availability due to climate change.

Wetlands are an integral part of the Canadian landscape, providing crucial ecohydrological services with globally significant benefits. Over the past 75 years, Canadian scientists have emerged as international leaders in wetland hydrological research, contributing to a better understanding of wetland form and function. Early Canadian research was instrumental in the development of a classification scheme that provided a foundation for later investigations into vadose zone processes, solute transport, evapotranspiration, ground-ice dynamics, biogeochemical cycling, and modelling. This work has coalesced into a better understanding of the factors that contribute to wetland presence and persistence on the landscape, and the internal processes that result in their unique functions of carbon sequestration, water storage, flood mitigation, water quality enhancement, and wildlife habitat. In Canada and across the world, wetlands are threatened at a range of scales and intensities by disturbances like climate change, resource extraction, wildfire, altered land use, and contamination. In response, Canadian researchers have become global leaders in characterizing the impacts of disturbance on wetland function and been at the forefront of innovative restoration and reclamation techniques. As the value of wetlandisre increasingly acknowledged by stakeholders and decision-makers, the need for evidence-based wetland research will only continue to grow. Canadian scientists are well-positioned to lead wetland hydrology into the next 75 years.Les milieux humides font partie integrante du paysage canadien, offrant des services ecohydrologiques essentiels avec des avantages d'importance mondiale. Au cours des 75 dernieres annees, les chercheurs canadiens se sont imposes comme des leaders internationaux dans la recherche hydrologique sur les milieux humides, contribuant a une meilleure comprehension de leur forme et de leur fonction. Les premieres recherches canadiennes ont joue un role cle dans l'elaboration d'un systeme de classification qui a servi de fondement a des etudes ulterieures sur les processus de la zone non saturee, le transport des solutes, l'evapotranspiration, la dynamique de la glace du sol, le cycle biogeochimique et la modelisation. Ces travaux ont mene a une meilleure comprehension des facteurs qui contribuent a la presence et a la durabilite des milieux humides dans le paysage, les processus internes qui donnent lieu a leurs fonctions uniques de sequestration du carbone, de stockage de l'eau, de mitigation des inondations, d'amelioration de la qualite de l'eau, et d'habitats fauniques. Au Canada et partout dans le monde, les milieux humides sont menaces a diverses echelles et intensites par des perturbations telles que le changement climatique, l'extraction de ressources, les feux de foret, l'utilisation des terres modifiee et la contamination. En reponse, les chercheurs canadiens sont devenus des leaders mondiaux dans la caracterisation des impacts des perturbations sur la fonction des milieux humides et ont ete a l'avant-garde de techniques innovantes de restauration et de remise en etat. A mesure que la valeur des milieux humides est de plus en plus reconnue par les parties prenantes et les decideurs, le besoin de recherche sur les milieux humides basee sur des preuves ne fera que croitre. Les chercheurs canadiens sont bien positionnes pour continuer a diriger la recherche en hydrologie des milieux humides au cours des 75 prochaines annees.

Patterned bog and fen peatlands of the Hudson Bay Lowlands, which form one of the largest continuous peatland complexes in the world, are globally significant stores of carbon and important water conveyance and storage features in the landscape. However, expansion of resource exploration and extraction combined with warmer temperatures associated with climate change may result in reduced water availability to these peatland complexes, potentially disrupting peatland hydrological connectivity and hydrogeochemical cycling. A case study on the effects of reduced water availability on peatland hydrological and geochemical function was conducted near the De Beers Victor Diamond Mine, located 90 km west of Attawapiskat. Active dewatering occurred here over a 12-year period (2007-2019) during which a 1.5 km transect was monitored within the mine impacted radius. Hydrological (streamflow and groundwater levels) and chemical (porewater and surface water samples) parameters were collected at the impacted transect and two nearby unimpacted reference sites. Results demonstrated that impacted peatlands had depleted water storage and spent an average of 50% less time hydrologically connected than unimpacted peatlands. By the end of the study period, increasingly depleted water storage within the dewatering radius resulted in disproportionately lower flowrates in two tributaries downgradient of the mine-impacted peatlands when compared with the reference sites. Moreover, diminished water storage allowed solute-depleted precipitation to reach greater depths within the peat profile, while stronger downwards gradients suppressed upwards flow into fens, limiting the amount of solute-enriched water reaching the surface. The recovery of fen solute concentrations will be a prolonged process (i.e., decades to centuries) due to the slow rate of upwards diffusion, which may result in the transition of these systems towards ombrotrophic bogs. Further studies should focus on the susceptibility of these impacted systems to further reductions in water availability due to climate change.

Surface mining operations for bitumen have fundamentally altered large areas of boreal forest and fen peatland in the Athabasca Oil Sands Region (AOSR) of Alberta, Canada. Pilot projects intended to assess the feasibility of fen construction as a reclamation option have been designed, built, and are currently undergoing monitoring. Initial assessments of ecohydrologic function have been conducted for these systems but offer limited insight into their evolution and likely successional pathway. Thus, this study projects the hydrologic and geochemical behaviour of a constructed fen watershed to understand whether the system will be capable of supporting peatland processes into the future. A numerical groundwater flow and sodium transport model was calibrated and validated with 7 years of hydraulic head, water flux, and water chemistry data. Based on Monte Carlo simulations, the projected fen water table would be stable and remain close to the surface (<15 cm), indicating that the design of the system can generate sufficient water quantity to meet evaporative demand and maintain surface water discharge. However, water quality was more sensitive to climatic variability, which induced a large range in potential sodium concentrations at the fen surface (450-850 mg L-1). Evapoconcentration of salts across the surface of the fen will likely limit moss establishment for decades following construction. Yet stress-thresholds of salt-tolerant vegetation like sedges will not be exceeded. Ultimately, these projections support the original design principles and philosophy that guided the creation of the watershed. Nonetheless, this work indicates that increasing the area of the fen relative to the upland would not have a detrimental impact on the ability of the system to maintain a high water table. This could allow for the proportion of peatlands on the reclamation landscape to reflect the pre-disturbance environment more faithfully.

At the Nikanotee Fen Watershed, a pioneering reclamation project in the Athabasca Oil Sands Region, elevated sodium (Na+) in the porewater of mine-waste materials has been shown to migrate to the fen through groundwater, likely influencing fen vegetation health. Given the potential of Na+ to steer the ecological development of the fen, the goal of this research is to quantify the spatial distribution of Na+ and to characterize the Na+ mass balance of the surface and shallow subsurface of the fen. For a given time, the highest Na+ concentrations were generally found in the wettest part of the fen in the southwestern corner, and the lowest in the relatively dry northeast corner near the drainage outlet. Na+ concentrations in ponded surface water were responsive to rainfall-induced dilution and evapoconcentration, whereas porewater salinity in shallow groundwater was insensitive to meteorological conditions. Surface discharge controlled the mass efflux of Na+ from the system at an estimated average rate of 4 kg∙day−1 between June and August. Given the relatively small proportion of salt being flushed annually, and the greater rate of mass inflow relative to export, elevated salinity will likely be sustained for several decades. Since elevated Na+ concentrations are impacting the rooting zone of vegetation and have exceeded the salinity stress-threshold of mosses, targeting salt-tolerant vegetation will be important to maintain carbon accumulation in constructed systems.

Millions of tonnes of coarse tailings sand are produced every year as a byproduct of the bitumen extraction process in the Athabasca Oil Sands Region. These tailings materials contain residual quantities of mobile solutes, which can be transported through groundwater to downgradient terrestrial and aquatic ecosystems. The anticipated ubiquity of coarse tailings sand on the post-mined landscape necessitates the characterization of its hydraulic and transport properties. Hydraulic conductivity and dispersivity was evaluated at multiple scales, and included the first field-scale tracer test conducted in a tailings sand aquifer. Average hydraulic conductivity derived using laboratory cores, single-well response tests, and the tracer test were 3.2 m d(-1), 2.9 m d(-1), and 3.4 m d(-1), respectively. These measurements demonstrated close agreement and were consistent with expectations of a material that experiences some grain-size segregation and homogenization due to the oil sands process and the nature of deposition. The field-scale tracer test appeared to obtain the asymptotic dispersivity of the coarse tailings sand aquifer, reaching a maximum value of 0.5 m after 18 m of displacement. Coarse tailings in the oil sands that experience similar processes of segregation, settling, and deposition on the reclamation landscape could be expected to have similar hydraulic properties.

The modeling of seasonal ground ice (SGI) freeze/thaw a common feature in boreal peatlands, has often been completed using a unidirectional approach, where melting is driven by energy inputs from the surface. However, bi-directional melt is known to occur, and can potentially increase the spring melt rate. Accurate modelling of the timing of ice-free conditions in peatlands is important because SGI can impede spring infiltration and lead to substantial spring snowmelt runoff from peatlands. However, when modelling melt only from above, erroneous results in the model estimation of ice-free conditions can occur, which can lead to knock on-effects for modelling peatland hydrological function. Furthermore, as the climate warms, it is unclear how this role of SGI may change in the future. This study used the Stefan Equation to model unidirectional and bi-directional melt to assess which performed better in modelling the timing of ice-free conditions compared to observed values (BI: 3.9 +/- 2.1 days, UNI: 9.0 +/- 4.7). Including bi-directional melt improved model performance by reducing this difference by approximately 5 days. Model performance for SGI freeze/thaw cycles were similar, with BI being slightly more accurate in freezing (RMSE:2.7 cm versus 3.3 cm) and melting (RMSE: 2.6 cm vs 3.7 cm) compared to the unidirectional approach. While the model improvement in the timing of ice-free conditions was substantial, careful consideration is needed in determining when a peatland is functionally ice free in future modelling studies. The Stefan Equation was found to be most sensitive to changes in soil moisture, compared to ground surface temperature and peat porosity, likely due to the relationship between thermal conductivity and frozen and liquid water content. Comparisons with future climate change projections suggest that the timing of ice-free conditions 'could shift by as much as 2 weeks earlier in the 2050's and by almost a month earlier in the 2080's. However, the timing of snowfall, and rain on snow events continues to be a source of model uncertainty. Future studies should work to investigate the potential positive feedbacks this could create. In conclusion, the Stefan Equation presents a relatively easy path for incorporating bi-directional melt into peatland models. This process should be included in peatland ecohydrological models in order to properly model the timing of melt and ice-free conditions.

Study region: A peatland watershed was constructed on a post-mined oil sands lease in Northern Alberta, Canada, with the intention of replicating the function of natural wetlands removed by surface mining. Study focus: Given the potential for moisture limited conditions due to the sub-humid regional climate, ensuring sufficient water availability in these landscapes is a principal concern. This research demonstrates how small recharge basins can modify the hydrology to promote groundwater recharge critical for sustaining saturated conditions in a downgradient wetland. New hydrological insights for the region: Location was important in determining the efficacy of recharge basins. Specifically, basins placed at the confluence of two hillslopes detained substantial volumes of runoff due to large upslope areas, contributing similar to 30% of the groundwater budget to the fen, while only occupying 1% of the upland area. Basins situated near low relief hillslopes or altogether isolated from a hillslope did not detain appreciable runoff and therefore had a minor role in recharging groundwater. Groundwater in the vicinity and downgradient of active recharge basins had considerably lower solute concentrations because of dilution. This suggests that basins can not only enhance recharge within engineered landscapes, providing a consistent and focused supply of water to upland aquifers, but offer relatively fresh groundwater to downgradient ecosystems. This could ameliorate the impact of high salinity present in oil sands process-affected materials.

Reclamation watersheds that integrate fen peatlands into the design require the inclusion of uplands that are capable of supporting forest development while concurrently supplying sufficient groundwater recharge to downgradient wetland ecosystems. This necessitates selecting materials with suitable soil hydraulic properties and identifying the appropriate thickness and layering to fulfill the dual function of uplands as water storage, and water conveyance features. Currently, these systems incorporate tailings sand - a mine waste material - overlain by a cover soil of fine forest-floor material. The developmental pathway of these uplands is currently unknown, and it is unclear whether these landforms will provide enough groundwater recharge once a climax vegetation community establishes. Therefore, this research attempts to estimate the maximum density of vegetation, and associated water balance fluxes of a constructed upland integrated into a peatland watershed. The numerical modelling software HYDRUS-1D simulated soil moisture dynamics using a 65-year meteorological record, and a plant water stress algorithm was used to estimate the maximum sustainable leaf area index that the upland could support. Based on the thickness of the cover soil, the upland could support an average leaf area index of 1.2. Under this vegetation density, average annual groundwater recharge was 83 mm, and predominantly supplied by snowmelt (64%). Given this quantity of recharge, the model indicates that the upland will continue to provide enough groundwater to offset the anticipated water deficit in the downgradient fen ecosystem. However, by altering the design of the upland, specifically the spatial arrangement and thickness of cover soil, the same recharge could be supplied while also allowing for a higher average vegetation density. Such a design could allow for the creation of watersheds with a higher proportion of peatland.

Mine reclamation landscapes typically comprise layers of mine waste materials such as tailings sands, capped with a cover soil. In addition to the arrangement and placement of these materials, their hydraulic properties govern the performance of the built system. Soil evolution due to freeze-thaw cycling can result in dramatically altered soil hydraulic properties compared to the as-built material. Therefore, prediction of present and future hydrologic behaviour relies on understanding the nature and magnitude of this change and the elapsed time associated with stabilization. This research quantifies the transient hydraulic properties of mine reclamation materials at a constructed upland within a reclaimed watershed, and models the effect of this evolution on the partitioning of soil moisture between evaporation and groundwater recharge. Soil moisture dynamics were simulated using HYDRUS-1D for the ice-free period two, three, and five years after construction. A capillary barrier between the fine-grained cover soil and coarse-grained tailings sand regulated percolation past the interface. Soil evolution of the cover soil was responsible for an increase in saturated hydraulic conductivity by an order of magnitude, decrease in air-entry pressure by a factor of 4, and decrease in the van Genuchten n parameter by a factor of 2. The altered soil hydraulic properties associated with the weathered cover soil ultimately resulted in a 64% increase in groundwater recharge as a consequence of the capillary barrier weakening. The cover soil exhibited minor spatial heterogeneity in soil hydraulic properties, and did not contribute substantial uncertainty to the estimates of groundwater recharge and evaporation. Cover soil thickness exerted a strong influence on the partitioning of soil moisture. Reclaimed uplands will provide the most recharge to downgradient ecosystems in the period following the completion of soil evolution (similar to 4 years) but preceding substantial vegetation development. (C) 2019 Elsevier B.V. All rights reserved.

Mine reclamation requires the reconstruction of entire landforms and drainage systems. The hydrological regime of reclaimed landscapes will be a manifestation of the processes operating within the individual landforms that comprise it. Hydrology is the most important process regulating wetland function and development, via strong controls on chemical and biotic processes. Accordingly, this research addresses the growing and immediate need to understand the hydrological processes that operate within reconstructed landscapes following resource extraction. In this study, the function of a constructed fen watershed (the Nikanotee Fen watershed) is evaluated for the first two years following construction (2013-2014) and is assessed and discussed within the context of the construction-level design. The system design was capable of sustaining wet conditions within the Nikanotee Fen during the snow-free period in 2013 and 2014, with persistent ponded water in some areas. Evapotranspiration dominated the water fluxes from the system. These losses were partially offset by groundwater discharge from the upland aquifer, which demonstrated strong hydrologic connectivity with the fen in spite of most construction materials having lower than targeted saturated hydraulic conductivities. However, the variable surface infiltration rates and thick placement of a soil-capping layer constrained recharge to the upland aquifer, which remained below designed water contents in much of the upland. These findings indicate that it is possible to engineer the landscape to accommodate the hydrological functions of a fen peatland following surface oil sands extraction. Future research priorities should include understanding the storage and release of water within coarse-grained reclaimed landforms as well as evaluating the relative importance of external water sources and internal water conservation mechanisms for the viability of fen ecosystems over the longer-term.