Fresh water supplies in mountainous regions are at risk as snow and ice stores continue to decline under rising global temperatures, earlier winter snowmelt and changing climate regimes. Alpine forests are of particular importance due to their hydrological connectivity within watersheds controlling groundwater base flow, influencing evapotranspiration (ET) and snow storage dynamics. A change in the water availability to subalpine vegetation via changes in winter snowpack accumulation and quantities or differing summer precipitation (P) regimes could have a drastic effect on the long-term health of these forests. This makes it imperative to understand and quantify their hydrological connectivity within these watersheds. Study sites located at Fortress Mountain in Kananaskis, Alberta are composed of co-occurring coniferous tree stands of Abies lasiocarpa and Picea engelmannii. Little is known about water use dynamics of these species at high elevations, specifically the quantity and timing of transpiration (T) in addition to the water sources most important for T during the entire length of the growing season. This study used a combination of hydrological and meteorological tools to address coniferous subalpine tree water use behaviours before, during and after the growing season (June-September). Methodologies focussed on determining seasonal T patterns using the non-invasive stem-heat balance method to determine sap flow and eddy covariance to capture stand ET. The source water of the studied trees was determined using δ18O and δ2H stable water isotopes and further partitioned using the MixSIAR Bayesian Mixing Model (BMM). Groundwater monitoring wells, soil tensiometers, P gauges, and meteorological stations were used to determine baseline environmental conditions. Stable water isotopes δ18O and δ2H were collected from all source waters (P, snow cover, soil water, groundwater) in addition to xylem water samples from the coniferous trees within the study area. Understanding tree response to P and drying events was the main objective addressed, yielding stark differences between the growing seasons of 2016 and 2017. Stand T was higher in 2017 (165 mm) than 2016 (118 mm) despite a much drier and warmer season (155 mm of rain in 2017 compared to 283 mm in 2016). A deeper, sustained snowpack in 2017 coupled with higher net radiation allowed for higher T rates. Paired with δ18O and δ2H stable isotope source partitioning, this study was able to identify soil water as the most important source to season-long tree productivity, with groundwater the most important for early growing season. Well-drained soils and shallow depth to bedrock inhibited groundwater access for the studied trees after the snowmelt period concluded. Thus soil moisture supplied a majority of water to the tree population during mid growing season, determined both hydrometrically and isotopically. Dry conditions in 2017 showed a clear trend between soil moisture levels and tree water use, with 2016 having almost double the soil moisture and tree productivity in the tail end of the growing season. By closely examining the patterns of subalpine tree water use, we can begin to clarify how these important ecosystems services will be impacted under a changing climate in addition to helping us better manage our forest and freshwater resources.

Peatlands cover approximately 50% of the total landscape of the Western Boreal Forest, which includes the sub-humid Boreal Plains (BP) ecozone. The BP experiences persistent water deficit conditions, promoting anaerobic conditions, which has the potential to increase decomposition, transforming the peatlands from carbon sinks to carbon sources. With evapotranspiration (ET) being the dominant source of water loss in the BP, peatland persistence is hydrologically precarious, and as such, it is necessary to understand the dynamics and controls on ET within these systems. Due to the heterogeneity of the landscape, surrounding upland forests often shelter peatlands from wind. This results in spatially varying evaporative rates, which can influence surface moisture and vegetation regimes across a peatlands surface. High-resolution turbulent models allow for such flow scenarios to be resolved as they resolve flow in a 3D domain. Therefore, high-resolution turbulent models are essential in assessing the spatial variability of stresses placed on surface scalars such as ET, by displacement height transition. This study uses a canopy resolving large-eddy simulation (RAFLES) to study the impact of displacement height transitions on surface-atmosphere exchanges of moisture within peatlands of the BP. The dimensions, vegetation structure and energy dynamics of the modeled peatlands were generated from observations of natural peatlands of the BP. Within the sheltered region leeward of a backward-facing step transition, the simulated peatlands experienced higher resistances to surface-atmosphere exchanges of moisture when compared to the reattachment and recovery regions. However, this trend was muted when the surface roughness of the peatland was increased as the roughness lowered the overall resistance of the surface. This study also found that the length of the peatland did not influence the flow reattachment dynamics within the peatland. However, it was observed that the peatlands with a narrow shape and a curved front-facing step geometry resulted in faster regional wind velocities. Understanding the turbulent dynamics within heterogeneous landscapes can help to control the rate and variability of surface to atmosphere exchanges of moisture within disrupted and reclaimed landscapes which can increase the predictability of moisture demands within future landscapes.

Carbon storage in northern peatlands is estimated to be ~795 Tg, equivalent to ~40% of atmospheric CO2. Peatlands are dominant features of the Western Boreal Plains (WBP), which are experiencing a regime shift to a warmer and drier climate, as well as an increase in forest fire disturbance. Burning of the upper layers of rich organic matter peat releases enormous quantities of C to the atmosphere. The projected response of peatlands to forest fire is concerning, but widely understudied and could be of the utmost importance for the biogeochemical function and future net C balance of peatland. Impacts of climate change driven drying on peatland nutrient dynamics have been explored previously, however, the impacts of wildfire on nutrient dynamics have not been examined. This study assessed the impact of wildfire on N and P bioavailability and nutrient mineralization, plant nutrients balance, and the C and macronutrient stoichiometry and stock in a fen one-year post-wildfire by comparing a Burned and Unburned area. The results show that bioavailable P increased up to 200 times in surface water leachate, 125 times in groundwater and 5 times in peat. Surface ash leachate had increased concentrations in ammonium (NH4+) and nitrate (NO3-), and through groundwater mobility, the entire fen experienced increased bioavailable N. Mineralization of N and P were minimal at the Burned sites, relative to Unburned sites. Fire affected plant nutrient limitation patterns, switching from dominantly N-limited to NP co-limited in moss and P-limitation in vascular species. Burned site C stock (~14000 kg/ha) was higher relative to the Unburned site, which also increased CN and CP ratios. These findings suggest that long-term effects of elevated C, N, and P concentrations on plant productivity and decomposition must be re-evaluated for fire disturbance to understand the resiliency of peatland biogeochemistry post-wildfire. Environmental controls, including hydrologic, biologic, and edaphic variables modified by the fire and their effect on CO2 fluxes have not been studied holistically. In this thesis, I studied a treed fen burned during the Horse River wildfire in Fort McMurray, AB, comparing CO2 fluxes between a Burned and Unburned area of the fen. We see that both gross ecosystem productivity (GEP) and total respiration (Rtot) were reduced in magnitude at the Burned sites in comparison to the Unburned site, with peak fluxes in the Unburned site occurring in late June, whereas the Burned site CO2 fluxes peaked later in the growing season. GEP and net ecosystem exchange (NEE) increased in carbon uptake in the Burned sites along a depth of burn (DOB) gradient, with the deepest burned areas having an increased potential to uptake more CO2 than the Unburned site. The data also showed that both bioavailable P and moss recolonization were highest in the deepest burned areas. Unburned environmental controls on CO2 fluxes were dominated by soil temperature, whereas the Burned sites CO2 fluxes were controlled by leaf area index. One-year post-wildfire, the deepest burned areas had between 5-200 times greater concentration of P than the Unburned site, the most moss recolonization, and the greatest CO2 uptake, showing that deeper burning could potentially increase the recovery trajectory and resiliency of northern peatlands after fire disturbance.