Postglacial Reconstruction of Fire History Using Sedimentary Charcoal and Pollen From a Small Lake in Southwest Yukon Territory, Canada

Previous research suggests climate warming during the current century is likely to lead to an increase in the frequency and severity of wildfire. Recent wildfire seasons in northern Canada generally support these studies, with some of the worst fire seasons on record occurring during the past decade. While we can readily track the spatial and temporal distribution of these events during recent decades using satellite-derived data, these records of past fire activity are relatively short. Proxy records of past fire activity are needed to fully understand how fire regimes may be shifting in response to changing climatic conditions. A high-resolution fire record for the full Holocene was developed using a 539.5-cm sediment core collected from a small lake in southwest Yukon Territory, Canada. Macroscopic charcoal was counted throughout the core at contiguous 0.5-cm intervals. The core was also analyzed for loss-on-ignition and magnetic susceptibility. Fossil pollen preserved in the lake sediment was analyzed to determine vegetation change throughout the Holocene. Macroscopic charcoal analysis indicates an active fire history throughout the record, with 91 fires recorded during the Holocene. Results suggest the fire regime in this region responds to both top-down (climate) and bottom-up (vegetation) factors. Fire return intervals changed in response to shifts in precipitation and temperature as well as the expansion of lodgepole pine into the region. The shifts in precipitation and temperature were attributed to the oscillation of the Aleutian Low pressure system and fluctuations in climate associated with the Medieval Climate Anomaly and the Little Ice Age

Postglacial Reconstruction of Fire History Using Sedimentary Charcoal and Pollen From a Small Lake in Southwest Yukon Territory, Canada

Previous research suggests climate warming during the current century is likely to lead to an increase in the frequency and severity of wildfire. Recent wildfire seasons in northern Canada generally support these studies, with some of the worst fire seasons on record occurring during the past decade. While we can readily track the spatial and temporal distribution of these events during recent decades using satellite-derived data, these records of past fire activity are relatively short. Proxy records of past fire activity are needed to fully understand how fire regimes may be shifting in response to changing climatic conditions. A high-resolution fire record for the full Holocene was developed using a 539.5-cm sediment core collected from a small lake in southwest Yukon Territory, Canada. Macroscopic charcoal was counted throughout the core at contiguous 0.5-cm intervals. The core was also analyzed for loss-on-ignition and magnetic susceptibility. Fossil pollen preserved in the lake sediment was analyzed to determine vegetation change throughout the Holocene. Macroscopic charcoal analysis indicates an active fire history throughout the record, with 91 fires recorded during the Holocene. Results suggest the fire regime in this region responds to both top-down (climate) and bottom-up (vegetation) factors. Fire return intervals changed in response to shifts in precipitation and temperature as well as the expansion of lodgepole pine into the region. The shifts in precipitation and temperature were attributed to the oscillation of the Aleutian Low pressure system and fluctuations in climate associated with the Medieval Climate Anomaly and the Little Ice Age.Funding was provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada Discovery and Discovery Northern Supplements programs to MFJP and KT, the Northern Scientific Training Program (NSTP) of Polar Knowledge Canada to TP,Ontario Graduate Scholarship (OGS) and Brock University Research Fellowship to TP.We acknowledge and thank the Brock University Library Open Access Publishing Fund for financial support

Impacts of Road Dust on Small Subarctic Lake Systems

Arctic regions have been experiencing increasing pressures from multiple environmental stressors, most notably rapid climate change and human development. Previous research has demonstrated the impacts of calcareous dust from gravel roads on surrounding vegetation and permafrost, whereas aquatic systems have remained largely unstudied. Here, we explore whether 1) the chronic generation of dust from the 740 km long Dempster Highway has affected water chemistry and diatom assemblages in lakes in the Peel Plateau region of the Northwest Territories, and 2) accelerated regional warming has affected these lakes. A suite of 27 water chemistry variables was assessed from 28 lakes along a 40 m – 26 km distance from the highway. Paleolimnological analyses of biological proxies (diatoms, visible reflectance spectroscopy-derived chlorophyll-a, and an index of chrysophyte scales to diatoms [S:D]) were undertaken on dated sediment cores from two lakes near the highway and one lake situated far from the highway, outside the expected range of dust transport. Conductivity and calcium exhibited a wide range of measurements across our 28 sites; lakes within 1 km of the highway generally exhibited higher ions and related variables than more distant lakes. Analyses of diatom assemblages indicated that the two shallower sites near the highway underwent modest compositional changes over the past approximately 100 years, whereas changes recorded at the farther site were more pronounced. The diatom records, supported by chlorophyll-a and S:D indices, indicated that changes in both the near and far lakes were consistent with warming, with little discernable impact from road dust. Whilst chemical changes associated with the half-century old highway corridor appear clear, they are not yet of sufficient magnitude to elicit a directional biological response in algal assemblages

Forests, fire histories, and futures of Columbian and Rocky Mountain forests, western Canada

Throughout the past few decades, shifting perspectives on fire management have led to the recognition that disturbance by fire is critical in maintaining ecological resilience in fire-adapted forests and grasslands. Long-term fire histories provide important information for land and resource managers seeking to understand the controls on wildfire dynamicsin western North America. In this paper we summarize fire history research that has recently been undertaken in the Canadian Cordillera. Using proxy records to reconstruct fire activity and vegetation change, these studies shared the overarching goal of identifying factors that control long-term fire regimes.A further aim was to identify how human activity has measurably altered various aspects of fire regimes. Looking to the future, these studies highlight the need to continue integrating information about local fire regimes and historical land-use activities when developing responsible fire and resource management strategies and identifying conservation priorities.Foothills Research Institute (fRI), Natural Sciences and Engineering Research Council (NSERC

Have natural lake expansion and landscape inundationresulted in mercury increases in flooded lakes of the GreatSlave Lowlands (Northwest Territories, Canada)?

The inundation of terrestrial vegetation following landscape flooding is an important potential source of mercury to aquatic ecosystems, and may modify mercury cycling, such as through increased methylation. In the Great Slave Lowlands of Canada’s Northwest Territories, remarkable landscape flooding has occurred over the recent past, which is the most notable in at least the last several centuries. The potential for this flooding to increase inorganic mercury flux to the lakes of the region has not yet been explored. In this study we used sediment cores from five lakes experiencing a range of recently documented lake expansion to test whether inundation of terrestrial areas has increased the total mercury concentrations in sediments, and resulted in increased total mercury flux. Increases in sedimentary mercury concentrations and fluxes in sediment cores from the expanding lakes were relatively small and within the range of non-expanded systems, suggesting that, to date, flooding has not resulted in major total mercury enrichment, unlike in experimental and natural reservoir impoundments. The potential for increased methylation of existing inorganic mercury following expansion was not explored in this paper because methylmercury is dynamic in sediments and does not preserve well, but is an important consideration for future work.This research was funded by the Cumulative Impact Monitoring Program (Government of the Northwest Territories), the W. Garfield Weston Foundation (postdoctoral fellowship to JRT), the Brock University Chancellor’s Chair for Research Excellence (MFJP), and the Natural Sciences and Engineering Research Council of Canada (Discovery Grants to MFJP and JMB, Northern Supplement to MFJP and a PDF to JBK)

Moisture-driven shift in the climate sensitivity of white spruce xylem anatomical traits is coupled to large-scale oscillation patterns across northern treeline in northwest North America

Tree growth at northern treelines is generally temperature-limited due to cold and short growing seasons. However, temperature-induced drought stress was repeatedly reported for certain regions of the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree-ring width (TRW) analysis. We investigated white spruce growth at latitudinal treeline across a >1,000\ua0km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cell-wall thickness, cell number) and TRW were correlated with the drought-sensitive standardized precipitation-evapotranspiration index of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925-1946), cool/wet (1947-1976) and again warm/dry (1977-1998) climate regimes. Xylem anatomical traits revealed water-limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisture-driven shift in growth-limiting factors between PDO periods. TRW reflected only the last shift of 1976/1977, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to TRW. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture-driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity

Using Multiple Sources of Knowledge to Investigate Northern Environmental Change: Regional Ecological Impacts of a Storm Surge in the Outer Mackenzie Delta, N.W.T.

Field data, remote sensing, and Inuvialuit knowledge were synthesized to document regional ecological change in the outer Mackenzie Delta and to explore the timing, causes, and implications of this phenomenon. In September 1999, a large magnitude storm surge inundated low-lying areas of the outer Mackenzie Delta. The storm was among the most intense on record and resulted in the highest water levels ever measured at the delta front. Synthesis of scientific and Inuvialuit knowledge indicates that flooding during the 1999 storm surge increased soil salinity and caused widespread vegetation death. Vegetation cover was significantly reduced in areas affected by the surge and was inversely related to soil salinity. Change detection analysis, using remotely sensed imagery bracketing the 1999 storm event, indicates severe impacts on at least 13 200 ha of terrestrial vegetation in the outer delta. Inuvialuit knowledge identifying the 1999 surge as anomalous is corroborated by geochemical profiles of permafrost and by a recently published paleo-environmental study, which indicates that storm surge impacts of this magnitude have not previously occurred during the last millennium. Almost a decade after the 1999 storm surge event, ecological recovery has been minimal. This broad-scale vegetation change is likely to have significant implications for wildlife and must be considered in regional ecosystem planning and in the assessment and monitoring of the cumulative impacts of development. Our investigations show that Inuvialuit were aware of the 1999 storm surge and the environmental impacts several years before the scientific and regulatory communities recognized their significance. This study highlights the need for multidisciplinary and locally informed approaches to identifying and understanding Arctic environmental change.La synthèse des données d’exploitation et de télédétection de même que des connaissances des Inuvialuit a été effectuée afin de répertorier les changements écologiques enregistrés dans la région extérieure du delta du Mackenzie et d’explorer la temporisation, les causes et les incidences de ce phénomène. En septembre 1999, une onde de tempête de grande magnitude a inondé les zones de faible élévation de l’extérieur du delta du Mackenzie. Il s’agit de la tempête la plus intense à n’avoir jamais été enregistrée, ce qui s’est traduit par les niveaux d’eau les plus élevés à n’avoir jamais été mesurés à la hauteur du delta. La synthèse des données scientifiques et des connaissances des Inuvialuit nous montre que l’inondation de 1999 a eu pour effet d’augmenter la salinité du sol et a entraîné la mort de la végétation à grande échelle. La couverture végétale a été réduite considérablement dans les zones visées par l’onde et était inversement reliée à la salinité du sol. L’analyse des détections de changement effectuée au moyen de l’imagerie télédétectée dans le cas de la tempête de 1999 laisse entrevoir de fortes incidences sur au moins 13 200 hectares de végétation terrestre dans l’extérieur du delta. Les connaissances des Inuvialuit, qui affirment que l’onde de 1999 était anormale, sont corroborées par les profils géochimiques du pergélisol ainsi que par une étude paléoenvironnementale qui indique que des incidences de cette ampleur découlant d’une onde de tempête ne se sont pas produites à un autre moment donné du dernier millénaire. Près d’une décennie après l’onde de tempête de 1999, le rétablissement écologique était minime. Ce changement de végétation à grande échelle aura vraisemblablement d’importantes incidences sur la faune et doit entrer en considération dans la planification de l’écosystème régional ainsi que dans l’évaluation et la surveillance des incidences cumulatives des travaux d’aménagement et de mise en valeur. Nos enquêtes nous ont permis de constater que les Inuvialuit étaient conscients des incidences environnementales de l’onde de tempête de 1999 plusieurs années avant que les scientifiques et le personnel s’occupant de la réglementation ne reconnaissent leur importance. Cette étude fait ressortir la nécessité d’avoir des méthodes multidisciplinaires et de faire appel aux gens de la région pour déterminer et comprendre les changements environnementaux dans l’Arctique

Spring-Summer Temperatures Since AD 1780 Reconstructed from Stable Oxygen Isotope Ratios in White Spruce Tree-Rings from the Mackenzie Delta, Northwestern Canada

High-latitude delta(exp 18)O archives deriving from meteoric water (e.g., tree-rings and ice-cores) can provide valuable information on past temperature variability, but stationarity of temperature signals in these archives depends on the stability of moisture source/trajectory and precipitation seasonality, both of which can be affected by atmospheric circulation changes. A tree-ring delta(exp 18)O record (AD 1780-2003) from the Mackenzie Delta is evaluated as a temperature proxy based on linear regression diagnostics. The primary source of moisture for this region is the North Pacific and, thus, North Pacific atmospheric circulation variability could potentially affect the tree-ring delta(exp 18)O-temperature signal. Over the instrumental period (AD 1892-2003), tree-ring delta(exp 18)O explained 29% of interannual variability in April-July minimum temperatures, and the explained variability increases substantially at lower-frequencies. A split-period calibration/verification analysis found the delta(exp 18)O-temperature relation was time-stable, which supported a temperature reconstruction back to AD 1780. The stability of the delta(exp 18)O-temperature signal indirectly implies the study region is insensitive to North Pacific circulation effects, since North Pacific circulation was not constant over the calibration period. Simulations from the NASA-GISS ModelE isotope-enabled general circulation model confirm that meteoric delta(exp 18)O and precipitation seasonality in the study region are likely insensitive to North Pacific circulation effects, highlighting the paleoclimatic value of tree-ring and possibly other delta(exp 18)O records from this region. Our delta(exp 18)O-based temperature reconstruction is the first of its kind in northwestern North America, and one of few worldwide, and provides a long-term context for evaluating recent climate warming in the Mackenzie Delta region

Impacts of Road Dust on Small Subarctic Lake Systems

Arctic regions have been experiencing increasing pressures from multiple environmental stressors, most notably rapid climate change and human development. Previous research has demonstrated the impacts of calcareous dust from gravel roads on surrounding vegetation and permafrost, whereas aquatic systems have remained largely unstudied. Here, we explore whether 1) the chronic generation of dust from the 740 km long Dempster Highway has affected water chemistry and diatom assemblages in lakes in the Peel Plateau region of the Northwest Territories, and 2) accelerated regional warming has affected these lakes. A suite of 27 water chemistry variables was assessed from 28 lakes along a 40 m – 26 km distance from the highway. Paleolimnological analyses of biological proxies (diatoms, visible reflectance spectroscopy-derived chlorophyll-a, and an index of chrysophyte scales to diatoms [S:D]) were undertaken on dated sediment cores from two lakes near the highway and one lake situated far from the highway, outside the expected range of dust transport. Conductivity and calcium exhibited a wide range of measurements across our 28 sites; lakes within 1 km of the highway generally exhibited higher ions and related variables than more distant lakes. Analyses of diatom assemblages indicated that the two shallower sites near the highway underwent modest compositional changes over the past approximately 100 years, whereas changes recorded at the farther site were more pronounced. The diatom records, supported by chlorophyll-a and S:D indices, indicated that changes in both the near and far lakes were consistent with warming, with little discernable impact from road dust. Whilst chemical changes associated with the half-century old highway corridor appear clear, they are not yet of sufficient magnitude to elicit a directional biological response in algal assemblages.Les régions de l’Arctique subissent de plus en plus de pressions en provenance d’agresseurs environnementaux, plus particulièrement le changement climatique rapide et le développement humain. Des recherches ont permis de démontrer les incidences de la poussière calcaire émanant des routes en gravier sur la végétation et le pergélisol environnants, mais les systèmes aquatiques ont fait l’objet de très peu d’études. Ici, nous explorons : 1) si la production chronique de poussière par la route de Dempster d’une longueur de 740 km a une influence sur la chimie de l’eau et les assemblages de diatomées dans les lacs de la région du plateau Peel, dans les Territoires du Nord-Ouest; et 2) si le réchauffement régional accéléré a un effet sur ces lacs. Un ensemble de 27 variables de chimie des eaux a été évalué à partir de 28 lacs sur une distance variant entre 40 m et 26 km de la route. Des analyses paléolimnologiques de substituts biologiques (diatomées, chlorophylle-a dérivée de la spectroscopie en réflectance visible (chl-a) et indice d’échelles de chrysophytes à diatomées [S:D]) ont été effectuées sur des carottes de sédiments datées, prélevées dans deux lacs situés près de la route et dans un lac situé loin de la route, à l’extérieur de l’étendue possible du transport de la poussière. Dans les 28 sites, les taux de conductivité et de calcium enregistrés se sont répartis sur une vaste gamme de mesures. De manière générale, les lacs se trouvant à moins d’un kilomètre de distance de la route avaient une plus forte teneur en ions et en variables connexes que les lacs plus éloignés. Les analyses d’assemblages de diatomées ont permis de constater que les deux sites moins profonds à proximité de la route avaient connu des changements de composition modestes au cours des cent dernières années environ, tandis que les changements enregistrés au site plus éloigné étaient plus prononcés. Les enregistrements de diatomées, taux de chl-a et indices S:D à l’appui, ont permis de constater que les changements caractérisant tant les lacs situés à proximité qu’à distance coïncidaient avec le réchauffement, et que l’incidence de la poussière de route était à peine perceptible. Bien que les changements chimiques liés au corridor routier d’un demi-siècle semblent clairs, leur ampleur n’est toujours pas suffisante pour obtenir une réponse biologique directionnelle dans les assemblages d’algues