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

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

Temperature-growth divergence in white spruce forests of Old Crow Flats, Yukon Territory, and adjacent regions of northwestern North America

This is the accepted manuscript of an article published by Wiley.We present a new 23-site network of white spruce ring-width chronologies near boreal treeline in Old Crow Flats, Yukon Territory, Canada. Most chronologies span the last 300 years, and some reach the mid-16th century. The chronologies exhibit coherent growth patterns before the 1930s. However, since the 1930s they diverge in trend and exhibit one of two contrasting, but well-replicated patterns we call Group 1 and Group 2. Over the instrumental period (1930-2007) Group 1 sites were inversely correlated with previous-year July temperatures while Group 2 sites were positively correlated with growth-year June temperatures. At the broader northwestern North America (NWNA) scale, we find that the Group 1 and Group 2 patterns are common to a number of white spruce chronologies, which we call NWNA 1 and NWNA 2 chronologies. The NWNA 1 and NWNA 2 chronologies also share a single coherent growth pattern prior to their divergence (~1950s). Comparison of the NWNA 1/NWNA 2 chronologies against gridded 20th-century temperatures for NWNA and reconstructed Northern Hemisphere summer temperatures (A.D. 1300-2000) indicates that all sites responded positively to temperature prior to the mid-20th century (at least back to A.D. 1300), but that some changed to a negative response (NWNA 1) while others maintained a positive response (NWNA 2). The spatial extent of divergence implies a large-scale forcing. As the divergence appears to be restricted to the 20th century, we suggest the temperature response shift represents a moisture stress caused by an anomalously warm, dry 20th-century climate in NWNA, as indicated by paleoclimatic records. However, because some sites do not diverge, and are located within a few kilometres of divergent sites, we speculate that site-level factors have been important in determining the susceptibility of sites to the large-scale drivers of divergence.This research was supported by a NSERC Discovery Grant, NSERC Northern Supplement and Government of Canada IPY grant to M. Pisaric; and a NSERC Graduate Scholarship and Northern Scientific Training Program grant to T. Porter

Forest vegetation change and disturbance interactions over the past 7500 years at Sasquatch Lake, Columbia Mountains, western Canada

Fire is the most important abiotic disturbance in the interior cedar-hemlock (ICH) and Engelmann spruce-subalpine fir (ESSF) forest zone of southeastern British Columbia, Canada. Other disturbances are also important, such as defoliator and boring insect outbreaks, windthrow, diseases, and rapid mass movements. Few studies have examined the interaction between multiple types of disturbances in these forests over long timescales. Here we present high-resolution analyses of biomass burning, erosion, and vegetation assemblage changes at Sasquatch Lake (NEL02), a valley lake in the Columbia Mountains. The 531.5 cm sediment core was radiocarbon dated and provided a 7500-year stratigraphy that was used for pollen, macroscopic charcoal (>150 μm), and sedimentologic analyses. Pollen and charcoal data provided evidence of forest composition changes and fire activity. Magnetic susceptibility, loss-on-ignition, and particle size distribution analyses characterised changes in erosion into the basin. The results show that coniferous forests, with a high abundance of Pinus pollen, had established in the catchment by the beginning of the record and were subject to intermittent burning and high-energy erosive events. Tsuga heterophylla expanded by 4400 cal BP and the modern interior cedar-hemlock forests expanded throughout the lower elevations due to increased regional continentality since 4500 cal BP. High-energy erosional inputs to the lake were less frequent from 3500 to 750 cal BP and rapid mass movements may have increased in frequency during the Little Ice Age. Dendrochronological evidence in these stands suggests a mixed-severity fire regime during past ∼300 years, which has not been fully examined for charcoal-based fire event reconstruction. Here we use identified peaks as an indicator of increased biomass burning and charcoal movement in the catchment in relation to peaks in allochthonous clastic material to understand the potential relationships between biomass burning and erosion events at multiple temporal scales in the catchment. This suggests that post-fire conditions, up to several decades, were subject to increased erosion to the lake and erosion events were more common during the early Holocene. Establishment of dense ESSF and ICH forests decreased siliciclastic input to the lake throughout the mid Holocene until a recent rockslide. The high-resolution sampling of this lake sediment record provides long-term evidence of variability in the relationships between vegetation cover, fire and erosion at a catchment scale

A ring-width-based reconstruction of June–July minimum temperatures since AD 1245 from white spruce stands in the Mackenzie Delta region, northwestern Canada

This is the accepted manuscript of an article published by Elsevier.We present a reconstruction of June-July minimum temperatures since AD 1245 for the Mackenzie Delta region based on a 29-site network of white spruce (Picea glauca) ring-width series. Most, but not all trees experienced a divergent temperature-growth response, similar to the divergence that has affected other white spruce trees across Yukon and Alaska. However, divergence in the study region began as early as AD 1900 and we have documented our methods to avoid including divergent signals in the reconstruction. Calibration/verification testing based on local temperature data, and multi-century coherence with nearby and large-scale temperature proxy records, confirm our reconstruction is robust. The reconstruction shows cool conditions in the late 13th, early 18th and early 19th centuries, corresponding with solar minima and increased volcanism. These cool periods are interrupted by warm periods consistent with early to mid-20th-century warmth. The late 20th century is the warmest interval, and the last decade is estimated to be 1.4°C warmer than any decade before the mid-20th century. The reconstructed climate history corroborates other proxy-based inferences and supports the notion that high-latitude regions such as the Mackenzie Delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries.This work received funding and logistical support from Aboriginal Affairs and Northern Development Canada, Cumulative Impact Monitoring Program and Northern Scientific Training Program; the Natural Sciences and Engineering Research Council of Canada; and the Polar Continental Shelf Program

Climatic signals in δ13C and δ18O of tree-rings from White Spruce in the Mackenzie Delta Region, Northern Canada

This is the publisher's version of an article published by the University of Colorado at Boulder, Institute of Arctic and Alpine Research.Here we present the first tree-ring series (1850–2003) of stable carbon (δ13C) and oxygen (δ18O) isotope ratios from a high-latitude treeline site in northwestern Canada. Both δ13C and δ18O were measured at annual resolution from whole-ring α-cellulose of three white spruce trees (Picea glauca [Moench] Voss) growing in the Mackenzie Delta. There is a strong positive association between δ13C and maximum summer temperatures. This relation likely results from the influence of temperature-induced drought stress on stomatal conductance. Mean summer relative humidity is also significantly correlated, inversely, with δ13C reflecting its direct influence on stomatal conductance. The δ18O record is strongly and positively correlated with early-spring to mid-summer minimum temperatures likely owing to the temperature dependence of δ18O in precipitation and uptake of this water during the growing season. Mean summer relative humidity is also significantly and inversely correlated with δ18O due to leaf water evaporative enrichment. Our δ13C and δ18O records contain a large amount of climate-driven variability indicating their considerable potential to infer past climate changes in the Mackenzie Delta region.Financial support was provided by Indian and Northern Affairs Canada: Water Resources Division and a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to M.F.J. Pisaric

Dung analysis of the East Milford mastodons: dietary and environmental reconstructions from central Nova Scotia at ~75 ka yr BP.

To reconstruct a mastodon diet and provide a ‘snapshot’ view of environmental conditions in eastern Canada prior to the onset of the Wisconsinan glaciation, we analysed the faunal and floral components of dung associated with juvenile mastodon remains from East Milford, Nova Scotia, dated to 74.9 5.0 ka cal BP. The diverse assemblage of pollen, non-pollen palynomorphs, plant macrofossils and macroinvertebrate remains in the dung suggests that the mastodons lived in a spruce-dominated mixed coniferous-deciduous forest with a strong boreal aspect interspersed with wetlands rich in charophytes, sedges, cattails, bulrushes and bryophytes. The abundance of spruce needles and birch samaras in the dung sample is consistent with an inferred browsing behaviour, having been reported for other mammutid species previously. The limited diversity and near-absence of coprophilous fungi, such as Sporormiella, in the dung could have an impact on understanding the influence of feeding strategies on the presence of coprophilous taxa in sedimentary records, and thus interpretations of megafaunal abundance. The dung also yielded the earliest known Canadian remains of the bark beetle Polygraphus cf. rufipennis, gemmulae of the freshwater sponge Eunapius cf. fragilis and loricae of the rotifer Keratella cochlearis.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A multi-century eastern white pine tree-ring chronology developed from salvaged river logs and its utility for dating heritage structures in Canada's National Capital Region

This is the accepted manuscript of an article published by Elsevier.The early settlement history of Canada’s National Capital Region, including Ottawa (Ontario) and Gatineau (Québec), was shaped in large part by the towering eastern white pine (Pinus strobus) forests that once covered the Ottawa Valley and fuelled a lucrative lumber export industry spanning the 19th and much of the 20th century. Some of the first dwellings and farmsteads of this era are still standing and serve as reminders of this history. A crucial piece of information in the assessment of a structure’s heritage value is its date of construction. Unfortunately, this information is not always known and is approximated based on construction styles and other sources of information. In this study, dendroarchaeology methods are applied to constrain the construction dates of six historic structures in the National Capital Region of 19th century vintage. A multi-century (AD 1670-2009) eastern white pine ring-width chronology was developed for dating the study structures using cross sections from sunken logs recovered from the Ottawa River and cores from live trees from the Petawawa Research Forest. The tree-ring inferred construction dates for the six structures ranged from 1830 to 1878. For most structures, historical records about the property or first inhabitants were available to corroborate the results. The ring-width chronologies of the individual structures were well correlated with the regional chronology (ravg = 0.63, p < 0.01), and this regional coherence clearly demonstrates the value of tree-rings for heritage structure assessments and reconstructing the settlement history of this region.Financial support for this research was provided through a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to M.F.J. Pisaric