À la chasse aux métaux traces dans un Nord canadien en évolution rapide : approches limnologiques, écologiques et collaborative = Hunting for trace metals in a rapidly changing North : limnological, ecological, and collaborative approaches

Actuellement, l’Arctique canadien subit de grands changements, tant climatiques que socio- environnementaux, auxquels s’ajoute une pression croissante d’y exploiter les ressources naturelles. Les écosystèmes arctiques étant d’importants indicateurs des changements globaux futurs, il s’avère essentiel de mieux comprendre l’impact de ces changements sur la santé humaine et celle des écosystèmes. Pourtant, notre compréhension des cycles biogéochimiques des contaminants présente des lacunes importantes, notamment pour le cycle des métaux traces, qui subit d’importants déséquilibres en réponse aux changements climatiques. Dans la présente thèse, j’ai cherché à mieux comprendre les tendances écologiques à grande échelle des métaux traces dans les écosystèmes du Grand Nord canadien. Dans un premier temps, j’ai étudié les effets potentiels d’un climat en changement sur le cycle du mercure dans les lacs et les étangs nordiques. Cette étude pluriannuelle à grande échelle cherchait à déterminer si les mares thermokarstiques à forte activité microbienne pourraient être une source de méthylmercure dans l’est de l’Arctique canadien. Nos résultats démontrent que les mares de fonte de petite taille, omniprésentes dans le Grand Nord, pourraient devenir des sources de méthylmercure pour les écosystèmes aquatiques voisins, en réponse aux changements climatiques. Dans un second temps, cette thèse a examiné l’effet de la productivité aquatique sur la bioaccumulation de méthylmercure dans les organismes aquatiques à la base des réseaux trophiques. J’ai échantillonné des écosystèmes suivant une gamme décroissante de productivité afin d’étudier les implications des changements de productivité sur la bioaccumulation de mercure. Nos résultats suggèrent que dans ces lacs nordiques peu productifs, les indicateurs de la productivité, tels que la biomasse algale et la stoechiométrie des nutriments, ne sont pas les facteurs contrôlant l’accumulation de mercure à la base des réseaux aquatiques. Les troisième et quatrième chapitres de cette thèse se sont concentrées sur le comportement et le destin des éléments de terres rares dans les écosystèmes nordiques. Peu d’études écotoxicologiques ont été menées sur ces métaux et notre objectif principal était d’établir la base de référence avant la prolifération de projets d’exploitation minière aux latitudes nordiques. Nos résultats démontrent que les terres rares suivent des patrons de bioaccumulation spécifiques aux taxons et aux tissus, et que ces contaminants ne sont pas bioamplifiés dans les réseaux trophiques naturels. J’ai également identifié les facteurs environnementaux clés qui influencent la bioaccumulation de terres rares dans le zooplancton d’eau douce, incluant le pH, le carbone organique dissous, et la concentration de terres rares sous forme d’ion libre. Nos études soulignent la pertinence du zooplancton dans le suivi biologique de ces contaminants dans les écosystèmes d’eau douce. Dans un dernier temps, cette thèse met en lumière l’importance de mener de la recherche collaborative avec les communautés autochtones en Arctique, en examinant le succès d’un programme de suivi environnemental communautaire au Nunavik. J'ai contribué à ce projet de surveillance environnementale et à la création d’activités éducatives participatives visant l’intégration du savoir autochtone dans la recherche en écologie. J’ai également examiné comment la mise en place d’ateliers pour chercheurs en début de carrière pouvait jouer un rôle de plateforme-clé pour la réflexion sur les avantages et les défis de la recherche collaborative avec les communautés autochtones. En somme, la présente thèse a grandement amélioré notre compréhension de l’effet des changements socio-environnementaux sur la biodisponibilité et les dynamiques trophiques de mercure et des éléments de terres rares dans les écosystèmes de l’est de l’Arctique canadien. Mieux comprendre les répercussions des changements futurs sur le devenir des métaux traces dans l’environnement est crucial à l’évaluation de l’impact de ces changements sur le Nord et sur les communautés qui y vivent.Climate change will have wide-ranging effects on Arctic ecosystems and communities. Accelerated warming combined with significant pressure to exploit natural resources has led to Arctic ecosystems vulnerable to both climatic and socio-environmental change. As the Arctic is an important indicator of future global changes, it is important to study the impact of these changes on human and ecosystem health. A key knowledge gap in our understanding is how rapid changes in the North will affect the transport and biogeochemical cycling of key contaminants, including trace metals. In this thesis, I used a large-scale ecological approach to study the environmental fate, bioaccumulation, and trophic transfer of trace metals in Canada’s northern ecosystems. In the first chapter of this thesis, I studied the potential impacts of a changing climate on mercury cycling within Arctic lakes and ponds. This large-scale, multi-year study investigated whether microbially-active permafrost thaw ponds were potential sources of mercury in the eastern Canadian Arctic. Our results showed that thaw ponds are small but abundant sources of methylmercury, with potentially significant downstream effects linked to permafrost thaw. The second chapter of this thesis examined the effects of aquatic productivity on the uptake of methylmercury in biota at the base of freshwater food webs. I sampled a gradient in ecosystem productivity to study the implications of climate-induced changes in productivity on mercury bioaccumulation. Our results suggested that indicators of productivity, such as algal biomass and nutrient stoichiometry, are not the main drivers of methylmercury accumulation within unproductive Arctic lakes. The third and fourth chapters of this thesis focused on the behaviour and environmental fate of rare earth elements in Arctic ecosystems. Few ecotoxicological studies exist for rare earth elements and our goal was to establish baseline data before the proliferation of rare earth mining projects at northern latitudes. Our results found that rare earth element bioaccumulation patterns appear to be species- and tissue-specific and they do not biomagnify in natural food webs. I also identified key environmental drivers of bioaccumulation in zooplankton, including, pH, dissolved organic carbon and the rare earth element free-ion concentrations. These studies highlight the utility of zooplankton as a biomonitor for rare earth elements in freshwater ecosystems. Lastly, my thesis highlights the importance of collaborative research with Indigenous communities by examining a successful community-based environmental monitoring program in Nunavik. I participated in a collaborative and land-based environmental monitoring and science education program with the aim of integrating Indigenous knowledge into ecological research. I also examined the role of peer-led workshops as an effective platform for early-career researchers to reflect on the benefits and challenges of conducting community-collaborative research in Indigenous communities. Overall, my thesis greatly improves our understanding of how rapid socio-environmental change may affect the bioavailability and trophic transfer of mercury and rare earth elements in the eastern Canadian Arctic. Understanding the impact of future changes on the environmental fate of metals is crucial to ensuring the health of Arctic ecosystems and communities

Fate and trophic transfer of rare earth elements in temperate lake food webs

Many mining projects targeting rare earth elements (REE) are in development in North America, but the background concentrations and trophic transfer of these elements in natural environments have not been well characterized. We sampled abiotic and food web components in 14 Canadian temperate lakes unaffected by mines to assess the natural ecosystem fate of REE. Individual REE and total REE concentrations (sum of individual element concentrations, ΣREE) were strongly related with each other throughout different components of lake food webs. Dissolved organic carbon and dissolved oxygen in the water column, as well as ΣREE in sediments, were identified as potential drivers of aqueous ΣREE. Log10 of median bioaccumulation factors ranged from 1.3, 3.7, 4.0, and 4.4 L/kg (wet weight) for fish muscle, zooplankton, predatory invertebrates, and nonpredatory invertebrates, respectively. [ΣREE] in fish, benthic macroinvertebrates, and zooplankton declined as a function of their trophic position, as determined by functional feeding groups and isotopic signatures of nitrogen (δ15N), indicating that REE were subject to trophic dilution. Low concentrations of REE in freshwater fish muscle compared to their potential invertebrate prey suggest that fish fillet consumption is unlikely to be a significant source of REE to humans in areas unperturbed by mining activities. However, other fish predators (e.g., piscivorous birds and mammals) may accumulate REE from whole fish as they are more concentrated than muscle. Overall, this study provides key information on the baseline concentrations and trophic patterns for REE in freshwater temperate lakes in Quebec, Canada

Contributions and perspectives of Indigenous Peoples to the study of mercury in the Arctic

Arctic Indigenous Peoples are among the most exposed humans when it comes to foodborne mercury (Hg). In response, Hg monitoring and research have been on-going in the circumpolar Arctic since about 1991; this work has been mainly possible through the involvement of Arctic Indigenous Peoples. The present overview was initially conducted in the context of a broader assessment of Hg research organized by the Arctic Monitoring and Assessment Programme. This article provides examples of Indigenous Peoples' contributions to Hg monitoring and research in the Arctic, and discusses approaches that could be used, and improved upon, when carrying out future activities. Over 40 mercury projects conducted with/by Indigenous Peoples are identified for different circumpolar regions including the U.S., Canada, Greenland, Sweden, Finland, and Russia as well as instances where Indigenous Knowledge contributed to the understanding of Hg contamination in the Arctic. Perspectives and visions of future Hg research as well as recommendations are presented. The establishment of collaborative processes and partnership/co-production approaches with scientists and Indigenous Peoples, using good communication practices and transparency in research activities, are key to the success of research and monitoring activities in the Arctic. Sustainable funding for community-driven monitoring and research programs in Arctic countries would be beneficial and assist in developing more research/ monitoring capacity and would promote a more holistic approach to understanding Hg in the Arctic. These activities should be well connected to circumpolar/international initiatives to ensure broader availability of the information and uptake in policy development

High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic

Permafrost thaw ponds are ubiquitous in the eastern Canadian Arctic, yet little information exists on their potential as sources of methylmercury (MeHg) to freshwaters. They are microbially active and conducive to methylation of inorganic mercury, and are also affected by Arctic warming. This multiyear study investigated thaw ponds in a discontinuous permafrost region in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a continuous permafrost region in the Arctic tundra (Bylot Island, NU). MeHg concentrations in thaw ponds were well above levels measured in most freshwater ecosystems in the Canadian Arctic (>0.1 ng L−1). On Bylot, ice-wedge trough ponds showed significantly higher MeHg (0.3−2.2 ng L−1) than polygonal ponds (0.1−0.3 ng L−1) or lakes (<0.1 ng L−1). High MeHg was measured in the bottom waters of Subarctic thaw ponds near Kuujjuarapik (0.1−3.1 ng L−1). High water MeHg concentrations in thaw ponds were strongly correlated with variables associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems

Environmental drivers of rare earth element bioaccumulation in freshwater zooplankton

Human activities have resulted in significant release of rare earth elements (REEs) into the environment. However, the pathways of REEs from waters and soils into freshwater food webs remain poorly understood. Recent studies suggest that aquatic invertebrates may be good biomonitors for REEs, yet there is little information on factors that control REE bioaccumulation in these organisms. Our goal was to study the environmental drivers of REE levels in zooplankton, a key component in plankton food webs, across lakes from geographic areas with different bedrock geology. From 2011 to 2014, bulk zooplankton samples were collected for REE analysis from 39 lakes in eastern Canada. We observed a more than 200 fold variation in surface water REE concentrations and a 10-fold variation in sediment REE concentrations. These concentration gradients were associated with a range of more than an order of magnitude in zooplankton REE concentrations (∑REEY 3.2−210 nmol g−1 ). We found higher REE bioaccumulation in zooplankton from lakes with lower pH and higher REE to dissolved organic carbon ratios. Bioaccumulation was also strongly linked to the free ion concentrations of REEs (REE3+) in surface waters. Our study suggests that zooplankton REE bioaccumulation is an excellent predictor of bioavailable REEs in freshwaters

Highlighting the potential of peer-led workshops in training early-career researchers for conducting research with Indigenous communities

For decades, Indigenous voices have called for more collaborative and inclusive research practices. Interest in community-collaborative research is consequently growing among university-based researchers in Canada. However, many researchers receive little formal training on how to collaboratively conduct research with Indigenous communities. This is particularly problematic for early-career researchers (ECRs) whose fieldwork often involves interacting with communities. To address this lack of training, two peer-led workshops for Canadian ECRs were organized in 2016 and 2017 with the following objectives: (i) to cultivate awareness about Indigenous cultures, histories, and languages; (ii) to promote sharing of Indigenous and non-Indigenous ways of knowing; and (iii) to foster approaches and explore tools for conducting community-collaborative research. Here we present these peer-led Intercultural Indigenous Workshops and discuss workshop outcomes according to five themes: scope and interdisciplinarity, Indigenous representation, workshop environment, skillful moderation, and workshop outcomes. Although workshops cannot replace the invaluable experience gained through working directly with Indigenous communities, we show that peer-led workshops can be an effective way for ECRs to develop key skills for conducting meaningful collaborative research. Peer-led workshops are therefore an important but insufficient step toward more inclusive research paradigms in Canada

Environmental Drivers of Rare Earth Element Bioaccumulation in Freshwater Zooplankton

Human activities have resulted in significant release of rare earth elements (REEs) into the environment. However, the pathways of REEs from waters and soils into freshwater food webs remain poorly understood. Recent studies suggest that aquatic invertebrates may be good biomonitors for REEs, yet there is little information on factors that control REE bioaccumulation in these organisms. Our goal was to study the environmental drivers of REE levels in zooplankton, a key component in plankton food webs, across lakes from geographic areas with different bedrock geology. From 2011 to 2014, bulk zooplankton samples were collected for