Giant Mine, located in the city of Yellowknife (Northwest Territories, Canada), is a dramatic example of subarctic legacy contamination from mining activities, with remediation costs projected to exceed $1 billion. Operational between 1948 and 2004, gold extraction at Giant Mine released large quantities of arsenic and metals from the roasting of arsenopyrite ore. We examined the long-term ecological effects of roaster emissions on Pocket Lake, a small lake at the edge of the Giant Mine lease boundary, using a spectrum of palaeoenvironmental approaches. A dated sedimentary profile tracked striking increases (approx. 1700%) in arsenic concentrations coeval with the initiation of Giant Mine operations. Large increases in mercury, antimony and lead also occurred. Synchronous changes in biological indicator assemblages from multiple aquatic trophic levels, in both benthic and pelagic habitats, indicate dramatic ecological responses to extreme metal(loid) contamination. At the peak of contamination, all Cladocera, a keystone group of primary consumers, as well as all planktonic diatoms, were functionally lost from the sediment record. No biological recovery has been inferred, despite the fact that the bulk of metal(loid) emissions occurred more than 50 years ago, and the cessation of all ore-roasting activities in Yellowknife in 1999.

One of the most ominous predictions related to recent climatic warming is that low-lying coastal environments will be inundated by higher sea levels. The threat is especially acute in polar regions because reductions in extent and duration of sea ice cover increase the risk of storm surge occurrence. The Mackenzie Delta of northwest Canada is an ecologically significant ecosystem adapted to freshwater flooding during spring breakup. Marine storm surges during the open-water season, which move saltwater into the delta, can have major impacts on terrestrial and aquatic systems. We examined growth rings of alder shrubs (Alnus viridis subsp. fruticosa) and diatoms preserved in dated lake sediment cores to show that a recent marine storm surge in 1999 caused widespread ecological changes across a broad extent of the outer Mackenzie Delta. For example, diatom assemblages record a striking shift from freshwater to brackish species following the inundation event.What is of particular significance is that the magnitude of this recent ecological impact is unmatched over the >1,000-year history of this lake ecosystem. We infer that no biological recovery has occurred in this lake, while large areas of terrestrial vegetation remain dramatically altered over a decade later, suggesting that these systems may be on a new ecological trajectory. As climate continues to warm and sea ice declines, similar changes will likely be repeated in other coastal areas of the circumpolar Arctic. Given the magnitude of ecological changes recorded in this study, such impacts may prove to be long lasting or possibly irreversible.paleoecology | paleolimnology | dendrochronology | limnology | salinization

Summary 1. Rapid environmental change occurring in high‐latitude regions has the potential to cause extensive thawing of permafrost. Retrogressive thaw slumps are a particularly spectacular form of permafrost degradation that can significantly impact lake–water chemistry; however, to date, the effects on aquatic biota have received little attention. 2. We used a diatom‐based palaeolimnological approach featuring a paired lake study design to examine the impact of thaw slumping on freshwater ecosystems in the low Arctic of western Canada. We compared biological responses in six lakes affected by permafrost degradation with six undisturbed, reference lakes. 3. Slump‐affected lakes exhibited greater biological change than the paired reference systems, although all systems have undergone ecologically significant changes over the last 200 years. Four of the six reference systems showed an increase in the relative abundance of planktonic algal taxa (diatoms and scaled chrysophytes), the earliest beginning about 1900, consistent with increased temperature trends in this region. 4. The response of sedimentary diatoms to thaw slumping was understandably variable, but primarily related to the intensity of disturbance and associated changes in aquatic habitat. Five of the slump‐affected lakes recorded increases in the abundance and diversity of periphytic diatoms at the presumed time of slump initiation, consistent with increased water clarity and subsequent development of aquatic macrophyte communities. Slump‐affected lakes generally displayed lower nutrient levels; however, in one system, thaw slumping, induced by an intense fire at the site in 1968, ostensibly led to pronounced nutrient enrichment that persists today. 5. Our results demonstrate that retrogressive thaw slumping represents an important stressor to the biological communities of lakes in the western Canadian Arctic and can result in a number of limnological changes. We also show that palaeolimnological methods are effective for inferring the timing and response of aquatic ecosystems to permafrost degradation. These findings provide the first long‐term perspective on the biological response to permafrost thaw, a stressor that will become increasingly important as northern landscapes respond to climate change.

Seabirds represent a well documented biological transport pathway of nutrients from the ocean to the land by nesting in colonies and providing organic subsidies (feces, carcasses, dropped food) to these sites. We investigated whether seabirds that feed at different trophic levels vary in their potency as biovectors of metals, which can bioaccumulate through the marine foodweb. Our study site, located on a small island in Arctic Canada, contains the unique scenario of two nearby ponds, one of which receives inputs almost exclusively from upper trophic level piscivores (Arctic terns, Sterna paradisaea) and the other mainly from lower trophic level molluscivores (common eiders, Somateria mollissima). We used dated sediment cores to compare differences in diatoms, metal concentrations and also stable isotopes of nitrogen (δ 15 N), which reflect trophic position. We show that the seabirds carry species-specific mixtures of metals that are ultimately shunted to their nesting sites. For example, sediments from the tern-affected pond recorded the highest levels of δ 15 N and the greatest concentrations of metals that are known to bioaccumulate, including Hg and Cd. In contrast, the core from the eider-affected site registered lower δ 15 N values, but higher concentrations of Pb, Al, and Mn. These metals have been recorded at their greatest concentrations in eiders relative to other seabirds, including Arctic terns. These data indicate that metals may be used to track seabird population dynamics, and that some metal tracers may even be speciesspecific. The predominance of large seabird colonies on every continent suggests that similar processes are operating along coastlines worldwide.biological transport | paleolimnology | Arctic terns | common eiders | bioaccumulation S eabirds often carry elevated contaminant loads as a result of biomagnification and bioaccumulation through the marine foodweb (1). As a result of their gregarious nature and propensity to form large breeding colonies, seabirds can create localized "hotspots" of contamination by shunting marine-derived contaminants from the ocean to the land via their guano and mortality (2). This biological transport pathway can lead to contaminant concentrations that far surpass those conducted by abiotic processes alone (e.g., winds, ocean currents) and, in some instances, reach toxic levels. For example, Brimble et al. (3) studied several ponds located near a large colony of northern fulmars (Fulmarus glacialis) on Devon Island, Nunavut, in High Arctic Canada, and recorded sedimentary metal concentrations that exceeded Canadian environmental guidelines for protecting wildlife. Likewise, in the Norwegian Arctic, Evenset et al. (4) recorded higher than background concentrations of persistent organic pollutants (POPs) in aquatic organisms from a seabird-affected lake, providing evidence that seabird-transported contaminants were entering local foodwebs. Similar results have been recorded for Antarctic penguin populations (5, 6).The contaminant burden of seabirds is infl...

[1] The combined effects of climate warming (i.e., increased storminess, reduced sea ice extent, and rising sea levels) make low-lying Arctic coastal regions particularly susceptible to storm surges. The Mackenzie Delta, a biologically significant and resource-rich region in northwestern Canada, is particularly vulnerable to flooding by storm surges. To properly manage the consequences of climate warming for Arctic residents, infrastructure, and ecosystems, a better understanding of the influence of climate change on storm surge activity is required. Here we use particle size analysis of lake sediment records to show that the occurrence and magnitude of storm surges in the outer Mackenzie Delta are significantly related to temperature and that the frequency and intensity of storm surges is increasing. Our results demonstrate the effects of changing climate on storm surge activity and provide a cautionary example of the threat of inundation to low-lying Arctic coastal environments under future climate warming scenarios.