Limnological Characteristics Reveal Metal Pollution Legacy in Lakes near Canada’s Northernmost Mine, Little Cornwallis Island, Nunavut

We compared modern limnological characteristics of three lakes near the world’s northernmost base metal (lead-zinc) mine, Polaris Mine, which operated from 1981 to 2002 on Little Cornwallis Island (Nunavut, Canada), to a suite of sites from Resolute Bay (Qausuittuq), Cornwallis Island. Although both study regions are underlain by broadly similar geology and experience nearly identical climatic conditions, present-day water chemistry variables differed markedly between sites on the two islands. Specifically, the lakes near the Polaris Mine recorded substantially higher concentrations of zinc and lead, as well as several other heavy metals (cadmium, molybdenum, nickel, uranium, vanadium), relative to the sites on Cornwallis Island. Although the Polaris Mine closed in 2002, elevated levels of heavy metals in our 2017 survey are likely a legacy of contamination from prior operations. Nous avons comparé les caractéristiques limnologiques modernes de trois lacs situés à proximité de la mine de métaux communs (plomb-zinc) la plus au nord du globe, soit la mine Polaris exploitée de 1981 à 2002 sur la Petite île Cornwallis (Nunavut, Canada), à une série de sites de la baie Resolute (Qausuittuq) sur l’île Cornwallis. Même si les deux régions à l’étude possèdent une géologie grandement similaire et qu’elles connaissent des conditions climatiques quasi identiques, les variables de la composition chimique de l’eau actuelle affichaient des différences considérables entre les sites des deux îles. Plus précisément, les lacs à proximité de la mine Polaris avaient des concentrations de plomb et de zinc nettement supérieures ainsi que plusieurs autres métaux lourds (cadmium, molybdène, nickel, uranium, vanadium) comparativement aux sites de l’île Cornwallis. Même si la mine Polaris a fermé ses portes en 2002, la présence de taux élevés de métaux lourds dans notre levé de 2017 découle vraisemblablement de la contamination émanant d’activités antérieures.&nbsp

PERSISTENT ORGANIC POLLUTANTS IN THE LIVERS OF MOOSE HARVESTED IN THE SOUTHERN NORTHWEST TERRITORIES, CANADA

Moose (Alces alces) are an important traditional and spiritual resource for residents of the southern Northwest Territories and local residents are concerned about contaminants that may be present in the country foods they consume. As part of a larger program looking at contaminants in moose organs, we collected liver samples from moose harvested in two separate but adjoining regions within the Mackenzie River drainage area, the Dehcho and South Slave. We analyzed liver samples for a wide range of persistent organic pollutants (POPs) including polychlorinated biphenyls (PCBs), DDT related compounds, toxaphene, brominated diphenyl ethers (PBDEs) and perfluorinated alkyl substances (PFASs). Overall concentrations of major groups of POPs (total (Σ) PCBs, ΣPBDEs, ΣPFASs were consistently low (generally < 2 ng/g wet weight) in all samples and comparable to the limited data available from moose in Scandinavia. PFASs were the most prominent group with geometric means (range) of 1.3 (0.81–2.5) ng/g ww in the Dehcho and 0.93 (0.63–1.2) ng/g ww in the South Slave region. Decabromodiphenyl ether (BDE-209) was the most prominent PBDE congener, similar to that found in other arctic/subarctic terrestrial herbivores. In general, BDE-209 and PFASs, which are particle-borne and relatively non-volatile, were the predominant organic contaminants

Patterns in the limnology of lakes and ponds across multiple local and regional environmental gradients in the eastern Canadian Arctic

This study examined water chemistry from 113 lakes and ponds across the eastern Canadian Arctic to address the lack of limnological data and understanding of relationships among limnological variables across key local and regional gradients. Environmental and geochemical variables were compared at both the local and regional scale with the use of multivariate analysis. A principal components analysis indicated that there was a primary gradient in temperature, nutrients, and conductivity between sampled regions. In addition, there were significant regional differences observed for nutrients total nitrogen (TN) and total phosphorus (TP), chlorophyll a, and dissolved major ions determined via canonical variates analysis. Across all regions TN:TP ratios were high, indicating phosphorus limitation, and mid-summer surface water temperature was strongly correlated to dissolved nitrogen concentrations. Local landscape characteristics were also examined, with multiple samples from lakes of varying elevations, surface area, and depth within the same area. Shallow pond systems (<2 m depth) were found to have significantly higher variability for major ions, especially in areas with influences from local geology. Likewise, the concentration of nutrients and ions in ponds were strongly correlated to concentrations of dissolved organic carbon, likely indicating the influence of watershed inputs and resuspended sediments on the limnology of ponds. Although there was higher regional variation in the limnology of pond systems than lakes, the general patterns within each region were similar

Analysis of the stress ratio of anisotropic rocks in uniaxial tests

The effect of structural discontinuities on the progressive failure process of anisotropic rocks should be paid particular attention. The crack damage stress σcd, also considered as the yield strength, and the relationship between σcd and the uniaxial peak strength σucs of anisotropic rocks for different orientations θ of the isotropy planes with respect to the loading directions were investigated theoretically and experimentally. A theoretical relation of σcd/σucs with the function of the shape parameter m was established. Additionally, uniaxial compression tests of shale samples were conducted for several inclinations θ. The test result of σcd/σucs was close to the theoretical value for a given orientation. Furthermore, both experimental results and theoretical solutions of σcd/σucs were independent of the inclination θ while σcd and σucs were strongly affected by θ. The strength ratio σcd/σucs may therefore be an intrinsic property of anisotropic rocks and could be used to predict the failure of rock samples. Keywords: Anisotropic rocks, Uniaxial compression test, Brittle failure, Crack damage stress, Stress rati

Evidence for biomagnification of rubidium in freshwater and marine food webs

Rubidium (Rb), a rarely studied alkali metal, may be an essential ultra-trace element for humans and other organisms. However, very little information exists in regard to the concentrations and distribution of Rb in freshwater and marine food webs. We measured Rb concentrations in freshwater fish from Lake Erie and two Arctic lakes (Lake Hazen and Resolute Lake) and in seabirds, ringed seals, and invertebrates from the marine Northwater Polynya in Baffin Bay. The alkali analogues of Rb, cesium (Cs), and potassium (K) were also analysed in a subset of fish from Lakes Erie and Hazen. Rb and Cs concentrations and Cs:K ratios in the sampled biota are significantly regressed against δ15N values, indicating biomagnification through the food web in diverse ecosystems. However, there is no relationship between K concentrations and δ15N values, indicating a lack of biomagnification and the presence of homeostatistic mechanisms for this essential trace element. Rb must be included with mercury and Cs as metals that consistently biomagnify in diverse food webs and should be considered in multi-element biomagnification studies. © 2005 NRC

Physical and Chemical Limnology of a 61-lake Transect across Mainland Nunavut and Southeastern Victoria Island, Central Canadian Arctic

We describe the physical and chemical properties of sixty-one tundra lakes, sampled in a latitudinal transect (65-71°N, 105-108°W) across mainland and island regions of Nunavut, central Canadian Arctic, and examine the influence of geology, geography, climate, and vegetation on lake water chemistry. This dataset complements earlier limnological surveys of the Canadian Arctic and provides valuable information for evaluating the vulnerability of tundra lakes to predicted climate change. Principal components analysis revealed a geographical clustering of lakes; pH, DIC, specific conductivity, and trace metal concentrations reflected major lithological differences between the mainland and Victoria Island. Clustering of mainland lakes by ecoregion was also detected. Lakes of the Queen Maud Gulf Lowland and Garry Lake Lowland ecoregions (north) differed from lakes of the Takijuq Lake Upland ecoregion (south) in depth, pH, and specific conductivity as well as nutrient, DOC, and chlorophyll-a concentrations. Ionic composition of the northern mainland lakes also indicated that the influence of marine aerosols and/or leaching of residual marine salts from post-glacial marine deposits exposed by isostatic rebound. The northern mainland lakes were the most nutrient-rich and biologically productive of the three lake clusters and were characterized by median concentrations of total dissolved nitrogen (518 μg l−1) and chlorophyll-a (1.6 μg l−1) that were higher than previously reported for tundra lakes in the Canadian Arctic. These lakes were chemically similar to lakes of the Tuktoyaktuk Peninsula, in the western Canadian Arctic. Lakes of the southern mainland were dilute, acidic, and nutrient-poor, in accord with earlier limnological surveys in this ecoregion. Concentrations of nutrients, DOC, and chlorophyll-a in Victoria Island lakes fell in the middle of the ranges reported from other islands in the Canadian Arctic. Lithologic and edaphic factors strongly influenced the limnological properties of the tundra lakes surveyed and must be controlled for in order to fully evaluate the influence of future climate and vegetation change

Evidence for biomagnification of rubidium in freshwater and marine food webs

Abstract: Rubidium (Rb), a rarely studied alkali metal, may be an essential ultra-trace element for humans and other organisms. However, very little information exists in regard to the concentrations and distribution of Rb in freshwater and marine food webs. We measured Rb concentrations in freshwater fish from Lake Erie and two Arctic lakes (Lake Hazen and Resolute Lake) and in seabirds, ringed seals, and invertebrates from the marine Northwater Polynya in Baffin Bay. The alkali analogues of Rb, cesium (Cs), and potassium (K) were also analysed in a subset of fish from Lakes Erie and Hazen. Rb and Cs concentrations and Cs:K ratios in the sampled biota are significantly regressed against δ 15 N values, indicating biomagnification through the food web in diverse ecosystems. However, there is no relationship between K concentrations and δ 15 N values, indicating a lack of biomagnification and the presence of homeostatistic mechanisms for this essential trace element. Rb must be included with mercury and Cs as metals that consistently biomagnify in diverse food webs and should be considered in multi-element biomagnification studies

Growth and structure of Cu and Au on the nonpolar ZnO(101̄0) surface: STM, XPS, and DFT studies

The morphology and electronic structure of Cu and Au clusters deposited via thermal evaporation onto ZnO(101̄0) substrates have been studied via scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The initial stages of nucleation and growth (∼0.2 ML) of both Cu and Au are compared with density functional theory (DFT) calculations, which show an excellent agreement with the cluster morphologies observed by STM, with Cu nucleating three-dimensional (3D) islands even at small coverage while Au nucleates single-layer islands that grow layer by layer. DFT also gives insight into the diffusion behavior of Cu and Au adatoms on the ZnO substrate, showing strongly anisotropic diffusion barriers for Cu atoms which results in the experimentally observed preferential cluster nucleation along [0001] step edges, whereas Au shows no such anisotropy and Au clusters are observed to have no preferred nucleation sites. XPS results show a slight positive charging of the small Cu clusters at 0.2 ML coverage, which disappears at higher coverage. The single-layer Au islands formed at low coverage show some evidence of positive charging as well, which likewise disappears with increasing cluster size. Additionally, the Au clusters show a trend of increasing metallicity as the clusters grow and transition from single-layer islands to 3D structures, demonstrated by the increasing asymmetry in the Au 4f line shape as a function of Au coverage. In general, the observed charge transfer trends are supported by Bader charge analysis. © 2013 American Chemical Society