43 research outputs found
Limnological Characteristics Reveal Metal Pollution Legacy in Lakes near Canadaâs Northernmost Mine, Little Cornwallis Island, Nunavut
We compared modern limnological characteristics of three lakes near the worldâs 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 comparĂ© les caractĂ©ristiques limnologiques modernes de trois lacs situĂ©s Ă proximitĂ© de la mine de mĂ©taux communs (plomb-zinc) la plus au nord du globe, soit la mine Polaris exploitĂ©e de 1981 Ă 2002 sur la Petite Ăźle Cornwallis (Nunavut, Canada), Ă une sĂ©rie de sites de la baie Resolute (Qausuittuq) sur lâĂźle Cornwallis. MĂȘme si les deux rĂ©gions Ă lâĂ©tude possĂšdent une gĂ©ologie grandement similaire et quâelles connaissent des conditions climatiques quasi identiques, les variables de la composition chimique de lâeau actuelle affichaient des diffĂ©rences considĂ©rables entre les sites des deux Ăźles. Plus prĂ©cisĂ©ment, les lacs Ă proximitĂ© de la mine Polaris avaient des concentrations de plomb et de zinc nettement supĂ©rieures ainsi que plusieurs autres mĂ©taux lourds (cadmium, molybdĂšne, nickel, uranium, vanadium) comparativement aux sites de lâĂźle Cornwallis. MĂȘme si la mine Polaris a fermĂ© ses portes en 2002, la prĂ©sence de taux Ă©levĂ©s de mĂ©taux lourds dans notre levĂ© de 2017 dĂ©coule vraisemblablement de la contamination Ă©manant dâactivitĂ©s antĂ©rieures. 
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 (ÎŁ) PCBs, ÎŁPBDEs, ÎŁPFASs 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 (0.81â2.5) ng/g ww in the Dehcho and 0.93 (0.63â1.2) 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 Ïcd, also considered as the yield strength, and the relationship between Ïcd and the uniaxial peak strength Ïucs of anisotropic rocks for different orientations Ξ of the isotropy planes with respect to the loading directions were investigated theoretically and experimentally. A theoretical relation of Ïcd/Ïucs with the function of the shape parameter m was established. Additionally, uniaxial compression tests of shale samples were conducted for several inclinations Ξ. The test result of Ïcd/Ïucs was close to the theoretical value for a given orientation. Furthermore, both experimental results and theoretical solutions of Ïcd/Ïucs were independent of the inclination Ξ while Ïcd and Ïucs were strongly affected by Ξ. The strength ratio Ïcd/Ïucs 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 Ύ15N values, indicating biomagnification through the food web in diverse ecosystems. However, there is no relationship between K concentrations and Ύ15N 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 ÎŒg lâ1) and chlorophyll-a (1.6 ÎŒg lâ1) 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 ÎŽ 15 N values, indicating biomagnification through the food web in diverse ecosystems. However, there is no relationship between K concentrations and ÎŽ 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(101Ì0) surface: STM, XPS, and DFT studies
The morphology and electronic structure of Cu and Au clusters deposited via thermal evaporation onto ZnO(101Ì0) substrates have been studied via scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The initial stages of nucleation and growth (âŒ0.2 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