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Hing Man Chan - One of the best experts on this subject based on the ideXlab platform.
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assessment of neurotoxic effects of mercury in beluga whales delphinapterus leucas ringed seals pusa hispida and polar bears ursus maritimus from the canadian Arctic
Science of The Total Environment, 2015Co-Authors: Anke Krey, Sonja K Ostertag, Hing Man ChanAbstract:Abstract Marine mammals are indicator species of the Arctic Ecosystem and an integral component of the traditional Inuit diet. The potential neurotoxic effects of increased mercury (Hg) in beluga whales (Delphinapterus leucas), ringed seals (Pusa hispida), and polar bears (Ursus maritimus) are not clear. We assessed the risk of Hg-associated neurotoxicity to these species by comparing their brain Hg concentrations with threshold concentrations for toxic endpoints detected in laboratory animals and field observations: clinical symptoms (> 6.75 mg/kg wet weight (ww)), neuropathological signs (> 4 mg/kg ww), neurochemical changes (> 0.4 mg/kg ww), and neurobehavioral changes (> 0.1 mg/kg ww). The total Hg (THg) concentrations in the cerebellum and frontal lobe of ringed seals and polar bears were 3 mg/kg ww. Our results suggest that brain THg levels in polar bears are below levels that induce neurobehavioral effects as reported in the literature, while THg concentrations in ringed seals are within the range that elicit neurobehavioral effects and individual ringed seals exceed the threshold for neurochemical changes. The relatively high THg concentration in beluga whales exceeds all of the neurotoxicity thresholds assessed. High brain selenium (Se):Hg molar ratios were observed in all three species, suggesting that Se could protect the animals from Hg-associated neurotoxicity. This assessment was limited by several factors that influence neurotoxic effects in animals, including: animal species; form of Hg in the brain; and interactions with modifiers of Hg-associated toxicity, such as Se. Comparing brain Hg concentrations in wildlife with concentrations of appropriate laboratory studies can be used as a tool for risk characterization of the neurotoxic effects of Hg in Arctic marine mammals.
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estimated dietary exposure to fluorinated compounds from traditional foods among inuit in nunavut canada
Chemosphere, 2009Co-Authors: Sonja K Ostertag, Brett Tague, Murray M Humphries, Sheryl A Tittlemier, Hing Man ChanAbstract:Abstract Increasing evidence shows that persistent organic pollutants such as perfluorinated compounds (PFCs) are found in the Arctic Ecosystem and their prevalence is causing human health concerns. The objective of this study was to estimate dietary exposure to PFCs among Inuit in northern Canada. Perfluorooctane sulfonate (PFOS), perfluorinated carboxylates (PFCA C 7 –C 11 ) and fluorotelomer unsaturated carboxylic acids (6:2, 8:2 and 10:2 FTUCA) were measured in 68 traditional foods collected in Nunavut between 1997 and 1999. Total PFC concentrations were highest in caribou liver (mean ± standard deviation; 6.2 ± 5.5 ng g −1 ), ringed seal liver (minimum, maximum; 7.7, 10.2 ng g −1 ), polar bear meat (7.0 ng g −1 ), and beluga meat (minimum, maximum; 7.0, 5.8 ng g −1 ). Inuit food intake data from 24-h recalls conducted in Nunavut between 1997 and 1999 were used for the calculation of PFC exposure. Mean daily dietary exposure was calculated to range from 210 to 610 ng person −1 (0.6–8.5 ng kg body weight −1 ) for 754 individuals. Dietary exposure to PFCs was statistically significantly higher in men in the 41–60 year age group ( p
Connie Lovejoy - One of the best experts on this subject based on the ideXlab platform.
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milne fiord epishelf lake a coastal Arctic Ecosystem vulnerable to climate change
Ecoscience, 2011Co-Authors: Julie Veillette, Tommy Harding, Dermot Antoniades, Caroline Chenard, Connie Lovejoy, Marianne Potvin, Curtis A. Suttle, Anne-dorothee Jungblut, Warwick F. VincentAbstract:Milne Fiord in the Canadian High Arctic contains the last known ice-dammed fiord lake (epishelf lake) in the Northern Hemisphere. This freshwater Ecosystem is retained by the Milne Ice Shelf and is underlain by sea water that is connected to the Arctic Ocean. Using microscopy, photosynthetic pigment analyses, and molecular techniques we examined the planktonic communities present in Milne Fiord to determine the biotic characteristics of the epishelf lake and the sea water below. Net sampling of the water column of Milne Fiord revealed a mixture of marine, freshwater, and brackish zooplankton taxa, and high performance liquid chromatography (HPLC) pigment analysis showed pronounced differences in phytoplankton composition through the highly stratified water column. Chlorophytes dominated in the epishelf lake, prasinophytes prevailed in the halocline, and the bottom layer harboured mainly fucoxanthin-containing groups. Clone libraries of a dark-incubated, concentrated sample from below the halocline (30 m depth) yielded marine Archaea (mainly Crenarchaeota) and known bacterial taxa from the Pacific and Arctic oceans (e.g., Roseobacter, Oleispira, Colwellia). An equivalent sample from the epishelf lake (5 m depth) yielded many bacterial taxa that are characteristic of cold, freshwater habitats (e.g., Polynucleobacter, Variovorax, Flavobacterium), the euryhaline genus Polaromonas, and freshwater eukaryotes, notably ciliates. Similarly, denaturing gradient gel electrophoresis (DGGE) analyses of T4-like bacteriophages showed different viral assemblages in the upper and lower water column. This diverse, stratified Ecosystem is dependent on the integrity of the bounding ice shelf and is therefore vulnerable to the ongoing effects of climate change in this region.
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mesopelagic protists diversity and succession in a coastal Arctic Ecosystem
Aquatic Microbial Ecology, 2009Co-Authors: Ramon Terrado, Warwick F. Vincent, Connie LovejoyAbstract:We investigated marine protist diversity from below the euphotic zone during 4 consec- utive seasons (November 2003 to July 2004) from a fixed station in the Canadian Arctic (Franklin Bay, Beaufort Sea). DGGE analysis and 18S rRNA gene clone libraries showed that this mesopelagic pro- tist community was dynamic, with marked changes in taxonomic and functional community compo- sition in different seasons. The most frequently recovered sequences in autumn were related to heterotrophic dinoflagellates. In late December 2003, an abrupt change in the community composi- tion occurred following an influx of water from the lower Pacific halocline that flowed onto the Arc- tic continental shelf and into Franklin Bay. Subsequently, the most frequently retrieved sequences matched uncultured marine alveolates, which are thought to be primarily parasites. This community changed little over the winter, with modest changes in spring marked by the addition of taxa. Sum- mer libraries from 2004 were once more dominated by dinoflagellate sequences with a community very similar to that at the end of autumn 2003. These summer and autumn communities corresponded to periods of higher phytoplankton sedimentation rates in the euphotic zone. We suggest that the deep protist community may reform annually in response to primary production higher in the water column and that the winter mesopelagic protist community is dynamically coupled to the deep off- shore ocean.
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Importance of particle-associated bacterial heterotrophy in a coastal Arctic Ecosystem
Journal of Marine Systems, 2008Co-Authors: Marie-Ève Garneau, Ramon Terrado, Warwick F. Vincent, Connie LovejoyAbstract:Abstract The large quantities of particles delivered by the Mackenzie River to the coastal Beaufort Sea (Arctic Ocean) have implications for the spatial distribution, composition and productivity of its bacterial communities. Our objectives in this study were: (1) to assess the contribution of particle-associated bacteria (fraction ≥ 3 µm) to total bacterial production and their relationships with changing environmental conditions along a surface water transect; (2) to examine how particle-based heterotrophy changes over the annual cycle (Nov 2003–Aug 2004); and (3) to determine whether particle-associated bacterial assemblages differ in composition from the free-living communities (fraction
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seasonal dynamics of bacterial biomass and production in a coastal Arctic Ecosystem franklin bay western canadian Arctic
Journal of Geophysical Research, 2008Co-Authors: Connie Lovejoy, Mariea Ve Garneau, Sebastien Roy, Yves Gratton, Warwick F. VincentAbstract:[1] The Canadian Arctic Shelf Exchange Study (CASES) included the overwintering deployment of a research platform in Franklin Bay (70°N, 126°W) and provided a unique seasonal record of bacterial dynamics in a coastal region of the Arctic Ocean. Our objectives were (1) to relate seasonal bacterial abundance (BA) and production (BP) to physico-chemical characteristics and (2) to quantify the annual bacterial carbon flux. BA was estimated by epifluorescence microscopy and BP was estimated from 3H-leucine and 3H-thymidine assays. Mean BA values for the water column ranged from 1.0 (December) to 6.8 × 105 cells mL−1 (July). Integral BP varied from 1 (February) to 80 mg C m−2 d−1 (July). During winter-spring, BP was uncorrelated with chlorophyll a (Chl a), but these variables were significantly correlated during summer-autumn (rs = 0.68, p < 0.001, N = 38), suggesting that BP was subject to bottom-up control by carbon supply. Integrated BP data showed three distinct periods: fall-winter, late winter–late spring, and summer. A baseline level of BB and BP was maintained throughout late winter–late spring despite the persistent cold and darkness, with irregular fluctuations that may be related to hydrodynamic events. During this period, BP rates were correlated with colored dissolved organic matter (CDOM) but not Chl a (rs BP.CDOM∣Chl a = 0.20, p < 0.05, N = 176). Annual BP was estimated as 6 g C m−2 a−1, implying a total BP of 4.8 × 1010 g C a−1 for the Franklin Bay region. These results show that bacterial processes continue throughout all seasons and make a large contribution to the total biological carbon flux in this coastal Arctic Ecosystem.
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microbial community diversity and heterotrophic production in a coastal Arctic Ecosystem a stamukhi lake and its source waters
Limnology and Oceanography, 2008Co-Authors: Pierre E Galand, Connie Lovejoy, Marie-Ève Garneau, Jeremie Pouliot, Warwick F. VincentAbstract:Stamukhi lakes are vast but little-explored Arctic Ecosystems. They occur throughout winter, spring, and early summer near large river inflows along the Arctic coastline, and are the result of freshwater retention behind the thick barrier of rubble ice (stamukhi) that forms at the outer limit of land-fast sea ice. We examined the molecular biodiversity within all three microbial domains (Bacteria, Archaea, and Eukaryota) and the heterotrophic productivity in Lake Mackenzie, a stamukhi lake in the western Canadian Arctic, and made comparative measurements in the freshwater (Mackenzie River) and marine (Beaufort Sea) source waters. Bacterial and eukaryotic communities in the stamukhi lake differed in composition and diversity from both marine and riverine environments, whereas the archaeal communities were similar in the lake and river. Bacteria 16S ribosomal RNA sequences from the lake were mostly within freshwater clusters of Betaproteobacteria and Bacteroidetes and the Archaea were within the Lake Dagow sediment and Rice cluster-V clusters of Euryarchaeota. The eukaryotes were mainly ciliates from the subclass Choreotrichia, and there was a notable lack of flagellates. Heterotrophic production rates in the lake were lower than in the river and more similar to those in the sea, despite much higher bacterial concentrations than in either. The lake samples had markedly higher ratios of 3H leucine to 3H thymidine incorporation than in the river and sea, implying some physiological stress. Lake Mackenzie is an active microbial Ecosystem with distinct physical and microbiological properties. This circumpolar Ecosystem type, vulnerable to the ongoing effects of climate change, likely plays a key functional role in processing riverine inputs to the Arctic Ocean.
Robert J. Letcher - One of the best experts on this subject based on the ideXlab platform.
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sled dogs as sentinel species for monitoring Arctic Ecosystem health
2020Co-Authors: Christian Sonne, Robert J. Letcher, Bjorn Munro Jenssen, Jeanpierre Desforges, Igor Eulaers, Emilie Andersenranberg, Kim Gustavson, Rosanna Bossi, Bjarne Styrishave, Mikkel-holger S. SindingAbstract:Here we review sled dogs as a sentinel monitoring species of Ecosystem health across the Arctic focusing on environmental changes including pollution, climate change, and infectious diseases. Studies on environmental contaminants have been carried out mostly in Alaska and Greenland. While the majority of reports focus on mercury exposure and health effects, a major classical case-controlled study of exposure and effects from persistent organic pollutants (POPs) has been carried out on Greenland sled dog bitches and their pups. Altogether, the studies show that mercury and POPs affect multiple health endpoints across physiological systems, including reproductive, endocrine, and immune systems, that ultimately affect systems such as the liver and kidney. Therefore, sled dogs have proved to be a good model for assessing the health effects from contaminant exposure of top predators and Northerners in the Arctic. Furthermore, they are widely distributed across the Arctic and show similar correlations to important health indicators reported in Northerners and polar bears. With respect to climate change and disease dynamics of zoonosis, most studies have taken place in Canada. However, at present sled dogs are not utilized in monitoring studies of zoonotic diseases. Such an inclusion will increase the understanding of environmental changes, pollution, and diseases dynamics in Northerners and wildlife. We therefore recommend that Ecosystem health assessments in the Arctic including that of Northerners start to include analyses of sled dogs combined with modeling tools. Doing so in a circumpolar perspective will further increase our understanding and monitoring possibilities of Ecosystem health and Northerners exposure to contaminants, diseases, and climate change in the Arctic.
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is dietary mercury of neurotoxicological concern to wild polar bears ursus maritimus
Environmental Toxicology and Chemistry, 2009Co-Authors: Niladri Basu, Robert J. Letcher, Christian Sonne, Erik W. Born, A M Scheuhammer, Rune DietzAbstract:Polar bears (Ursus maritimus) are exposed to high concentrations of mercury because they are apex predators in the Arctic Ecosystem. Although mercury is a potent neurotoxic heavy metal, it is not known whether current exposures are of neurotoxicological concern to polar bears. We tested the hypotheses that polar bears accumulate levels of mercury in their brains that exceed the estimated lowest observable adverse effect level (20 μg/g dry wt) for mammalian wildlife and that such exposures are associated with subtle neurological damage, as determined by measuring neurochemical biomarkers previously shown to be disrupted by mercury in other high-trophic wildlife. Brain stem (medulla oblongata) tissues from 82 polar bears subsistence hunted in East Greenland were studied. Despite surprisingly low levels of mercury in the brain stem region (total mercury = 0.36 ±0.12 μg/g dry wt), a significant negative correlation was measured between N-methyl-D-aspartate (NMDA) receptor levels and both total mercury (r = —0.34, p < 0.01) and methylmercury (r = —0.89, p < 0.05). No relationships were observed among mercury, selenium, and several other neurochemical biomarkers (dopamine-2, gamma-aminobutyric acid type A, muscarinic cholinergic, and nicotinic cholinergic receptors; cholinesterase and monoamine oxidase enzymes). These data show that East Greenland polar bears do not accumulate high levels of mercury in their brain stems. However, decreased levels of NMDA receptors could be one of the most sensitive indicators of mercury's subclinical and early effects.
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immunoquantitation and microsomal monooxygenase activities of hepatic cytochromes p4501a and p4502b and chlorinated hydrocarbon contaminant levels in polar bear ursus maritimus
Toxicology and Applied Pharmacology, 1996Co-Authors: Robert J. Letcher, Ross J Norstrom, Malcolm A. RamsayAbstract:Contamination of the Arctic Ecosystem by anthropogenic compounds has resulted in exposure of polar bear (Ursus maritimus) to lipophilic chlorinated hydrocarbon contaminants (CHCs) accumulated through the marine food web. Liver samples were collected from 16 adult male polar bears in the Canadian Arctic and subjected to chemical analysis for CHCs and metabolites, determination of alkoxyresorufinO-dealkylase activities, and immunoquantitation of cytochrome P450 (CYP) protein levels. We report on the relationships between the hepatic microsomal levels of immunoreactive CYP1A and CYP2B isozymes, catalytic activities, and hepatic CHC and metabolite concentrations in polar bear. We specifically explored the influence of several CHCs on the induction of hepatic CYP in polar bear and the potential use of immunoassay quantitation as a bioindicator of CHC exposure. Polychlorinated biphenyls (PCBs) classed as CYP1A and mixed CYP1A/CYP2B inducers accounted for about 25% of the total PCB residues present (18,680 ± 5053 ng/g lipid). CYP1A protein content correlated strongly with hepatic levels of PCBs, PCDDs (0.032 ± 0.018 ng/g lipid), and PCDFs (0.011 ± 0.007 ng/g lipid) and their corresponding toxic equivalents (TEQ, 0.377 ± 0.182 ng/g lipid). Mono-ortho-CB-156, CB-157, and CB-105 were the predominant TEQ contributors. Correlations between CYP2B protein content and CHC residue levels in polar bear liver suggested thatortho-chlorine-substituted PCBs and chlordanes were the major contributors to CYP2B induction. CYP1A and CYP2B contents were therefore good indicators of CHC exposure in polar bear liver. Ethoxyresorufin, pentoxyresorufin, and benzyloxyresorufinO-dealkylase activities increased with increasing CYP1A protein content up to protein levels of approximately 5 pmol/mg, suggesting that all three activities were primarily CYP1A-mediated. These results were substantiated by antibody inhibition experiments. In summary, immunoquantitated CYP1A and CYP2B isozymes are a more reliable measure of exposure to CHC inducers than alkoxyresorufinO-dealkylase activities in polar bear.
Warwick F. Vincent - One of the best experts on this subject based on the ideXlab platform.
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milne fiord epishelf lake a coastal Arctic Ecosystem vulnerable to climate change
Ecoscience, 2011Co-Authors: Julie Veillette, Tommy Harding, Dermot Antoniades, Caroline Chenard, Connie Lovejoy, Marianne Potvin, Curtis A. Suttle, Anne-dorothee Jungblut, Warwick F. VincentAbstract:Milne Fiord in the Canadian High Arctic contains the last known ice-dammed fiord lake (epishelf lake) in the Northern Hemisphere. This freshwater Ecosystem is retained by the Milne Ice Shelf and is underlain by sea water that is connected to the Arctic Ocean. Using microscopy, photosynthetic pigment analyses, and molecular techniques we examined the planktonic communities present in Milne Fiord to determine the biotic characteristics of the epishelf lake and the sea water below. Net sampling of the water column of Milne Fiord revealed a mixture of marine, freshwater, and brackish zooplankton taxa, and high performance liquid chromatography (HPLC) pigment analysis showed pronounced differences in phytoplankton composition through the highly stratified water column. Chlorophytes dominated in the epishelf lake, prasinophytes prevailed in the halocline, and the bottom layer harboured mainly fucoxanthin-containing groups. Clone libraries of a dark-incubated, concentrated sample from below the halocline (30 m depth) yielded marine Archaea (mainly Crenarchaeota) and known bacterial taxa from the Pacific and Arctic oceans (e.g., Roseobacter, Oleispira, Colwellia). An equivalent sample from the epishelf lake (5 m depth) yielded many bacterial taxa that are characteristic of cold, freshwater habitats (e.g., Polynucleobacter, Variovorax, Flavobacterium), the euryhaline genus Polaromonas, and freshwater eukaryotes, notably ciliates. Similarly, denaturing gradient gel electrophoresis (DGGE) analyses of T4-like bacteriophages showed different viral assemblages in the upper and lower water column. This diverse, stratified Ecosystem is dependent on the integrity of the bounding ice shelf and is therefore vulnerable to the ongoing effects of climate change in this region.
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ecological implications of changes in the Arctic cryosphere
AMBIO: A Journal of the Human Environment, 2011Co-Authors: Warwick F. Vincent, Margareta Johansson, Dorthe Dahljensen, Terry V Callaghan, Terry D Prowse, James D Reist, Kit M Kovacs, Christine Michel, Martin SharpAbstract:Snow, water, ice, and permafrost are showing evidence of substantial change in the Arctic, with large variations among different geographical areas. As a result of these changes, some habitats and their associated Ecosystems are expanding, while others are undergoing rapid contraction. The warming of the Arctic cryosphere is limiting the range for cold-adapted biota, and less specialized taxa including invasive species from the south are likely to become increasingly common. Extreme climate events such as winter thawing are likely to become more frequent, and may accelerate shifts in community structure and processes. Many Arctic Ecosystems are interdependent, and changes in the cryosphere are altering physical, biogeochemical, and biological linkages, as well as causing positive feedback effects on atmospheric warming. All of these climate-related effects are compounded by rapid socio-economic development in the North, creating additional challenges for northern communities and indigenous lifestyles that depend on Arctic Ecosystem services.
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mesopelagic protists diversity and succession in a coastal Arctic Ecosystem
Aquatic Microbial Ecology, 2009Co-Authors: Ramon Terrado, Warwick F. Vincent, Connie LovejoyAbstract:We investigated marine protist diversity from below the euphotic zone during 4 consec- utive seasons (November 2003 to July 2004) from a fixed station in the Canadian Arctic (Franklin Bay, Beaufort Sea). DGGE analysis and 18S rRNA gene clone libraries showed that this mesopelagic pro- tist community was dynamic, with marked changes in taxonomic and functional community compo- sition in different seasons. The most frequently recovered sequences in autumn were related to heterotrophic dinoflagellates. In late December 2003, an abrupt change in the community composi- tion occurred following an influx of water from the lower Pacific halocline that flowed onto the Arc- tic continental shelf and into Franklin Bay. Subsequently, the most frequently retrieved sequences matched uncultured marine alveolates, which are thought to be primarily parasites. This community changed little over the winter, with modest changes in spring marked by the addition of taxa. Sum- mer libraries from 2004 were once more dominated by dinoflagellate sequences with a community very similar to that at the end of autumn 2003. These summer and autumn communities corresponded to periods of higher phytoplankton sedimentation rates in the euphotic zone. We suggest that the deep protist community may reform annually in response to primary production higher in the water column and that the winter mesopelagic protist community is dynamically coupled to the deep off- shore ocean.
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Importance of particle-associated bacterial heterotrophy in a coastal Arctic Ecosystem
Journal of Marine Systems, 2008Co-Authors: Marie-Ève Garneau, Ramon Terrado, Warwick F. Vincent, Connie LovejoyAbstract:Abstract The large quantities of particles delivered by the Mackenzie River to the coastal Beaufort Sea (Arctic Ocean) have implications for the spatial distribution, composition and productivity of its bacterial communities. Our objectives in this study were: (1) to assess the contribution of particle-associated bacteria (fraction ≥ 3 µm) to total bacterial production and their relationships with changing environmental conditions along a surface water transect; (2) to examine how particle-based heterotrophy changes over the annual cycle (Nov 2003–Aug 2004); and (3) to determine whether particle-associated bacterial assemblages differ in composition from the free-living communities (fraction
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seasonal dynamics of bacterial biomass and production in a coastal Arctic Ecosystem franklin bay western canadian Arctic
Journal of Geophysical Research, 2008Co-Authors: Connie Lovejoy, Mariea Ve Garneau, Sebastien Roy, Yves Gratton, Warwick F. VincentAbstract:[1] The Canadian Arctic Shelf Exchange Study (CASES) included the overwintering deployment of a research platform in Franklin Bay (70°N, 126°W) and provided a unique seasonal record of bacterial dynamics in a coastal region of the Arctic Ocean. Our objectives were (1) to relate seasonal bacterial abundance (BA) and production (BP) to physico-chemical characteristics and (2) to quantify the annual bacterial carbon flux. BA was estimated by epifluorescence microscopy and BP was estimated from 3H-leucine and 3H-thymidine assays. Mean BA values for the water column ranged from 1.0 (December) to 6.8 × 105 cells mL−1 (July). Integral BP varied from 1 (February) to 80 mg C m−2 d−1 (July). During winter-spring, BP was uncorrelated with chlorophyll a (Chl a), but these variables were significantly correlated during summer-autumn (rs = 0.68, p < 0.001, N = 38), suggesting that BP was subject to bottom-up control by carbon supply. Integrated BP data showed three distinct periods: fall-winter, late winter–late spring, and summer. A baseline level of BB and BP was maintained throughout late winter–late spring despite the persistent cold and darkness, with irregular fluctuations that may be related to hydrodynamic events. During this period, BP rates were correlated with colored dissolved organic matter (CDOM) but not Chl a (rs BP.CDOM∣Chl a = 0.20, p < 0.05, N = 176). Annual BP was estimated as 6 g C m−2 a−1, implying a total BP of 4.8 × 1010 g C a−1 for the Franklin Bay region. These results show that bacterial processes continue throughout all seasons and make a large contribution to the total biological carbon flux in this coastal Arctic Ecosystem.
Rune Dietz - One of the best experts on this subject based on the ideXlab platform.
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mercury and neurochemical biomarkers in multiple brain regions of five Arctic marine mammals
Neurotoxicology, 2021Co-Authors: J P Desforges, Rune Dietz, Christian Sonne, Bjarni Mikkelsen, Maria Dam, Frank F Riget, Signe Sveegaard, Niladri BasuAbstract:Abstract Mercury is a neurotoxic chemical that represents one of the greatest pollution threats to Arctic Ecosystem health. Evaluating the direct neurotoxic effects of mercury in free ranging wildlife is challenging, necessitating the use of neurochemical biomarkers to assess potential sub-clinical neurological changes. The objective of this study was to characterize the distribution and speciation of mercury, as well as exposure-associated changes in neurochemistry, across multiple brain regions (n = 10) and marine mammal species (n = 5) that each occupy a trophic niche in the Arctic Ecosystem. We found consistent species differences in mean brain and brain region-specific concentrations of total mercury (THg) and methyl mercury (MeHg), with higher concentrations in toothed whales (narwhal, pilot whales and harbour porpoise) compared to fur-bearing mammals (polar bear and ringed seal). Mean THg (μg/g dw) in decreasing rank order was: pilot whale (11.9) > narwhal (7.7) > harbour porpoise (3.6) > polar bear (0.6) > ringed seal (0.2). The higher THg concentrations in toothed whales was associated with a marked reduction in the percentage of MeHg ( 70 %) that had lower brain THg concentrations. This pattern in mercury concentration and speciation corresponded broadly to an overall higher number of mercury-associated neurochemical biomarker correlations in toothed whales. Of the 226 correlations between mercury and neurochemical biomarkers across brain regions, we found 60 (27 %) meaningful relationships (r>0.60 or p
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is dietary mercury of neurotoxicological concern to wild polar bears ursus maritimus
Environmental Toxicology and Chemistry, 2009Co-Authors: Niladri Basu, Robert J. Letcher, Christian Sonne, Erik W. Born, A M Scheuhammer, Rune DietzAbstract:Polar bears (Ursus maritimus) are exposed to high concentrations of mercury because they are apex predators in the Arctic Ecosystem. Although mercury is a potent neurotoxic heavy metal, it is not known whether current exposures are of neurotoxicological concern to polar bears. We tested the hypotheses that polar bears accumulate levels of mercury in their brains that exceed the estimated lowest observable adverse effect level (20 μg/g dry wt) for mammalian wildlife and that such exposures are associated with subtle neurological damage, as determined by measuring neurochemical biomarkers previously shown to be disrupted by mercury in other high-trophic wildlife. Brain stem (medulla oblongata) tissues from 82 polar bears subsistence hunted in East Greenland were studied. Despite surprisingly low levels of mercury in the brain stem region (total mercury = 0.36 ±0.12 μg/g dry wt), a significant negative correlation was measured between N-methyl-D-aspartate (NMDA) receptor levels and both total mercury (r = —0.34, p < 0.01) and methylmercury (r = —0.89, p < 0.05). No relationships were observed among mercury, selenium, and several other neurochemical biomarkers (dopamine-2, gamma-aminobutyric acid type A, muscarinic cholinergic, and nicotinic cholinergic receptors; cholinesterase and monoamine oxidase enzymes). These data show that East Greenland polar bears do not accumulate high levels of mercury in their brain stems. However, decreased levels of NMDA receptors could be one of the most sensitive indicators of mercury's subclinical and early effects.