163 research outputs found
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Imaging of brain metabolism with positron emission tomography and magnetic resonance spectroscopy in connection with the pathophysiology of focal brain diseases
Spatial patterns of mercury in biota of Adirondack, New York lakes
We studied the spatial distribution patterns of mercury (Hg) in lake water, littoral sediments, zooplankton, crayfish, fish, and common loons in 44 lakes of the Adirondacks of New York State, USA, a region that has been characterized as a “biological Hg hotspot”. Our study confirmed this pattern, finding that a substantial fraction of the lakes studied had fish and loon samples exceeding established criteria for human and wildlife health. Factors accounting for the spatial variability of Hg in lake water and biota were lake chemistry (pH, acid neutralizing capacity (ANC), percent carbon in sediments), biology (taxa presence, trophic status) and landscape characteristics (land cover class, lake elevation). Hg concentrations in zooplankton, fish and common loons were negatively associated with the lake water acid-base status (pH, ANC). Bioaccumulation factors (BAF) for methyl Hg (MeHg) increased from crayfish (mean log10 BAF = 5.7), to zooplankton (5.9), to prey fish (6.2), to larger fish (6.3), to common loons (7.2). MeHg BAF values in zooplankton, crayfish, and fish (yellow perch equivalent) all increased with increasing lake elevation. Our findings support the hypothesis that bioaccumulation of MeHg at the base of the food chain is an important controller of Hg concentrations in taxa at higher trophic levels. The characteristics of Adirondack lake-watersheds (sensitivity to acidic deposition; significant forest and wetland land cover; and low nutrient inputs) contribute to elevated Hg concentrations in aquatic biota
Mercury toxicity in livers of northern pike (Esox lucius) from Isle Royale, USA
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology 147 (2008): 331-338, doi:10.1016/j.cbpc.2007.12.003.Many laboratory studies have documented that mercury can be toxic to fish, but it is
largely unknown if mercury is toxic to fish in their natural environments. The objective of our
study was to investigate the toxic effects of mercury on northern pike (Esox lucius) at Isle
Royale, Michigan. In 124 northern pike from eight inland lakes, concentrations of total mercury
in skin-on fillets ranged from 0.069 to 0.622 µg/g wet wt. Concentrations of total mercury in
livers increased exponentially compared with concentrations in fillets, to a maximum of 3.1 µg/g
wet wt. Methylmercury constituted a majority of the mercury in livers with total mercury
concentrations <0.5 µg/g wet wt, but declined to 28-51% of the mercury in livers with total
mercury concentrations >0.5 µg/g wet wt. Liver color (absorbance at 400 nm) varied among
northern pike and was positively related to liver total mercury concentration. The pigment
causing variation in liver color was identified as lipofuscin, which results from lipid peroxidation
of membranous organelles. An analysis of covariance revealed lipofuscin accumulation was
primarily associated with mercury exposure, and this association obscured any normal
accumulation from aging. We also documented decreased lipid reserves in livers and poor
condition factors of northern pike with high liver total mercury concentrations. Our results
suggest (i) northern pike at Isle Royale are experiencing toxicity at concentrations of total
mercury common for northern pike and other piscivorous fish elsewhere in North America and
(ii) liver color may be useful for indicating mercury exposure and effects in northern pike at Isle
Royale and possibly other aquatic ecosystems and other fish species.Financial support was provided by the U.S. Environmental Protection Agency STAR Graduate Fellowship Program to P.E.D
Global Change Could Amplify Fire Effects on Soil Greenhouse Gas Emissions
Background: Little is known about the combined impacts of global environmental changes and ecological disturbances on ecosystem functioning, even though such combined impacts might play critical roles in shaping ecosystem processes that can in turn feed back to climate change, such as soil emissions of greenhouse gases.[br/]
Methodology/Principal Findings: We took advantage of an accidental, low-severity wildfire that burned part of a long-term global change experiment to investigate the interactive effects of a fire disturbance and increases in CO(2) concentration, precipitation and nitrogen supply on soil nitrous oxide (N(2)O) emissions in a grassland ecosystem. We examined the responses of soil N(2)O emissions, as well as the responses of the two main microbial processes contributing to soil N(2)O production - nitrification and denitrification - and of their main drivers. We show that the fire disturbance greatly increased soil N(2)O emissions over a three-year period, and that elevated CO(2) and enhanced nitrogen supply amplified fire effects on soil N(2)O emissions: emissions increased by a factor of two with fire alone and by a factor of six under the combined influence of fire, elevated CO(2) and nitrogen. We also provide evidence that this response was caused by increased microbial denitrification, resulting from increased soil moisture and soil carbon and nitrogen availability in the burned and fertilized plots. [br/]
Conclusions/Significance: Our results indicate that the combined effects of fire and global environmental changes can exceed their effects in isolation, thereby creating unexpected feedbacks to soil greenhouse gas emissions. These findings highlight the need to further explore the impacts of ecological disturbances on ecosystem functioning in the context of global change if we wish to be able to model future soil greenhouse gas emissions with greater confidence
Using public participation to sample trace metals in lake surface sediments: the OPAL Metals Survey
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