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291.
The (109)Cd K-shell X-ray fluorescence (XRF) technique was used to measure in vivo tibia lead concentrations of 34 young adults living in the state of Vermont (USA) and the province of New Brunswick (Canada). The subjects ranged in age from 18 to 35 years, and had no known history of elevated lead exposure. Measurement parameters were varied, using the same XRF system for both populations. Tibia lead concentrations were low for both groups, with mean values of 0.7 microg lead g(-1) bone mineral (Vermont) and 0.5 microg g(-1)(New Brunswick). No individual measurement exceeded 7 microg g(-1). Mean uncertainty values obtained for the Vermont and New Brunswick subjects were 4.1 microg g(-1) and 2.6 microg g(-1), respectively. Improved measurement uncertainty in the New Brunswick group was attributed to the use of a reduced source-to-skin distance (approximately 5 mm) and a longer measurement time (3600 seconds) using a weaker radioisotope source (< or =0.42 GBq). Measurement uncertainty tended to increase with body mass index. For a given body mass index, female subjects returned a measurement uncertainty approximately 1 microg g(-1) greater than males. 相似文献
292.
Jud Harvey Jesus Gomez‐Velez Noah Schmadel Durelle Scott Elizabeth Boyer Richard Alexander Ken Eng Heather Golden Albert Kettner Chris Konrad Richard Moore Jim Pizzuto Greg Schwarz Chris Soulsby Jay Choi 《Journal of the American Water Resources Association》2019,55(2):369-381
Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off‐channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality — too little connectivity limits the amount of river water exchanged and leads to biogeochemically inactive water storage, while too much connectivity limits the contact time with sediments for reactions to proceed. Using a metric of reaction significance based on river connectivity, we provide evidence that intermediate levels of connectivity, rather than the highest or lowest levels, are the most efficient in removing nitrogen from Northeastern United States’ rivers. Intermediate connectivity balances the frequency, residence time, and contact volume with reactive sediments, which can maximize the reactive processing of dissolved contaminants and the protection of downstream water quality. Our simulations suggest denitrification dominantly occurs in riverbed hyporheic zones of streams and small rivers, whereas vertical turbulent mixing in contact with sediments dominates in mid‐size to large rivers. The metrics of connectivity and reaction significance presented here can facilitate scientifically based prioritizations of river management strategies to protect the values and functions of river corridors. 相似文献
293.
Robert R. Carlton Peter G. Waterman Alexander I. Gray Stanley G. Deans 《Chemoecology》1992,3(1):55-59
Summary The antifungal activity of volatile oil obtained from the leaves of sweet gale (Myrica gale) has been investigated. Fungi, isolated from the leaves ofM. gale, were grown in liquid medium containing the oil and its effect on biomass production was gauged. The oil inhibited growth of all species of fungi to greater or lesser extent. Sesquiterpenes were more active than monoterpenes, and among the sesquiterpenes germacrone was marginally more active than -elemenone. These results support the proposition that the volatile oil ofM. gale has a role in resistance to fungal pathogens. 相似文献
294.
Connectivity of Streams and Wetlands to Downstream Waters: An Integrated Systems Framework 总被引:1,自引:0,他引:1
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Scott G. Leibowitz Parker J. Wigington Jr. Kate A. Schofield Laurie C. Alexander Melanie K. Vanderhoof Heather E. Golden 《Journal of the American Water Resources Association》2018,54(2):298-322
Interest in connectivity has increased in the aquatic sciences, partly because of its relevance to the Clean Water Act. This paper has two objectives: (1) provide a framework to understand hydrological, chemical, and biological connectivity, focusing on how headwater streams and wetlands connect to and contribute to rivers; and (2) briefly review methods to quantify hydrological and chemical connectivity. Streams and wetlands affect river structure and function by altering material and biological fluxes to the river; this depends on two factors: (1) functions within streams and wetlands that affect material fluxes; and (2) connectivity (or isolation) from streams and wetlands to rivers that allows (or prevents) material transport between systems. Connectivity can be described in terms of frequency, magnitude, duration, timing, and rate of change. It results from physical characteristics of a system, e.g., climate, soils, geology, topography, and the spatial distribution of aquatic components. Biological connectivity is also affected by traits and behavior of the biota. Connectivity can be altered by human impacts, often in complex ways. Because of variability in these factors, connectivity is not constant but varies over time and space. Connectivity can be quantified with field‐based methods, modeling, and remote sensing. Further studies using these methods are needed to classify and quantify connectivity of aquatic ecosystems and to understand how impacts affect connectivity. 相似文献
295.
Alexander Paulsson 《Journal of Environmental Policy & Planning》2018,20(4):419-433
This paper investigates where and how sustainable transport goals are translated into public transport planning and operations. The case where this is explored is the Regional Public Transport Authority (RPTA) in Stockholm, Sweden. By drawing upon recent discussions on policy translation and political–administrative relationships, sustainable transport is found to be translated in two different collaborative spaces in the RTPA. In the market side of the authority, which is mainly preoccupied with procurement of traffic and compliance issues, sustainable transport is translated into quantitative goals (including biofuels, emissions, noise, etc.) and mechanically reproduced from the politicians via the civil servants to the private operators. In the planning side of the authority, sustainability measurements have been hard to quantify and the challenge to integrate land-use and transport planning is resolved in an organic manner, in specific projects, between the strategic transport planners in the RPTA and the land-use planners in the municipalities, at a distance from the politicians’ involvement. Throughout the RPTA, sustainable transport has broadened to also include social sustainability, although this has been difficult to translate into quantitative measurements, which is the desired mode of governance by the politicians. 相似文献
296.
Alexander Heeren Gabriel Karns Jeremy Bruskotter Eric Toman Robyn Wilson Harmony Szarek 《Conservation biology》2017,31(3):657-665
Decisions concerning the appropriate listing status of species under the U.S. Endangered Species Act (ESA) can be controversial even among conservationists. These decisions may determine whether a species persists in the near term and have long‐lasting social and political ramifications. Given the ESA's mandate that such decisions be based on the best available science, it is important to examine what factors contribute to experts’ judgments concerning the listing of species. We examined how a variety of factors (such as risk perception, value orientations, and norms) influenced experts’ judgments concerning the appropriate listing status of the grizzly bear (Ursus arctos horribilis) population in the Greater Yellowstone Ecosystem. Experts were invited to complete an online survey examining their perceptions of the threats grizzly bears face and their listing recommendation. Although experts’ assessments of the threats to this species were strongly correlated with their recommendations for listing status, this relationship did not exist when other cognitive factors were included in the model. Specifically, values related to human use of wildlife and norms (i.e., a respondent's expectation of peers’ assessments) were most influential in listing status recommendations. These results suggest that experts’ decisions about listing, like all human decisions, are subject to the use of heuristics (i.e., decision shortcuts). An understanding of how heuristics and related biases affect decisions under uncertainty can help inform decision making about threatened and endangered species and may be useful in designing effective processes for protection of imperiled species. 相似文献
297.
Stephen D. Preston Richard B. Alexander David M. Wolock 《Journal of the American Water Resources Association》2011,47(5):887-890
Preston, Stephen D., Richard B. Alexander, and David M. Wolock, 2011. SPARROW Modeling to Understand Water‐Quality Conditions in Major Regions of the United States: A Featured Collection Introduction. Journal of the American Water Resources Association (JAWRA) 47(5):887‐890. DOI: 10.1111/j.1752‐1688.2011.00585.x 相似文献
298.
Alexander Yevgenyevich Galashev 《Environmental Chemistry Letters》2011,9(1):37-41
Carbon dioxide and methane are major compounds involved in global warming. The process of CO2 and CH4 molecules absorption by water clusters was investigated by the molecular dynamics method. The frequency spectra of dielectric
permittivity for systems consisting of (H2O)
n
, (CO2)
i
(H2O)10 and (CH4)
i
(H2O)10 clusters mixed in various proportions were determined. The IR radiation absorption spectra of these systems were calculated
and compared. Also, the radiating power of these systems was established. The capture of greenhouse gases’ molecules by ultra
disperse water media reduces the ability of the media to absorb the Earth’s radiation, i.e., it reduces the greenhouse effect. 相似文献
299.
Mass exchange in a shallow channel flow with a series of groynes: LES study and comparison with laboratory and field experiments 总被引:2,自引:2,他引:0
George Constantinescu Alexander Sukhodolov Andrew McCoy 《Environmental Fluid Mechanics》2009,9(6):587-615
The exchange of dissolved matter between a straight open channel and a series of shallow embayments present at one of its sides is investigated using large eddy simulation (LES). The direct link between the mechanism of mass exchange and the dynamics of coherent structures is demonstrated. It is shown that for the geometrical configuration considered in the present study, the mass exchange process is very non-uniform over the depth in the vicinity of the channel–embayment interface. Most of the contaminant is ejected from the embayments close to the free surface. The amount of contaminant re-entrained into the embayments situated downstream of the one in which contaminant was introduced is quantified. The mass exchange coefficient predicted by LES does not vary significantly with the embayment rank and is in very good agreement with the one predicted by the model proposed by Weitbrecht et al. (J Hydraul Eng 134(2):173–183, 2008) based on the value of a dimensionless morphometric groyne-field parameter. Field experiments were purposely performed in a natural stream with embayments whose length over width ratios were close to the ratio in the LES study. The concentration fields predicted by LES are compared with video-records of colored dye used to visualize the mass exchange in the field experiment. It is shown that, for both LES and the field experiment, the dominant passage frequency of the eddies inside the interfacial mixing layer is well predicted by the analytical model of Sukhodolov and Sukhodolova (in: Cowen et al (eds) Hydraulic measurements & experimental methods. Proceedings of international conference, Lake Placid, USA, pp 172–177, 2007). The model is then used to scale the time in the LES animations and field video-records showing the temporal evolution of the concentration field. The results of the comparison indicate several similarities in the mixing process, despite the differences in the bathymetry and the large difference in the Reynolds number between LES and the field experiment. This proves the usefulness of performing detailed LES and laboratory studies in well-controlled environments to understand mass-exchange processes around river groyne fields. 相似文献
300.
Gymnocanthus is the most widely distributed genus in the family Cottidae, with six species distributed in the high-latitude area of northern hemisphere. To clarify the phylogenetic relationships and to estimate the divergence times of species in the genus, 2,548 bp of the partial sequences of the 12–16S rRNA, cytochrome oxidase subunit I and cytochrome b gene were analyzed. Our results suggest the monophyletic genus, which arose in the Aleutian Archipelago, divided into a shallow-water group and a deep-water group 8.1 million years ago (Ma). G. tricuspis of the shallow-water group firstly migrated from the Pacific to the Arctic Ocean 5.0 Ma when the Bering Strait first opened. A second migration occurred in the late Pliocene to early Pleistocene after which G. pistilliger and G. intermedius diverged 3.9 Ma. Our findings are discussed within an evolutionary and zoogeographic context. 相似文献