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排序方式: 共有393条查询结果,搜索用时 46 毫秒
81.
Paula Méndez-Fernandez Graham J. Pierce Paco Bustamante Tiphaine Chouvelon Marisa Ferreira Angel F. González Alfredo López Fiona L. Read M. Begoña Santos Jérôme Spitz José V. Vingada Florence Caurant 《Marine Biology》2013,160(11):2825-2840
This study aims to assess niche segregation among the five main toothed whales that frequent the NW Iberian Peninsula waters: the common dolphin, the harbour porpoise, the bottlenose dolphin, the striped dolphin and the long-finned pilot whale. We used cadmium (Cd) and stable isotope ratios (δ13C and δ15N) as ecological tracers to assess degree of segregation in diet/trophic level and in foraging habitat, over various time-scales. δ13C values highlighted different habitats, while Cd concentrations highlighted feeding differences between oceanic and neritic species. Moreover, δ15N values suggest different trophic levels of prey targeted within oceanic and neritic species. Hence, results revealed long-term ecological segregation among five toothed whales that coexist in the NWIP and demonstrated the ability of ecological tracers to discriminate ecological niches among closely related species. 相似文献
82.
83.
Simple analytical models are derived to assess how a series of cattle animal farms affect the transport and fate of an indicator organism (Escherichia coli) and a zoonotic pathogen (Campylobacter) in a stream. Separate steady-state mass-balance models are developed and solved for the ultimate minimum and maximum concentrations for the two organisms. The E. coli model assumes that the organism is ubiquitous and abundant in the animals’ digestive tracts. In contrast, a simple dose-response model is employed to relate the Campylobacter prevalence to drinking water drawn from the stream. Because faecal indicators are commonly employed to assess the efficacy of best management practice (BMP) interventions, we also employ the models to assess how BMPs impact pathogen levels. The model provides predictions of (a) the relative removal efficacy for Campylobacter and (b) the prevalence of Campylobacter infection among farm animals after implementation of BMPs. Dimensionless numbers and simple graphs are developed to assess how prevalence is influenced by a number of factors including animal density and farm spacing. A significant outcome of this model development is that the numerous dimensional input and parameter variables are reduced to a group of just four dimensionless Campylobacter-related quantities, characterizing: animal density; in-stream attenuation; animal-to-animal transmission; and infection recovery. Calculations reveal that for some constellations of these four quantities there can be a greater-than-expected benefit in that the proportional reduction of stream Campylobacter concentrations post-BMP can substantially exceed the proportional reduction of concentrations of E. coli in that stream. In addition, a criterion for system sterility (i.e., the conditions required for the farm infection rate to decrease with downstream distance) is derived. 相似文献
84.
Helen A. Cruse Jonathan E.H. Buston Luc N. Véchot Graham A. Tickle Ralph Rowlands 《Process Safety and Environmental Protection》2011,89(6):415-423
This paper describes part of a programme of work undertaken at the Health and Safety Laboratory (HSL) to investigate the behaviour of selected water-reactive chemicals. Following an accidental release, such substances react exothermically with any water present, generating acidic vapours. The STAWaRS (Source Term Assessment of Water Reactive Substances) software was developed for the Health and Safety Executive (HSE) by ESR Technology to model this complex process. The aims of the study described here were to provide experimental validation of the heats of hydrolysis used within STAWaRS, and to perform sensitivity studies on selected STAWaRS input parameters.The heat of hydrolysis of acetyl chloride was measured and showed good correlation with the value used within STAWaRS. Some of the variables that influence the severity of acetyl chloride spills are examined, with reference to predictions made by the STAWaRS model. The heats of hydrolysis of titanium tetrachloride previously measured at HSL are also discussed, and the effect of adopting these experimentally derived values for modelling spills is shown for a hypothetical land use planning case. This study demonstrates the importance of using experimentally validated values for STAWaRS input parameters. 相似文献
85.
Charles T. Garten Deanne J. Brice Hector F. Castro Robin L. Graham Melanie A. Mayes Jana R. Phillips Wilfred M. Post Christopher W. Schadt Stan D. Wullschleger Donald D. Tyler Phillip M. Jardine Julie D. Jastrow Roser Matamala R. Michael Miller Kelly K. Moran Timothy W. Vugteveen R. Cesar Izaurralde Allison M. Thomson Tristram O. West James E. Amonette Jeffrey L. Smith 《Agriculture, ecosystems & environment》2011,140(1-2):289-297
Switchgrass (Panicum virgatum) is a perennial, warm-season grass that has been identified as a potential biofuel feedstock over a large part of North America. We examined above- and belowground responses to nitrogen fertilization in “Alamo” switchgrass grown in West Tennessee, USA. The fertilizer study included a spring and fall sampling of 5-year old switchgrass grown under annual applications of 0, 67, and 202 kg N ha?1 (as ammonium nitrate). Fertilization changed switchgrass biomass allocation as indicated by root:shoot ratios. End-of-growing season root:shoot ratios (mean ± SE) declined significantly (P ≤ 0.05) at the highest fertilizer nitrogen treatment (2.16 ± 0.08, 2.02 ± 0.18, and 0.88 ± 0.14, respectively, at 0, 67, and 202 kg N ha?1). Fertilization also significantly increased above- and belowground nitrogen concentrations and decreased plant C:N ratios. Data are presented for coarse live roots, fine live roots, coarse dead roots, fine dead roots, and rhizomes. At the end of the growing season, there was more carbon and nitrogen stored in belowground biomass than aboveground biomass. Fertilization impacted switchgrass tissue chemistry and biomass allocation in ways that potentially impact soil carbon cycle processes and soil carbon storage. 相似文献
86.
Semi-volatile and particulate emissions from the combustion of alternative diesel fuels 总被引:8,自引:0,他引:8
Motor vehicle emissions are a major anthropogenic source of air pollution and contribute to the deterioration of urban air quality. In this paper, we report results of a laboratory investigation of particle formation from four different alternative diesel fuels, namely, compressed natural gas (CNG), dimethyl ether (DME), biodiesel, and diesel, under fuel-rich conditions in the temperature range of 800-1200 degrees C at pressures of approximately 24 atm. A single pulse shock tube was used to simulate compression ignition (CI) combustion conditions. Gaseous fuels (CNG and DME) were exposed premixed in air while liquid fuels (diesel and biodiesel) were injected using a high-pressure liquid injector. The results of surface analysis using a scanning electron microscope showed that the particles formed from combustion of all four of the above-mentioned fuels had a mean diameter less than 0.1 microm. From results of gravimetric analysis and fuel injection size it was found that under the test conditions described above the relative particulate yields from CNG, DME, biodiesel, and diesel were 0.30%. 0.026%, 0.52%, and 0.51%, respectively. Chemical analysis of particles showed that DME combustion particles had the highest soluble organic fraction (SOF) at 71%, followed by biodiesel (66%), CNG (38%) and diesel (20%). This illustrates that in case of both gaseous and liquid fuels, oxygenated fuels have a higher SOF than non-oxygenated fuels. 相似文献
87.
We examined the taxonomic resolution of zooplankton data required to identify ocean basin scale biogeographic zonation in
the Southern Ocean. A 2,154 km transect was completed south of Australia. Sea surface temperature (SST) measured at 1 min
intervals showed that seven physical zones were sampled. Zooplankton were collected at a spatial resolution of ~9.2 km with
a continuous plankton recorder, identified to the highest possible taxonomic resolution and enumerated. Zooplankton assemblage
similarity between samples was calculated using the Bray–Curtis index for the taxonomic levels of species, genus, family,
order and class after first log10(x + 1) (LA) and then presence/absence (PA) transformation of abundance data. Although within and between zone sample similarity
increased with decreasing taxonomic resolution, for both data transformations, cluster analysis demonstrated that the biogeographic
separation of zones remained at all taxonomic levels when using LA data. ANOSIM confirmed this, detecting significant differences
in zooplankton assemblage structure between all seven a priori determined physical zones for all taxonomic levels when using
the LA data. In the case of the PA data for the complete data set, and both LA and PA data for a crustacean only data set,
no significant differences were detected between zooplankton assemblages in the Polar frontal zone (PFZ) and inter-PFZ at
any taxonomic level. Loss of information at resolutions below the species level, particularly in the PA data, prevented the
separation of some zones. However, the majority of physical zones were biogeographically distinct from species level to class
using both LA and PA transformations. Significant relationships between SST and zooplankton community structure, summarised
as NMDS scores, at all taxonomic levels, for both LA and PA transformations, and complete and crustacean only data sets, highlighted
the biogeographic relevance of low resolution taxonomic data. The retention of biogeographic information in low taxonomic
resolution data shows that data sets collected with different taxonomic resolutions may be meaningfully merged for the post
hoc generation of Southern Ocean time series. 相似文献
88.
Graham Bird Mark G. Macklin Paul A. Brewer Sorin Zaharia Dan Balteanu Basarab Driga Mihaela Serban 《Environmental geochemistry and health》2009,31(6):741-758
Groundwater, accessed using wells and municipal springs, represents the major source of potable water for the human population
outside of major urban areas in northwestern Romania, a region with a long history of metal mining and metallurgy. The magnitude
and spatial distribution of metal contamination in private-supply groundwater was investigated in four mining-affected river
catchments in Maramureş and Satu Mare Counties through the collection of 144 groundwater samples. Bedrock geology, pH and
Eh were found to be important controls on the solubility of metals in groundwater. Peak metal concentrations were found to
occur in the Lapuş catchment, where metal levels exceed Dutch target and intervention values in up to 49% and 14% of samples,
respectively. A 700 m wide corridor in the Lapuş catchment on either side of the main river channel was identified in which
peak Cd (31 μg l−1), Cu (50 μg l−1), Pb (50 μg l−1) and Zn (3,000 μg l−1) concentrations were found to occur. Given the generally similar bedrock geologies, lower metal levels in other catchments
are believed to reflect differences in the magnitude of metal loading to the local environment from both metal mining and
other industrial and municipal sources. Sampling of groundwater in northwestern Romania has indicated areas of potential concern
for human health, where heavy metal concentrations exceed accepted environmental quality guidelines. The presence of elevated
metal levels in groundwater also has implications for the implementation of the EU Water Framework Directive (WFD) and achieving
‘good’ status for groundwater in this part of the Danube River Basin District (RBD). 相似文献
89.
Optimising the preparation of activated carbon from digested sewage sludge and coconut husk. 总被引:18,自引:0,他引:18
Preparation of activated carbon from sewage sludge is a promising way to dispose of sewage sludge as well as to produce a low-cost adsorbent for pollutant removal. This research work aimed to optimise the condition for activated carbon preparation from anaerobically digested sewage sludge with the additive coconut husk. The sewage sludge sample was mixed with the additive coconut husk. The preparation condition variables investigated involved the concentration of the ZnCl2 solutions, heating temperature, dwell time and heating rate in pyrolysis and the mixing ratio of coconut husk to sewage sludge. Surface area, pore size distribution, aqueous phenol adsorption capacity and the production yield of the final products were determined and compared. Experimental results revealed that low concentrations of ZnCl2 solution tended to improve the microporosity of the final product. Heating temperature had a considerable impact on the surface area, pore size distribution and phenol adsorption capacity of the final products, whereas dwell time and heating rate performed comparatively insignificantly. The effect of increasing the mixing ratio of coconut husk to sewage sludge was principally to increase the microporosity of the final products. The activated carbon with the highest BET surface area was produced with the activation of 5 M ZnCl2 solution and, thereafter, pyrolysis at a heating temperature of 500 degrees C for 2 h with a heating rate of 10 degrees C/min. The mixing ratio of 1:4 in terms of coconut husk to sewage sludge based on their dried weights was found to be most cost effective. 相似文献
90.
Wayne J. Graham 《Journal of the American Water Resources Association》2000,36(5):953-963
ABSTRACT: The probable maximum flood (PMF) currently serves as the design standard for many U.S. dams. Floods used for design have increased and currently thousands of dams in the U.S. would be overtopped and possibly fail using the latest calculated PMF at each dam site. Some researchers have suggested that modifying dams to accommodate the PMF could be wasteful. Objections to using the PMF for dam modification include: (1) larger spillway capacity may increase annual downstream flood losses, (2) benefit‐cost ratios may be low, (3) construction accidents associated with dam modification may cause fatalities, and (4) the dollar amount spent to save lives by making dams safer is often very high. Based on these objections, a procedure is presented for evaluating the effectiveness of a proposed dam modification. A change in spillway design policy is recommended. Accepting the status quo at a dam that cannot accommodate the PMF may be the best course of action. 相似文献