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1.
Alan M Bond Julie R Bradbury Henry A Hudson John S Garnham Peter J Hanna Stanley Strother 《Marine Chemistry》1985,16(1):1-9
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent. 相似文献
2.
A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized
zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change
from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly
perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope
system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of
2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave.
−7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local
contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the
Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef
has generally higher plagioclase and pyroxene δ
18O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic
evidence for sub-solidus interaction with fluids, and the Δ
plagioclase–pyroxene values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope
system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative
δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ
plagioclase–pyroxene in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO2-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction
is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale.
The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination
played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO2 produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation. 相似文献
4.
K. Benzerara G. Morin J. Miot C. Casiot F. Farges G.E. Brown Jr. 《Geochimica et cosmochimica acta》2008,72(16):3949-3963
Spatial and seasonal variations of the oxidation of Fe(II) and As(III) have been previously documented in the Carnoulès (Gard, France) Acid Mine Drainage (AMD) by bulk analyses. These variations may be correlated with the variations in the activity of indigenous As(III)- and Fe(II)-oxidizing bacteria living in the As-rich Carnoulès water. The activity of these bacteria indeed plays an important role in the nature and composition of the solid phases that sequester arsenic at this site. In order to better understand the interactions of microbes with Fe and As in the Carnoulès AMD, we combined Transmission Electron Microscopy (TEM) and Scanning Transmission X-ray Microscopy (STXM) to collect near-edge X-ray absorption fine structure (NEXAFS) spectra at high spatial and energy resolution and to perform high spatial resolution imaging at the 30-50 nm scale. Spectromicroscopy was performed at the C K-edge, Fe L2,3-edge, and As L2,3-edge, which allowed us to locate living and/or mineralized bacterial cells and to characterize Fe and As oxidation states in the vicinity of those cells. TEM was used to image the same areas, providing higher resolution images and complementary crystallographic and compositional information through electron diffraction and EDXS analysis. This approach provides unique information on heterogeneous geochemical processes that occur in a complex microbial community in an AMD environment at the micrometer and submicrometer-scale. Bacterial cells in the Carnoulès AMD were frequently associated with mineral precipitates, and a variety of biomineralization patterns were observed. While many mineral precipitates were not associated with bacterial cells, they were associated with pervasive organic carbon. Finally, abundant biomineralized organic vesicles were observed in the Carnoulès AMD. Such vesicles may have been overlooked in highly mineralized extreme environments in the past and may represent an important component in a common biomineralization process in such environments. 相似文献
5.
Controlling geological and hydrogeological processes in an arsenic contaminated aquifer on the Red River flood plain,Vietnam 总被引:1,自引:0,他引:1
6.
Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引:1,自引:1,他引:1
7.
David J. Barber John R. Beckett Julie M. Paque Edward Stolper 《Meteoritics & planetary science》1994,29(5):682-690
Abstract The crystallography and crystal chemistry of a new calcium-titanium-aluminosilicate mineral (UNK) observed in synthetic analogs to calcium-aluminum-rich inclusions (CAIs) from carbonaceous chondrites was studied by electron diffraction techniques. The unit cell is primitive hexagonal or trigonal, with a = 0.790 ± 0.002 nm and c = 0.492 ± 0.002 nm, similar to the lattice parameters of melilite and consistent with cell dimensions for crystals in a mixer furnace slag described by Barber and Agrell (1994). The phase frequently displays an epitactic relationship in which melilite acts as the host, with (0001)UNK | (001)mel and <10T0>UNK | <100>mel. If one of the two space groups determined by Barber and Agrell (1994) for their sample of UNK is applicable (P3ml or P31m), then the structure is probably characterized by puckered sheets of octahedra and tetrahedra perpendicular to the c-axis with successive sheets coordinated by planar arrays of Ca. In this likely structure, each unit cell contains three Ca sites located in mirror planes, one octahedrally coordinated cation located along a three-fold axis and five tetrahedrally coordinated cations, three in mirrors and two along triads. The octahedron contains Ti but, because there are 1.3–1.9 cations of Ti/formula unit, some of the Ti must also be in tetrahedral coordination, an unusual but not unprecedented situation for a silicate. Tetrahedral sites in mirror planes would contain mostly Si, with lesser amounts of Al while those along the triads correspondingly contain mostly Al with subordinate Ti. The structural formula, therefore, can be expressed as with Si + Ti = 4. Compositions of meteoritic and synthetic Ti-bearing samples of the phase can be described in terms of a binary solid solution between the end-members Ca3TiAl2Si3O14 and Ca3Ti(AlTi)(AlSi2)O14. A Ti-free analog with a formula of Ca3Al2Si4O14 synthesized by Paque et al. (1994) is thought to be related structurally but with the octahedral site being occupied by Al, that is 相似文献
8.
The place of individuals in the politics of scale 总被引:1,自引:0,他引:1
Julie Cidell 《Area》2006,38(2):196-203
Conceptualizations and re-conceptualizations of scale have been powerful tools for explaining spatial processes that transcend traditionally-bounded territories. Examining the role of individuals within a politics of scale can do even more to explain multi-scalar conflicts. This paper does so by examining struggles over airport expansion in the US, showing how an understanding of the various roles of individuals in the politics of scale – as sites of multiple scales, as actors constituting other scales, and as scales in and of themselves – better explains multi-scalar conflicts and offers more opportunities for resolving them. 相似文献
9.
We have investigated a well-ordered sample of natural Cr-bearing dickite from Nowa Ruda (Lower Silesia, Poland) using electron
paramagnetic resonance (EPR) at X- and Q-band frequencies (9.42 and 33.97 GHz, respectively) and optical diffuse reflectance
spectroscopy. The observation of the spin-forbidden transitions at 15500 and 14690 cm−1 allows us to unambiguously identify the major contribution of octahedrally coordinated Cr3+ ions in the optical spectrum. The X- and Q-band EPR spectra show two superposed Cr3+ signals. The corresponding fine-structure parameters were determined at room temperature and 145 K. These results suggest
the substitution of Cr3+ for Al3+ in equal proportions in the two unequivalent octahedral sites of the dickite structure. In kaolin group minerals, the distortion
around Cr3+ ions (λ≈ 0.2–0.4) in Al sites is significantly less rhombic than that observed around Fe3+ ions (λ≈ 0.6–0.8).
Received: 29 June 2001 / Accepted: 22 October 2001 相似文献
10.
Magmatic processes that generated the rhyolite of Glass Mountain, Medicine Lake volcano, N. California 总被引:13,自引:1,他引:13
Timothy L. Grove Julie M. Donnelly-Nolan Todd Housh 《Contributions to Mineralogy and Petrology》1997,127(3):205-223
Glass Mountain consists of a 1 km3, compositionally zoned rhyolite to dacite glass flow containing magmatic inclusions and xenoliths of underlying shallow crust.
Mixing of magmas produced by fractional crystallization of andesite and crustal melting generated the rhyolite of Glass Mountain.
Melting experiments were carried out on basaltic andesite and andesite magmatic inclusions at 100, 150 and 200 MPa, H2O-saturated with oxygen fugacity controlled at the nickel-nickel oxide buffer to provide evidence of the role of fractional
crystallization in the origin of the rhyolite of Glass Mountain. Isotopic evidence indicates that the crustal component assimilated
at Glass Mountain constitutes at least 55 to 60% of the mass of erupted rhyolite. A large volume of mafic andesite (2 to 2.5
km3) periodically replenished the magma reservoir(s) beneath Glass Mountain, underwent extensive fractional crystallization and
provided the heat necessary to melt the crust. The crystalline residues of fractionation as well as residual liquids expelled
from the cumulate residues are preserved as magmatic inclusions and indicate that this fractionation process occurred at two
distinct depths. The presence and composition of amphibole in magmatic inclusions preserve evidence for crystallization of
the andesite at pressures of at least 200 MPa (6 km depth) under near H2O-saturated conditions. Mineralogical evidence preserved in olivine-plagioclase and olivine-plagioclase-high-Ca clinopyroxene-bearing
magmatic inclusions indicates that crystallization under near H2O-saturated conditions also occurred at pressures of 100 MPa (3 km depth) or less. Petrologic, isotopic and geochemical evidence
indicate that the andesite underwent fractional crystallization to form the differentiated melts but had no chemical interaction
with the melted crustal component. Heat released by the fractionation process was responsible for heating and melting the
crust.
Received: 26 March 1996 / Accepted: 14 November 1996 相似文献