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61.
Mobile sediment in an urbanizing karst aquifer: implications for contaminant transport 总被引:1,自引:0,他引:1
Here we investigate geochemical characteristics of sediment in different compartments of a karst aquifer and demonstrate
that mobile sediments in a karst aquifer can exhibit a wide range of properties affecting their contaminant transport potential.
Sediment samples were collected from surface streams, sinkholes, caves, wells, and springs of a karst aquifer (the Barton
Springs portion of the Edwards (Balcones Fault Zone) Aquifer, Central Texas) and their mineralogy, grain-size distribution,
organic carbon content, and specific surface area analyzed. Statistical analysis of the sediments separated the sampling sites
into three distinct groups: (1) streambeds, sinkholes, and small springs; (2) wells; and (3) caves. Sediments from the primary
discharge spring were a mix of these three groups. High organic carbon content and high specific surface area gives some sediments
an increased potential to transport contaminants; the volume of these sediments is likely to increase with continued urbanization
of the watershed.
Received: 13 April 1998 · Accepted: 6 October 1998 相似文献
62.
西准噶尔包古图地区地层火山岩锆石LA-ICP-MS U-Pb年代学研究 总被引:13,自引:11,他引:13
包古图地区位于西准噶尔东南部,区内出露地层主要为石炭系太勒古拉组、包古图组和希贝库拉斯组,为一套巨厚的半深海相-大陆坡相火山-火山碎屑沉积建造。这套地层的时代归属和地层层序长期以来一直存在争议。本文报导了包古图地区实测地层剖面,并从太勒古拉组玄武岩和包古图组及希贝库拉斯组凝灰岩中分别选出锆石,进行了LA-ICP-MS U-Pb年代学研究,获得206Pb/238U加权平均年龄分别为357.5±5.4Ma、332.1±3.0Ma和336.3±2.5Ma。由此确定这套地层属于早石炭世的杜内阶到维宪阶,由下到上依次为太勒古拉组、包古图组和希贝库拉斯组。 相似文献
63.
64.
Traditionally, the Cretaceous has been considered as a long period of global warmth, a 'greenhouse' world. This view has been challenged in recent years by several lines of evidence; palaeobotany, stable isotopes, and palaeoclimatic modelling in particular. However, although these data demonstrate that cooling is likely, the only first-hand evidence which demonstrates the presence of substantial ice build-up in Cretaceous high palaeolatititudes are dropstones. These outsized or exotic clasts set in a fine-grained sediment are often interpreted as a direct result of ice rafting. The reliability of this dropstone evidence and particularly its validity is questioned in demonstrating ice age interludes within the Cretaceous greenhouse. 相似文献
65.
Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:
相似文献
ROR | E/kJ mol–1 | 1012 A/cm3 molecule–1 s–1 |
---|---|---|
dethyl ether | –2.8±0.4 | 3.5±0.6 |
di-n-propyl ether | –1.2±0.6 | 11.5±2.7 |
methylt-butyl ether | 0.85±0.59 | 4.0±1.3 |
ethyln-butyl ether | –1.3±0.5 | 8.7±1.7 |
ethylt-butyl ether | –1.2±0.6 | 3.0±0.8 |
66.
Ricardo Conceição Hugo Gonçalves Silva Alec Bennett Rui Salgado Daniele Bortoli Maria João Costa Manuel Collares Pereira 《Boundary-Layer Meteorology》2018,166(1):69-81
The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection. 相似文献
67.
C. R. L. Friend A. P. Nutman V. C. Bennett M. D. Norman 《Contributions to Mineralogy and Petrology》2008,155(2):229-246
Modern chemical sediments display a distinctive rare earth element + yttrium (REE + Y) pattern involving depleted LREE, positive
La/La*SN, Eu/Eu*SN, and YSN anomalies (SN = shale normalised) that is related to precipitation from circumneutral to high pH waters with solution complexation
of the REEs dominated by carbonate ions. This is often interpreted as reflecting precipitation from surface waters (usually
marine). The oldest broadly accepted chemical sediments are c. 3,700 Ma amphibolite facies banded iron-formation (BIF) units
in the Isua supracrustal belt, Greenland. Isua BIFs, including the BIF international reference material IF-G are generally
considered to be seawater precipitates, and display these REE + Y patterns (Bolhar et al. in Earth Planet Sci Lett 222:43–60,
2004). Greenland Eoarchaean BIF metamorphosed up to granulite facies from several localities in the vicinity of Akilia (island),
display REE + Y patterns identical to Isua BIF, consistent with an origin by chemical sedimentation from seawater and a paucity
of clastic input. Furthermore, the much-debated magnetite-bearing siliceous unit of “earliest life” rocks (sample G91/26)
from Akilia has the same REE + Y pattern. This suggests that sample G91/26 is also a chemical sediment, contrary to previous
assertions (Bolhar et al. in Earth Planet Sci Lett 222:43–60, 2004), and including suggestions that the Akilia unit containing G91/26 consists entirely of silica-penetrated, metasomatised,
mafic rock (Fedo and Whitehouse 2002a). Integration of our trace element data with those of Bolhar et al. (Earth Planet Sci Lett 222:43–60, 2004) demonstrates that Eoarchaean siliceous rocks in Greenland, with ages from 3.6 to 3.85 Ga, have diverse trace element signatures.
There are now geographically-dispersed, widespread examples with Isua BIF-like REE + Y signatures, that are interpreted as
chemically unaltered, albeit metamorphosed, chemical sediments. Other samples retain remnants of LREE depletion but are beginning
to lose the distinct La, Eu and Y positive anomalies and are interpreted as metasomatised chemical sediments. Finally there
are some siliceous samples with completely different trace element patterns that are interpreted as rocks of non-sedimentary
origin, and include metasomatised mafic rocks. The positive La/La*SN, Eu/Eu*SN and YSN anomalies found in Isua BIFs and other Eoarchaean Greenland samples, such as G91/26 from Akilia, suggests that the processes
of carbonate ion complexation controlling the REE − Y patterns were already established in the hydrosphere at the start of
the sedimentary record 3,600–3,850 Ma ago. This is in accord with the presence of Eoarchaean siderite-bearing marbles of sedimentary
origin, and suggests that CO2 may have been a significant greenhouse gas at that time. 相似文献
68.
Kevin G. Taylor Karen A. Hudson-Edwards Andrew J. Bennett Vladimir Vishnyakov 《Applied Geochemistry》2008
The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe–O and Fe–P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99–2.05 Å; 2P atoms at 3.17–3.25 Å). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 Å; 2P atoms at 3.17 Å). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption. 相似文献
69.
70.
Electrical conductivity measurements provide useful geotechnical information, particularly porosity data, and are well suited
for use in conjunction with acoustic profiling techniques. A proposed conductivity measurement system for surveying the seabed
is characterized by a towed inductive multifrequency probe operating underwater. It is integrated with a shipboard data acquisition
and processing system. 相似文献