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461.
Melanie J. Beazley Samuel M. Webb Martial Taillefert 《Geochimica et cosmochimica acta》2011,75(19):5648-5663
The biomineralization of U(VI) phosphate as a result of microbial phosphatase activity is a promising new bioremediation approach to immobilize uranium in both aerobic and anaerobic conditions. In contrast to reduced uranium minerals such as uraninite, uranium phosphate precipitates are not susceptible to changes in oxidation conditions and may represent a long-term sink for uranium in contaminated environments. So far, the biomineralization of U(VI) phosphate has been demonstrated with pure cultures only. In this study, two uranium contaminated soils from the Department of Energy Oak Ridge Field Research Center (ORFRC) were amended with glycerol phosphate as model organophosphate source in small flow-through columns under aerobic conditions to determine whether natural phosphatase activity of indigenous soil bacteria was able to promote the precipitation of uranium(VI) at pH 5.5 and 7.0. High concentrations of phosphate (1-3 mM) were detected in the effluent of these columns at both pH compared to control columns amended with U(VI) only, suggesting that phosphatase-liberating microorganisms were readily stimulated by the organophosphate substrate. Net phosphate production rates were higher in the low pH soil (0.73 ± 0.17 mM d−1) compared to the circumneutral pH soil (0.43 ± 0.31 mM d−1), suggesting that non-specific acid phosphatase activity was expressed constitutively in these soils. A sequential solid-phase extraction scheme and X-ray absorption spectroscopy measurements were combined to demonstrate that U(VI) was primarily precipitated as uranyl phosphate minerals at low pH, whereas it was mainly adsorbed to iron oxides and partially precipitated as uranyl phosphate at circumneutral pH. These findings suggest that, in the presence of organophosphates, microbial phosphatase activity can contribute to uranium immobilization in both low and circumneutral pH soils through the formation of stable uranyl phosphate minerals. 相似文献
462.
Mohammad Amir Hossain Bhuiyan M. Julleh Jalalur Rahman Samuel B. Dampare Shigeyuki Suzuki 《Journal of Geochemical Exploration》2011,111(3):113-137
This present study describes the elemental geochemistry of fluvial sediments in the Kurigram (upstream) to Sirajganj–Tangail (downstream) section of the Brahmaputra–Jamuna River, Bangladesh, with the aim of evaluating their provenance, weathering and tectonic setting. Petrographically, the sediments are rich in quartz (68%), followed by feldspars (8.5%) and lithic grains (7%). The bulk sediment chemistry is influenced by grain size. Concentrations of TiO2, Fe2O3, MgO, K2O, P2O5, Rb, Nb, Cr, V, Y, and, Ce, Th and Ga slightly decrease with increasing SiO2/Al2O3 and grain size, suggesting clay matrix control. In contrast, concentrations of CaO, Na2O, Sr and Pb increase with increasing SiO2/Al2O3 and grain size, suggesting residence of these substances in feldspar. Decrease in Zr as grain size increases is likely controlled both by clay matrix and heavy minerals. In addition, heavy minerals' sorting also influences Ce, Th, Y and Cr abundances in some samples. The sediments are predominantly quartzose in composition with abundant low-grade metamorphic and sedimentary lithics, low feldspars and trace volcanic detritus, indicating a quartzose recycled orogen province as a source of the sediments. Discriminant diagrams together with immobile element ratio plots show that, the Brahmaputra–Jamuna River sediments are mostly derived from rocks formed in an active continental margin. Moreover, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the sediments of Brahmaputra–Jamuna River from felsic rock sources of upper continental crust (UCC). The chemical indices of alteration suggest that Brahmaputra–Jamuna River sediments are chemically immature and experienced low chemical weathering effects. In the A–CN–K ternary diagram, most of the samples close to the plagioclase–K-feldspar join line and to the UCC plot, and in the field of various lithologies of Higher Himalayan Crystalline Series, suggesting that rocks in these series are likely source rocks. Therefore, the elemental geochemistry of the Brahmaputra–Jamuna River sediments is controlled mostly by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz. 相似文献
463.
Water quality assessment of groundwater in some rock types in parts of the eastern region of Ghana 总被引:2,自引:2,他引:0
Samuel Y. Ganyaglo Bruce Banoeng-Yakubo Shiloh Osae Samuel B. Dampare Joseph R. Fianko 《Environmental Earth Sciences》2011,62(5):1055-1069
A baseline study involving analyses of subsurface water samples from the Cape Coast granitoid complex, Lower Birimian, Togo
Formation and the Voltaian Group, was carried out to assess their suitability for drinking, domestic and agricultural purposes.
Study results show that pH within the range (3.0 ≤ pH ≤ 6.5) constitutes 74% of the boreholes analysed, and 51% have hardness
values ranging from 7.89 to 73.24 mg/l as CaCO3 and are described as soft. Total dissolved solids are less than 1,000 mg/l and generally characterized by low conductivity
values, of which 95% are within the range (55 ≤ EC ≤ 1,500 μS/cm). The mean values of the major cations (Ca2+, Mg2+, Na+, K+) and anions (SO42−, Cl−, HCO3−) are all within the World Health Organisation (WHO) standards. Five (5) of the boreholes sampled have nitrate (NO3−) contamination. Even though NO3− contamination and acidic waters exist in some of the boreholes, the majority of the boreholes are excellent for drinking
and domestic purposes. Assessment of the groundwaters for agricultural irrigation revealed three main categories. These are
low salinity–low sodicity (C1–S1), medium salinity–low sodicity (C2–S1) and high salinity–low sodicity (C3–S1), using the
US Salinity Laboratory (USSL) classification scheme. As much as 95% of the samples plotted in the ‘excellent to good’ and
‘good to permissible’ categories on the Wilcox diagram. The groundwater in the study area may therefore be regarded as good
for irrigation activities. The major identifiable geochemical processes responsible for the evolution of the various ions
are mineral weathering and chemical reactions. 相似文献
464.
Robust Resampling Confidence Intervals for Empirical Variograms 总被引:1,自引:0,他引:1
The variogram function is an important measure of the spatial dependencies of a geostatistical or other spatial dataset. It
plays a central role in kriging, designing spatial studies, and in understanding the spatial properties of geological and
environmental phenomena. It is therefore important to understand the variability attached to estimates of the variogram. Existing
methods for constructing confidence intervals around the empirical variogram either rely on strong assumptions, such as normality
or known variogram function, or are based on resampling blocks and subject to edge effect biases. This paper proposes two
new procedures for addressing these concerns: a quasi-block-bootstrap and a quasi-block-jackknife. The new methods are based
on transforming the data to decorrelate it based on a fitted variogram model, resampling blocks from the decorrelated data,
and then recorrelating. The coverage properties of the new confidence intervals are compared by simulation to a number of
existing resampling-based intervals. The proposed quasi-block-jackknife confidence interval is found to have the best properties
of all of the methods considered across a range of scenarios, including normally and lognormally distributed data and misspecification
of the variogram function used to decorrelate the data. 相似文献
465.
Jean-Benoît Le Cam Jérôme Fournier Samuel Etienne Jérôme Couden 《Estuarine, Coastal and Shelf Science》2011
Mechanical properties of the biomineralised cement from tube-building marine worms are poorly known. Secreted from an organ connected to the polychaetes specialised glands, the cement glues sand grains and calcareous shell fragments of a given size and, on a larger scale, ensures the resistance of the reef to waves. In this study, three kinds of mechanical tests were performed with worm tubes to establish the nature of the cement behaviour. Results obtained show that cement behaves like a visco-elastic material. This property allows the tubes to dissipate the mechanical energy from the waves to which they are subject and to reduce the mechanical stress transmitted inside the tubes to the polychaetes. Comparison of “fresh” and “dry” cements highlights that the visco-elastic behaviour of the cement is maintained after five years. The viscosity of the cement is therefore not related to moisture but to its chemical composition. More generally, these results offer a better understanding of the role of cement on worm reefs strength and their persistence in the geological record. 相似文献
466.
Jens Carlsson Samuel Shephard James CoughlanClive N. Trueman Emer RoganTom F. Cross 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(6):627-636
Microsatellite and otolith chemistry variability were analysed to assess fine scale genetic structure in the deep-sea teleost orange roughy (Hoplostethus atlanticus). The Porcupine Bank located on the continental shelf west of Ireland, comprises a complex system of mounds and flat areas that are broken up by canyons. Orange roughy form spawning aggregations on mounds and flat areas, and were heavily fished until the resource was depleted. By analysing adults in spawning condition and juvenile orange roughy from six mounds and one flat area, shallow but significant genetic population structure was evident (FST=0.0031, Dest across loci=0.0306 and G-test). Most of the structure was accounted for by inclusion of a sample from the flats (six of ten significant pairwise FST estimates and G-tests, and five of the highest Dest estimates included the flat sample). While the flat sample contributed most to the genetic structure, there was still significant (albeit weaker) structure among mound samples. The observed structure was supported by otolith analyses. Fish caught as late juveniles in either the flat or mound areas showed consistent differences in chemistry at the otolith core throughout the initial 10 years of growth, which could indicate site fidelity. We hypothesise that seafloor topographic structures (mounds and flats) may provide discrete spawning areas for orange roughy and that the limited gene flow between these spawning areas is insufficient to counteract genetic drift. 相似文献
467.
Theoretical mean wave resistance and regional division of the energy of single-layer flow over topogra-phy is studied at the near-resonant region in the weakly nonlinear, long wave limit. The theoretical meanwave resistance is determined in terms of the 1st and 2nd conservation laws of the fKdV equation. It isproved by the asymptotic mean method that the theoretical mean wave resistance depends only on the intensityand moving velocity of the topography. The theoretical results of this paper are in good agreement withnumerical calculations. Comparisons between the theoretical and numerical results showed that the theoryof the present paper holds for any small compact topography. 相似文献
468.
A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC) 总被引:1,自引:0,他引:1
Delphine Yeghicheyan Jean Carignan Michel Valladon Martine Bouhnik Le Coz Florence Le Cornec Maryse Castrec-Rouelle Michel Robert Luc Aquilina Emmanuel Aubry Carine Churlaud Aline Dia Samuel Deberdt Bernard Dupré Rémi Freydier Gérard Gruau Odile Hénin Anne-Marie de Kersabiec Joël Macé Luc Marin Nicole Morin Patrice Petitjean Elodie Serrat 《Geostandards and Geoanalytical Research》2001,25(2-3):465-474
The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories. 相似文献
469.
470.
Samuel Y. K. Yee 《Boundary-Layer Meteorology》1988,43(1-2):85-90
The so-called ‘force-restore method’ has been used with considerable success in numerical weather prediction models to simulate
diurnal variations of ground temperature. This note demonstrates that the force-restore equation is no more nor less than
an approximation to the surface-energy-balance equation. The applicability of the method to the case of multi-component heating
functions and to the case in which the soil is covered by a litter layer is discussed. 相似文献