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81.
82.
Larry W. Finger Robert M. Hazen Anne M. Hofmeister 《Physics and Chemistry of Minerals》1986,13(4):215-220
High-pressure crystal structures and compressibilities have been determined by x-ray methods for MgAl2O4 spinel and its isomorph magnetite, Fe3O4. The measured bulk moduli, K, of spinel and magnetite (assuming K′=4) are 1.94±0.06 and 1.86±0.05 Mbar, respectively, in accord with previous ultrasonic determinations. The oxygen u parameter, the only variable atomic position coordinate in the spinel structure (Fd3m, Z=8), decreases with pressure in MgAl2O4, thus indicating that the magnesium tetrahedron is more compressible than the aluminum octahedron. In magnetite the u parameter is unchanged, and both tetrahedron and octahedron display the 1.9 Mbar bulk modulus characteristic of the entire crystal. This behavior contrasts with that of nickel silicate spinel (γ-Ni2SiO4), in which the u parameter increases with pressure because the silicon tetrahedron is relatively incompressible compared to the nickel octahedron. 相似文献
83.
Marie Sherwood 《Environmental Geology》1986,9(1):11-14
Agricultural activity is estimated to be responsible for only 6% (8 km) of the total length (135 km) of seriously polluted
river channel, but for over 30% (294 km) of the slightly or moderately polluted length (963 km) of channel recorded to date
in the state. This article examines the present sources and causes of pollution from agricultural wastes, and speculates on
the likely direction of future trends.
The most common sources of surface water pollution are animal manures, silage effluent, runoff from land following spreading,
and fertilizers. 相似文献
84.
Double-packer injection tests have been carried out in a borehole in the Chalk of Hampshire and a borehole in the Permian Penrith Sandstone of Cumbria, England. The tests have been supplemented by borehole logging and television inspections and by laboratory measurements on cores. A new mathematical treatment has enabled results to be calculated for injection test intervals containing fissures. In both formations, transmissivity immediately around the borehole is dominated by a few major fissures. In the Penrith Sandstone there is good agreement between intergranular hydraulic conductivity measurements and packer-test results in the portions of the borehole which do not contain major fissures. In the Chalk, the packer-test values are always higher than the intergranular measurements, suggesting that some degree of fissuring is present throughout. 相似文献
85.
One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turonian ages; and (3) the shallow aquifer system (Q) of Plio-Pleistocene ages. The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/Cl approximately 0.5 and Br/Cl approximately 7 x 10(-3). This composition is similar to that of thermal hypersaline spring that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep-seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio-Pleistocene Aquifer shows a wide range of Cl- (100-2000 mg/L), Na/Cl (0.4-1.0), Br/Cl (2-6 x 10(-3)), and SO4/Cl (0.01-0.4) ratios. These variations, together with the high SO4(2-), K+, and NO3- concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio-Pleistocene Aquifer, as suggested by the high SO4(2-) concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3- (80 mg/l) contents and low Br/Cl ratios (2 x 10(-3)). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes. 相似文献
86.
Lauren Patterson Marie Urban Aaron Myers Budhendra Bhaduri Eddie Bright Phillip Coleman 《GeoJournal》2007,69(1-2):93-102
Geospatial technologies and digital data have developed and disseminated rapidly in conjunction with increasing computing
efficiency and Internet availability. The ability to store and transmit large datasets has encouraged the development of national
infrastructure datasets in geospatial formats. National datasets are used by numerous agencies for analysis and modeling purposes
because these datasets are standardized and considered to be of acceptable accuracy for national scale applications. At Oak
Ridge National Laboratory a population model has been developed that incorporates national schools data as one of the model
inputs. This paper evaluates spatial and attribute inaccuracies present within two national school datasets, Tele Atlas North
America and National Center of Education Statistics (NCES).
Schools are an important component of the population model, because they are spatially dense clusters of vulnerable populations.
It is therefore essential to validate the quality of school input data. Schools were also chosen since a validated schools
dataset was produced in geospatial format for Philadelphia County; thereby enabling a comparison between a local dataset and
the national datasets.
Analyses found the national datasets are not standardized and incomplete, containing 76 to 90 percent of existing schools.
The temporal accuracy of updating annual enrollment values resulted in 89 percent inaccuracy for 2003. Spatial rectification
was required for 87 percent of NCES points, of which 58 percent of the errors were attributed to the geocoding process. Lastly,
it was found that by combining the two national datasets, the resultant dataset provided a more useful and accurate solution. 相似文献
87.
88.
Laurent Millet Boris Vannière Valérie Verneaux Michel Magny Jean Robert Disnar Fatima Laggoun-Défarge Anne Véronique Walter-Simonnet Gilles Bossuet Elena Ortu Jacques-Louis de Beaulieu 《Journal of Paleolimnology》2007,38(4):525-539
This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological,
environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages,
organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany,
Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the
chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional
climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main
lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical
of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids
through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development.
Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested
that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral
chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings
that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group
level, may be necessary to increase the sensibility of the indicators to lake-level changes. 相似文献
89.
This work proposes a complete method for automatic inversion of data from hydraulic interference pumping tests based on both homogeneous and fractal dual-medium approaches. The aim is to seek a new alternative concept able to interpret field data, identify macroscopic hydraulic parameters and therefore enhance the understanding of flow in porous fractured reservoirs. Because of its much contrasted sensitivities to parameters, the dual-medium approach yields an ill-posed inverse problem that requires a specific optimization procedure including the calculation of analytical sensitivities and their possible re-scaling. Once these constraints are fulfilled, the inversion proves accurate, provides unambiguous and reliable results. In the fractal context inverting several drawdown curves from different locations at the same time reveals more accurate. Finally, hydraulic parameters drawn from inversion should be taken into account to improve in various situations the conditioning of up-scaled flow in fractured rocks. 相似文献
90.
The influence of Daphnia galeata×hyalina grazing and of infochemicals released by the daphnids on the colony size and growth rate of the colonial gelatinous green alga Sphaerocystis schroeteri (Chlorococcales) was investigated in laboratory batch experiments run for 96 h. High zooplankton grazing pressure was exerted by a final concentration of 100 daphnids L−1 in the Daphnia treatments. Infochemicals were obtained by filtration (0.2 μm) of water from D. galeata×hyalina cultures (200 ind. L−1 exposed for 24 h). This filtrate was added to the S. schroeteri cultures in two concentrations corresponding to 7 and 50 daphnids L−1, respectively. The growth rate of S. schroeteri was neither affected significantly by direct Daphnia grazing nor by the presence of Daphnia infochemicals, in comparison to the control. However, the portion of inedible S. schroeteri colonies (diameter>50 μm) increased under direct grazing pressure, whereas the Daphnia infochemicals did not influence the colony size significantly. We conclude that the shift in colony size by direct zooplankton grazing denotes an effective defence mechanism against size selective feeding for colonial gelatinous green algae. This effective defence in combination with unchanged growth rates of the larger colonies (under non-limiting nutrient and light conditions) falsifies the assumption of a trade-off between minimising grazing losses and maximising growth by optimising the colony size. 相似文献