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51.
David A. McKeown 《Physics and Chemistry of Minerals》2008,35(5):259-270
Polarized Raman spectra were collected for single crystal buergerite (NaFe3Al6(BO3)3Si6O18(O0.92(OH)0.08)3F) from room temperature to near 1,375°C. Vibrational assignments to features in the room temperature spectra were determined
by lattice dynamics calculations, where internal BO3 motions dominate modes near 1,300 cm−1, internal SiO4 displacements dominate modes between 900 and 1,200 cm−1, while less localized displacements within the isolated Si6O18 ring mix with motions within Na, Fe, Al, F, and BO3 environments for fundamental modes below 780 cm−1. At elevated temperatures, most buergerite Raman features broaden and shift to lower frequencies up to 900°C. Above this
temperature, the lattice mode peaks evolve into broad bands, while OH stretch modes near 3,550 cm−1 disappear. According to Raman spectroscopy, X-ray diffraction, differential thermal analysis, and scanning electron microscopy,
buergerite undergoes a complex transition that starts near 700°C and extends over a 310°C interval, where initially, Al and
Fe probably become disordered within the Y- and Z-sites, and most F and all OH are later liberated. A reversible crystal-to-amorphous
transition is seen by Raman for buergerite fragments heated as high as 930°C. Buergerite becomes permanently altered when
heated to temperatures greater than 930°C; after cooling to room temperature, these altered fragments are comprised of mullite
and Fe-oxide crystals suspended in an amorphous borosilicate matrix. 相似文献
52.
Michelle A. Walvoord Brian J. Andraski David P. Krabbenhoft Robert G. Striegl 《Applied Geochemistry》2008
Mercury contained in buried landfill waste may be released via upward emission to the atmosphere or downward leaching to groundwater. Data from the US Geological Survey’s Amargosa Desert Research Site (ADRS) in arid southwestern Nevada reveal another potential pathway of Hg release: long-distance (102 m) lateral migration of elemental Hg (Hg0) through the unsaturated zone. Gas collected from multiple depths from two instrumented boreholes that sample the entire 110-m unsaturated zone thickness and are located 100 and 160 m away from the closest waste burial trench exhibit gaseous Hg concentrations of up to 33 and 11 ng m−3, respectively. The vertical distribution of gaseous Hg in the borehole closest to the disposal site shows distinct subsurface peaks in concentration at depths of 1.5 and 24 m that cannot be explained by radial diffusive transport through a heterogeneous layered unsaturated zone. The inability of current models to explain gaseous Hg distribution at the ADRS highlights the need to advance the understanding of gas-phase contaminant transport in unsaturated zones to attain a comprehensive model of landfill Hg release. 相似文献
53.
This paper queries the relevance of the ‘splintering urbanism’ thesis to postcolonial cities of the South, and responds to calls for the production of a decentered theory of urbanization through a case study of Jakarta. Drawing on archival and interview data, the paper demonstrates that Jakarta has, since its inception, been characterized by a high degree of differentiation of access to water supply, and of fragmentation of water supply networks. We document the origins of this fragmentation in the colonial era, and trace the legacy of the colonial constructions within the postcolonial city. Moreover, we demonstrate that the introduction of private sector management (in 1988) has not significantly disrupted, and certainly not caused, this pattern. In short, we provide evidence to support our claim that Jakarta’s water supply system is ‘splintered’ rather than ‘splintering’, and demonstrate that this phenomenon was not caused by the rise (or fall) of the ‘modern infrastructural ideal’. In order to explain this sustained fragmentation of infrastructure and access, the paper develops a conceptual framework of postcolonial governmentality that emphasizes the interrelationship between materiality, governmentality, identity, and urbanization, in particular through demonstrating how contested and evolving process of social differentiation are linked to the differentiation of water supply infrastructures and of urban spaces. Although we are wary of any simplistic comparisons between the colonial past and present, we argue that the optic of postcolonial governmentality provides a powerful lens for dissecting the power relations that continue to structure access to water supply and urban space in cities in the South. 相似文献
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The Central Valley in California (USA) covers about 52,000 km2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood-control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model, can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use. 相似文献
58.
Michelle Goman Gail M. Ashley R. Bernhart Owen Victoria C. Hover Dev K. Maharjan 《The Professional geographer》2017,69(3):438-454
Playa lake systems tend to be overlooked archives of paleoenvironmental change due to the likelihood of a short and intermittent record of deposition. Groundwater-fed wetlands associated with these climate-sensitive playas, however, preserve changes in hydrologic budget and are thus valuable archives for semiarid regions. This study examines the paleoecological record of a groundwater-fed wetland from Lake Solai, Kenya. Biological proxies are used to reconstruct paleoenvironmental change and climate impacts over the past millennium. Dry conditions persisted between CE 1115 and 1490, followed by wetter conditions during the Little Ice Age. Near surface sediments indicate increasing anthropogenic impact through pastoralism. 相似文献
59.
B. A. McKeown 《Marine environmental research》1981,5(4):295-300
The toxicity of crude oil and the dispersant BP1100X was tested in sea water and in each case was much less than the toxicity to fish in fresh water. Uptake of oil from water, with or without dispersant, was similar after a short exposure to 200 ppm. The oil was cleared from the fish in three weeks. A long-term exposure to oil or oil plus dispersant at a concentration of 5 ppm showed a slow accumulation but significantly above exposure levels. Thus, salmon exposed to oil in sea water can take up the hydrocarbons but appear to cleanse themselves rapidly. 相似文献
60.
An ion exchange technique has been used to determine the copper complexing capacity (CuCC) of strong organic complexing agents at 21 stations across the continental shelf of the southeastern United States and in the western Sargasso Sea. The concentration of dissolved organic carbon (DOC) and total particulate materal (TPM), two pools of potential complexing agents, was also measured at each station. The CuCC ranged from 0.014 to 1.681 μM Cu dm−3 on the inner shelf, from 0.043 to 0.095 μM Cu dm−3 in mid and outer shelf waters, and from < 0.010 to 0.036 μM Cu dm−3 at the Sargasso Sea stations. The correlation between CuCC and both DOC and TPM is highly significant (α < 0.01). Two synoptic surveys of the distribution of DOC and TPM across the shelf showed that DOC ranges from > 3 mg C dm−3 nearshore to <1 mg C dm−3 offshore and that TPM ranges from > 50 mg dm−3 nearshore to <1 mg dm−3 offshore. Both TPM and DOC are most variable on the inner shelf. These data are consistent with CuCC data which indicate that the CuCC of inner shelf waters was relatively high and very heterogeneous. In contrast, DOC, TPM and copper complexing capacity are low and nearly invariant at the Sargasso Sea stations. We present a model of the distribution of complexing agents in different marine environments and hypothesize that the mechanisms underlying differences between environments relate to differences in the source(s) and nature of complexing agents in each system. 相似文献