排序方式： 共有84条查询结果，搜索用时 218 毫秒
1.
Jonathan O. Sharp Juan S. Lezama-Pacheco Pilar Junier Kai-Uwe Ulrich Satya Chinni Camille Margot-Roquier Bradley M. Tebo John R. Bargar 《Geochimica et cosmochimica acta》2011,75(21):6497-6510
It has generally been assumed that the bioreduction of hexavalent uranium in groundwater systems will result in the precipitation of immobile uraninite (UO2). In order to explore the form and stability of uranium immobilized under these conditions, we introduced lactate (15 mM for 3 months) into flow-through columns containing sediments derived from a former uranium-processing site at Old Rifle, CO. This resulted in metal-reducing conditions as evidenced by concurrent uranium uptake and iron release. Despite initial augmentation with Shewanella oneidensis, bacteria belonging to the phylum Firmicutes dominated the biostimulated columns. The immobilization of uranium (∼1 mmol U per kg sediment) enabled analysis by X-ray absorption spectroscopy (XAS). Tetravalent uranium associated with these sediments did not have spectroscopic signatures representative of U-U shells or crystalline UO2. Analysis by microfocused XAS revealed concentrated micrometer regions of solid U(IV) that had spectroscopic signatures consistent with bulk analyses and a poor proximal correlation (μm scale resolution) between U and Fe. A plausible explanation, supported by biogeochemical conditions and spectral interpretations, is uranium association with phosphoryl moieties found in biomass; hence implicating direct enzymatic uranium reduction. After the immobilization phase, two months of in situ exposure to oxic influent did not result in substantial uranium remobilization. Ex situ flow-through experiments demonstrated more rapid uranium mobilization than observed in column oxidation studies and indicated that sediment-associated U(IV) is more mobile than biogenic UO2. This work suggests that in situ uranium bioimmobilization studies and subsurface modeling parameters should be expanded to account for non-uraninite U(IV) species associated with biomass. 相似文献
2.
Seunghee Han Joris Gieskes Anna Obraztsova Dimitri D. Deheyn Bradley M. Tebo 《Estuarine, Coastal and Shelf Science》2011
Understanding the biogeochemical process of Hg is critical in the overall evaluation of the ecological impacts resulting from the reuse of Hg-contaminated dredged sediment. Sediment banks (V1 and V2) were constructed with freshly dredged sediments from a navigational channel in Venice Lagoon, Italy, with the goal of clarifying potential differences in the biogeochemistry of Hg between the reused dredged sediments and those from surrounding sites (SS1 and S2). Toward this purpose, Hg and monomethylmercury (MMHg) concentrations, and Hg methylation rates (MMRs) in the surface 2.5 cm sediments were monitored, along with ammonium, iron, sulfate and sulfide concentrations in the pore waters of banks and surrounding sites from November 2005 to February 2007. Pore water analyses indicate that the bank sediments are characterized by lower levels of sulfate and iron, and by higher levels of ammonium and sulfide compared to the surrounding sediments. With respect to Hg speciation, the fractions of MMHg in total Hg (%MMHg/Hg) and the MMRs were significantly lower in the bank V1 compared to those in the reference site SS1, whereas the %MMHg/Hg and the MMRs were similar between V2 and S2. A negative correlation is found between the logarithm of the particle-water partition coefficient of Hg and the MMR, indicating that the reduced MMRs in V1 are caused by the limited concentrations of dissolved Hg. Organic matter appears to play a key role in the control of MMR via the control of Hg solubility. 相似文献
3.
《Geoforum》2015
The global sourcing of services from developing countries has made human capital a key local asset for attracting foreign direct investment. This paper analyses to what extent individual companies engage in linkages and collaborations with universities and how the education sector responds to the new demands of the knowledge economy. Offshore services are generally recognised as ‘footloose’ investments with limited local linkages. A case study of industry-academe linkages in the growing business process outsourcing sector in the Philippines finds that foreign investors engage in active embedding and develop linkages with human resource providers, leading to increased territorial embeddedness. This paper investigates the kind of linkages created, which actors engage in them and their motivations, to understand the resulting implications for local economic development. Interviews with foreign investors and higher education institutions reveal that most collaboration is initiated by large call centre companies and focuses on entry-level skills development for their operations. I argue that multinational corporations have been able to capture local institutions and introduce changes in the education system to supply mainly lower-end skills. While increasing the available talent pool and raising the competitiveness for further investments, this presents challenges for upgrading into higher value-added services and potentially transforms the country into a dependent market economy. 相似文献
4.
《Marine Policy》2015
Recent changes in marine policy in Panama are closely related to sustained expansion of the Panamanian economy in the past ten years. Important drivers of economic growth such as the Panama Canal expansion, tourism, and real estate development directly involve marine and coastal areas. Therefore, maintaining the quality of these environments, as well as the sustainability of the human communities that depend on them, calls for the implementation of adequate management and planning policies. In light of a complex history of marine and coastal policy in Panama, current institutional restructuring processes, and a growing recognition of the importance of marine and coastal geographies, the authors aim to document the current status of, and community response to, marine and coastal policy in Panama, analyzed in terms of three important cross-cutting sectors: tourism, fishing, and conservation. To do so, the authors introduce two case studies: one in the Pearl Islands Archipelago and one in Bocas del Toro, each with varying degrees of participation or involvement in each sector, to illustrate the range of adaptations to change occurring in coastal communities. Based on an in-depth policy analysis and the case studies, the authors suggest that there are important administrative and structural gaps in the legislation and institutions that enforce them, as well as a lack of integration across institutions. In particular, the authors highlight the lack of clear marine and coastal property regimes as an obstacle to the implementation of integrative marine policies in Panama. 相似文献
5.
Magdalena M. Krol 《Advances in water resources》2011,34(4):537-549
During thermal remediation the increase in subsurface temperature can lead to bubble formation and mobilization. In order to investigate the effect of gas formation on resulting aqueous concentrations, a 2D finite difference flow and mass transport model was developed which incorporates a macroscopic invasion percolation (MIP) model to simulate bubble expansion and movement. The model was used to simulate three soil scenarios with different permeabilities and entry pressures at various operating temperatures and groundwater velocities. It was observed that discrete bubble formation occurred in all three soils, upward mobility being limited by lower temperatures and higher entry pressures. Bubble mobilization resulted in a different aqueous mass distribution than if no discrete gas formation was modeled, especially at higher temperatures. This was a result of bubbles moving upwards to cooler areas, then collapsing, and contaminating previously clean zones. The cooling effect also led to possible non-aqueous phase liquid (NAPL) formation which was not predicted using a model without discrete bubble formation. 相似文献
6.
7.
L.M. Sorokovikova V.N. Sinyukovich O.G. Netsvetayeva I.V. Tomberg N.P. Sezko 《Geography and Natural Resources》2009,30(1):35-39
The dynamics of the entry of sulfates and nitrate nitrogen into Lake Baikal together with its influent waters is outlined. Changes in the discharge of chemical components by large water streams are largely determined by the entry of ingredients as part of effluents. It is shown that the current increase in the flow of pollutants from the atmosphere has a dramatic effect on chemical composition of water in small rivers of Southern Baikal with low mineralization. 相似文献
8.
Glacial Lake Benson formed in west-central Minnesota as the Des Moines lobe of the Laurentide ice sheet retreated north of a small moraine in the Minnesota River lowland. Although previous research has constrained the timing of glacial Lake Agassiz immediately to the north, little age control is available for the formation of glacial Lake Benson and ice-marginal positions to the south. In order to constrain the age of glacial Lake Benson and test the application of single-grain optically stimulated luminescence (OSL) dating to ice-marginal deposits, seven OSL samples were collected from a variety of depositional settings. These included deltaic deposits linked to specific lake levels, pro-glacial fluvial, ice-contact and supra-glacial deposits. Single-grain OSL results indicate evidence for incomplete resetting (partial bleaching) of the luminescence signal, as expected for glacial environments, and therefore ages were calculated using a minimum age model. OSL results constrain the timing of ice-margin retreat and lake formation to 14.4–14.8 ka. Analysis of single-grain equivalent dose distributions indicates that deposits created by glacial-dominated processes typically had higher over-dispersion (>50%) and greater positive skew (>0.9) than deposits originating from fluvial processes. These results suggest that water-lain deposits should be targeted for OSL sampling over those created by glacial processes when dating ice-proximal settings. 相似文献
9.
Proliferation of coastal observatories necessitates an objective approach to managing of observational assets. In this article, we used our experience in the coastal observatory for the Columbia River estuary and plume to identify and address common problems in managing of fixed observational assets, such as salinity, temperature, and water level sensors attached to pilings and moorings. Specifically, we addressed the following problems: assessing the quality of an existing array, adding stations to an existing array, removing stations from an existing array, validating an array design, and targeting of an array toward data assimilation or monitoring. 相似文献
10.
The full solution for the wavenumber equation in electromagnetic (EM) theory is available, but not routinely used when processing ground penetrating radar (GPR), and electromagnetic induction (EMI) data. The wavenumber approach is important as it is used for the development of concepts such as skin depth and phase velocity, as well as being the basis for more complete interpretation of EM data sets. Approximations that make the solution simpler are common, and sufficiently accurate, provided that the underlying assumptions are not grossly violated. With the advent of lower-frequency GPR systems (25 MHz and below) and higher-frequency EMI systems (greater than 100 kHz) such approximations need to be re-examined. This paper reviews the full wavenumber expression and then compares phase velocity and skin depth equations based on approximations with the equations for the same parameter based on the full solution. This comparison allows the conditions under which the assumptions are valid to be refined. In this paper it is shown that for GPR surveys conducted under transition band conditions, the error in phase velocity estimates based on low-loss assumptions may be 40%. Similarly, for EMI surveys the skin depth estimation errors may be more than 30% when the equation based on quasi-static assumptions is used instead of the full solution. 相似文献