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When fugitive methane migrates upward along boreholes of oil and gas wells, it may migrate into shallow ground water or pass through overlying soil to the atmosphere. Prior to this study, there was little information on the fate of fugitive methane that migrates into ground water. In a field study near Lloydminster, Alberta, Canada, we found hydrogeochemical evidence that fugitive methane from an oil well migrated into a shallow aquifer but has been attenuated by dissimilatory bacterial sulfate reduction at low temperature ( approximately 5 degrees C) under anaerobic conditions. Evidence includes spatial and temporal trends in concentrations of methane and sulfate in ground water and associated trends in concentrations of bicarbonate and sulfide. Within 10 m of the oil well, sulfate concentrations were low, and sulfate was enriched in both 34S and 18O. Sulfate concentrations had a strong positive correlation with delta13C values of bicarbonate, and sulfide was depleted in 34S compared to sulfate. These data indicate that bacterial sulfate reduction occurred near the production well. Near the oil well, elevated concentrations of bicarbonate were observed, and the bicarbonate was depleted in 13C. Modeling indicates that the main source of this excess 13C-depleted bicarbonate is oxidized methane. In concert with the sulfate concentration and isotope data, these results support an interpretation that in situ bacterial oxidation of methane has occurred, linked to bacterial sulfate reduction. Bacterial sulfate reduction may play a major role in bioattenuation of fugitive natural gas in ground water in western Canada. 相似文献
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It is time to move past the concept of sustainability. The realities of the Anthropocene warrant this conclusion. They include unprecedented and irreversible rates of human-induced biodiversity loss, exponential increases in per-capita resource consumption, and global climate change. These factors combine to create an increasing likelihood of rapid, nonlinear, social and ecological regime changes. The recent failure of the Rio + 20 provides an opportunity to collectively reexamine—and ultimately move past—the concept of sustainability as an environmental goal. We must face the impossibility of defining—let alone pursuing—a goal of “sustainability” in a world characterized by such extreme complexity, radical uncertainty and lack of stationarity. After briefly examining sustainability's failure, we propose resilience thinking as one possible new orientation and point to the challenges associated with translating resilience theory into policy application. 相似文献
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David Pino Harm J. J. Jonker Jordi Vilà-Guerau de Arellano Alessandro Dosio 《Boundary-Layer Meteorology》2006,121(3):537-556
The role of shear and inversion strength on the decay of convective turbulence during sunset over land is systematically studied by means of large-eddy simulations. Different decay rates have been found for the vertical and horizontal velocity fluctuations, resulting in an increase of the anisotropy for all the studied cases. Entrainment, which persists during the decay process, favours the appearance of vertical upward movements associated with a conversion from kinetic to potential energy. Particular attention is paid to the evolution of the characteristic length scale of the various turbulent variables during this process. The length scale evolution is found to depend on the wind shear characteristics, but not on the strength of the inversion. In general the length scales of the variables grow during decay because small-scale fluctuations dissipate faster than large-scale fluctuations. Only the length scale of the vertical velocity component remains nearly constant during decay. Spectral analysis of the variance budgets shows that pressure correlations are responsible for fixing this length scale, effectively compensating the strong but oscillating influence of buoyancy. In the shear cases, after an initial period of growth, the length scales start to decrease once the buoyancy-generated variance has sufficiently subsided. Also here the effect of pressure redistribution is crucial, as it transfers the spectral influence of shear to the other velocity components. 相似文献