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Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA 总被引：1，自引：2，他引：1
Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m3/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms. 相似文献
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Hydrographic data collected in cyclonic eddies in the Mozambique Channel and Basin revealed notable differences in temperature and salinity at a depth of 100 m, the upper mixed layer, the nitracline depths, and vertical distribution of chlorophyll-a (Chl-a). Differences in temperature and salinity did not show any consistent patterns. In contrast, the differences in the upper mixed layer, nitracline depths and the vertical Chl-a profile appeared to be driven by combined effects of eddy dynamics (i.e. shoaling of isopleths) and the seasonal variation in light availability and mixing conditions in the upper layers. Cyclonic eddies studied during austral spring and summer in the Mozambique Channel exhibited shallower upper mixed layers and nitracline depths, and deeper euphotic zones. Distinct subsurface Chl-a maxima (SCM) were associated with the stratified conditions in the upper layers of these eddies. In contrast, a cyclonic eddy studied during mid-austral winter in the Mozambique Basin had a shallower euphotic zone, deeper upper mixed layer and uniform Chl-a profiles. Another eddy sampled in the Mozambique Basin toward the end of winter showed a less pronounced SCM and roughly equal euphotic zone and upper mixed layer depths, suggestive of a transition from a well-mixed upper layer during winter to stratified conditions in summer. 相似文献
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PETER EMIL KALAND KNUT KRZYWINSKI BJØRG STABELL 《Boreas: An International Journal of Quaternary Research》1984,13(2):243-258
In three different areas in western Norway, large errors are obtained in the radiocarbon dates from lacustrine sediments close to marine/lacustrine sediment boundaries. Differences occur between radiocar-bon and pollenanalytic dates and between dates at isolation/ingression contacts for lakes of the same altitude above the present sea level. Younger radiocarbon dates are also obtained below older ones in undisturbed sediments. When divergent dates occur, the radiocarbon dates always seem to be the youngest. Large differences are also found between NaOH soluble and insoluble fractions of the same sediment samples. Insoluble fractions generally yield younger dates than the soluble. Differences are not found, however, for dates younger than about 8,000 B.P. The dating errors are connected to periods with more oligotrophic conditions with isoetides. Their roots penetrate older sediments. Due to contamination of the organic part of the sediment from partly decomposed roots, some radiocarbon dates will be too young. The isoetide vegetation and the dating errors disappear when the lakes become dystrophic. 相似文献
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A ROBUST PLS PROCEDURE 总被引：1，自引：0，他引：1
A robust partial least squares(PLS)regression algorithm is developed.This is achieved by substitutionof the univariate regression steps in the iterative PLS2 algorithm by a robust alternative.The anglebetween loading vectors from both perturbed and unperturbed solutions is used as a measure ofrobustness.By means of a perturbation study on a structure-activity data set,it is demonstrated thatthe stability of the robust method is superior to standard PLS. 相似文献
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During February 2010, studies of primary production (PP) and physiology were conducted at five selected sites in the KwaZulu-Natal (KZN) Bight of the Agulhas ecosystem as part of a programme to elucidate the influence of major physical driving forces and nutrient inputs on the structure and functioning of biological communities. These sites were located in the vicinity of the Durban lee eddy, in the midshelf region of the central part of the bight, off the Thukela Mouth, and to the north and south of Richards Bay. At four of the sites, chlorophyll a ranged from 0.10 to 1.44?mg m–3 and integrated PP ranged between 0.35 and 2.58?g C m–2 d–1. The highest biomass and PP, which were comparable to those observed in a wind-driven upwelling system, were associated with a diatom community observed at the midshelf site, and varied between 0.26 and 4.27?mg m–3 and 7.22 and 9.89?g C m–2 d–1, respectively. Environmental conditions at each of the sites differed substantially and appeared to be influential in initiating and controlling the development and distribution of phytoplankton biomass and production. Phytoplankton adaptation to variable environmental conditions was characterised by a decreased light-limited slope (αB) and increased rate of photosynthesis (Pm ) and light saturation (Ek) with elevated temperatures. The converse (increased αB and decreased Pm and Ek) was observed as irradiance levels declined. Generalised additive models indicated that irradiance, temperature and biomass were important variables influencing photosynthetic parameters and photosynthetic rates. 相似文献
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