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481.
Embryos of Fundulus heteroclitus in the 4–8 cell stage were exposed nine Hg++ (as mercuric chloride) concentrations from 0 to 100 μg/litre (ppb) for 32 days, 5 days, 2 days and 1 day. All but the chronically (32-day) exposed embryos were allowed to continue development in mercury-free water (20% S) after the exposure period to determine the effect of duration of exposure on three parameters of development. Ninety-six hour survival, total hatching success and per cent incidence of lateral spinal curvature were measured. Only embryos exposed to mercury for a single day showed a significant increase in survival in comparison with embryos exposed for a longer period of time after four days of development. Under all conditions of exposure, survival was reduced at concentrations greater than 40 ppb Hg++. Hatching success of chronically exposed embryos was significantly reduced at concentrations greater than 10 ppb Hg++. Significant increases in total hatchability were effected by reducing the duration of exposure to five days and one day. Of eleutheroembryos emerging following chronic exposure to mercury, increases in the incidence of lateral spinal curvature were noted at all concentrations above 20 ppb Hg++. Significant reductions of this disorder were observed among eleutheroembryos exposed to mercury for 5 days, 2 days or 1 day. Of the three parameters measured, the incidence of lateral spinal curvature and the resulting VH50 value gave a more sensitive evaluation of the embryotoxic effects of Hg++ as mercuric chloride on the estuarine teleost, Fundulus heteroclitus. 相似文献
482.
The Environmental Fluid Dynamic Code, an estuarine and coastal ocean circulation model, is used to simulate the distribution
of the salinity plume in the vicinity of the mouth of the Cape Fear River Estuary, North Carolina. The individual and coupled
effects of the astronomical tides, river discharge, and atmospheric winds on the spatial and temporal distributions of coastal
water levels and the salinity plume were investigated. These modeled effects were compared with water level observations made
by the National Oceanic and Atmospheric Administration and salinity surveys conducted by the Coastal Ocean Research and Monitoring
Program. Model results and observations of salinity distributions and coastal water level showed good agreement. The simulations
indicate that strong winds tend to reduce the surface plume size and distort the bulge shape near the estuary mouth due to
enhanced wind-induced surface mixing. Under normal discharge conditions, tides, and light winds, the southward outwelling
plume veers west. Relatively moderate winds can mechanically reverse the flow direction of the plume. Under conditions of
weak to moderate winds the water column does not mix vertically to the bottom, while in strong wind cases the plume becomes
vertically well mixed. Under conditions of high river discharge the plume increases in size and reaches the bottom. Vertical
mixing induced by strong spring tides can also enable the plume to reach the bottom. 相似文献
483.
For two decades leading to the late 1980s, the prevailing view from studies of glacial isostatic adjustment (GIA) data was that the viscosity of the Earth's mantle increased moderately, if at all, from the base of the lithosphere to the core–mantle boundary. This view was first questioned by Nakada & Lambeck , who argued that differential sea-level (DSL) highstands between pairs of sites in the Australian region preferred an increase of approximately two orders of magnitude from the mean viscosity of the upper to the lower mantle, in accord with independent inferences from observables related to mantle convection. We use non-linear Bayesian inference to provide the first formal resolving power analysis of the Australian DSL data set. We identify three radial regions, two within the upper mantle (110–270 km and 320–570 km depth) and one in the lower mantle (1225–2265 km depth), over which the average of viscosity is well constrained by the data. We conclude that: (1) the DSL data provide a resolution in the inference of upper mantle viscosity that is better than implied by forward analyses based on isoviscous regions above and below the 670 km depth discontinuity and (2) the data do not strongly constrain viscosity at either the base or top of the lower mantle. Finally, our inversions also quantify the significant bias that may be introduced in inversions of the DSL highstands that do not simultaneously estimate the thickness of the elastic lithosphere. 相似文献
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486.
Mathematical Geosciences - 相似文献
487.
Jerry C. Ritchie Jeffrey E. Herrick Carole A. Ritchie 《Journal of Arid Environments》2003,55(4):737-746
A hypothesis for understanding the stability of northern Chihuahuan Desert landscapes is that the distribution of soil resources changes from spatially homogeneous in arid grasslands to spatially heterogeneous in invading shrublands. Since radioactive fallout 137Cesium (137Cs) was deposited uniformly across the landscape during the 1950s and 1960s and was quickly adsorbed to soil particles, any redistribution of 137Cs across the landscape would be due to soil redistribution or instability at either plant-interspaces or on a landscape scale. The concentration of 137Cs in soils collected from different vegetation communities (black grama grass, tarbush, tobosa grass, and mesquite) at the USDA-ARS Jornada Experimental Range in the Northern Chihuahuan Desert in New Mexico was determined. At the black grama grass and tobosa grass sites, 137Cs was uniformly distributed at the plant interspace scale. At the mesquite sites, 137Cs was concentrated in the dune area under mesquite shrubs with little to no 137Cs in the interdune areas. 137Cs data support the hypothesis that significant soil redistribution has occurred at dune sites created by invading mesquite. In the arid grassland-shrub sites with black grama grass, tobosa grass, and tarbush the 137Cs data support the hypothesis of spatially homogeneous distribution of soil resources. High concentrations of 137Cs in the biological soil crusts (0–5 mm) at the tarbush sites indicate that biological soil crusts can contribute to the stability of these sites. 相似文献
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489.
Carmen Morales José F. Gómez Joaquín Trapero Stuart Bowyer Jerry Edelstein Eric Korpela 《Astrophysics and Space Science》1998,263(1-4):393-396
EURD (Espectrógrafo Ultravioleta extremo de Radiación Difusa), one of the instruments onboard the Spanish satellite MINISAT-01,
is a spectrograph specially designed to detect diffuse radiation, covering the wavelength range of 350-1100 Å, with a spectral
resolution of 6-8 Å. Its main scientific objectives are the detection of the emission line spectrum from the hot phase of
the interstellar medium and the spectrum of the upper atmospheric airglow. In order to reduce geocoronal noise, EURD always
observes in the anti-sun direction and only when the satellite is in orbital eclipse. After more than one year of observation
we have obtained the best spectrum of the upper atmospheric nightglow in this wavelength range, the spectrum of 15 OB stars
and the spectrum of the full Moon throughout the year.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
490.
Women, Disempowerment and Resistance: An Analysis of Logging and Mining Activities in the Pacific 总被引:1,自引:0,他引:1
There are many arguments supporting the need for a reduction of large scale logging and mining activities in Pacific Island countries. In addition to ecological and economic concerns, logging and mining have had significant social impacts, including gendered impacts. Women tend to be excluded from decision-making processes, and they have limited access to royalty payments and business and employment opportunities which emerge. Women also bear a disproportionate share of the responsibility for dealing with the social and environmental mess which accumulates. However, women are not simply passive victims of logging and mining activities, as this discussion of the Solomon Islands and Papua New Guinea will argue. They are often the first to feel dissatisfaction with logging and mining and it is such dissatisfaction which has fuelled civil unrest, from family break-ups to sabotage of machinery to civil war, in some communities. It may thus be useful for companies to more carefully monitor the effects of their activities on women and involve women more actively in decision-making bodies if they wish to avoid such unrest in the future. 相似文献