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61.
Bruce Mitchell 《Singapore journal of tropical geography》1995,15(2):145-156
Developing and implementing sustainable development strategies involve overcoming many obstacles. The experience in Bali, Indonesia, illustrates some key institutional challenges which most countries must handle to achieve sustainable development, such as realising cross-sectoral integration, combining top-down and bottom-up planning, and creating credibility for a new policy initiative. Indonesia in general and Bali in particular has, in theory, considerable capability to implement sustainable development. However, as in most countries, effective practice does not always follow from theoretical potential. Strengths and weaknesses related to institutional challenges are identified and assessed, and their general implications are considered. Some key implications are the need to develop sustainable development strategies which reflect the conditions and needs specific to the targetted region, and to address different national and regional perspectives. 相似文献
62.
The Australian Government policy on reduction of greenhouse gas emissions announced in 1990 includes exploring the scope for immediate, low cost reductions. Such measures can be taken as including ‘no regrets’ policies: those that, in addition to mitigating potential climate change, confer economic gains (including other environmental benefits) which exceed their costs. Some possible ‘no regrets’ opportunities and policies are identified relevant to energy use by the road transport sector over the period to 2020. The MARKALMENSA multi-period linear programming model of the Australian energy sector is used to investigate the cost-effectiveness of these policies. 相似文献
63.
Robert S. Webb Jonathan T. Overpeck David M. Anderson Bruce A. Bauer Mildred K. England Wendy S. Gross E. Ann Meyers Michael M. Worobec 《Journal of Paleolimnology》1993,9(1):69-75
Conclusion The World Data Center-A for Paleoclimatology, located in the NOAA/NGDC Paleoclimatology Program, is committed to providing the scientific community with easy access to all paleoenvironmental data. Efforts to make archived data readily available include international coordination of data acquisition, management, and distribution, sponsoring workshops and data cooperatives to facilitate the compilation of important data sets, development of a browse and visualization software package (PaleoVu), and dispersal of archived data on magnetic media or over ANONYMOUS FTP/INTERNET. The program publishes a semi-annual newsletter that highlights latest developments and accomplishments in the area of paleoenvironmental data for global change research. Contributions to the newsletter are welcome from researchers describing their efforts to coordinate the free flow of paleoclimate data throughout the international scientific community.For information on the program or to be added to the mailing list contact Mrs Mildred England (phone: 303-497-6227; Fax: 303 497-6513; e-mail: MKE@mail.ngdc.noaa.gov), NOAA National Geophysical Data Center, Paleoclimatology Program/World Data Center-A for Paleoclimatology, 325 Broadway, E/GC Boulder, CO 80303 USA 相似文献
64.
The behavior of apatite during crustal anatexis: Equilibrium and kinetic considerations 总被引:5,自引:0,他引:5
The solubility and dissolution kinetics of apatite in felsic melts at 850°–1500°C have been examined experimentally by allowing apatite crystals to partially dissolve into apatite-undersaturated melts containing 0–10 wt% water. Analysis of P and Ca gradients in the crystal/melt interfacial region enables determination of both the diffusivities and the saturation levels of these components in the melt. Phosphorus diffusion was identified as the rate-limiting factor in apatite dissolution. Results of four experiments at 8 kbar run in the virtual absence of water yield an activation energy (E) for P diffusion of 143.6 ± 2.8 kcal-mol?1 and frequency factor (D0) of 2.23+2.88?1.26 × 109cm2-sec?1. The addition of water causes dramatic and systematic reduction of both E and D0 such that at 6 wt% H2O the values are ~25 kcal-mol?1 and 10?5 cm2-sec?1, respectively. At 1300°C, the diffusivity of P increases by a factor of 50 over the first 2% of water added to the melt, but rises by a factor of only two between 2 and 6%, perhaps reflecting the effect of a concentration-dependent mechanism of H2O solution. Calcium diffusion gradients do not conform well to simple diffusion theory because the release of calcium at the dissolving crystal surface is linked to the transport rate of phosphorus in the melt, which is typically two orders of magnitude slower than Ca. Calcium chemical diffusion rates calculated from the observed gradients are about 50 times slower than calcium tracer diffusion.Apatite solubilities obtained from these experiments, together with previous results, can be described as a function of absolute temperature (T) and melt composition by the expression: In Dapatite/meltP = [(8400 + ((SiO2 ? 0.5)2.64 × 104))/T] ? [3.1 + (12.4(SiO2 ? 0.5))] where SiO2 is the weight fraction of silica in the melt. This model appears to be valid between 45% and 75% SiO2, 0 and 10% water, and for the range of pressures expected in the crust.The diffusivity information extracted from the experiments can be directly applied to several problems of geochemical interest, including I) dissolution times for apatite during crustal anatexis, and 2) pileup of P, and consequent local saturation in apatite, at the surfaces of growing major-mineral phases. 相似文献
65.
Any oxide and silicate mineral which is nominally anhydrous but crystallized in the presence of H2O incorporates traces of H2O in solid solution. In the case of MgO it can be shown that OH? pairs convert into H2+O 2 2? . If the H2 molecules are lost, the O 2 2? remain in the lattice as excess oxygen stabilized by excess cation vacancies. When the O 2 2? anions decay either thermally or by decompression unbound O? states (positive holes) are generated which lead to surface charges and subsurface space charge layers. Calculated space charge profiles are presented. O? concentrations as small as 10–20 ppm suffice to create electric surface fields of the order of 4·107 V·m?1. The diffusion mechanism which derives from these premises incorporates novel features: the cation diffusion is coupled to the counterdiffusion of unbound and vacancy-bound O? states. The cation diffusion is predicted to be very fast because first, it is field-enhanced (electrochemically driven) and second, it is not rate-limited by the intrinsic cation vacancy concentration nor by the counter-diffusion of other cations. The model may apply to cases of inverse zoning and diffusion rim formation in minerals under certain P-T conditions. 相似文献
66.
Pyroclastic rocks: another manifestation of ultramafic volcanism on Gorgona Island,Colombia 总被引:5,自引:0,他引:5
Tertiary ultramafic volcanism on Gorgona Island, Colombia, is manifested not only by komatiite flows, but also by a more voluminous sequence of tuff breccias, which is cut by comagmatic picrite dikes. The ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically-deformed, glassy globules. The entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst-laden picritic magma. MgO contents of tuff breccias and picrite dikes range from 21 to 27 wt%. Relative to nearby komatiite flows, these rocks are MgO-rich, and FeO-, TiO2- and Ni-poor. HREE concentrations are very low (N<0.2), indicating derivation from a more highly depleted mantle source region. Nd isotopic data suggest a cogenetic relationship between the picritic magma that formed the tuff breccia and associated dikes and that which produced the komatiite flows. Nevertheless Pb isotopic data as well as whole rock geochemistry preclude such a connection, either due to olivine fractionation/accumulation or to different degrees of partial melting. These ultramafic rock types crystallized from magmas which most likely were extracted from distinct mantle source regions. 相似文献
67.
A combination of both water chemistry and sedimentological information was used to investigate the carbonate-producing mechanism
in Littlefield Lake, a small lake located in Isabella County, central Michigan. Data on temperature, dissolved oxygen, pH,
calcium carbonate (CaCO3) saturation, alkalinity, calcium, and magnesium were obtained on a monthly basis over a 13-month period, with each parameter
determined at 1m intervals over a depth range of 20m. The loss of dissolved carbon dioxide (CO2) from warm surface waters during direct degassing, and to a lesser extent during photosynthetic uptake by lacustrine macrophytes
and phytoplankton during the summer, results in massive precipitation of the low-magnesium calcite which predominates in all
Littlefield Lake sedimentary facies However, despite the fact that carbonate precipitation in this rather typical temperate-region
marl lake is directly related to, and may be driven by, seasonal variation in these physiochemical parameters, most calcite
forms as encrustations around cyanophytic and chlorophytic macrophytes. Such relationships demonstrate that carbonate precipitation
in marl lakes may result from complex interactions between both biochemical and physiochemical processes. As such, marl formation
in this, and probably many other calcareous lake systems, can not be simply ascribed to one or the other of these two general
mechanisms. 相似文献
68.
Richard M. Adams Ronald A. Fleming Ching-Chang Chang Bruce A. McCarl Cynthia Rosenzweig 《Climatic change》1995,30(2):147-167
This study uses recent GCM forecasts, improved plant science and water supply data and refined economic modeling capabilities to reassess the economic consequences of long-term climate change on U.S. agriculture. Changes in crop yields, crop water demand and irrigation water arising from climate change result in changes in economic welfare. Economic consequences of the three GCM scenarios are mixed; GISS and GFDL-QFlux result in aggregate economic gains, UKMO implies losses. As in previous studies, the yield enhancing effects of atmospheric CO2 are an important determinant of potential economic consequences. Inclusion of changes in world food production and associated export changes generally have a positive affect on U.S. agriculture. As with previous studies, the magnitude of economic effects estimated here are a small percentage of U.S. agricultural value. 相似文献
69.
70.
Bruce A. Macler 《Ground Water Monitoring & Remediation》1995,15(4):77-84
The Safe Drinking Water Act directs EPA to promulgate requirements for disinfection of ground water-based drinking water systems. The Ground- water Disinfection Rule regulatory workgroup, made up of representatives from EPA, the states, and other interested parties, is actively considering the issues for the wide range of elements necessary to ensure a regulation that will protect public health and can be feasibly implemented. This regulation is likely to require disinfection of ground water sources and systems found to be contaminated or vulnerable to contamination. 相似文献