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941.
Porewater chemistry in compacted re-saturated MX-80 bentonite 总被引:2,自引:0,他引:2
Bentonites of various types are being investigated in many countries as backfill materials in high-level radioactive waste disposal concepts. Being able to understand the chemistry of the porewater in compacted bentonite is very important since it is critical to predicting radionuclide solubilities and to the synthesis of sorption data bases, and hence to repository safety studies. In this paper, porewater compositions in compacted bentonites are calculated, taking into consideration such factors as montmorillonite swelling, semi-permeable membrane effects, very low "free water" volumes, and the highly effective buffering characteristics of the exchangeable cations and the amphoteric edge sites. The former buffer the cation concentrations and the latter fix the pH in the porewater of a re-saturated bentonite. The above considerations are used in conjunction with previously measured physico-chemical characterisation data on MX-80 powder to calculate porewater compositions in compacted bentonites. For the MX-80 material specified, the porewaters calculated for initial dry densities between 1200 and 1600 kg m(-3) had relatively high ionic strengths (I approximately 0.3 M), similar cation concentrations and a pH equal to 8.0. The porewaters changed from being Na(2)SO(4)-rich at 1200 kg m(-3) to a NaCl/Na(2)SO(4) type water at 1600 kg m(-3). 相似文献
942.
Derwent RG Stevenson DS Doherty RM Collins WJ Sanderson MG Johnson CE Cofala J Mechler R Amann M Dentener FJ 《Ambio》2005,34(1):54-59
A global three-dimensional Lagrangian chemistry-transport model STOCHEM is used to describe the European regional acid deposition and ozone air quality impacts along the Atlantic Ocean seaboard of Europe, from the SO2, NOx, VOCs and CO emissions from international shipping under conditions appropriate to the year 2000. Model-derived total sulfur deposition from international shipping reaches over 200 mg S m(-2) yr(-1) over the southwestern approaches to the British Isles and Brittany. The contribution from international shipping to surface ozone concentrations during the summertime, peaks at about 6 ppb over Ireland, Brittany and Portugal. Shipping emissions act as an external influence on acid deposition and ozone air quality within Europe and may require control actions in the future if strict deposition and air quality targets are to be met. 相似文献
943.
Four phosphorus forms were investigated as potential soil amendments to decrease the bioavailability of Pb and Zn in two repository soils to the earthworm, Eisenia fetida. Treatments were evaluated by examining differences in bioaccumulation factors between amended and non-amended soils. Triple super phosphate at 5000 mg P/kg decreased both Pb and Zn bioavailability in both soils. Rock phosphate at 5000 mg P/kg decreased Zn bioavailability, but not Pb bioavailability in both repository soils. Monocalcium phosphate and tricalcium phosphate at 5000 mg P/kg did not significantly decrease Pb or Zn bioavailability to earthworms in either repository soil. In order to optimize phosphorus amendments, additional phosphorus (up to 15,000 mg P/kg) and lowered pH were used in a series of tests. The combination of lowering the pH below 6.0 and increasing phosphorus concentrations caused complete mortality in all triple super phosphate amended soils and partial mortality in the highest rock phosphate amended soils. Results indicate that triple super phosphate and rock phosphate are viable soil amendments, but care should be taken when optimizing amendment quantity and pH so that adverse environmental effects are not a by-product. 相似文献
944.
Jürgen Burhenne Marc Ludwig Michael Spiteller 《Environmental science and pollution research international》1997,4(2):61-67
Subsequent to irradiation with a xenon lamp simulating sunlight, fluoroquinolone carboxylic acids in aqueous solution form
polar pyridone dicarboxylic and tricarboxylic acids. After liquid/liquid partition with chloroform/water these substances
can be isolated by ion exchange chromatography of the aqueous phase. They can be regarded as intermediate compounds on the
route to a complete photomineralization. The structural elucidation is performed by such mass spectroscopic methods as MS,
GC/MS and HPLC/MS, whereby HPLC/MS shows the highest reliability. Additionally1H- and13C-NMR measurements confirm the structure of the main polar degradation product. 相似文献
945.
Die Modellierung des Ausbreitungsverhaltens von Stoffen unterschiedlicher Eigenschaften in der Umwelt stellt eine Herausforderung
dar, da die zugrundeliegenden physikalischen Transport-, chemischen Reaktions- und biologischen An- oder Abreicherungsprozesse
zeitlich variabel in r?umlich heterogen strukturierten Umweltsystemen wirken. Durch geschickt gew?hlte Vereinfachungen, Abgrenzungen
und Mittelungen sind bemerkenswerte Erfolge bis hin zur bedingt-prognostischen Simulation ausgew?hlter Stoffe und Stoffgruppen
erzielt worden. Forschungsbedarf besteht vor allem in der Modellierung der kleinr?umigen, medienübergreifenden Ausbreitung
von Stoffen in komplexen ?kosystemaren Zusammenh?ngen, einschlie?lich der Austausch- und Transfervorg?nge und der chemisch-biologischen
Transformationen.
Bericht vom 32. Tutzing-Symposium der DECHEMA e.V., 7. bis 10. M?rz 1994 相似文献
946.
Farming Endangered Turtles to Extinction in China 总被引:1,自引:0,他引:1
947.
Pat M. Fidopiastis Daniel J. Bezdek Michael H. Horn Judith S. Kandel 《Marine Biology》2006,148(3):631-642
The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive
tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California
(33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment,
and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse,
fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared
to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron
micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute
resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to
three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of
bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified,
Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the
breakdown of algal polysaccharides in the herbivorous diet of the fish. 相似文献
948.
Alternative male mating tactics in a cichlid, Pelvicachromis pulcher: a comparison of reproductive effort and success 总被引:2,自引:0,他引:2
Pelvicachromis pulcher is a small African cichlid which breeds in holes. Males may either reproduce monogamously (pair males), polygynously (harem
males), or be tolerated as helpers in a harem territory (satellite males). These helpers share in defence of the territory
against conspecifics, heterospecific competitors and predators. There are two male colour morphs that are fixed for life and
are apparently genetically determined. These differ in their potential mating strategy. Red morph males may become harem owners,
while yellow morph males may become satellite males, and males of both morphs may alternatively pair up monogamously. We compared
the reproductive effort and success of these three male reproductive strategies. Effort was measured as attack rates, time
expenditure and the risk of being injured or killed when attacking competitors or predators of three sympatric fish species.
Reproductive success was measured by observing how many eggs were fertilized by each male when this was possible, and by using
genetic markers. The number of fry surviving to independence of parental care was used as a criterion of success. The reproductive
success of harem males was 3.3 times higher than that of pair males and 7 times higher than that of the average satellite
male. Dominant satellite males, however, were as successful as monogamous pair males, using the measure of fertilized eggs.
To our knowledge, this has not been found previously in any fish species. Both harem and pair males had lower parental defence
costs per sired offspring, however, than males using the alternative satellite tactic. Defence effort was significantly related
to the risk of injury.
Received: 17 January 1996 / Accepted after revision: 9 June 1997 相似文献
949.
Threats to Imperiled Freshwater Fauna 总被引:10,自引:0,他引:10
Brian D. Richter David P. Braun Michael A. Mendelson & Lawrence L. Master 《Conservation biology》1997,11(5):1081-1093
Threats to imperiled freshwater fauna in the U.S. were assessed through an experts survey addressing anthropogenic stressors and their sources. Specifically, causes of historic declines and current limits to recovery were identified for 135 imperiled freshwater species of fishes, crayfishes, dragonflies and damselflies, mussels, and amphibians. The survey was designed to identify threats with sufficient specificity to inform resource managers and regulators faced with translating information about predominant biological threats into specific, responsive actions. The findings point to altered sediment loads and nutrient inputs from agricultural nonpoint pollution; interference from exotic species; and altered hydrologic regimes associated with impoundment operations as the three leading threats nationwide, accompanied by many lesser but still significant threats. Variations in threats among regions and among taxa were also evident. Eastern species are most commonly affected by altered sediment loads from agricultural activities, whereas exotic species, habitat removal/damage, and altered hydrologic regimes predominate in the West. Altered sediment loading from agricultural activities and exotic species are dominant problems for both eastern mussels and fishes. However, eastern fishes also appear to be suffering from municipal nonpoint pollution (nutrients and sediments), whereas eastern mussels appear to be more severely affected by altered nutrient impacts from hydroelectric impoundments and agricultural runoff. Our findings suggest that control of nonpoint source pollution associated with agriculture activities should be a very high priority for agricultural producers and governmental support programs. Additonally, the large number of hydropower dams in the U.S. subject to federal re-licensing in coming years suggests a significant opportunity to restore natural hydrologic regimes in the affected rivers. 相似文献
950.
Michael G. Dalton 《Journal of Environmental Economics and Management》1997,33(3):221-239
This article analyzes the welfare effects of climatic variability from global warming in a stochastic economic growth model and shows that these may be significant. An empirical analysis indicates that the effects of climate change with variability are greater than the corresponding effects without it. Effects with variability are also shown to be more sensitive to variations in the rate of climate change. 相似文献