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排序方式: 共有598条查询结果,搜索用时 281 毫秒
501.
Brose U Jonsson T Berlow EL Warren P Banasek-Richter C Bersier LF Blanchard JL Brey T Carpenter SR Blandenier MF Cushing L Dawah HA Dell T Edwards F Harper-Smith S Jacob U Ledger ME Martinez ND Memmott J Mintenbeck K Pinnegar JK Rall BC Rayner TS Reuman DC Ruess L Ulrich W Williams RJ Woodward G Cohen JE 《Ecology》2006,87(10):2411-2417
It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types. 相似文献
502.
Thomas K. Maurer 《补救:环境净化治理成本、技术与工艺杂志》1995,5(2):15-20
Thousands of contaminated sites around the country never get caught in the sticky web of Superfund. Instead, they are handled by state environmental agencies under state environmental laws and rules. Generally speaking, state environmental programs appear to function much more efficiently than Superfund. But even though they are easier to work with than Superfund, state contamination cleanup programs can still be daunting. This article offers some points and suggestions for making the state process work smoothly and efficiently. 相似文献
503.
504.
Sylke Ritter Werner H. Hauthal Gerd Maurer 《Environmental science and pollution research international》1995,2(3):153-160
Partition coefficients PO,w
(i) describing the distribution of a solute i onto coexisting phases of 1-octanol and water are needed in a large variety of
applications. They can be measured directly by HPLC as long as log PO,w
(i)≧ 3.5. For more hydrophobic substances, several experimental procedures have been proposed in the literature. The reliability
of those methods is questionable. Therefore, in the present work, PO,w
(i) is determined experimentally by three HPLC methods using reversed-phase HPLC [1]. Results from different procedures are compared
critically. The method of Braumann [2] proved to be superior over the OECD-guidelines [3]. It was therefore applied to determine
octanol/water partition coefficients for 23 substances at 25 °C. For eight of those substances (4-methylindole; 9-(hydroxymethyl)anthracene;
N-ethylcarbazol; ethylcyclohexane; trans-2-octene; l,l-dimethyl-(ethy])cyclohexane; heptylbenzene; 4-dodecyl-l,3-benzenediol)
no experimentally determined number for PO,w
(i) has been published before. 相似文献
505.
506.
507.
508.
509.
Nunn AJ Kozovits AR Reiter IM Heerdt C Leuchner M Lütz C Liu X Lo W M Winkler JB Grams TE Häberle KH Werner H Fabian P Rennenberg H Matyssek R 《Environmental pollution (Barking, Essex : 1987)》2005,137(3):494-506
Chamber experiments on juvenile trees have resulted in severe injury and accelerated loss of leaves along with reduced biomass production under chronically enhanced O3 levels. In contrast, the few studies conducted on adult forest trees in the field have reported low O3 sensitivity. In the present study, young beech in phytotrons was more sensitive to O3 than adult beech in the field, although employed O3 regimes were similar. The hypotheses tested were that: (1) differences in O3 uptake were caused by the ontogenetically higher stomatal conductance of young compared to adult trees, (2) the experimental settings in the phytotrons enhanced O3 uptake compared to field conditions, and (3) a low detoxification capacity contributes to the higher O3 sensitivity of the young trees. The higher O3 sensitivity of juvenile beech in the phytotrons is demonstrated to relate to both the experimental conditions and the physiological responsiveness inherent to tree age. 相似文献
510.
Fischer A Oehm C Selle M Werner P 《Environmental science and pollution research international》2005,12(6):381-386
Background Methyl tertiary butyl ether (MTBE) is a fuel additive which is used all over the world. In recent years it has often been
found in groundwater, mainly in the USA, but also in Europe. Although MTBE seems to be a minor toxic, it affects the taste
and odour of water at concentrations of < 30 μg/L. Although MTBE is often a recalcitrant compound, it is known that many ethers
can be degraded by abiotic means. The aim of this study was to examine biotic and abiotic transformations of MTBE with respect
to the particular conditions of a contaminated site (former refinery) in Leuna, Germany.
Methods Groundwater samples from wells of a contaminated site were used for aerobic and anaerobic degradation experiments. The abiotic
degradation experiment (hydrolysis) was conducted employing an ion-exchange resin and MTBE solutions in distilled water. MTBE,
tertiary butyl formate (TBF) and tertiary butyl alcohol (TBA) were measured by a gas chromatograph with flame ionisation detector
(FID). Aldehydes and organic acids were respectively analysed by a gas chromatograph with electron capture detector (ECD)
and high-performance ion chromatography (HPIC).
Results and Discussion Under aerobic conditions, MTBE was degraded in laboratory experiments. Only 4 of a total of 30 anaerobic experiments exhibited
degradation, and the process was very slow. In no cases were metabolites detected, but a few degradation products (TBF, TBA
and formic acid) were found on the site, possibly due to the lower temperatures in groundwater. The abiotic degradation of
MTBE with an ion-exchange resin as a catalyst at pH 3.5 was much faster than hydrolysis in diluted hydrochloric acid (pH 1.0).
Conclusion Although the aerobic degradation of MTBE in the environment seems to be possible, the specific conditions responsible are
widely unknown. Successful aerobic degradation only seems to take place if there is a lack of other utilisable compounds.
However, MTBE is often accompanied by other fuel compounds on contaminated sites and anaerobic conditions prevail. MTBE is
often recalcitrant under anaerobic conditions, at least in the presence of other carbon sources. The abiotic hydrolysis of
MTBE seems to be of secondary importance (on site), but it might be possible to enhance it with catalysts.
Recommendation and Outlook MTBE only seems to be recalcitrant under particular conditions. In some cases, the degradation of MTBE on contaminated sites
could be supported by oxygen. Enhanced hydrolysis could also be an alternative.
- * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on 'Chemistry and Environment', 29 August
to 1 September 2004, Bordeaux, France. 相似文献