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排序方式: 共有237条查询结果,搜索用时 15 毫秒
211.
Uncertainty assessment of contaminant plume length estimates in heterogeneous aquifers 总被引:1,自引:0,他引:1
The Virtual Aquifer approach is used in this study to assess the uncertainty involved in the estimation of contaminant plume lengths in heterogeneous aquifers. Contaminant plumes in heterogeneous two-dimensional conductivity fields and subject to first order and Michaelis-Menten (MM) degradation kinetics are investigated by the center line method. First order degradation rates and plume lengths are estimated from point information obtained along the plume center line. Results from a Monte-Carlo investigation show that the estimated rate constant is highly uncertain and biased towards overly high values. Uncertainty and bias amplify with increasing heterogeneity up to maximum values of one order of magnitude. Calculated plume lengths reflect this uncertainty and bias. On average, plume lengths are estimated to about 50% of the true plume length. When plumes subject to MM degradation kinetics are investigated by using a first order rate law, an additional error is introduced and uncertainty as well as bias increase, causing plume length estimates to be less than 40% of the true length. For plumes with MM degradation kinetics, therefore, a regression approach is used which allows the determination of the MM parameters from center line data. Rate parameters are overestimated by a factor of two on average, while plume length estimates are about 80% of the true length. Plume lengths calculated using the MM parameters are thus closer to the correct length, as compared to the first order approximation. This approach is therefore recommended if field data collected along the center line of a plume give evidence of MM kinetics. 相似文献
212.
213.
Mitigation and Adaptation Strategies for Global Change - The original version of this article unfortunately contained a mistake in the Acknowledgement section. 相似文献
214.
Sebastian U. Senger 《Umweltwissenschaften und Schadstoff-Forschung》2000,12(3):152-156
Zusammenfassung Im G?teborger Protokoll der UN ECE zur Bek?mpfung von Versauerung, Eutrophierung und bodennahem Ozon vom 1. Dezember 1999
werden Vorgaben zur Reduktion von Luftschadstoffkomponenten von 1990 bis 2010 festgelegt. In der vorliegenden Arbeit werden
Absch?tzungen, ob diese Werte für die Bundesl?nder NRW und Hessen erreichbar sind, gemacht. Um absch?tzen zu k?nnen, wie die
Konzentrationen einzelner Luftschadstoffe im Jahre 2010 sein werden, wurden aus den Daten der Jahre 1990-1999 die best-angepassten
Funktionen graphisch dargestellt und bis zum Jahr 2010 extrapoliert. Unter der Absch?tzung, dass die Luftschadstoffemission
sich weiterhin wie in den letzten 10 Jahren reduziert oder noch darüber hinaus verringert, wurden die bis zum Jahre 2010 zu
erwartenden prozentualen Reduktionen berechnet. Die im G?teborger Protokoll festgelegten Prozents?tze zur Reduzierung von
NOx, SO2 und NM-VOC sind nach den hier vorgelegten Absch?tzungen im Zeitraum von 1990-2010 erreichbar. Für CO, O3 und CO2 werden nur deutliche Abnahmen verlangt. Nach den vorliegenden Absch?tzungen werden CO um ca. 70% und O3 nur über verkehrsarmen, waldreichen Gebieten abnehmen. Für das globale Gas CO2 kann nur eine konstante Zunahme abgesch?tzt werden.
Online-First: 19. May 2000 相似文献
215.
In the last few years there has been a growing interest in transport policy concerning behaviour oriented ‘soft’ measures to reduce private car use. Besides an assessment of the methodological quality of available evaluation results, the present paper focuses on a quantitative, meta-analytical synthesis of this empirical evidence. For these purposes a data set of 141 studies evaluating three types of soft transport policy measures was compiled mainly from already published narrative research reviews. The ability to draw strong causal inferences from the available research evidence is limited by the fact that all the retrieved evaluation studies use weak quasi-experimental designs. At least for one policy measure type our analyses also indicate the presence of a reporting bias. Across all three soft policy measures we found a statistically significant random-effects pooled effect size of 0.15. Translated into the original metric such an effect size indicates an increase in the no-car use proportion from 39% to 46%. 相似文献
216.
Marvin Brinke Walter Traunspurger Sebastian Höss Peter Heininger 《Environmental Sciences Europe》2009,21(3):248-251
The aim of this short article is to deliver insight into the prospects and constraints of model ecosystems in the assessment of effects of contaminants on benthic communities, especially the meiofauna. Numerous substances accumulate in sediments and thus a complex contamination exists which is able to impair benthic organisms. Besides direct effects, indirect effects are of importance and should be considered. Changes in competition and predator-prey-relationships lead to a variety of effects in the benthic food web that cannot be explained by direct toxicity of contaminants. In this article two microcosm studies, one with the heavy metal cadmium and one with the veterinary pharmaceutical Ivermectin, are presented which both showed direct as well as indirect effects. A significant change in abundance and composition of the meiofauna community has been observed. The prediction of field-effects of a certain substance as well as the interpretation of field data are the aims of model ecosystems. Both studies proofed that the investigation of meiofauna in microcosms is a promising tool to achieve these aims. Furthermore, microcosms with meiofauna might be able to assist the effect-directed analysis (EDA) in a risk assessment by identifying the effect-causing contaminants of complex environmental samples. 相似文献
217.
Jessica Haapkylä Adrian S. Seymour Orit Barneah Itzchak Brickner Sebastian Hennige David Suggett David Smith 《Marine Biology》2009,156(5):1021-1027
This is the first quantitative study on the prevalence of epizoic Waminoa sp. acoel worms and their association with corals in the Wakatobi Marine National Park (WMNP), South-East Sulawesi, Indonesia.
Three replicate transects were laid on the reef crest, flat and slope at six sites in 2006 and eight sites in 2007. Four of
the sites were common in both years. In total 69 transects were surveyed in 2006, and 87 transects in 2007. A total of 4.8%
of all observed hard corals were associated with acoel worms in 2006 and 2.6% of hard and soft corals in 2007. Acoels were
present on 16 and 21 of the coral taxa studied in 2006 and 2007 respectively. The worms were strongly associated with the
azooxanthellate coral Tubastrea spp. and were rare or absent on the most abundant coral genera Montipora and Porites. The mean number of corals having acoels was highest on reef slopes, whereas acoels were virtually absent on reef flats. Corals
that had a high and a medium cover of worms were more common in 2007 than in 2006. No significant trend in the adaptation
of the zooxanthellae of Waminoa sp. to different depths at different sites was revealed. The impact of the worm on the coral is unknown, but high numbers
may have a shading effect and a negative impact on the coral’s photophysiology. This acoel merits more study of its life cycle,
its photophysiology, and its impact on its host corals.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
218.
Ian Moffatt 《国际发展与全球生态学杂志》2013,20(2):131-150
This paper discusses some of the potentials, problems, policies and progress in modelling sustainable development. After briefly describing ten approaches to modelling sustainable development, some of the methodological problems still to be resolved are addressed. It is then suggested that policies to promote sustainable development should operate at six different spatial levels connecting global, multinational, national, regional, local and individual. Attempting to model sustainable development in such a hierarchical manner is exceedingly difficult. One way of modelling sustainable development is to develop the concept of a sustainable corridor, combining ecological, economic and equity considerations in a hierarchical fashion and through space-time. A preliminary dynamic, hierarchical model is described connecting global and national patterns of development. Using global and national data for Scotland, the calibrated model, running under the business-as-usual scenario, shows that current development paths are unsustainable. It is shown that, by implementing a judicious choice of policies, a sustainable corridor for a global and a national system can be achieved. The ways in which this preliminary model can be developed to connect all six hierarchical levels are discussed. 相似文献
219.
Ian Moffatt 《国际发展与全球生态学杂志》2013,20(4):242-250
Seven measures of sustainable development for Scotland are examined for the period 1980-1993. These measures are green net national product, genuine savings, ecological footprint, environmental space, human appropriation of net primary production, the index of sustainable economic welfare and the genuine progress indicator. Very different messages concerning sustainable development in Scotland emerge from these measures. 相似文献
220.
Werle S 《Waste management (New York, N.Y.)》2012,32(4):753-758
Gasification of sewage sludge can provide clean and effective reburning fuel for combustion applications. The motivation of this work was to define the reburning potential of the sewage sludge gasification gas (syngas). A numerical simulation of the co-combustion process of syngas in a hard coal-fired boiler was done. All calculations were performed using the Chemkin programme and a plug-flow reactor model was used. The calculations were modelled using the GRI-Mech 2.11 mechanism. The highest conversions for nitric oxide (NO) were obtained at temperatures of approximately 1000-1200 K. The combustion of hard coal with sewage sludge-derived syngas reduces NO emissions. The highest reduction efficiency (>90%) was achieved when the molar flow ratio of the syngas was 15%. Calculations show that the analysed syngas can provide better results than advanced reburning (connected with ammonia injection), which is more complicated process. 相似文献