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871.
Albert M McGartland Wallace E Oates 《Journal of Environmental Economics and Management》1985,12(3):207-228
This paper develops a modified system of marketable emission permits that promises both savings in abatement costs to sources and improved environmental quality relative to an initial command-and-control (CAC) outcome. Using a model of TSP emissions for the Baltimore Air Quality Control Region (AQCR), a series of simulation exercises indicates that such a permit system could generate large cost savings while inducing significant reductions in TSP concentrations as compared to the existing CAC regime in Baltimore. 相似文献
872.
Ecological theory suggests that environmental variability can promote coexistence, provided that species occupy differential niches. In this study, we focus on two questions: (1) Do allocation trade-offs provide a sufficient basis for niche differentiation in succulent plant communities? (2) What is the relative importance of different forms of environmental variability on species diversity and community composition? We approach these questions with a generic, individual-based simulation model. In our model, plants compete for water in a spatially explicit environment. Species differ in their size at maturity and in the allocation of carbon to roots, leaves and storage tissue. The model was fully specified with independent literature data. Model output was compared to characteristics of a species-rich community in the semi-arid Richtersveld (South Africa). The model reproduced the coexistence of plants with different sizes at maturity, the dominance of succulent shrubs, and the level of vegetation cover. We analyzed the effects of three forms of environmental variability: (a) temporal fluctuations in precipitation (rain and fog), (b) spatial heterogeneity of water supply due to run-on and run-off processes and (c) ‘rock pockets’ that limit root competition in space. The three types of variability had differential effects on diversity: diversity exhibited a strong hump-shaped response to temporal variation. Spatial variability increased diversity, with the strongest increase occurring at intermediate levels of temporal variability. Finally, rock pockets had the weakest effect, but contributed to diversity by providing refuges for small species, particularly at low temporal variability. The model thus shows that spatio-temporal variation of resource supply can maintain diversity over long time scales even in small systems, as is the case in the Richtersveld succulent communities. Trade-offs in allocation provide the basis for necessary niche differentiation. By describing resource competition between individual plants, our model provides a mechanistic basis for the link from species traits to community composition at given environmental conditions. It thereby contributes to an understanding of the forces shaping plant communities. Such an understanding is critical to reduce the threats environmental change poses to biodiversity and ecosystem services. 相似文献
873.
Regine?Gries Aurélia ?Reckziegel Herman?Bogenschütz Hans-Günter?Kontzog Christian?Schlegel Wittko?Francke Jocelyn?G.?Millar Gerhard?GriesEmail author 《Chemoecology》2004,14(2):95-100
Summary. Our objective was to identify sex pheromone
components of the oak processionary moth, Thaumetopoea
processionea (Lepidoptera: Thaumetopoeidae), whose larvae
defoliate oak, Quercus spp., forests in Eurasia and impact
human health. Coupled gas chromatographic-electroantennographic
detection (GC-EAD) and GC-mass spectrometric
(MS) analyses of pheromone gland extract of female
T. processionea revealed two consistently EAD-active compounds.
They were identified as (Z,Z)-11,13-hexadecadienyl
acetate (Z11,Z13-16:OAc) and (Z,E)-11,13,15-hexadecatrienyl
acetate (Z11,E13,15-16:OAc) by comparative GC,
GC-MS and GC-EAD analyses of insect-produced compounds
and authentic standards. In replicated field experiments
(2000, 2001) in Nordbaden, Südbaden and Sachsen-Anhalt
(Germany), Z11,Z13-16:OAc and Z11,E13,15-16:OAc in
combination, but not singly, attracted significant numbers of
male moths. It will now be intriguing to investigate whether
Z11,E13,15-16:OAc, or its corresponding alcohol or aldehyde,
serves as a pheromone component also in other species of
the Thaumetopoeidae. 相似文献
874.
Multiple Chemical Sensitivity (MCS) is a systemic disorder causing central nervous, irritative and gastrointestinal symptoms, and can be included in the category of “idiopathic environmental intolerance” (IEI). This term describes phenomena with multiple, recurrent symptoms associated with various environmental factors that are tolerated by most people without problems. Those advocating these concepts attribute the symptoms to exogenous substances. Those opposing them explain the phenomena by classical conditioning or other psychopathological processes. To the extent that controlled studies are available, they have not furnished any hard evidence for toxic or immunological causes. In addition to psychopathological origins, neurobiological processes are also implicated. 相似文献
875.
Meckenstock RU Morasch B Griebler C Richnow HH 《Journal of contaminant hydrology》2004,75(3-4):215-255
The assessment of biodegradation in contaminated aquifers has become an issue of increasing importance in the recent years. To some extent, this can be related to the acceptance of intrinsic bioremediation or monitored natural attenuation as a means to manage contaminated sites. Among the few existing methods to detect biodegradation in the subsurface, stable isotope fractionation analysis (SIFA) is one of the most promising approaches which is pronounced by the drastically increasing number of applications. This review covers the recent laboratory and field studies assessing biodegradation of contaminants via stable isotope analysis. Stable isotope enrichment factors have been found that vary from no fractionation for dioxygenase reactions converting aromatic hydrocarbons over moderate fractionation by monooxygenase reactions (epsilon=-3 per thousand) and some anaerobic studies on microbial degradation of aromatic hydrocarbons (epsilon=-1.7 per thousand) to larger fractionations by anaerobic dehalogenation reactions of chlorinated solvents (epsilon=between -5 per thousand and -30 per thousand). The different isotope enrichment factors can be related to the respective biochemical reactions. Based on that knowledge, we discuss under what circumstances SIFA can be used for a qualitative or even a quantitative assessment of biodegradation in the environment. In a steadily increasing number of cases, it was possible to explain biodegradation processes in the field based on isotope enrichment factors obtained from laboratory experiments with pure cultures and measured isotope values from the field. The review will focus on the aerobic and anaerobic degradation of aromatic hydrocarbons and chlorinated solvents as the major contaminants of groundwater. Advances in the instrumental development for stable isotope analysis are only mentioned if it is important for the understanding of the application. 相似文献
876.
Soil vapor extraction (SVE) is commonly used to remediate nonaqueous phase liquids (NAPLs) from the vadose zone. This paper aims to determine the effect of grain size heterogeneity on the removal of NAPL in porous media during SVE. Magnetic resonance imaging (MRI) was used to observe and quantify the amount and location of NAPL in flow-through columns filled with silica gel grains. MRI is unique because it is nondestructive, allowing three-dimensional images to be taken of the phases as a function of space and time. Columns were packed with silica gel in three ways: coarse grains (250-550 microm) only, fine grains (32-63 microm) only, and a core of fine grains surrounded by a shell of coarse grains. Columns saturated with water were drained under a constant suction head, contaminated with decane, and then drained to different decane saturations. Each column was then continuously purged with water-saturated nitrogen gas and images were taken intermittently. Results showed that at residual saturation, a sharp volatilization front moved through the columns filled with either coarse-grain or fine-grain silica gel. In the heterogeneous columns, the volatilization front in the core lagged just behind the shell because gas flow was greater through the shell and decane in the core diffused outward to the shell. When decane saturation in the core was above residual saturation, decane volatilization occurred near the inlet, the relative decane saturation throughout the core dropped uniformly, and decane in the core flowed in the liquid phase to the shell to replenish volatilized decane. These results indicate that NAPL trapped in low-permeability zones can flow to replenish areas where NAPL is lost due to SVE. However, when residual NAPL saturation is reached, NAPL flow no longer occurs and diffusion limits removal from low-permeability zones. 相似文献
877.
Mikael Gillner Birgitta Fernstrm Jan-ke Gustafsson Jan Bergman Christian Cambillau 《Chemosphere》1986,15(9-12):1673-1680
We have investigated the capacity of various indoles to inhibit specific binding of [1,6-3H]2,3,7,8-tetrachlorodibenzo-
-dioxin ([3H]TCDD) in rat liver cytosol, as analyzed by electrofocusing in polyacrylamide gels. Of these indoles, indolo[3,2-
]carbazole was the most active. The IC50 value for TCDD receptor binding of indolo[3,2-
]carbazole as well as for 2,3,7,8-tetrachlorodibenzofuran was 3.6 nM. We have also studied the influence on binding exerted by introduction of some substituents on indolo[3,2-
]carbazole. Substitution with methyl groups at the 5 and 11 positions resulted in an increased affinity (IC50 1.2 nM) for the TCDD receptor as compared to the parent compound. Computer-supported molecular structure studies indicated that if the van der Waals radii of atoms are included, a rectangle of 6.8 × 13.7 Å may account for the binding of high-affinity ligands to the TCDD receptor. 相似文献
878.
Increasing atmospheric antimony contamination in the northern hemisphere: snow and ice evidence from Devon Island, Arctic Canada 总被引:8,自引:0,他引:8
Krachler M Zheng J Koerner R Zdanowicz C Fisher D Shotyk W 《Journal of environmental monitoring : JEM》2005,7(12):1169-1176
Adopting recently developed clean laboratory techniques, antimony (Sb) and scandium (Sc) deposition were measured in a 63.72 m-long ice core (1842-1996) and a 5 m deep snow pit (1994-2004) collected on Devon Island, Canadian High Arctic. Antimony concentrations ranged from 0.07 to 108 pg g(-1) with a median of 0.98 pg g(-1)(N= 510). Scandium, used as a conservative reference element, revealed that dust inputs were effectively constant during the last 160 years. The atmospheric Sb signal preserved in the ice core reflects contamination from industrialisation, the economic boom which followed WWII, as well as the comparatively recent introduction of flue gas filter technologies and emission reduction efforts. Natural contributions to the total Sb inventory are negligible, meaning that anthropogenic emissions have dominated atmospheric Sb deposition throughout the entire period. The seasonal resolution of the snow pit showed that aerosols deposited during the Arctic winter, when air masses are derived mainly from Eurasia, show the greatest Sb concentrations. Deposition during summer, when air masses come mainly from North America, is still enriched in Sb, but less so. Snow and ice provide unambiguous evidence that enrichments of Sb in Arctic air have increased 50% during the past three decades, with two-thirds being deposited during winter. Most Sb is produced in Asia, primarily from Sb sulfides such as stibnite (Sb2S3), but also as a by-product of lead and copper smelting. In addition there is a growing worldwide use of Sb in automobile brake pads, plastics and flame retardants. In contrast to Pb which has gone into decline during the same interval because of the gradual elimination of gasoline lead additives, the enrichments of Sb have been increasing and today clearly exceed those of Pb. Given that the toxicity of Sb is comparable to that of Pb, Sb has now replaced Pb in the rank of potentially toxic trace metals in the Arctic atmosphere. 相似文献
879.
Christian Condevaux‐Lanloy Emmanuel Fragnière 《Environmental Modeling and Assessment》2000,5(3):145-155
This paper presents a new concept to include uncertainty management in energy and environmental planning models developed in algebraic modeling languages. SETSTOCH is a tool for linking algebraic modeling languages with specialized stochastic programming solvers. Its main role is to retrieve from the modeling language a dynamically ordered core model (baseline scenario) that is sent automatically to the stochastic solver. The case presented herein concerns such a study realized with the IEAMARKAL model used by many research teams around the world. 相似文献
880.