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排序方式: 共有203条查询结果,搜索用时 15 毫秒
161.
Annelies De Backer Stefanie Adam Jaak Monbaliu Erik Toorman Magda Vincx Steven Degraer 《Estuaries and Coasts》2009,32(6):1121-1129
The present study aims to test the application of remote sensing to address the impact of bioturbation on physical sediment
properties. Therefore, a laboratory experiment was developed, using microcosms mimicking a marine intertidal water–sediment
interface to test the influence of Corophium volutator densities on sediment properties. Three main variables (water content, clay content, and mean grain size) were measured in
three treatments (no Corophium, 5,000 Corophium per square meter, and 20,000 Corophium per square meter) after 16 days of bioturbation. Results obtained with conventional—destructive—techniques showed a significant
increase of water content and a significant, but small decrease of clay content in the presence of Corophium. The remote sensing technique detected the impact of Corophium on water content as an increase in absorption at 1,450 nm, but was not able to detect the animal impact on clay content.
This study demonstrates that remote sensing data could be significantly modified by bioturbation activities and that remote
sensing can be applied in the laboratory to address the impact of bioturbation on sediment properties. This possibly opens
new perspectives for long-term experiments concerning the role of bioturbation on sedimentary processes. 相似文献
162.
The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for
the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique
opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough
characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted
from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the
EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations
of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase,
followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means
of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the
calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted
unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could
not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model,
the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the
EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of
the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the
numerous seasonal variations cycles and the resulting shrinkage. 相似文献
163.
Evidence for herbivorous cave bears (Ursus spelaeus) in Goyet Cave,Belgium: implications for palaeodietary reconstruction of fossil bears using amino acid δ15N approaches
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164.
The investigation focuses on the analysis of dissolved sulfonamides, tetracyclines, analgesics, anticonvulsants and hormones in surface water. Runoff event and baseflow samples were analysed in two small river catchments of different land use in Luxembourg. For most of the flood events, similar pollutant loads to those transported during 1 day with average baseflow discharge were observed. The maximum contents during flood events and the event mean concentrations are controlled by pre‐event hydro‐climatological conditions. For all substances under investigation, maximum concentrations and event mean concentrations show a decrease with raising antecedent rainfall. In addition, the interstorm and intrastorm variability of the pollutant transport was determined. Runoff generation and corresponding transport of xenobiotic compounds show a complex pattern with many interrelated processes, taking place within bedrock, soil, anthropogenic facilities and channel and in different parts of the basins under investigation. Different sources of pollutants can be identified and related to particular locations in the basin. The influence of the sewer systems is obvious. In the agricultural Mess basin, higher rainfall amounts lead to greater quantities of laterally inflowing soil water with higher concentrations of dissolved oxytetracycline. This originates from veterinary medicines administered to livestock and enters the environment through the application of organic fertilisers, especially by slurry that is applied to the fields. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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166.
Anna Jesußek Ralf Köber Sibylle Grandel Andreas Dahmke 《Environmental Earth Sciences》2013,69(5):1763-1771
Aquifer thermal energy storage in urban and industrial areas can lead to an increase in subsurface temperature to 70 °C and more. Besides its impacts on mineral and sorption equilibria and chemical reaction kinetics in an aquifer, temperature sensitively influences microbial activity and thus redox processes, such as sulphate reduction. Microorganism species can only operate within limited temperature ranges and their adaptability to temperature is a crucial point for the assessment of the environmental consequences of subsurface heat storage. Column experiments with aquifer sediment and tap water at 10, 25, 40, and 70 °C showed that under the constant addition of acetate sulphate reduction could be initiated after 26–63 pore volumes exchanged at all temperatures. Fastest initiation of sulphate reduction with the highest reduction rates was found at 40 °C. Maximum rate constants during experimental run-time were 0.56 h?1 at 40 °C and 0.33, 0.36, and 0.25 h?1 at 10 and, 25, and 70 °C, respectively. Hence, microbial activity was enhanced by a temperature increase to 40 °C but was significantly lowered at 70 °C. At 25 °C methane was found in solution, indicating the presence of fermenting organisms; at 10, 40, and 70 °C no methane production was observed. It could be shown that redox processes in an aquifer generally can adapt to temperatures significantly higher than in situ temperature and that the efficiency of the reduction process can be enhanced by temperature increase to a certain limit. Enhancement of sulphate reduction in an aquifer due to temperature increase could also allow enhanced degradation of organic ground water contaminants such as BTEX, where sulphate is an important electron acceptor. 相似文献
167.
In this article, we contribute to a better understanding of contextual differences related to residential segregation. We illuminate one specific contextual factor—housing oversupply—and how it intersects with historically inherited patterns of socio-spatial differentiation and other drivers of residential segregation. The study is based on an analysis of how segregation has developed over the last 20 years in the city of Leipzig, Germany. This case offers the rare possibility of studying the impact of city-wide housing oversupply on residential segregation, rather than concentrating on decline or decay in specific areas. We examine how oversupply emerged at the meeting point of changes in market structures, housing preferences, welfare state interventions, and migration trends in the post-socialist transition. Using existing statistical data, we demonstrate how oversupply has fostered a fast and thorough reshuffling of residential patterns. After a period of resolving segregation patterns from the socialist era, oversupply acts as a catalyst for recently emerging residential segregation patterns. 相似文献
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