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排序方式: 共有212条查询结果,搜索用时 31 毫秒
21.
Annekatrin Wagner Stephan Hülsmann Lothar Paul Rüdiger J. Paul Thomas Petzoldt René Sachse Thomas Schiller Bettina Zeis Jürgen Benndorf Thomas U. Berendonk 《Marine Biology》2012,159(11):2543-2559
To predict the coherence in local responses to large-scale climatic forcing among aquatic systems, we developed a generalized approach to compare long-term data of dimictic water bodies based on phenomenologically defined hydrographic events. These climate-sensitive phases (inverse stratification, spring overturn, early thermal stratification, summer stagnation) were classified in a dual code (cold/warm) based on threshold temperatures. Accounting for a latitudinal gradient in seasonal timing of phases derived from gradients in cumulative irradiation (2.2?days per degree latitude), we found a high spatial and temporal coherence in warm–cold patterns for six lakes (84?%) and the Baltic Sea (78?%), even when using the same thresholds for all sites. Similarity to CW-codes for the North Sea still was up to 72?%. The approach allows prediction of phase-specific warming trends and resulting instantaneous or time-delayed ecological responses. Exemplarily, we show that warming during early thermal stratification controls food-web-mediated effects on key species during summer. 相似文献
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Polypropylene (PP) meltblown fibers were coated with titanium dioxide (TiO2) nanoparticles using layer-by-layer (LbL) deposition technique. The fibers were first modified with 3 layers of poly(4-styrenesulfonic acid) (PSS) and poly(diallyl-dimethylammonium chloride) (PDADMAC) to improve the anchoring of the TiO2 nanoparticle clusters. PDADMAC, which is positively charged, was then used as counter polyelectrolyte in tandem with anionic TiO2 nanoparticles to construct TiO2/PDADMAC bilayer in the LbL fashion. The number of deposited TiO2/PDADMAC layers was varied from 1 to 7 bilayer, and could be used to adjust TiO2 loading. The LbL technique showed higher TiO2 loading efficiency than the impregnation approach. The modified fibers were tested for their photocatalytic activity against a model dye, Methylene Blue (MB). Results showed that the TiO2 modified fibers exhibited excellent photocatalytic activity efficiency similar to that of TiO2 powder dispersed in solution. The deposition of TiO2 3 bilayer on the PP substrate was sufficient to produce nanocomposite fibers that could bleach the MB solution in less than 4 hr. TiO2-LbL constructions also preserved TiO2 adhesion on substrate surface after 1 cycle of photocatalytic test. Successive photocatalytic test showed decline in MB reduction rate with loss of TiO2 particles from the substrate outer surface. However, even in the third cycle, the TiO2 modified fibers are still moderately effective as it could remove more than 95% of MB after 8 hr of treatment. 相似文献
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Roland Axt-Fliedner Andrii Kurkevych Maciej Slodki Maria Respondek-Liberska Katarzyna Zych-Krekora Rüdiger Stressig Jochen Ritgen Guiseppe Rizzo Martin Krapp Luc de Catte Gunther Mielke Stephan Bosselmann Mathias Meyer-Wittkopf Andreea Kawecki Aline Wolter Marios Mamalis Christian Enzensberger 《黑龙江环境通报》2017,37(8):812-819
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Calcareous or dolomitic, often secondarily silicified, laminated microbial structures known as stromatolites are important
keys to reconstruct the chemical and biotic evolution of the early ocean. Most authors assume that cyanobacteria-associated
microbialitic structures described from Shark Bay, Western Australia, and Exuma Sound, Bahamas, represent modern marine analogues
for Precambrian stromatolites. Although they resemble the Precambrian forms macroscopically, their microstructure and mineralogical
composition differ from those characterizing their purported ancient counterparts. Most Precambrian stromatolites are composed
of presumably in situ precipitated carbonates, while their assumed modern marine analogues are predominantly products of accretion
of grains trapped and bound by microbial, predominantly cyanobacterial, benthic mats and biofilms and only occasionally by
their physicochemical activity. It has therefore been suggested that the carbonate chemistry of early Precambrian seawater
differed significantly from modern seawater, and that some present-day quasi-marine or non-marine environments supporting
growth of calcareous microbialites reflect the hydrochemical conditions controlling the calcification potential of Precambrian
microbes better than modern seawater. Here we report the discovery of a non-marine environment sustaining growth of calcareous
cyanobacterial microbialites showing macroscopic and microscopic features resembling closely those described from many Precambrian
stromatolites. 相似文献
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The aim of this contribution was the ecological characterization of 32 selected terrestrial Central-European enchytraeid species regarding factors of land use, pH-value, grain-size distribution, humus form, and soil moisture. The background of this characterization is generated by the so-called Soil Biological Site-Classification (abbreviated BBSK), a concept for the soil-biological assessment of soils. The crucial point within this concept is the comparison of the theoretically expected soil biocoenosis with the biocoenosis actually detected at a single site. Intending to obtain a simplified management of the parameters mentioned, these were each divided into three to five classes. The data-basis for the ecological characterization was formed by analysing suitable sources of literature with both biological and abiotic data given for one site. The result of the analysis was the frequency of a single species regarding the classes of the viewed soil parameters. On the basis of these results, the enchytraeid coenosis of three adjacent Bavarian sites of different use was predicted exemplarily and the enchytraeid community of these sites was investigated. The comparison of the predicted and detected coenoses showed that the sureness of the forecast varied between the different land uses: for wood and grassland, the prognosis was very precise and satisfactory, whereas the forecast for the agricultural site differed quite extensively. This was mainly due to the narrow data basis for agricultural sites. 相似文献
30.
Stephan F. J. De Wekker D. G. Steyn J. D. Fast M. W. Rotach S. Zhong 《Environmental Fluid Mechanics》2005,5(1-2):35-62
Data from a comprehensive field study in the Riviera Valley of Southern Switzerland are used to investigate convective boundary layer structure in a steep valley and to evaluate wind and temperature fields, convective boundary layer height, and surface sensible heat fluxes as predicted by the mesoscale model RAMS. Current parameterizations of surface and boundary layer processes in RAMS, as well as in other mesoscale models, are based on scaling laws strictly valid only for flat topography and uniform land cover. Model evaluation is required to investigate whether this limits the applicability of RAMS in steep, inhomogeneous terrain. One clear-sky day with light synoptic winds is selected from the field study. Observed temperature structure across and along the valley is nearly homogeneous while wind structure is complex with a wind speed maximum on one side of the valley. Upvalley flows are not purely thermally driven and mechanical effects near the valley entrance also affect the wind structure. RAMS captured many of the observed boundary layer characteristics within the steep valley. The wind field, temperature structure, and convective boundary layer height in the valley are qualitatively simulated by RAMS, but the horizontal temperature structure across and along the valley is less homogeneous in the model than in the observations. The model reproduced the observed net radiation, except around sunset and sunrise when RAMS does not take into account the shadows cast by the surrounding topography. The observed sensible heat fluxes fall within the range of simulated values at grid points surrounding the measurement sites. Some of the scatter between observed and simulated turbulent sensible heat fluxes are due to sub-grid scale effects related to local topography. 相似文献