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排序方式: 共有174条查询结果,搜索用时 15 毫秒
81.
Virginie Chapon Laurie Piette Marie-Hélène Vesvres Frédéric Coppin Claire Le Marrec Richard Christen Nicolas Theodorakopoulos Laureline Février Sviatoslav Levchuk Arnaud Martin-Garin Catherine Berthomieu Claire Sergeant 《Applied Geochemistry》2012
The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of 137Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity. 相似文献
82.
The blue crab, Callinectes sapidus, is an ecologically and economically valuable species in Chesapeake Bay. Field surveys and laboratory experiments indicate
that blue crab mortality is significant during severe winters. We applied a temperature and salinity-dependent survival model
to empirical temperature and salinity data to explore spatial and interannual patterns in overwintering mortality. Harmonic
regression analysis and geostatistical techniques were used to create spatially explicit maps of estimated winter duration,
average temperature, average salinity, and resulting crab survival probability for the winters of 1990–2004. Predicted survival
was highest in the warmer, saline waters of the lower Bay and decreased with increasing latitude up bay. There was also significant
interannual variation with survival being lowest after the severe winters of 1996 and 2003. We combine the survival probability
maps with maps of blue crab abundance to show how winter mortality may reduce blue crab abundance prior to the start of the
harvesting season. 相似文献
83.
Laurie J. Burn-Nunes Paul Vallelonga Graeme R. Burton Mark Curran Sungmin Hong Ross Edwards Vin I. Morgan Kevin J.R. Rosman 《Geochimica et cosmochimica acta》2011,75(1):1-20
Lead (Pb) isotopic compositions and concentrations, and barium (Ba) and indium (In) concentrations have been determined at monthly resolution in five Law Dome (coastal Eastern Antarctica) ice core sections dated from ∼1757 AD to ∼1898 AD. ‘Natural’ background Pb concentrations in ∼1757 AD average ∼0.2 pg g−1 and can be attributed to mineral dust and volcanic emissions, with 206Pb/207Pb ratios reaching up to 1.266 ± 0.002. From ∼1887 AD to ∼1898 AD, Pb concentrations reached ∼5 pg g−1 and 206Pb/207Pb ratios decreased to 1.058 ± 0.001 as a result of additional inputs of Pb from anthropogenic sources. Seasonal variability in the late 1880s has been investigated by decoupling volcanic Pb from the total measured Pb concentrations, revealing spring and autumn maxima, and consistent winter minima, in anthropogenic Pb and mineral dust (Ba) concentrations. We link this variability to the annual cycle in the position and strength of the Antarctic Circumpolar Trough and, the Southern Ocean westerly winds to the north of the trough region. During the autumn and spring seasons, these systems increase in strength, transporting more impurity laden air from the Southern Hemisphere continental regions to Eastern Antarctica and Law Dome. As this Pb is isotopically identical to that emitted from south-eastern Australia (Broken Hill, Port Pirie) this implies a relatively direct air trajectory pathway from southern Australia to Law Dome (Eastern Antarctica). 相似文献
84.
Jamey E. Redding Roxanna L. Myers-Miller David M. Baker Marilyn Fogel Laurie J. Raymundo Kiho Kim 《Marine pollution bulletin》2013
The goals of this study were to evaluate the contribution of sewage-derived N to reef flat communities in Guam and to assess the impact of N inputs on coral disease. We used stable isotope analysis of macroalgae and a soft coral, sampled bimonthly, as a proxy for N dynamics, and surveyed Porites spp., a dominant coral taxon on Guam’s reefs, for white syndrome disease severity. Results showed a strong influence of sewage-derived N in nearshore waters, with δ15N values varying as a function of species sampled, site, and sampling date. Increases in sewage-derived N correlated significantly with increases in the severity of disease among Porites spp., with δ15N values accounting for more than 48% of the variation in changes in disease severity. The anticipated military realignment and related population increase in Guam are expected to lead to increased white syndrome infections and other coral diseases. 相似文献
85.
Joachim W. Stock Christopher S. Boxe Ralph Lehmann J. Lee Grenfell A. Beate C. Patzer Heike Rauer Yuk L. Yung 《Icarus》2012,219(1):13-24
The chemical composition of a planetary atmosphere plays an important role for atmospheric structure, stability, and evolution. Potentially complex interactions between chemical species do not often allow for an easy understanding of the underlying chemical mechanisms governing the atmospheric composition. In particular, trace species can affect the abundance of major species by acting in catalytic cycles. On Mars, such cycles even control the abundance of its main atmospheric constituent CO2. The identification of catalytic cycles (or more generally chemical pathways) by hand is quite demanding. Hence, the application of computer algorithms is beneficial in order to analyze complex chemical reaction networks. Here, we have performed the first automated quantified chemical pathways analysis of the Martian atmosphere with respect to CO2-production in a given reaction system. For this, we applied the Pathway Analysis Program (PAP) to output data from the Caltech/JPL photochemical Mars model. All dominant chemical pathways directly related to the global CO2-production have been quantified as a function of height up to 86 km. We quantitatively show that CO2-production is dominated by chemical pathways involving HOx and Ox. In addition, we find that NOx in combination with HOx and Ox exhibits a non-negligible contribution to CO2-production, especially in Mars’ lower atmosphere. This study reveals that only a small number of chemical pathways contribute significantly to the atmospheric abundance of CO2 on Mars; their contributions to CO2-production vary considerably with altitude. This analysis also endorses the importance of transport processes in governing CO2-stability in the Martian atmosphere. Lastly, we identify a previously unknown chemical pathway involving HOx, Ox, and HO2-photodissociation, contributing 8% towards global CO2-production by chemical pathways using recommended up-to-date values for reaction rate coefficients. 相似文献
86.
Stéphane Audry Henriette Ateba Bessa Jean-Pierre Bedimo Bedimo Jean-Loup Boeglin Laurie Boithias Jean-Jacques Braun Bernard Dupré Mikael Faucheux Christelle Lagane Jean-Christophe Maréchal Jules Remy Ndam-Ngoupayou Bernadette Nka Nnomo Justin Nlozoa Jean-Claude Ntonga Olivier Ribolzi Jean Riotte Emma Rochelle-Newall Laurent Ruiz 《水文研究》2021,35(5):e14138
Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics. 相似文献
87.
Karen E. Samonds Brooke E. Crowley Tojoarilala Rinasoa Nadia Rasolofomanana Miora Christelle Andriambelomanana Harimalala Tsiory Andrianavalona Tolotra Niaina Ramihangihajason Ravoniaina Rakotozandry Zafindratsaravelo Bototsemily Nomenjanahary Mitchell T. Irwin Neil A. Wells Laurie R. Godfrey 《第四纪科学杂志》2019,34(6):379-392
Madagascar is a complex ‘biodiversity hotspot’ with a rapidly dwindling biota. The Late Quaternary subfossil record includes many extinct species whose loss is attributed to natural climate change and human impacts. Investigation of the chronology of these events is challenging because few localities document pre‐Holocene communities not impacted by humans. Caves with extinct lemurs of large body size comprise some of Madagascar's richest subfossil sites, but provide only a limited window into the island's past. Open highland sites may have fewer primates, but may better document other megafauna, and allow the analysis of the role of the Central Highlands as refugia and as corridors for the dispersal of vertebrates before and after human arrival. Here we present a new subfossil site, Tsaramody (Sambaina basin, Central Madagascar), a high‐altitude wetland area that preserves a diverse late glacial and postglacial vertebrate community. Tsaramody bears testimony to fluctuations in the highland flora during the transition from glacial to postglacial conditions, and the composition of a highland vertebrate community before humans arrived. We compare its biota to those of other sites to begin to document the decline and disappearance of megafauna from some of Madagascar's open ecosystems – wetlands dominated by hippopotamuses and crocodylians. © 2019 John Wiley & Sons, Ltd. 相似文献
88.
Tzu‐Yi Pai Terng‐Jou Wan Yung‐Pin Tsai Chwen‐Jeng Tzeng Hsiao‐Hsing Chu Yao‐Sheng Tsai Ching‐Yuan Lin 《洁净——土壤、空气、水》2010,38(2):167-172
In this study, the effect of sludge retention time on ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in an anaerobic/oxic (AO) process, was explored. The results indicated that the growth rate constants of AOB were 0.97, 0.88, and 0.79 d–1, respectively, meanwhile, those of NOB were 1.22, 1.03, and 0.93 d–1, respectively, when the sludge retention time (SRT) was 15 days, 10 days and 5 days. The relation between the growth rate constant and the SRT could be best described using a simple exponential curve and a second type hyperbolic curve. The lysis rate constants for AOB and NOB were 0.13 and 0.18 d–1, respectively. The yield coefficients values of AOB and NOB were 0.22 and 0.21, respectively. The percentage of AOB to mixed liquid suspended solids (MLSS) was 0.64%, 0.53%, and 0.35%, respectively. Meanwhile, the percentage of NOB was 2.24%, 1.87%, and 1.11%, respectively, at SRT values of 15 days, 10 days and 5 days. When the SRT value decreased, the AOB and NOB biomass levels decreased by 12.75 and 47.01 mg L–1, respectively. Meanwhile the removal efficiency of NH4+‐N decreased from 90 to 26%, while the removal efficiency of total nitrogen (TN) decreased from 14 to 8%. 相似文献
89.
90.
合成层析成像可由有限几个投影数据重建三维物体,与传统CT相比,该方法所需的射线剂量少得多.由于投影数据不完备,导致的重建图像伪影是合成层析成像的一个主要问题.本文提出一种对感兴趣区域进行合成层析成像方法,和其他方法相比可以得到更好的重建图像质量.该方法首先对目标进行低分辨率全局扫描,然后对感兴趣区域进行高分辨率局部扫描,最后,利用两次扫描的投影数据集合重建感兴趣区域的图像.数值仿真结果表明,用本方法重建感兴趣区域图像,要明显好于没有使用全局扫描信息的方法. 相似文献