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441.
Shang Wang Raymond M. Dong Christina Z. Dong Liuqin Huang Hongchen Jiang Yuli Wei Liang Feng Deng Liu Guifang Yang Chuanlun Zhang Hailiang Dong 《地学前缘(英文版)》2012,3(3):335-349
The Three Gorges Dam(TGD) of the Yangtze River.China,is one of the largest irrigation and hydroelectric engineering projects in the world.The effects of huge man-made projects like TGD on fauna and macrophyte are obvious,mainly through changes of water dynamics and flow pattern;however, it is less clear how microorganisms respond to such changes.This research was aimed to examine differences in microbial diversity at different seasons and locations(in front of and behind the TGD).In addition, differences between particle-attached and free-living communities were also examined.The community structures of total and potentially active microorganisms in the water columns behind and in front of the TGD were analyzed with the DNA- and RNA-based 16S rRNA gene phylogenetic approaches over three different seasons.Clone libraries of 16S rRNA genes were prepared after amplification from extracted DNA and.for some samples,after preparing cDNA from extracted rRNA.Differences were observed between sites at different seasons and between free-living and particle-attached communities.Both bacterial and archaeal communities were more diverse in summer than in winter, due to higher nutrient levels and warmer temperature in summer than in winter.Particle-attached microorganisms were more diverse than free-living communities,possibly because of higher nutrient levels and heterogeneous geochemical micro-environments in particles.Spatial variations in bacterial community structure were observed,i.e..the water reservoir behind the TGD(upstream) hosted more diverse bacterial populations than in front of the dam(downstream),because of diverse sources of sediments and waters from upstream to the reservoir.These results have important implications for our understanding of responses of microbial communities to environmental changes in river ecosystems affected by dam construction. 相似文献
442.
Water source partitioning among trees growing on carbonate rock in a subtropical region of Guangxi, China 总被引:1,自引:0,他引:1
It is not clear how the water sources are used by trees in typical karst areas of Guangxi, China. Trees growing on rigid carbonate
rock can primarily use spring water, precipitation-recharged soil water or a mixture of the two. In this study, the Nongla
karst dynamic monitoring station in the southwest of Guangxi, China, was observed. To determine the water sources accessed
by trees growing on rigid carbonate rock, seasonal change of isotope ratios (δ18O and δ D) in twig sap, soil water, rainfall and spring water were measured. Stem water samples plotted to the right of the
meteoric water line indicates utilization of water sources subject to evaporative isotopic enrichment. Trees growing on rigid
carbonate rock in the southwest of China used rainfall directly in the rainy season. Adult trees tended to use deeper water
stored in the epikarst zone, while the young ones used soil water when precipitation decreased. In the dry season, all trees
sampled depend mostly on water stored in the epikarst zone. Spring water was the major water source for all of the tree species
investigated in the dry season. In conclusion, these data indicate that trees growing on rigid carbonate rock in southwest
China depend mostly on water stored in the epikarst zone. Therefore, water storage in the epikarst zone is the essential water
source for trees growing on carbonate rock in southwest China. 相似文献
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MSDP软件在单台数字地震记录分析中的应用 总被引:1,自引:1,他引:0
根据MSDP分析软件的基本功能和测震分析常用方法,结合Dimas分析软件的使用经验,从台站工作的实际出发,以单台地震震相分析整个流程的形式,总结了在MSDP下地震震相的单台分析识别方法.利用这些方法,有助于提高地震台站工作人员震相分析识别的工作效率. 相似文献
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Field observations of suspended particulate matter (SPM) in the Bohai Bay, China have not been widely reported. The aim of this paper is to describe the horizontal and vertical distribution of mass and volume concentrations of SPM, respectively, based on observed data at 312 stations in the northern Bohai Bay during summer of 2006. A numerical model ECOMSED coupled with a sediment transport module was also established to further discuss the mechanism of the thermocline effect on the vertical distribution of SPM. The mass concentrations of SPM exhibited high inshore values and low offshore values in the horizontal distribution; while in the vertical direction, characteristics of the volume concentration of SPM can be divided into two types: one with a sharp peak at depth of 10–15 m and another without. The peak value at the depth of the thermocline was resulted from concentrated phytoplankton. A numerical experiment further displayed that the thermocline can also prevent particles from being resuspended upward. 相似文献
450.
Food safety and its related influencing factors in China are the hot research topics currently, and cultivated land conversion
is one of the significant factors influencing food safety in China. Taking the North China Plain as the study area, this paper
examines the changes of cultivated land area using satellite images, estimates land productivity from 1985 to 2005 using the
model of Estimation System for Land Productivity (ESLP), and analyzes the impact of cultivated land conversion on the land
production. Compared with the grain yield data from statistical yearbooks, the results indicate that ESLP model is an effective
tool for estimating land productivity. Land productivity in the North China Plain showed a slight decreasing trend from 1985
to 2005, spatially, increased from the north to the south gradually, and the net changes varied in different areas. Cultivated
land area recorded a marginal decrease of 8.0 × 105 ha, mainly converted to other land uses. Cultivated land conversion had more significant negative impacts on land production
than land productivity did. Land production decreased by about 6.48 × 106 t caused by cultivated land conversion between 1985 and 2005, accounting for 91.9% of the total land production reduction.
Although the land productivity increased in Anhui and Jiangsu provinces, it can not offset the overall adverse effects caused
by cultivated land conversion. Therefore, there are significant meanings to control the cultivated land conversion and improve
the land productivity for ensuring the land production in the North China Plain. 相似文献