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The spatial distribution of ammonia-oxidizing Betaproteobacteria ( β AOB) was investigated by FISH (fluorescence in situ hybridization) and DGGE (denaturing gradient gel electrophoresis) techniques in the sediment off the Changjiang River Estuary.Sediment samples were collected from eight stations in June before the formation of hypoxia zone in 2006.The abundance of β AOB ranged from 1.87 × 10 5 to 3.53 × 10 5 cells/g of sediment.β AOB abundance did not present a negative correlation with salinity,whereas salinity was implicated as the primary factor affecting nitrification rates.The DGGE profiles of PCR-amplified amo A gene fragments revealed that the β AOB community structure of sample S2 separated from other samples at the level of 40% similarity.The variations in composition of β AOB were significantly correlated with the salinity,temperature,absorption ability of sediments and TOC. The statistical analysis indicates that the β AOB abundance was a main factor to influence nitrification rates with an influence ratio of 87.7% at the level of 40% biodiversity similarity.Considering the good correlation between β AOB abundance and nitrification estimates,the abundance and diversity of β AOB community could be expected as an indirect index of nitrification activity at the study sea area in summer. 相似文献
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We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1–5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes. 相似文献
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与降雨有关的边坡表层变形位移,其根源是基质吸力降低引起的非饱和土体积应变。利用某滑坡体的原状样及其重塑样,分别在100kPa、200kPa围压作用下,采用单纯增加基质吸力的应力路径,对基质吸力引起的体积应变,进行试验测试。结果显示: (1)试样的体应变,随基质吸力的增大,单调增大,服从对数函数关系;(2)围压由100kPa增加到200kPa的试样体积模量,随基质吸力的增大,单调增大,服从幂函数关系;(3)与基质吸力有关的体积变化系数,随基质吸力的增大,单调减小,服从幂函数关系;并且当基质吸力大于200kPa以后,随基质吸力增大,体积变化系数接近于常数,约为0.0059左右。在此基础上,本文针对这种由单纯基质吸力变化引起的非饱和土体积应变规律及机理,进行了探讨。 相似文献