排序方式: 共有27条查询结果,搜索用时 15 毫秒
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大部分绿岩通过俯冲作用于度进入地幔的2.5-2.2Ga和1.65-1.35Ga年龄段的极小值,可能与超级大陆的活动时代相关。根据绿岩的年代分布和新生大陆壳,地球历史可被分为3个阶段:(1)2.8Ga,虽然一直到3.0Ga才形成超级大陆,但是在此时以前绿岩和微型陆块就开始形成并持续发生碰撞;(2)2.8-1.3Ga期间绿岩喷发和碰撞就明显 相似文献
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Mak KC Yu H Choi MC Shen X Lam MH Martin M Wu RS Wong PS Richardson BJ Lam PK 《Marine pollution bulletin》2005,51(8-12):1010-1017
Green-lipped mussels (Perna viridis) were collected from seven fish culture zones (FCZs) in Hong Kong and analyzed for okadaic acid (OA). A conventional HPLC method was modified by incorporating a proteinase K digestion step. Results suggest that a higher recovery (2.5 times higher) of OA was obtained from spiked samples after the addition of 1.08 mg proteinase K in comparison with samples incubated without the proteolytic enzyme. For the hepatopancreas (HP) of individual field-collected mussels, the additional digestion step can enhance OA extraction by 3.1 times. Spatial and temporal variations in OA concentrations in the mussels from various FCZs were investigated. The highest concentration of OA in mussel HP samples was 1164.9 ng/g HP wet wt. With respect to OA concentrations in whole mussel tissues from seven sites and four seasonal samplings, the concentrations were between 70.0 and 131.0 ng/g wet wt., which did not exceed the generally recognized international regulatory criteria (>200 ng/g) for OA. 相似文献
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Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes, Hong Kong 总被引:5,自引:0,他引:5
This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) approximately P) being the dominant P fraction. Given the considerable average Fe(OOH) approximately P concentration of 912 microg g(-1), Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m(-2)d(-1) recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642-3582 mg kg(-1)), the high zero equilibrium P concentrations (0.02-0.51 mg L(-1)) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes. 相似文献