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771.
PHILLIP S. LEVIN† ELIZABETH E. HOLMES† KEVIN R. PINER† CHRIS J. HARVEY† 《Conservation biology》2006,20(4):1181-1190
Abstract: As in many regions of the world, marine fishes and invertebrates along the Pacific coast of the United States have long been subjected to overexploitation. Despite this history, however, we lack basic information on the current status of many fishes along this coastline. We used data from a quarter century of fishery-independent, coast-wide trawl surveys to study systematically the demersal fish assemblages along the U.S. Pacific coast. We documented fundamental shifts in this fish assemblage. Average fish size, across a diversity of species, has declined 45% in 21 years. There have been major shifts in the constituent species of the assemblage, with some species achieving annual population growth rates of >10% and others declining in excess of 10% per year. Annual rate of change in population size appeared to be a function of life history interacting with fishing pressure. Negative trends in population size were particularly apparent in rockfish ( Sebastes spp.). However, across all taxa examined, trends in population size were associated with size of maturity, maximum size, and growth rate. Trends in population size were associated inversely with harvest levels, but stocks that mature late tended to decline faster than would be predicted by catch rates alone. Our results are disquieting because they raise the possibility that fishing-induced phase shifts in fish communities may affect the recovery of fishes, even after the implementation of severe fishing restrictions. 相似文献
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刘国海 《石油化工环境保护》1997,(4):23-24
介绍了螺旋式管道静态混合器的结构和原理.在PTA污水处理装置上,采用三级静态混合器进行得水混合,代替了均质池加搅拌机的传统混合方法.收到了良好的效果.实现了投资省、耗能低、维修容易、混合效果好的目的.为污水处理领域进行污水混合提供了新的行之有效的方法. 相似文献
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自然界中的能量与物质系统的运动是遵循热力学定律的.从熵的角度来看,现在人类开发利用资源的方式,使系统熵增加速,不利于环境系统的有序和稳定.而人类作为智慧圈的主体,是可以通过智慧和知识,向其输入负熵,以延缓熵增速度.目前的形式下,可以采取适当的对策,坚持科学的发展观,实行节约型经济模式,从熵的角度出发寻找高效的新能源,充分利用不可逆过程的建设性作用,通过知识技术的进步提高资源能源的利用率. 相似文献
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Ma Xiaoyan Gao Naiyun Chen Beibei Li Qingsong Zhang Qiaoli Gu Guofen 《Frontiers of Environmental Science & Engineering in China》2007,1(3):286-291
Two sample preparation methods were introduced and compared in this paper to establish a simple, quick and exact analysis
of geosmin and 2-methylisoborneol. LC-18 column was employed in solid phase extraction (SPE), 1.0 mL of hexane was adopted
in liquid-liquid extraction (LLE), and the extracts were analyzed by gas chromatograph mass spectrum (GCMS) in selected ion
mode. Mean recoveries of SPE were low for 2-methylisoborneol (2-MIB) and geosmin (GSM) with values below 50%. For LLE, the
recoveries were satisfyingly above 50% for 2-MIB and 80% for GSM. Detection limits of the LLE method were as low as 1.0 ng/L
for GSM and 5.0 ng/L for 2-MIB. A year-long investigation on odor chemicals of drinking water in Shanghai demonstrated that
in the summer, there was a serious odor problem induced by a high concentration of 2-MIB. The highest concentration of 152.82
ng/L appeared in July in raw water, while GSM flocculation was minimal with concentrations below odor threshold. 相似文献
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BAI Yu |bo SHI Guang |yu {* } Koichi Tamura Takashi Shibata Yasunobu Iwasaka Kaneta Shin′ichi Takamura Tamio 《环境科学学报(英文版)》2000,(4)
IntroductionAerosolshavethepotentialtochangetheglobalclimatebecauseoftheirdirectradiativeeffectsandtheirindirecteffectsascloudcondensationnuclei.Aerosolsarealsoimportantcomponentsinbiogeochemicalcyclesandinheterogeneouschemistry ,whichcanaffecttrace ga… 相似文献