Shifts in a Pacific Ocean Fish Assemblage: the Potential Influence of Exploitation

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.     

低溶解氧条件下生物脱氮研究中的新现象

活性污泥法中 ,曝气主要起供氧和扰动混合的作用 ,曝气提供的氧被微生物用来氧化有机物并合成细胞 .反应器中的溶解氧 (DO)浓度是重要的运行参数 ,曝气池中DO偏低 ,好氧微生物不能正常生长和代谢 ;DO过高 ,不仅能耗增加 ,而且细菌的活力也会降低 .一般要求曝气池中DO不低于 2mgL-1的水平 ,但在实践中常常会出现曝气强度过高的情况 .因而有必要通过有效手段将DO控制在适当的水平 ,既不影响微生物的正常生长和有机物的去除 ,同时又避免过多能耗 .传统观点认为 ,低DO条件会促进丝状菌生长 ,破坏污泥絮体的沉降性能 ;使胞外多聚物的产生量…     

COD与DO对好氧颗粒污泥同步硝化反硝化脱氮的影响

COD和DO浓度对好氧颗粒污泥的同步硝化反硝化反应有明显影响．COD浓度在400～1200mg／L范围内，好氧颗粒污泥去除COD的能力均在85％以上．颗粒污泥能吸附有机物，使废水中COD浓度快速下降．COD浓度小于800mg／L，好氧颗粒污泥具有良好的脱氮能力，氮去除率最高达85．3％．在溶氧浓度为1-4mg／L条件下，颗粒污泥对COD去除率均在90％以上．不同的溶氧浓度对氮的去除率有一定影响，在溶氧浓度3mg／L时，氮去除率最高，达83％．图7参7     

论成人高等教育办学主体的竞争与共生

借鉴生物种群间存在的竞争与共生理论，对我国成人高等教育的办学主体之间的两种主要关系进行了深入的探讨，认为竞争和共生都是有效改善和提高成人高等教育发展与管理的重要思路，对规范当前竞争市场环境中存在的不良竞争具有重要作用，对建立办学主体之间全新的关系具有启发意义，在良好的运行机制下，互利共生应当成为今后成人高教的发展方向，对促进成人高等教育的健康发展具有体制创新价值．     

30CrMnSiNi2A钢壳体毛坯的温挤压成形工艺研究

针对30CrMnSiNi2A超高强度钢制壳体毛坯的结构特点和材料工艺特性,对该壳体毛坯的温挤压成形工艺进行了大量的试验研究;并采用"正交试验方法"对温挤压工艺参数进行了优化设计。经过理化检测和使用结果表明,采用温挤压工艺生产的30CrMnSiNi2A钢制壳体毛坯锻件完全满足壳体的使用要求,各项性能指标合格。     

水体中多环芳烃的来源,迁移及转化

本文概述了环境中多环芳烃(PAH)的三种主要来源:生物合成、化石燃料的开采与利用、有机物的热分解;迁移入水体的四种主要途径:石油泄漏、空中沉降、土壤雨水径流、污水排放;以及水体中PAH的两种主要转化方式:光氧化、生物降解。     

绿地,水体对减轻城市热灾害和对空气净化作用的研究

本文通过卫星对城市不同下垫面的探测和气象要素的地面布点观测分析了绿地,水体对减轻热灾害,调节气候和对空气的净化作用,为保护环境,促进人们的身体健康提供科学依据。     

Body condition and reproductive characteristics of female water voles (Arvicola terrestris L.)

The relationship between long-term dynamics of reproductive parameters and body condition were studied in female water voles from a cycling population. Body condition was estimated from the deviation of body weight (excluding the weight of the uterus with embryos) from the theoretically expected weight calculated from the equation of body weight regression with respect to body length. As the index of body condition increases upon transition from decline to peak in the population cycle, the numbers of corpora lutea and live embryos also increase and the risk of resorption of the entire litter becomes lower.     

高氢分压下厌氧颗粒污泥演变过程研究

为了探究厌氧颗粒污泥用于氢辅助原位生物法沼气提纯的可行性，在高氢分压ASBR中对厌氧颗粒污泥演变过程进行了考察，包括反应器性能和厌氧颗粒污泥特性变化情况.结果表明，在进水COD负荷低于5g/（L·d）时，氢辅助原位生物法沼气提纯中高氢分压、高进水COD负荷和高剪切力新环境促使厌氧颗粒污泥向小粒径方向演变，系统运行性能良好、高效，此时厌氧颗粒污泥可以通过营造具有极低氢分压的微环境强化基于HIT（种间氢传递）途径丙酸降解；但随着进水COD负荷进一步提高，超过6g/（L·d）时，系统出现不可控的丙酸积累.因此，需要寻求其他技术手段来缓解更高进水COD负荷条件下氢辅助原位生物法沼气提纯系统中丙酸积累问题.