Spatial and temporal variability in feeding and condition of age-0 walleye pollock (Theragra chalcogramma) in frontal regions of the Bering Sea     

Brodeur  Richard D.; Wilson  Matthew T.; Ciannelli  Lorenzo 《ICES Journal of Marine Science》2000,57(2):256-264

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长江三角洲土地利用变化与粮食安全分析   总被引：14，自引：0，他引：14  

曾科军  陈逸  高中贵  彭补拙 《地理与地理信息科学》2006,22(6):58-61

定量描述粮食产量对土地资源波动响应的程度对理解区域土地利用变化与粮食生产关系具有重要意义。分析长江三角洲地区耕地面积变化与粮食生产相关性及耕地质量变化对粮食单产的影响,分析粮食生产对土地利用变化响应的敏感性。结果表明:粮食产出与土地利用变化具有强相关性,耕地质量和数量的变化对粮食生产的影响及粮食安全敏感系数在不同时间段呈规律性变化,且在波动中平衡,耕地数量与质量变化是粮食安全的重要制约因素。  相似文献   

Seasonal Response of Planktonic Foraminifera to Surface Ocean Condition: Sediment Trap Results from the Central North Pacific Ocean     

Nobuhisa O. Eguchi  Hodaka Kawahata  Asahiko Taira 《Journal of Oceanography》1999,55(6):681-691

The fluxes of planktonic foraminifera (calcareous shell producing zooplankton) were examined in order to clarify temporal and regional variations in production in the upper ocean in relation to hydrographic conditions. Three time-series sediment traps were deployed in the central North Pacific along 175°E for about one year, beginning in June 1993. Trap sites were located in the subarctic, the transition, and the subtropical water masses, from north to south. The southernmost site was under the influence of the transition zone in January to May. Both temporal and regional fluxes of planktonic foraminifera showed large variations during the experiment. In the subarctic water mass, high total foraminiferal fluxes (TFFs) and high organic matter fluxes (OMFs) were observed during summer to fall, suggesting that food availability is the most important factor for the production of planktonic foraminifera. Furthermore, low TFFs during winter were ascribed to low food availability and low temperatures. The OMFs and TFFs correlated well and increased rapidly after the disruption of the seasonal thermocline during winter, peaking in late February to early March in the transition zone. In the subtropical water mass, both OMFs and TFFs remained low due to lower productivity under oligotrophic conditions. In general, TFFs show a positive correlation with OMFs during the trap experiment, suggesting that food availability is one of the factors controlling the production of planktonic foraminifera in the central North Pacific. Relatively low TFFs during summer to fall in the subtropical water mass may be caused by the thermal structure of the upper ocean. Low SST possibly reduces the production of foraminifera during winter in the subarctic region.  相似文献   

Determination of adsorbed and absorbed polychlorinated biphenyls (PCBs) in seawater microorganisms     

Petra Wallberg  Agneta Andersson   《Marine Chemistry》1999,64(4):51

To distinguish between adsorbed and absorbed PCBs in seawater microorganisms, 2,2′,4,4′,5,5′-hexachlorobiphenyl (IUPAC #153; HCB) was added to a pure culture of Chrysochromulina apheles Moestrup et H.A. Thomsen. After the addition of the HCB, the cells were immediately harvested onto 2 μm polycarbonate filters and rinsed with a gradient of ethanol concentrations. Rinsing with 40% ethanol (v/v) was found to remove 80% of the HCB, which was loosely adsorbed to the cell surfaces, but did not extract the interior of the cells, as tested by chlorophyll a analysis. This method was used in a time course experiment which estimated PCBs adsorption and absorption to different groups of plankton organisms. Three different ¹⁴C-PCBs, 4-chlorobiphenyl (IUPAC #3; MCB), 2,2′,5,5′-tetrachlorobiphenyl (IUPAC #52; TCB), and 2,2′,4,4′,5,5′-hexachlorobiphenyl (IUPAC #153, HCB), were incubated in seawater from the northern Baltic Sea during a spring bloom. Samples were taken every third day and separated by filtration into three fractions; 0.2–2 μm (bacteria), 2–10 μm (flagellates), and >10 μm (microplankton; phytoplankton and protozoa). Two subsamples were retained from each size fraction. One of the subsamples was left untreated, to obtain adsorbed plus absorbed PCB, while the other subsample was rinsed with 40% of ethanol, to obtain the absorbed PCB. The sorption was found to vary depending on the hydrophobicity of the compounds, the structure of the cell membranes, and the lipid content and composition of the cells. The absorption increased for the TCB and the HCB in the largest size fraction over time, which coincided with an increase of the neutral and non-polar lipids.  相似文献   

专家系统和神经网络相结合用于钻进过程安全监控   总被引：1，自引：0，他引：1  

史玉升  张嗣伟  樊启蕴  李相方 《现代地质》1999,(3)

提出了把专家系统和神经网络混合起来使用的新方法, 这种方法可以克服专家系统和神经网络单独使用时的缺陷。以钻进过程的安全监控为例, 研究了这种方法在确定性和不确定性条件下的使用步骤及效果。  相似文献   

平衡剖面技术在新疆焉耆盆地断裂和圈闭研究中的应用     

陶建元  欧少佳  张永华  钟俊义 《河南国土资源》1999,(4)

简要地介绍了平衡剖面技术的基本原理及在新疆焉耆盆地断裂演化和圈闭研究中的应用。借助该项技术确定了盆地内断裂发育的时空关系及性质,指出盆地内中、新生代的断裂发育过程中有早缓晚骤、早正晚逆（ 反转） 的特征,认为盆地内的构造圈闭主要有两个形成时期,即侏罗纪末的燕山运动时期和第三纪末的喜山运动时期,并且前者形成的圈闭有效性要好于后者。  相似文献   

冻结食品解冻时间的数值计算     

关志强  戴午子  朱立向  曾广达 《广东海洋大学学报》1999,(4)

给出描述平板状冻结食品解冻过程的数学模型 ,并用有限差分法求解。以牛肉为例 ,通过与实测值和经验公式计算值进行比较 ,结果表明 ,数值法预测冻结食品解冻时间具有较高的精度。  相似文献   

海湾扇贝体内重金属含量研究   总被引：3，自引：0，他引：3  

马元庆  秦华伟  李磊  张秀珍  靳洋 《海洋湖沼通报》2010,(1)

采用用微波消解对海湾扇贝样品进行处理,用原子吸收光谱仪测定海湾扇贝合组织中重金属Pd、Cu、Cd、Zn的含量,对重金属含量进行评价,并对海湾扇贝养殖水体进行同步监测。结果表明:Pb、Cu、Cd、Zn在海湾扇贝各组织中的含量不同,Pb、Cu、Cd在内脏中含量最高,Zn在扇贝柱中含量最高,与标准值相比,Pb、Cu在各组织中的含量均符合标准,而Cd在除体液外各组织部位中的含量均超过《无公害食品水产品中有毒有害物质限量》规定的1.0mg/kg标准值,而海湾扇贝养殖水体及沉积物中重金属含量均符合一类海水水质标准。  相似文献   

Saltwater sport fishing for food or income in the Northeastern US: Statistical estimates and policy implications     

Scott Steinback  Kristy Wallmo  Patricia Clay 《Marine Policy》2009

In the Northeast US fishery managers have attempted to control marine recreational fishing mortality through annual adjustments to the number and/or size of fish that can be kept. These measures, with a few exceptions, have generally failed to prevent recreational fishing mortality rates from exceeding annual target levels. In this study, we show that one of the reasons why keep limits may have failed is that a substantial number of anglers obtain little value from being able to keep self-caught fish. Our findings are based on a telephone survey administered to marine anglers in all of the coastal counties in the Northeast US in 2004/2005. To evaluate the importance of keeping self-caught fish, we provide estimates of the size of the marine angling population in the Northeast US that keeps fish for food or income and also for those that fish primarily for recreation and place little or no value on keeping fish. Demographic characteristics of the two groups of anglers are compared statistically and differences related to consumption of self-caught marine resources and to health warning advisories are discussed. We also estimate the size of the Northeast US angling population that relies on their self-caught marine resources as a cost-saving food source or as a supplement to household income. This information could improve the effectiveness of fisheries regulations and the ability of policy analysts to predict how anglers might be affected by proposed fishery management actions.  相似文献   

China’s potential of grain production due to changes in agricultural land utilization in recent years   总被引：3，自引：1，他引：2  

Liangjie Xin  Xiubin Li  Huiyi Zhu  Minghong Tan 《中国地理科学(英文版)》2009,19(2):97-103

The changes in utilization of agricultural land have gradually grown into one of the major factors impacting grain output in China. This study explores the various components of agricultural production in China from the land utilization perspective, involving changes in grain production per unit area, multi-cropping index, and adjustment of agricultural structure. Compared with the record values, different research methodologies are used to analyze the potential of above three components. The results indicate that grain production potential of 65.68×109kg was unexploited in 2006, in which 45.8×109kg came from the restructuring in agriculture. So we can infer that the reduction of grain production in China could be primarily attributed to agricultural restructuring in recent years. So the productive potential can be fully restored by increasing agricultural investment, or recovering agricultural structure in favorable conditions. So we can say that China's current condition of food security is good.  相似文献