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191.
Great attention should be paid to the possible impacts of various nanoparticles on aquatic organism. Freshwater diatoms are essential components of phytoplankton and play a critical role in bioassessment of nanoparticle exposure in the environment. In this study, cell growth was inhibited by TiO2-NPs and MWCNTs, the 24?h EC50 values of TiO2-NPs and MWCNTs to Nitzschia frustulum were 20.75 and 24.64?mg?L?1, respectively. Significant decreases of Chl a content after TiO2-NPs exposures were detected and the Chl a content of N. frustulum was obviously increased by MWCNTs treatment at lower concentration. The ROS was detected in N. frustulum after TiO2-NPs and MWCNTs exposures. The MDA content was significantly induced by TiO2-NPs at lower concentrations of 24 and 48?h exposure; meanwhile, it increased at all tested concentrations at 24?h MWCNTs exposure. The SOD enzyme was induced by 72 and 96?h TiO2-NPs exposure, and increased by MWCNTs treatment at 96?h in N. frustulum. Scanning electron microscopy results revealed that N. frustulum had obvious cell deformation after TiO2-NPs treatment. The result showed that the physiological and biochemical response mechanisms after NPs exposure of diatom were species-specific, and in relation to the exposure concentration and time. 相似文献
192.
The acute toxicity of three formula grade pesticides namely, triazophos (an organophosphate, OP), deltamethrin (a pyrethroid) and combined pesticide (triazophos?+?deltamethrin) was determined in earthworm, Eudrilus eugeniae. They were exposed to different concentrations of these pesticides for 48 h by paper contact toxicity method. The LC50 values for triazophos, deltamethrin and of combination were determined as 0.076, 0.031 and 0.065?μg/cm2, respectively. To study the sublethal effect of these pesticides, E. eugeniae were exposed to 5% and 10% of LC50 of pesticides for 48 h. Morphological alterations such as coiling, clitellar swelling, mucus release and bleeding followed by body segmentation were observed in exposed earthworm. Acetylcholinesterase (AChE) activity assayed in different regions of body segment exhibited a significant (p?<?0.05) decrease in its activity particularly in the pre-clitellar region as compared to other regions. The altered behavioural responses in pesticides exposed earthworms would have been due to decline in AChE activity of the nervous system. 相似文献
193.
Aung M Khaing Swe K Oo T Kyaw Moe K Leimgruber P Allendorf T Duncan C Wemmer C 《Journal of environmental management》2004,72(4):205-216
We reconstructed the history of Chatthin Wildlife Sanctuary (CWS) to understand how social and economic events, and policy changes affected the sanctuary's condition. We surveyed 25 villages surrounding CWS to evaluate past and present ecological conditions, compare the results with historical accounts and identify causal relationships. During the first half of the 20th century, the primary threat was the government's reduction of old growth forest to supply fuel wood for the British-built railway. The railroad opened the area to colonization, but the villagers' impact on timber and wildlife was low. From 1945 to 1988, villagers became the primary force of landscape degradation. The post-war windfall of firearms increased hunting pressure, and populations of large mammal started to decline. With the economic decline of the 1970s and 1980s, the community's demand for game and forest products intensified, and the large mammal fauna was reduced from eleven to four species. From 1988-2003, the forests surrounding the sanctuary were fragmented and degraded. The absence of large predators rendered the park safe for livestock, and the combined effects of grazing and removal of forest products seriously degraded habitat within CWS. Major threats to CWS during the past two decades have resulted from land use decisions in which government-planned economic enterprises caused encroachment by villagers. Stabilization and recovery of this sanctuary will require management compatible with human needs, including expanded buffer zones, better core area protection, community forestry projects, and probably relocation of villages within the park. 相似文献
194.
Dae-lyoung Lim Seung-soon Im Jeong-seok Han Sang-hyun Yim Jin-sung Kim Young-mok Lee 《Journal of Polymers and the Environment》1997,5(4):191-197
Extrusion with an intermeshing corotating twin-screw extruder with a limited amount of water caused structural changes in
corn starch. The structural changes resulted in a transformation-from a semicrystalline to an amorphous state and the development
of orientation of molecular chains in the amorphous region during extrusion. These structural changes, in turn, caused an
increase in theT
g, tensile strength, and resilience of the extruded corn starch. Our experimental results showed that the tensile properties
and resilience of the expanded corn starch extruded at 240‡C were the best: tensile strength, 1.7 kPa; tensile modulus, 40.4
kPa; and resilience, 57.2%. Extrusion produced an expanded corn starch suitable for protective loose-fill. 相似文献
195.
不同时间尺度气候变化的分维研究 总被引:6,自引:1,他引:6
探讨了从一维时间序列中提取气候分维的方法,计算了不同时间尺度气候变化的分数维,并讨论了维数与气候变化的相关系。 相似文献
196.
How integrated is river basin management? 总被引:2,自引:0,他引:2
Land and water management is increasingly focused upon the drainage basin. Thirty-six terms recently used for schemes of “integrated
basin management” include reference to the subject or area and to the aims of integrated river basin management, often without
allusion to the multiobjective nature. Diversity in usage of terms has occurred because of the involvement of different disciplines,
of the increasing coherence of the drainage basin approach, and the problems posed in particular parts of the world. The components
included in 21 different approaches are analyzed, and, in addition to showing that components related broadly to water supply,
river channel, land, and leisure aspects, it is concluded that there are essentially five interrelated facets of integrated
basin management that involved water, channel, land, ecology, and human activity. Two aspects not fully included in many previous
schemes concern river channel changes and the dynamic integrity of the fluvial system. To clarify the terminology used, it
is suggested that the termcomprehensive river basin management should be used where a wide range of components is involved, whereasintegrated basin management can signify the interactions of components and the dominance of certain components in the particular area.Holistic river basin management is advocated as a term representing an approach that is both fully comprehensive and integrated but also embraces the energetics
of the river system and consideration of changes of river channels and of human impacts throughout the river system. The paradigm
of working with the river can be extended to one of working with the river in the holistic basin context. 相似文献
197.
Jackie Sellers R. M. North 《Journal of the American Water Resources Association》1979,15(6):1677-1690
ABSTRACT: This article offers a procedure for identifying the primary effects of financing and cost sharing rates on four basic levels: program, technical, incidence, and comprehensive impacts. A process is developed for identifying these effects based upon two alternative approaches. One method would follow the effects of rate changes through the four levels of impact, another would look in depth at the consequences of rate changes on a particular impact. For this study the information and suggested changes found in the Section 80(c) Study were used to illustrate possible impacts. The process suggested herein could be used in anticipating impacts of any major policy change. 相似文献
198.
经济发展与耕地变化的关系--以江苏省为例 总被引:5,自引:0,他引:5
一直以来,对于经济发展与耕地变化间的关系问题,许多学者都认为两者是负相关的关系.辨证地分析了经济发展与耕地变化之间的关系,并结合对江苏省的实证研究,对这一问题有了更深的认识:即经济发展对耕地变化不仅有负面作用,还在一定程度上存在着正向作用.从总体来看,经济发展所消耗的耕地数量将先上升后下降,呈现明显的倒"U"型曲线状. 相似文献
199.
Utilization of amniocentesis for prenatal diagnosis because of the indication of advanced maternal age (≥ 35 years at delivery) was examined in the population of B.C. over an 8-year period (1976–1983). As of 1983, approximately one out of three eligible women (≥ 35 years at delivery) is having the test. In the older group (≥ 38 years at delivery) approximately one out of two eligible women is having the test. The data do not indicate that the proportion of eligible women having amniocentesis has reached a plateau; utilization is continuing to increase. It appears that prenatal diagnosis is an ethically acceptable alternative for a large proportion of the population. 相似文献
200.
根据“十五”、“十一五”期间“创模”指标体系,分析了各阶段指标体系差异和变化,而最新的指标体系能更全面地反映环境质量。同时,“创模”指标的变化趋势分析表明,“创模”指标的发展必然是反映当时的环保工作重点,“创模”的基本条件门槛会不断提升,“创模”指标的内涵会不断丰富,以确保国家环境保护模范城市的先进性和示范性。 相似文献