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291.
舟山群岛港口发展有广阔前景 总被引:2,自引:1,他引:1
舟山海域位于长江水道和我国南北洋通道交汇的前沿,是我国南北海运的要冲与江海联运的枢纽,地理位置非常优越。舟山的三大优势资源“鱼、港、景”中,港的优势得天独厚拥有极为丰富的深水岩线,建设第四、五代大型集装箱泊位及其他大型深水泊位,发展潜能很大。舟山港域的发展提出了三点建议:1、充分利用区域优势,北依上海,南托宁波,定位于华东沿海重要的区域性洪口,成为长江三角洲口群体中的一个重要组成部分。2、利用岛屿 相似文献
292.
MacDonald LH 《Environmental management》2000,26(3):299-315
Since any proposed activity could contribute to a wide range of potential CEs at different spatial and temporal scales, a
tiered or nested approach should be followed to assess CEs. The difficulty of assessing and predicting CEs also suggests that
in many cases the most efficient approach is to focus on minimizing on-site impacts. Under some circumstances adaptive management
can also be a viable alternative to detailed CE assessments. Regular monitoring and feedback is critical to the successful
management and regulation of CEs. 相似文献
293.
Abstract: Habitat fragmentation is the transformation of once-extensive landscapes into smaller, isolated remnants surrounded by new types of habitat. There is ample evidence of impoverished biodiversity as a consequence of habitat fragmentation, but its most profound effects may actually result from functional changes in ecological processes such as trophic interactions. We studied the trophic processes of herbivory and parasitism in insect-plant food webs composed of hundreds of species in a fragmented woodland landscape. We recorded all plant species, collected mined leaves, and reared leafminers and parasitoids from 19 woodland remnants. Herbivory and parasitism rates were then analyzed in relation to woodland size and edge or interior location. Herbivory by leaf-mining insects and their overall parasitism rates decreased as woodland remnants became smaller. For each remnant the intensity of both processes differed between edge and interior. Our results provide novel evidence of the magnitude of habitat fragmentation effects, showing they can be so pervasive as to affect trophic processes of highly complex food webs and suggesting a response associated with trophic specialization of the involved organisms as much as with their trophic level. 相似文献
294.
G. L. Samsel 《Journal of the American Water Resources Association》1973,9(6):1145-1152
ABSTRACT: Investigations were initiated to evaluate the effects of sedimentation on the algal composition, primary productivity rates and chemical nutrient concentrations of a 17 acre recreational impoundment in central Virginia. Comparisons during the winter seasons of 1972–1973 indicated that as a result of sedimentation, from lake front home construction, the total numbers of algal genera in the lake decreased from 24 to 16, productivity as measured by 14CO2 and total extractable chlorophyll decreased two fold, and several important nutrients, i.e. NH4+-N, SiO2 and PO4-P increased significantly. 相似文献
295.
P. Louka G. Vachon J.-F. Sini P. G. Mestayer J.-M. Rosant 《Water, Air, & Soil Pollution: Focus》2002,2(5-6):351-364
The thermal effects on the airflow within a street canyon, which are produced by the variation of direct solar heating of the street sides and ground, are examined in this article. The investigation is based on the experimental results of the Nantes'99 campaign and numerical simulations performed with the Computational Fluid Dynamics (CFD) code CHENSI using the standard k- model. The Nantes'99 experimental campaign was performed in a North-to-South oriented central street canyon of Nantes, France. It was observed that a thin thermal layer develops locally within a few centimetres from the heated wall. It is anticipated that, the convective flow close to the windward wall, which was visualised during the experiment, carries air masses from the street level upwards, where normally cleaner air is transported. Consequently, thermal effects may be important for the air quality in the street.Based on the temperature and wind flow measurements, the flow and temperature fields were simulated first in two dimensions with the CFD code CHENSI. It was found that CHENSI overestimates the thermal effects on the canyon airflow showing the main re-circulation simulated in the isothermal case to change into two counter-rotating vortices after the inclusion of the heating of the windward wall. A reason for this overestimation is possibly the temperature wall function implemented for such thin thermal boundary layers in conjunction with the limitations in grid resolution. 相似文献
296.
Understanding the earth system requires that the two-way linkages between regions and the global system be well understood
and predictable. Most studies of global change are undertaken thematically across limited disciplinary boundaries; few are
attempted holistically across many disciplines within regions. The regional approach offers many advantages. Here a variety
of linkages associated with the regions of Southern Africa, South Asia, East Asia and Southeast Asia are presented to illustrate
the power of a regional approach to earth system science. Major findings include the extent to which long-range transport
of aerosols and nutrients affect terrestrial and marine ecosystem functioning in and around southern Africa. Aerosol transport,
and the development of a regional haze layer, over South Asia are shown to alter significantly the radiative forcing of change
in the atmosphere over the region. Changes in land cover and use over East Asia over along period of time are shown to have
affected the strength of the monsoon circulation significantly. Finally, rampant economic development and globalization in
Southeast Asia are demonstrated to have been a significant driver of regional change.
Electronic Publication 相似文献
297.
典型醛类污染物与细胞DNA分子的结合作用 总被引:14,自引:1,他引:13
为了研究甲醛、乙醛和丙烯醛等 3种典型醛类污染物与细胞DNA的结合作用 ,探讨其遗传毒性效应和机制 ,采用体外测试系统 ,应用紫外光谱移动法和高效液相色谱法研究结合位点 .结果表明 ,醛类污染物染毒细菌DNA紫外吸收峰位移不显著 ;但提取的细菌DNA与甲醛进行试管反应体系紫外位移显著 ;醛类污染物染毒真核细胞致DNA分子紫外吸收峰位移显著 ;乙醛与脱氧鸟苷酸的试管反应经NaBH4 还原后经HPLC分离检测 ,产物初步定性为N2-乙基鸟苷加合物 .说明 3种醛类污染物能够与细胞DNA结合而体现遗传毒性 ,鸟苷的N2位可能是共价加合的位点 . 相似文献
298.
禁牧政策及其效应解析 总被引:23,自引:2,他引:21
近年来,各地对脆弱生态环境的改善手段逐步从生态建设为主转向建设和保护并重的方向。禁牧政策便是影响重大的保护措施之一。通过对实施禁牧政策较早的、位于农牧交错带的内蒙古伊金霍洛旗的实地调查和分析发现,全年禁牧政策对保护和恢复面积广大的林草地生态环境很有效,但它与当地农牧户畜牧业生产的现实矛盾较大,执行率只有52.98%。因此,提出改变限制性禁牧政策为引导性禁牧政策的观点,实行有弹性的禁牧政策,以及农牧户改变畜牧业生产方式和调整畜种结构等政策调适建议。 相似文献
299.
Managing Aquatic Species of Conservation Concern in the Face of Climate Change and Invasive Species 总被引:2,自引:0,他引:2
Abstract: The difficult task of managing species of conservation concern is likely to become even more challenging due to the interaction of climate change and invasive species. In addition to direct effects on habitat quality, climate change will foster the expansion of invasive species into new areas and magnify the effects of invasive species already present by altering competitive dominance, increasing predation rates, and enhancing the virulence of diseases. In some cases parapatric species may expand into new habitats and have detrimental effects that are similar to those of invading non-native species. The traditional strategy of isolating imperiled species in reserves may not be adequate if habitat conditions change beyond historic ranges or in ways that favor invasive species. The consequences of climate change will require a more active management paradigm that includes implementing habitat improvements that reduce the effects of climate change and creating migration barriers that prevent an influx of invasive species. Other management actions that should be considered include providing dispersal corridors that allow species to track environmental changes, translocating species to newly suitable habitats where migration is not possible, and developing action plans for the early detection and eradication of new invasive species. 相似文献
300.