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51.
In order to investigate the conversion of kinetic energy from a synoptic scale disturbance (SSD; period≤seven days) to a low-frequency fluctuation (LFF; period〉seven days), the budget equation of the LFF kinetic energy is derived. The energy conversion is then calculated and analyzed for the summers of 1997 and 1999. The results show that the energy conversion from the SSD to the LFF is obviously enhanced in the middle and lower troposphere during the heavy rainfall, suggesting this to be one of mechanisms inducing the heavy rainfall, although the local LFF kinetic energy may not be enhanced. 相似文献
52.
Julian M. Szeicz Barbara A. Zeeb K.D. Bennett John P. Smol 《Journal of Paleolimnology》1998,20(3):235-252
A 1600 year paleoecological record of environmental change is developed from a small lake in the Nothofagus forest of southern Chile (45.5°S, 72°W). High resolution fossil pollen, charcoal, sedimentological, and chrysophycean stomatocyst analyses are used to investigate the impacts of natural and anthropogenic disturbances on terrestrial and lacustrine environments. Chronological control is based on a combination of 210Pb and 14C dating. Temporal resolution during the past 150–200 yr is ca. 8 yr/sample. The macroscopic charcoal record correlates very closely with historical and dendroecological records of 20th century anthropogenic burning in this region. The chrysophyte stratigraphy indicates that this burning had immediate impacts on the lake itself, while the pollen record provides evidence for a succession of vegetation changes lagging slightly behind the disturbance. These palynological changes are very similar to the pollen signal of European disturbance in northeastern North America. Pre-European shifts in chrysophyte assemblages may be due to the influence of earthquake activity on the lake, though there is no corroborative evidence in the pollen or charcoal records. This study demonstrates that high resolution paleoecological methods can be used to help bridge the temporal gap between traditional ecological and paleoecological studies of environmental change in the temperate forests of southern South America. 相似文献
53.
Zhao-Yong Xu Run-Hai Yang Bin Wang Jin-Ming Zhao Yu-Feng Yao Pei-Zhong Hua Shi-Rong Mei 《地震学报(英文版)》1998,11(6):737-744
A multi-functional high-frequency seismometer, a new instrumental system, is used for recording multi-point strain variations
of rock samples in the process of fracture development. The results indicate that strain in each point appears burst disturbance
synchronously besides a tendency variation before main fracture. The burst disturbance could probably be one of the short-impending
precursors before great earthquake. 相似文献
54.
Burst strain disturbance—A new test study on fracture precursor 总被引:1,自引:0,他引:1
ZHAO YONG XU ) RUN HAI YANG ) BIN WANG ) JIN MING ZHAO ) YU FENG YAO ) PEI ZHONG HUA ) SHI RONG MEI ) ) Seismological Bureau of Yunnan Province Kunming China ) Center for Analysi 《地震学报(英文版)》1998,(6)
IntroductionBeforeanearthquakeocuurs,deformationvariationsobviouslyappearinseismogenicareaandnearbywhichwerereportedalot.Earl... 相似文献
55.
Hurricane Isabel reached the Eastern seaboard of North America on 18 September 2003 causing estimated damage >3 billion US dollars and the death of ∼50 people. Isabel is considered to be one of the most significant tropical cyclones to affect Virginia, since the Chesapeake Potomac Hurricane of 1933 and Hurricane Hazel in 1954. A study of the temporal changes in the benthic fauna pre- and post-hurricane was conducted on an intertidal sandflat within the dynamic barrier island system near Wachapreague, Eastern Virginia. Replicate sediment cores were collected 3 weeks before Isabel made landfall and further samples were collected on 5 occasions over the following 20 months. An immediate effect of Isabel was a doubling in the number of species, a significant increase in invertebrate species diversity (H′) and a rise in opportunistic species and deposit feeders, but a non-significant increase in the total number of organisms. Changes in infauna occurred such that by the end of the study there were significantly increased numbers of species, faunal abundances and community diversity measures, as compared with pre-hurricane samples, suggesting a potentially positive medium-term effect of this hurricane perturbation. The most notable direct effects of the hurricane were on the relative abundances of feeding guilds with a reduction in interface feeders from 87% pre-hurricane to 64% post-hurricane, and an increase in surface deposit feeders from 7% pre-hurricane to 20% post-hurricane. The study highlights potential problems in interpreting post-perturbation data when insufficient pre-perturbation data exist. 相似文献
56.
VAV��ETERNA��ϫ���������ıȽϺ��о� 总被引:3,自引:3,他引:0
??VAV??ETERNA??????????????????????????????????????????????????????????????????????人???????????????з????????????, ??????VAV?????????????????ETERNAС,??????????????????????????????????????????????????????????VAV??ETERNA????????????? 相似文献
57.
Macrofauna along the Sudanese Red Sea coast: potential effect of mangrove clearance on community and trophic structure 下载免费PDF全文
Mangroves along the Sudanese Red Sea coast are under constant anthropogenic pressure. To better understand the influence of mangrove clearance on the intertidal benthic community, we investigated the composition, biodiversity and standing stock of the macrofauna communities at high‐, mid‐ and low‐water levels in three contrasting habitats: a bare sand flat, a cleared mangrove and an intact mangrove. In addition, a community‐wide metric approach based on taxon‐specific carbon and nitrogen isotope values was used to compare the trophic structure between the three habitats. The habitats differed significantly in terms of macrofaunal standing stock, community composition and trophic structure. The high‐ and mid‐water levels of the intact mangroves showed a distinct macrofaunal community characterized by elevated densities and biomass, largely governed by higher decapod and gastropod abundances. Diversity was similar for cleared and intact mangroves, but much lower for the bare sand flat. Community‐wide metrics indicated highest trophic diversity and community niche breadth in the intact mangroves. Differences between the cleared and intact mangroves can be partly attributed to differences in sediment characteristics resulting from mangrove clearance. These results suggest a significant impact of mangrove clearance on the macrofaunal community and trophic structure. This study calls for further investigations and management actions to protect and restore these habitats, and ensure the survival of this ecologically valuable coastal ecosystem. 相似文献
58.
Historic land use can exert strong land-use legacies, i.e., long-lasting effects on ecosystems, but the importance of land-use legacies, alongside other factors, for subsequent forest-cover change is unclear. If past land use affects rates of forest disturbance and afforestation then this may constrain land use planning and land management options, and legacies of current land management may constrain future land use. Our goal was to assess if and how much land-use legacies affect contemporary forest disturbance, and the abundance of different forest types in the Carpathian region in Eastern Europe (265,000 km2, encompassing parts of Poland, Slovakia, Ukraine, Romania, Hungary, and Czech Republic). We modeled contemporary forest disturbance (based on satellite image analysis from 1985 to 2010) as a function of historic land use (based on digitized topographic maps from 1860 and 1960). Contemporary forest disturbance was strongly related to historic land use even when controlling for environmental, accessibility and socio-political variation. Across the Carpathian region, the odds of forest disturbance were about 50% higher in areas that were not forested in 1860 (new forests) compared to areas that were forested then (old forests). The forest disturbance in new forests was particularly high in Poland (88% higher odds), Slovakia (69%) and Romania (67%) and persisted across the entire range of environmental, accessibility and socio-political variation. Reasons for the observed legacy effects may include extensive plantations outside forest ranges, predominantly spruce, poplar, and black locust, which are prone to natural disturbances. Furthermore, as plantations reach harvestable age of about 70 years for pulp and 120 year for saw-timber production, these are likely to be clear-cut, producing the observed legacy effects. Across the Carpathians, forest types shifted towards less coniferous cover in 2010 compared to the 1860s and 1960s likely due to extensive historic conifer harvest, and to recent natural disturbance events and clear-cuts of forest plantations. Our results underscore the importance of land-use legacies, and show that past land uses can greatly affect subsequent forest disturbance for centuries. Given rapid land use changes worldwide, it is important to understand how past legacies affect current management and what the impact of current land management decisions may be for future land use. 相似文献
59.
通过"双三次曲面拟合—时间步长积分—双三次曲面拟合……",实现成为一种双三次曲面拟合新算法数值模式。它对模式大气作非线性(空间二阶可导)描述,是用数值分析(三次样条/双三次曲面)与计算方法近似求解大气运动非线性偏微分方程组。用Z坐标系高分辨率双三次数值模式,采用原始大气运动方程组和采用欧拉时间积分方案,设置理想扰动,对大气声波Lamb波做数值模拟;采用大气不可压假定,除去声波,对大气重力波龙卷扰动做数值模拟。对比模拟发现:理想Lamb波以声速在水平方向传播,扰动能量频散快,仅能在原地持续数秒钟;理想龙卷扰动则在原地可持续约1 min,且波动内圈(外圈)自下至上始终处于风场辐合(辐散)状态,具冷心结构和气压驻波特征,可因水汽进入扰动与借助凝结潜热释放而得到发展。 相似文献
60.
Echavarri-Erasun B Juanes JA García-Castrillo G Revilla JA 《Marine pollution bulletin》2007,54(7):941-954
An investigation on the effects of deepwater outfall discharges on the status of rocky reef communities was carried out. The sanitation system was found to be an environmentally suitable option for the protection of those habitats situated in high energy coastal environments. Sediments occurring between the predominating rocky substrates showed low values of the fine fraction (<63microm) and organic matter content. In addition, high average concentrations of Cd, Hg and Zn were found in these sediments, though these values were similar to those registered in non-affected sites, far away from the outfall. On the other hand, those assemblages typical of hard substrates that settled near the outfall showed an increase in total richness and abundance of macroinvertebrates. Moreover, the average number of species of each taxonomic group, a good indicator of the maintenance of the previous trophic structure, only varied considerably over time at the rip-rap protection. In a global context, those changes were not directly related to the discharge disturbances, but to the natural variability or the successional processes occurring within those communities. Only communities dwelling in the rip-rap protection area were affected by the proximity of the discharges. 相似文献