干旱-半干旱区兰州兴隆山现代森林典型植被和土壤中类脂物分子特征及其意义   总被引：4，自引：2，他引：2       下载免费PDF全文

雷国良  张虎才  杨明生  张文翔  蒲阳  常凤琴  类延斌  杨伦庆 《第四纪研究》2009,29(1):159-164

利用GC－MS对西北干旱区-半干旱区兰州兴隆山森林区典型植被与现代土壤样品中可抽提的类脂物进行了系统分析,检测出包括正构烷烃和α正构脂肪酮等一系列类脂物分子化石。在未进行族分离的情况下,检出兴隆山现代森林木本植物的正构烷烃以C₂₇或C₂₉为主峰,草本植物则以C₃₁为主峰;  土壤样品中均保留有很强的、几乎均势的C₂₇,C₂₉和C₃₁信号; α正构脂肪酮具有明显的奇碳优势,植物中以C₂₃,C₂₅或C₂₉为主峰,土壤样品以C₂₇或C₂₉为主峰;  其反映的信息是植被与微生物共同作用的结果。本研究为理解现代土壤和古土壤中类脂物所指示的植被信息、进一步探讨类脂物分子在植被(有机质)-微生物-土壤-湖泊沉积体系中存在与相互转换关系这一基础理论问题提供了科学资料。同时,为分子化石分析方法的改进和不同处理过程所得数据之间的对比和科学解释提供资料。  相似文献   

Paleoenvironmental and paleoecological reconstruction of a freshwater oasis in savannah grassland at FLK North, Olduvai Gorge, Tanzania     

Gail M. Ashley  Doris Barboni  Manuel Dominguez-Rodrigo  Henry T. Bunn  Audax Z.P. Mabulla  Fernando Diez-Martin  Rebeca Barba  Enrique Baquedano   《Quaternary Research》2010,74(3):333-343

The records of early hominins are commonly localized both temporally and spatially even in archaeologically rich basins like Olduvai Gorge, Tanzania. The FLK North site was discovered in 1960, but the reason for the exact location of this dense concentration of fossils and stone tools on a lake-margin flat has not been explained. We present new geological and geochemical information from six excavations in upper Bed I, which revealed up to 1.4-m-thick carbonate deposits, attesting to the presence of freshwater springs in the area surrounding FLK North. The δ¹⁸O signatures of the tufa are typical for meteoric water that has evolved during evaporation. Tuff IF that caps the sequence was deposited on uneven topography with the highest area a low-relief ridge between two faults at the archaeological site and lowest areas being sites of groundwater discharge. The model proposed here is that rainfall on adjacent highlands was transported to the basin where faults acted as conduits for water. Similar hydrogeological settings at modern lakes Manyara and Eyasi, currently support lush groundwater forest and woodland despite arid climate. FLK North may have been an “oasis” offering freshwater and shelter for consuming meat by both carnivores and hominins.  相似文献   

Criteria for Selecting and Adjusting Ground-Motion Models for Specific Target Regions: Application to Central Europe and Rock Sites   总被引：6，自引：2，他引：6  

Fabrice Cotton  Frank Scherbaum  Julian J. Bommer  Hilmar Bungum 《Journal of Seismology》2006,10(2):137-156

A vital component of any seismic hazard analysis is a model for predicting the expected distribution of ground motions at a site due to possible earthquake scenarios. The limited nature of the datasets from which such models are derived gives rise to epistemic uncertainty in both the median estimates and the associated aleatory variability of these predictive equations. In order to capture this epistemic uncertainty in a seismic hazard analysis, more than one ground-motion prediction equation must be used, and the tool that is currently employed to combine multiple models is the logic tree. Candidate ground-motion models for a logic tree should be selected in order to obtain the smallest possible suite of equations that can capture the expected range of possible ground motions in the target region. This is achieved by starting from a comprehensive list of available equations and then applying criteria for rejecting those considered inappropriate in terms of quality, derivation or applicability. Once the final list of candidate models is established, adjustments must be applied to achieve parameter compatibility. Additional adjustments can also be applied to remove the effect of systematic differences between host and target regions. These procedures are applied to select and adjust ground-motion models for the analysis of seismic hazard at rock sites in West Central Europe. This region is chosen for illustrative purposes particularly because it highlights the issue of using ground-motion models derived from small magnitude earthquakes in the analysis of hazard due to much larger events. Some of the pitfalls of extrapolating ground-motion models from small to large magnitude earthquakes in low seismicity regions are discussed for the selected target region.  相似文献   

桂林靖江王城防雷方案初探     

方琼玉  黎梓华  姚立宏 《气象研究与应用》2007,28(3):59-61

根据靖江王城古建筑物的特点、分布情况及所处的地理环境特征,结合雷击风险评估结果,对不同的保护物划分防雷类别,提出了雷电保护方案。  相似文献   

Late Holocene paleoenvironmental change in a Great Lakes coastal wetland: integrating pollen and diatom datasets   总被引：1，自引：0，他引：1  

Sarah?A.?Finkelstein  Matthew?C.?PerosEmail author  Anthony?M.?Davis 《Journal of Paleolimnology》2005,33(1):1-12

Multiple proxy indicators are regularly used to present robust arguments for paleoenvironmental change. We use fossil pollen and diatoms from a 495-cm core taken from Cootes Paradise, a coastal wetland in the western end of Lake Ontario, to investigate ecological changes in the late Holocene. We use consensus analysis to demonstrate that pollen diagrams are best zoned after the data have been split into source area, in this case upland and wetland taxa, because each group responds differently to environmental change. We also use consensus analysis to demonstrate the sensitivity of clustering to the distance measure used. The record begins at 2400 ¹⁴C years BP, when the wetland was dominated by shallow water emergents and epiphytic diatoms. At 2100 ¹⁴C years BP, a decline in the epiphytic diatoms Epithemia spp., a rise in Poaceae (cf. Zizania aquatica) pollen and a coincident increase in pollen concentration suggest a water level rise at this time. At about 800 ¹⁴C years BP, the diatom record shows a pulse in small benthic Fragilaria species; shortly after, a shift occurs in the upland tree pollen spectra involving an increase in Pinus and a decline in Fagus. This shift in upland forest trees has been associated elsewhere with the Little Ice Age and the diatom data present some evidence for impacts of this climatic event on aquatic systems. The diatom and pollen records both indicate large changes associated with the effects of European settlement, including rises in Ambrosia as well as Typha angustifolia pollen. Planktonic diatoms dominate post-settlement assemblages indicating large-scale hydrological and ecological changes, probably associated with the introduction of carp and alterations to the Iroquois bar which separates the wetland from Lake Ontario. Our work at Cootes Paradise is important for multi-proxy coastal wetland studies in general, in addition to the late Holocene environmental history and prehistory of the Great Lakes region.  相似文献   

BOOK REVIEWS     

《The Professional geographer》1988,40(4):471-499

Books reviewed in this article: USA, Eine Geographische Landeskunde , Vol. I, Der Grossraum in Strukturellem, Wandel, 3rd Ed. Helmut Blume . Introduction to Remote Sensing . James B. Campbell . The Sounds of People and Places: Readings in the Geography of American Folk and Popular Music . George O. Carney , ED. Development and Underdevelopment . John Cole . Mobility and Employment in Urban Southeast Asia: Example from Indonesia and the Philippines . Michael A. Costello , Thomas R. Leinbach , AND Richard Ulack . Soviet Asia: Economic Development and National Policy Choices . Leslie Dienes . The Third World City . David Drakakis -Smith . Scholars' Guide to Washington, DC for Cartography and Remote Sensing Imagery (maps, charts, aerial photographs, satellite images, cartographic literature and geographic information systems). Ralph E. Ehrenberg . Population and Development in the Third World . Allan AND Anne Findlay . The Early Mapping of Hawaii . Gary L. Fitzpatrick . Energetics of Physical Environment: Energetic Approaches to Physical Geography . K. J. Gregory , ED. Wildland Recreation: Ecology and Management . William E. Hammitt and David N. Cole . Agricultural Commercialization and Government Policy in Africa . J. Hinderink AND J. J. Sterkenburg . The Dynamics of American Housing . James W. Hughes AND George Sternlieb . Thailand: Buddhist Kingdom as Modern Nation State . Charles F. Keyes . Resolving Locational Conflict . Robert W. Lake , ED. Lands at Risk in the Third World: Local-level Perspectives . Peter D. Little and Michael M. Horowitz , EDS. Nathaniel Southgate Shaler and the Culture of American Science . David N. Livingstone . Regions: The Economics and Politics of Territory . Ann R. Markusen . Wetlands . William J. Mitsch and James G. Gosselink . Historical Geography: Progress and Prospect . Michael Pacione , ED. Loess and Periglacial Phenomena . Marton P$eacsi and Hugh M. French , EDS. Regional Management of Metropolitan Floodplains, Experience in the United States and Abroad . Rutherford H. Platt , ED. Human Cartography: Mapping the World of Man . Janos Szegö . Atlas of Great Lakes Indian History . Helen H. Tanner , ED. The Botany of Mangroves . P. B. Tomlinson . Urban Spatial Traffic Patterns . Rodney Vaughan . The Night After … Climatic and Biological Consequences of a Nuclear War . Yevgeni Velikhov , ED. Industrial Geography . H. D. Watts . Dictionary of Quotations in Geography . James O. Wheeler and Francis M. Sibley . Vermont Townscape . Norman Wiliams , Jr. , Edmund K. Kellogg and Peter M. Lavigne .  相似文献   

Evapotranspiration modelled from stands of three broad‐leaved tropical trees in Costa Rica     

Seth Bigelow 《水文研究》2001,15(14):2779-2796

  相似文献   

黄淮海平原风沙化土地果树栽培技术研究   总被引：2，自引：1，他引：2  

李晓云  张小军 《中国沙漠》1996,16(3):319-325

为治理、开发黄淮海平原风沙化土地，３年间，从国内外引入１４９个果树品种，建果园１５．３ｈｍ２。历时７年，选择出良种２８个，有苗百万株，推广、辐射面积０．６６ｈｍ２。研究表明：在现有条件下，本区采用引进选择、试验示范、推广辐射的办法，进行大穴栽植，截断淤积层，矮化密植，四季修剪，植物生长剂调控树体，少量、多次、浅施肥料，增施有机肥，间作留茬，冬春少耕、免耕，早防病虫害等一整套果树栽培、管理技术，是发展黄淮海风沙化地区果林业的一条快速、可靠、有效的方法。  相似文献   

犯罪共生空间的类型识别及其特征分析   总被引：2，自引：1，他引：1  

柳林  杜方叶  宋广文  龙冬平  姜超  肖露子 《地理科学》2018,38(8):1199-1209

以ZG市公共空间盗窃、入室盗窃、寻衅滋事、接触诈骗、抢劫抢夺犯罪为研究对象,采用K均值聚类法识别不同类型的犯罪共生空间;并通过决策树模型分析了不同犯罪共生空间的特征。结果表明,ZG市犯罪共生空间可划分为4种类型：① 无犯罪类型共生区;② 公共空间盗窃和接触诈骗犯罪共生区;③ 所有类型犯罪共生区;④ 入室盗窃、寻衅滋事和抢劫抢夺犯罪共生区。城市中各异的社会环境和建成环境产生了不同类型的犯罪机会,而且各类社会环境和建成环境之间存在着条件交互性作用。研究结果为制定犯罪的联合防控策略和实现有限警力的合理布控并且提高执法效率提供了理论基础。  相似文献   

A comparative approach to modelling multiple urban land use changes using tree-based methods and cellular automata: the case of Greater Tokyo Area     

Guodong Du  Liang Yuan  Shunsuke Managi 《International journal of geographical information science》2018,32(4):757-782

Urban multiple land use change (LUC) modelling enables the realistic simulation of LUC processes in complex urban systems; however, such modelling suffers from technical challenges posed by complicated transition rules and high spatial heterogeneity when predicting the LUC of a highly developed area. Tree-based methods are powerful tools for addressing this task, but their predictive capabilities need further examination. This study integrates tree-based methods and cellular automata to simulate multiple LUC processes in the Greater Tokyo Area. We examine the predictive capability of 4 tree-based models – bagged trees, random forests, extremely randomised trees (ERT) and bagged gradient boosting decision trees (bagged GBDT) – on transition probability prediction for 18 land use transitions derived from 8 land use types. We compare the predictive power of a tree-based model with multi-layer perceptron (MLP) and among themselves. The results show that tree-based models generally perform better than MLP, and ERT significantly outperforms the three other tree-based models. The outstanding predictive performance of ERT demonstrates the advantages of introducing bagging ensemble and a high degree of randomisation into transition probability modelling. In addition, through variable importance evaluation, we found the strongest explanatory powers of neighbourhood characteristics for all land use transitions; however, the size of the impacts depends on the neighbourhood land use type and the neighbourhood size. Furthermore, socio-economic and policy factors play important roles in transitions ending with high-rise buildings and transitions related to industrial areas.  相似文献