中国兴凯湖北岸平原晚全新世花粉记录及泥炭沼泽形成   总被引：7，自引：1，他引：7  

张淑芹  邓伟  阎敏华  李小强  王升忠 《湿地科学》2004,2(2):110-115

通过兴凯湖北岸平原泥炭剖面高分辩率花粉分析研究，对晚全新世花粉划分4个组合带。XKH-4组合时期(1857～1746aB．P．)为沼泽发育前期，这一时期花粉浓度小，陆生草本植物占优势，气候干冷。XKH-3组合时期(1746～1287aB．P．)为沼泽发育早期，这一时期花粉浓度较大，且水生植物花粉含量为剖面最高，喜温落叶阔叶植物大发展时期，气候温和湿润。XKH-2组合时期(1287～602aB．P．)为沼泽发育中期，这一时期花粉浓度最小，但以陆生草本植物为主，木本植物为辅，水生植物急剧减少，针叶植物出现两次高峰，气候向冷干方向发展。XKH-1组合时期(602aB．P．至今)为沼泽发育盛期，这一时期花粉浓度最大，陆生草本植物大发展时期，气候波动较大。  相似文献   

洪湖的环境变迁与生态保护   总被引：16，自引：2，他引：16  

卢山  李世杰  王学雷 《湿地科学》2004,2(3):234-237

洪湖历史上经历了多次变迁，在同类型湖泊中表现出其生态的复杂性和多样性。通过分析洪湖从成湖以来所发生的的湖泊环境变化，阐述了人类活动对洪湖环境带来的一系列生态问题，对洪湖生态环境的恢复与优化提出对策与建议；同时，对于洪湖省级湿地自然保护区的建设和管理提出了科学的、可操作的具体措施。  相似文献   

Channel adjustments of the lower Trinity River,Texas, downstream of Livingston Dam     

Jonathan D. Phillips  Michael C. Slattery  Zachary A. Musselman 《地球表面变化过程与地形》2005,30(11):1419-1439

Channel cross‐sectional changes since construction of Livingston Dam and Lake Livingston in 1968 were studied in the lower Trinity River, Texas, to test theoretical models of channel adjustment, and to determine controls on the spatial extent of channel response. High and average flows were not significantly modified by the dam, but sediment transport is greatly reduced. The study is treated as an opportunistic experiment to examine the effects of a reduction in sediment supply when discharge regime is unchanged. Channel scour is evident for about 60 km downstream, and the general phenomena of incision, widening, coarsening of channel sediment and a decrease in channel slope are successfully predicted, in a qualitative sense, by standard models of channel response. However, there is no consistent channel response within this reach, as various qualitatively different combinations of increases, decreases or no change in width, depth, slope and roughness occur. These multiple modes of adjustment are predicted by the unstable hydraulic geometry model. Between about 60 km and the Trinity delta 175 km downstream of the dam, no morphological response to the dam is observed. Rather than a diminution of the dam's effects on fluvial processes, this is due to a fundamental change in controls of the fluvial system. The downstream end of the scour zone corresponds to the upstream extent of channel response to Holocene sea level rise. Beyond 60 km downstream, the Trinity River is characterized by extensive sediment storage and reduced conveyance capacity, so that even after dam construction sediment supply still exceeds transport capacity. The channel bed of much of this reach is near or below sea level, so that sea level rise and backwater effects from the estuary are more important controls on the fluvial system than upstream inputs. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The lacustrine sedimentary records of coal-burning atmospheric pollution     

E. Appel  V. Hoffmann 《中国科学D辑(英文版)》2005,48(10)

With the acceleration of industrialization, coal- burning atmospheric pollution is getting more and more serious in many regions in China. However, there are only about ten odd years literature records about pollution in some large and mid-sized cities, where the atmosphere has perhaps been polluted for several decades, and therefore it is difficult to know the process and characteristic of pollution, and diffi-cult to evaluate its damage to environment. Lacustrine sediment, a natural record w…  相似文献   

Leaf area index retrieval based on canopy reflectance and vegetation index in eastern China     

JIANG Jianjun  CHEN Suozhong  CAO Shunxian  WU Hongan  ZHANG Li  ZHANG Hailong 《地理学报》2005,15(2):247-254

The aim of this paper is to investigate the feasibility of using Landsat TM data to retrieve leaf area index (LAI). To get a LAI retrieval model based ground reflectance and vegetation index, detailed field data were collected in the study area of eastern China, dominated by bamboo, tea plant and greengage. Plant canopy reflectance of Landsat TM wavelength bands has been inversed using software of 6S. LAI is an important ecological parameter. In this paper, atmospheric corrected Landsat TM imagery was utilized to calculate different vegetation indices (VI), such as simple ratio vegetation index (SR), shortwave infrared modified simple ratio (MSR), and normalized difference vegetation index (NDVI). Data of 53 samples of LAI were measured by LAI-2000 (LI-COR) in the study area. LAI was modeled based on different reflectances of bands and different vegetation indices from Landsat TM and LAI samples data. There are certainly correlations between LAI and the reflectance of Tm3, TM4, TM5 and TM7. The best model through analyzing the results is LAI = 1.2097*MSR + 0.4741 using the method of regression analysis. The result shows that the correlation coefficient R2 is 0.5157, and average accuracy is 85.75%. However, whether the model of this paper is suitable for application in subtropics needs to be verified in the future.  相似文献   

Present environment and historic changes from the record of lake sediments, Dhaka City, Bangladesh   总被引：1，自引：0，他引：1  

Faruque Ahmed  M. Hawa Bibi  M. Hussain Monsur  Hiroaki Ishiga 《Environmental Geology》2005,48(1):25-36

Changes in the urban environment of Dhaka City have been evaluated from the geochemical compositions of bottom sediments from two lakes, Gulshan-1 and –2. Abundances of Pb, Zn, Fe₂O₃ and total sulfur in a Gulshan-1 core gradually increase toward the sediment–water interface. Three stages of condition change can be recognized in Gulshan-1, based on trace metal concentration patterns. The basal Stage I corresponds to background Dhaka sedimentation, whereas gradual increase in Stage II represents the beginning of pollution. Marked increases in Pb and Zn in Stage III reflect rapid urban development and increased emissions to the atmosphere. The condition of the Dhaka environment is compared to that of Japan based on Zn–Fe₂O₃ and Pb–Fe₂O₃ relations. Zn–Fe₂O₃ ratios in Stage I Dhaka sediments are similar to normal Japanese sediments, whereas Stage II data lie on the same trend as Japan urban sediments. Dhaka Stage III samples have greater Zn:Fe₂O₃ ratios than Japanese urban sediments, suggesting Zn pollution from poorly-controlled industrial sources. In contrast, the Dhaka Pb–Fe₂O₃ trend lies between normal and urban Japanese sediments. Although vehicle emissions in Dhaka are now significant, the data suggest that Pb pollution from this source remains in its early stages.  相似文献   

New evidence for an extended occupation of the Provo shoreline and implications for regional climate change, Pleistocene Lake Bonneville, Utah, USA     

Holly S. Godsey  Donald R. Currey  Marjorie A. Chan 《Quaternary Research》2005,63(2):212-223

Lake Bonneville was a climatically sensitive, closed-basin lake that occupied the eastern Great Basin during the late Pleistocene. Ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the Bonneville basin and for facilitating correlations with regional and global records of climate change. Radiocarbon data from this and other studies suggest that the lake oscillated at or near the Provo level much longer than depicted by current models of lake level change. Radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed. These revisions to the Lake Bonneville hydrograph, coupled with independent evidence of climate change from vegetation and glacial records, have important implications for conditions in the Bonneville basin and during the Pleistocene to Holocene transition.  相似文献   

洱海环境演变与大理城市发展的关系研究   总被引：1，自引：0，他引：1  

沈明洁  崔之久  易朝路 《云南地理环境研究》2005,17(6):63-68

针对洱海特殊的生态环境和对大理城市发展所起的举足轻重的作用，2002年通过实地环境调查和系列历史及动态资料分析进行了洱海和大理城市之问人地关系的互动研究。概括出大理城市发展的5个阶段，结果表明人类生存场所发展的总趋势是从高处往低处下移，从山前台地向下迁往山缘冲积洪积扇平原，直至湖滨平原地带。并着重分析了变迁的原因和人类活动的影响状况，从而使人们在开发利用洱海的同时，促进人类活动和城市发展建设相得益彰，并建议选择旅游和供水为主的和谐可持续发展道路，强化政府的宏观管理，增大科技投入。  相似文献   

Age of Gimli beach of Lake Agassiz based on new OSL dating     

James T. Teller  Lewis A. Owen 《第四纪科学杂志》2021,36(1):56-65

Gimli beach in Manitoba is one of the lowest elevation beaches in the southern Lake Agassiz basin, and is a distinct ridge composed of bedded sand and gravel that rises above the lake plain and extends for more than 40 km. Ten new optically stimulated luminescence (OSL) ages from Gimli beach yield ages mostly ranging from 9.7 ± 0.7 to 10.5 ± 0.8 ka (average 10.3 ± 0.5 ka), which is older by 0.6 to >1.0 ka than age estimates of previous researchers. Two of our new OSL ages are notably older than the others, dating to ~11.3 ± 0.8 and 13.9 ± 1.0 ka, which we attribute to poorly bleached sands. We ascribe an age of about 10 ka to Gimli beach, which is several centuries before overflow from Lake Agassiz and its vast drainage basin shifted from the western Great Lakes to glacial Lake Ojibway and the St. Lawrence Valley.  相似文献   

流域尺度土地利用调蓄视角的雨洪管理探析     

苏伟忠  汝静静  杨桂山 《地理学报》2019,74(5):948-961

发达国家雨洪管理焦点历经管网设计、不透水面阈值控制、低影响开发及土地利用管理等过程,呈现“多尺度多视角衔接”趋势。本文聚焦太湖流域土地利用调蓄功能变化机制及管理应用,揭示了1985-2015年来建设占用耕地是调蓄功能降低的主要原因;发现基于小流域的调蓄功能变化与建设用地强度整体低关联,但局部高相关,高相关的地区位于大城市或某些乡镇周边的建设增长热区,而这些热区的建设用地与调蓄空间规模较大且接触机会更多,是开发之前调蓄空间保护、开发控制以及开发之后综合管理等3个土地利用调蓄目标因子协调不当的结果;最后提出流域尺度土地利用调蓄视角的雨洪管理“345”模式,即以3个目标因子和5类控制要素为基础,实施土地利用调蓄创建、防御、拓展与保护等4类差别化战略模式,从更大尺度认识老城区和新区的雨洪关联,拓展海绵城市建设的本土认知和视野。  相似文献