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171.
172.
甘青地区中晚全新世植被变化与人类活动 总被引:5,自引:5,他引:5
史前时期人类对环境的影响是近几年来国际研究的热点。在甘青地区,全新世的孢粉资料比较多。但在中晚全新世,该区人类对环境的影响作用及其程度仍不清楚,许多孢粉分析资料中并没有充分考虑人类活动的影响。本文选取孢粉分辨率较高、代表性较好的青海湖、兰州、秦安大地湾三地的资料,着重研究了其中乔木成分的变化。分析发现,孢粉组合中乔木成分的变化与气候变化的趋势并不一致。通过对考古及历史资料的分析,笔者认为,该区的植被很早就受到人类活动的影响。自全新世中期,本区植被中的乔木成分波动下降。5000-3000a BP期间,史前农业对植被的影响较大。3000-2000a BP期间,植被略有恢复。2000a BP以后,人为影响加剧,植被中乔木成分迅速下降。研究者认为,依赖孢粉资料重建中晚全新世的气候变化历史应当慎重。 相似文献
173.
Juha Miettinen Elisabeth Grönlund Heikki Simola Pertti Huttunen 《Journal of Paleolimnology》2002,27(1):29-44
The post-glacial history of Lake Pieni-Kuuppalanlampi, western Lake Ladoga region, was studied by means of stratigraphic pollen and diatom analyses. Diatoms were analysed to track the isolation history of the basin and the limnological effects of the early land-use phases indicated by pollen analysis. Chrysophycean stomatocysts and Isoëtes spores were also employed in the limnological reconstructions. Sediment dating was provided by six conventional radiocarbon dates.The lower part of the 370-cm long sediment sequence represents early Holocene, large lake conditions: the (freshwater) Yoldia and Ancylus stages of the Baltic basin, with a short-term lagoonal or isolation phase at the end of Yoldia. The basin was isolated due to Ancylus lake regression at 9785 cal B.P. For the small-lake sequence (0–250 cm) we used diatom inferences (WA-method) for hindcasting water chemistry. The post-isolation limnology of Pieni-Kuuppalanlampi reflects the development of vegetation on its small hill-top catchment. In its early development, the lake was mesotrophic, but became more acidic (pH about 6) and oligotrophic after the decline of temperate hardwood trees and the spread of spruce to the area after around 5000 B.P. The lake ecosystem appears to have reacted sensitively to agricultural land-use in the catchment from AD 400–800 onwards: inferred total phosphorus levels and pH both rise during these periods. 相似文献
174.
Testate amoebae as paleoindicators of surface-moisture changes on Michigan peatlands: modern ecology and hydrological calibration 总被引:6,自引:0,他引:6
Robert K. Booth 《Journal of Paleolimnology》2002,28(3):329-348
Peatland testate amoebae are sensitive indicators of local hydrology and have been used as proxies for surface moisture conditions in fossil studies. However, few regional calibration datasets exist in North America, and knowledge of testate amoeba ecology and distribution patterns are limited. The objectives of this study were to (1) investigate the relationship between testate amoebae, environment, and Sphagnum species in Michigan peatlands; (2) generate transfer functions from this dataset that can be applied to fossil data; and (3) describe vertical variation of testate amoebae inhabiting Sphagnum moss. Testate amoeba assemblages from 139 microsites within 11 peatlands in Michigan were compared to assess variability between and within peatlands. Most peatlands contained similar testate amoeba assemblages, although within individual peatlands the amount of assemblage variability is correlated to the amount of environmental heterogeneity. Of the measured environmental variables, depth to water table showed the strongest relationship with testate amoebae. Depth to water table can be reconstructed from fossil data with a mean error of ±7.5 cm, although predictive ability deteriorates in extremely dry environments (>30 cm water table depth). Vertical variation in testate amoeba assemblages was investigated at 89 Sphagnum-dominated microsites by directly comparing amoeba assemblages and the abundance and frequency of common taxa in upper and lower portions of the Sphagnum stem. Except for extremely dry microsites, considerable vertical variation in assemblage composition exists. Many agglutinate taxa are more abundant on lower portions of the Sphagnum stem, and taxa containing symbiotic zoochlorellae are more abundant on upper portions. Refinements in sampling procedures and analysis may improve the predictive ability of transfer functions. 相似文献
175.
Placing geographies of public health 总被引:6,自引:0,他引:6
Following the move to a 'post–medical' geography, a large amount of research has come to focus on public health issues. This paper explores these current geographies of public health and argues for the development of a more critical perspective. In particular, it draws on commentary that has emerged out of debates that have taken place within a body of literature usually identified as the critical 'new' public health. The paper goes on to argue that such scholarship offers crucial insights for the production of a critical geography of public health. 相似文献
176.
《The Professional geographer》2002,54(3):454-478
Books Reviewed Colbert C. Held, Middle East Patterns: Places, People, and Politics Barbara A. Weightman, Dragons and Tigers: A Geography of South, East, and Southeast Asia Henry J. Bruman, Alcohol in Ancient Mexico Brian W. Blouet, Geopolitics and Globalization in the Twentieth Century M. A. B. Siddique (ed.), International Migration into the 21st Century: Essays in Honour of Reginald Appleyard Michael R. Haines and Richard H. Steckel (eds.), A Population History of North America Emilio Moran, Human Adaptability: An Introduction to Ecological Anthropology Jeremy Leggett, The Carbon War: Global Warming and the End of the Oil Era Susan B. Marriott and Jan Alexander (eds.), Floodplains: Interdisciplinary Approaches William S.Logan, Hanoi: Biography of a City Alex Krieger and David Cobb (eds.) with Amy Turner, Mapping Boston Eric Sandweiss, St. Louis: The Evolution of an American Urban Landscape Carl Abbott, Greater Portland: Urban Life and Landscape in the Pacific Northwest Arthur D. Murphy, Colleen Blanchard and Jennifer A. Hill (eds.), Latino Workers in the Contemporary South Yanek Mieczkowski, The Routledge Historical Atlas of Presidential Elections 相似文献
177.
模糊区域拓扑关系模型 总被引:4,自引:1,他引:4
拓扑关系是地理信息系统中空间要素之间最基本也是最重要的关系之一,是进行绝大多数空间查询和分析的基础。非模糊空间要素之间的拓扑关系在一般拓扑学等理论的基础上已有相关的模型和描述,并在实践中得到广泛的应用,如何建立模糊空间要素这间的拓扑关系是建立模糊要素地理信息系统的基础。该文在模糊扑扑学的基础上提出了模糊区域的定义,建立了用于分析模糊区域之间拓扑关系的理论和模型,提出了4*4-intersection模型拓扑关系矩阵,并分析了不同拓扑关系矩阵对于非模糊区域之间、模糊区域之间建立拓扑关系的区别和联系,最后采和不同公式对模糊区域之间的关系进行了系统的描述。 相似文献
178.
京、津、冀区域群发性强沙尘暴分析 总被引:1,自引:2,他引:1
利用1954—2002年82个站的气象观测资料,探讨京、津、冀区域群发性强沙尘暴的认定标准,构建较完整的群发性强沙尘暴序列,并分析该地区群发性强沙尘暴的时空分布特征和气候变化趋势。近50a京、津、冀区域共出现了39例群发性强沙尘暴,河北省的冀西北高原区和石家庄、保定、衡水、沧州四市交接处饶阳一带是京、津、冀区域强沙尘暴天气的多发区。多发季节为3—5月,占全年总数的76.9%,其中4月份最多,占全年总数的51.3%。群发性强沙尘暴年代际变化呈现总体减少趋势,其发生次数、覆盖面积均是以20世纪90年代为最低值. 相似文献
179.
180.