Holocene Paleoenvironmental Change in the Kenyan Central Rift as Indicated by Micromammals from Enkapune Ya Muto Rockshelter     

Curtis W. Marean  Nina Mudida  Kaye E. Reed 《Quaternary Research》1994,41(3)

An assemblage of micromammals, recovered from the Holocene levels of a rockshelter at 2400 m in the montane forest of the Mau Escarpment, were examined with the goal of testing and contributing to prior reconstructions of paleoenvironments in the Central Rift Valley of Kenya. Species representation in the assemblage is consistent with a drying of the Rift Valley lakes in the middle Holocene and suggests a decrease in forest accompanied by expanding grasslands near the site. Changes in the abundance of grassland species suggests an increase in the frequency of fires, probably the result of pastoral burning. The body size of the root rat (Tachyoryctes splendens) decreases from the early Holocene to the middle Holocene, and this may indicate increasing aridity or increasing temperature. We compare measures of species diversity (number of taxa, species richness, and the Shannon diversity index) for both micromammals and macromammals since species diversity may change with paleoenvironmental change. The macromammals show no changes in species diversity that are assignable to paleoenvironmental change, while the micromammals show a trend toward decreasing diversity from the early to middle Holocene, and then show an increase in diversity during the peak of the middle Holocene dry phase, though sample size effects may be confounding the patterning.  相似文献   

Water chemistry and sedimentological observations in littlefield lake,michigan: Implications for lacustrine marl deposition     

Nina M. Duston  Robert M. Owen  Bruce H. Wilkinson 《Environmental Geology》1986,8(4):229-236

A combination of both water chemistry and sedimentological information was used to investigate the carbonate-producing mechanism in Littlefield Lake, a small lake located in Isabella County, central Michigan. Data on temperature, dissolved oxygen, pH, calcium carbonate (CaCO₃) saturation, alkalinity, calcium, and magnesium were obtained on a monthly basis over a 13-month period, with each parameter determined at 1m intervals over a depth range of 20m. The loss of dissolved carbon dioxide (CO₂) from warm surface waters during direct degassing, and to a lesser extent during photosynthetic uptake by lacustrine macrophytes and phytoplankton during the summer, results in massive precipitation of the low-magnesium calcite which predominates in all Littlefield Lake sedimentary facies However, despite the fact that carbonate precipitation in this rather typical temperate-region marl lake is directly related to, and may be driven by, seasonal variation in these physiochemical parameters, most calcite forms as encrustations around cyanophytic and chlorophytic macrophytes. Such relationships demonstrate that carbonate precipitation in marl lakes may result from complex interactions between both biochemical and physiochemical processes. As such, marl formation in this, and probably many other calcareous lake systems, can not be simply ascribed to one or the other of these two general mechanisms.  相似文献   

Tracing of water movement through the unsaturated zone of a coarse gravel aquifer by means of dye and deuterated water     

Nina Mali  Janko Urbanc  Albrecht Leis 《Environmental Geology》2007,51(8):1401-1412

To better understand the movement and transport of water and pollution through the coarse gravel unsaturated zone, the presented research was conducted to estimate water flow and transport processes with a tracing experiment in a lysimeter in the Selniška Dobrava. A combined tracing experiment was performed with deuterated water and the fluorescent dye—uranine. The fastest and dominant flow velocities were calculated based on injection time, the first tracer appearance time and the time of highest concentration. Mean flow velocity and vertical dispersion were estimated by an analytical best-fit method using one-dimensional convection–dispersion model. Deuterium was confirmed as an ideal conservative tracer and a more suitable tracer than dye (uranine) for the study of water flow in the unsaturated zone of a coarse gravel aquifer. The retardation factor of the dye as compared with deuterium was 1.13–1.75, which is in agreement with previously published results. Artificial tracers, especially deuterated water, were also identified as a very useful tool to assess other properties and differences in water flow in the unsaturated zone of a coarse gravel aquifer such as velocity and dispersion.  相似文献   

环境与健康的评估问题和空间分析   总被引：1，自引：0，他引：1  

林绍颜 《地理学报》2001,56(2):239-247

评估环境污染对人民健康影响的研究需要结合空间，时间和统计分析，并吸引不同学科背景的研究人员合作研究，可是，在这个研究领域内，最重要的问题是研究结论的不可靠性程度很高，不同的研究方法会导致不同的结论，一个有系统的研究架构拥有不同的空间分析方法将会减少结论的可疑程度，有效的环保政策是需要可靠的研究成果，文中首先介绍在环境与健康的评估研究领域的四大重要问题，指出这项研究需要这项研究需要空间分析和地理信息系统方法，从而提出一个空间分析的研究框架和内裹的方法，通过路易斯安纳州的一个污染地点和肿瘤发病率关系研究实例，指出这项研究领域的各种问题和空间分析架构的重要性。  相似文献   

Weather categorization in climate change research: Preliminary results     

Ivana Nemešová  Nina Klimperová  Radan Huth  Jaroslava Kalvová 《Studia Geophysica et Geodaetica》1992,36(4):370-375

Summary The results of an objective weather categorization are presented. The 9 meteorological variables recorded daily during winter seasons of 1961–66 at Prague-Clementinum represent the input dataset. The principal component analysis and a few clustering procedures have been evaluated. 5 component solution and the average linkage clustering method were found optimal. The winter days have been grouped, according to their meteorological character, into 14 clusters. The warm categories represent 20% of the time and the cold categories less than 15% of the days. The mean maps of 1000 hPa and 500 hPa are shown for a few selected categories. Clustering techniques applied to long-time instrumental series can provide a better basis for attempting to detect temperature changes which have taken place over a long time span.  相似文献   

旱作地膜小麦玉米带田一膜两用热效应研究     

仇化民  王宁珍  马妮娜 《干旱气象》1995,(4)

旱作地膜小麦—玉米带田一膜两用技术热效应显著，可提高地温２—６℃，保证了小麦安全越冬，促进了作物早发。热资源利用率高达０．９９７，比单作提高２５％—４０％，变作物一年一熟为一年两熟。  相似文献   

Deconstructing the best case scenario: lessons from water politics in La Paz-El Alto, Bolivia     

Nina Laurie  Carlos Crespo 《Geoforum》2007,38(5):841-854

For nearly a decade the La Paz-El Alto concession in Bolivia was heralded by donor organizations, the state and the commercial water industry alike as an emblematic ‘pro-poor’ water concession under the private sector model. Managed by one of the largest water multinationals in the world (the French company Suez), the network was extended beyond the new connections required by the original ‘pro-poor’ contract, acclaimed as a pioneer of new pro-poor technologies and frequently disseminated internationally as an example of best practice. This paper analyses the La Paz-El Alto concession’s pro-poor image focusing on issues of social exclusion and network extension, contract negotiation, participation and transparency. It documents the rise of social protest about the concession and critiques the failure of neoliberal regulatory systems to promote accountability to the poor. In the context of the continued transnationalisation of the water industry the paper highlights the need for new mechanisms and delivery models to ensure greater national control over private companies and the development of a framework for international water governance.  相似文献   

Introduction: How to dialogue for pro-poor water     

Nina Laurie 《Geoforum》2007,38(5):753-755

  相似文献   

TL age-estimates for the Middle Palaeolithic layers at Theopetra cave (Greece)     

Helene Valladas  Norbert Mercier  Laurence Froget  Jean-Louis Joron  Jean-Louis Reyss  Panajotis Karkanas  Eleni Panagopoulou  Nina Kyparissi-Apostolika 《Quaternary Geochronology》2007,2(1-4):303-308

The lowest stratigraphic unit of Theopetra cave (Greece) contains a Middle Palaeolithic sequence radiocarbon dated to between 46 and 35 ka BP; at the limit of this dating method. The upper part of this sequence has yielded late Middle Palaeolithic lithic assemblages containing several early Upper Palaeolithic artifacts. To get more precise dates for the human occupation of the cave, burnt flint specimens from these Middle Palaeolithic layers were dated by thermoluminescence. The dates obtained are coherent and indicate that the first human occupation of the cave took place at the end of isotopic stage 6 or more probably at the beginning of stage 5, much earlier than previously proposed. In the light of this new evidence, it is reasonable to assume that: (a) Theopetra contains the oldest dated Middle Palaeolithic deposits of Greece and (b) that the assemblages first interpreted as “Transitional Middle/Upper Palaeolithic” industries may be the result of post-depositional mixing of cultural material.  相似文献   

An effective method of frequency analyses of time series of geo-physical quantities     

František Pechala  Nina Věková  Reviewer J. Anděl 《Studia Geophysica et Geodaetica》1980,24(3):302-313

a u uma naau ¶rt; m¶rt; ¶rt; aaua ¶rt;auu uu. naau ¶rt; naam , ¶rt;mu mau a, m aa naau ¶rt;am n a au aauu uu auumu m amu m aaa um ¶rt;uam. m¶rt; m ¶rt;mam mu ¶rt;a nu auu u m mu, ma m nuu ma a a .  相似文献