Hydrologic and climatic implications of a multidisciplinary study of late Holocene sediment from Kenosee Lake, southeastern Saskatchewan, Canada     

R. E. Vance  W. M. Last  A. J. Smith 《Journal of Paleolimnology》1997,18(4):365-393

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the region's water resources to climate change.  相似文献   

An auto-biographical approach to understanding migration: the case of Hong Kong emigrants   总被引：1，自引：0，他引：1  

A M Findlay  F L N Li 《Area》1997,29(1):34-44

Summary This paper seeks to make a methodological contribution by evaluating the autobiographical approach and its application to migration research. The migration act is seen as a manifestation of an individual's identity. This is moulded by many social influences over an individual's lifecourse. The paper explores the realm of practical consciousness (Giddens 1984) using a biographical approach in an attempt to identify the values underpinning the intentions of professional emigrants from Hong Kong.  相似文献   

Time-domain computation of scattering from a heterogeneous layer     

Xiaofan Li  J. A. Hudson 《Geophysical Journal International》1997,128(1):197-203

Adopting Born and ray approximations, time-domain synthetic seismograms for P-P and P-S scattering from a plane wave incident on a thin, laterally heterogeneous layer are presented in this paper. The time-domain P coda is a convolution between a structure function and the second-order derivative of the time function of the incident P wave. Examples of synthetic seismograms are given using a time function from a computed short-period seismogram for a point explosive source in a half-space. These show that it is impossible, with realistic values of the parameters involved, to generate significant codas when only single scattering is involved.  相似文献   

The forward problem of electromagnetic induction: accurate finite-difference approximations for two-dimensional discrete boundaries with arbitrary geometry   总被引：3，自引：0，他引：3  

Claudia Aprea  John R. Booker  J. Torquil Smith 《Geophysical Journal International》1997,129(1):29-40

We describe finite-difference approximations to the equations of 2-D electromagnetic induction that permit discrete boundaries to have arbitrary geometrical relationships to the nodes. This allows finite-difference modelling with the flexibility normally ascribed to finite-element modelling. Accuracy is demonstrated by comparison with finite-element computations. We also show that related approximations lead to substantially improved accuracy in regions of steep, but not discontinuous, conductivity gradient.  相似文献   

利用不纯净十水芒硝与纯净氯化钾制取硫酸钾的研究   总被引：1，自引：0，他引：1       下载免费PDF全文

张树群  牛自得 《盐湖研究》1997,5(2):30-35

本文通过相图分析，对利用不纯净十水芒硝与纯净氯化钾通过二步转化制取硫酸钾进行了物料配比计算．给出了最佳物料配比及十水芒硝中氯离子的最大含量，对实际生产有指导意义。  相似文献   

利用遥感监测和分析珠江三角洲的城市扩张过程——以东莞市为例   总被引：23，自引：3，他引：23  

黎夏  叶嘉安 《地理研究》1997,16(4):56-62

伴随着经济的快速增长,珠江三角洲近年来出现了迅速的城市化以及乡村城市化的过程。沿着城镇边缘和公路两旁,大片的农田被侵占来单方面地满足城市开发的需要,忽略了粮食产量减少以及环境质量恶化等问题。利用遥感可以有效地监测珠江三角洲的城市扩张过程。在遥感多时相监测的基础上通过熵的计算,可以定量地描述城市扩张的空间规律及扩散过程。  相似文献   

腾格里沙漠东南缘降尘粒度特征和沉积速率   总被引：15，自引：9，他引：15  

消洪浪  张继贤 《中国沙漠》1997,17(2):127-132

从多年降尘实测资料入手，分析了粉尘粒度特征、沉积速率和时变过程。提出了气象要素相关估测模型．确定０．２５ｍｍ为本区粉尘沉积粒径上限。周围沙漠是粉尘沉积细砂部分的尘源，粉砂和粘土部分沉积来自一个较大的时空范围，二者几乎各占降尘量的１／２。研究区年平均粉尘沉积速率４３５８ｋｇ／ｈｍ２，每年５月的季风转期具有年内最大沉积速率。  相似文献   

宁夏盐池县土地沙质荒漠化的发展趋势及其防治   总被引：5，自引：3，他引：5  

曲志正  王峰 《中国沙漠》1997,17(2):173-179

宁夏盐池县是我国北方农牧交错带沙质荒漠化强烈发展的地区之一。通过分析该区土地沙质荒漠化的发展趋势及其成因，认为该区土地沙质荒漠化有日趋扩大、日益严重的发展趋势；在潜在自然因素的基础上，人为因素是造成该区土地沙质荒漠化的主要因素。针对该区土地沙质荒漠化的发展趋势及其成因，结合沙质荒漠化土地的农林牧综合开发，提出了防治土地沙质荒漠化的目标、实施步骤及基本对策。  相似文献   

Aspects of German unification     

Mark Blacksell  Fiona M. Smith 《Applied geography (Sevenoaks, England)》1997,17(4):255-256

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天山北坡降水对河流水沙情势影响     

陈亚宁  李卫红 《山地学报》1997,(1)

以天山北坡头屯河流域为例，在对山区不同海拔的降水特征、侵蚀产沙情势以及河流水沙运移特点分析的基础上，详尽就山区降水对河流水沙情势的年际变化、年内变化以及月变化的影响进行了分析研究，并就降水对不同海拔的河流水沙情势的影响强度及相互关系作了探讨．  相似文献