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391.
392.
Darrell A. Norris 《The Professional geographer》1987,39(1):23-32
The commercial non-metropolitan exit clusters of America's interstate highway system exhibit regularities of basic form, scale, mix of services provided, and the ordinal placement of establishments relative to the exit proper. An examination of 354 exits serving 1-75 indicates the typical morphology of interstate exit clusters. 相似文献
393.
Potential implications of differential preservation of testate amoeba shells for paleoenvironmental reconstruction in peatlands 总被引:1,自引:0,他引:1
Edward A. D. Mitchell Richard J. Payne Mariusz Lamentowicz 《Journal of Paleolimnology》2008,40(2):603-618
Testate amoebae are now commonly used in paleoenvironmental studies but little is known of their taphonomy. There is some
experimental evidence for differential preservation of some testate amoeba shell types over others, but it is unclear what,
if any impact this has on palaeoenvironmental reconstruction. To investigate this issue we looked at palaeoecological evidence
for the preservation of different shell types. We then investigated the possible impact of selective preservation on quantitative
palaeoenvironmental inference. We first used existing palaeoecological data sets to assess the vertical patterns of relative
abundance in four testate amoeba shell types: (1) shells made of secreted biosilica plates (idiosomes, e.g. Euglypha), (2) idiosomes with thick organic coating (Assulina), (3) proteinaceous shells (e.g. Hyalosphenia), (4) shells built from recycled organic or mineral particles (xenosomes) (e.g. Difflugia, Centropyxis). In three diagrams a clear pattern of decay was only observed for the idiosome type. In order to assess the implications
of differential preservation of testate amoeba taxa for paleoenvironmental reconstruction we then carried out simulations
using three existing transfer functions and a wide range of scenarios, downweighting different test categories to represent
the impact of selective test decomposition. Simulation results showed that downweighting generally reduced overall model performance.
However downweighting a shell type only produced a consistent directional bias in inferred water table depth where that shell
type is both dominant and shows a clear preference along the ecological gradient. Applying a scenario derived from previous
experimental work did not lead to significant difference in inferred water table. Our results show that differential shell
preservation has little impact on paleohydrological reconstruction from Sphagnum-dominated peatlands. By contrast, for the minerotrophic peatlands data-set loss of idiosome tests leads to consistent underestimation
of water table depth. However there are few studies from fens and it is possible that idiosome tests are not always dominant,
and/or that differential decomposition is less marked than in Sphagnum peatlands. Further work is clearly needed to assess the potential of testate amoebae for paleoecological studies of minerotrophic
peatlands. 相似文献
394.
Jean-Claude Thouret Jean-François Oehler Avijit Gupta Akhmad Solikhin Jonathan N. Procter 《Bulletin of Volcanology》2014,76(10):1-26
Erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on Earth. Episodic sediment yields after large eruptions have been evaluated, but not the long-term and continuous patterns on persistently active volcanoes. We have used high-spatial resolution satellite imagery and DEMs/DSMs along with field-based geologic mapping to assess accurately sediment budgets for the active Semeru Volcano in Java, Indonesia. Patterns of aggradation and degradation on Semeru differ from that of other active volcanoes because (1) both episodic pyroclastic density currents (PDC) and continuous supplies of tephra generate pulses of sediment, (2) sediment is transferred via cycles of aggradation and degradation that continue for >15 years in river channels after each PDC-producing eruption, and (3) rain-triggered lahars remove much greater material than fluvial transport during long, intense rainfall events. The geomorphic response of two of Semeru’s rivers to volcanic sediment migration indicates that (1) each river experiences alternating aggradation and degradation cycles following PDC-producing eruptions and (2) spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches. Usually high degradation in the steep source reach is followed by a long bypassing middle reach. Aggradation predominates in the depositional reaches further down valley on the ring plain. Average sediment yields (103–105 t/km2/year) at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions, but the continuous and steady sediment transfer in rivers removes more sediment on a mid-term (10 years) to long-term (30 years) basis. In contrast to the trend observed on composite cones after large and infrequent eruptions, decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from BAF eruptions, superimposed on the background remobilization of daily tephra, have a greater cumulative effect. 相似文献
395.
396.
Di Baofeng Katsenis Loukas Stamatopoulos Constantine A. Panoskaltsis Vassilis P. 《Landslides》2021,18(6):2297-2307
Landslides - Earthquake-induced landslides involve excessive movement of slopes, usually along slip surfaces. This seismic movement of slopes may depend crucially on (a) the soil response along the... 相似文献
397.
高分辨率全球尺度水文模型发展综述 总被引:1,自引:0,他引:1
主要从高分辨率全球尺度水文模型(HRGHM)的发展历程、模型的一般结构与特点、模型数据集的发展和模型所面临的主要问题等几个方面对全球尺度水文模型的发展情况进行了综述。HRGHM能够使水文学家从全球的角度深入了解水资源的产生及循环过程,并且对相关环境问题的解决、气候的模拟与预报以及水资源的管理具有重要的意义。经过几十年的发展和努力,在全球尺度数据集的研究和发展方面已经取得了丰硕的成果,并且在HRGHM的实践中得以应用,但空间数据的缺乏仍然是其发展的最大羁绊。HRGHM所面临的问题除了数据的匮乏还在于非线性问题、尺度问题和确定性问题等水文机理和技术层面的问题。 相似文献
398.
This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part. 相似文献
399.
An ecotoxicological assessment is given to the state of small lakes in specially protected natural areas in Northwestern and Central European Russia, which suffer from aerotechnogenic acidification. The toxicity of water and bottom sediments is shown to increase with decreasing water pH. The most sensitive characteristics of aquatic organisms in different trophic groups are chosen, allowing the state of lakes to be monitored. 相似文献
400.
A. V. Mityukov A. M. Nikishin O. A. Almendinger S. N. Bolotov V. A. Lavrishchev N. K. Myasoedov E. V. Rubtsova 《Moscow University Geology Bulletin》2012,67(2):81-92
This work is based on the results of 2-D and 3-D surveys in the Tuapse Basin and field works in the Crimea-Caucasus region. Seven zones were outlined in the model of sedimentation starting from the eroded mountain structure of the Greater Caucasus down to deep water sediments of the Tuapse Basin. The slope and deep-water sediments of channels and fan complexes are characterized. Volume models of the sedimentation system in the Black Sea are shown for the first time. 相似文献