How a wet tropical rainforest copes with repeated volcanic destruction     

Leigh C.F. Jago  William E. Boyd 《Quaternary Research》2005,64(3):399-406

The Holocene Period for the province of West New Britain, Papua New Guinea, is characterised by periodic catastrophic volcanism. The region is mantled in dense wet tropical rainforest, and has been occupied by people since the Pleistocene. Analyses of peat from two nearby sites within a lowland rainforest environment provide us with a macro-level landscape account of the periodic destruction and recovery of the coastal forests during seven periods of volcanic activity in the latter part (2900 yr ago to present) of the Holocene. Radiocarbon dating shows the very close correlation of the peat and tephra layers at both sites, yet the pollen analysis reveals different vegetation communities. These initial results allow us to begin identifying the processes of recovery, and to recognise different ecological pressures placed on vegetation at these neighbouring sites. Evidence of hydrological changes are observed beginning with a marine incursion recorded at Garu Site 3 1360 ¹⁴C yr B.P. The distinct differences in the vegetation re-establishment and community regeneration rates suggest the greater level of disturbance at Garu Site 1 could be related to the depth of the ashfall, although the proximity of a known human settlement may also be a contributing factor. Of note, palynologically, we found that the fern spore flora is particularly rich and believe it will be useful for ecological interpretation.  相似文献   

Analysis of pressuremeter geometry effects in clay using critical state models   总被引：1，自引：0，他引：1  

H. S. Yu  M. T. Charles  C. D. Khong 《国际地质力学数值与分析法杂志》2005,29(8):845-859

The conventional interpretation methods of pressuremeter testing effectively approximate pressuremeter membranes as infinitely long. As a result, the effects of the two‐dimensional geometry of pressuremeters are ignored, leading to an overestimation of soil shear strength by pressuremeter testing, as demonstrated in several previous studies. This paper presents results of a numerical study of two‐dimensional geometry effects on self‐boring pressuremeter tests in undrained clay. The results are obtained using critical state soil models with an effective stress formulation. This is in contrast to most (if not all) existing studies on pressuremeter geometry effects, which were based on perfectly plastic soil models (e.g. Yu (Cavity expansion theory and its application to the analysis of pressuremeters. DPhil Thesis, The University of Oxford, 1990), Yeung and Carter (Proc. 3rd Int. Symp. on Pressuremeters, 1990), and Houlsby and Carter (Géotechnique, 1993; 43 (4):567–576)). The present study suggests that the overestimation of soil strength due to the neglect of finite pressuremeter length is significantly affected by the soil model used in the calculations. It is found that for clays with a high overconsolidation ratio (OCR) the strength overestimation predicted using critical state soil models could be considerably smaller than that predicted using perfectly plastic soil models. The main conclusion of this numerical study is that care must be exercised before directly applying any numerically determined pressuremeter geometry correction factors in practice. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Characterization of hydrogeologic properties for a multi-layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey     

Jeong-Woo Kim  Heechul Choi  Jin-Yong Lee 《Environmental Geology》2005,48(8):991-1001

A multi-layered aquifer, typical of riverbank alluvial deposits in Korea, was studied to determine the hydrologic properties. The geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units: silt, sand, highly weathered and fresh bedrock layers. The electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings. The laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5.00×10⁻² cm/s. The slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4.32–7.72×10⁻⁴ cm/s. Hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2.08×10⁻³ and 2.44×10⁻² cm/s with a geometric mean of 6.89×10⁻³ cm/s, which is 7 times smaller than that from the laboratory column experiment. The trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested. The combined hydrogeologic site characterization using hydraulic tests, tracer tests, and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multi-layered alluvial aquifer.  相似文献   

Reply to the comment of Krinitzsky on J.U. Klügel's “Problems in the application of the SSHAC probability method for assessing earthquake hazards at Swiss nuclear power plants”, in Engineering Geology, vol. 78, pp. 285-307     

J.-U. Klügel 《Engineering Geology》2005,82(1):69-70

  相似文献   

利用可见光/近红外反射光谱估算土壤总氮含量的实验研究   总被引：25，自引：0，他引：25  

徐永明  蔺启忠  黄秀华  沈艳  王璐 《地理与地理信息科学》2005,21(1):19-22

利用土壤的室内反射率光谱，探讨土壤氮元素的高光谱机理。利用土壤光谱各吸收带的特征参数与总氮含量进行逐步回归运算，确定与氮元素关系比较密切的几个吸收带。计算出这几个特征吸收带内土壤反射率的变化形式：一阶导数(FDR)、倒数(1/R)、倒数之对数(log(1/R))、波段深度(Depth)，并与总氮含量进行逐步回归分析，得到比较理想的结果：建模样本的Ra^2(修正的判定系数)分别为0．789、0．753、0．736、0．699，验证样本的Ra^2分别为0．759、0．468、0．794、0．725。可见土壤的反射率光谱与氮元素含量之间存在比较明显的相关性，可见光／近红外反射光谱具有快速估算土壤中氮元素含量的潜力。  相似文献   

空间分析与自然地理综合研究   总被引：2，自引：1，他引：2  

郝成元  吴绍洪  杨勤业 《地理与地理信息科学》2005,21(1):52-55

通过对空间分析技术和自然地理综合研究发展历程与趋势的分析，得出两个结论：1)现代地理学的快速发展越来越离不开空间分析的支撑，即空间分析技术在地理学中的应用空间愈来愈广，在自然地理综合研究中尤为如此，其主要原因就是空间分析在综合研究中的优势愈来愈明显；2)空间分析技术随其理论与实践的迅速发展及逐步拓展，愈来愈成为自然地理学发展的巨大推动力，也越来越离不开自然地理综合研究这个促使其发展壮大的空间和能发挥其主导作用的领域。空间分析技术和自然地理综合研究的结合已经成为现代自然地理学以及地球空间信息学研究的主要发展趋势之一。  相似文献   

Statistical identification of orographic effects in the regional analysis of extreme rainfall          下载免费PDF全文

Pierluigi Furcolo  Anna Pelosi  Fabio Rossi 《水文研究》2016,30(9):1342-1353

Regional models of extreme rainfall must address the spatial variability induced by orographic obstacles. However, the proper detection of orographic effects often depends on the availability of a well‐designed rain gauge network. The aim of this study is to investigate a new method for identifying and characterizing the effects of orography on the spatial structure of extreme rainfall at the regional scale, including where rainfall data are lacking or fail to describe rainfall features thoroughly. We analyse the annual maxima of daily rainfall data in the Campania region, an orographically complex region in Southern Italy, and introduce a statistical procedure to identify spatial outliers in a low order statistic (namely the mean). The locations of these outliers are then compared with a pattern of orographic objects that has been a priori identified through the application of an automatic geomorphological procedure. The results show a direct and clear link between a particular set of orographic objects and a local increase in the spatial variability of extreme rainfall. This analysis allowed us to objectively identify areas where orography produces enhanced variability in extreme rainfall. It has direct implications for rain gauge network design criteria and has led to promising developments in the regional analysis of extreme rainfall. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

大菱鲆体重和主要体型比率性状的遗传动态分析     

王新安  马爱军 《海洋学报(英文版)》2020,39(2):22-27

The objective of this study was to estimate genetic parameters of body width(BW)to body length(BL)ratio(BW/BL)and of body weight traits(BWT)in turbot,and to elucidate the genetic mechanism of the two traits during ontogeny by dynamic genetic analysis.From 3 to 27 months,BW,BL and BWT of each communally stocked fish were measured every 3 months.The BW/BL ratio was measured at different sampling ages.A twotrait animal model was used for genetic evaluation of traits.The results showed that the heritability values of BW/BL ratio ranged from 0.2168 to 0.3148,corresponding to moderate heritability.The BWT heritability values ranged from 0.2702 to 0.3479 corresponding to moderate heritability.The heritability of BW/BL ratio was lower than that of BWT,except at 3 months of age.Genetic correlation between BW/BL ratio and BWT decreased throughout the measurement period.Genetic correlations were higher than the phenotypic correlations.The current results for estimating genetic parameters demonstrate that the BW/BL ratio could be used as a phenotypic marker of fast-growing turbot,and the BW/BL ratio and BWT could be improved simultaneously through selective breeding.  相似文献   

Discrete element method modeling of inherently anisotropic rocks under uniaxial compression loading          下载免费PDF全文

K. Duan  C.Y. Kwok  M. Pierce 《国际地质力学数值与分析法杂志》2016,40(8):1150-1183

A new numerical approach is proposed in this study to model the mechanical behaviors of inherently anisotropic rocks in which the rock matrix is represented as bonded particle model, and the intrinsic anisotropy is imposed by replacing any parallel bonds dipping within a certain angle range with smooth‐joint contacts. A series of numerical models with β = 0°, 15°, 30°, 45°, 60°, 75°, and 90° are constructed and tested (β is defined as the angle between the normal of weak layers and the maximum principal stress direction). The effect of smooth‐joint parameters on the uniaxial compression strength and Young's modulus is investigated systematically. The simulation results reveal that the normal strength of smooth‐joint mainly affects the behaviors at high anisotropy angles (β > 45°), while the shear strength plays an important role at medium anisotropy angles (30°–75°). The normal stiffness controls the mechanical behaviors at low anisotropy angles. The angle range of parallel bonds being replaced plays an important role on defining the degree of anisotropy. Step‐by‐step procedures for the calibration of micro parameters are recommended. The numerical model is calibrated to reproduce the behaviors of different anisotropic rocks. Detailed analyses are conducted to investigate the brittle failure process by looking at stress‐strain behaviors, increment of micro cracks, initiation and propagation of fractures. Most of these responses agree well with previous experimental findings and can provide new insights into the micro mechanisms related to the anisotropic deformation and failure behaviors. The numerical approach is then applied to simulate the stress‐induced borehole breakouts in anisotropic rock formations at reduced scale. The effect of rock anisotropy and stress anisotropy can be captured. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

2000-2015年三江平原主要作物需水量征及影响因素分析          下载免费PDF全文

任修琳  李宏亮  张玉虎  蒲晓  张立林 《干旱区地理》2019,42(4):854-866

全生育期内作物需水量的研究是农业水资源有效利用和进行合理灌溉的重要依据。基于三江平原22个气象站点2000—2015年逐日气象观测资料及中国区域地面气象要素数据集，利用国际粮农组织 （FAO）Penman-Monteith模型和分段单值平均作物系数法，分别对三江平原水稻、玉米和大豆的作物需水量进行计算，分析作物需水量年际变化特征，采用通径分析法研究作物需水量的变化成因。结果表明：（1）三江平原16 a来年均参考作物蒸散量为537.4 mm，日均为 3.5 mm，呈波动减少趋势。（2）生长季内，水稻在分蘖期需水量最大，为177.1 mm，玉米在七叶期需水量最大，为99.7 mm，大豆在结荚期需水量最大，为96.1 mm；水稻、玉米和大豆的净灌溉需水量分别为195.4 mm、130.8 mm和72.2 mm，对灌溉的依赖程度水稻>玉米>大豆。（3）由通径分析结果可知，三江平原作物需水量的主要影响因素为净辐射、气温和日照时数。  相似文献