A cladoceran-based paleolimnological assessment of the impact of forest harvesting on four lakes from the central interior of British Columbia, Canada   总被引：1，自引：0，他引：1  

Emma L. Bredesen  Darren G. Bos  Kathleen R. Laird  Brian F. Cumming 《Journal of Paleolimnology》2002,28(4):389-402

To investigate the impact of forest harvesting on lake ecosystems, six lakes (four impact, two reference) from central British Columbia, Canada were assessed using cladoceran remains preserved in the lake sediment cores. Two temporal resolutions were analyzed: a decadal scale for the past 70 years, and a high-resolution scale (2 year intervals for ten years before and after harvesting). Three lakes which experienced forestry activity in their watersheds in the early 1960s, and one lake which experienced forestry activityin the mid 1970s, showed subtle but statistically significant changes in cladoceran species composition following forest harvesting (analysis of similarity tests) at the decadal scale, whereas only two of these lakes showed significant changes at the higher resolution. These changes may be due to increased nutrient levels that might be associated with forest harvesting. The two reference lakes, which had not experienced any known large-scale anthropogenic watershed disturbances in the past century, showed no significant shifts in the cladoceran species assemblages at either temporal scale.  相似文献   

The influence of petrophysical properties on the salt weathering of porous building rocks   总被引：1，自引：0，他引：1  

D. Benavente  N. Cueto  J. Martínez-Martínez  M. A. García del Cura  J. C. Cañaveras 《Environmental Geology》2007,52(2):215-224

The influence of pore structure, water transport properties and rock strength on salt weathering is evaluated by means of a thorough rock characterisation and a statistical analysis. The pore structure was described in terms of its porosity, pore size distribution (quantified by mean pore radius) and specific surface area, density and water transport was characterised by means of water permeability (saturated flow) and capillary imbibition (unsaturated flow); whilst the rock strength test was carried out using uniaxial compressive strength, compressional and shear wave velocities, dynamic elastic constants and waveform energy and attenuation were obtained from the digital analysis of the transmitted signal. A principal component analysis and a stepwise multiple regression model was carried out in order to examine the direct relationships between salt weathering and petrophysical properties. From the principal component analysis, two main components were obtained and assigned a petrophysical meaning. The first component is mostly linked to mechanical properties, porosity and density whereas the second component is associated with the water transport and pore structure. Salt weathering, quantified by the percentage of weight loss after salt crystallisation, was included in both principal components, showing its dependence on their petrophysical properties. The stepwise multiple regression analysis found that rock strength has a predominant statistical weight in the prediction of salt weathering, with a minor contribution of water transport and pore structure parameters.  相似文献   

库仑法测定煤中全硫必须重视的问题     

雷翠琼 《云南地质》2007,26(4):458-460

煤中全硫测定是煤质分析的一项重要指标。本文从煤样的粒度和均匀性,载气流量,电解液的使用,电解池和电极片的处理,库仑测硫仪的校正等方面对应用库仑法测定煤中全硫应注意的问题及原因进行分析,以确保测定结果的准确性。  相似文献   

Error inflation in Probabilistic Seismic Hazard Analysis     

Jens-Uwe Klügel   《Engineering Geology》2007,90(3-4):186-192

Based on a consistent interpretation of earthquake occurrence as a stochastic process I demonstrate that the mathematical model of Probabilistic Seismic Hazard Analysis (PSHA) as it is in use today is inaccurate and leads to systematic errors in the calculation process. These mathematical errors may be regarded as an important contributor to the unrealistic results obtained by traditional PSHA for low probabilities of exceedance in recent projects.  相似文献   

区域开发累积环境影响及其全幕景分析法评价   总被引：3，自引：0，他引：3  

陈剑霄 《地下水》2007,29(2):73-76

在分析区域开发活动及其特点的基础上,论述了区域开发累积环境影响及其累积效应.通过总结常用的累积环境影响评价方法的实质,考察传统幕景分析法评价累积环境影响的工作方法,提出广义的幕景分析法--"全幕景分析法",阐述其用于区域开发累积环境影响分析评价的工作程序与优势."全幕景分析法"可在区域开发累积环境影响评价中起到综合、优化、直观的作用.  相似文献   

连续小波变换系数的主成分分析法及其重力固体潮应用     

全海燕  山秀明  周挚  刘增力  梁虹 《地震研究》2007,30(2):175-178

针对连续小波变换中各尺度系数间存在较大相关性的特点,建立协方差矩阵,用主成分分析法去除各尺度系数间的相关性,提取原信号中的主要频率成分。利用给定样本信号对该方法的有效性进行检验,同时,作为应用,利用该方法提取出重力固体潮信号中的半日波分量和日波分量,为信号特征频率提取提供了一种可行和有效的分析方法。  相似文献   

喀什地磁台数字与模拟记录K指数对比分析   总被引：1，自引：0，他引：1  

孙海军  高守全 《内陆地震》2007,21(4):348-353

介绍了喀什地磁台地磁数字记录K指数的计算机FM I测定方法和传统的模拟测定K指数方法,分析比较了数字和模拟测定K指数存在的差异和原因。与国家地磁台网2005年统计的平均数据进行了比较,数字记录测定比模拟测定的值更好,数字记录更真实、更准确地反映出地磁场活动状态,因此在实际量算K指数时应以数字测定为准。  相似文献   

基于PCA/NDVI的森林覆盖遥感信息提取方法研究   总被引：2，自引：0，他引：2  

邓书斌  武红敢  江涛 《国土资源遥感》2007,18(2):82-85

摘要： 以大兴安岭为试验区，提出将主成分分析（PCA）得到的第1分量、归一化植被指数（NDVI）和Landsat TM 1~TM 7某一波段进行合成，增强森林覆盖区和背景区信息的反差，并利用最大似然法对影像进行监督分类，分类精度超过92%。通过对不同云雾量和森林覆盖的2个时相影像试验表明，本方法提高了遥感影像森林覆盖信息提取的自动化程度和精度。  相似文献   

The mechanics of mudslides as a cyclic undrained–drained process     

Luca Comegna  Luciano Picarelli  Gianfranco Urciuoli 《Landslides》2007,4(3):217-232

Data collected by monitoring suggest that the movement of mudslides essentially develops through alternating stages of undrained–drained deformation. Undrained conditions are established as a consequence of landslide mobilisation or reactivation. Every acceleration phase is followed by progressive deceleration associated with dissipation of excess pore pressure. This paper reports the results of some simple numerical analyses performed to investigate the role of pore pressure on mudslide behaviour.  相似文献   

连云港市城市空气质量预报方法研究   总被引：6，自引：0，他引：6       下载免费PDF全文

姜有山  陈飞  班欣  李军 《气象科学》2007,27(2):220-225

本文利用高空大气探测资料和有限区细网格模式的数值预报产品,分别建立统计预报和数值预报等适合连云港市城市空气质量预报业务发展所需要的客观预报方法,最终利用动态分权法,综合决策集成连云港市城市空气质量预报。结果表明:动态分权法能够有效地提高空气质量的预报准确率。  相似文献