Short-term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach   总被引：1，自引：0，他引：1  

GERHARD MASSELINK  NIGEL AUGER†  PAUL RUSSELL†  TIM O'HARE† 《Sedimentology》2007,54(1):39-53

This paper describes the morphological and sedimentological evolution of a macrotidal beach over a 20 day period under varying hydrodynamic conditions (significant breaker heights of 0·3–2 m and tidal ranges of 2–5 m). During the field campaign, an intertidal bar developed around the mid‐tide level, migrated onshore, welded to the upper beach and was then flattened under energetic wave conditions. The bar had a wave breakpoint origin and its formation was triggered by a reduction in tidal range, causing more stationary water‐level conditions, rather than an increase in wave height. Most of the onshore bar migration took place while the bar was positioned in the inner to mid‐surf zone position, such that the bar moved away from the breakpoint and exhibited ‘divergent’ behaviour. The depth of disturbance over individual tidal cycles was 10–20% of the breaker height. Such values are more typical of steep reflective beaches, than gently sloping, dissipative beaches, and are considered to reflect the maximum height of wave‐generated ripples. The grain size distribution of surficial sediments did not vary consistently across the beach profile and temporal changes in the sedimentology were mostly unrelated to the morphological response. The lack of clear links between beach morphology and sedimentology may be in part due to shortcomings in the sampling methodology, which ignored the vertical variability in the sediment size characteristics across the active layer.  相似文献   

北京市土层GPS连续站数据的初步利用     

赵桂儒  徐平  吴培稚  邢成起  李国江  张卫新  熊焰 《华北地震科学》2007,25(3):37-41

处理了北京地区GPS连续站的数据,发现京郊一些土层连续站水平分量变化和基岩站差别不大,垂直分量与基岩站不完全一致.利用北京地区GPS连续站的观测数据结合北京地区周围10个IGS站,用GAMIT软件进行解算,讨论了土层连续站数据在地震研究中应用的可能性.  相似文献   

扰动重力数据精度对GPS/重力边值问题的影响研究     

张利明  李斐  岳建利 《武汉大学学报(信息科学版)》2007,32(1):15-18

以GPS／重力边值问题为基本的数学模型，通过数值模拟方法，对不同精度的扰动重力数据对GPS／重力边值问题的影响厦误差量级进行了模拟和分析，得出了一些有意义的结论。  相似文献   

风浪扰动对太湖水体悬浮物重金属含量的影响   总被引：8，自引：2，他引：8  

池俏俏  朱广伟  张战平  秦伯强 《湖泊科学》2006,18(5):495-498

通过离心浓缩的方法,获取太湖梅梁湾口东岸处(即梅梁湾与贡湖湾的交界处)不同风浪条件下的悬浮颗粒物．冷冻干燥,微波消解,ICP-AES的方法测定了其中Co、Cr、Cu、Ni、Pb、Zn等重金属元素及Al、Ca、Fe、Mn等相关金属元素的含量．结果发现,小风浪(2 m/s)、中风浪(7 m/s)和大风浪(11 m/s)下：①水体总悬浮颗粒态金属的量依次大幅度增加；②单位悬浮颗粒物中各金属元素的含量在不同风浪下变化不同．Ca在小、中、大风浪下含量依次增大；Zn在小、中、大风浪下含量依次减少；Mn和Cu的含量变化趋势相同：与小风浪相比,中风浪下Mn、Cu的含量显著增大；与中风浪相比,大风浪下含量显著减少；其它元素Al、Fe、Ni、Pb、Co、Cr等在单位悬浮物中,中风浪与小风浪相比含量减少,大风浪与中风浪相比含量略微增加．研究表明：①金属元素在水体总悬浮物中的含量主要受风浪影响,但风浪对单位悬浮物中金属含量的影响则因元素而异；②除Cu、Mn、Zn外,悬浮物中重金属含量随粒径增大含量减少．  相似文献   

徐庄子地震台地磁观测干扰因素剖析     

毕金孟  马永  马朝晖 《地震地磁观测与研究》2020,41(2):130-137

为充分认识地磁观测环境中的各种干扰因素,提升台站观测人员对数据异常的识别能力,确保提供真实有效的高质量观测数据,以天津市徐庄子地震台地磁观测为例,阐述地磁观测中存在的多种干扰因素及形态特征和预处理方法。分析表明,徐庄子地震台地磁GM4磁通门磁力仪主要受高压直流输电、地铁运营、过往车辆、地电供电、GPS整点授时、磁扰以及雷电等因素的影响,干扰形态主要表现为尖峰、台阶、扰动等,并总结说明高压直流输电线路的干扰鉴定方式、幅度及干扰时段等。  相似文献   

新疆43号泉的降水影响及震例分析     

李茂玮  田志坚 《内陆地震》1996,10(2):113-120

分析了新疆４３号泉水流量的地震前兆特征及大气降水影响。结果表明，一次大气降水过程对流量的影响甚微，影响幅度一般小于１％，但年降水量对流量的趋势变化影响较大，这可能与降水补给经历较长的地下径流有关。对于１５０ｋｍ范围内的中强震，４３号泉可观测到明显的中短期异常，异常一般在震前５个月左右出现；短临异常也较显著。对一些ＭＬ３～４级的地方震，往往仅有短临异常显示。从异常开始至发震一般１０～２０天，据此可与中强震异常相区分。  相似文献   

西安地电台环境噪声干扰的实验研究     

王秀生  张秀香 《地震工程学报》1996,18(1):67-70,76

对西安地电台周围环境噪声声干扰进行了实验研究，结果表明，环境噪声的衰减是很快的，地电测区避开企带来单位２００ｍ，环境噪声电平即可衰减１个数量级。只工作认真仔细，在大城市近郊能够选出较好的地电台址。  相似文献   

基于Oracle数据库的电磁扰动数据转换     

王莉森  张云昌  殷金平  边鹏飞 《地震地磁观测与研究》2011,32(6):168-172

为提供丰富的观测数据产品,编制基于Oracle数据库的电磁扰动产品数据计算软件.本软件能够将秒采样观测数据转换为分钟值、小时值、日均值数据,为应用人员提供丰富的研究数据.  相似文献   

Regional- and district-level drivers of timber harvesting in European Russia after the collapse of the Soviet Union   总被引：1，自引：0，他引：1  

Kelly J. Wendland  David J. Lewis  Jennifer Alix-Garcia  Mutlu Ozdogan  Matthias Baumann  Volker C. Radeloff 《Global Environmental Change》2011,21(4):1290-1300

After the collapse of the Soviet Union, the forestry sector in Russia underwent substantial changes: the state forestry sector was decentralized, the timber industry was privatized, and timber use rights were allocated through short- and long-term leases. To date, there has been no quantitative assessment of the drivers of timber harvesting in European Russia following these changes. In this paper we estimate an econometric model of timber harvesting using remote sensing estimations of forest disturbance from 1990–2000 to 2000–2005 as our dependent variable. We aggregate forest disturbance to administrative districts – equivalent to counties in the United States – and test the impact of several biophysical and economic factors on timber harvesting. Additionally, we examine the impact that regions – equivalent to states in the United States and the main level of decentralized governance in Russia – have on timber harvesting by estimating the influence of regional-level effects on forest disturbance in our econometric model. Russian regions diverged considerably in political and economic conditions after the collapse of the Soviet Union, and the question is if these variations impacted timber harvesting after controlling for district-level biophysical and economic drivers. We find that the most important drivers of timber harvesting at the district level are road density, the percent of evergreen forest, and the total area of forest. The influence of these variables on timber harvesting changed over time and there was more harvesting closer to urban areas in 2000–2005. Even though district-level variables explain more than 70 percent of the variation in forest disturbance in our econometric model, we find that regional-level effects remain statistically significant. While we cannot identify the exact mechanism through which regional-level effects impact timber harvesting, our results suggest that sub-national differences can have a large and statistically significant impact on land-use outcomes and should be considered in policy design and evaluation.  相似文献   

The Effects of Hermit Crabs
on Hydractiniid Hydroids The effects of hermit crabs on hydractiniid hydroids     

David H. Van Winkle  Krista Longnecker  & Neil W. Blackstone 《Marine Ecology》2000,21(1):55-67

Abstract. Hermit crab shells are often encrusted with diverse communities of epibionts. To explore the effects of hermit crabs on the interactions of these encrusting species, two species of hydractiniid hydroids, Hydractinia symbiolongicarpus and Podocoryna carnea , were examined in the presence and absence of Pagurus longicarpus hermit crabs. Colonies growing on Littorina littorea snail shells with hermit crab hosts were compared to those growing on shells without crabs. These experiments suggest that hermit crabs variably affect colony polyp number, colony morphology and the outcome of interspecific competition, according to the size and number of crabs; other factors include water temperature, food availability and hydroid clonal genotype. In order to allow image analysis of perturbations of colony morphology, hydroids were grown on glass surfaces both exposed and unexposed to hermit crabs. Relative to colonies growing on unexposed surfaces, colonies growing on exposed surfaces exhibited larger within-colony patches, thus decreasing the total encrusted surface area and polyp number of colonies. Further, on glass surfaces, hermit crabs accelerated the time to the resolution of interspecific competition ( i.e. , the overgrowth of one colony by the other). While a number of factors may contribute to the relative abundance of these encrusting species, under most circumstances P. longicarpus have large effects on hydractiniid hydroids. Mechanisms underlying these effects likely include hydrodynamics and mechanical disturbance.  相似文献