巽他陆坡下部陆源碎屑粒度分布的控制因素     

赵玉龙  刘志飞  成鑫荣  翦知湣 《海洋地质与第四纪地质》2006,26(2):73-78

通过对“太阳号”115航次18268-2孔陆源碎屑高分辨率沉积粒度分析,获取了大约2.5万年以来巽他陆坡下部沉积物粒度分布特征的详细记录。结果显示,该孔陆源碎屑颗粒较细,粒径在2~10μm之间的含量最高,几乎不含大于63μm的颗粒。沉积物粒度分布的均值和中值与粒径在10~63μm之间的百分含量相关性较好,说明古水流速度决定着沉积物粒度分布在短时间尺度上的变化。14.6~14.3 kaBP期间海平面迅速上升造成海岸线后退数百千米,使本地区沉积物供应产生了明显的变化,从而造成所有统计参数及各组分相对百分含量在15 kaBP前后均发生了明显变化,这说明沉积物供应控制着沉积物粒度分布较长时间尺度上的变化。  相似文献   

Evidence of a phase shift to Epizoanthus gabrieli Carlgreen, 1951 (Order Zoanthidea) and loss of coral cover on reefs in the Southwest Atlantic          下载免费PDF全文

Igor C. S. Cruz  Ruy K. P. de Kikuchi  Leila L. Longo  Joel C. Creed 《Marine Ecology》2015,36(3):318-325

There is at present a ‘coral reef crisis’; one of the more drastic consequences of this is a phase shift, in which reef‐building corals are replaced by non‐reef building benthos such as macroalgae and soft corals. Previous studies have principally focused on the shift to macroalgae. Our goal was to investigate whether the dominance of the zoanthid Epizoanthus gabrieli on some reefs of Todos os Santos Bay, Brazil, represented a non‐algal phase shift. In 2003, we identified a high cover of this species on two reefs (52% and 70%), but only in 2007 was it possible to confirm a reduction in coral cover. This dominance has persisted for over 9 years, characterizing a true phase shift. This loss of coral cover may be a result of anthropogenic disturbances within the bay; however, given the large number of human impacts, further studies are needed to identify specific causes of this shift. Although there are some reports of phase shift involving species pertaining to the Class Anthozoa, this is the first report of this phenomenon involving the order Zoanthidea.  相似文献   

The contested and negotiated dominance of Anglophone geography in Greece     

Dina Vaiou 《Geoforum》2004,35(5):529-531

In this comment, I discuss the dominance of Anglophone geographical literature in Greece, arguing that it is a recent and still contested phenomenon, to do with broader historical/political circumstances, as well as with the development of geographical studies at university level. In the context of the power-knowledge system, in which Anglophone debates, theory production and spaces of academic communication and exchange dominate, radical academics in Greece are caught in a complex web of contradictions, have to negotiate their/our paths across languages, plural voices, local and international communities.  相似文献   

水洞沟:东西方文化交流的风向标?——兼论华北小石器文化和“石器之路”的假说          下载免费PDF全文

侯亚梅 《第四纪研究》2005,25(6):750-761

水洞沟文化从发现之初便以其所具有的西方旧石器中、晚期特点而引起了学者们的注意,并被后来的很多学者引证为东西方交流的有利证据。但是对于在这一文化现象里所发生的交流模式的探讨依然含糊,或者它不言而喻是一种“西来”的模式。随着对该文化中存在的“勒瓦娄哇石核”技术的揭示,这一观点似乎只会被加强。然而新的研究证据使人们有可能质疑过去的观点,而重新审视水洞沟文化的内涵和意义。文章通过水洞沟文化中“东谷坨石核”的再现,对水洞沟文化在东西方文化交流中的位置提出新的看法,进而探讨华北小石器文化的主导性与传播性,并指出确立旧石器时代早期“华北中心说”和“华北小石器文化自源性”概念的必要性,提出历史时期东西方文化交流中“丝绸之路”的前身应为史前时期即已存在的“石器之路”的假说,认为水洞沟是东西方文化交流与传播的风向标。  相似文献   

河北昌黎生态监控区8月份大型底栖动物多样性研究          下载免费PDF全文

赵志楠  梁晓林  张月明  韩晓庆  张鉴达  高伟明 《海洋科学进展》2014,32(3)

根据2011-2013年每年8月昌黎生态监控区大型底栖动物监测数据,以Simpson优势度为指标分析了研究区大型底栖动物的物种组成及群落结构年际变化。运用物种多样性指数(H')、均匀度指数(J)、丰富度指数(dMa)深入探究了监控区底栖动物的多样性变化趋势。研究结果显示:1)多毛类、甲壳类、软体类动物是该海域大型底栖动物的主要类群;2)2011-08监控区平均密度为43个/m2,平均生物量为3.14g/m2;2012-08监控区平均密度为41个/m2,平均生物量为3.21g/m2;2013-08监控区平均密度为28.74个/m2,平均生物量为7.72g/m2;3)2013年监控区19个站位多样性指标均值远高于前两年;4)2011-08监控区第一优势种为绒毛细足蟹其Y值为0.029 4;2012-08监控区第一优势种为裸盲蟹其Y值为0.007 3;2013-08监控区第一优势种为长吻沙蚕其Y值为0.007 0。  相似文献   

Evolution of regional transport dominance in China 1910-2012     

HU Hao  WANG Jiaoe  JIN Fengjun  DING Nan 《地理学报(英文版)》2015,25(6)

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中国县域陆路交通优势度格局演化及经济效应     

陈舒婷  李裕瑞  潘玮  王武林  金凤君 《地理学报》2022,77(8):1937-1952

基于2009年、2014年和2018年全国陆路交通数据,集成路网密度、人口加权平均交通邻近度和区位优势度3个指标,构建陆路交通优势度评价模型,刻画2009—2018年中国县域陆路交通的规模、邻近水平和通达水平,揭示陆路交通优势度的空间格局、演化特征及经济效应。研究表明：① 2009—2018年中国陆路交通建设取得显著成效,陆路交通优势度增长热点具有由城镇密集区向区际通道拓展的特征,与“两横三纵”城市化战略密切相关,陆路交通劣势主要位于西部、东北和省际边界地区,是交通均衡发展补短板的关键区域。② 中国陆路交通优势区域的空间结构在不同区域和发展阶段存在差异,其演化过程大致经历极核式、点轴式和轴辐式3个阶段,未来交通建设应强化重要区域、交通主轴、关键走廊之间的衔接。③ 中国陆路交通优势度的总体经济效应为显著正效应,其间接效应约为直接效应的1.5倍。但是交通建设并不总是促进县域经济增长,交通优势的不同维度对经济发展的作用不同,在不同区域背景和经济发展阶段也存在差异,需要重视区位优势度改善可能带来的负面效应。  相似文献   

Sediment macrobenthos off eastern Waiheke Island,Hauraki Gulf,New Zealand     

KL Clara Wong  Steve O'Shea 《新西兰海洋与淡水研究杂志》2013,47(3):149-165

Aspects of sea-bed structure and benthic-macroinvertebrate species composition, distribution, richness and diversity in coastal waters off eastern Waiheke Island, Hauraki Gulf, are reported. In contrast to the sole historical account of sea-bed community structure from this same region, no widely distributed assemblages of species are recognised throughout it; no two sites share the exact same complement of species; and almost all sites are less than 80% similar in their taxonomic composition, most considerably so. Species richness and diversity are reported to vary with substratum type and depth, and spatially; species occurring within muds are the least diverse and species rich, followed by those of muddy gravels, and then gravels; many taxa prove common to the three substratum types; and dominance of taxa is recognised to decrease with an increase in substratum complexity, from muds to gravels, and species richness. With the exception of invasive marine species, apparent changes in the composition of assemblages throughout this region over the eight-decade period that data span are considered artefacts of the way in which such assemblages were historically defined. We recommend historical accounts of sea-bed community distributions throughout Hauraki Gulf be interpreted with caution, especially when attempting to use such schematic depictions to determine whether changes have occurred in assemblage composition.  相似文献   

Groundwater control on the suspended sediment load in the Na Borges River, Mallorca, Spain   总被引：1，自引：0，他引：1  

Joan Estrany  Celso Garcia  Ramon J. Batalla   《Geomorphology》2009,106(3-4):292-303

Groundwater dominance has important effects on the hydrological and geomorphological characteristics of river systems. Low suspended sediment concentrations and high water clarity are expected because significant inputs of sediment-free spring water dilute the suspended sediment generated by storms. However, in many Mediterranean rivers, groundwater dominance is characterised by seasonal alternations of influent and effluent discharge involving significant variability on the sediment transport regimes. Such areas are often subject to soil and water conservation practices over the centuries that have reduced the sediment contribution from agricultural fields and favour subsurface flow to rivers. Moreover, urbanisation during the twentieth century has changed the catchment hydrology and altered basic river processes due to its ‘flashy’ regime. In this context, we monitored suspended sediment fluxes during a two-year period in the Na Borges River, a lowland agricultural catchment (319 km²) on the island of Mallorca (Balearic Islands). The suspended sediment concentration (SSC) was lower when the base flow index (i.e., relative proportion of baseflow compared to stormflow, BFI) was higher. Therefore, strong seasonal contrasts explain the high SSC coefficient of variation, which is clearly related to dilution effects associated with different groundwater and surface water seasonal interactions. A lack of correlation in the Q-SSC rating curves shows that factors other than discharge control sediment transport. As a result, at the event scale, multiple regressions illustrate that groundwater and surface water interactions are involved in the sedimentary response of flood events. In the winter, the stability of baseflow driven by groundwater contributions and agricultural and urban spills causes hydraulic variables (i.e., maximum discharge) to exert the most important control on events, whereas in the summer, it is necessary to accumulate important volumes of rainfall, creating a minimum of wet conditions in the catchment to activate hydrological pathways and deliver sediment to the drainage network. The BFI is also related to sediment delivery processes, as the loads are higher with lower BFI, corroborating the fact that most sediment movement is caused by stormflow and its related factors. Overall, suspended sediment yields were very low (i.e., < 1 t km^− 2 yr^− 1) at all measuring sites. Such values are the consequence of the limited sediment delivery attributable to soil conservation practices, low surface runoff coefficients and specific geomorphic features of groundwater-dominated rivers, such as low drainage density, low gradient, steep valley walls and flat valley floors.  相似文献   

贵州关岭县喀斯特峰丛石漠区苔藓群落生态特征   总被引：8，自引：6，他引：2  

张天汉  代玉  王智慧  张朝晖 《中国岩溶》2014,33(2):192-200

为了了解喀斯特峰丛石漠化区苔藓植物的种类和群落特征,本文选取贵州省安顺市关岭县喀斯特峰丛石漠化区的三种典型生境（裸地、人工植被和自然植被）,对苔藓植物进行样地调查,并利用种间相遇几率（PIE）、生态优势度、Shaanon-Wiener信息指数(衡量生态位宽度)和Morisita-Horn指数(衡量生态位重叠)来分析该区苔藓植物群落的组成、分布规律及生态特征。结果表明:（1）该区苔藓植物共有11科17属22种,真藓科为优势科,苔藓植物群落有19个类型。（2）苔藓群落PIE值与植被覆盖度呈正比,与岩石裸露率呈反比,自然植被生境的苔藓群落PIE值高于人工植被和裸地生境,但研究区苔藓群落PIE总体偏低,反映了喀斯特峰丛地区恶劣的生境条件。（3）研究区内卷叶湿地藓群落(Hyophiletum)、直蒴卷柏藓群落(Racopietum)和皱叶牛舌藓群落(Anomodetum)有着较高的生态优势度和生态位宽度,并且与其它苔藓群落的生态位重叠值很高。表明这三种苔藓群落对不同类型的峰丛石漠化生境都有着较好的适应能力,能够很好地与其它苔藓群落互利共生。   相似文献