New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution     

Dilce de Fátima Rossetti  Peter Mann de Toledo 《Quaternary Research》2005,63(1):78-89

Although many of the current hypotheses to explain the origin and distribution of the Amazon biodiversity has been based directly or indirectly on geological data, the reconstruction of the geological history of the Amazon region is still inadequate to analyze its relationship with the biodiversity. This work has the main goal to characterize the sedimentary successions formed in the Brazilian Amazon in the Neogene-Quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap. Radar image interpretation, sedimentological studies, and radiocarbon dating allowed the mapping of Plio-Pleistocene to Holocene units along the Solimões-Amazonas River, Brazil. This integrated work led to the characterization of five sedimentary successions overlying Miocene deposits of the Solimões/Pebas Formation, which include the following: Içá Formation (Plio-Pleistocene), deposits Q1 (37,400-43,700 ¹⁴C yr B.P.), deposits Q2 (27,200 ¹⁴C yr B.P.), deposits Q3 (6730-2480 ¹⁴C yr B.P.), and deposits Q4 (280-130 ¹⁴C yr B.P.). These deposits occur mostly to the west of Manaus, forming NW-SE elongated belts that are progressively younger from SW to NE, indicating a subsiding basin with a depocenter that migrated to the NE. The reconstruction of the depositional history is consistent with significant changes in the landscapes. Hence, the closure of a large lake system at the end of the Miocene gave rise to the development of a Plio-Pleistocene fluvial system. This was yet very distinct from the modern drainage, with shallow, energetic, highly migrating, braided to anastomosed channels having an overall northeast outlet. This fluvial system formed probably under climatic conditions relatively drier than today's. During the early Pleistocene, there was pronounced erosion, followed by a renewed depositional phase ca. 40,000 ¹⁴C yr B.P., with the development of prograding lobes and/or crevasse splays associated with a lake system (i.e., fan-delta) and/or fluvial flood plain areas. After a period of erosion, a fluvial system with eastward draining channels started to develop at around 27,000 ¹⁴C yr B.P. The fluvial channels were overflooded in mid-Holocene time. This flooding is attributed to an increased period of humidity, with a peak between 5000 and 2500 ¹⁴C yr B.P. The data presented herein support that, rather than being a monotonous area, the Amazonia was a place with frequent changes in landscape throughout the Neogene-Quaternary, probably as a result of climatic and tectonic factors. We hypothesize that these changes in the physical environment stressed the biota, resulting in speciation and thus had a great impact on modern biodiversity.  相似文献   

地慢柱与热点的成矿作用   总被引：3，自引：0，他引：3  

王登红 《地球学报》1996,17(4):393-400

地幔往与热点是当今地质学前沿课题之一，但研究程度较低，国内更是刚刚起步。本文从时空演化的角度探讨了地幔柱一热点的成矿作用。地幔柱与热点既可见于板块内部，也可见于洋中脊和造山带等板块边界，既可见于现代更可见于古代，因此它可能影响到地表各处以及地史上各阶段的成矿作用．而且在其自身演化的各个阶段都有不同类型的矿化特征。已知的矿床类型包括锡、铜、铅锌、铀、稀土及宝石等。我国华南东钨西锡、东老西新的成矿规律、二叠纪峨眉山玄武岩、白云鄂博稀土矿以及阿尔泰与碱性岩有关的锡多金属成矿系列等，都可能与地幔柱－热点作用有关。  相似文献   

植被冠层热点的季相和日相变化     

苏理宏  李小文  A.Stralher  E.Tsvetsinskay  王锦地 《遥感学报》2002,6(4):241-245

随着热点卫星Triana的即将发射，地表热点季相和日相变化的研究变得日益重要。以几种植被冠层为例，采用计算机模拟的方法考查冠层热点的季相和日相变化。  相似文献   

基于CNKI期刊文献数据库的沙产业研究进展分析   总被引：1，自引：1，他引：0  

张晓琴  苏志珠  马义娟  刘婷 《中国沙漠》2021,41(3):56-65

近30年来,沙产业的理论性研究和实践性成果取得了显著的进展。基于CNKI中国知网知识发现网络平台数据库,使用文献计量方法搜索以沙产业为关键词的文献,定量分析了沙产业概念提出至今的研究进展,包括沙产业的发文量、发文期刊、研究作者、文献引用情况,通过关键词共现知识图谱的归类分析得到了有关沙产业研究领域的“防沙治沙”、“企业管理”、“区域研究”、“发展对策”四大类热点关键词,分别解释了沙产业为什么发展、在哪里发展和怎样发展的问题。沙产业发端于甘肃的河西走廊,成长于内蒙古的库布齐沙漠、乌兰布和沙漠,在新疆、宁夏等西部受荒漠化危害严重的省区也得到了迅速发展,取得了一定的生态效益和经济效益,成为了沙区防治沙漠化和发展经济最有效的途径,但依然存在科技成果转化慢、缺乏对沙区资源的定量评价和区域发展不协调等问题亟待解决,因此沙区要充分利用当地发展优势结合国家政策推动沙产业更快更好发展。  相似文献   

Policy Contestation over the Ecosystem Services Approach in Sweden     

Erik Hysing  Rolf Lidskog 《社会与自然资源》2018,31(4):393-408

Ecosystem services (ES) is an important approach to biodiversity protection in political rhetoric and policy practice, but it is also highly contested. This paper analyzes the introduction of ES in Swedish environmental policy and how it is contested by key stakeholders and discusses its implications for biodiversity governance. The results show that although ES is widely accepted on an abstract and conceptual level, critical features and functions are highly contested. These primarily concern the valuation of nature, appropriateness of different policy instruments, and institutional structures. The paper concludes that while the controversy surrounding ES fills an important role by reinvigorating debate and stimulating reflections on biodiversity loss, it also illustrates how ES is used to further particular values and beliefs and to challenge traditional biodiversity-protecting strategies. Understanding these policy controversies is central to addressing the challenges of transforming the promises of ES into practical policies.  相似文献   

西南山区河流阶梯-深潭系统的生态学作用   总被引：12，自引：1，他引：11  

王兆印  程东升  何易平  王洪铸 《地球科学进展》2006,21(4):409-416

山区河流发育的阶梯—深潭系统具有显著的生态学作用。阶梯—深潭系统增大水流阻力和河床抗冲刷力,稳定了河床和岸坡。大卵石堆积成阶梯,细颗粒泥沙在深潭河段的缓流滞流区沉积下来形成淤泥层,形成适宜多种生物的栖息地。选择小江支流——深沟、蒋家沟和小白泥沟,以及四川九寨沟和金沙江进行野外实验、取样分析。结果发现阶梯—深潭系统较发育的深沟和九寨沟底栖动物密度高达552个/m2,生物量高达5.96 g/m2。而邻近的小白泥沟和蒋家沟底栖动物密度仅0.75个/m2,生物量不到0.006 g/m2。考虑河流不同部位底质、水深、流速等特性,提出了生物栖息地多样性及其计算方法,研究发现大型无脊椎动物的生物多样性随栖息地多样性增加而增加。利用阶梯—深潭系统治理山区河流,既能保持河道稳定,又能维持较高的生物多样性,保持健康的河流生态系统。  相似文献   

全球恐怖袭击事件时空演变与态势分析     

王诚聪  刘亚静  刘明月 《地球信息科学学报》2019,21(11):1710-1720

恐怖主义具有极大的破坏性与杀伤力,已成为世界和平与安全的最大威胁之一。本文以全球恐怖主义数据库（GTD）为基础,采用伤亡人数的热点分析以及各区域事件频次的层次聚类方法,对全球恐怖主义袭击事件的时空演变特征与态势进行分析研究,探讨了2013-2017年内全球高伤亡率热点区域的空间分布与变化,并对不同地区的袭击频次进行统计并划分了事发率严重等级。研究表明：① 5年内,伤亡人数在2014年为最高达103 134人,而后逐年递减的趋势;袭击频次呈现一种锯齿状为“猖狂-治理-收敛-不治理-再次猖狂”的模式;② 中东及北非地区是恐怖主义袭击的严重区与策源地,也是高伤亡率的热点区域,平均每年伤亡人数约占全球的49%,事件发生频次约占40%,而南亚伤亡人数约占22.8%,袭击频次约31.1%,撒哈拉以南的非洲地区次之,东南亚及西欧、东欧、南美地区也为恐怖主义的暴动区域;③ 全球恐怖主义的时空演变趋势已形成以中东及北非地区以及与撒哈拉以南的非洲交界区域为爆发中心,逐渐向南亚、东南亚、西欧地区扩散的趋势,为新的恐怖主义活跃区。通过对5年内全球恐怖主义的时空演变和态势,以及造成恐怖主义发生的原因进行分析,可为反恐组织以及避免袭击事件的发生提供有效的参考和决策辅助。  相似文献   

Ross-Li核驱动模型热点参数化及其校正—以POLDER数据为例   总被引：1，自引：1，他引：0  

常雅轩  焦子锑  董亚冬  张小宁  何丹丹  尹思阳  崔磊  丁安心 《遥感学报》2019,23(4):661-672

半经验、核驱动二向性反射分布函数(BRDF)模型是多角度遥感领域的一个重要模型,其热点效应在应用BRDF反演其它地表参数时有重要作用。本研究针对树冠内部叶片的间隙对热点的影响,对几何光学核的重叠函数进行热点效应的改进,并利用POLDER多角度观测数据集,对改进热点效应后的不同核函数组合模型的最优热点参数进行了确定。通过最小均方根误差(RMSE)筛选出最优热点参数,进一步分析不同模型对热点参数的敏感性和RMSE随热点参数的变化情况。结果表明:(1)该热点参数化方法可用于Ross-Li核驱动模型不同核函数组合的情况,热点校正后的模型相对于原模型很好地改善了对热点反射率的拟合能力;(2)热点参数最优值在几何光学核为LSRC (LiSparseRChen)与LDRC (LiDenseRChen)组成的模型中出现明显差别,C1在LDRC模型中的值远小于LSRC模型,主要是因为LDRC核函数自身较好考虑了树冠尺度下的热点效应,所以该热点参数改进方法起到的补偿作用较小;(3)总体上,同一模型的C1参数比C2参数对热点的变化更敏感。本研究为Ross-Li核驱动模型的热点效应进一步校正及热点参数的取值范围提供了依据,对Ross-Li模型的推广有重要意义,改进热点效应后的模型可用于未来国产多角度卫星的数据处理流程中,以获取加精确的地物热点反射率信息。  相似文献   

瓯江口海域春秋季鱼类多样性及群落结构研究     

颜文超  宋伟华  俞存根  周青松  郑基  邓小艳  张平  谢旭 《海洋湖沼通报》2018,(6):132-141

根据2013年5月(春)、2013年10月(秋)在温州瓯江口海域进行渔业资源定点拖网调查获得的鱼类数据,利用渔获率作为数量分布的指标,对瓯江口海域的鱼类生态类群和鱼类种类组成、优势种、物种数目空间分布及多样性和鱼类群落结构进行了分析。结果显示:两次调查共鉴定鱼类66种,隶属12目37科51属,其中暖温性鱼类29种,占44%,暖水性鱼类37种,占66%,种类季节间变化较为稳定,优势种季节更替明显,春季优势种有银鲳Pampus argenteus、花鲈Lateolabrax japonicus、日本鳀Engraulis japonicus、棕腹刺鲀Gastrophysus spadiceus 4种,而秋季为花鲈、斑鰶Konosirus punctatus、龙头鱼Harpodon nehereus 3种;种类数平面分布结果显示,种类数春季沿岸区域高,秋季岛礁区域高,生物多样性春季高于秋季;多样性指数与种类数平面分布结果相似,均为江口外部海域高于内部,近岸和岛礁处高于中部,地形、台湾暖流和瓯江淡水团对其分布影响较大;春、秋季鱼类群落结构差异不大,种级和属级之间具有相似性。  相似文献   

Reduced abundance but increased diversity of chironomid larvae under higher trophic pressure from fish in semi-permanent ponds     

《Limnologica》2020

Fish may affect macrobenthic communities through trophic interactions and modification of habitat conditions. We compared the density, diversity and taxonomic composition of larval chironomids under low vs high fish impact, created by stocking semi-natural ponds with either young/small common carp Cyprinus carpio at low biomass densities or with high biomass densities of older/large common carp, supplemented by other cyprinids and predatory fish species.Over the study season, May–August, total chironomid abundance was considerably lower in ponds with high fish biomass than in low fish biomass ponds. In July–August larval densities declined significantly, irrespective of the fish status of the ponds. The composition of larval communities diverged between ponds with different fish status. Chironomus riparius and C. plumosus accounted for most of the observed dissimilarity. C. plumosus densities were not affected by the fish status of the pond, constituting on average >38 % of chironomid specimens in both types of ponds. C. riparius was abundant in ponds with low fish biomass (on average 30 %), but rare in ponds with high fish biomass (4 %). Other common taxa were Glyptotendipes pallens (15 % and 13 %, respectively) and Procladius sp. (14 % in ponds with low fish impact). Canonical correspondence analysis showed that fish biomass was more important in determining chironomid community composition than environmental variables indicative of pond eutrophication (total N, P, chlorophyll a and conductivity).Despite adverse effects on total abundance, chironomid diversity was higher under apparently stronger trophic pressure by fish. Fish may have relieved some chironomid species from invertebrate predation and competition with dominant Chironomus larvae. Other important drivers of chironomid assemblage and diversity patterns may include species-specific feeding modes and prey size selectivity of fish, the ability of chironomid larvae to attain size- and depth-refuge from small fish but not larger fish, and differential vulnerability of free-living and tube-dwelling larvae relative to ontogenetic niche shifts of fish.  相似文献