The concept of ecological succession applied to phytoplankton over four consecutive years in five ponds featuring a salinity gradient     

Hajer Khemakhem  Jannet Elloumi  Mahmoud Moussa  Lotfi Aleya  Habib Ayadi 《Estuarine, Coastal and Shelf Science》2010

The distribution of phytoplankton abundance, biomass and species composition coupled with environmental factors and metazooplankton was studied relatively intensively and over a period of four consecutive years in five ponds featuring a gradient of increasing salinity from near to that of sea water to a nine-fold concentration from 2000 to 2003. The results indicate that the physical characteristics of the water (temperature and salinity) were quite similar over the years. Nutrients, which were concentrated in pond A1, decreased with increases in salt concentration. The composition of the phytoplankton community showed strong seasonality. Diatoms dominated in the first ponds A1, A16 and C2-1, followed by dinoflagellates. Chlorophyceae dominated the phytoplankton community in the hypersaline ponds M2 and TS. Cyanobacteriae were relatively abundant in ponds M2 and TS. The highest phytoplankton density and biomass were found in the ponds with the highest salinity due to the proliferation of Dunaliella salina (Chlorophyta: Volvocales). The inter-annual study of phytoplankton succession in the Sfax solar salterns showed slight differences among the years of study due to the stability of the environmental conditions. Phytoplankton communities were permanently primitive, stage 1 – structured as they failed to build complexity because of salt stress which operates for longer and above any other variables. This reduced frequency of disturbance to the existing course of regulation, allowed the community to “mature” from its “primitive” state, rather than experience frequent structural setbacks.  相似文献   

海南昌江沿岸海域石珊瑚的物种多样性及其分布     

牛文涛  张潇娴  林荣澄  王初升 《台湾海峡》2010,29(3):389-393

2009年3月,采用水下照相及摄像方法,对海南昌江沿岸海域的石珊瑚物种多样性、分布及覆盖度进行了调查.结合历史资料,共发现石珊瑚10科15属28种和1未定种.其中鹿角珊瑚属（Acropora）、角蜂巢珊瑚属（Favites）、叶状珊瑚属（Lobophyllia）等为优势类群,常见分布珊瑚种类有角孔珊瑚（Gonioporasp.）、标准蜂巢珊瑚（Favia speciosa）、五边角蜂巢珊瑚（Favites pentagona）、多孔鹿角珊瑚（Acropora millepora）、十字牡丹珊瑚（Pavona decussata）、伞房叶状珊瑚（Lobophyllia corymbosa）等.石珊瑚主要分布于海尾镇三联村以南海域,覆盖率最高为12%.本次调查在海南昌江沿岸海域记录的珊瑚种类数多于以前的记录,但少于海南南岸的三亚鹿回头,也少于北部的广西涠洲岛、广东徐闻、香港等海域,随着调查次数的增加,预计会有更多的种类被发现.该海域是北部湾珊瑚幼虫交流的中间过渡区,对珊瑚礁的保护与恢复具有重要意义.  相似文献   

Evaporitic sedimentation and microbial mats in a salina system (Port Fouad,Egypt)     

A. G. Taher  S. Abdel Wahab  G. Philip  W. E. Krumbein  A. M. Wali 《International Journal of Salt Lake Research》1995,4(2):95-116

A salina system along the Mediterranean coast of Egypt was investigated. Five sedimentary facies are described. For each facies, the evaporitic sedimentation and the biological conditions are considered. Comparisons of evaporite precipitates in the salina with ancient deposits are made.  相似文献   

A Preliminary Study of the Self-Directed Photography of Middle-Class,Homeless, and Mobility-Impaired Children*     

Stuart C. Aitken  Joan Wingate 《The Professional geographer》1993,45(1):65-72

Understanding the ways in which children with different life experiences come to terms with day-to-day contexts and constraints has become an important topic of social science research. This study applies the technique of auto-photography to the study of children-environment transactions. How children apprehend their environments is described through a leitmotif analysis and an interpretation of photographs taken by children from middle-class families, homeless children, and children whose mobility is impaired by cerebral palsy. We speculate upon the social and physical contexts of these children based upon the images that they selected to photograph. Although impressionistic, our findings suggest the importance of auto-photography as a method for uncovering children-environment transactions.  相似文献   

叠层石与沉积矿产的关系     

张录易 《西北地质科学》1991,(32)

本文通过笔者实际考察资料及国内外学者研究资料,综合分析了叠层石与沉积矿产关系的研究现状,探讨了叠层石和造叠层石底栖微生物群落对铁、铜、多金属、磷、锰等矿产的成矿作用。叠层石可以溉括为直接的和间接的两种成矿作用:①叠层石为容矿体,其本身就是一种矿石类型;②叠层石不含矿,其岩礁为矿的间隔体。后者是一种金属硫化物避开叠层石岩礁而在礁侧沉积成巨大的富矿模式。  相似文献   

藏北高山嵩草草旬植被和多样性在沙漠化过程中的变化     

魏兴琥李森  杨萍董玉祥  张春来 《中国沙漠》2007,27(5):750-757

为确定沙漠化对高山嵩草草甸植被组成、结构和物种多样性的影响，了解高寒区草甸沙漠化的原因，选择西藏那曲安多县南部沙漠化严重区域为调查区，按照沙漠化的不同程度设置样地，系统调查了轻度、中度、重度和极重度沙化草甸的植被变化，结果表明：中度、重度和极重度沙化区的植被与轻度沙化草甸有显著的差异；在中度和重度沙化区，高寒草甸的建群种高山嵩草已被家畜不喜食或更具抗性的植物种所取代，而在极重度沙化的流动沙丘上无植被生长；从过牧的退化草甸到半流动、流动沙丘，植物种多样性呈显著的降低趋势。轻度沙化草甸物种数、个体密度和丰富度指数最多；中度沙化草甸的Shannon-Wiener指数和均匀度指数最大，而优势度指数最小；在沙化过程中，高寒草甸的植被盖度显著下降，地上生物量也在下降，虽然轻度、中度和重度沙化草地的地上生物量显著高于极重度沙化区，但前者之间却无显著差异。地下根系生物量也呈显著下降的趋势。过牧是造成高山嵩草草甸沙化的主要原因。  相似文献   

向海湿地自然保护区鸟类多样性评价方法的比较研究   总被引：1，自引：1，他引：1  

何春光  崔丽娟  盛连喜  赵俊  邹丽芳 《干旱区地理》2007,30(6):858-864

鸟类多样性是评价湿地生态环境质量极其敏感的指标。向海湿地自然保护区地处半干旱区,受气候和人为影响,生态环境变化极为剧烈,因此,寻求一种行之有效且简单易行的鸟类多样性评价手段,对于及时了解湿地生态环境质量的动态变化信息,提出湿地和鸟类多样性的管理和保护对策至关重要。稀疏标准化法是一种建立在物种-面积关系上的生物多样性评价方法,主要用于区域尺度上的生物多样性评估。运用改进的稀疏标准化程序,利用多年调查和收集的鸟类数据,来评价和分析向海自然保护区鸟类多样性及其变化,结合香农-威纳多样性指数和均匀度指数,分析了两种方法获取结果的相关性。评估结果表明:稀疏标准化法获取的鸟类多样性和均匀度信息与传统的香农-威纳多样性指数和Pielou均匀度指数间具有显著的相关关系,可以用于鸟类的多样性和均匀度评价,且具有科学、直观、运算简捷、快速等优势。  相似文献   

山东龙宝山岩体稀土元素特征及矿源研究     

夏庆霖  陈永清 《物探与化探》2002,26(2):110-112117

龙宝山岩体是燕山期多阶段岩浆活动形成的中偏碱性杂岩体,其稀土元素特征为:wΣREE为地壳丰度的2.5倍,wLREE/wHREE为地壳的近9倍,轻稀土强烈富集,δEu、δCe均呈弱负异常,各期侵入岩及含金石英脉的稀土元素分布型式基本相似,呈向右陡倾斜线,但石英脉中稀土总量更高、轻稀土更为富集。研究结果表明:岩浆和成矿物质最初可能均来源于上地幔的同一岩浆房,并在岩浆上侵过程中不同程度地同化混染了地壳物质。  相似文献   

Effects of fire, grazing, and the presence of shrubs on Chihuahuan desert grasslands     

Paul B. Drewa  Kris M. Havstad 《Journal of Arid Environments》2001,48(4):429

Responses of herbaceous and suffrutescent species to fire, grazing, and presence of Prosopis glandulosa were examined in a Chihuahuan desert grassland in south-central New Mexico. Treatments were assigned randomly to eight 12×8 m plots within each of two blocks. Following fires in June 1995, unfenced plots were exposed to livestock grazing over 4 years. Plots were established that either included or excluded P. glandulosa. Perennial grass cover, primarilyBouteloua eriopoda , decreased by 13% in burned plots but increased 5% in unburned areas. Conversely, perennial forb cover was 4% greater after fire. Perennial grass frequency decreased 30% more and perennial forb frequency increased 10% more following burning. Further, increases in evenness after fire resulted in a 225% increase in species diversity. Grazing also resulted in a decrease in perennial grass cover while frequency decreased 22% more in grazed than ungrazed plots. Only frequency and not cover of perennial forbs and annual grasses increased more following grazing. Presence of P. glandulosa had no differential effect on responses of non-shrub species. Fires were conducted during near drought conditions while grazing occurred during years of precipitation equivalent to the long-term average. Precipitation immediately following fire may be critical for recovery of B. eriopoda -dominated desert grasslands; relationships between fire and post-fire precipitation patterns require future investigation.  相似文献   

太平洋中部微生物与多金属结核的生成关系   总被引：13，自引：3，他引：13  

阎葆瑞  张胜 《地质学报》1992,66(2):122-134

作者采用洋底水-岩-微生物相互作用系统的观点首次对太平洋中部洋底多金属结核开展了微生物成矿作用的研究。通过洋底各介质中微生物活动与多金属结核生成机制、成矿物质转化的微生物作用及化学作用对比模拟实验研究、观察和测定系统中成矿物质浓度及环境参数的变化,揭示了成矿组分由微生物活动引起的反应速度和演变方向;从微生物地球化学作用的观点,论证了多金属结核微生物成矿机制和成矿模式;提出了多金属结核微生物成矿阶段和成矿理论。  相似文献