Carbon isotope composition of long chain leaf wax n-alkanes in lake sediments: A dual indicator of paleoenvironment in the Qinghai-Tibet Plateau     

《Organic Geochemistry》2015

The carbon isotope composition (δ¹³C values) of long chain n-alkanes in lake sediments has been considered a reliable means of tracking changes in the terrigenous contribution of plants with C₃ and C₄ photosynthetic pathways. A key premise is that long chain leaf wax components used for isotope analysis are derived primarily from terrigenous higher plants. The role of aquatic plants in affecting δ¹³C values of long chain n-alkanes in lacustrine sediments may, however, have long been underestimated. In this study, we found that a large portion of long chain n-alkanes (C₂₇ and C₂₉) in nearshore sediments of the Lake Qinghai catchment was contributed by submerged aquatic plants, which displayed a relatively positive carbon isotope composition (e.g. −26.7‰ to −15.7‰ for C₂₉) similar to that of terrestrial C₄ plants. Thus, the use of δ¹³C values of sedimentary C₂₇ and C₂₉ n-alkanes for tracing terrigenous vegetation composition may create a bias toward significant overestimation/underestimation of the proportion of terrestrial C₄ plants. For sedimentary C₃₁, however, the contribution from submerged plants was minor, so that the δ¹³C values for C₃₁ n-alkane in surface sediments were in accord with those of the modern terrestrial vegetation in the Lake Qinghai region. Moreover, we found that changes in the δ¹³C values of sedimentary C₂₇ and C₂₉ n-alkanes were closely related to water depth variation. Downcore analysis further demonstrated the significant influence of endogenous lipids in lake sediments for the interpretation of terrestrial C₄ vegetation and associated environment/climate reconstruction. In conclusion, our results suggest that the δ¹³C values of sedimentary long chain n-alkanes (C₂₇, C₂₉ and C₃₁) may carry different environmental signals. While the δ¹³C values of C₃₁ were a reliable proxy for C₄/C₃ terrestrial vegetation composition, the δ¹³C values of C₂₇ and C₂₉ n-alkanes may have recorded lake ecological conditions and sources of organic carbon, which might be affected by lake water depth.  相似文献   

云南罗平大凹子与上石坎剖面牙形类动物群研究进展   总被引：1，自引：0，他引：1  

黄金元  张克信  张启跃  吕涛  周长勇  胡世学 《地质科技情报》2011,30(3):1-17

从大凹子剖面118件样品和上石坎剖面78件样品的系统研究中获得了丰富的牙形石标本,特征分子为Nicoraella kockeli Ni.germanicus,同时还获得了众多未能鉴定到种的片形分子Nicoraella sp.,Neospathodus sp.,以及大量的枝形分子,Cornudina? latidentata,Cornudina tortilis,Xaniognathus sp.,Hibbardellasp.,Cypridodella of.delicatula,Cypridodella cf.conflexa,Enantiognathus ziegler,Enantiognathus incurvus,Enantiognathus latus,Neohindeodella triassica,Hindeodella bogschi.对这些可识别到种级别的分子进行了鉴定描述,大凹子与上石坎剖面中获得的牙形石分子Nicoraella kockeli指示出罗平生物群的时代为Anisian期的Pelsonian亚期.  相似文献   

Evolution of the Ediacaran Doushantuoian Meta-Paleo-Community in Northeast Guizhou, South China     

WANG Yue  CHEN Hongde  WANG Xunlian  HUANG Yuming 《《地质学报》英文版》2011,85(3):533-543

Macroscopic organisms lived in the Yangtze Sea of South China during the Late Doushantuo period of the Ediacaran. The results of the specimen collections and statistics within each meter show that the macroscopic biota from the Ediacaran Doushantuo Formation in northeast Guizhou, South China, can be subdivided into Globusphyton, Cucullus, Sectoralga–Longifuniculum, Beltanelliformis, and Baculiphyca–Gesinella paleo-communities. The paleo-community evolution indicates the relationship not only between biota and environment, but also between metaphytes and metazoans. From the Globusphyton paleo-community, through to the Sectoralga–Longifuniculum paleo-community, to the Cucullus paleo-community, the increase in the abundance and diversity of metaphytes (especially the branching macroalgae) and metazoans implies that the oxygen content in the seawater increased gradually. Both the Beltanelliformis and Baculiphyca–Gesinella paleo-communities could be related to a deteriorated environment and fragile ecosystem. The emergence, abundance, and diversity of macroscopic metaphytes, which were closely connected with the environmental microchanges, accelerated the process, improving the environment and increasing oxygen, and established an important platform for the development of macroscopic metazoans.  相似文献   

八臂仙母虫(Eoandromeda octobrachiata)新材料及其意义     

唐烽  Stefan Bengtson  尹崇玉  高林志 《地球学报》2011,32(6):641-651

在中国贵州江口地区陡山沱组新发现的化石材料表明,伊迪卡拉/震旦纪(Ediacaran/Sinian)的宏体化石——八臂仙母虫Eoandromeda octobrachiata的原始生活状态可能为一个较高的圆锥形生命体,具有沿着侧面锥状螺旋排列的八条旋臂.旋臂表面保存有与栉水母动物的栉板可能同源的横向有机质条带,规则排列...  相似文献   

山东省海洋水产原、良种产业的发展和对策          下载免费PDF全文

田敬云  张守都  姜勇  赵喜喜  郑冰  刘学庆  胡建廷 《海洋开发与管理》2018,35(12):42-46

为进一步提高山东省海洋水产种业的发展水平，促进海水养殖业和渔业经济的可持续发展，文章总结山东省海洋水产原、良种产业的发展特点，分析存在的问题，并提出对策建议。研究结果表明：山东省海洋水产原、良种产业具有起步较晚但发展速度较快，品种多、覆盖面广，代际连续性较强以及原、良种场建设全国领先的特点；目前仍然存在海洋水产良种的市场化程度较低、水产企业良种研发能力较弱以及国家级原、良种场的作用未有效发挥的问题；今后应重点推动育种技术进步，推进育、繁、推一体化发展模式，树立品牌意识，建立良种独立技术体系，加大对水产企业的支持力度，加强种质资源保护以及建立市场准入制度。  相似文献   

Forest-steppe oxbows in limnophase — Abiotic features and biodiversity     

《Limnologica》2019

The aim of our study was to identify the main abiotic factors that influence the biodiversity of forest-steppe oxbows in limnophase. Experiments were performed in 2016–2017 in Penza oblast, Central Russia. In addition to disturbed water exchange, isolated oxbows experienced such human influence as logging and plowing on watersides, and the construction of roads and mounds. Under those conditions, some water bodies became unstable and temporal, while others remained stable and were relatively unaffected. Higher light intensity in unstable oxbows led to higher plant diversity because of the mass occurrence of helophytes. However, the diversity of hydrophytes in stable oxbows remained higher, which contributed to higher vegetation coverage. This resulted in increased zooplankton diversity, which was also influenced by lower fluctuations in water level and oxygen level. Disturbed water regimes impacted organisms with a full aquatic life cycle (phyto- and zooplankton, fish). The diversity of unstable oxbows decreased due to their isolation from the river and from drying. The absence of fish may positively affect the abundance and biomass of benthos; however, we found no influence on zooplankton. Instability and high fluctuations in water level may lead to the high diversity of organisms that spawn in water. The higher diversity of benthos may also be influenced by the abundance of amphibian larvae which are a necessary food resource. In addition to predation, amphibians are at risk of mass larval mortality because of drying. Although the degradation of oxbows in limnophase is an undesirable consequence of anthropogenic impact, the coexistence of all types of oxbows is necessary to conserve the freshwater biodiversity of forest-steppes.  相似文献   

Establishing habitat-specific indicator species in Tierra del Fuego with freshwater macroinvertebrates     

Christopher B. Anderson  Montana Johnson  María Eugenia Lopez 《新西兰海洋与淡水研究杂志》2018,52(1):145-154

As a tool to understand Tierra del Fuego’s basic ecology and detect changes due to human pressures, this study develops habitat bioindicators. We compared the freshwater benthic macroinvertebrates at 61 study sites in six habitat types: grassland streams, urbanised streams, forested streams, beaver ponds, lakes and peat bog ponds. Forty-nine taxa were identified; insects were the most diverse group. Beaver pond, lake and grassland stream assemblages were similar, as were those from lakes, grassland streams and peat bog ponds. Fourteen taxa were habitat-specific. In forests, these included mayfly scrapers (Andesiops, Meridialaris) and blackfly filterers (Gigantodax). In lakes, two copepod filterers were indicators, and in urban streams, one shredder (Aphroteniella) and three collector-gatherers (springtail, earthworm, aquatic worm). Predators (Corixa, Aeshna) were characteristic of peat bog ponds. Beaver ponds had no indicator species. Establishing links between species and ecosystems constitutes the beginning of a broader effort to understand anthropogenic impacts to Fuegian watersheds.  相似文献   

老碳对水生态系统食物网的贡献     

胡恩  张振文  王文科  孙长顺  苏雅玲  刘正文 《湖泊科学》2018,30(5):1187-1195

传统理论认为,支撑水生态系统食物网的碳主要来自于系统内部的初级生产者,如藻类、大型水生植物等,或者来自陆源输入的新鲜且容易分解的有机质;而部分生物或非生物生产的有机碳,在冰川、冻土等环境中可停留数百年至数千年(定义为老碳),由于储存环境稳定、物理化学性质顽固,难以参与水生生态系统有机碳循环.近年来这一观念不断被挑战.研究表明老碳能够参与水生态系统食物网碳循环:可以被微生物分解利用;被浮游动物、无脊椎动物直接或者间接摄取、或沿着营养级传递至鱼类、水禽等高级消费者.这意味着除了内部初级生产,老碳是支撑水生态系统重要的碳源.本文概述了当前老碳与水生态系统食物网关系研究最新进展和所取得的研究成果,介绍放射性14C同位素技术在水生态学领域的应用,同时提出研究中存在的问题以及未来研究应关注的方向,以期促进我国水生态系统碳循环研究的进一步发展.  相似文献   

Trophic guilds of EPT (Ephemeroptera,Plecoptera, and Trichoptera) in three basins of the Brazilian Savanna     

《Limnologica》2017

Insects of the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) are prominent among stream biota and are associated with many ecological processes in these environments, meaning that a proper definition of their habits is essential. We studied EPT from three watersheds in Brazil (Paraguai, Paraná, and São Francisco) in order to (i) determine the trophic guilds of EPT genera sampled; (ii) determine whether trophic guilds reflect EPT phylogenetic component (taxonomic distance); (iii) compare trophic guild composition among watersheds; and (iv) verify the effect of environmental components in trophic guild composition. Eight trophic guilds were determined based on gut content analysis: detritivores, fine-detritivores, fine-detritivores/algivores, coarse-detritivores, coarse-detritivore/algivores, periphytivores, carnivores, and omnivores. Caddisflies presented the most variable diet and many genera belonged to different trophic guilds in different basins. Overall trophic guild composition did not reflect the taxonomic distance among taxa and it did not differ among the three basins. Instead, EPT guilds were related to local environmental variables, evidencing that their diet probably varies according to local resource availability, highlighting the importance of empirical assessments of diet for ecological studies.  相似文献   

人类干扰对洪泽湖湿地植被分布格局的影响     

李爱民  高振美  段娟娟 《湿地科学与管理》2014,(3):57-60

洪泽湖具有防洪、调蓄、灌溉、水产、航运、发电等多个功能,人类干扰对洪泽湖湿地植被的影响对湿地管理具有重要意义。分析了人工水位调控、渔业生产及水质恶化等人类干扰对湿地植被分布格局的影响。结果表明:在长期且密集的人类干扰下,洪泽湖水位表现出春低、夏高、秋冬平稳的格局,使得洪泽湖湿地植被表现出明显的年际和年内波动;洪泽湖的水位每年5-6月达全年最低,这使得一些耐涝性较强的湿生植物在挺水植被分布区广泛分布;受渔业生产和水质恶化的影响,洪泽湖湿地植被分布总体呈下降的趋势,随着南水北调东线工程的竣工,还将面临新的挑战。  相似文献