Sesquiterpenoids in sediments of a hypersaline lagoon: A possible algal origin     

V. O. Elias  A. M. A. De Barros  A. B. de Barros  B. R. T. Simoneit  J. N. Cardoso 《Organic Geochemistry》1997,26(11-12)

Core samples were collected in Lagoa Vermelha, a hypersaline lagoon located about 100 km east of Rio de Janeiro (Brazil). The sediment composition is predominantly carbonate in amounts up to 93%. Analysis of δ¹³C of the total organic matter in the sediments showed that marine organic matter predominates throughout the core (δ¹³C ranges from −15.84 to −22.64‰ vs. PDB). Organic carbon contents (TOC) ranged from 0.81 to 13.28%. A series of cadinane-type sesquiterpenoids can be recognized in the gas chromatography-mass spectrometry data. Essentially the same components are present in all the samples, with variations only in their relative abundances. The most abundant compounds are α- and β-cubebene, α- and β-cedrene, cadinenes (different isomers), α-curcumene and calamenene, with minor amounts of calarene, humulene, calacorene and cadalene. Since this lagoon is surrounded by dunes with only minor vegetation typical of this environment (grasses, small non-resinous shrubs and no forest) with no potential source for sesquiterpenoids, a terrestrial origin for these compounds is excluded and an algal origin is more consistent with the locale and the recognition of sesquiterpenoids (including cadinol) in microbial mats from the lagoon. Only the natural product precursor sesquiterpenoids are present in the microbial mats with no detectable diagenetic derivatives (e.g. calamenene and cadalene). This indicates that the compounds in the mats are from recent input and those found in the sediments are most likely derived from former algal biomass in this lagoon, a fact confirmed by the recognition of a series of diagenetic aromatic components in the sediments. Surface sediments contain n-alkanes with no even-to-odd predominance indicating that microbial activity is higher in shallower sediments. Moreover, mass fragmentograms (m/z 191) of biomarkers revealed the presence of 17α(H),21β(H)-hopanes, the mature isomers, together with their ββ precursors and low amounts of the intermediates with the βα configuration (moretanes). This indicates a contribution of mature organic matter to these immature sediments.  相似文献   

Preliminary paleolimnological study of rocha lagoon, SE Uruguay     

Felipe García-Rodríguez  Laura Del Puerto  Carola Castieira  Hugo Inda  Roberto Bracco  Peter Spechmann  Burkhard Wilhelm Scharf 《Limnologica》2001,31(3)

Physical, chemical and biological data from a sedimentary profile of Rocha lagoon (Uruguay) are presented. Analyses of silica remains showed that opal phytoliths, diatoms, sponge spicules and chrysophyte cysts were the most important contributors to biogenic silica. Organic matter, total nitrogen and total phosphorus were used to infer past trophic development. Physical analysis of sediments allowed us to identify five lithological units related to sea level variation and climatic events.  相似文献   

ROBUST: The ROle of BUffering capacities in STabilising coastal lagoon ecosystems     

Rutger de Wit  Lucas J. Stal  Bente Aa. Lomstein  Rodney A. Herbert  Hans van Gemerden  Pierluigi Viaroli  Victor-Ugo Cecherelli  Francisco Rodríguez-Valera  Marco Bartoli  Gianmarco Giordani  Roberta Azzoni  Bart Schaub  David T. Welsh  Andrew Donnelly  Ana Cifuentes  Josefa Antn  Kai Finster  Lise B. Nielsen  Anne-Grethe Underlien Pedersen  Anne Turi Neubauer  Marina A. Colangelo  Sander K. Heijs 《Continental Shelf Research》2001,21(18-19)

“Buffer capacities” has been defined in ecology as a holistic concept (e.g., Integration of Ecosystem Theories: A Pattern, second ed. Kluwer, Dordrecht, 1997, 388pp), but we show that it can also be worked out in mechanistic studies. Our mechanistic approach highlights that “buffering capacities” can be depleted progressively, and, therefore, we make a distinction between current and potential “buffering capacities”. We have applied this concept to understand the limited “local stability” in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities. We explored the following processes and studied how they confer buffering capacities to the seagrass ecosystem: (i) net autotrophy is persistent in Zostera noltii meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy; (ii) the Z. noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, i.e., it was found that in situ nitrogen fixation always exceeded denitrification; (iii) the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments, (iv) habitat diversification in seagrass meadows provides shelter for meiofauna and hence buffering against adverse conditions, (v) sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading). On the other hand, in the coastal system we studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant–microbe interactions in the seagrass meadows.  相似文献   

Architecture interne d'une vallée incisée sur une côte à forte énergie de houle et de marée (vallée de la Leyre,côte aquitaine,France)     

Hugues Féniès  Gilles Lericolais 《Comptes Rendus Geoscience》2005,337(14):1257-1266

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渤海湾牡蛎礁平原中部兴坨剖面全新世地质环境变迁   总被引：9，自引：8，他引：9  

李建芬　王宏李凤林  张金起张玉发　王云生 《地质通报》2004,23(2):169-176

渤海湾牡蛎礁平原中部兴坨剖面的有孔虫组合划分为5种沉积环境7个带(亚环境)，从下向上依次为晚更新世陆相(Ⅶ带)、早全新世海陆过渡相(Ⅵ带：沿海低地与潮间带)、中晚全新世海相(Ⅴ带：潮下带-浅海，Ⅳ带：低潮线附近)、晚全新世海陆过渡相(Ⅲ带：开放潮间带，Ⅱ带：渴湖)和河流泛滥相(Ⅰ带：古土壤及洪积层)。^14C确定了全新世底泥炭始于9486 cal BP，Ⅳ带始于约4696 cal BP。Ⅱ带所处的渴湖环境，从约4000 cal BP直至隋唐温暖期之前，历时约2700年。隋唐暖期古土壤发育向南东减弱至逐渐消失，说明在比兴坨更靠近渤海湾的地方，潟湖持续的时间更长。广泛存在的潟湖，是牡蛎礁平原晚全新世的重要地貌景观。  相似文献   

渤海湾泥质海岸带近现代地质环境变化研究(Ⅱ):成果与讨论   总被引：15，自引：1，他引：14       下载免费PDF全文

王宏 《第四纪研究》2003,23(4):393-403

渤海湾泥质海岸带国土资源大调查以其特有的方法、手段和要求,获得了一批带有地质调查特点的、关于全新世地层与近现代地质环境变化的阶段性成果,主要包括:1)该地区海岸带全新世地层具有4种沉积类型:(A)远离海岸的传统的"三分"型;(B)海相层与陆(海陆过渡)相层的多次交替;(C)末次冰期后期未接受沉积,全新统半咸水的海陆过渡相直接覆于历时约10～20ka的沉积间断面上,向上,进一步发育为海相层;(D)沿海低洼地区在末次盛冰期后的晚更新世晚期即已进入海侵阶段,晚更新世晚期与全新世早期的海陆过渡相沉积是连续的,向上继续发育海相层.2)从以海水影响为主的开放潮坪(及浅海区)环境转变为(陆源影响逐渐加强的)湖-盐沼环境,是研究区中晚全新世地质环境转变的重要特征,建立了表征这两种不同环境的非正式地层单位("灰色单元"与"黄色单元").3)牡蛎礁与贝壳堤的对比方案,以牡蛎礁对应潮坪的贝类繁盛期,牡蛎礁中的水平再搬运夹层和/或上覆泥质盖层(往往形成"岭地")对应贝壳堤成堤.4)大比例尺区调地质点(浅孔)揭示了中晚全新世(近现代)地质环境变化,编绘出约4500calB.P.以来小于1ka时段的二维、假三维环境系列图.一个实例是Ⅱ贝壳堤向陆侧的洼地甚至早于该堤的形成,推测洼地边缘的NNW向的埋藏线性凸起可能受同一方向的新构造活动控制.5)渤海湾沿海平原线性砂坝(障壁岛)-湖/盐沼成因假说.作为堆积贝壳堤正地形的补偿,堤前因"簸选"贝壳导致的潮坪负地形,同样可发育湖沉积.6)210pb/137Cs测年研究提供了该地区现代沉积速率的初步结果(＜0.1cm/a或＞3cm/a不等),据此将海岸带划分为不同的沉积类型区.  相似文献   

Transport and dispersion of particulate Hg associated with a river plume in coastal Northern Adriatic environments     

Covelli S  Piani R  Acquavita A  Predonzani S  Faganeli J 《Marine pollution bulletin》2007,55(10-12):436-450

The role of suspended particulate matter (SPM) as an important carrier of mercury (Hg) dispersed into the Gulf of Trieste and in the adjacent Grado lagoon (Northern Adriatic Sea) was studied during a high Isonzo River inflow and the resulting river plume formation. Despite the fact that extreme flood events are rare during the year, they account for most of the PHg influx (37-112 ngL(-1)) into the Gulf of Trieste. When the river plume is diverted to the SW under the influence of an E-NE wind, the tidal flux acts as a "transport belt" carrying the PHg, mostly inorganic, into the Grado lagoon. A preliminary estimation indicates that the amount of PHg entrapped in the lagoon basin following a tidal semi-cycle accounts for 1.4 kg/12h, which corresponds to about 49% of the total Hg carried by the tidal flow. These findings should be considered in future remediation strategies in the lagoon environment.  相似文献   

The Mar Menor lagoon (SE Spain): A singular natural ecosystem threatened by human activities     

Conesa HM  Jiménez-Cárceles FJ 《Marine pollution bulletin》2007,54(7):839-849

The Mar Menor lagoon is one of the most important ecological singularities in the Mediterranean area. At the same time, it is an area where many economic and industrial activities meet. The sum of the impacts of mining, agriculture and urban development in the surroundings to the lagoon during the last decades has affected its ecosystem. In this paper, we have reviewed the studies done by researchers over two decades regarding the impacts of human activities in the lagoon, reporting data of contamination levels and the effects generated in the ecosystem of the lagoon. The discharge of enriched nutrient waters seems to be the most important input in the lagoon. Changes to more friendly agricultural techniques in the surrounding areas are therefore necessary. After our review, we can conclude that it is necessary to have higher efforts from the public administrations and stricter environmental regulations in order to preserve, on one hand, the important ecological values of the lagoon, and on other hand, public health.  相似文献   

Palynology of Lagoa dos Patos sediments,Rio Grande do Sul,Brazil     

Suzane Hilgert Cordeiro  Maria Luisa Lorscheitter 《Journal of Paleolimnology》1994,10(1):35-42

With the purpose of studying the vegetation and climatic changes in the last millenia of the Coastal Plain of Rio Grande do Sul, Brazil, a palynological study was made of the sediments of the northern part of Lagoa dos Patos lagoon. Twenty-four samples from a 2.26 m core taken at a depth of 7.70 m (30° 50 50 S and 50° 59 05 W) were collected.The analyses revealed marine transgression at 5170±120 years B.P., giving rise to local vegetation consisting chiefly of xerophytes and halophytes. Vegetation characteristic of a humid environment was present along adjacent portions of the Coastal Plain at this time. Transgression increased at about 4080±110 years B.P., when the greatest level of tidewater was reached. This coincided with the beginning of forest vegetation development along the inner portions of the Coastal Plain. These data suggest that marine transgression may have been a consequence of higher temperatures and more humidity. After 4000 years B.P., regression occurred, resulting in fresh waters characteristics in the northern portion of the lagoon. The development of forest vegetation began at this time.This is the fourth in a series of papers published in this issue on Paleolimnology in Southern South America. Dr. C. A. Fernández served as guest editor for these papers.  相似文献   

Diatom paleoecology of the Mar Chiquita lagoon delta,Argentina   总被引：1，自引：0，他引：1  

Marcela A. Espinosa 《Journal of Paleolimnology》1994,10(1):17-23

A 68 cm thick outcrop of diatomaceous sediments at the head of Mar Chiquita Lagoon on the Argentine coast near Buenos Aires provides evidence of Holocene paleoenvironmental changes related to sea level changes and freshwater input to the lagoon system. Salinity tolerances of extant diatom taxa were used for the reconstruction and multivariate analytical techniques were applied to reduce subjective interpretations of the diatom percentage data.The basal half of the record was deposited before 3000 years ago and fossil diatoms indicate generally freshwater conditions with one fluctuation in mesohalobous diatoms suggesting brackish water conditions at a depth of about 60 cm. Polyhalobous (marine) diatoms characterize the record after 3000 years ago and large numbers of epiphytic diatoms indicate salt marsh environments with episodic seawater fluctuations to supratidal levels. Freshwater diatoms returned at the top of the outcrop, presumably as a result of the restriction of the historic marine inlet to the lagoon and the effects of freshwater inflow to the basin.This is the second in a series of papers published in this issue on Paleolimnology in Southern South America. Dr. C. A. Fernández served as guest editor for these papers.  相似文献