Radiocaesium dispersion and fixation in the lagoon systems of “Ria de Aveiro”, Portugal     

Iuliu Bobos  Fernando Rocha 《Journal of Geochemical Exploration》2006,88(1-3):367

Radiocaesium (¹³⁷Cs) dispersion and Cs⁺ fixation were studied in the sediments collected from the lagoon systems of “Ria de Aveiro”. The Cs⁺ sorption was tested for the fine mica grains and for the < 2 μm clay fractions extracted from silty clays. The Cs⁺ exchange is found strongly onto mica-rich fractions than smectite-rich fractions. The distribution coefficient increases if the silty material is constituted by rich-mica clay fractions or if the non-clay minerals are removed from the silty-clay material. The samples studied behave as multisite ion exchange, where Cs⁺ engages in ion-exchange reactions with hydrated cations on planar sites on expansible layer silicates. Higher concentrations of the ¹³⁷Cs were found associated with mica-rich silty clays. The ¹³⁷Cs ranges from 3.2 to 3.9 Bq kg^− 1 in the < 38 μm fractions and from 2.9 to 3.3 Bq kg^− 1 in the < 64 μm fractions.  相似文献   

南沙群岛永暑礁澙湖沉积的晚全新世风暴事件记录   总被引：1，自引：0，他引：1  

施祺  余克服 《热带地理》2007,27(1):1-5

位于南沙群岛永暑礁西南小澙湖的南永4井岩芯柱中含多层珊瑚枝和珊瑚砾石的堆积,反映了突发性风暴事件造成的珊瑚碎屑快速搬运和堆积。全新世晚期约4 000 aBP以来,澙湖珊瑚砾堆积记录了1 400870BC、660BC390AD、600770AD和940-1992AD 4个主要的风暴事件频发时期,并且风暴的强度呈阶段性增强。风暴事件还表现出千年和百年尺度的周期性波动,具有1 280 a、370 a、210230 a、140150 a和90 a的准周期,与全新世气候环境的周期性变化相对应,很大程度上受太阳活动周期变化的影响。  相似文献   

Comment on the report “Significance of enhanced infiltration due to groundwater extraction on the disappearance of a headwater lagoon system: Toluca Basin, Mexico” by D.L. Rudolph, R. Sultan, J. Garfias, R.G. McLaren. Hydrogeology Journal (2006) 14(1–2):115–130     

Gordon James MacMillan 《Hydrogeology Journal》2007,15(4):823-826

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Long-term macrozoobenthos changes in a shallow boreal lagoon: Comparison of a recent biodiversity inventory with historical data     

Michael L. Zettler  Darius Daunys 《Limnologica》2007,37(2):170-185

The European water framework directive (WFD) aims at achieving good ecological status of water bodies, which implies assessment of their current ecological quality status in respect to defined reference (pristine) conditions. In this paper, two historical biodiversity datasets (from 1920s and 1950s) and results from the recent inventory are used to trace the long-term changes of the macrozoobenthos in the eutrophic boreal lagoon of the Baltic Sea.In comparison of datasets the highest congruence was obtained for molluscs and malacostracan crustaceans, which also had a similar level of taxonomic emphasis between studies. Considering inconsistencies in methodology and taxonomic determination, only few species extinctions in these groups did likely occur during the last 100 years. Two amphipod species (Gammarus pulex and Gammarus lacustris) were not found during the recent survey, whereas five new species of this taxonomic group occurred in the lagoon since 1950s. The causes of these extinctions remain unclear; however displacement by established new amphipods cannot be excluded. Theodoxus fluviatilis was recently recorded in the very restricted area of the lagoon, while in earlier studies the species was mentioned as common and widely distributed in the water body. On the other hand, 10 gastropod species and 9 bivalves were reported for the first time in the lagoon and most likely have been overlooked in earlier surveys. Approximately 10% of the species have their origin outside the Baltic Sea basin and the number of invasions considerably exceeds the number of likely extinctions. Assessment scheme of such changes is unclear following WFD guidelines, therefore elaboration of a framework for evaluation of the alien species diversity in a context of local biodiversity should attain more effort when implementing the WFD.  相似文献   

Morphodynamic evolution and stratal architecture of translating tidal point bars: Inferences from the northern Venice Lagoon (Italy)     

《Sedimentology》2018,65(4):1354-1377

The widespread distribution of tidal creeks and channels that undertake meandering behaviour in modern coasts contrasts with their limited documentation in the fossil record, where point‐bar elements arising from the interaction between a mix of both fluvial and tidal currents are mainly documented. The sedimentary products of tidal channel‐bend evolution are relatively poorly known, and few studies have focused previously on specific facies models for tidal point bars present in modern settings. This study improves understanding of tidal channel meander bends through a multi‐disciplinary approach that combines analyses of historical aerial photographs, measurements of in‐channel flow velocity, high‐resolution facies analyses of sedimentary cores and three‐dimensional architectural modelling. The studied channel bend (12 to 15 m wide and 2 to 3 m deep) drains a salt marsh area located in the north‐eastern sector of the microtidal Venice Lagoon, Italy. Historical photographs show that, during the past 77 years, the bend has translated seaward ca 15 m. Results show that the channel bend formed on a non‐vegetated mud flat that was progressively colonized by vegetation. Seaward translation occurred under aggradational conditions, with an overall migration rate of 0·2 to 0·3 m year⁻¹, and was promoted by the occurrence of cohesive, poorly erodible outer bank deposits. Ebb currents are dominant, and translation of the channel bend promotes erosion and deposition along the landward and seaward side of the bar, respectively. Tidal currents show a clear asymmetry in terms of velocity distribution, and their offset pattern provides a peculiar grain‐size distribution within the bar. During the flood stage, sand sedimentation occurs in the upper part of the bar, where the maximum flow velocity occurs. During the ebb stage, the bar experiences the secondary helical flow that accumulates sand at the toe of the bar. Lateral stacking of flood and ebb deposits has caused the formation of localized coarsening‐upward and fining‐upward sedimentary packages, respectively.  相似文献   

Structuring factors and recent changes in subtidal macrozoobenthic communities of a coastal lagoon, Arcachon Bay (France)     

Hugues Blanchet  Xavier de Montaudouin  Pierre Chardy  Guy Bachelet 《Estuarine, Coastal and Shelf Science》2005,64(4):561-576

Sediment stability in the shallow Venice Lagoon was investigated by means of numerical modelling. Results from a hydrodynamic model allowed for the determination of the wave climate and bottom effective parameters so that simulations with a Lagrangian model for suspended particulate matter could be performed. A spring–neap cycle in summer 1998 was chosen as integration period since data for calibration and verification were collected within the European project F-ECTS between summer 1998 and spring 1999. Deposition on shallow mud flats as well as short term erosion during a strong wind event were reproduced and mass balances for two areas computed. A relation of patterns of SPM in the water and in the sediment was found and can be ascribed to the displacement of material during storm events from shallow areas to the bottom of very small channels. Assuming about 10 to 14 storm events during the year comparable to the Bora event during the integration time, estimates for long-term trends of sediment loss on shallow flats by Day et al. [Day, J.W., Rybczyk, J., Scarton, F., Rismondo, A., Are, D., Cecconi, G., 1999. Soil accretionary dynamics, sea-level rise and the survival of wetlands in Venice Lagoon: a field and modelling approach. Estuarine, Coastal and Shelf Science 49, 607–628] are met by the simulation results. Evidently, long-term sediment evolution of the lagoon is therefore not dominated by the average (residual) processes that occur in the lagoon, but by the few peak events that happen randomly over the year.  相似文献   

Trophic characteristics of the Manila clam (Tapes philippinarum Adams and Reeve)     

Sorokin  Yu. I.; Giovanardi  O. 《ICES Journal of Marine Science》1995,52(5):853-862

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芝罘连岛沙坝北端封闭泻湖成因与发育过程     

张振克 《海洋科学》1996,20(5):59-63

芝罘连岛沙坝北端泻湖是６０００ａ Ｂ．Ｐ．以来海平面变化过程中的产物，其形成受海平面变化，气候变化，海岸古环境与近岸物质迁移的影响，泻湖附近地貌发育经历了水下沙嘴，砾石堤发育，封闭泻湖形成４个阶段。  相似文献   

The Role of a Macroalgal Covering Event on the Microphytobenthos Community in Intertidal Sediment (Marano Lagoon, Northern Adriatic Sea)   总被引：1，自引：0，他引：1  

Elisabetta Sdrigotti  Chiara Welker 《Marine Ecology》2002,23(S1):370-383

Abstract. This study examines the variation in microphytobenthos structure and functioning in an intertidal lagoon during a macroalgal covering event. Multivariate techniques, applied on the recorded data, highlighted a clear seasonal pattern except for the July sample. The sudden macroalgae ( Cladophora sp.) development, which occurred in that month, enabled us to identify the massive covering as a disturbance factor on the benthic ecosystem. This biotic anomaly affected benthic microalgal production and community respiration, shifting the ecosystem from a highly photoautotrophic to an heterotrophic condition as shown by the BTS Index. This trophic index is therefore a useful tool for identifying episodic stress events mainly in intertidal habitats.  相似文献   

On crafting a fisheries co-management arrangement in the estuary of Patos Lagoon (Brazil): opportunities and challenges faced through implementation     

Daniela C. Kalikoski  Theresa Satterfield 《Marine Policy》2004,28(6):742

This paper aims to analyze a fisheries co-management regime in Brazil. The Forum of the Patos Lagoon, a collaborative partnership among communities, governmental and non-governmental organizations, was established to move fisheries management toward a negotiation-style decision processes. We find that while many successes are evident including the delegation of decision power, greater protection of artisanal fisheries, and greater legitimacy assigned the Forum as a decision-making body, several problems remain. These include conflicting institutional arrangements; minimal recognition of local fishers’ interests as concerns rules established; and less than optimal participation of fishers in the Forum. The paper closes with multiple suggestions for improvements of this co-management regime.  相似文献