Tidal currents and wind waves controlling sediment distribution in a subtidal point bar of the Venice Lagoon (Italy)     

Massimiliano Ghinassi  Andrea D'Alpaos  Laura Tommasini  Lara Brivio  Alvise Finotello  Cristina Stefani 《Sedimentology》2019,66(7):2926-2949

The present study aims to improve current understanding of the sedimentation of subtidal point bars, analyzing interaction between tidal currents and waves in shaping a submerged meander bend of the microtidal Venice Lagoon (Italy), and it is based on coupling of sedimentological studies, geophysical analyses and numerical modelling. The Venice Lagoon is characterized by an average depth of about 1·5 m over subtidal platforms and a mean tidal range of about 1·0 m. The morphodynamic evolution of the lagoon is strongly affected by intense seasonal windstorms, which promote the formation of wind waves triggering sediment resuspension and bottom erosion. The study channel is 70 to 100 m wide, it has a radius of curvature of about 260 m and cuts through a permanently submerged subtidal platform. Water depth ranges from 1·0 to 5·0 m below mean sea level on the subtidal platform and channel thalweg, respectively. Different from classical architectural models, the study point‐bar beds do not show sigmoidal geometries, but consist of horizontally‐bedded deposits abruptly overlying clinostratified beds. Sedimentation in the study bar is hypothesized to stem from the interaction between the in‐channel secondary helical flow, as for most meander bends, and wave winnowing of the subaqueous overbank areas. Laterally accreting point‐bar deposits point out that the curvature‐induced helical flow redistributed sediment from the channel thalweg to the bar top and contributed to the development of the ‘classical’ fining‐upward grain size trend. The marked truncation surface, separating clinostratified bar deposits from overlying horizontally‐bedded platform sediments is interpreted here as due to bar top wave‐winnowing, which also possibly promoted bank collapses. In the proposed model, sediments remobilized from bar top and subaqueous overbank areas were transported into the channel, forming peculiar ‘apron‐like’ accumulations, where sand accumulated through avalanching processes and mud settled down from suspension.  相似文献   

山东荣成湾月湖地区的潟湖-潮汐汊道体系   总被引：3，自引：0，他引：3  

魏合龙  庄振业 《湖泊科学》1997,(2)

潟湖－潮汐汊道体系为一复杂的反馈体系，其中任一参数的改变即可导致整个体系的复杂反映．以月湖为例探讨了潟湖地貌演化的过程中，及人工作用潟湖各主要参数的变化规律；提出了月湖目前由于人工围堵特别是残余坝基对潮流的限制作用，致使P／A值较高而饱满系数K值偏低，潟湖－潮汐汊道体系稳定性较差的问题．  相似文献   

Metal pollution loading,Manzalah lagoon,Nile delta,Egypt: Implications for aquaculture   总被引：1，自引：0，他引：1  

F. R. Siegel  M. L. Slaboda  D. J. Stanley 《Environmental Geology》1994,23(2):89-98

High cultural enrichment factors are found for Hg (13×), Pb (22.1×), and other potentially toxic metals (e.g., Sn, Zn, Cu, Ag) in the upper 20 cm of sediment cores from the southeastern Ginka subbasin of Manzalah lagoon, Nile delta, Egypt. Cores from other areas of the lagoon show little metal loading. Metal loading followed the closure of the Aswan High Dam, the availability of abundant cheap electricity, and the development of major power-based industries. Industrial wastes containing potentially toxic metals are dumped into the Nile delta drain system. The load carried by Bahr El-Baqar drain discharges into the Ginka subbasin, which acts as a sink and results in metal loading of the sediment deposited there. Further development of aquaculture in this subbasin, of food-stuff agriculture on recently reclaimed lagoon bottom, or where irrigation waters come from Bahr El-Baqar drain or its discharge should be halted or strictly limited until potentially toxic metals in the drain waters and sediment are removed and polluted input drastically reduced. This environmental assessment of heavy metals in aquaculture or agriculture development should extend to other waterbodies in the northern Nile delta, particularly Idku lagoon and lake Mariut, where industrial metal-bearing wastes discharge into the waterbodies.  相似文献   

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   

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   

利用插值试验分析采样网格对粒度趋势分析的影响   总被引：10，自引：0，他引：10  

贾建军  程鹏  高抒 《海洋地质与第四纪地质》2004,24(3):135-141

利用地理信息系统软件ArcView3．2的空间分析功能,采用三次样条插值方法,对采自山东半岛月湖的表层沉积物的粒度参数进行插值。应用“粒度趋势分析”方法,选取一系列的特征距离值进行试验,从原始数据和插值后数据中提取净输运方向的信息。结果显示,原始的不规则采样点所得粒度趋势对于特征距离的选择很敏感,而插值后的规则格网在不同的特征距离下均表现出比较统一的粒度趋势信息。研究表明,规则格网较不规则格网采样点有许多优势,应用插值方法可有效地提高原始数据的信息含量及其质量。  相似文献   

篑筜湖大型海藻群落的几种钩虾亚目端足类的种群产量研究   总被引：1，自引：0，他引：1  

郑新庆  黄凌风  贾晓燕  傅迅毅  徐向伟  黄邦钦 《海洋学报》2011,33(6):134-141

于2007年12月到2008年5月在厦门筼筜湖采集端足类样品,分析了筼筜湖大型海藻群落中端足类的种群结构并估算其种群产量.结果显示,生活在筼筜湖大型海藻群落的端足类生活史短暂,上野蜾赢蜚(Corophium uenoi)、日本大螯蜚(Grandidierella japonica)和强壮藻钩虾(Ampithoe val...  相似文献   

Seabed sediments and foraminifera over the Lido Inlet: Comparison between 1983 and 2006 distribution patterns     

Alberto D. Albani  Sandra Donnici  Rossana Serandrei-Barbero  Peter C. Rickwood 《Continental Shelf Research》2010

Extensive sampling in the Lagoon and Gulf of Venice during the 1980s provided material to establish ‘base’ conditions for subsequent studies of distributions of benthic foraminiferal biotopes and sediments.  相似文献