Changes in Venice Lagoon dynamics due to construction of mobile barriers     

Michol Ghezzo  Stefano Guerzoni  Andrea Cucco  Georg Umgiesser 《Coastal Engineering》2010

The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon's inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios.  相似文献   

Partitioning,bioavailability and origin of heavy metals from the Nador Lagoon sediments (Morocco) as a basis for their management   总被引：2，自引：0，他引：2  

I. González  E. Águila  E. Galán 《Environmental Geology》2007,52(8):1581-1593

Nador Lagoon sediments show low trace element concentrations, and, in relation to the lagoon geochemical baseline, only some anomalies for As, Cd, Cu and Pb in the NW of the lagoon deserve to be outstanding. The distribution of major, minor and trace elements in the lagoon allows a breakdown in four zones. Between “Beni Ensar” and “Atelouane” (zone A), a quite confined zone rich in organic matter and S, the most important trace-element anomalies (As, Cd, Co, Cu, Mn, Pb, Zn) were found, mainly around industry and old mining activities. In the surrounding of the city of Nador (zone B), the anomalies correspond to Mn, Cu and Zn. The coastal barrier and Kebdana channel (zone C) show moderately concentrations of Cd, Cr and Ni at specific sites. The less polluted area is the SE of the lagoon (zone D), with no outstanding anomaly. In lagoon sediments, metal bioavailability is very low. The metal partitioning patterns show that Cu, Pb and Zn present a low availability because they are bounded to the residual, non-mobile phases of the sediments. Only in some sites, the fraction was associated with organic matter, which could be liberated easily. Arsenic is concentrated in both the residual phases and the organic matter, the latter being more available. Cadmium is mainly concentrated in some samples in the interchangeable fraction, which could be considered as a potentially toxic element because it is easily released. Concerning the origin of these trace elements, those found in zone A correspond mostly to a natural source by weathering of mount Gourougou volcanic rocks (As, Co, Cu, Pb and Zn), and to an anthropogenic origin (Cd) owing to the presence of industry and old mines. In zone B, contributions of Cu and Zn enter the lagoon through soil weathering and river-borne, and as anthropogenic pollution from urban wastes. In zone C the most important pollutant is Cd deduced to be of anthropogenic origin from the close industry and intensive agriculture area. In spite of the intense socio-economic activities developed in the Nador Lagoon (agriculture, industry, fishing, tourism) trace element concentrations in the sediments are low and with scarce bioavailability. Only the NW sector is relativity polluted because of geogenic features.  相似文献   

Negotiating changing livelihoods: The sampan dwellers of Tam Giang Lagoon, Vi?t Nam     

Elsa DaCosta 《Geoforum》2007,38(1):190-206

Central Vi?t Nam is one of the most vulnerable areas in the country to natural disasters. In 1985 a major typhoon hit the Tam Giang Lagoon coastal area in the province of Th?a Tiên-Hu?, Central Vi?t Nam, with severe impacts on the sampan dwellers who lived there on boats and fished for their livelihoods. Since then, the government has attempted to resettle them on land in order to decrease their vulnerability to such events. Consequently, this process has changed the livelihood options as well as the social networks of the sampan dwellers. This study of the resettlement village of Th?y ?i?n analyses the social networks and different forms of social capital being utilised by the resettled sampan dwellers as part of their changing livelihoods and questions whether the social capital formed will indeed lead to a long term decrease in vulnerability. It is found that while bonding and linking social capital have been newly formed, the trust required for bridging social capital formation is still missing, and this in turn is hindering the possibilities of sustainable livelihood formation.  相似文献   

An Experimental Test of the Capacity of Food Web Interactions (Fish–Epiphytes–Seagrasses) to Offset the Negative Consequences of Eutrophication on Seagrass Communities     

E. Gacia  M. M. Littler  D. S. Littler   《Estuarine, Coastal and Shelf Science》1999,48(6):757

A mechanism of competition between epiphytes and seagrasses potentially modulated by grazers was studied in a high-nutrient Thalassia testudinum meadow in the Indian River Lagoon (Florida, U.S.A.). The effects of fish grazing on epiphytes, and likely enhancing T. testudinum growth, was tested through an exclusion experiment. Twelve (2×2m) independent experimental plots were selected within a shallow monospecific bed to which three randomized treatments (exclusion fences, open fences and controls) with four replicates each were assigned. The epiphyte load was monitored on T. testudinum leaves inside the plots from January 1995 to March 1996. Treatment effects occurred during a chlorophyte bloom in March 1995, when the epiphyte biomass was significantly higher inside the exclusion cages than in either of the controls. The composition of the epiphytic community in March 1995 was dominated by sheet-like Enteromorpha and filamentous algae such as Cladophora , which are less resistant to herbivory than the coarsely-branched forms of red algae (e.g. Hypnea , Chondria and Acanthophora) that bloomed subsequently. These results suggest that herbivory change seasonally depending on the availability of different prey species to fish-grazers, which preferentially utilize the fleshy green algae typical of bloom conditions over the thicker coarsely-branched red algae. In the nutrient-rich lagoon the role of top-down interactions in enhancing T. testudinum growth is limited to the reduction of shading by green macroalgae.  相似文献   

海南新村潟湖潮汐、潮流特征及其对营养盐的影响          下载免费PDF全文

张奕璞  于硕  黄大吉  周泽斌 《海洋学研究》2022,40(2):69-82

基于海南新村潟湖2020年12月水文和水质多要素实测数据,研究了该海域的潮汐、潮流变化特征,并探讨了潮位变化对潟湖营养盐的影响。结果表明,新村潟湖的潮汐为不规则全日潮,潟湖口门处的潮流为往复流,涨潮历时15 h,落潮历时10 h。大、小潮期间3个观测站点溶解性无机氮(DIN)浓度变化范围为0.91~20.87 μmol/L,磷酸盐(PO3-4)浓度变化范围为0.11~5.92 μmol/L,硅酸盐(SiO2-3)浓度变化范围为2.36~134.75 μmol/L。大、小潮期间,潟湖内3个观测站点DIN、PO3-4、SiO2-3浓度随着涨、落潮过程发生变化。潟湖口门处流速对观测站点潮位变化有着重要的影响,潮通量基本决定了潮位的变化。潟湖口门处和渔排密集区域的营养盐浓度与潮位呈现显著的负相关关系,潮流流速对口门处和渔排密集区域的营养盐变化有着重要影响。该研究结果将为新村潟湖的污染治理及生态修复提供科学依据。  相似文献   

Unraveling rift margin evolution and escarpment development ages along the Dead Sea fault using cosmogenic burial ages     

A. Matmon  D. Fink  M. Davis  S. Niedermann  D. Rood  A. Frumkin 《Quaternary Research》2014

The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by ~ 10 Ma. Sediments of the Sedom Formation, dated here between 5.0 ± 0.5 Ma and 6.2_− 2.1^+ inf Ma, yielded extremely low ¹⁰Be concentrations and ²⁶Al is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.3_− 0.8^+ 0.9 Ma. Burial ages of fluvial sediments within caves (3.4 ± 0.2 Ma and 3.6 ± 0.4 Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian–African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today.  相似文献   

Distribution and partitioning of major and trace elements in pyrite-bearing sediments of a Mediterranean coastal lagoon     

《Chemie der Erde / Geochemistry》2015,75(2):219-236

The formation of iron sulphide minerals exerts significant control on the behaviour of trace elements in sediments. In this study, three short sediment cores, retrieved from the remote Antinioti lagoon (N. Kerkyra Island, NW Greece), are investigated concerning the solid phase composition, distribution, and partitioning of major (Al, Fe) and trace elements (Cd, Cu, Mn, Pb, and Zn). According to ²¹⁰Pb, the sediments sampled correspond to depositions of the last 120 years. The high amounts of organic carbon (4.1–27.5%) result in the formation of Fe sulphides, predominantly pyrite, already at the surface sediment layers. Pyrite morphologies include monocrystals, polyframboids, and complex FeS–FeS₂ aggregates. According to synchrotron-generated micro X-ray fluorescence and X-ray absorption near-edge structure spectra, authigenically formed, Mn-containing, Fe(III) oxyhydroxides (goethite type) co-exist with pyrite in the sediments studied. Microscopic techniques evidence the formation of galena, sphalerite and CuS, whereas sequential extractions show that carbonates are important hosts for Mn, Cd, and Zn. However, significant percentages of non-lattice held elements are bound to Fe/Mn oxyhydroxides that resist reductive dissolution (on average 60% of Pb, 46% of Cd, 43% of Zn and 9% of Cu). The partitioning pattern changes drastically in the deeper part of the core that is influenced by freshwater inputs. In these sediments, the post-depositional pyritization mechanism, illustrated by overgrowths of Fe monosulphides on pre-existing pyrite grains, results in relatively high degree of pyritization that reaches 49% for Cd, 66% for Cu, 32% for Zn and 7% for Pb.  相似文献   

天津七里海古泻湖湿地环境演变研究   总被引：3，自引：0，他引：3  

秦磊 《湿地科学》2012,10(2):181-187

七里海古泻湖湿地位于天津市宁河县西南部,是全新世以来海退过程在天津平原留下的众多古泻湖湿地之一。分析了七里海古泻湖湿地形成、演变的区域地质背景,指出七里海古泻湖至少经历了3次大规模萎缩,其西南部萎缩较快,东北部萎缩相对较慢。利用历史资料研究了近5000a七里海古泻湖湿地的形成、演变过程,并以1950年航空照片和1976年、1981年、1987年、2000年、2005年的MSS、TM和ETM+影像数据为主要数据源,用遥感和地理信息系统技术研究了近百年七里海古泻湖湿地的环境变化。结果表明,距今5000a,七里海地区为海相沉积环境,海岸线穿越宁河的潘庄镇、大海北、小海北一带;距今3800～3000a,海岸线退至造甲城、七里海镇一带;到清朝乾隆年间,七里海湿地逐渐被分割成前海、后海、曲里海3部分,湖底不断淤积,水面不断萎缩,逐渐演变为湖泊、沼泽湿地;1926～2005年间,七里海湿地大致经历了3个变化阶段:1926～1950年为自然变化阶段,七里海湿地的变化主要受自然因素的影响,该阶段七里海湿地仍由前海、后海、曲里海3部分组成;1951～1981年为改造治理阶段,七里海被潮白河拦腰截断,分为东、西七里海,后海被改造为农田;1982～2005年为围垦和水产养殖阶段,东、西七里海的大面积水域以及湿地周围的大片农田都被改建为养殖池,自然湿地在减少,人工湿地在不断增加,导致七里海湿地景观类型日趋单一,生物多样性明显减少。  相似文献   

渤海湾西北岸泻湖自然演变及其人为陆化     

冯金良 《海洋科学进展》1998,(2)

渤海湾西北岸发育有中纬度地区典型的滨外沙坝泻湖及沿岸沙坝泻湖。泻湖不仅是该海岸区域内的一个重要组成部分,同时亦是海岸带自然资源丰富的地带。然而,由于泻湖的自然演变退化,更重要的是人类活动的影响,致使泻湖生境遭到严重破坏,同时也加速了泻湖陆化消亡过程。本文以渤海湾西北岸泻湖为例,讨论了泻湖的自然演变及其人为陆化问题。  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：7，自引：0，他引：7  

魏合龙  庄振业 《湖泊科学》1997,9(2):135-140

泻湖－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。以月湖为例探讨了泻湖地貌演化的过各,及人工作用泻湖各主要参数的变化规律;提出了月湖目前由于人工署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值偏代,泻湖－潮汐汊道体系稳定性较差的问题。  相似文献