Daily availability of nutrients and metals in a eutrophic meso-tidal coastal lagoon (Óbidos lagoon, Portugal)     

Patrícia Pereira  Hilda de Pablo  Carlos Vale 《Marine pollution bulletin》2010,60(10):1868-1872

This baseline reports daily variations of physico-chemical parameters, nutrients and metals in water of two sites [eutrophic conditions (BB) versus reference (LL)] in Óbidos coastal lagoon (Portugal). Dissolved oxygen in BB varied between 40% saturation levels (night) and 190% (daylight). , and ratios to Al of Mn, Fe and Pb in suspended particulate matter increased during the period of lower oxygenation, indicating exportation of nutrients and metals from the sediment to water at night. At LL, O₂ values oscillated always around 100%. and Mn/Al ratio at LL were always lower than at BB and no increases were found during the night. The input of and Mn provided from the sediment at BB during the night could surpass the contribution of freshwater discharges. PCA confirmed the separation of most samples from BB and LL. These results pointed to the importance of assessing chemical conditions over day-night cycles.  相似文献   

Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia     

Sylvain Ouillon  Pascal Douillet  Renaud Fichez  Jean-Yves Panch 《Comptes Rendus Geoscience》2005,337(16):231

The variability in salinity and temperature in the southwest lagoon of New Caledonia (2100 km²) under non-storm conditions is analysed using a 4-year dataset (1997–2001). Seasonal and interannual variations in salinity are amplified nearshore. Temperature is larger in bays than in the open lagoon during summer, the reverse is true in winter. El Niño Southern Oscillation (ENSO) related nearshore temperature variations parallel those at regional scale, but with seasonal variations amplified. Haline stratification, if any, is enhanced in coastal areas. To cite this article: S. Ouillon et al., C. R. Geoscience 337 (2005).  相似文献   

Geochemical evaluation of the Lagos lagoon sediments     

Akinade S. Olatunji Akinlolu F. Abimbola 《中国地球化学学报》2006,25(B08):246-246

Lagos lagoon is underlain by the Tertiary to recent coastal plain sands of the Dahomey Basin and receives a huge volume of sediments from surface runoffs, canals, rivers and other drainage networks. The dumping of domestic and industrial wastes into these drainage channels open up the possibility of deleterious materials, which carry with them toxic metallic ions, being discharged as wastes into the channels, these eventually find their ways into the lagoon. Sediments being sinks for metals, the identification and quantitative evaluation of metallic ions in the Lagos lagoon sediments is desirable. This study aimed at ascertaining the concentrations of these metallic ions in the sediments. One hundred samples of sediment were systematically obtained along the banks, drainage channels （waste discharge points）, shelves and the center of the lagoon. These samples were dried, disaggregated and sieved for grain size （granulometric） analysis to evaluate the transport and depositional mechanism; X-ray diffraction and heavy mineral separation were used to determine the mineralogy. The 〈75 μm sieved portions of the samples were digested using aqua regia at 96℃ for two hours. The resulting clear solutions were analyzed for major oxides and trace metals using the Inductively Coupled Plasma-Optical Emission Spectrometry （ICP-OES）. X-ray diffraction analysis revealed quartz as the preponderant mineral. The geochemical result revealed that SiO2 ranges from 78.57%-98.88%; TiO2, 0.01%-0.32%; A1203, 0.15%-6.32%; Fe2O3, 0.44%-11.62%; K2O, 0.10%-9.60%; CaO, 0.04%-5.50%; MgO, 0.04%-0.98% and P2O5, 0.01%-0.30%, The major oxide compositions indicate the dominance of sand particles over clay in the sediments.  相似文献   

Beach face and berm morphodynamics fronting a coastal lagoon     

Felicia M. Weir  Michael G. Hughes  Tom E. Baldock 《Geomorphology》2006,82(3-4):331-346

This study documents two different modes of berm development: (1) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode 1 sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth.  相似文献   

The sedimentary and geochemical record of Neogene-Quaternary water bodies in the Dead Sea Basin - inferences for the regional paleoclimatic history     

Mordechai Stein 《Journal of Paleolimnology》2001,26(3):271-282

Several waterbodies occupied the tectonic depressions along the Dead Sea transform during the NeogeneQuaternary. The earliest of these water bodies was the marine Sedom lagoon, which produced the SedomDead Sea brine. After the disconnection of the Sedom lagoon from the open sea several lakes were developed in the Dead Sea basinJordan Valley. Lake Amora (Samra) that existed from early to late Pleistocene, Lake Lisan (~ 70–15 kyr B.P.), and the Holocene Dead Sea. The lacustrine water bodies in the Dead Sea basin behave as amplifier lakes whose size and depth reflect the changing climatic conditions in the region. Lake level and limnological conditions of Lake Amora are not yet known, nevertheless, the lake probably extended over a large part of the Dead Sea basin-Jordan Valley. Lake Lisan level changed between ~ 330 and ~ 150 meters below sea level (m b.s.l.). Its maximum elevation was reached at ~ 27–23 kyr B.P. during marine isotope stage 2. Its minimum elevation was reached at ~ 47–43 kyr during marine isotope stage 3. Lake Lisan began to recede at ~ 17–15 kyr B.P. and at 12–11 kyr B.P. the postLisan water body declined to its minimum level. During most of the Holocene the lake (paleoDead Sea) stabilized at ~ 400 m b.s.l.The limnological evolution of water bodies in the Dead Sea basin reflects the climatic conditions in the region during the late Pleistocene, which fluctuated between wetter and drier periods. During Lisan time these fluctuations appear to be modulated by the cold and warm cycles, respectively in the northern Hemisphere. This relation is less obvious in the postLisan water body, where the strongest lake drop appears to occur during the Younger Dryas cold event.  相似文献   

海陆过渡相页岩气层系沉积研究进展与页岩气新发现   总被引：2，自引：2，他引：0  

董大忠  邱振  张磊夫  李树新  张琴  李星涛  张素荣  刘翰林  王玉满 《沉积学报》2021,39(1):29-45

四川盆地海相页岩气成功规模效益开发,使我国页岩气跨入了高速发展的快车道,确立了页岩气在我国能源安全保障中的重要战略地位。我国海陆过渡相页岩气资源丰富,有望成为我国页岩气增储上产的现实领域。目前海陆过渡相页岩气勘探开发和地质评价还处在初期阶段,海陆过渡相富有机质页岩发育特征与分布、沉积模式、有机质富集机理等非常规油气沉积学相关研究有待深入。通过系统厘定海陆过渡相相关概念与特征,明确了国内外典型海陆过渡相页岩气层系;系统总结海陆过渡相页岩沉积研究现状与新进展,揭示了海陆过渡相中富有机质页岩有利发育环境、主要沉积模式和页岩气储层基本特征。系统梳理鄂尔多斯、四川、渤海湾等盆地海陆过渡相页岩气勘探开发新发现,指出了我国海陆过渡相页岩气具有良好勘探开发前景。海陆过渡相页岩层系常伴有煤层,可进行页岩气、煤层气等联合开采,实现“体积开发”,以期有效推动我国天然气产业高质量大发展。  相似文献   

Facies and depositional settings of the Middle Eocene-Oligocene carbonates in Kutch     

Santanu Banerjee  Sonal Khanolkar  Pratul Kumar Saraswati 《Geodinamica Acta》2018,30(1):119-136

Middle Eocene Fulra Limestone and Oligocene Maniyara Fort Formation represent platform carbonate deposits of Kutch at the north-western margin of India. These carbonates contain larger benthic foraminifera, including Alveolina, Assilina, Discocyclina, Lepidocyclina, Miogypsina, Nummulites and Spiroclypeus. This study presents paleodepositional and paleobathymetric interpretations for both formations using benthic foraminifera in combination with lithological association, sedimentary structures and early diagenetic features. The six carbonate facies comprising the Fulra Limestone indicate a depositional spectrum ranging from bar-lagoon to mid-ramp depositional conditions. It records several shallowing upward cycles, leading to emergence and formation of paleokarst. The four carbonate facies of the Maniyara Fort Formation represents deposition within the inner ramp setting in bar-lagoon and patch-reef environment, while intervening fine siliciclastics correspond to episodes of relative sea level fall. Nummulitic accumulations form low-relief bars within the fair weather wave base in both the formations. The depositional setting of the Paleogene carbonate in Kutch broadly resembles Eocene platformal deposits in the circum-Tethys belt.  相似文献   

海南新村港潟湖表层沉积物粒度特征及其沉积环境   总被引：5，自引：2，他引：3  

杨阳  高抒  周亮  王韫玮  李高聪  汪亚平  贾培宏 《海洋学报》2016,38(1):94-105

对2013年8月在海南新村港潟湖采集的表层沉积物样品进行粒度分析,揭示了该区表层沉积物的粒度特征和沉积物类型,结合高空间分辨率的水动力和水深数据,采用系统聚类和主成分相结合的方法划分现代沉积环境。结果表明,研究区表层沉积物主要有4种类型,以粉砂和粉砂质砂为主,分别分布在潟湖中部和近岸浅水区域。沉积物平均粒径变化较大(0~8.0 Ф),均值为4.6 Ф,沉积物随水深增大而逐渐变细;沉积物粒度组分以砂(平均含量43%)和粉砂(平均含量为52%)为主,黏土含量较少,平均含量为5%。聚类结果表明,平均粒径可分为两组:第一组平均粒径均大于5.5 Ф,均值为6.8 Ф;而第二组平均粒径均小于3.5 Ф,均值为2.2 Ф。此外,平均粒径与分选、偏态和峰态系数之间呈现出两种不同的相关关系。研究区大潮和小潮期间的均方根流速(RMSV)均值是7.5和6.9 cm/s,标准偏差分别是15.3和14.9 cm/s。当RMSV大于4 cm/s,RMSV与极细砂(63~125 μm)含量呈明显的正相关关系,这表明RMSV决定了潟湖沉积物中极细砂含量。聚类和主成分分析结果表明,平均粒径、峰态和分选系数是对沉积环境最为敏感的粒度参数组合,同时结合高空间分辨率的水动力和水深数据,将研究区沉积环境划分为3类。这样划分充分考虑了水动力、物源、地形及其相互作用,更能有效地揭示沉积环境的差异,尤其体现了适宜的粒度参数组合和高空间分辨率的水动力数据在沉积环境划分中的重要性。  相似文献   

海岸潟湖遥感信息提取与精度验证方法          下载免费PDF全文

孙伟富  张杰  马毅  夏东兴 《应用海洋学学报》2016,35(3):426-432

潟湖是水陆交接的地貌体,结合遥感手段实现水陆的准确、快速分割对于潟湖岸线长度和面积信息提取具有重要意义.以山东半岛的海岸潟湖为研究对象,利用7景2010年左右覆盖研究区域的Landsat TM图像,在图像几何校正和信息增强的基础上,采用敏感波段组合的阈值分割方法,通过对比归一化植被指数(NDVI)、归一化水体指数(NDWI)和改进的归一化差异水体指数(MNDWI)方法处理潟湖边界信息的敏感性,确定了基于NDWI的潟湖水陆分割方法,并通过栅矢转换完成了潟湖边界范围的自动提取,为了避免由于栅格精度限制而导致的边界信息提取结果不圆滑,采用样条函数法的插补算法进行平滑处理.同时,为了验证潟湖信息自动提取的精度,提出了一种基于相同地理位置的斑块精度验证方法,利用人工目视解译的结果,从潟湖的形状、岸线长度和面积3个角度评价自动提取的结果,该方法可验证潟湖边界自动提取结果与真实潟湖边界的形状相似度,并对相似度较好的潟湖信息提取结果进行精度分析.  相似文献