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人类活动和自然因素共同但有区别的作用引起了长江口及邻近海域富营养化,造成夏季底层水体低氧现象加剧,成为近海生态健康恶化的重要征兆。本文梳理了国内外学者在该海域低氧研究中获得的重要认识,分析了底层水体溶解氧的潮周期尺度、事件尺度和年际尺度的变化特征,重点从层化与物质输运角度,介绍了长江冲淡水、台湾暖流、海洋锋面、风和潮等过程影响底层水体中氧气消耗或补充的机制,揭示了本海域主要低氧现象分别位于长江口和浙江近海的特征,对比了两处低氧区形成与演变的异同机制。目前,对低氧形成机制的定性认识和多尺度变化特征的了解已经有较好的基础,未来需要从多学科交叉角度加强现场试验和定量研究,掌握低氧的长期演变趋势,研发底层水体低氧的预测预警技术,支撑我国河口近海的生态预警监测工作。 相似文献
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夏季,长江口底层极易发生大面积低氧甚至缺氧.比较2016和2017年夏季长江口缺氧区(DO<2 mg/L)、低氧区(2 mg/L3 mg/L)浮游动物群落(>160μm)特征发现:2016年群落丰度和生物量均表现为缺氧区明显高于低氧区和正常海区;中小型桡足类、胶质浮游动物丰度表现为缺氧区和低氧区均高于正常海区;胶质浮游动物的组成,在低氧程度较严重的2016年夏季,以滤食性的海樽纲和有尾纲为主,在2017年夏季,以肉食性毛颚动物为主. 相似文献
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基于水动力ROMS与BOX耦合模型的长江口及邻近水域水通量及水体交换特性 总被引：1，自引：0，他引：1
本研究将水动力模型ROMS(regional oceanic modeling system,区域海洋模式系统)与箱式(box)模型结合,详细阐述了长江口及邻近水域四个季节的水通量特征及水体交换特性。研究发现:总的水通量整体受季风控制,季风的作用在于使水体在南北方向上交替输送,而台湾暖流对春夏季底层水南向输运具有重要作用;直接进入123.5°E以东外海区域的水通量很小,而是先从南边界流出研究区域,然后通过海洋环流系统进入外海。在强烈季风下,水体更新依赖于季风方向的水平通量,主要是同层水体而不是表底层水体之间的交换。虽然水体更新时间较长的区域与缺氧区基本一致,但本研究认为该区域底层水体缺氧的本质原因是跃层阻隔了表底层水体之间的交换。 相似文献
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提要 本研究成功将水动力模型ROMS(the regional oceanic modeling system model)与箱式模型结合,详细阐述了长江口及邻近水域四个季节的水通量特征及水体交换特性,为其物质通量研究提供准确的水量基础。研究发现,总的水通量整体受季风控制,季风的重要作用在于使得水体在南北方向上交替输送,而台湾暖流对春夏季底层水体南向输运具有重要作用;直接进入123.5°E以东外海区域的水通量很少,而是先从南边界流出研究区域,然后通过海洋环流系统进入外海。长江径流是影响水体更新的重要因素,但在强烈季风下,水体更新主要依赖于季风方向的水平水通量,主要是同层水体而不是表底层水体之间的交换。所以不能简单的以水体更新时间长短作为强烈季风区底层缺氧高发与否的标准。因此,虽然水体更新时间较长的区域与缺氧区基本一致,本研究认为该区域底层水体缺氧的本质原因是跃层阻隔了表底层水体之间的交换。 相似文献
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近50年来长江口及邻近海域溶解氧的时空分布变化 总被引：2，自引：0，他引：2
长江口及邻近海域是我国最重要的河口海岸区域之一。基于多源、长时间序列的溶解氧资料,本文对近50年来长江口及邻近海域溶解氧的时空分布特征进行了研究。结果表明,近50年来,长江口及邻近海域表层溶解氧基本保持稳定,仅冬季呈现出一定的上升趋势。冬、春两季溶解氧浓度范围在7-11 mg/L,夏、秋两季为6-8 mg/L。长江口及邻近海域低氧值首先出现于5月,浙闽沿岸底层海域形成低氧水舌。水舌在夏季不断向北推进,北部断面低氧程度明显高于南部断面。到了秋季,低氧区逐渐消退,至冬季完全消失。在过去的50年中,长江口及邻近海域的低氧现象始于20世纪80年代。2000年起,低氧程度逐渐加深,低氧分布深度逐渐升高。本文基于大量的溶解氧历史数据开展研究,研究结论对于探讨长江口及邻近海域低氧区的发展变化具有非常重要的意义。 相似文献
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1999年和2009年夏季珠江口环境要素的对比与分析 总被引：1，自引：0，他引：1
对1999年和2009年夏季珠江口的温、盐、溶解氧、叶绿素和径流量等数据进行分析。结果表明,由于1999年航次期间珠江较大的径流量,1999年冲淡水的扩展范围要大于2009年。1999年夏季珠江口水体存在较强的盐度层结,而2009年夏季受较小的珠江径流量和热带风暴浪卡的共同作用,水体盐度层结较弱,0—5m层水体垂向混合良好。两年夏季珠江口表层溶解氧(DO)的分布较为相似,而底层溶解氧的分布则有显著差异,主要表现在河口西岸浅滩区和河口口门外。1999年河口西岸浅滩区DO小于3mg.L-1,河口口门外DO在4—5mg.L-1之间,2009年河口西岸浅滩DO大于5mg.L-1,河口口门外DO小于3mg.L-1。1999年夏季伶仃洋海域内较强的盐度层结是其底层出现低氧环境的主要原因,2009年夏季强化的垂向混合使得表底层溶解氧得到了及时交换,阻碍了西岸浅滩区底层低氧环境的出现,而盐度层化和浪卡带来的浮游生物的耗氧作用可能是口门外底层出现低氧环境的原因。 相似文献
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长江口南部赤潮区春季表层沉积物中色素组成、含量与分布状况 总被引：1，自引：0，他引：1
为剖析长江口邻近海域春季硅藻藻华后期藻类沉降与底层水体缺氧现象之间的关系,作者于2011年春季,在长江口南部赤潮区采集了表层沉积物样品,并通过高效液相色谱法(HPLC),对浮游植物色素进行了分析。结果表明,硅藻藻华发生后,表层沉积物中叶绿素a(Chl a)、岩藻黄素(Fuco)和19’-丁酰氧基岩藻黄素(But-Fuco)含量有显著增加,高值区主要分布在调查海域东南侧50 m等深线外侧,与底层低氧水体分布区基本吻合。因此,硅藻藻华后沉降的藻类对于该海域夏季缺氧区的形成应具有一定作用,其具体过程和机制仍有待于研究。 相似文献
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长江口外缺氧区柱样沉积物元素的分布及其百年沉积环境效应 总被引：3，自引：0，他引：3
在210Pb定年的基础上,对取自长江口外缺氧区内外的柱样沉积物开展了10种常量元素、13种微量元素和粒度的测定分析,研究了其物源及分布特征。结果表明,缺氧区外柱样沉积物主要来源于老黄河口海岸泥沙,大部分元素具有"粒度控制"规律。缺氧区内沉积物主要来源于夏季长江陆源的输入和海洋自生生物死亡后的沉降,部分氧化还原敏感元素(RSE)和亲生物元素不受控于"粒控效应",其中Mo、Cd、As等氧化还原敏感元素自20世纪70年代以来明显富集,分别增加了83%、73%和50%,而Mn出现贫化,指示了缺氧区水体富营养化加剧和底层水体季节性缺氧,引起底层水-沉积物界面氧化还原环境变化;亲生物元素Ca、Sr、P含量自20世纪70年代起分别增加了129%、65%和38%,反映了受化肥使用等人类活动影响,近40年来长江口外水体生产力提高和生物量增加。 相似文献
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三角洲型河口河海划界 总被引：4，自引：0，他引：4
河海界限不是一个固定的断面，受制于径流、潮汐、风暴和地形等自然因素，河水与海水接触处的时空变化大。通过对黄河口和珠江口地区的河海划界的讨论，认为三角洲型的河口区海陆划界不能以咸水内侵、淡水冲出及生态环境等具有明显季节性的特征为依据，而应根据河口三角洲典型的地貌特征、沿着三角洲平原与水下三角洲前缘的界线划分，符合自然特征。 相似文献
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Analyses of sea level and current-meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non-local coastal forcing and local tidal forcing in the northern reach of San Francisco Bay, a partially mixed estuary. Low-frequency variations in sea level are dominated by non-local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations. Low-frequency currents demonstrate a gravitational circulation which is modified by changes in tidal-current speed over the spring-neap tidal cycle. Transients in gravitational circulation induce internal oscillations with periods of two to four days. 相似文献
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O. Magnus Karlsson J. Mikael Malmaeus Sarah Josefsson Karin Wiberg Lars Håkanson 《Estuarine, Coastal and Shelf Science》2010
A dynamical, process-based mass-balance model was applied to quantify the transports of polychlorinated-p-dibenzodioxins and dibenzofurans (PCDD/Fs) to, within and from the Kallrigafjärden Bay, a coastal estuary in the Baltic Sea, and to predict the PCDD/F levels in the water and sediments of the bay. Before the modelling, a one-year sampling programme was implemented in 2007–2008 to measure the flows of PCDD/Fs in tributaries entering the system, the fluxes from the adjacent sea and the levels in water, sediment and fish within the estuary. The collected data set was used as input data to the model and for validation purposes. 相似文献
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Sea level fluctuations in central California at subtidal to decadal and longer time scales with implications for San Francisco Bay, California 总被引：1，自引：0，他引：1
Sea level elevations from near the mouth of San Francisco Bay are used to describe the low-frequency variability of forcing of the coastal ocean on the Bay at a variety of temporal scales. About 90% of subtidal fluctuations in sea level in San Francisco Bay are driven by the sea level variations in the coastal ocean that propagate into the Bay at the estuary mouth. We use the 100-year sea level record available at San Francisco to document a 1.9 mm/yr mean sea level rise, and to determine fluctuations related to El Nino-Southern Oscillation (ENSO) and other climatic events. At time scales greater than 1 year, ENSO dominates the sea level signal and can result in fluctuations in sea level of 10–15 cm. Alongshore wind stress data from central California are also analyzed to determine the impact of changes in coastal elevation at the mouth of San Francisco Bay within the synoptic wind band of 2–30 days. At least 40% of the subtidal fluctuations in sea level of the Bay are tied to the large-scale regional wind field affecting sea level variations in the coastal ocean, with little local, direct wind forcing of the Bay itself. The majority of the subtidal sea level fluctuations within the Bay that are not related to the coastal ocean sea level signal are forced by an east–west sea level gradient resulting from tidally induced variations in sea level at specific beat frequencies that are enhanced in the northern reach of the Bay. River discharge into the Bay through the Sacramento and San Joaquin River Delta also contributes to the east–west gradient, but to a lesser degree. 相似文献
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ABSTRACTThis paper explores the geotechnical feasibility for constructing coastal reservoir in Arabian Sea off Mangaluru coast. This envisages storing fresh water in a reservoir along the coast by building a sea dike to impound the flood waters of Netravati River. On one side, the dike will ensure the required quantity of freshwater flow from Netravati River to the reservoir without being drained to the sea. On the other side, the sea dike will prevent seawater from entering the reservoir, avoiding the salt contamination of the freshwater supply. Present study presents detailed investigation of the soil profiles of surrounding region of Mangaluru to explore the site condition at off Ullal beach. Lithological data on the Netravati estuary were also presented with key observation on the soil profiles in the area proposed for location of coastal reservoirs. The key finding of the study is that the region offshore of Ullal is devoid of sand and is comprised mainly of soft Silty clays. Lithological data of nine foundations at Netravati Bridge near Ullal are also presented in this paper. Based on the findings of geotechnical investigations, the paper concludes that construction of sea dike in Arabian Sea off Mangaluru coast is feasible. 相似文献
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Tidal effect on nutrient exchange in Xiangshan Bay, China 总被引：1，自引：0，他引：1
Xiangshan Bay is an estuary in China which borders on the East China Sea. The circulation in the estuary is driven by tidal movement, residual current, the internal density distribution, and synoptic wind forcing; however, the last three are not the main dynamic factors affecting nutrient transport. Because the estuary tends to be eutrophic, a synoptic study was carried out to assess the influence of tidal movement on the nutrient distribution patterns within the estuary and to estimate the fluxes of nutrient transport between the estuary and the sea. Nitrate and ammonium are found to be exported from the estuarine water to the coastal water under usual tidal conditions, except for storm tides which result in large amounts being imported because of the extremely high concentrations in the coastal bottom water. Exports of phosphate and silicate are shown to be consistent during spring tides and neap tides in all seasons. However, the usual tidal regimes resulted in only minor nutrient exchange except during abnormal events. 相似文献
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渤海湾海岸带开发对近海水环境影响分析 总被引：13，自引：0，他引：13
应用水动力学、水质数学模型,以渤海湾海岸带的几种典型开发活动--围海造地、海水淡化和河口建闸为例,模拟分析海岸带开发活动对渤海湾近岸海域水环境的影响.研究沿海围垦造成的潮通量、近岸流场水动力条件和污染物输移的变化;分析海水淡化工程浓缩海水的排放,高盐度高浓缩污染物对局部生态环境的影响;分析河口建闸后蓄积的污水排放方式对河口及近岸海域造成的影响,大量污水一次性排放会增大河口及近岸海域污染面积和污染程度. 相似文献
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海平面上升的风险评估研究进展与展望 总被引：3，自引：0，他引：3
海岸带是海陆交互作用的集中区域,人类活动密集,面对未来海平面上升带来的影响具有敏感性和脆弱性。评估未来海平面上升对海岸带的风险,具有理论与实际意义。根据海平面上升风险评估研究框架,总结了海平面上升、海岸侵蚀、风暴潮淹没、海水入侵、湿地丧失等方面的研究现状,在此基础上,分析了目前研究存在的不足,并提出了海平面上升风险评估未来研究的关键问题。 相似文献
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Z.A. Kuzyk R.W. Macdonald M.A. Granskog R.K. Scharien R.J. Galley C. Michel D. Barber G. Stern 《Estuarine, Coastal and Shelf Science》2008
A conceptual scheme for the transition from winter to spring is developed for a small Arctic estuary (Churchill River, Hudson Bay) using hydrological, meteorological and oceanographic data together with models of the landfast ice. Observations within the Churchill River estuary and away from the direct influence of the river plume (Button Bay), between March and May 2005, show that both sea ice (production and melt) and river water influence the region's freshwater budget. In Button Bay, ice production in the flaw lead or polynya of NW Hudson Bay result in salinization through winter until the end of March, followed by a gradual freshening of the water column through April–May. In the Churchill Estuary, conditions varied abruptly throughout winter–spring depending on the physical interaction among river discharge, the seasonal landfast ice, and the rubble zone along the seaward margin of the landfast ice. Until late May, the rubble zone partially impounded river discharge, influencing the surface salinity, stratification, flushing time, and distribution and abundance of nutrients in the estuary. The river discharge, in turn, advanced and enhanced sea ice ablation in the estuary by delivering sensible heat. Weak stratification, the supply of riverine nitrogen and silicate, and a relatively long flushing time (∼ 6 days) in the period preceding melt may have briefly favoured phytoplankton production in the estuary when conditions were still poor in the surrounding coastal environment. However, in late May, the peak flow and breakdown of the ice-rubble zone around the estuary brought abrupt changes, including increased stratification and turbidity, reduced marine and freshwater nutrient supply, a shorter flushing time, and the release of the freshwater pool into the interior ocean. These conditions suppressed phytoplankton productivity while enhancing the inventory of particulate organic matter delivered by the river. The physical and biological changes observed in this study highlight the variability and instability of small frozen estuaries during winter–spring transition, which implies sensitivity to climate change. 相似文献