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1.
In order to depict the distribution of diatom fossils in surface sediments and to establish a reliable reference data for further paleoenvironmental study in the Changjiang (Yangtze) River estuary and its adjacent waters, the diatom fossils from 34 surface sediment samples and their relationship with environmental variables were analyzed by principal component analysis and redundancy correspondence analysis. The diversity and abundance of diatom fossils were analyzed. Some annual average parameters of the overlying water (salinity, temperature, turbidity, dissolved oxygen, depth, dissolved inorganic nitrogen, dissolved inorganic phosphate and dissolved inorganic silicate) were measured at each sampling site. A total of 113 diatom taxa and one silicoflagellate species were identified in the investigation area. Diatom fossils were better preserved in fine sediments. The absolute abundance of diatom fossils did not significantly diff er between inshore and off shore areas, the species diversity decreased from inshore to off shore. This may be because high nutrients and low salinity promoted the growth of more brackish species in coastal waters. The diatom taxa were divided into three groups, on the basis of their response and indication to environmental changes. For example, Actinocyclus ehrenbergii and Cyclotella stylorum were dominant in coastal waters (Group 1 and Group 3) with high nutrients and low salinity;the relative abundances of Paralia sulcata and Podosira stelliger were significantly higher in off shore sites (Group 2, average 39.5%), which were characterized by high salinity and deep water. Four environmental variables (salinity, dissolved inorganic nitrogen, temperature and water depth) explained the composition and distribution of diatom taxa independently ( P< 0.05), this finding can be applied in further paleoenvironmental reconstruction research in this area. 相似文献
2.
The concentrations of rare earth elements in the dissolved, acid-soluble and residual phases in surface waters of the Changjiang
Estuary were determined using ICP-MS. The main purposes of the study are to understand the estuarine geochemistry of rare
earth elements and to explore water-particle interactions in the Changjiang estuarine mixing zone. The results show that there
are two distinct processes operating on dissolved rare earth elements in the estuary: large scale removal at low salinities
due to salt-induced coagulation and remarkable release at mid to high salinities. These processes result in modification of
the effective river water flux and the systematical fractionation of the dissolved rare earth elements toward the East China
Sea. The increase in concentration of dissolved rare earth elements in the mid to high salinity waters of the Changjiang Estuary
suggests a sediment source in the mixing zone of the estuary, which is located over a shallow, broad shelf where there is
extensive physical contact between bottom sediment and estuarine waters. Acid-soluble rare earth elements, the concentrations
of which also dropped sharply in the low salinity region, appear to be controlled by salt-induced coagulation process and
intense deposition of suspended particulate matter in the low salinity region. In the mid to high salinities, all acid-soluble
rare earth element concentrations increase slightly with increasing salinity, suggesting that resuspension of sediments occurred.
In contrast, the residual rare earth element concentrations are relatively constant with salinity variation in the Changjiang
estuarine surface waters. 相似文献
3.
台风能够对黄海的水文结构及人民群众的生产生活产生重要的影响,严重威胁了人们的生命财产安全。利用ROMS(regional ocean modeling system)模式,分析了台风"灿鸿"在过境黄海期间对黄海温度及环流结构的影响过程。结果表明,台风期间强烈的风致混合能够使温跃层的深度增大,强度减弱,同时,使得近岸的底层温度迅速升高,推动底层的温度锋面向黄海内区移动。台风过境也会对黄海冷水团环流产生重要的影响,台风过境前,混合层中的北向流会迅速加深增强,同时伴随着混合层及温跃层的下移,从而使得黄海冷水团环流的流核下移至跃层以下。当台风过境时,黄海上空的气旋式风场会加剧黄海上层的气旋式环流,导致黄海冷水团环流的流幅及流量迅速增加。当台风登陆后,黄海上层的温度及黄海冷水团环流的结构开始逐渐恢复。 相似文献
4.
Baodong Wang 《Marine environmental research》2009,67(1):53-58
Based on the seasonal surveying data and long-term data, the annual changes in the geographical locations, occurrence frequency, affected areas and the minimum oxygen level as well as the formation mechanism of the summer hypoxia off the Changjiang estuary are summarized and discussed in this paper. The historical data indicates that there were episodes of hypoxia in the past 50 years but not every year, and the event of summer hypoxia could be traced back to as early as late 1950s off the Changjiang estuary. The minimum oxygen levels in the hypoxia zone did not show any decline in the past 50 years, but all the events with large size of affected area (>5000 km2) were observed after the late 1990s, suggesting an enlarging trend. The author argues that the development of summer hypoxia off the Changjiang estuary was related not only to stratification and input of suspended particulate matter, but also to the inflow of Taiwan warm current water as well as the bottom topography. 相似文献
5.
潮致余流和潮混合对长江口外东北海域低盐水团的作用 总被引：1，自引：0，他引：1
长江冲淡水对黄海、东海水文环境有重要影响,它主要以羽状形态向外海扩展,在某些年份的特殊时间段也存在孤立的低盐水团现象。在低盐水团的动力机制研究中,风、径流量、台湾暖流、天文潮和斜压不稳定的作用已得到讨论。天文潮对冲淡水及低盐水团的影响主要包括潮致余流和潮混合,潮致余流作用仍缺乏讨论。本文对1983年8月低盐水团的动力机制进行数值模拟分析,重点讨论了潮致余流和潮混合的影响。结果表明:潮致Lagrange余流促使一部分冲淡水从口门向北输运,在32°N附近呈舌状转向东,有利于在口外东北海域形成低盐水团;小潮转大潮的垂向混合作用加强,浅水区表层盐度升高的速度快于较深水区,也有利于在口外东北海域形成低盐水团。 相似文献
6.
7.
低氧/缺氧已成为严重威胁河口/近海与陆架浅海生态系统安全的要素之一。生物地球化学过程大量耗氧与水体分层限制表、底层水体交换是河口/近海低氧/缺氧问题的直接原因;而河口/近海和陆架海的各种物理过程控制了营养盐和有机质输运、水体层化,成为导致低氧/缺氧发生的根本原因之一。先讨论了近几年来国内外主要大河河口/近海和陆架浅海低氧现象发生的物理机制:径流冲淡水、潮汐、风、环流对低氧的影响,以及低氧对海-气大尺度变化和气候变化的响应等。再以长江口为例,重点分析了水动力过程对长江口夏季底层低氧的具体影响,同时对溶解氧统计模型和动力学模型的研究工作进行了阐述。最后对各种研究方法的优缺点进行总结,对长江口外海夏季底层低氧的研究工作进行了展望。 相似文献
8.
The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal strati?cation,and anaerobic conditions arise. The determination of hypolimnetic oxygen demand(HOD) and areal hypolimnetic oxygen demand(AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes dif fering by size and af fected by dif ferent anthropogenic sources, are investigated in this respect. At?rst, bathymetric studies were conducted to determine the depth, surface area, and volume relationships.Then, based on monitoring studies conducted in 2013 and 2014, the thermal strati?cation dynamics and layer properties were established using the relative thermal resistance to mixing(RTRM) index based on temperature and density pro?les. Following this, the oxygen depletion rates were determined by oxygen and temperature pro?ling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic in?uences, were found to be 0.848 and 0.569 g O 2/(m·d), respectively.The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O 2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes. 相似文献
9.
2015年9月台风“灿鸿”经过黄海海域的QF111浮标,该浮标观测到黄海海洋的温度和流速响应。受台风影响,黄海海表温度有明显的下降,降温幅度在2~4°C,且在台风路径右侧形成了海表面温度低于20°C的低温斑块。流速的响应主要表现为台风过境期间流速增强,达1.2~1.5 m/s,呈现出全水深强化的特征。风一直对海洋有能量输入,且在台风过境期间风输入海洋的能量最大,旋转功率谱的分析结果表明台风输入海洋的能量向海洋内部传播。黄海海域由台风激发出的近惯性振荡衰减较快,近惯性振荡e折时间尺度约为2 d。 相似文献
10.
三峡截流后长江口秋季TSM、POC和PN的分布特征 总被引：2，自引：0，他引：2
基于2004年11—12月长江口56个站位的悬浮体调查资料,分析了长江口区悬浮体总量(TSM)、颗粒有机碳(POC)和颗粒氮(PN)质量浓度的平面分布特征,探讨该区TSM及颗粒有机质的物质来源和三峡截流对长江三角洲的影响。结果表明,表、底层TSM与POC、PN质量浓度之间存在显著的正线性相关关系并都呈现出南高北低的格局,说明了长江悬浮颗粒物入海后主要沿东南方向输运。POC、PN质量分数与POC、PN的质量浓度不同,它们与TSM质量浓度对数有负相关关系。由于河口区底质再悬浮作用显著,TSM和POC、PN质量浓度呈现表层低、底层高的特点。长江口悬浮体主要来自长江径流和底质沉积物的再悬浮。与三峡截流前数据的对比表明,截流对目前长江口区的TSM和POC尚未造成明显的影响。 相似文献
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12.
In this study,typhoon waves generated during three typhoons(Damrey(1210),Fung-wong(1416),and Chan-hom(1509))in the Yellow Sea and East China Sea were simulated in a simulating waves nearshore(SWAN)model,and the wind forcing was constructed by combining reanalyzed wind data with a Holland typhoon wind model.Various parameters,such as the Holland fitting parameter(B)and the maximum wind radius?,were investigated in sensitivity experiments in the Holland model that affect the wind field construction.Six different formulations were considered and the parameters determined by comparing the simulated wind results with in-situ wind measurements.The key factors affecting wave growth and dissipation processes from deep to shallow waters were studied,including wind input,whitecapping,and bottom friction.Comparison with in-situ wave measurements suggested that the KOMEN scheme(wind input exponential growth and whitecapping energy dissipation)and the JONSWAP scheme(dissipation of bottom friction)resulted in good reproduction of the significant wave height of typhoon waves.A preliminary analysis of the wave characteristics in terms of wind-sea and swell wave revealed that swell waves dominated with the distance of R to the eye of the typhoon,while wind-sea prevailed in the outer region up to six to eight times the R values despite a clear misalignment between wind and waves.The results support the hypothesis that nonlinear wave-wave interactions may play a key role in the formation of wave characteristics. 相似文献
13.
长江口北槽一期工程后滩槽沉积物分布特征及其影响因素 总被引：1，自引：0，他引：1
根据2000年7月和2001年5—6月份长江口北槽航道及两侧滩地进行的沉积物采样分析结果,对长江口深水航道一期工程实施后的滩槽泥沙交换情况以及在自然与工程双重影响下的沉积物分布情况进行了较为详细的讨论。长江口深水航道工程的实施,影响了长江口尤其是北槽及两侧滩地的水沙条件和沉积物分布。强劲的径流和潮流作用和风浪作用造成航槽及两侧滩地的冲淤转换及沉积物分布的变化;深水航道治理工程的实施使工程段内航槽泥沙粒径粗化,两侧滩地和工程段下游泥沙中值粒径变细,这反映了在工程实施后滩槽泥沙交换的变化。 相似文献
14.
基于水下自主航行器(AUV)的神狐峡谷谷底块体搬运沉积特征及其对深水峡谷物质输运过程的指示 总被引：2，自引：0，他引：2
海底峡谷是陆源物质向深海运移的重要通道.对于远离陆地的海底峡谷,通常认为浊流是物质搬运的主要营力.受限于探测精度和复杂作业环境影响,使用常规地球物理资料对深水海底峡谷尤其是对谷底沉积体的形态和结构特征的刻画不够精细.基于水下自主航行器(AUV,Autonomous Underwater Vehicle)采集的高分辨率多... 相似文献
15.
本文基于2015年7月长江口的现场调查资料,分析讨论了长江河口区溶解态铁(DFe)的含量分布与混合行为及其影响因素。结果表明:长江径流携带大量的DFe入海,且口内区(Ⅰ)浓度高于混合区(Ⅱ)和外海区(Ⅲ),平均浓度分别为166.45±6.26nmol/L,14.04±8.80nmol/L和6.18±1.51nmol/L。受去除作用和海水稀释的影响,在河口区DFe的浓度下降率达到96.92%。DFe浓度与盐度的关系符合指数模型,由模型与理论稀释线估算的长江口海域DFe的理论最大去除率为97.75%,与实际测得的最大浓度下降率相近。长江冲淡水、苏北沿岸流和台湾暖流影响DFe的水平分布。受长江冲淡水影响,长江口外海域DFe浓度高达176.50nmol/L。苏北沿岸流主要影响研究区域北部的表层水,其携带的DFe浓度低于长江冲淡水。台湾暖流是导致研究区域东南部DFe浓度较低的主要原因,使得中层和底层水中浓度分别低至4.04nmol/L和4.79nmol/L。另外,在表层海水中DFe的分布受到叶绿素a、溶解有机碳和溶解氧的共同影响,DFe与叶绿素a、溶解氧呈显著负相关,与溶解有机碳呈显著正相关。 相似文献
16.
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
17.
长江口邻近海域海水pH的季节变化及其影响因素 总被引：1，自引：0，他引：1
基于对2015—2016年长江口邻近海域现场调查数据的分析,探讨了其海水pH的季节变化和影响因素。结果表明:长江口邻近海域四季pH在7.76—8.32之间,其中夏季最高,秋季最低;夏季具有明显的分层现象,冬季水体pH垂直分布相对均一。长江冲淡水对长江口邻近海域水体pH的影响是局域性的。浮游植物光合作用是影响春、夏、秋季海水pH区域分布的重要过程。春、冬季节表层海水pH分布受海-气界面CO2交换的影响较大。温度、生物作用及长江冲淡水扩展是导致长江口邻近海域表层海水pH季节变化的主要因素。 相似文献
18.
基于2018年早春和夏季长江口邻近海域的调查数据,分析溶解氧(DO)的时空分布,并讨论其影响因素.结果表明,夏季DO浓度变化范围为1.58～9.37 mg/L,浮游生物光合作用产生的DO是夏季表层水体过饱和的主要因素;夏季调查海域受台湾暖流北上引起海水层化加强,同时水体富营养化导致表层生物大量繁殖所引起有机碎屑的沉降和耗氧分解作用是底层低氧区存在的主要因素.夏季在台湾暖流影响下底层水体表观耗氧量(AOU)与营养盐成正相关关系,底层有机物耗氧降解过程与营养盐的再生密切相关.早春DO浓度变化范围为7.90～10.1 mg/L,长江口外北部海域和浙江近岸海域海水混合均匀,DO浓度主要受温度控制,而台湾暖流影响区海水出现层化现象,其低DO含量也为低氧区的形成奠定了基础. 相似文献
19.
The partial pressure of carbon dioxide and air-sea fluxes in the Changjiang River Estuary and adjacent Hangzhou Bay 总被引：3，自引：0，他引：3
The distributions of partial pressure of carbon dioxide (p CO2 ) in the surface waters of the Changjiang River Estuary and adjacent Hangzhou Bay were examined in the summer of 2010. Surface water p CO2 ranged from 751-2 095 μatm (1 atm=101 325 Pa) in the inner estuary, 177-1 036 μatm in the outer estuary, and 498-1 166 μatm in Hangzhou Bay. Overall, surface p CO2 behaved conservatively during the estuary mixing. In the inner estuary, surface p CO2 was relatively high due to urbanized pollution and a high respiration rate. The lowest p CO2 was observed in the outer estuary, which was apparently induced by a phytoplankton bloom because the dissolved oxygen and chlorophyll a were very high. The Changjiang River Estuary was a significant source of atmospheric CO2 and the degassing fluxes were estimated as 0-230 mmol/(m2 d) [61 mmol/(m2 d) on average] in the inner estuary. In contrast, the outer estuary acted as a CO2 sink. 相似文献