Threshold of motion of bivalve and gastropod shells under oscillatory flow in flume experiments     

Cristiano Fick  Eduardo Puhl  Elírio Ernestino Toldo Jr 《Sedimentology》2020,67(1):627-648

The threshold of motion of non-fragmented mollusc shells was studied for the first time under oscillatory flow. In this regard, flume experiments were used to investigate the threshold of motion of three bivalve and three gastropod species, two typical mollusc classes of coastal coquina deposits. The sieve diameters ranged from 2·0 to 15·9 mm. These experiments were performed on a flat-bottom setup under regular non-breaking waves (swell) produced by a flap-type wave generator. The critical Shields values for each species of mollusc were plotted against the sieve and nominal diameter. Moreover, the dimensionless Corey shape factor of the shells was evaluated in order to investigate the effect of mollusc shell shapes on the threshold of motion. According to their critical Shields parameter, the mollusc threshold data under oscillatory flow present smaller values than the siliciclastic sediments when considering their sieve diameter. In addition, the mollusc datasets are below the empirical curves built from siliciclastic grain data under current and waves. When considering the nominal diameter, the critical Shields parameter increases and the mollusc data are closer to siliciclastic sediments. Bivalves, which have a flat-concave shape (form factor: 0·27 to 0·37), have a higher critical Shields parameter for smaller particles and more uniform datasets than the gastropod scattered data, which have a rounded shape (form factor: 0·58 to 0·62) and have varied morphologies (ellipsoidal, conical and cubic). The comparison between previous current-driven threshold data of bioclastic sediment motion and the data of mollusc whole shells under oscillatory flow shows a fair correlation on the Shields diagram, in which all datasets are below the mean empirical curves for siliciclastic sediments. These findings indicate that the shape effect on the transport initiation is predominant for smaller shells. The use of the nominal diameter is satisfactory to improve the bioclastic and siliciclastic data correlation.  相似文献   

海洋表层沉积物中金属镉的来源解析     

谭赛章  杨涛  可愚  刘材材  张昊飞 《海洋通报》2019,38(6):683-689

利用2015年8月份对长江口及其邻近海域表层沉积物的监测数据,基于主成分分析/绝对主成分分数(PCA/APCS)受体模型定量解析了重金属元素镉(Cd)的可能来源,并结合地统计学插值了Cd的源贡献量的空间分布状况,结果表明沉积物中镉污染主要存在3个可能来源,源头及贡献率分别为工业污染(18.8%)、陆地径流输入(66.0%)、生物活动等自然因素(13.6%),并且各个源头贡献量具有不同的空间分布状况,其中工业污染的高值区主要集中在靠近陆地区域,陆地径流输入的分布呈现由近岸向外海逐减降低的特征,生物活动等自然因素的高值区主要集中在远离陆地的外海区域。  相似文献   

Levels and distribution of tris-(2,3-dibromopropyl) isocyanurate and hexabromocyclododecanes in surface sediments from the Yellow River Delta wetland of China     

Ling Wang  Mengyuan Zhang  Yinghua Lou  Runhui Ke  Minggang Zheng 《Marine pollution bulletin》2017,114(1):577-582

The levels and distribution of tris-(2,3-dibromopropyl) isocyanurate (TBC) and hexabromocyclododecanes (HBCDs) of surface sediments in the Yellow River Delta wetland had been investigated. The concentrations of TBC and ∑ HBCDs ranged from 0.20 to 29.03 ng·g^? 1 dw and below limits of detections (LODs) to 20.25 ng·g^? 1 dw. The average composition profile of three HBCDs isomers were 10.1%, 6.1% and 83.8% for α-, β- and γ-HBCD, respectively. Moreover, correlation analysis indicated there are similar sources among three isomers and positive correlations between total organic carbon (TOC) content and concentrations of TBC and HBCDs. The mass inventory of TBC,α-, β-, γ-HBCD, ΣHBCDs in surface sediments of Yellow River Delta wetland were estimated about 725.50, 72.76, 44.29, 548.34, 665.39 kg. Therefore, further investigations on potential human health and environmental risk assessments of TBC and HBCDs were needed.  相似文献   

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia     

José Tasso Felix Guimarães  Prafulla Kumar Sahoo  Mariana Maha Jana Costa De Figueiredo  Karen da Silva Lopes  Markus Gastauer  Silvio Junio Ramos  Cecilio Frois Caldeira  Pedro Walfir M. Souza-Filho  Luiza Santos Reis  Marcio Sousa Da Silva  Paulo Rogenes Pontes  Renato Oliveira Da Silva Junior  Tarcísio Magevski Rodrigues 《第四纪科学杂志》2021,36(2):255-272

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.  相似文献   

湖南台地泥盆纪末绝灭事件后的微生物沉积   总被引：1，自引：0，他引：1       下载免费PDF全文

侯鸿飞  周怀玲  刘建波 《地质学报》2011,85(1):145-156

湖南中南部浅水碳酸岩台地,泥盆系顶部假整合面之上,石炭纪海进最早期,相当四射珊瑚Cystophrentis-Uralinia间隔带和单房室有孔虫带的层位,普遍发育厚度不等(7~30m)的微生物沉积.宏观上为条带状或斑块、瘤状构造,大部分由核形石组成,局部发育凝块构造内碎屑.它们均属微生物成因,代表汉根卑尔格绝灭事件后(...  相似文献   

沉积物中磷的赋存形态及磷形态顺序提取分析方法   总被引：11，自引：1，他引：10  

许春雪  袁建  王亚平  王苏明  代阿芳 《岩矿测试》2011,30(6):785-794

阐述了当前我国水体富营养化的现状,水体的富营养化与水体中磷、氮的浓度以及二者的浓度比值有着密切的关系。水体富营养化时氮和磷的浓度均很高,但没有一个固定的值,是在一个较宽泛的富营养范围内,氮和磷的浓度比值大多在10∶1～20∶1。湖泊沉积物作为湖泊水体中磷的重要蓄积库,是湖泊流域磷循环的重要归属,也是湖泊水体内源性磷的主要来源,沉积物中极少量的稳定磷转化为活性磷就会造成湖泊水体富营养化。文中介绍了沉积物中无机磷形态的分类,评述了欧盟标准局在研制湖泊沉积物磷形态标准物质时比对采用的4种提取方法(Willimas法、Hieltjes-Lijklema法、Ruttenberg法、Golterman法),总结了国内外学者所应用的沉积物中磷的各种形态提取方法和磷各形态的分析测定方法,国内学者应用的方法是在国外学者方法的基础上提出的,阐述了顺序提取方法及其地球化学意义。简要评述了湖泊沉积物中磷的生物释放、物理释放和化学释放三种释放机制,这三种释放机制相辅相成,在一特定的环境条件下某一过程可能占主导地位来控制沉积物磷的释放。最后提出应该加强对沉积物中磷的各种形态的专属提取剂及其提取有效性的分子表征和检测,更加细化对于沉积物中磷形态的分类和创新各种磷形态的分析方法,建立沉积物-水体磷的迁移、循环和转化模型,这对于从根本上解决富营养化问题具有重要意义。  相似文献   

微波消解-电感耦合等离子体质谱法测定土壤和沉积物中痕量稀土元素   总被引：11，自引：6，他引：5  

陈永欣  黎香荣  韦新红  吕泽娥  谢毓群  蔡维专 《岩矿测试》2011,30(5):560-565

建立了微波消解-电感耦合等离子体质谱法测定土壤和沉积物中15种痕量稀土元素的分析方法。研究了溶样试剂、微波消解程序、标准溶液配制、质谱干扰与内标元素对稀土元素测定的影响。加入氢氟酸能有效打开样品,以HNO3-HF-H2O2混合酸溶解样品,稀土元素的溶出率较高。采用模拟土壤、沉积物中稀土元素天然组成比值的校正溶液,对稀土元素间的干扰具有明显的抑制作用。通过测定单个La、Ce、Pr、Nd和Ba的氧化物及氢氧化物产率,计算出等效干扰浓度,进而校正多原子离子干扰。利用103Rh内标校正系统,有效地抑制了分析信号的动态漂移。方法检出限为1.2～7.1 ng/g,精密度(RSD)≤5.3%(n=6),加标回收率为86.1%～110.1%。使用土壤、沉积物标准物质进行验证,测定结果与标准值相符。建立的方法样品处理程序简单快速、线性范围宽、分析重现性好、结果准确,适用于大批量地质样品的分析。  相似文献   

长江入海口浅层沉积物中典型有机氯农药分布特征   总被引：2，自引：2，他引：0  

马健生  胡璟珂  沈加林  魏峰  沈小明 《岩矿测试》2011,30(5):606-610

对长江入海口包括江苏启东,上海崇明岛、长兴岛、横沙岛等地区的浅层沉积物中典型有机氯农药(OCPs)的分布情况进行了研究。采用气相色谱-电子捕获检测器进行检测,方法检出限为0.10 ng/g,回收率为62.4%～116.7%,精密度(RSD)为2.7%～8.3%。调查分析结果显示,长江入海口沿岸均存在轻度和中度的OCPs污染,主要检出物总滴滴涕(DDTs)浓度范围为1.22～626.43 ng/g。深度(0～80 cm)采样检测结果表明,研究区表层及深度样品中DDTs均有不同程度检出,浅层沉积物中DDTs在0～20 cm区域占检出总量的58.1%;其次是20～40 cm区域,DDTs占总量的30.8%;40～60 cm区域DDTs占总量的8.2%;60～80 cm区域DDTs占总量的2.9%,即浅层沉积物中DDTs主要集中在0～40 cm区域,部分点位40～80 cm能够检出少量DDTs。本研究提供的数据为该地区OCPs垂直分布提供参考。  相似文献   

A multi-method approach for the study of lanthanum speciation in coastal and estuarine sediments     

Parthasarathi Chakraborty  P.V. Raghunadh BabuV.V. Sarma 《Journal of Geochemical Exploration》2011

Two independent analytical methods (sequential extraction and kinetic extraction methods) were applied in order to understand the distribution and speciation of La in the coastal and estuarine sediments from the central east coast of India. Sequential extraction study revealed that La was primarily present as inert complexes (~ 50–60% of the total La) in all the sediments. Amounts of ~ 20–30% of the total La in all the sediments were found to associate with the total organic carbon (TOC) in the sediments. The dissociation rate constants of La–sediment complexes obtained from kinetic extraction studies revealed that the concentration of thermodynamically weak complexes of La gradually increased with the increasing La/TOC ratio in the sediments.  相似文献   

不同前处理方法和测量时间对泥炭中无机矿物颗粒粒度的影响     

张瑞虎  刘韬  黎兵 《沉积学报》2011,29(2):374-380

用常规方法分析长江口泥炭全样粒度数据时,发现粒度频率分布曲线末端出现含量很低的一个或两个次主峰的奇怪现象.不同的前处理方法对泥炭粒度的测量结果表明:粒度数据应选取样品上机后第3 min内的测量结果;由于长江口泥炭样品中碳酸盐含量很少,粒度分析采用加H2O2加热去除有机质再加分散剂经超声波处理后的前处理方法测量即可.频率...  相似文献