Long-term changes in sedimentary diatom assemblages and their environmental implications in the Changjiang (Yangtze) River estuary,China     

程芳晋  俞志明  宋秀贤 《中国海洋湖沼学报》2014,32(1):155-161

Long-term data on diatom assemblages in a sediment core （60 cm） obtained from the Changjiang （Yangtze） River estuary were analyzed in order to assess the environmental changes that took place in the approximately 38 years （as determined by 210pb measurements）, i.e., between 1974 and 2012, of sediment accumulation. From the sediment core, 62 diatom taxa and genera were identified. The diatom biomass in the core generally increased beginning in the mid-1990s （core depth： 35 cm）, accompanied by a shift in the dominant species from Podosira stelliger and two species of Cyclotella （C. stylorum and C. striata） to Paralia sulcata, three species of Thalassiosira （ T. eccentria, I＂. oestrupii, and T. excentrica）, Actinoptychus undulates, and Thalassionema nitzschioides. The changes in both species diversity and abundance suggested that since the 1980s the estuary has undergone extensive eutrophication. This conclusion was supported by the increased proportion of planktonic species, another indicator of high nutrients inputs, in the Changjiang River estuary.  相似文献   

High resolution records of flood deposition in the mud area off the Changjiang River mouth during the past century     

胡刚  李安春  刘健  徐刚  梅西  孔祥淮 《中国海洋湖沼学报》2014,32(4):909-920

This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 210 Pb dating and was sampled at 1–2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size(14.32–96.39 μm) contribution30%, Zr/Rb ratio1.5, and magnetic susceptibility16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods.  相似文献   

A neural network method for monitoring snowstorm: A case study in southern China     

Kebiao Mao  Ying Ma  Lang Xia  Xinyi Shen  Zhiwen Sun  Tianjue He  Guanhua Zhou 《中国地理科学(英文版)》2014,24(5):599-606

It has been observed that low temperature, rainfall, snowfall, frost have never occurred over the past 50 years in the southern China, and weather in this area is very complex, so the monitoring equipments are few. Optical and thermal infrared remote sensing is influenced much by clouds, so the passive microwave Advanced Microwave Scanning Radiometer-Earth Observing System （AMSR-E） data are the best choice to monitor and analyze the development of disaster. In order to improve estimation accuracy, the dynamic learn- ing neural network was used to retrieve snow depth. The difference of brightness temperatures of TB18.7v and TB36.sv, TBI8.7H and TB36.sH, TB23,sv and TB89v, TBz3.8H and TB89H are made as four main input nodes and the snow depth is the only one output node of neural network. The mean and the standard deviation of retrieval errors are about 4.8 cm and 6.7 cm relative to the test data of ground measurements. The application analysis indicated that the neural network can be utilized to monitor the change of snow intensity distribution through passive microwave data in the complex weather of the southern China.  相似文献   

Decadal Anomalies of Winter Precipitation over Southern China in Association with El Nio and La Nia   总被引：1，自引：0，他引：1       下载免费PDF全文

YUAN Yuan  LI Chongyin  YANG Song 《Acta Meteorologica Sinica》2014,28(1):91-110

Using multiple datasets, this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of E1 Nifio-Southern Oscillation during 1948 2011. The study proves that E1 Nifio is an important external forcing factor resulting in above-normal winter precipitation in southern China. The study also reveals that the impact ofLa Nifia on the winter precipitation in southern China has a decadal variability. During the winter of La Nifia before 1980, the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia, and the western Pacific subtropical high weakens with its high ridge retreating more eastward. Therefore, anomalous northerly winds dominate over southern China, leading to a cold and dry winter. During La Nifia winter after 1980, however, the East Asian trough is weaker than normal, unfavorable for the southward invasion of the winter monsoon. The India-Burma trough is intensified, and the anomalous low-level cyclone excited by La Nifia is located to the west of the Philippines. Therefore, anomalous easterly winds prevail over southern China, which increases moisture flux from the tropical oceans to southern China. Meanwhile, La Nifia after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter. Since southern China is rightly located on the right side of the jet entrance region, anomalous ascending motion dominates there through the secondary vertical circulation, favoring more winter precipitation in southern China. Therefore, a cold and wet winter, sometimes with snowy and icy weathers, would occur in southern China during La Nifia winter after 1980. Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Nifia mature phase, as well as the decadal variation of the Northern Hemisphere atmospheric circulation, would be the important reasons for the decadal variability of the La Nifia impact on the atmospheric circulation in East Asia and winter precipitation over southern China after 1980.  相似文献   

Seasonal Changes in Phytoplankton Biomass and Dominant Species in the Changjiang River Estuary and Adjacent Seas：General Trends Based on Field Survey Data 1959-2009     

YANG Shu  ;HAN Xiurong  ;ZHANG Chuansong  ;SUN Baiye  ;WANG Xiulin  ;SHI Xiaoyong 《青岛海洋大学学报(英文版)》2014,(6):926-934

The characteristics of seasonal variation in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas were discussed based on field investigation data from 1959 to 2009. The field data from 1981 to 2004 showed that the Chlorophyll-a concentration in surface seawater was between 0.4 and 8.5 ktg dm-3. The seasonal changes generally presented a bimodal trend, with the biomass peaks occurring in May and August, and Chlorophyll-a concentration was the lowest in winter. Seasonal biomass changes were mainly controlled by temperature and nutrient levels. From the end of autumn to the next early spring, phytoplankton biomass was mainly influenced by temperature, and in other seasons, nutrient level （including the nutrient supply from the terrestrial runoffs） was the major influence factor. Field investigation data from 1959 to 2009 demonstrated that dia- toms were the main phytoplankton in this area, and Skeletonerna costatum, Pseudo-nitzschia pungens, Coscinodiscus oculus-iridis, Thalassinoema nitzschioides, Paralia sulcata, Chaetoceros lorenzianus, Chaetoceros curvisetus, and Prorocentrum donghaiense Lu were common dominant species. The seasonal variations in major dominant phytoplankton species presented the following trends： 1） Skeletonema （mainly S. costatum） was dominant throughout the year; and 2） seasonal succession trends were Coscinodiscus （spring） →Chaetoceros （summer and autumn） → Coscinodiscus （winter）. The annual dominance of S. costatum was attributed to its environmental eurytopicity and long standing time in surface waters. The seasonal succession of Coscinodiscus and Chaetoceros was associated with the seasonal variation in water stability and nutrient level in this area. On the other hand, long-term field data also indicated obvious interannual variation of phytoplankton biomass and community structure in the Changjiang River Estuary and adjacent seas： average annual phytoplankton biomass and dinoflagellate proportion both presented inc  相似文献   

黑河市西岗子盆地南部区块煤层对比     

董超然  ;邓婷婷  ;张建良  ;苏循新 《黑龙江国土资源》2014,(11):40-40

一、区块位置、交通 黑龙江省西岗子盆地南部区块位于我省黑河市爱辉区和黑龙江省北安农垦分局红色边疆农场境内。区块中心距黑河市北东直距约40千米,西岗子镇位于本区的北部,铁路有哈黑（哈尔滨市一黑河市）线,公路有国道G202（北安一黑河段）、省道S301（嫩江一黑河段）均在工作区中经过,航空有黑河市直飞哈尔滨市航线,水运有黑龙江,由黑河市通往下游佳木斯、同江等地市,因此交通较为方便。  相似文献   

川南地区中二叠统茅口组碳酸盐岩储层孔隙特征与储层成因     

任梦怡  汪泽成  江青春  胡光义  范廷恩  范洪军 《东北石油大学学报》2021,45(3):32-43

川南地区中二叠统茅口组碳酸盐岩储层孔隙结构复杂、非均质性强,孔隙类型的差异影响储层渗流能力.基于岩心观察、薄片鉴定和扫描电镜成像等资料,采用FIB—SEM三维成像技术,分析川南地区中二叠统茅口组碳酸盐岩储层特征.结果表明:川南地区中二叠统茅口组碳酸盐岩储层受白云石化和溶蚀作用等影响,形成晶间溶蚀孔、粒间孔和粒内孔等次生孔隙,为油气储存和运移提供重要的储集空间.茅口组孔隙—孔洞型储层主要存在粒间孔、粒内孔、晶间孔、有机质孔和微裂缝5种孔隙类型.主要储集空间组合类型为粒间孔—晶间溶蚀孔—微裂缝;次要储集空间组合类型为粒内孔—晶间孔—有机质孔—生物体腔溶孔.以亮晶生屑灰岩为主的储层大孔数量多,但孔隙连通性差,非均质性较强,有利于形成裂缝—孔隙型储层.以泥晶生屑灰岩为主的储层广泛发育粒间孔和粒内孔,孔隙连通性较好,非均质性弱,有利于形成优质孔隙—孔洞型储层.该结果为证实孔隙—孔洞型储层具备优质储集性能提供实验依据,为四川盆地中二叠统茅口组勘探提供参考.  相似文献   

琼东南盆地南部梅山组丘状体沉积特征及成因机制          下载免费PDF全文

熊鹏飞  姜涛  匡增桂  程聪  任金锋  赖洪飞 《地质科技通报》2021,40(4):11-21

琼东南盆地南部梅山组具有独特的丘状反射特征,关于其成因机制引起了广泛关注和讨论。以琼东南盆地大量二维地震资料和高分辨率三维地震资料解释为基础,在深水钻井标定下,从地震相特征、沉积物物源、沉积搬运通道、古地貌特征以及海平面变化和构造活动6个方面,阐明了梅山组丘状体的沉积特征,并讨论了其成因机制。研究结果表明,中中新统梅山组沉积时期,受强制性海退影响,琼东南盆地范围内海平面下降至低水位,南部隆起局部暴露剥蚀,提供了大量沉积物源;上中新统黄流组沉积时期,盆地局部构造活动使得南部隆起物源发生重力失稳,通过深水水道向盆地中央以重力流方式搬运沉积物。琼东南盆地梅山组地层的丘状反射特征是黄流组沉积时期以南部隆起沉积物为物源的浊流侵蚀下伏梅山组地层所致。对该丘状体成因机制的深入研究,不但有助于丰富对丘状地震反射现象的认识,而且揭示了其沉积构成为粗碎屑沉积物而非生物礁滩沉积,对深水油气勘探储层特征及评价具有重要意义。   相似文献   

春季长江口及其邻近海域溶解有机物的分布、组成及降解行为研究     

陈博洋  陈容  陈岩  杨桂朋 《海洋科学》2022,46(11):1-14

2021年3月对长江口及其邻近海域9个断面溶解氨基酸(THAA)、溶解有机碳(DOC)和溶解有机氮(DON)的分布和组成进行了调查研究。结果表明:THAA的浓度范围为1.24~4.71μmol/L,平均浓度为(2.61±0.85)μmol/L;DOC的浓度范围为118.17~450.58μmol/L,平均浓度为(149.73±33.34)μmol/L;DON的浓度范围为10.48~24.45μmol/L,平均浓度为(13.80±1.81)μmol/L。THAA、DOC和DON的水平分布表现出近岸高于远岸的特点,表明陆源输入对调查区域的THAA等分布有重要影响。而THAA与D-天门冬氨酸、D-谷氨酸、D-丝氨酸和D-丙氨酸的D/L比均呈显著负相关,与天门冬氨酸/β-丙氨酸(Asp/β-Ala)呈正相关,表明细菌活动是影响THAA浓度变化的重要因素。长江口及邻近海域的优势氨基酸为L型氨基酸,D型氨基酸和非蛋白型氨基酸的占比仅为7.34%。基于C/N比值分析,长江口及其邻近海域溶解有机物(DOM)的来源受到长江冲淡水和台湾暖流的共同影响。THAA-C%、THAA-N%、降解因子和反应活性指数表明:水平方向上盐度接近于0的淡水区域和盐度高于34的远海区域降解程度较高;垂直方向上随着深度的增加,有机物的降解程度逐渐升高。调查区域有机物的降解程度主要受到陆源输入和细菌活动的影响。  相似文献   

夏季长江口海域溶解态铁的分布及混合行为研究     

吴瑶  姚佳佳  杨茹君  刘媛  张莹莹 《海洋科学》2022,46(11):15-28

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