Seasonal variations of particulate silicon in the Changjiang (Yangtze River) Estuary and its adjacent area

Temporal and spatial distribution of biogenic （BSi） and lithogenic （LSi） silica were studied in the Changjiang （Yangtze River） Estuary and its adjacent area. The annual average BSi and LSi concentrations were （1.714-1.79） #mol/L and （0.564-1.41） mmol/L, respectively. Both BSi and LSi were high ii~. tbe inshore ar- eas, where they received terrigenous discharge from the Changjiang, and decreased towards the offshore region. BSi and LSi were most abundant at the near bottom layer due to the high sedimentation rates and resuspension of sediment. Diatom blooms occurred in summer with high Chl a concentration in the sur- face layer, which induced that BSi in the surface layer during summer was obviously higher than that in the surface layer of other seasons. LSi concentration was maximal in autumn and spring and minimum in summer, associated with the seasonal variation of SPM values. Drifting investigation and mesocosm exper- iments were conducted during dinoflagellate bloom, aiming to understand the effect of nutrients on BSi by changing the phytoplankton composition. The results show that the low dissolved inorganic phosphorus concentration and high molar ratio of N/P （dissolved inorganic nitrogen vs. dissolved inorganic phospho- rus）, were the important factors for decreasing diatom biomass in the study area, and it would subsequently decrease the BSi concentration in aquatic ecosystem.

Spatial distributions of organic carbon and nitrogen and their isotopic compositions in sediments of the Changjiang Estuary and its adjacent sea area

The spatial distribution patterns of total organic carbon and total nitrogen show significant correlations with currents of the East China Sea Shelf. Corresponding to distributions of these currents, the study area could be divided into four different parts. Total organic carbon, total nitrogen, and organic carbon and nitrogen stable isotopes in sediments show linear correlations with mean grain size, respectively, thus ＂grain size effect＂ is an important factor that influences their distributions. C/N ratios can reflect source information of organic matter to a certain degree. In contrast, nitrogen stable isotope shows different spatial distribution patterns with C/N and organic carbon stable isotope, according to their relationships and regional distributions. The highest contribution （up to 50%） of terrestrial organic carbon appears near the Changjiang Estuary with isolines projecting towards northeast, indicating the influence of the Changjiang dilution water. Terrestrial particulate organic matter suffers from effects of diagenesis, benthos and incessant inputting of dead organic matter of plankton, after depositing in seabed. Therefore, the contribution of terrestrial organic carbon to particulate organic matter is obviously greater than that to organic matter in sediments in the same place.

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

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 μg 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 diatoms were the main phytoplankton in this area, and Skeletonema 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 increased trends during the 1950 s-2000 s.

Study of radioactive status in the Zhujiang Estuary and adjacent sea area in South China Sea (SCS)

Through the investigation on radioactive activities of water, sediment and some marine organismsin the Zhujiang Estuary, adjacent sea area and the distributary mouths of the Zhujiang River, activities of total α. radioactivity, total β radioactivity, artificial radioactive 90Srand 157Cs, and factors inflencing the distribution and the content of U in seawater are studied.The mainly radioactive pollution substances and their sources in the sea area are studied by γ spectra obtained from sediment in the sea area. The results show that the main radioactivity substances are natural radioactivity U,Th series and 40K. which were produced by the modern industry and transported into the sea through the main current of the Zhujiang River.

Concentrations and sinking rates of transparent exopolymer particles(TEPs)in a coastal sea:the Changjiang River(Yangtze River)Estuary

Transparent exopolymer particles(TEPs)are ubiquitous throughout the oceans,and their sedimentation is considered an efficient biological carbon sink pathway.To investigate the role of coastal TEPs in sinking carbon from the upper layer,samples were collected in the spring and summer of 2011 in the Changjiang River(Yangtze River)Estuary,a typical coastal water.The concentrations and sinking rates of TEPs were measured,and potential sedimentation flux of TEPs was estimated.TEPs concentrations ranged from 40.00μg/L to 1040.00μg/L(mean=(209.70±240.93)μg/L)in spring and 56.67μg/L to 1423.33μg/L(mean=(433.33±393.02)μg/L)in summer,and they were higher at bloom stations than at non-bloom stations during both cruises.A significant positive correlation between TEPs concentration and chlorophyll a(Chl a)concentration was detected,suggesting that phytoplankton was the primary source of TEPs in this area.TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of(0.28±0.14)m/d in spring and 0.10 m/d to 1.08 m/d with a mean of(0.34±0.31)m/d in summer.The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d)to 29.40 mg/(m2·d)with a mean of(14.66±8.83)mg/(m2·d)in spring and 6.80 mg/(m2·d)to 30.45 mg/(m2·d)with a mean of(15.71±8.73)mg/(m2·d)in summer,which was^17.81%to 138.27%(mean=65.15%±31.75%)of sedimentation flux of phytoplankton cells in the study area.Due to the increase of TEPs concentrations and their sinking rates,sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises.This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary,especially during bloom events,and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.

The characteristics of Quaternary activity of faults in the sea area near the Yangtze River mouth

By shallow seismic prospecting, it is showed that the faults in the sea area near the Yangtze River mouth are mainly the NE and NW-trending faults. The main activity time of fault is Pliocene to Early Pleistocene, and the latest activity is up to Middle Pleistocene. The maximum of fault is generally several tens meters with the throw decreased upward. The dislocation near the bottom of Middle Pleistocene is 12~13 m. The average vertical dis-placement rate is on a level of 10-3 mm/a.

Preliminary Study on Cenozoic Group and Fault Activity in the Sea Area Near the Yangtze River Mouth

By shallow seismic prospecting, the Cenozoic Group in the sea area near the Yangtze River Mouth can be divided into five seismic sequences. They correspond to the Quaternary, Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. The Quaternary System covers all the detecting area. The Tertiary System overlaps and thins out from NE to SW. The sedimentary basement mainly consists of volcanic rock (J 3) and acidic rock (r 3 5). Paleogene or Late Cretaceous basins are not found there. The faults that have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) by their trend. The NE and NW trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of the EW trending faults. The activity of the NE trending faults is different in different segments. The SW segment is a Quaternary fault, the middle segment is a Neogene fault, The NE is Paleogene. But the segment of the NW trending fault is not obvious. The average vertical displacement rate is about 0 015mm/a.

Peaked abundance of Calanus sinicus earlier shifted in the Changjiang River (Yangtze River) Estuary:a comparable study between 1959,2002 and 2005

The sea surface temperature （SST） of the East China Sea （ECS） increased in the past decades, which may have a great impact on the ecosystem of the ECS, including the changes in planktonpopulation structure. In this paper, the changes in peaked abundance of Calanus sinicus in the Changjiang River （Yangtze River） Estuary were compared between 1959 and 2002, based on the data collected from the seasonally oceanographic cruises and those performed in spring of 2005. It was much higher in spring compared with that in other seasons both in 1959 and 2002. Furthermore, in spring 2005, the time for occurrence and decrease of the peaked C. sinicus abundance advanced about one month, accompanying the increase in the sea surface water temperature （SST）. It peaked in June and decreased in July in 1959, however, in 2005, it peaked in May and attenuated sharply in early June. The earlier decrease of peaked C. sinicus abundance may further deteriorate the ecosystem in the Changjiang River Estuary and north nearshore of the ECS.

Effect of regional warming on the abundance of P seudeuphausia sinica Wang et Chen(Euphausiacea)off the Changjiang River(Yangtze River)Estuary

Distribution and abundance of Pseudeuphausia sinica off the Changjiang River Estuary （30 ° 00′ – 32 ° 00′ N, 122 ° 00′ –123 ° 30 ′E）, the East China Sea were studied in relation to environmental features associated with the regional warming. P. sinica is a subtropical species. Off the Changjiang River Estuary, its abundance reached maximum in summer. To examine spatial and temporal changes of P. sinica off the Changjiang River Estuary, the authors have combined all available sampling data in 1979, 1981, and 2000–2007. This database shows that a significant increase in abundances of P. sinica was observed in spring of 2000–2007 as compared with 1979, 1981. The abundance of P. sinica increased from 0.18–0.21 ind./m 3 in 1979 and 1981 to 0.68–4.00 ind./m 3 in 2000–2007. Accordingly, the sea temperature increased obviously from spring of 1979, 1981 to the 2000s. The authors further found a positive relationship between average surface temperature and average abundance of P. sinica. Regional warming, together with the release of predator induced stress due to a sharp decline in the abundance of its predator （e.g., fishes）, were thought to be responsible for the increase in abundance of P. sinica in water off the Changjiang River Estuary.

Validation and application of soil moisture active passive sea surface salinity observation over the Changjiang River Estuary

Using sea surface salinity(SSS)observation from the soil moisture active passive(SMAP)mission,we analyzed the spatial distribution and seasonal variation of SSS around Changjiang River(Yangtze River)Estuary for the period of September 2015 to August 2018.First,we found that the SSS from SMAP is more accurate than soil moisture and ocean salinity(SMOS)mission observation when comparing with the in situ observations.Then,the SSS signature of the Changjiang River freshwater was analyzed using SMAP data and the river discharge data from the Datong hydrological station.The results show that the SSS around the Changjiang River Estuary is significantly lower than that of the open ocean,and shows significant seasonal variation.The minimum value of SSS appears in July and maximum SSS in December.The root mean square difference of daily SSS between SMAP observation and in situ observation is around 3 in both summer and winter,which is much lower than the annual range of SSS variation.In summer,the diffusion direction of the Changjiang River freshwater depicted by SSS from SMAP is consistent with the path of freshwater from in situ observation,suggesting that SMAP observation may be used in coastal seas in monitoring the diffusion and advection of freshwater discharge.

NUMERICAL SIMULATION OF SUMMER CIRCULATION IN THE EAST CHINA SEA AND ITS APPLICATION IN ESTIMATING THE SOURCES OF RED TIDES IN THE YANGTZE RIVER ESTUARY AND ADJACENT SEA AREAS

Based on the COHERENS （a Coupled Hydrodynamical Ecological model for Regional Shelf seas）, a three-dimensional baroclinic model for the summer of East China Sea （ECS） was established with the sigma-coordinate in the vertical direction and spherical coordinate in the horizontal direction. The circulation patterns of the Kuroshio Current, the Taiwan Warm Current （TWC）, the Tsushima Current and the Yangtze Diluted Water （YDW） were successfully simulated with this model. The calculated results are fairly consistent with previous observations and studies. Based on this baroclinic current field, the Lagranian particles tracking was simulated to estimate the possible origins of the red tides frequently occurring in the Yangtze River estuary and its adjacent sea areas. If there are ＂seeds＂ （cysts） of the red tide algae at the seabed of the Taiwan Strait, the offshore of Fujian and Zhejiang Provinces and the northeast Taiwan Island, those are extremely possible sources of the red tides in the Yangtze River estuary and its adjacent sea areas. Field data are needed to confirm it. Numerical simulation to estimate the source of the red tides is a new application of the Lagrangian transport in the marine ecology.

长江口横沙地区演化过程及保护利用思考

长江口横沙地区的保护和利用一直是近年来的热门话题。本文对横沙岛、横沙新洲的成陆过程以及浅滩的近期演化特征进行了总结和回顾,基于国家战略和前人的利用设想,提出了横沙地区目前面临的灾害和未来利用需要论证的制约因素。横沙岛于1958年定界成陆,横沙新洲(东滩)在历史大洪水切割以及航道工程和促淤圈围等作用下于2021年成陆,横沙浅滩目前“长高不长大”,处于萎缩性演化态势。文章基于“长江大保护”国家战略,总结了前人提出的一些利用设想,认为需要综合研判横沙地区的保护利用模式。目前横沙地区主要面临流域输沙偏低和海平面上升带来的浅滩侵蚀问题,建议结合固沙保滩工程利用周围航道的疏浚土资源,未来利用也需要深入研究横沙地区生态保护、基底稳定、航道冲淤、盐水入侵以及极端气候等承载力问题。

基于空间插值的长江口邻近海域春季悬浮物和叶绿素a空间分布分析

针对目前利用实测数据对长江口邻近海域水质状况进行分析研究相对偏少的情况,基于“淞航”号2018年春季航次对该海域的综合观测,利用实验室水样分析数据对船载温盐深仪(CTD)的测量数据进行校正,并对该区域2018年春季时节悬浮物(TSM)和叶绿素a(Chl-a)浓度的空间插值结果进行分析。研究结果表明:CTD观测数据与水样分析数据呈较强线性相关关系。反距离权重插值对TSM和Chl-a浓度空间分布具有整体最优的效果。TSM浓度在近岸和近海底较高,在观测区域内出现两个高值中心;Chl-a浓度在近岸海域较高,有较明显的片状高值结构,垂向上表层较高。TSM与Chl-a浓度分布在长江口南北表现出不同的特征,且两者具有一定的负相关性。长江径流、外海洋流、潮汐混合等水动力过程是影响该区域TSM和Chl-a浓度分布的主要因素。

冬、夏季长江口海域二甲基硫化物的时空分布及对海水酸化和铁添加的响应

本文于2022年2和7月测定了长江口及其邻近海域表层海水及重要断面海水中的二甲基硫(Dimethylsulfide, DMS)、二甲基巯基丙酸内盐(Dimethylsulfoniopropionate, DMSP)浓度;基于DMS生产速率、消耗速率和溶解态DMSP(DMSPd)降解速率,综合评价了DMS的迁移转化速率,并通过船基培养实验探究了二甲基硫化物对海水酸化和Fe添加的响应。结果表明:冬季长江口海域DMS、DMSPd、颗粒态DMSP(DMSPp)平均浓度分别为(1.55±0.96)、(3.55±2.38)和(4.42±3.11) nmol·L^(-1);夏季分别为(8.45±5.76)、(18.90±6.86)和(22.41±15.99) nmol·L^(-1)。冬、夏两季长江口二甲基硫化物高浓度主要出现在远岸,垂直方向上呈现出表层到底层逐渐降低的变化特征。冬季和夏季的DMS海气通量分别为2.23和22.96μmol·m^(-2)·d^(-1)。夏季DMSPd的转化率和DMS生物产率高于冬季,使得夏季DMS浓度较高。微生物消耗是长江口海域DMS的主要去除途径。船基培养实验表明,在pH=7.7、7.9条件下,海水酸化抑制了DMS和DMSP的产生,而Fe的添加促进了它们的释放。因此,未来海水酸化和Fe的输入会对长江口DMS的生物地球化学循环产生重要影响。

长江口及其邻近海域表层水中溶解Mn浓度的季节变化特征

锰(Mn)是海洋中的生命必需痕量元素。河口位于河流和海洋的交界区域,其对Mn的改造作用会影响陆源Mn向海输送的生物地球化学过程。本研究使用自动固相萃取−电感耦合等离子体联用技术对2019年9月(秋季)、2021年3月(春季)和2021年7月(夏季)长江口及其邻近水域的表层溶解Mn浓度进行了测定和分析。结果显示,溶解Mn的平均浓度和河口行为表现出了季节性差异:夏季的溶解Mn浓度最高,表现为先移除后添加的分布特征;秋季的溶解Mn浓度次之,表现为添加型分布;春季的溶解Mn浓度最低,表现为保守型分布。显著性分析结果表明,长江携带的溶解Mn仅在淡水端元浓度值较高的季节会显著影响长江口及其邻近水域溶解Mn的分布;当长江淡水端元浓度值较低时,长江口溶解Mn则受多种生物地球化学过程的共同主导。长江口的中低盐度海水中高悬浮颗粒物浓度是造成该区域溶解Mn移除的重要因素,而高盐度海水中溶解Mn的添加机制则有待进一步研究。

秋季长江口及邻近海域有色溶解有机物的分布及河口混合行为

【目的】探究秋季长江口及邻近海域有色溶解有机物(chromophoric dissolved organic matter,CDOM)的分布特征与河口混合行为及影响CDOM分布的因素,以深入了解本研究区域CDOM动态变化机制。【方法】测定研究海域溶解有机碳(dissolved organic carbon,DOC)质量浓度、吸收系数a(350)等参数,分析CDOM含量水平;使用三维荧光光谱-平行因子分析(EEMs-PARAFAC)技术鉴别研究海域CDOM荧光组分。运用物理稀释模型分析CDOM河口混合行为。【结果】研究海域b-a4断面DOC质量浓度的变化范围为0.92~2.36 mg·L^(-1),c-a6断面DOC质量浓度的变化范围为1.00~2.40 mg·L^(-1)。b-a4断面a(350)的变化范围为0.22~1.60 m^(-1),c-a6断面a(350)的变化范围为0.15~1.42 m^(-1)。b-a4断面光谱斜率S275-295的变化范围为0.014~0.022 nm^(-1),c-a6断面S275-295的变化范围为0.016~0.024 nm^(-1)。鉴定出4个荧光组分:类腐殖质组分C1(激发波长265 nm、发射波长445 nm)、类蛋白质组分C2(275、325 nm)、类腐殖质组分C3(245、390 nm)和类蛋白质组分C4(235、340 nm)。【结论】长江口及邻近海域DOC质量浓度和a(350)均呈现出由长江口内向口外逐渐减小的趋势,陆源输入是影响CDOM分布的主要因素;远岸S275-295值高于近岸,主要受浮游生物生产活动的影响,陆源输入影响小;4个荧光组分的高值都出现在河口处,且随离岸距离增加而降低,这是受到陆源输入的影响;两个断面的4个荧光组分均符合理论稀释线,CDOM整体呈现保守混合行为。

Effects of sea level rise on storm surge and waves within the Yangtze River Estuary

Sea level rise (SLR) can cause water depth increase (WDI) and coastal inundation (CI).By applying the coupled FVCOM + SWAN model,this study investigates the potential impacts of WDI and CI,induced by a 1.0 m SLR,on storm surge and waves within the Yangtze River Estuary.A 1.0 m WDI decreases the maximum storm surge by 0.15 m and increases the maximum significant wave height by 0.35 m.The CI effect size is smaller when compared with WDI.CI decreases the maximum storm surge and significant wave height by 0.04 and 0.07 m,respectively.In the near-shore area,WDI significantly alters the local hydrodynamic environment,thereby stimulating changes in maximum storm surges and wave heights.Low-lying regions are negatively impacted by CI.Conversely,in deep-water areas,the relative change in water depth is minimal and the effect of CI is gradually enhanced.The combined effect of WDI and CI decreases the maximum surge by 0.31 m and increases the maximum significant wave height by 0.21 m.As a result,CI may be neglected when designing deep-water infrastructures.Nonetheless,the complex interactions between adoption and neglect of CI should be simulated to achieve the best seawall flood control standards and design parameters.

粤港澳大湾区近海中小型浮游动物分布特征及影响因素

为阐明粤港澳大湾区近海水文动力和人为活动引起的环境变化对浮游动物群落结构的影响,于2019年7月(夏季)和2020年12月(冬季)在粤港澳大湾区近海珠江口、大亚湾、黄茅海三个断面进行浮游动物采样,比较分析中小型浮游动物的群落特征,并探讨引起其季节和区域差异的影响因素。调查海域共鉴定中小型浮游动物211种(包括浮游幼虫),其中桡足类占总种数的42.18%,浮游动物的多样性、丰度呈现明显的季节和区域差异。浮游动物种数和平均丰度均为夏季高于冬季,远岸海域物种多样性高于近岸。浮游动物丰度高值区在两个季节均位于珠江口咸淡水交汇区域;夏季河口水域的平均丰度高于大亚湾水域的,冬季丰度分布无明显差异。聚类分析结果显示,调查海域夏季整体分为河口、海湾、远岸3个类群,珠江口水域受径流影响较大,与大亚湾之间群落结构差异明显;而冬季河口与海湾近岸水域群落结构差异不明显。强额孔雀哲水蚤(Parvocalanus crassirostris)、短角长腹剑水蚤(Oithona brevicornis)在夏季和冬季均为优势种,厦门矮隆哲水蚤(Bestiolina amoyensis)、中华异水蚤(Acartiella sinensis)、简长腹剑水蚤(Oithona simplex)等为夏季优势种,小拟哲水蚤(Paracalanus parvus)等为冬季优势种。Pearson相关性分析与冗余分析表明大湾区近海浮游动物丰度与温度、盐度、叶绿素a浓度及营养物质的关系存在种间、季节和区域差异,表明湾区复杂的水体环境条件对中小型浮游动物群落结构存在潜在影响。

长江口及邻近海域现代生物扰动构造定量表征及影响因素

生物扰动构造是表征海底环境状态的重要指标,是古沉积环境重建的主要依据,且它影响沉积物早期成岩作用以及物质的再分配,成为百年尺度沉积记录解读的干扰因素。本文基于长江口及其邻近海域的21个站位的沉积物岩心,利用高分辨X射线计算机断层扫描技术,通过matlab的数据处理,定性和定量表征了该区生物扰动构造,分析了影响生物扰动构造的主要因素。研究表明:长江口及邻近海域生物扰动构造较为发育,从功能上划分为生物扩散构造、运输构造、交换构造和廓道扩散构造4种类型,运输构造和廓道扩散构造常见;生物扰动构造在岩心中分布形式多样,包括指数衰减型、波动衰减型、均匀分布型、脉冲分布型等垂向分布形式;扰动深度深浅不一,多数在20cm以内,但也有超过40cm者;生物扰动构造空间上不均一,长江口及内陆架较发育,扰动构造体积在0~13972mm^(3)之间,而苏北沿岸、中陆架则较少,扰动构造体积在351~3212mm^(3)之间,从岸向外生物扰动构造有减少趋势。生物扰动构造发育程度主要受底质类型、沉积速率制约,黏土质粉砂以及适宜的沉积速率(0.52~1.34cm/a)有利于生物扰动构造发育和保存。