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.

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 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 increased trends during the 1950s - 2000s.

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

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.

Simulating the responses of a low-trophic ecosystem in the East China Sea to decadal changes in nutrient load from the Changjiang(Yangtze) River

Using a three-dimensional coupled biophysical model,we simulated the responses of a lowtrophic ecosystem in the East China Sea(ECS)to long-term changes in nutrient load from the Changjiang(Yangtze)River over the period of 1960–2005.Two major factors aff ected changes in nutrient load:changes in river discharge and the concentration of nutrients in the river water.Increasing or decreasing Changjiang discharge induced different responses in the concentrations of nutrients,phytoplankton,and detritus in the ECS.Changes in dissolved inorganic nitrogen(DIN),silicate(SIL),phytoplankton,and detritus could be identified over a large area of the ECS shelf,but changes in dissolved inorganic phosphate(DIP)were limited to a small area close to the river mouth.The high DIN:DIP and SIL:DIP ratios in the river water were likely associated with the diff erent responses in DIN,DIP,and SIL.As DIP is a candidate limiting nutrient,perturbations in DIP resulting from changes in the Changjiang discharge are quickly consumed through primary production.It is interesting that an increase in the Changjiang discharge did not always lead to an increase in phytoplankton levels in the ECS.Phytoplankton decreases could be found in some areas close to the river mouth.A likely cause of the reduction in phytoplankton was a change in the hydrodynamic field associated with the river plume,although the present model is not suitable for examining the possibility in detail.Increases in DIN and DIP concentrations in the river water primarily led to increases in DIN,DIP,phytoplankton,and detritus levels in the ECS,whereas decreases in the SIL concentration in river water led to lower SIL concentrations in the ECS,indicating that SIL is not a limiting nutrient for photosynthesis,based on our model results from 1960 to 2005.In both of the above-mentioned cases,the sediment accumulation rate of detritus exhibited a large spatial variation near the river mouth,suggesting that core sample data should be carefully interpreted.

Laboratory Simulation on Phosphorus Releasing near the Water/Sediment Interface in the East China Sea off the Changjiang Estuary

Surface sediment samples taken from the East China Sea off the Changjiang estuary are used as raw materials for phosphorus releasing experiment. It is found that after being thoroughly mixed with seawater for about 10 minutes, phosphorus released from the sediments reaches its maximum value. Adsorption kinetics can be fitted with both Elovich equation and two-constant rate equation. The releasing amount is closely related to the composition of the sediments. Phosphorus release from silty and muddy sediment is higher than from that dominated by sandy composition. For the desorption reaction, iron-phosphorus (Fe-P) is the most active one, with a releasing ratio higher than other phosphorus forms, followed by absorbed-phosphorus (Ad-P) and organic bound phosphorus (OP). All of them can be referred to as bio-available phosphorus. The results demonstrate that phosphorus in sediments can be released into seawater under suitable hydrodynamic conditions, and have a great impact on the nutrition state and primary productivity of marine biosphere.

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.

Phosphorus forms in sediments of the East China Sea and its environmental significance

By means of SEDEX, ASPILA and XRF, depth-dependent changes of different phosphorus forms in sediment cores from specific areas of the offshore Changjiang Estuary (Yangtze Estuary) in 1998 were analyzed. Results show that contents of total phosphorus (TP), organic-phosphorus (OP) and iron-phosphorus (Fe-P) decreased down-core, while those of absorbed-phosphorus (Ad-P) and calcium-phosphorus (Ca-P) increased. The distribution tendency of detritus-phosphorus (De-P) is not obvious. Results also show that TP, Fe-P and OP contents at Meso station of the Changjiang Estuary and Hangzhou Bay are higher than that of the other stations. This suggests that the pollutants carried by the Changjiang and the Qiantang rivers from inland have affected the natural environment in offshore area. TP, Fe-P and OP contents of each station become higher from bottom to top, indicating the amount of the terrestrial pollutants carried by the two rivers has been enhanced since the last 30-50 years. Ad-P, Ca-P, Fe-P and OP are all active phosphorus in sediments, and their re-cycling in sediment is closely related to each other.

Characteristics of Suspended Sediment Concentrations over the Areas Adjacent to Changjiang River Estuary, the Summer of 1998

A major flood event occurred within the drainage basin of the Changjiang River in June-August, 1998. Survey over the East China Sea adjacent to the Changjiang River estuary shows that during the flood the turbid water (with a suspended sediment concentration of higher than 10 mg l-1) °°′reached 123E. Stratification of the concentration layers was present near 12215E, with the concentration in the bottom layer being 3 times that in the upper layer, in response to sediment °°settling processes. The concentration is the lowest in the area of 126E^127E, representing a characteristic of the Kuroshio water. Although there was some expansion of the turbid water extension compared with the winter situations with low freshwater discharges, the suspended sediment does not appear to disperse towards the northeast from the Changjiang River. Further, several secondary high suspended sediment concentration centers were present on the East China Sea continental shelf, which may result from resuspension of the seabed sediment or advection of seawater containing suspended matter. In order to understand the processes of fine-grained sediment transport/deposition and their impact on the flux of chemical constituents on the shelf, further studies on the hydrodynamics, temperature, salinity and nutrient characteristics are required.

Effects of dissolved oxygen and nutrients from the Kuroshio on hypoxia off the Changjiang River estuary

The intrusion of the Kuroshio into the East China Sea(ECS)aff ects the development of hypoxia off the Changjiang(Yangtze)River estuary;however,quantitative analysis of its impacts is lacking.In this study,the Regional Ocean Modeling Systems(ROMS)model coupled with the Carbon,Silicate and Nitrogen Ecosystem(CoSiNE)model was used to investigate the relative importance of dissolved oxygen(DO)and diff erent nutrients(silicate,nitrate,and phosphate)in the Kuroshio on hypoxia in the ECS.Results show that changes in DO concentrations in the Kuroshio modify the distribution and intensity of hypoxia through direct onshore transport by hydrodynamic processes.An increase in Kuroshio DO concentration by 25%or 50%would result in a decrease of the maximum hypoxia extent(MHE)in the ECS by 76%or 86%,respectively,while a 25%decrease in Kuroshio DO would increase the MHE by up to 219%.The contribution of DO in the Taiwan Strait is almost negligible.In contrast to Kuroshio DO,nutrients aff ect hypoxia in the ECS through onshore transport by hydrodynamic and biochemical processes.Changes in phosphate and nitrate concentrations by 25%in the Kuroshio would change the MHE by up to 30%and 18%,respectively,accompanied by apparent changes in surface chlorophyll-a concentrations.The eff ect of silicate on hypoxia is negligible because a 25%change in silicate concentrations in the Kuroshio would result in less than 1%change in the MHE.Our results reveal a hierarchical rank of importance for environmental variables in the Kuroshio(i.e.,DO>phosphate>nitrate>silicate)in modifying the development of hypoxia in the ECS.

Temporal and spatial distribution of dissolved copper,lead,zinc and cadmium in the Changjiang Estuary and its adjacent waters

Heavy metal concentrations were measured in the Changjiang Estuary and its adjacent waters. Results from a systematic survey in April 2002 to March 2003 indicate that the ranges of the concentrations of dissolved copper, lead, zinc and cadmium in the study waters are 1.01 - 6.86, 0. 10 - 0.39,3.17 - 9.12 and 0.011 - 0. 049 μg/dm^3 , respectively. Similar to zinc, the behavior of dissolved copper was essentially conservative, but high scatter has been observed for high salinity samples, which can be attributed to the decomposition or mineralization of organic matter by bacteria. Dissolved lead may have active behavior with an addition at high salinity. Overall concentrations of dissolved cadmium increase with salinity. The mean values of these dissolved metals calculated for the surface waters were higher than those for the middle and bottom ones. External inputs of dissolved heavy metals to the surface waters were the likely explanation for these higher values. The maximum seasonal average values of dissolved copper and zinc were found in summer, reflecting higher amounts of riverine input in this season. In contrast, the maximum seasonal average values of dissolved lead and copper were found in winter and the lowest ones in summer, respectively, which might be asso- ciated with a combination of low concentration with heterogeneous scavenging. Concentrations of these dissolved metals found for the Changjiang Estuary fall in the range observed for the other estuaries but are noticeably higher than those from uncontaminated rivers, except for cadmium. Compared with observations for the Changjiang Estuary in the last two decades, it is clear that the Changjiang estuarine waters has been contaminated with copper, lead, zinc and cadmium during China＇ s industrialization, but concentrations of them have decreased in the last few years.

Potential impacts of Three Gorges Dam in China on the ecosystem of East China Sea

The Changjiang River in China was dammed in 2003. The possible changes in matters fluxes from the river downstream after the completion of Three Gorges Dam and their potential impacts on the ecosystem of the East China Sea are discussed . The estuarine and coastal waters in the East China Sea were heavily fertilized by the inflow of nutrient-rich freshwater from the Changjiang River, which has led to severe eutrophication and frequent harmful algal blooms ,thus worsening the ecosystem health in this area. Analy- sis showed that the nutrient loadings are very likely to be reduced in the lower Changjiang River due to the construction of Three Gorges Dam. Especially for the total phosphorus, the discharges to the East China Sea will be reduced by one-third, which would relieve the severe eutrophication in this area. However, the expected decrease in the riverine silicate discharge would lead the ratio of silicon to nitrogen to be much less than 1 in the estuarine and coastal waters and thus may cause an elevation of flagellate growth. The changes in the annual water discharges and their seasonal distributions below the dam will be minor. Reduction of suspended particulate matter loading, due to the sedimentation behind the dam, will reduce the nutrient loadings of the particulate form especially for phosphorus, and decrease the turbidity of estuarine and coastal waters. On the other hand, this may enhance the erosion of the delta and the coasts as well as modifythe benthic ecosystem.

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.

Regulation of Water Masses to Hypoxia Zones in the Changjiang Estuary

The regulating ways of different water masses affecting the locations and intensities of hypoxia zones were studied based on the time-space continuum data from August 2011 to 2013–2017.The 6-year distribution of the hypoxic area in the Changjiang Estuary(CE)and its adjacent waters show that the hypoxic area can be divided into two segments.The southern segment is out of the south branch of the CE,whereas the northern segment is in the junction zone between the South Yellow Sea and the CE.The two segments were divided along the 31.5°–32°N latitude line.The northern and southern segments were dominated by the East China Sea shelf water(ECSSW)and Kuroshio subsurface water(KSW),respectively.When the KSW(salinity>34)intrusion reached the east of 123°E and south of 31°N,hypoxia zones mainly occurred in the southern segment covered by the Changjiang Diluted Water(CDW),meanwhile the Yellow Sea cold water mass may emerge in the northeastern area.When the KSW intensely invaded westward to the region between 122°and 122.5°E and northward to 31.5°N or further north,hypoxia zones appeared in the northern segment.The strength of the KSW with low dissolved oxygen concentration is the basic driving factor for the hypoxia occurrence in the CE.Moreover,the stratification is crucial for the southern segment,whereas the organic matter decomposition is dominated for the northern segment,even with severe hypoxia across the sea surface in the study area.

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.

Benthic microbial biogeography along the continental shelf shaped by substrates from the Changjiang River plume

Coastal zones are active reactors of continental material including that transported by rivers via a series of microbiota-mediated reactions. Nevertheless, current knowledge of the ecology and functioning of the microbiota in coastal areas affected by large riverine inputs remains insufficient on a global scale. Here, an investigation on sediment microbial composition, including taxonomy and metabolic network, as well as their relationship with major benthic reaction substrates, namely carbon, nitrogen, sulphur and phosphorus, was conducted in the continental shelf affected by the spread of the Changjiang River plume. Surface sediment samples(48 samples)were collected during March 2018, obtaining a mean Operational Taxonomic Units(OTUs) number of 3 341.Proteobacteria, Acidobacteria and Actinobacteria were abundant phyla in the studied sediments. Bray-Curtis distance analysis classified the 48 samples into 4 clusters(MG1 to MG4) at the phylum-level. MG1 and MG2 are found near the river mouth, receiving substantial land-derived particles from the Changjiang River runoff.Particle-attached microbes may be settled in these regions and influenced the observed sediment microbial diversity and biomass, e.g., increased Crenarchaeota relative abundance. The relative enrichment of these two groups in heterotrophic microbes further suggests a reliance of benthic microbiota on substrates with terrestrial origin, particularly specialized on processing sulphur-rich substrates. Regions MG3 and MG4 are located in the outer margin of the area affected by the Changjiang River plume, mainly fed by settling pelagic particles from phytoplankton. Compared to MG1 and MG2, a significant increase in the abundance of Thaumarcheota(phylumlevel) and Nitrosopumilus(genus-level) was found in MG3, suggesting nitrogen-related transformations as the key reactions to sustain microbial metabolism in this region. Coupled with the identified variations in the taxonomic composition, significant differences in the keystone taxa between MG1/MG2 and MG3/MG4 were identified via OTU co-occurrence analyses. A higher abundance of Actinobacteria, Thaumarchaeota and Acidobacteria in MG3 and MG4 reinforced the identified spatial variability in benthic metabolism and highlighted the significance of substrate inputs on the sediment microbial structure and biogeography.

长江口-东海陆架黏土中高活性铁的富集效应及环境控制机制

铁元素的化学相态分析是深入理解沉积物的来源、环境演化以及铁参与的生物地球化学循环的关键手段,但不同粒级沉积物中铁化学相态研究薄弱,制约了表生铁循环的研究认知。本文选择长江口-东海陆架表层沉积物,通过六步提取法分析沉积物全样及其黏土组分中总铁(FeT)、高活性铁(FeHR)、弱活性铁(Fe_(PR))和不活性铁(Fe_(U))的含量,含量均遵循Fe_(HR)>Fe_(PR)>Fe_(U)。全样中Fe_(T)和Fe_(HR)的含量与平均粒径、黏土、有机碳和铝含量密切相关,表明富含有机质的黏土矿物易于富集高活性铁;相较于全样,黏土组分中Fe_(HR)/Fe_(T)比值升高10%,而Fe_(PR)/Fe_(T)比值则降低10%,反映黏土组分对高活性铁的富集效应。河口动力环境基本控制沉积物中Fe的相态分布,长江口最大浑浊带沉积物全样中Fe_(T)和Fe_(HR)含量较高,且受粒度的影响显著;黏土组分可以显著消除粒度效应的影响,Fe_(T)和Fe_(HR)被大量截留在最大浑浊带前缘的河口低盐度区域;而在中高盐度的口外区域,Fe的来源相对稳定,主要为富Fe_(HR)的长江源和贫Fe_(HR)的陆架源沉积物混合。本研究揭示黏土组分在流域-河口-陆架的迁移可能主导了高活性Fe在陆海界面的分布和循环过程,这对深入理解入海颗粒态Fe的源汇过程、地球化学循环及其环境效应有重要参考价值。

长江口和东海内陆架黏土矿物与黏土粒级碎屑矿物构成及物源指示意义

黏土矿物以及黏土粒级碎屑矿物颗粒细小、搬运距离远,是进行长江口及浙闽内陆架泥质区多物源示踪的良好指标。本研究利用改进的黏土矿物XRD(X射线衍射分析)预处理方法,制作了供多面XRD衍射分析的方形样品,实现了部分黏土矿物种的鉴定,结合黏土粒级中碎屑矿物鉴定,探讨了长江口及内陆架沉积物来源。研究表明:长江口及内陆架表层沉积物中的黏土矿物种属包括伊利石(含2M1、2M2两个多型)、高岭石、珍珠陶土、斜绿泥石以及弹性绿泥石,非黏土矿物主要有石英、钾长石、斜长石、白云石、铁白云石、方解石以及硬石膏。依据黏土矿物、黏土粒级碎屑矿物空间分布差异把长江口及东海内陆架划分为两个物源区:长江口及内陆架北部物源区、内陆架南部物源区,前者受废黄河物质影响,后者受浙闽中小河流物质影响。本研究表明来自苏北废黄河的沉积物不仅跨过了长江冲淡水进入长江水下三角洲,而且一直向南达到浙闽泥质区的北部。

Environmental control of mesozooplankton community structure in the Hangzhou Bay, China

A quarterly study of mesozooplankton community structure and environmental variables in the Hangzhou Bay was conducted to examine the response of mesozooplankton community to the variation of water mass and environmental condition. The southeast coast of China is a typical region under the intensive influence of Asia monsoon and freshwater discharge from rivers. The water mass and environmental condition of the Hangzhou Bay, which were influenced by the interaction of currents, freshwater discharge of the Qiantang River and Changjiang River Plume, showed significant seasonal variation. Our results showed that both biomass and abundance were significantly higher in summer（（247.7±148.8） mg/m^3 and（350.9±215.6） ind./m^3, respectively）than those in other seasons. Four eco-geographical regions were divided based on the cluster analysis of zooplankton community of the Hangzhou Bay throughout the year, except for winter. Monsoon and the dissolved inorganic nitrogen（DIN） input from freshwater discharge of the Qiantang River and Changjiang River resulted in temporal and spatial variations of environmental gradient in the Hangzhou Bay, which significantly influenced the structure of mesozooplankton community. Redundancy analysis（RDA） indicated that the mesozooplankton community structure was strictly correlated with the DIN gradient, while salinity gradient showed a weak influence in the Hangzhou Bay.

长江口及邻近海域沉积物中四醚脂类的来源及其对底层溶解氧指示作用探究

甘油二烷基甘油四醚(glycerol dialkyl glycerol tetraethers,GDGTs)作为一种重要的膜脂化合物,广泛存在于海洋水体和沉积物中。基于GDGTs对温度的敏感性,TEX86(TetraEther indeX of tetraethers consisting of 86 carbons)指标被广泛用于海洋古温度重建。然而,研究表明GDGTs母源生物古菌也会受到环境中溶解氧(DO)变化的影响,进而影响其膜脂组成,但边缘海DO对GDGTs组成的影响仍不清楚。本文研究了夏季长江口及其邻近海域颗粒物与表层沉积物中GDGTs的含量与组成,探讨了表层沉积物中GDGTs的来源及其组成对底层DO的响应。结果表明,长江口及其邻近海域颗粒物GDGTs的含量随水深的增加而增加,同时表层沉积物中的GDGT-2/GDGT-3和GDGT-0/Cren比值均与底层颗粒物相近,表明沉积物中GDGTs主要来源于底层颗粒物的沉降输入。进一步对受陆源有机质输入影响较小的站位研究发现有机质来源BIT(Branched and Isoprenoid Tetractter)指标<0.2。研究发现,随着底层DO的降低,表层沉积物中GDGT-0/Cren比值与底层DO具有较好的正相关性(R2=0.57,P<0.01),提示GDGT-0/Cren具有指示夏季长江口及邻近海域底层DO变化的潜力。未来还需结合颗粒物与表层沉积物中古菌生物群落和完整极性GDGTs的分析,进一步阐明GDGTs指示DO的机制及适用性。