Stability of the Stratification of Water Bodies in the North Passage of the Yangtze River Estuary Based on the EFDC Model

To study the stratified stability of a water column in the North Passage of the Yangtze River Estuary,a numerical model of the hydrodynamics of this estuary is established using the EFDC model.On the basis of EFDC results,this paper derives and pro-vides the discriminative index of water body stability caused by salinity and analyzes the along-range variation in water body strati-fication stability in the North Passage of the Yangtze River Estuary and the periodic variation at a key location(bend area)based on the simulation results of the numerical model.This work shows that the water body in the bend area varies between mixed and strati-fied types,and the vertical average flow velocity has a good negative correlation with the differential velocity between the surface and bottom layers of the water body.The model simulation results validate the formulae for the stratified stability discriminant during spring tides.

Variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang(Yangtze River) Estuary

Dissolved inorganic nutrient elements were analyzed from the samples collected in the South Passage of the Changjiang (Yangtze River) Estuary in March 2003, including NH4+, NO3-, NO2- and PO43-. The water samples were collected with a Niskin sampler hourly at the near-surface, middle and near-bottom depths at the three stations -A1, A2 and A3-during two complete tidal cycles of neap tide and spring tide. Results showed that 1) the concentrations of NH4+, NO3- and NO2- were a little higher respectively during the neap tide than those during the spring tide, while PO43- showed an opposite trend, and each was higher in the ebb tide than in the flood tide, either for the neap tidal cycle or the spring tidal cycle; 2) higher stratification of the nutrients existed obviously in this area, with the concentrations of which increased from the bottom to the surface, especially for NH4+ and NO3-; 3) the coefficient of variation (C.V.) values of all dissolved inorganic nutrients varied from 4.06% to 36.8% beyond different influences of the tidal current and Changjiang runoff; 4) with increasing suspended matter in the water column, the concentrations of PO43- became lower in the filtered water; and 5) the total transport of each tidal cycle was much more in the spring tide than in the neap tide, and the positive values indicated that the nutrients had been exported to the East China Sea. Studies on the variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang Estuary will provide the scientific basis for the study of the mechanism of red tide in the East China Sea.

In-Situ Observation of Fluid Mud in the North Passage of Yangtze Estuary, China

Observations of fluid mud were made in the lower North Passage of the Yangtze Estuary in February 2000, on 10～11 August 2000, on 30～31 August 2000 (after two strong typhoons), on 21～24 August 2000 (neap tide) and on 3～6 September 2000 (mean tide) respectively. In situ data show that the fluid mud in this area consists of fine cohesive sediment (median size 7.23 μm). The formation and movement of fluid mud varied during the neap-spring and flood-ebb tidal cycle. Observations suggest that fluid mud phenomena in this area may be categorised in a three-fold manner as slack water, storm and saltwedge features. The thickness of the fluid mud layer of slack water during the neap tide ranged from 0.2 to 0.96 m, whereas during the mean tide, the thickness ranged from 0.17 to 0.73 m, and the thickness of the fluid mud layer was larger during slack water than at the flood peak. Shoals cover an area of 800 km2 with a water depth smaller than 5 m. Erosion of these extensive intertidal mudflats due to storm action provides an abundant sediment source. This is particularly significant in this estuary when the tidal level is lower than 5 m. The lower North Passage is a typical zone of saltwater wedging, so the saltwedge fluid mud has the most extensive spatial range in the estuary.

Morphological Evolution and Its Response to the Navigational Improvements in the North Passage,Yangtze Estuary

By use of bathymetric chart, recent change of the riverbed in the North Passage of the Yangtze Estuary has been studied in this paper. The main channel of the upper, middle and lower （section） in the North Passage has been successively eroded and its groin field significantly deposited. At the same time, sediment has been deposited on the entrance region. Erosion and deposition had responded rapidly to the construction of the regulation engineering. There was about one year duration of lagging between erosion in the deep channel and the construction of the regulation engineering. The siltation lag of time in the groin field varied with the initial depth, but the average deposited thickness was about 0.5 m per year. Volumetric analysis demonstrates that there is a increasing trend of siltation in the North Passage after 2002, because of the difference in duration and quantity between erosion in the deep channel and deposition in the groin field. The water volume of the North Passage was reduced by =9% （280 million m^3） between 2002 and 2006. Sediment budget reveals that the main sediment deposited in the North Passage takes its source from the river and the ocean. The decreasing water volume was attributable to shoaling in the groin field. Its triggering factors for increased sedimentation are the navigational improvements（jetties and groins） after 1998, which altered the passage boundary and destroyed the equilibrium state on the average ebb and flood sediment fluxes. The establishment of a stable estuary is attributed to a reduction in depth of the groin field. The forecast on the sediment deposition quantity and continuous infilling time in the groin system is about 325 × 10^6m^3 and 6 - 7 years, respectively.

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.

Spatial distribution and deposition history of nonylphenol and bisphenol A in sediments from the Changjiang River(Yangtze River) Estuary and its adjacent East China Sea

Nonylphenol（NP） and bisphenol A（BPA） are endocrine disruptors causing harmful effects including feminization and carcinogenesis to various organisms,and consequently,their contamination in natural environment has received wide concerns.This study reports the distribution characteristics of NP and BPA in surface sediments and their deposition history based on a dated sediment core in the Changjiang River（Yangtze River） Estuary and its adjacent East China Sea.The contents of NP and BPA in surface sediments ranged from 1.56-35.8 and 0.72-13.2 ng/g（dry mass）,respectively,with high values recorded in the two mud zones,the Changjiang River Estuarine Mud Zone and the Zhejiang Coastal Mud Zone.High values in the Zhejiang Coastal Mud Zone suggest the possibility of long distance transport of both contaminants through the Changjiang riverine plume.The contents were not correlated with the distance from the pollution source,indicating other factors including particle deposition rate and sediment grain size obviously affecting the distribution pattern.NP was also detected in a sediment core at layers deposited from the year of 1971 to 2001 with contents of up to 20.9 ng/g（dry mass）.The deposition fluxes of NP varied from 0.68 to 17.9 ng/（cm^2 · a） with peaks and valleys reflecting the traces of economic development history in China during the previous three decades.BPA was detected at sediment layers deposited from 1973 to 2001 with contents of up to 3.66 ng/g.The fluxes of BPA varied from 0.62 to 3.13 ng/（cm^2 · a） showing a similar pattern as NP.The contents of NP and BPA also indicated potential risks on benthic organisms in the study area.

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.

The environment effect on fish assemblage structure in waters adjacent to the Changjiang(Yangtze) River estuary(1998-2001)

We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors.We used a multivariate analysis,including community ordination methods such as detrended correspondence analysis(DCA) and canonical correspondence analysis(CCA),and two-way indicator species analysis(TWINSPAN).We analyzed the biological community structure and environmental factors to determine their spatial distributions,temporal dynamics,and seasonal variations.Among the fish species,five exceeded 5% of the total abundance:Harpodon nehereus(42.82%),Benthosema pterotum(13.85%),Setipinna taty(11.64%),Thryssa kammalensis(9.17%) and Apogonichthys lineatus(6.49%).These were separated into four ecological assemblages:hypsithermal-saline,hypsithermal-brackish,hypothermal-brackish,and hypothermal-saline.We evaluated the degree of influence of environmental factors on the fish community.Our analyses suggested that environmental factors including water depth,salinity,turbidity,transparency,nutrient,and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas.Ecological and environmental factors changed temporally from 1998 to 2001,and drove the fish community succession.The environmental factors driving the fish community structure included bottom temperature,water depth,bottom and surface pH,surface total phosphorous,and bottom dissolved oxygen.This investigation was completed before completion of the Three Gorges Dam;therefore the results of this study provide an important foundation for evaluating the influence of the human activities.

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.

Grain size composition and transport of sedimentary organic carbon in the Changjiang River(Yangtze River) Estuary and Hangzhou Bay and their adjacent waters

Surface sediments from the Changjiang River （Yangtze River） Estuary, Hangzhou Bay, and their adjacent waters were analyzed for their grain size distribution, organic carbon （OC） concentration, and stable carbon isotope composition （δ13C）. Based on this analysis, about 36 surface sediment samples were selected from various environments and separated into sand （〉0.250 ram, 0.125-0.250 ram, 0.063-0.125 mm） and silt （0.025-0.063 mm） fractions by wet-sieving fractionation methods, and further into silt- （0.004-0.025 mm） and clay-sized （〈0.004 mm） fractions by centrifugal fractionation. Sediments of six grain size categories were analyzed for their OC and 613C contents to explore the grain size composition and transport paths of sedimentary OC in the study area. From fine to coarse fractions, the OC content was 1.18%, 0.51%, 0.46%, 0.42%, 0.99%, and 0.48%, respectively, while the δ13C was -21.64‰, -22.03‰, -22.52‰, -22.46‰, -22.36‰, and -22.28%0, respectively. In each size category, the OC contribution was 42.96%, 26.06%, 9.82%, 5.75%, 7.09%, and 8.33%, respectively. The OC content in clay and fine silt fractions （〈0.025 ram） was about 69.02%. High OC concentrations were mainly found in offshore modern sediments in the northeast of the Changjiang River Estuary, in modern sediments in the lower estuary of the Changjiang River and Hangzhou Bay, and in Cyclonic Eddy modern sediments to the southwest of the Cheju Island. Integrating the distribution of terrestrial OC content of each grain size category with the δ13C of the bulk sediment indicated that the terrestrial organic material in the Changjiang River Estuary was transported seaward and dispersed to the Cyclonic Eddy modern sediments to the southwest of the Cheju Island via two pathways： one was a result of the Changjiang River Diluted Water （CDW） northeastward extending branch driven by the North Jiangsu Coastal Current and the Yellow Sea Coastal Current, while the other one was the result of the CDW southward extending branch driven by the Taiwan Warm Current.

Size-fractionated phytoplankton biomass in autumn of the Changjiang(Yangtze) River Estuary and its adjacent waters after the Three Gorges Dam construction

A cruise was undertaken from 3rd to 8th November 2004 in Changjiang(Yangtze) River Estuary and its adjacent waters to investigate the spatial biomass distribution and size composition of phytoplankton.Chlorophyll-a(Chl-a) concentration ranged 0.42-1.17 μg L-1 and 0.41-10.43 μg L-1 inside and outside the river mouth,with the mean value 0.73 μg L-1 and 1.86 μg L-1,respectively.Compared with the Chl-a concentration in summer of 2004,the mean value was much lower inside,and a little higher outside the river mouth.The maximal Chl-a was 10.43 μg L-1 at station 18(122.67°E,31.25°N),and the region of high Chl-a concentration was observed in the central survey area between 122.5°E and 123.0°E.In the stations located east of 122.5°E,Chl-a concentration was generally high in the upper layers above 5 m due to water stratification.In the survey area,the average Chl-a in sizes of >20 μm and <20 μm was 0.28 μg L-1 and 1.40 μg L-1,respectively.High Chl-a concentration of <20 μm size-fraction indicated that the nanophytoplankton and picophytoplankton contributed the most to the biomass of phytoplankton.Skeletonema costatum,Prorocentrum micans and Scrippsiella trochoidea were the dominant species in surface water.The spatial distribution of cell abundance of phytoplankton was patchy and did not agree well with that of Chl-a,as the cell abundance could not distinguish the differences in shape and size of phytoplankton cells.Nitrate and silicate behaved conservatively,but the former could probably be the limitation factor to algal biomass at offshore stations.The distribution of phosphate scattered considerably,and its relation to the phytoplankton biomass was complicated.

Assessment of trophic status in Changjiang (Yangtze) River estuary

The integrated methodology for the assessment of estuarine trophic status (ASSETS), which was extended and refined from the United States National Estuarine Eutrophication Assessment (NEEA), is a multi-parameter assessment system and has been widely used in eutrophication assessment in estuarine and coastal waters. The ASSETS was applied to evaluate the trophic status of the Changjiang (Yangtze) River estuary, one of the largest estuaries in the world. The following main results were obtained: (i) The estuarine export potential is "moderate susceptibility" due to the "moderate" dilution potential and "moderate" flushing potential; (ii) The overall human influence (OHI) index classified the impact of nutrients in the system as "high" due to the high level of nutrient discharge by the river which channels anthropogenic impacts in the catchments to the estuarine system; (iii) The overall eutrophic condition (OEC) in the estuary was classified into the "high" category due to frequent occurrence of nuisance and toxic algal blooms in the mixing and seawater zones; (iv) Since the nutrient loadings (e.g., DIN) in the river is expected to continue to increase in the near future following the population increase and rapid economic growth throughout the drainage basin, the nutrient-related symptoms in the estuary are likely to substantially worsen, which leads to the "worsen high" category for the definition of future outlook (DFO). The combinations of the three components (i.e., OHI, OEC, and DFO) lead to an overall grade as "bad" for the trophic status in the Changjiang River estuary.

Approach of moving boundary and its application in 3D tidal current simulation of Changjiang (Yangtze) River Estuary based on ECOMSED model

Considering three-dimensional model ECOMSED can not simulate wetting-drying of shoal with its fixed boundary, an approach to represent moving boundary in the model is introduced here. This approach smoothly joints the internal and external mode by making use of wetting and drying technique and is verified by a numerical test which presents a good agreement with the previous test results obtained by other researchers. A three dimensional numerical model is established to simulate the hydrodynamics in spring tide in the Changjiang （Yangtze） River estuary by this modified ECOMSED model which is also validated through the observed field data, the simulation presents a good periodic tidal change. It also successfully simulates the tidal current of computational areas and reproduces the tidal flat intermittent appearance.

Spatial distribution and diurnal variation of chemical oxygen demand at the beginning of the rainy season in the Changjiang (Yangtze) River Estuary

A field observation was carried out in the Changjiang (Yangtze) River Estuary from May 19 to 26, 2003. A total of 29 stations, including 2 anchored stations, were occupied through almost the whole salinity gradient. Based on the observation data, biogeochemistry of chemical oxygen demand (COD) was examined. Spatial distribution pattern of COD shows that it decreased downstream. The COD concentration varied generally within a narrow range of 1.24–1.60 mg/L in the zone around the river mouth, beyond which it decreased rapidly to 0.20 mg/L. In the mixed water zone, the fluctuation in COD was smaller at 2 m above the bottom layer than at the surface layer in 48 h. In the seawater zone, the 48-h fluctuation at the surface was the largest, followed by that of 5 m below the surface and 2 m above the bottom layers in a range of from 2.50 to 0.55 mg/L. Freshwater discharge was the dominant source of COD in the estuary. The average COD beyond the river mouth was 2.7 mg/L, which accorded with the Chinese seawater quality Grade I. Relationships between dissolved oxygen and biogeochemical parameters such as suspended particulate matter, dissolved organic matter and chlorophyll-a were also discussed.

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.

Analysis of the characteristics of offshore currents in the Changjiang(Yangtze River) estuarine waters based on buoy observations

A buoy of 10 m in diameter was used to record the current speed and direction in a vertical profile in the offshore area of the Changjiang（Yangtze River） Estuary（with an average water depth of 46.0 m） for one year.The results include：（1） the currents rotate clockwise and the current direction is consistent in a vertical profile without clear seasonal variations.（2） The horizontal current speeds are generally high,with a maximum of 128.5 cm/s occurring in summer and 105.5 cm/s appearing in winter commonly close to the surface.The average current speeds in the vertical profile fall in the same range（the differences are less than 8.0 cm/s）,with the maximum of47.0 cm/s occurring in summer and 40.8 cm/s in winter.The average current speed during spring tides is twice that during neap tides（26.5 cm/s）.（3） Significant differences of speeds are observed in the vertical profile.The maximum current speed occurs at either surface（spring and winter） or sub-surface（summer and autumn）,with the minimum current speed appearing at the bottom.The maximum average current speed of all layers is 57.9cm/s,which occurs in the 18-m layer during summer.（4） The average speed of the residual currents ranges from7.5 cm/s to 11.3 cm/s,with the strongest occurring in spring and weakest in winter.The residual currents of all layers are eastward during spring and winter,whereas northeastward or northward during summer and autumn.（5） The currents in the offshore of Changjiang Estuary are impacted collectively by diluted Changjiang River discharge,the Taiwan Warm Current,monsoon and tides.

Numerical simulation of the transport and diffusion of dissolved pollutants in the Changjiang (Yangtze) River estuary

Based on a coupled hydrodynamic–ecological model for regional and shelf seas (COHERENS), a three-dimensional baroclinic model for the Changjiang (Yangtze) River estuary and the adjacent sea area was established using the sigma-coordinate in the vertical direction and spherical coordinate in the horizontal direction. In the study, changing-grid technology and the "dry-wet" method were designed to deal with the moving boundary. The minimum water depth limit condition was introduced for numerical simulation stability and to avoid producing negative depths in the shallow water areas. Using the Eulerian transport approaches included in COHERENS for the advection and dispersion of dissolved pollutants, numerical simulation of dissolved pollutant transport and diffusion in the Changjiang River estuary were carried out. The mass centre track of dissolved pollutants released from outlets in the south branch of the Changjiang River estuary water course has the characteristic of reverse current motion in the inner water course and clockwise motion offshore. In the transition area, water transport is a combination of the two types of motion. In a sewage-discharge numerical experiment, it is found that there are mainly two kinds of pollution distribution forms: one is a single nuclear structure and the other is a double nuclear (dinuclear) structure in the turbid zone of the Changjiang River estuary. The rate of expansion of the dissolved pollutant distribution decreased gradually. The results of the numerical experiment indicate that the maximum turbid zone of the Changjiang River estuary is also the zone enriched with pollutants. Backward pollutant flow occurs in the north branch of the estuary, which is similar to the backward salt water flow, and the backward flow of pollutants released upstream is more obvious.

Benthic nutrient fluxes in the intertidal flat within the Changjiang (Yangtze River) Estuary

In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang (Yangtze River) Estuary. Except for NH4+, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrifica- tion rates, that utilizing NO3- transported from overlying water (DW) in Dongtan sediments, were estimated to be from -16 to 193 μmol·h-1·m-2 with an average value of 63 μmol·h-1·m-2 (n=18). These estimated values are still un- derestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3- production via nitrification.

Recent changing patterns of the Changjiang(Yangtze River) Estuary caused by human activities

To evaluate the controlling factors for coastline change of the Changjiang（Yangtze River） Estuary since 1974,we extracted the mean high tide line from multi-temporal remote sensing images that span from 1974 to 2014 at 2-year intervals.We chose 42 scenes to constrain the changing pattern of the Changjiang Estuary coastline,and implemented GIS technology to analyze the area change of the Changjiang（Yangtze） Subaerial Delta.Runoff,sediment discharge and coastal engineering were withal considered in the analysis of the coastline changes.The coastline has transgressed seaward since 1974,and a part of it presents inter-annual variations.The area of the Changjiang Subaerial Delta increased by 871 km2,with a net accretion rate of 21.8 km2/a.Based on the change of sediment discharge due to the major projects in the Changjiang River Basin,we divided the changing pattern of the coastline into three stages：the slow accretion stage（1974–1986）,the moderate accretion stage（1987–2002）,and the rapid accretion stage（2003–2014）.Liner regression analysis illustrated that there is a significantly positive correlation between the area changes and sediment discharge in the Chongming Eastern Shoal and Jiuduansha.This suggested that sediment load has a fundamental effect on the evolution of the Changjiang Estuary.Construction of Deep Waterway in the North Passage of the Changjiang River（1998–2010） led to a rapid accretion in the Hengsha Eastern Shoal and Jiuduansha by influencing the hydrodynamics in North Passage.Coastal engineering such as reclamation and harbor construction can also change the morphology of the Changjiang Estuary.We defined a contribution rate of area change to assess the impact of reclamation on the evolution of Changjiang Estuary.It turned out that more than 45.3% of area increment of the Changjiang Estuary was attributed to reclamation.

Carbon biomass,production rates and export flux of copepods fecal pellets in the Changjiang(Yangtze) River estuary

Copepod fecal pellets are ubiquitous throughout the oceans. Their production and export can represent a highly efficient pathway of carbon export. However, the role these fecal pellets play in carbon export in the Changjiang(Yangtze) River estuary is not well known. Two cruises were carried out in the Changjiang estuary in the spring and summer of 2013, during which time carbon biomass, production, and export of copepod fecal pellets were studied. Spring and summer fecal pellet carbon biomass ranged 0.30–1.01 mg C/m^3(mean=0.56±0.20 mg C/m^3) and 0.31–1.18 mg C/m^3(mean=0.64±0.24 mg C/m^3), respectively, significantly lower than phytoplankton. At most stations, fecal pellet carbon biomass was higher in surface or subsurface layers than deeper layers. Production rates ranged 0.65–1.49 pellets/(ind.?h)(mean=1.02±0.27 pellets/(ind.?h)) in spring and 0.62–1.34 pellets/(ind.?h)(mean=0.98±0.22 pellets/(ind.?h)) in summer, within the range reported in previous studies. Higher production rates of fecal pellets occurred at stations with higher chlorophyll a concentrations, and production rates of copepods of size 500–1 000 μm greater than copepods >1 000 μm during both cruises. The potential export flux of fecal pellets was slightly higher in summer(mean=68.95±14.37 mg C/(m^2 ?d)) than spring(mean=52.08±11.33 mg C/(m^2 ?d)) owing to higher summer copepod abundances. To our knowledge, this study is the first of its kind in the Changjiang estuary, and it confirms the significant role of copepod fecal pellets in local carbon export.