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.

Biogeochemistry of sedimentary organic matter in the Yongjiang River estuary in the southern part of Hangzhou Bay,China,since the Late Pleistocene

A sediment core(YJK19-02)collected from the southern outlet of Hangzhou Bay near the Yongjiang River estuary in East China was analyzed for grain size,lignin,bulk elemental composition,stable carbon isotope,and rare earth elements(REEs)to determine the sources and diagenesis of sedimentary organic matter(OM)of the estuary and adjacent areas since the Late Pleistocene.δ^(13)C values(-24.80‰–-23.60‰),total organic carbon/total nitrogen(TOC/TN)molar ratios(8.00–12.14),and light rare earth element/heavy rare earth element ratios(LREE/HREE=8.34–8.91)revealed the predominance of terrestrial sources of OM,mainly from the Changjiang(Yangtze)River.The lignin parameters of syringyl/vanillyl(S/V=0.20–0.73)and cinnamyl/vanillyl(C/V=0.03–0.19)ratios indicate the predominance of nonwoody angiosperms,and the vanillic acid/vanillin ratios[(Ad/Al)_(V)=0.32–1.57]indicate medium to high degrees of lignin degradation.An increasing trend ofΛ(total lignin in mg/100-mg OC)values from ca.14500 a BP to ca.11000 a BP reflected the increase in temperature during the Late Pleistocene.However,a time lag effect of temperature on vegetation abundance was also revealed.The relatively higher and stableΛvalues correspond to the higher temperature during the mid-Holocene from ca.8500 a BP to ca.4500 a BP.Λvalues decreased from ca.4000 a BP to the present,corresponding to historical temperature fluctuations during this time.Our results show that the vegetation abundance in the Yongjiang River Basin since the Late Pleistocene was related to the temperature fluctuation duo to climate change.

Semantic Segmentation of the Intertidal Zone of an Estuary—In Search of the Best Solution

An aerial photographic coverage acquired on two consecutive days in October 2021 with a ground resolution of 20 cm and a spectral resolution of 4 bands (red, green, blue and near infrared), allowed to distinguish most of the classes of interest present in the intertidal zone of the Sado estuary. We explored the possibilities of thematic classification in the powerful and complex software ArcGIS Pro;we presented the methodology used in a detailed way that allows others with minimal knowledge of GIS to reproduce the classification process without having to decipher the specifics of the software. The classification implemented used ground truth from four classes related to the macro-occupations of the area. In a first phase we explore the standard algorithms with object-based capabilities, like K-Nearest Neighbor, Random Trees Forest and Support Vector Machine, and in a second phase we proceed to test three deep learning classifiers that provide semantic segmentation: a U-Net configuration, a Pyramid Scene Parsing Network and DeepLabV3. The resulting classifications were quantitatively evaluated with a set of 500 control points in a test area of 37,500 × 12,500 pixels, using confusion matrices and resorting to Cohen’s kappa statistic and the concept of global accuracy, achieving a Kappa in the range [0.72, 0.81] and a global accuracy between 88.9% and 92.9%;the option U-Net had the most interesting results. This work establishes a methodology to provide a baseline for assessing future changes in the distribution of Sado estuarine habitats, which can be replicated in other wetland ecosystems for conservation and management purposes.

Three Dimensional Baroclinic Numerical Model for Simulating Fresh and Salt Water Mixing in the Yangtze Estuary

For simulating fresh and salt water mixing in estuaries, a three dimensional nonlinear baroclinic numerical model is developed, in which the gradients of horizontal pressure contain die gradient of barotropic pressure arising from the gradient of tidal level and the gradient of baroclinic pressure due to the gradient of salinity. The Eulerian-Lagrangian method is employed to descretize both the momentum equations of tidal motion and the equation of salt water diffusion so as to improve the computational stability and accuracy. The methods to provide the boundary conditions and the initial conditions are proposed, and the criterion for computational stability of the salinity fields is presented. The present model is used for modeling fresh and salt water mixing in the Yangtze Estuary. Computations show that the salinity distribution has the characteristics of partial mixing pattern, and that the present model is suitable for simulation of fresh and salt water mixing in the Yangtze Estuary.

Wave-current bottom shear stresses and sediment re-suspension in the mouth bar of the Modaomen Estuary during the dry season

On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.

Sediment Deposition and Resuspension in Mouth Bar Area of the Yangtze Estuary

A comprehensive analysis is conducted based on observations on topography, tidal current, salinity, suspended sediment and bed load during the years of 1982, 1983, 1988, 1989. 1996, and 1997 in the Yangtze Estuary. Results show that the deformation of tidal waves is distinct and the sand carrying capacity is large within the mouth bar due to strong tidal currents and large volume of incoming water and sediments. Owing to both temporal and spatial variation of tidal current, deposition and erosion ore extremely active. In general a change of up to 0.1 m of bottom sediments takes place during a tidal period. The maximum siltation and erosion are around 0.2 m in a spring to neap tides cycle. The riverbed is silted during flood when there is heavy sediment load, eroded during dry season when sediment lo:ld is low. The annual average depth of erosion anti siltation on the riverbed is around 0.6 m. In particular cases, it may increase to 1.4 m to 2.4 m at some locations.

Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

The long-term spatiotemporal changes of surface biogenic elements in the Changjiang River Estuary and adjacent waters during the summer of 2008–2016 were analyzed in this study.The concentrations of dissolved inorganic nitrogen(DIN),soluble reactive phosphate(PO_(4)^(3−))and silicate(SiO_(3)^(2−))were generally stable,with a slight decrease of DIN and PO_(4)^(3−),and a slight increase of SiO_(3)^(2−),which mainly occurred in the estuarine waters.The grey correlation analysis was carried out between biogenic elements and chlorophyll a(Chl-a).Results showed that compared with the absolute values of biogenic elements,the correlations between the concentration ratio of nitrogen to phosphorus(N/P),ratio of silicon to nitrogen(Si/N)and Chl-a were closer,indicating the important influence on phytoplankton by the structure of biogenic elements.The study area was generally in a state of potential P limitation,and could have potential impact on the phytoplankton community,triggering the shift of red tide dominant species from diatoms to dinoflagellates.

Morphometric relationships and reproductive maturation of the mudskipper, Periophthalmus barbarus from subsistence catches in the mangrove swamps of IMO estuary, Nigeria

From April 1992 and March 1993, morphometric characteristics and reproductive maturation were studied in Periophthalmus barbarus from subsistence catches in the mangrove swamps of Imo estuary. Morphometric equations for males and females at different stages of ovarian maturation are presented. Generally males were significantly heavier in weight than females, but the latter were heavier than the former of the same body length. Females with developing and mature ovaries were generally heavier than immature females of the same length. Analyses of the gonadosomatic index and percentage of mature males and females indicate all year\|round breeding such that: February\|May was spawning, June\|October postspawning and November to January recovery period. Fecundity varied between 900 and 23933 eggs per spawn and increased with fish size.

Trophic attributes of the mudskipper, Periophthalmus barbarus (Gobiidae: Oxudercinae) in the mangrove swamps of Imo River Estuary, Nigeria

Aspects of the trophic attributes of the mudskipper, Periophthalmus barbarus occurring in the mangrove swamps of Imo River Estuary, Nigeria, were investigated during a 12 month period (April, 1992\_March, 1993). Feeding intensity increased with size, it was higher in the dry season(November\_April) than in the wet season(May\_October), monthly changes in the indices of feeding intensity were significantly correlated. Major food objects comprised detritus and benthic algae; crustaceans, insects, macrophyte matter and sand grains were minor food objects while fish, molluscs, Chilopoda, nematodes and fungi were unconsciously devoured objects. Diet varied seasonally; algae and sesarmid crabs were generally more in the dry season than during the rains whereas FPOM and fish increased in the wet over dry season. The mudskipper display a high degree of euryphagy and can be considered as a generalist and an omnivore. The lower trophic status of P. barbarus qualifies it as a good aquaculture candidate. Food richness was higher in big sized class(BSC) than small sized class(SSC). Size based and seasonal variations were not apparent in food richness. Diet breadth was higher in the BSC than the SSC, there was dry season increase in diet breadth.

Regulation of Navigation Channel on Mouth Bar of Guanhe Estuary

-Based on the feasibility study of developing the navigation resources of the Guanhe River and the model test results of the mouth bar regulation, this paper presents some basic principles for the regulation of the channel on the mouth bar, for instance, the direction of navigation channel should be identical with that of the ebb tide current and the main waves, and perpendicular to the bathymetric contours. The principles for regulating mouth bars are also discussed in this paper.

Morphological evolution of a large sand bar in the Qiantang River Estuary of China since the 1960s

A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November since the 1960s,this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP)implemented in the last decades.The results show that three timescales,namely the seasonal,interannual and decadal timescales,can be distinguished for the sand bar evolution.The first two are related to the seasonal and interannual variations of river discharge.During high discharge seasons or years,erosion took place at the upper reach and sedimentation at the lower reach.Consequently,the bar apex shifted seaward.The opposite development took place during low discharge seasons or years.The decadal timescale is related to LRNP.Due to the implementation of LRNP,the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached;whereas the lower reach has been accumulated seriously and the accumulation still continues.Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established.Compared with the earlier stage of LRNP,the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m.The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.

Foraging habitat use of breeding barn swallow (<i>Hirundo rustica</i>) in farmland, estuary, and island

The decline of barn swallow populations may be mainly caused by the reduction of their foraging habitat. A clear understanding of the links between proportions of available and used microhabitats of foraging barn swallows in farmland, estuary, and island habitats would enhance our understanding of the foraging habitat requirements of this species and on the effects of anthropogenic activities, such as habitat conversion (e.g., land to water, crop fields to non-arable land), on their distribution. We hypothesized that: 1) foraging swallows would be more abundant in the most common microhabitat;and 2) swallow abundance would decrease with increased foraging distance from the nest-site. As predicted by our first hypothesis, swallows were more abundant in the most common microhabitat (i.e., crop fields in farmland and non-arable land on the island). Our data also support our second hypothesis that increased foraging distances from the nest-site negatively affected foraging swallow abundance. In summary, barn swallows foraged in the habitats most convenient to nest-sites, however, management of agricultural lands should include non-arable lands in the composition of available foraging microhabitats.

Seasonal implications for taxonomic sufficiency to simplify M-AMBI methodology in the coastal area adjacent to a eutrophic estuary

Taxonomic sufficiency(TS)refers to identifying taxa to a taxonomic level sufficient to detect community changes in stressed environments and may provide a cost-effective approach in routine monitoring programs.However,there is still limited information regarding the seasonal impact of applying TS and its implications for the ecological quality evaluation in the estuarine ecosystem.This study investigated the relationship between the multivariate-AZTI’s Marine Biotic Index(M-AMBI)and environmental variables in three seasons(i.e.,spring,summer,and autumn)in the Liaohe River Estuary.We tested the reliability of TS for simplifying the M-AMBI methodology.The results showed that family and genus level data could reproduce the spatial-temporal patterns of community structure at the species level.The M-AMBI values showed a consistent spatial distribution pattern in all sampling seasons,with a decreasing trend with the increasing distance from the estuary mouth.Both genus and family level data performed nearly as well as species level in detecting the seasonal variations of pollutants(i.e.,nutrients and total organic content).The family level M-AMBI was feasible to discern stress in the Liaohe River Estuary because of the high aggregation ratios at different taxonomic levels in all sampling seasons.These findings suggest that applying taxonomic sufficiency based on the M-AMBI provides an efficient approach for evaluating ecological quality in the Liaohe River Estuary.

Exploration of the Mechanisms for the Low Sensitivity of Deposition Flux to Upstream Sediment Reduction in the North Passage, Yangtze Estuary

Deltas are densely populated industrialized regions,and home to important ports and navigation channels.Due to human interferences,the Yangtze Estuary has experienced a significant reduction in sediment load caused by the Three Gorges Dam(TGD),as well as adjustment to local morphodynamics by the Deep-water Navigation Channel(DNC).While the dramatic reduction in sediment triggers the increased channel erosion,the deposition flux of the DNC located at the estuary mouth has little change.To explore the physical mechanism of this phenomenon,a two-dimensional model is used to establish the relationship between sediment load and the sediment budget of channels based on the bathymetry in 2016.Model results show that the tidal reach and the inner estuary have a negative sediment budget.And the seasonal characteristics of water and sediment fluxes become less obvious downstream.Sensitivity analysis shows that the influence of upstream sediment load on deposition flux decreases along the channel,with a transition from deposition to erosion occurring in the tidal reach.For the last-level bifurcation,the annual siltation of sediment in the North Passage(NP)decreases by 4.5%with low sensitivity.This is attributed to the reduction of sediment load partially mitigated by riverbed erosion and cascade bifurcations.In addition,the lateral sediment supply,which accounts for 68%of the sediment input in the NP,is stable.Overall,this study strengthens the understanding of the relationship between sediment load and artificially deepened systems,thus allowing for better management of estuarine sediment and navigation channel.

Microbiota of a seepage face at the mouth of a subterranean estuary:diversity,distribution and substrate dependence

Subterranean estuaries,i.e.,the mixing zone between terrestrial groundwater and recirculated seawater,host a wide range of microbiota.Here,field campaigns were conducted at the mouth of the subterranean estuary at the Sanggou Bay(Shandong Province,China)over four consecutive seasons at a seepage face(0−20 cm depth).The diversity of benthic microbiome was characterized via 16S rRNA gene sequencing and metagenomics,combined with physic-chemical parameters,e.g.,organic carbon,total nitrogen and sulfate contents in sediments.During spring,the dominant species were assigned to the phylum Proteobacteria.Important opportunistic species was assigned to Acidobacteria,Actinobacteria and Bacteroidetes.The key components were identified to be species of the genera Pseudoalteromonas,Colwellia and Sphingobium,indicating the involvement of sediment microbiota in the degradation of sedimentary organic carbon,particularly that of pelagic origin,e.g.,phytoplankton detritus and bivalve pseudo-feces.During spring,the microbial community was statistically similar along the depth profiles and among the three sampled stations.Similar spatial distributions were obtained in the remaining seasons.By contrast,the dominant species assemblages varied significantly among seasons,with key genera being Thioprofundum and Nitrosopumilus during summer and autumn and Thioprofundum and Ilumatobacter during winter.Network analysis revealed a seasonal shift in benthic nitrogen and sulfur metabolism associated with these variations in microbial community composition.Overall,our findings suggested that macro elements derived from pelagic inputs,particularly detrital phytoplankton,shaped the microbial community compositions at the seepage face,resulting in significant seasonal variations,while the influence of terrestrial materials transported by groundwater on the sediment microbiota at the seepage face found to be minor.

Potential Impacts of Exogenous Nitrogen Enrichment on Distribution and Transfer of Nitrogen in Plant-Soil System of Suaeda salsa Marsh in the Yellow River Estuary, China

To determine the potential impacts of exogenous nitrogen(N)enrichment on distribution and transfer of N in Suaeda salsa marsh in the Yellow River Estuary,the variations of N in plant-soil system during the growing season were investigated by field N addition experiment.The experiment included four treatments:NN(no N input treatment,0gNm^(−2) yr^(−1)),LN(low N input treatment,3.0 gNm^(−2) yr^(−1)),MN(medium N input treatment,6 gNm^(−2) yr^(−1))and HN(high N input treatment,12 gNm^(−2) yr^(−1)).Results showed that N additions generally increased the contents of total nitrogen(TN),ammonia nitrogen(NH_(4)^(+)-N)and nitrate nitrogen(NO_(3)^(−)-N)in different soil layers and the increasing trend was particularly evident in topsoil.Compared with the NN treatment,the average contents of TN in topsoil in the LN,MN and HN treatments during the growing season increased by 10.85%,30.14%and 43.98%,the mean contents of NH_(4)^(+)-N increased by 8.56%,6.96%and 14.34%,and the average contents of NO_(3)^(−)-N increased by 35.73%,45.99%and 46.66%,respectively.Although exogenous N import did not alter the temporal variation patterns of TN contents in organs,the N transfer and accumulation differed among tissues in different treatments.With increasing N import,both the N stocks in soil and plant showed increasing trend and the values in N addition treatments increased by 9.43%–38.22%and 13.40%–62.20%,respectively.It was worth noting that,compared with other treatments,the S.salsa in the MN treatments was very likely to have special response to N enrichment since not only the period of peak growth was prolonged by about 20 days but also the maximum of TN content in leaves was advanced by approximately one month.This paper found that,as N loading reached MN level in future,the growth rhythm of S.salsa and the accumulation and transference of N in its tissues would be altered significantly,which might generate great impact on the stability and health of S.salsa marsh ecosystem.

Seasonal metal fluxes derived by the interaction of surface water and groundwater in an aquaculture estuary

Submarine groundwater discharge(SGD)plays a major role as a conveyor of metals to coastal waters.However,the seasonal change of metal fluxes derived through SGD is unclear.Here,we evaluated the behaviours and fluxes of trace metals(Mn,Fe,Ba,Pb,U,Cr,Zn,Cu)in an estuary under different seasonal conditions.The behaviours of trace metals revealed that SGD was the source of Mn(3.51 mmol/(m^(2)·d)),Fe(0.174 mmol/(m^(2)·d))and Ba(0.024 mmol/(m^(2)·d)),but the Cu sink(−0.55μmol/(m^(2)·d))and other metals exhibited a seasonal source‒sink conversion.The seasonal variation of dissolved organic matter and the fresh groundwater proportion in subterranean estuaries may have an important effect on metals fluxes especially for the Fe,Mn and Ba.Our result shows that the single seasonal metal fluxes estimation applied to the annual scale will cause a large deviation,up to 3.6 times for Fe,5.5 times for Mn,and 15 times for Ba.Therefore,the influence of seasonal fluctuations on SGDderived metal fluxes cannot be ignored,and our findings will be important for comprehending the metal budget and cycle in nearshore environment.

Distribution and Controlling Factors of Dissolved Gaseous Mercury and Reactive Mercury in Seawater Near Yangtze River Estuary

Complex hydrocultural conditions in the estuary affect the migration and transformation of mercury.Using two voyages in July and October 2018,Dissolved Gaseous Mercury(DGM)and Reactive Mercury(RHg)were determined to explore the source,transformation and influence of DGM content in the adjacent waters of Yangtze River Estuary in summer and autumn.The results showed the contents of DGM and RHg in summer were higher than those in autumn,and both of them were higher than those in open sea.In summer and autumn,the Yangtze River brought a higher concentration of DGM,and different flow direction and runoff resulted in differences in the high value region of the surface.The emergence of low-oxygen zones in summer was conducive to the production of DGM.In autumn,windy weather allowed seawater disturbances to promote the release of mercury from the underlying sediments,especially in shallow sea in northwest.RHg showed a higher concentration in the offshore than in the open sea in summer,but there was no such trend in autumn,reflecting the influence of less runoff input.DGM is the main product of RHg reduction,and there was a significant positive correlation between DGM and RHg in summer(r=0.356,P<0.05),while the correlation between DGM and RHg was not significant in autumn due to the influence of light intensity,wind speed and nutrients.The exchange flux of mercury in the adjacent waters of the Yangtze River Estuary was higher than that in the open sea.There was no significant difference of the release flux of mercury in summer and autumn.This article highlighted that the input of mercury from the Yangtze River runoff promotes the release of mercury in seawater,and the hypoxic zone caused by eutrophication is conducive to the production of DGM.

Diel,seasonal,and annual variations of fish assemblages in intertidal creeks of the Changjiang River estuary

The use patterns of salt marsh habitats by fish assemblages were investigated in two welldeveloped intertidal creeks in the Changjiang(Yangtze)River estuary on spatial and temporal scales.Samples were collected using fyke nets at two sites during day and night in each season throughout four years.Notable changes in fish assemblages were detected over seasonal and interannual cycles,with many more marine species present in winter assemblages,whereas freshwater and estuarine species characterized the other seasonal samplings.The appearance of catadromous species in intertidal creeks mainly depended upon their specific physiological requirements,such as spawning migration.No significant diel shifts were observed in fish assemblages.This diel pattern may be a combined consequence of avian predation pressure and other drivers(i.e.,inherent living behaviors,food availability,and predation by piscivorous fishes).The spatial difference in fish community was insignificant even though the two intertidal creeks were different in size.Intertidal creeks with different size could possess similar ecological value for fish fauna.Redundancy analysis(RDA)showed that biological factors exerted greater effects on fish assemblages than physical variables.Temporal variations were strongly facilitated by food availability,but negatively impacted by avian predation.Salinity,water temperature,and river runoff had weak influence on temporal variations of fish communities.The lengthfrequency distribution showed that the fish collected in these two sites mainly consisted of young-of-year and juvenile fish,which confirmed that the creeks provided important nursery and forage roles in the process of fish ontogenetic development.Further,we proposed that salt marsh conservation management should be equally applied to all well-developed intertidal creeks regardless of creek size.

Study on Volume Variation and Stability of Riverbed in the Yangtze Estuary

In recent years,regional floods and typhoons have occurred in the Yangtze Estuary.Changing dynamic conditions and dramatic reduction of sediment discharge in the basin are affecting the dynamic equilibrium pattern of the Yangtze Estuary.Based on the field measurement data and theoretical derivation,this paper analyzed the changing process of runoff-sediment discharge into the sea after the operation of the Three Gorges Project(TGP),and the tidal dynamics and sediment variation characteristics of the Yangtze Estuary.The erosion of South Branch mainly occurs in the channel below-10 m contour,and the riverbed volume below contours 0 m and-10 m has a good correlation with the sediment discharge of Datong Station in the previous year.On this basis,the ratio of the horizontal distance from the starting point to the section centroid below the average water level(B_c)and the water depth at the section centroid(H_c)was proposed to describe the change of the section shape.The relationships between the water-diverting ratio,the sediment-diverting ratio and the water-diverting angle,the conditions of runoff and sediment discharge from the upper reach and the characteristics of the riverway section were established,and the theoretical calculation equations of the water-diverting ratio,the sediment-diverting ratio and the diverting angle of each bifurcation were also established.