Search

Existing knowledge about groyne-induced effects is primarily based on riverine or coastal environments where salinity gradients are absent or limited. However, in estuaries, salinity gradients drive physical processes such as longitudinal and lateral residual flows. The effect of groynes is much more complex because they can modulate channel hydrodynamics and directly affect lateral salinity gradients. In this study, an idealized model is applied to investigate the effects of groyne layouts in estuarine environments, including effects on (1) channel hydrodynamics, (2) lateral water exchange, (3) Coriolis effects, and (4) saltwater intrusion. Model results show that the aspect ratio (the width of groyne fields to the length of groynes) of groyne fields plays an important role. Groynes also induce asymmetry of lateral flows, for example, increasing near-bottom shoal-to-channel flows during low water slack. The aspect ratio has opposite effects on horizontal and vertical components of water exchange. A large aspect ratio strengthens horizontal exchange and weakens density-driven currents. For a large-scale groyne field (several kilometers), Coriolis effects introduce a substantial difference in exchange mechanisms along the north and south banks. A medium range of aspect ratio (2.0–3.0) leads to the strongest saltwater intrusion during both neap and spring tides. Dikes and groynes are common engineering structures in waterways designed to increase along-channel flow velocities and prevent sediment deposition, thereby maintaining navigability. However, especially in estuarine environments, cross-channel flow velocities resulting from these structures may generate sediment transport toward the channel, in contrast to their original intention. Another important impact of these structures is on saltwater intrusion, which is crucial to freshwater resource management. Therefore, this research investigates the groyne-induced effects on cross-channel flows and the saltwater intrusion problem by comparing different layouts of groynes and their consequences. Two important findings may benefit practical applications. First, the interaction between saltwater and freshwater in estuaries enhances cross-channel flows during certain periods, thereby influencing sediment transport. Second, the maximal saltwater intrusion occurs for intermediate width-to-length ratios of the groynes, with lower saltwater intrusion for either very small or very wide groyne fields. [ABSTRACT FROM AUTHOR]

The Krone–Partheniades (K-P) framework has been used for decades to quantify and analyze the sediment exchange at a water–bed interface. Measuring the erosion and deposition parameters that are part of this framework requires time-consuming field observations. Additionally, the erosion parameters are measured independently of deposition parameters, while in reality they are coupled. In numerical models applying the K-P framework these parameters are often assumed to be constant in time and mutually independent. In this study, we develop a relatively simple methodology to determine the erosion and deposition parameters, using conventional near-bed observations of bed level, sediment concentration and flow velocity. This methodology is subsequently applied to tripod observations collected in the Changjiang estuary, China, to compute continuous time-varying erosion and settling parameters. We propose a diagram to visualize the interdependency and accuracy of erosion and deposition parameters, which is the input for K-P framework models requiring this interdependency. [ABSTRACT FROM AUTHOR]

Saltwater intrusion is a common feature in the Changjiang Estuary affected by river discharges and tidal flows. It leads to a two‐layer flow structure during the flood‐to‐ebb tidal transient period: the seaward tidal flow in the upper water column and onshore intruded salt flow in the lower column, even though the lower column water usually experiences an ebb flow eventually. Our recent measurements with a tripod deployed in a tidal channel of the North Branch in the East China Sea challenged this feature. We detected that the two‐layer flow structure disappeared in the ebb tide period during the neap cycle due to intense saltwater intrusion. A constant onshore flood‐like flow predominated the entire water column. The physical mechanism for the flow reversal was examined using the Finite Volume Community Ocean Model (FVCOM). The FVCOM was robust to capture the observed flow reversal in the tidal channel during the neap tidal cycle. The momentum balance analysis results suggest that the flow reversal occurred when the saltwater intrusion‐induced onshore baroclinic pressure gradient force and baroclinic tidal rectification overwhelmed the seaward barotropic pressure gradient force. A parameter‐driven criterion was derived theoretically to determine the potential occurrence of a stable ebb flow reversal in the tidal channel. Plain Language Summary: Many estuaries experience saltwater intrusion, bringing saltwater from offshore regions to nearshore and river channels. In the Changjiang Estuary, it could create a two‐layer flow structure during the flood‐to‐ebb transient period, a seaward fresher ebb tidal flow in the upper water column, and an onshore intruded salt flow in the lower water column. Could the increased saltwater intrusion destroy this two‐layer flow structure and form an onshore flow throughout the water column in the ebb‐tidal period during a neap tidal cycle? If it does, what is the critical driving mechanism? To answer these questions, we deployed a tripod system integrated with state‐of‐the‐art marine instruments in a tidal channel of North Branch in the Changjiang Estuary, an area where saltwater intrusion frequently occurs. The observational data captured a flow‐overtured feature, showing a stable flood‐like intruded flow throughout the entire water column in the ebb‐tidal period during a neap tidal cycle. We applied the Finite‐Volume Community Ocean Model to examine the physical driving mechanism for flow‐overturning. The results suggest that the flow‐overturning could occur when the along‐channel saltwater intrusion‐induced baroclinic pressure gradient force and stratified tidal rectification overwhelmed the along‐channel tide‐induced barotropic pressure gradient force. Key Points: The bottom tripod system identified an overturned tidal flow in the North Branch channelA numerical model revealed the baroclinic gradient force from saltwater intrusion dominated the overturnThe balance criteria were proposed to estimate competition between these two dynamics [ABSTRACT FROM AUTHOR]

Massive floating macroalgal blooms in the ocean result in many ecological consequences. Tracking their drifting pattern and predicting their biomass are essential for effective marine management. In this study, a physical–ecological model, the Floating Macroalgal Growth and Drift Model (FMGDM), was developed. Based on the tracking, replication, and extinction of Lagrangian particles, FMGDM is capable of determining the dynamic growth and drift pattern of floating macroalgae, with the position, velocity, quantity, and represented biomass of particles being updated synchronously between the tracking and the ecological modules. The particle tracking is driven by ocean flows and sea surface wind, and the ecological process is controlled by the temperature, irradiation, and nutrients. The flow and turbulence fields were provided by the unstructured grid Finite-Volume Community Ocean Model (FVCOM), and biological parameters were specified based on a culture experiment of Ulva prolifera , a phytoplankton species causing the largest worldwide bloom of green tide in the Yellow Sea, China. The FMGDM was applied to simulate the green tide around the Yellow Sea in 2014 and 2015. The model results, e.g., the distribution, and biomass of the green tide, were validated using the remote-sensing observation data. Given the prescribed spatial initialization from remote-sensing observations, the model was robust enough to reproduce the spatial and temporal developments of the green tide bloom and its extinction from early spring to late summer, with an accurate prediction for 7–8 d. With the support of the hydrodynamic model and biological macroalgae data, FMGDM can serve as a model tool to forecast floating macroalgal blooms in other regions. [ABSTRACT FROM AUTHOR]

Salt marshes are ecologically and physically essential habitats in coastal intertidal flats. In addition to providing nursery grounds for various wildlife, vegetation in marshes acts as a buffer zone that slows flooding waters. Extensive marsh platforms can also attenuate wave energy to protect coastal communities. Complex geometries make it challenging for models to capture the spatiotemporal variabilities in the transport of lateral water and sediment over tidal creek‐marsh complexes. To study water exchange processes between tidal creeks and marshes, field observations were conducted within tidal creeks in the Chongming Dongtan Shoal of the Changjiang Estuary, an area dominated by Phragmites australis, Scirpus mariqueter, and Spartina alterniflora. A coupled wave‐current‐sediment‐vegetation model that parameterized the three vegetation species was developed and applied to the tidal creek complex of Chongming Dongtan. Validated with the observational data, the modeling results were used to examine the influence of vegetation on flooding/draining processes within tidal creeks and mudflats. The model showed that vegetation not only modified the flow pattern at high tide in the high‐elevation marsh but also significantly intensified the tidal flows in tidal creeks in the low‐elevation regions. Both the observations and model detected significant transport of water and sediment from the marsh to tidal creeks, seaward sediment export over tidal cycles. The simulated salinity exhibited a considerable spatial gradient, matching well with the salt tolerances of the major vegetation types. This model can be potentially used to determine how future scenarios of hydrodynamics could affect vegetation zonation. Key Points: A vegetation model was developed to simulate the impacts of multiple vegetation species on flow, turbulence, waves and sedimentThree vegetation species were parameterized in the module, which was successfully applied to the tidal creek complex of Chongming DongtanModel demonstrated seaward sediment export from creeks, and consistency between the predicted salinity and the vegetation zonation [ABSTRACT FROM AUTHOR]

Estuarine fronts have significant effects on estuarine circulation, water quality, and productivity. However, there are limited studies on the joint ecological effects of sediment and plume fronts caused by tidal mixing and a low-salinity plume in and off the Changjiang River Estuary (CRE). Based on observational data during the summers of 1988–2016, we analyzed the spatial correlations between environmental factors and chlorophyll-a (Chl-a) concentrations along the two frontal boundaries. The water mass that is shoreward of the sediment front was characterized by the highest nutrients and total suspended matter (TSM); extensive light limitation caused by TSM consequently led to the lowest Chl-a. The water mass between the sediment and plume fronts displayed the highest Chl-a, which benefited from increased light availability due to rapid deposition of TSM across the sediment front and higher nutrients contributed by the plume and coastal upwelling. Shelf water mass beyond the plume front showed the lowest TSM and nutrients; the distinct reduction of nutrient supply resulted in a relatively low Chl-a. The spatial pattern of summer phytoplankton biomass tended to be a result of the balance of light and nutrients constructed by the two fronts and coastal upwelling in and off the CRE. [ABSTRACT FROM AUTHOR]

Lateral flows redistribute sediment and influence the morphodynamics of channel‐shoal systems. However, our understanding of lateral transport of suspended sediment during high and low water slack is still fairly limited, especially in engineered estuaries. Human interventions such as dike‐groyne structures influence lateral exchange mechanisms. The present study aims to unravel these mechanisms in a heavily engineered, turbid channel‐shoal system in the Changjiang Estuary, using a high‐resolution unstructured‐grid three‐dimensional model and in situ observations. Analysis of model results reveals two typical transport patterns during slack‐water conditions, that is, shoal‐to‐channel transport during low water slack and channel‐to‐shoal transport during high water slack. A momentum balance analysis is carried out to explain mechanisms driving the lateral transport of suspended sediment during high water slack, revealing the importance of lateral pressure gradients, Coriolis force, and the curvature‐induced term. Groyne fields play a crucial role in sediment transport, especially during low water slack. A model scenario in which one groyne is removed reveals that groyne fields strongly influence lateral sediment transport. The decomposition of the sediment transport flux reveals that the turbidity maximum is shaped by a balance between seaward advection by residual flows, and landward transport by tidal pumping and gravitational circulation. Within the turbidity maximum, sediment is laterally redistributed by lateral flows during slack‐water conditions, greatly influencing estuarine channel morphology. Plain Language Summary: Sediment deposition in navigation channels requires regular maintenance dredging. To minimize channel siltation, in‐depth knowledge of transport mechanisms and the effect of mitigation measures (such as groyne fields) is needed. These mechanisms include both longitudinal (along‐channel) and lateral (cross‐channel) processes. It is now well established that longitudinal processes play a key role in sediment convergence. However, during high and low water slack when the longitudinal velocity is small, lateral transport of suspended sediment becomes more important. These lateral transport mechanisms have a large influence on channel morphology. In this study, we investigate longitudinal and lateral transport of suspended sediment with a numerical model, revealing two typical lateral sediment transport patterns during high and low water slack which greatly influence the exchange of sediment between the channel and the shoals. The model also demonstrates the effect of groyne fields on lateral sediment transport. These findings expand our understanding of sediment transport in channel‐shoal systems in general, but in engineered systems in particular. Key Points: During stratified slack‐water conditions, the lateral pressure gradients drive sediment transport between the shoal and the main channelLongitudinal sediment convergence primarily results from advection, tidal pumping, and longitudinal vertical circulationLateral transport of suspended sediment and distribution patterns are influenced by groynes [ABSTRACT FROM AUTHOR]

Fluid mud (FM) is a unique sedimentary feature in high‐turbidity estuaries, where it can make a rapid contribution to morphodynamics. Insufficient field measurements and fixed‐point monitoring lead to deficient understandings of the formation, transport, and breakdown of the FM under extreme weather conditions. A field survey was conducted in the Changjiang Estuary during the period of turbidity maximum, just after Typhoon Haikui. The measurements captured the formation of the FM beneath the suspended layers, particularly around the lower reach of the North Passage. The thickness of the observed FM gradually decreased landward along the channel, with the maximum value reaching ~0.9 m. The major features of the observed storm‐induced FM were simulated using the Finite‐Volume Community Ocean Model. The results indicated that the initial appearance of the FM was the result of a typhoon‐intensified, salinity‐induced stratification in the outlet region. The subsequent landward propagation of the FM was driven by the combined effects of the FM‐induced mud surface pressure gradient force and saltwater intrusion near the bottom. Weak mixing during the subsequent neap tidal period sustained the FM as it rapidly extended into the middle region of the North Passage. This produced a large velocity shear at the interface of the FM and upper suspension layer, increasing the entrainment from the FM to the upper suspension layer. As a result of the increased tidal mixing, the FM weakened and then finally broke down in the subsequent spring tidal period. Plain Language Summary: The environment along the large river to estuary continuum is generally turbid and frequently produces highly concentrated benthic sediment suspensions, that is, fluid mud (FM). The FM is a sediment feature, with a concentration mostly in the range of 10 to >100 g/L. It is difficult to track the FM's movement and breakdown. The response of the FM to extreme atmospheric and oceanic conditions is therefore not well understood. In this study, a comprehensive field campaign identified the large‐scale formation of the FM after a severe tropical storm in the Changjiang Estuary. The life cycle of the FM in this estuary cannot, however, be determined through the field observation alone. A two‐layer FM model was developed to achieve this goal. The experiments suggested that the key physical factor was the stratification resulting from the typhoon‐enhanced saltwater intrusion. This led to the formation of the FM in the near‐bottom layer. After the FM formed, it extended onshore along the channel under the influence of an ambient saltwater intrusion. The FM was constrained in the benthic layer as a consequence of weak mixing from the saltwater intrusion. The breakdown of the FM was governed by enhanced tidal mixing in the subsequent spring tide. Key Points: A strong fluid mud (FM) formed during the passage of a tropical stormA storm‐increased stratification initially triggered a massive formation of the FMThe FM was sustained and transported by saltwater intrusion, and it subsequently broke down during the strong‐mixing spring tide [ABSTRACT FROM AUTHOR]

Lateral flow significantly contributes to the near‐bottom mass transport of salinity in a channel‐shoal system. In this study, an integrated tripod system was deployed in the transition zone of a channel‐shoal system of the Changjiang Estuary (CE), China, to observe the near‐bottom physics with high temporal/spatial resolution, particularly focusing on the lateral‐flow‐induced mass transport. These in situ observations revealed a small‐scale salinity fluctuation around low water slack during moderate and spring tidal conditions. A simultaneous strong lateral current was also observed, which was responsible for this small‐scale fluctuation. A high‐resolution unstructured‐grid Finite‐Volume Community Ocean Model has been applied for the CE to better understand the mechanism of this lateral flow and its impact on salinity transport. The model results indicate that a significant southward near‐bed shoal‐to‐channel current is generated by the salinity‐driven baroclinic pressure gradient. This lateral current affects the salinity transport pattern and the residual current in the cross‐channel direction. Cross‐channel residual current shows a two‐layer structure in the vertical, especially in the intermediate tide when the lateral flow notably occurred. Both observation and model results indicate that near‐bottom residual transport of water moved consistently southward (shoal to channel). Mechanisms for this intratidal salinity variation and its implications can be extended to other estuaries with similar channel‐shoal features. Plain Language Summary: In channel‐shoal systems, lateral processes sometimes can be of great significance, for example, influencing salinity and sediment transport, even some biogeochemical matters that influence the water environment. Salinity and sediment transport will have a further effect on navigability, ecology, and so on, for example, sediment deposition issues, which significantly decrease the shipping capacity. Consequently, knowing the accurate information about the flow field and finding a criterion for pronounced lateral processes are important to better understand hydrodynamics and sediment behaviors in channel‐shoal systems. Here in this study, we conducted an in situ observation and used numerical simulation to detect and predict a strong lateral flow in the North Passage of the Changjiang Estuary. This shoal‐to‐channel lateral flow occurred around the end of ebb and caused an intratidal salinity variation at the observation site, close to the deep channel. Therefore, a link between pronounced lateral flows and typical salinity variation can be established. This link can also be found in other estuaries like Hudson River estuary. Findings presented here will help to easily distinguish pronounced lateral flows and better understand the effect of lateral flows. Key Points: Intratidal salinity variation (ISV) and a strong lateral flow in a channel‐shoal system were identified by an integrated tripod systemNumerical simulation reveals that lateral flows were primarily driven by the salinity‐induced pressure gradient forceLateral flows can be generated or enhanced by human interventions such as groyne fields [ABSTRACT FROM AUTHOR]

The concentrated benthic suspension (CBS) of mud, as a major contributor of sediment transport in the turbidity maximum of the estuary, is of great challenge to be correctly monitored through field measurements, and its formation mechanism is not well understood. A tripod system equipped with multiple instruments was deployed to measure the near‐bed hydrodynamics and sediments in the North Passage of the Changjiang Estuary, with the aim at determining the formation mechanisms of CBS. The measurements detected a significant dominance of high sediment concentration in the near‐bed 1‐m layer: ~20 g/L at the southern site and ~47 g/L at the northern site. Strong CBS occurred under weak tidal mixing condition and was directly relevant to the sediment‐induced suppression of turbulent kinetic energy and the enhanced water stratification due to saltwater intrusion and sediment suspension. During the weak‐mixing neap period, the typical thickness of CBS was about 0.2–0.3 m, with a life time of ~2.83 hr (suspended‐sediment concentration > 15.0 g/L). Enhanced water stratification reduced vertical mixing and confined the sediment entrainment from the near‐bed layer to the upper column. This enhancement was due to the suppression of turbulent kinetic energy as a result of the sediment accumulation in the near‐bottom column during the slack waterand also due to the appearance of a two‐layer salinity structure in the vertical as a result of saltwater intrusion near the bottom. These physical processes worked as a positive feedback loop during the formation of CBS and can be simulated with a process‐oriented, one‐dimensional vertical CBS model. Plain Language Summary: In the turbidity maximum, concentrated benthic suspension (CBS) frequently dominates the near‐bed sediment transport, which, however, is difficult to be correctly observed, especially in the stratified condition. And the formation mechanism of CBS is complex due to the interaction of sediment and hydrodynamics. In a stratified tide channel of the Changjiang Estuary, China, a comprehensive tripod system, integrated with many cutting‐edge instruments, is developed and deployed to measure the CBS and to determine the formation process. This system detected the existence of CBS in the lower near‐bed 1‐m layer, ~20 g/L at the southern site and ~47 g/L at the northern site, with the mean thickness of 20–30 cm. The corresponding salinity, tidal velocities, wave, and turbulent kinetic energy were also recorded. During the formation of CBS, tidal mixing is weak. And the salinity/sediment‐induced stratification greatly limits the vertical mixing and suppresses the turbulent kinetic energy production. The saltwater intrusion creates a two‐layer structure of salinity, leading to stratification and decreasing the mixing. These physical effects work like a positive feedback loop. A one‐dimensional vertical model had been developed to successfully simulate the formation process of CBS, indicating the stable CBS during weak‐tidal‐mixing neap cycle. Key Points: Concentrated benthic suspension (CBS) of mud in the turbidity maximum zone was observed by a comprehensive near‐bed tripod systemThe dynamics for the formation of CBS are determinedA one‐dimensional vertical model is developed to analyze the physical mechanisms responsible for the formation of CBS [ABSTRACT FROM AUTHOR]

Denitrification and anaerobic ammonium oxidization (anammox) are considered the most important processes of removing reactive nitrogen from natural aquatic environments. We measured and compared in situ rates of the two processes across the sediment-water interface of Jinpu Bay using continuous-flow experiments combined with a NO tracing technique to determine their relative importance in this hypereutrophic coastal ecosystem. Rates of denitrification and anammox ranged from 1.76 to 327.97 and 0.33 to 36.32 μmol N m day, respectively. Both the denitrification and anammox processes were observed to be associated closely with the bioavailability of organic matter and concentrations of sulfide and iron oxides in sediments. Denitrification was the dominant pathway of eliminating reactive nitrogen and on average accounted for about 90 % of the total removed nitrogen. Totally, both the denitrification and anammox processes removed about 20 % of the externally derived inorganic nitrogen within the system. Most of the external nitrogen was still retained in the ecosystem, which may cause the severe eutrophication and algae blooms occurring at the study area. [ABSTRACT FROM AUTHOR]

Zhao, C.; Ge, J., and Ding, P., 2014. Impact of sea level rise on storm surges around the Changjiang Estuary. The potential impacts of sea level rise (SLR) on storm surge around the Changjiang Estuary and the Hangzhou Bay are investigated using a shallow-water circulation model ADCIRC coupled with a spectral wave model SWAN. The validated model is applied to two typical typhoons under three scenarios: 1.0 m SLR, 0.483 m SLR and present sea-level condition. In consideration of interactions of tide, waves and surge, the impact exerted by SLR on tide and waves are also discussed. The migration of the amphidromes generated by SLR causes the co-phase lines to defect relatively counterclockwise near the Changjiang Estuary. The amplitude of tide increases slightly at the inner mouth of the Changjiang River, and more notable increases are presented at the northern part of the Changjiang River Mouth. The amplitude of tide decreases in adjacent areas of the Hangzhou Bay. The wave heights respond to the sea level rise in a non-linear and spatially non-uniform manner. Comparing the maximum wave height between each scenario, the wave height increase is found to be significant in shallow areas due to the increase in water depth. The breaking locations of the wave shift shoreward. The general patterns in wave height change are approximately determined by the typhoon path and topography. As for changes in surge and elevation, time series of water surface curves and peak value distribution are all analyzed. The curves of surges and water elevations accelerate slightly relative to that of the control scenario. The surges are not very sensitive to the SLR and the variations in elevation could mainly attribute changes in tide, with the changing extents ranging from a few to a dozen centimeters. Taking the value of SLR into account, the peak of elevation near shore could experience a significant increase in the future. All the properties respond to sea level rise in a non-linear and spatially non-uniform manner. [ABSTRACT FROM AUTHOR]

A high-resolution numerical model system is essential to resolve multi-scale coastal ocean dynamics. So a multi-scale unstructured grid-based finite-volume coastal ocean model (FVCOM) system has been established for the East China Sea and Changjiang Estuary (ECS-CE) with the aim at resolving coastal ocean dynamics and understanding different physical processes. The modeling system consists of a three-domain-nested weather research and forecasting model, FVCOM model with the inclusion of FVCOM surface wave model in order to understand the wave-current interactions. The ECS-CE system contains three different scale models: a shelf-scale model for the East China Sea, an estuarine-scale model for the Changjiang Estuary and adjacent region, and a fine-scale model for the deep waterway regions. These three FVCOM-based models guarantee the conservation of mass and momentum transferring from outer domain to inner domain using the one-way common-grid nesting procedure. The model system has been validated using data from various observation data, including surface wind, tides, currents, salinity, and wave to accurately reveal the multi-scale dynamics of the East China Sea and Changjiang Estuary. This modeling system has been demonstrated via application to the seasonal variations of Changjiang diluted water and the bottom saltwater intrusion in the North Passage, and it shows strong potential for estuarine and coastal ocean dynamics and operational forecasting. [ABSTRACT FROM AUTHOR]

This paper compares the Yangtze Estuary in China and the Western Scheldt Estuary in The Netherlands by their morphodynamic and ecological systems, their engineering works and estuarine management issues, and the major challenges in studying them. Physically speaking, the two estuaries are very different. The Yangtze Estuary is much larger and much more influenced by the upstream river than the Western Scheldt. Yet, they also have a number of morphological and ecological features in common. Both estuaries have a multi-channel system and extensive intertidal flats and wetlands with ecologically valuable flora and fauna. These eco-morphological systems are influenced by similar societal developments and human activities. Examples of the latter are engineering works and dredging activities for improving and maintaining the navigation channels, and shoreline management activities including land reclamations and setbacks. The fundamental eco-morphological phenomena that remain to be analysed and understood are the same for the two estuaries and will be discussed in this paper. [ABSTRACT FROM AUTHOR]

Sediment transport in the Hangzhou Bay is extremely complicated due to its bathymetry and hydrodynamic conditions. The ECOMSED model is employed to simulate three-dimensional (3-D) cohesive sediment transport in Hangzhou Bay. Dynamical factors such as Coriolis force, tides, salinity, river discharges, and waves are considered in the model. The wave parameters, including the significant wave height, period, and direction, are calculated with the SWAN model. The Grant-Madsen model is introduced for the bed shear stress due to the combined effect of waves and currents. The formulation of bed shear stress used to calculate the sink/source terms is modified based on previous research that sufficiently validated the formulation with measurement data. The integrated model of the above-mentioned models is applied to simulate sediment transport in Hangzhou Bay. The results of the simulation agree well with field observations concerning the distribution of suspended sediment, indicating that the sediments are remarkably suspended in Hangzhou Bay under the action of waves and currents. [ABSTRACT FROM AUTHOR]

Non-barrier mudflats in the Changjiang Estuary is examined to obtain preservation potentials and deposition rates over different time scales. The preservation potential of couplet is ca. 46.6% within daily scale and decreases as the time-interval extending, with 9.2% on a semi-lunar scale and 3.7% on a seasonal scale. In the long term, only 1.6% of daily deposition can potentially be preserved in the tidal flat sequence and other 98.4% have been eroded and leave sedimentary discordances, discernable or un-discernable, in the mudflat deposits. A negative log-linear relationship is examined between sedimentation rates and the time spans. The length of sedimentary hiatuses on the mudflat deposition were estimated with considerable uncertainty, but it can provide from an actualistic base some further insights into the nature and origin of ancient mudflat deposits with emphasis on the sedimentary discordances. [ABSTRACT FROM AUTHOR]

Seasonal changes in sea level, tidal range, wind, riverine discharges, nearshore SSC (suspended sediment concentration) and bed-level of intertidal flat at 4 different sites were shown. In addition, the statistical relationships between the dynamics and the behavior of the sediment surface were examined. The average intertidal elevation seems negatively correlated to sea level while positively correlated to nearshore SSC. The effect of wind on seasonal cycle of average intertidal elevation is not evident although wind is an important factor governing short-term erosion/accretion events. The influence of riverine discharges on seasonal cycle of deltaic intertidal flats is masked by other factors. It is concluded that seasonality on mudflats is more complicated than on beaches. [ABSTRACT FROM AUTHOR]

Waves can have a significant impact on nearshore currents. A three-dimensional baroclinic current model including the influence of waves is presented for shallow water areas from Navier-Stokes equations. It has been found that the effects of waves on currents can be expressed in terms of the momentum flux by waves. The model uses non-orthogonal curvilinear coordinates in the horizontal directions and a Sigma coordinate in the vertical direction so that it can be more reasonably applied in estuarine and coastal regions. [ABSTRACT FROM AUTHOR]

There is a common hypothesis for the presently popular mild-slope equations that wave particle motion is irrotational. In this paper, an attempt is made to abandon the irrotational assumption and to set up new sea wave packet equations on slowly varying topography by use of the WKBJ method. To simplify the deduction, the two-dimensional shallow water equations are used to describe the sea wave particle motion in the very shallow nearshore area. The established equations can give some characteristics of wave propagation near shore. [ABSTRACT FROM AUTHOR]

Coastal ecosystems are strongly influenced by terrestrial inputs of freshwater, sediments, and nutrients, particularly in a megariver estuary of the Changjiang River. A remarkable increase in nutrient loading from the Changjiang River to the shelf has been observed over the period from 1999 to 2016 and turned the region into a high eutrophication condition. The Finite‐Volume Community Ocean Model and the European Regional Seas Ecosystem Model were coupled to assess the impact of the nutrient loading on the interannual variability of nutrients and phytoplankton. The model was first validated via observational data, and then dynamical analysis were conducted. Singular vector decomposition analysis indicated that the rapid change of local ecosystem was highly correlated with the change in river nutrient contributions. The Changjiang estuarine ecosystem was phosphate limited. The phosphate exhibited local variation, while the abundant nitrate from the river was diluted by the low‐nitrate oceanic water. The suspended sediment was significantly correlated with phytoplankton but not with nutrients. The ratio of diatom biomass to dinoflagellate biomass respected a rapid response to strong oscillations in the river nutrient input. High diatom primary production occurred near the sediment front, whereas the dinoflagellate bloom extended significantly offshore. The spring diatom and dinoflagellate blooms had major peaks in the empirical orthogonal function Modes 1 and 2, and the autumn bloom is characterized by secondary peaks from Mode 2 in the autumn. Plain Language Summary: There was an increase in the nutrient input into the Changjiang Estuary with an increased use of agricultural fertilizer as food demand rises globally. Further, there will be additional changes to river and estuary fluxes due to global anthropogenic activities in the future. This study presented the results of a novel coupled physical‐biogeochemical model which was designed to examine the seasonal and interannual variability of nutrients and phytoplankton dynamics in the Changjiang Estuary over the period of 1999–2016. The variations of nutrient source from the Changjiang Estuary in the last 18 years had been identified. The model demonstrated that this estuary ecosystem had a rapid response to the changes in riverine nutrients. The total nutrient concentrations, as well as their fluxes of the system, had similar variation patterns with river discharge, indicating that the river was the principal source of nutrients for the nearshore and offshore regions in that area. The phytoplankton population in terms of the ratio between diatoms and dinoflagellates responded quickly to changes in river nutrient fluxes. Key Points: Physical and biogeochemical models have been coupled to study pelagic planktonic ecosystem variability in a river estuary systemConsequences of changing nutrient fluxes over the last 18 years into the estuary on nutrient biogeochemistry and plankton were studiedPelagic ecosystem responded rapidly to river discharge and nutrient flux but exhibited different patterns for nutrients and phytoplankton [ABSTRACT FROM AUTHOR]