On the mechanism behind the shift of the turbidity maximum zone in response to reclamations in the Yangtze (Changjiang) Estuary, China

Teng, Lizhi; Cheng, Heqin; Swart, H.E. de; Dong, Ping; Li, Zhanhai; Li, Jiufa; Wang, Yajun

doi:10.1016/j.margeo.2021.106569

Cited by 20 publications

(11 citation statements)

References 39 publications

(61 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The dynamic mechanisms of why the suspended sediments concentration distribution was changed were beyond the focus of this study; hence, readers are referred to previous studies (e.g., Zhu L. et al, 2016;Xie et al, 2017;Teng et al, 2021). Basically, it is a consequence of the change of currents.…”

Section: Effect Of the Mega Estuarine Constructions-induced Suspended Sediment Concentration Variationmentioning

confidence: 99%

Regulation of Algal Bloom Hotspots Under Mega Estuarine Constructions in the Changjiang River Estuary

Wang

2022

Front. Mar. Sci.

View full text Add to dashboard Cite

Massive large-scale engineering projects have been built in river estuaries around the world, but their effects on environments in the surrounding coastal waters were less emphasized compared to those due to the watershed projects. In this study, we used the Changjiang River Estuary as an example to show that a significant consequence can be resulted in such a situation. Through analyzing the harmful algal bloom events data and the chlorophyll satellite data, we investigate the spatiotemporal variations of algal blooms in the estuary and its adjacent water. The results indicate that the location of algal bloom hotspot changed over the period of the estuarine constructions. Furthermore, using a well-validated numerical model, we explored the mechanisms responsible for such an ecosystem regime shift. It was found that after the estuarine constructions were built, the surface chlorophyll maximum was attenuated and part of it migrated landward north of the river mouth but was strengthened south of the river mouth and extended seaward. Alternations of the nutrient concentration distribution and turbidity distribution induced by river plume deviation are responsible for the redistribution of the high chlorophyll concentration area. By contrast, the direct impact of the Three Gorges Dam through changing the runoff and sediments flux, which has been highlighted in numerous studies, was less important than expected. Given the fact that Three Gorges Dam and mega estuarine constructions were built in a similar period, any observed regime shift of hydrodynamic and ecological status outside the estuary should be interpreted with particular caution.

show abstract

Section: Effect Of the Mega Estuarine Constructions-induced Suspended Sediment Concentration Variationmentioning

confidence: 99%

Regulation of Algal Bloom Hotspots Under Mega Estuarine Constructions in the Changjiang River Estuary

Wang

2022

Front. Mar. Sci.

View full text Add to dashboard Cite

show abstract

“…The North Channel of the Yangtze Estuary experienced narrowing and reduction in width convergence as the consequence of a land reclamation project. The ETM indeed shifts downstream, as reported by Teng et al (2021). To explain this, by careful analysis of remote sensing date in the North Channel under various flow conditions, a conceptual model is proposed to argue that the seaward shift is partly due to the enhanced ebbdominance that causes a seaward shift of the convergence in sediment transport.…”

Section: Local Deepening and Narrowingmentioning

confidence: 74%

Turbidity maxima in estuarine networks: Dependence on fluvial sediment input and local deepening/narrowing with an exploratory model

2022

View full text Add to dashboard Cite

An estuarine turbidity maximum (ETM) results from various subtidal sediment transport mechanisms related to, e.g., river, tides, and density gradients, which have been extensively analysed in single-channel estuaries. However, ETMs have also been found in estuaries composed of multiple interconnected tidal channels, where the water and suspended fine sediments are exchanged at the junctions with possible occurrence of sediment overspill. The overall aim of this study is to understand the processes that determine the ETM dynamics in such channel networks. Specifically, focusing on the ETMs formation due to sediment transport by river flow and density-driven flow, the dependence of ETM locations in an idealised three-channel network on fluvial sediment input and the local deepening and narrowing of a seaward channel is investigated. It is found that the ETM dynamics in channels of a network is coupled, and hence, changes in one channel affect the ETM pattern in all channels. Sensitivity results show that, keeping river discharge fixed, a larger fluvial sediment input leads to the upstream shift of ETMs and an increase in the overall sediment concentration. Both deepening or narrowing of a seaward channel may influence the ETMs in the entire network. Furthermore, the effect of either deepening or narrowing of a seaward channel on the ETM locations in the network depends on the system geometry and the dominant hydrodynamic conditions. Therefore, the response of the ETM location to local geometric changes is explained by analysing the dominant sediment transport mechanisms. In addition to the convergence of sediment transport mechanisms in single-estuarine channels, ETM dynamics in networks is found to be strongly affected by net exchange of sediment between the branches of a network. We find that considering the sensitivity of net sediment transport to geometric changes is needed to understand the changing ETM dynamics observed in a real estuarine network.

show abstract

“…In the last two decades, due to the reduction in sediment from the basin and the constructions of the reclamations in estuary, there were erosion in the channel and deposition on the shoal in the NC [24]. The numerical simulation results in the NC showed that, during spring tide, due to the deepening and narrowing of the channel in turbidity maximum zone, stratification was enhanced and the maximum stratification occurred near the maximum ebb in main channel; the increase in the stratification was less on the shoal resulting from the higher bottom friction [44].…”

Section: Impact Of Tidal Mixing Asymmetry On Longitudinal Net Sedimen...mentioning

confidence: 99%

“…As the major channel of YE, about 50% of the runoff flows through the NC into the East China Sea [23]. In the middle segment of NC, where the landward boundary of turbidity maximum zone is located, the volume of shoal (beyond −5 m depth) accounted for 56.20% of the total volume in 2018, the maximum difference of water depth between channel and shoal was more than 10 m [24].…”

Section: Introductionmentioning

confidence: 99%

Lateral Variation of Tidal Mixing Asymmetry and Its Impact on the Longitudinal Sediment Transport in Turbidity Maximum Zone of Salt Wedge Estuary

Teng

Cheng

Zhang

et al. 2022

JMSE

Self Cite

View full text Add to dashboard Cite

The lateral bathymetry in the estuary results in different degrees of tidal mixing asymmetry, which has significant impacts on the longitudinal sediment transport by changing the temporal variation of vertical eddy diffusion. This study focus on the lateral variation of tidal mixing asymmetry and longitudinal sediment transport at the landward boundary of turbidity maximum zone in the North Channel of Yangtze estuary, which is a typical time-dependent salt wedge estuary. A transect survey was carried out in December, 2018; five vertical profiles of flow velocity, salinity and suspended sediment concentration were simultaneously measured covering a spring tidal cycle. Analysis of the data revealed that, after the maximum ebb, the stratification in the main and secondary channel was stronger than that on the shoal. In the channel, during ebb tide, the stronger stratification restrained the turbulent mixing induced by vertical shear, vertical mixing during the flood tide was stronger than that during ebb tide and vertical mixing coefficients ranged from 0.06 to 0.12, showing regular tidal mixing asymmetry over a flood–ebb tidal cycle. Therefore, stronger eddy diffusion caused by vertical mixing resulted in higher suspended sediment concentrations during flood tide, the larger landward tidally averaged sediment transport rate was induced by tidal pumping with the transportation of flood tidal current and the net sediment transport over a flood–ebb tidal cycle in the channel was landward. Meanwhile, on the shoal, under the effect of vertical shear, the vertical mixing during flood tide was weaker than that during ebb tide; vertical mixing coefficients ranged from −0.27 to −0.02, showing the reversed tidal mixing asymmetry. Higher suspended sediment concentration was transported seaward by the ebb current, the tidally averaged sediment transport rate by both tidal pumping and advection was seaward and the net sediment transport was seaward. Furthermore, large river discharge increased the seaward advection sediment flux on the surface layer in the main channel, resulting in the seaward tidally averaged sediment flux. Strong resuspension increased the seaward advection sediment flux near the bottom in the main and secondary channel, resulting in the seaward tidally averaged sediment flux.

show abstract

On the mechanism behind the shift of the turbidity maximum zone in response to reclamations in the Yangtze (Changjiang) Estuary, China

Cited by 20 publications

References 39 publications

Regulation of Algal Bloom Hotspots Under Mega Estuarine Constructions in the Changjiang River Estuary

Regulation of Algal Bloom Hotspots Under Mega Estuarine Constructions in the Changjiang River Estuary

Turbidity maxima in estuarine networks: Dependence on fluvial sediment input and local deepening/narrowing with an exploratory model

Lateral Variation of Tidal Mixing Asymmetry and Its Impact on the Longitudinal Sediment Transport in Turbidity Maximum Zone of Salt Wedge Estuary

Contact Info

Product

Resources

About