The impact of the change in vegetation structure on the ecological functions of salt marshes: the example of the Yangtze estuary

2013 ◽  
Vol 14 (2) ◽  
pp. 623-632 ◽  
Author(s):  
Xiuzhen Li ◽  
Linjing Ren ◽  
Yu Liu ◽  
Christopher Craft ◽  
Ülo Mander ◽  
...  
Keyword(s):  
Salt Marshes ◽  
Vegetation Structure ◽  
Yangtze Estuary ◽  
Ecological Functions ◽  
The Yangtze Estuary ◽  
The Impact

scholarly journals THE BRANCHING CHANNEL NETWORK IN THE YANGTZE ESTUARY

2012 ◽  
Vol 1 (33) ◽  
pp. 69
Author(s):  
Zheng Bing Wang ◽  
Pingxing Ding
Keyword(s):  
Yangtze Estuary ◽  
River Delta ◽  
Sediment Supply ◽  
Channel Structure ◽  
The South ◽  
Channel Network ◽  
The Yangtze Estuary ◽  
The North ◽  
Navigation Channel ◽  
The Impact

The channels in the Yangtze Estuary have an ordered-branching structure: The estuary is first divided by the Chongming Island into the North Branch and the South Branch. Then the South Branch is divided into the North Channel and South Channel by the Islands Changxing and Hengsha. The South Channel is again divided into the North and South Passage by the Jiuduansha Shoal. This three-level bifurcation and four-outlet configuration appears to be a natural character of the estuary, also in the past (Chen et al., 1982), although the whole system has been extending into the East China Sea in the southeast direction due to the abundant sediment supply from the Yangtze River. Recently, the natural development of the system seems to be substantially disturbed by human interferences, especially the Deep Navigation Channel Project. For the understanding of the behaviour of the bifurcating channel system in the estuary we present analysis on two aspects: (1) the equilibrium configuration of river delta distributary networks, and (2) influence of tidal flow on the morphological equilibrium of rivers. Based on the analyses we conclude that the branching channel structure of the Yangtze Estuary can be classified as tide-influenced river delta distributary networks. Its basic structure is the same as in case of river dominated delta. The empirical relations describing the basic features of the river-dominated distributary delta networks can be explained by theoretical analysis, although they are not fully satisfied by the Yangtze Estuary because of the influence of the tide. Two major influences of the tide are identified, viz. increasing the resistance to the river flow into the sea and increasing the sediment transport capacity. As consequence of these two influences the cross-sectional area of the river/estuary increases in the seawards direction and the bed slope decreases. The insights from the analyses are helpful for the understanding of the impact of the Deep Navigation Channel Project on the large scale morphological development of the estuary.

Analysis of tidal average saturated suspended sediment concentration of cohesive sediment in the Yangtze Estuary

2021 ◽  
Author(s):  
Junyu Tao ◽  
Peng Hu ◽  
Wei Li ◽  
Zhiguo He
Keyword(s):  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Sediment Concentration ◽  
Cohesive Sediment ◽  
Yangtze Estuary ◽  
Shear Stresses ◽  
The Yangtze Estuary ◽  
Erosion And Deposition ◽  
Deposition Fluxes ◽  
The Impact

<p>It is generally believed that sediment erosion and deposition can’t occur simultaneously, which is also reflected in the classical Partheniades-Krone formulas used to calculate erosion and deposition flux. In this study, the erosion and deposition fluxes of cohesive sediment are integrated in the tidal period respectively, and when they are equal, the corresponding suspended cohesive sediment concentration is called ‘tidal average saturated concentration of cohesive sediment’. Theoretical analysis of the factors affecting the saturated concentration indicates that a large erosion coefficient results in a high saturated concentration level. The corresponding critical erosion and deposition shear stresses (i.e., τ<sub>e </sub>and τ<sub>d</sub>) at saturated concentration have many possibilities. Therefore, it is understandable that good agreement of suspended sediment concentration between simulation and observation have been obtained by adjusting τ<sub>e </sub>and τ<sub>d </sub>in the previous numerical simulation calibration. According to the relative magnitude of τ<sub>e </sub>and τ<sub>d</sub> at saturated concentration, the erosion and deposition fluxes of cohesive sediment can be divided into four situations: weak erosion (i.e., τ<sub>e  ></sub> τ<sub>d</sub>), intense erosion (i.e., τ<sub>e  <</sub> τ<sub>d</sub>), intense deposition (i.e., τ<sub>e  <</sub> τ<sub>d</sub>), and weak deposition (i.e., τ<sub>e > </sub>τ<sub>d</sub> ). A two-dimensional numerical model is applied to calculate the temporal and spatial variation of the saturated concentration of cohesive sediment in the Yangtze Estuary. Simulation results shows the following findings. 1) The impact of the fraction of the kth size class in the surface (top) layer of bed material on erosion flux of non-uniform cohesive sediment is necessary to be considered. Otherwise, the calculated saturated concentration of cohesive sediment is greater than the measured. 2) The differences between saturated concentration and the field calculated/measured suspended sediment concentration can be applied to infer bed erosion/deposition characteristics to some extent, and compared it with the measured erosion/deposition result, which in turn verifies the values of  τ<sub>e </sub>and τ<sub>d</sub> in the model. This finding provides insights for the following research on transport and diffusion of cohesive sediment in estuary and coastal areas.</p>

scholarly journals Modeling the impact of river discharge and wind on the hypoxia off Yangtze Estuary

2016 ◽  
Vol 16 (12) ◽  
pp. 2559-2576 ◽  
Author(s):  
Jingjing Zheng ◽  
Shan Gao ◽  
Guimei Liu ◽  
Hui Wang ◽  
Xueming Zhu
Keyword(s):  
Wind Speed ◽  
River Discharge ◽  
Three Dimensional ◽  
Yangtze Estuary ◽  
Physical Factors ◽  
Observation Data ◽  
The Yangtze Estuary ◽  
Physical Forcing ◽  
Synoptic Variability ◽  
The Impact

Abstract. The phenomenon of low dissolved oxygen (known as hypoxia) in a coastal ocean system is closely related to a combination of anthropogenic and natural factors. Marine hypoxia occurs in the Yangtze Estuary, China, with high frequency and long persistence. It is related primarily to organic and nutrient enrichment influenced by river discharges and physical factors, such as water mixing. In this paper, a three-dimensional hydrodynamic model was coupled to a biological model to simulate and analyze the ecological system of the East China Sea. By comparing with the observation data, the model results can reasonably capture the physical and biochemical dynamics of the Yangtze Estuary. In addition, the sensitive experiments were also used to examine the role of physical forcing (river discharge, wind speed, wind direction) in controlling hypoxia in waters adjacent to the Yangtze Estuary. The results showed that the wind field and river discharge have significant impact on the hypoxia off the Yangtze Estuary. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in the river discharge, but integrated hypoxic areas were sensitive to the whole magnitude of river discharge. Increasing the river discharge was shown to increase hypoxic areas, while decreasing the river discharge tended to decrease hypoxic areas. The variations of wind speed and direction had a great impact on the integrated hypoxic areas.

The impacts of biotic and abiotic interaction on the spatial pattern of salt marshes in the Yangtze Estuary, China

2020 ◽  
Vol 238 ◽  
pp. 106717 ◽  
Author(s):  
Lifang Cui ◽  
Lin Yuan ◽  
Zhenming Ge ◽  
Haobing Cao ◽  
Liquan Zhang
Keyword(s):  
Spatial Pattern ◽  
Salt Marshes ◽  
Yangtze Estuary ◽  
The Yangtze Estuary

scholarly journals Modeling the impact of river discharge and wind on the hypoxia off Yangtze Estuary

2016 ◽  
Author(s):  
Jingjing Zheng ◽  
Shan Gao ◽  
Guimei Liu ◽  
Hui Wang
Keyword(s):  
Wind Speed ◽  
River Discharge ◽  
Three Dimensional ◽  
Yangtze Estuary ◽  
Physical Factors ◽  
Observation Data ◽  
The Yangtze Estuary ◽  
Physical Forcing ◽  
Synoptic Variability ◽  
The Impact

Abstract. The phenomenon of low dissolved oxygen (known as hypoxia) in coastal ocean system is closely related to a combination of anthropogenic and natural factors. Marine hypoxic occurs in the Yangtze Estuary, China with high frequency and long persistence. It’s known that it related primarily to organic and nutrient enrichment influenced by river discharges and physical factors, such as water mixing. In this paper, a three-dimensional hydrodynamic model was coupled to a biological model to simulate and analyze the ecological system of the East China Sea. By comparing with the observation data, the model results can reasonably capture the physical and biochemical dynamics of the Yangtze Estuary. In addition, the sensitive experiments were also used to examine the role of physical forcing (river discharge, wind speed, wind direction) in controlling hypoxia in waters adjacent to the Yangtze Estuary. The results showed that the wind field and river discharge have significant impact on the hypoxia off the Yangtze Estuary. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in the river discharge, but integrated hypoxic areas were sensitive to the whole magnitude of river discharge. Increasing the river discharge was shown to increase hypoxic areas, while decreasing the river discharge was tended to decrease hypoxic areas. And the variations of wind speed and direction had great impact on the seasonal variability of hypoxia and the integrated hypoxic areas.

Pattern-regulated wave attenuation by salt marshes in the Yangtze Estuary, China

2021 ◽  
Vol 209 ◽  
pp. 105686
Author(s):  
Liming Xue ◽  
Xiuzhen Li ◽  
Benwei Shi ◽  
Bin Yang ◽  
Shiwei Lin ◽  
...  
Keyword(s):  
Salt Marshes ◽  
Wave Attenuation ◽  
Yangtze Estuary ◽  
The Yangtze Estuary
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